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  • Green and Sustainable Separation of Natural Products from Agro-Industrial Waste: Challenges, Potentialities, and Perspectives on Emerging Approaches
    Top. Curr. Chem. (IF 4.033) Pub Date : 2018-01-17
    Vânia G. Zuin, Luize Z. Ramin

    New generations of biorefinery combine innovative biomass waste resources from different origins, chemical extraction and/or synthesis of biomaterials, biofuels, and bioenergy via green and sustainable processes. From the very beginning, identifying and evaluating all potentially high value-added chemicals that could be removed from available renewable feedstocks requires robust, efficient, selective, reproducible, and benign analytical approaches. With this in mind, green and sustainable separation of natural products from agro-industrial waste is clearly attractive considering both socio-environmental and economic aspects. In this paper, the concepts of green and sustainable separation of natural products will be discussed, highlighting the main studies conducted on this topic over the last 10 years. The principal analytical techniques (such as solvent, microwave, ultrasound, and supercritical treatments), by-products (e.g., citrus, coffee, corn, and sugarcane waste) and target compounds (polyphenols, proteins, essential oils, etc.) will be presented, including the emerging green and sustainable separation approaches towards bioeconomy and circular economy contexts.

  • Precisely Defined Polymers for Efficient Gene Delivery
    Top. Curr. Chem. (IF 4.033) Pub Date : 2018-01-15
    Dongsheng He, Hao Lin, Yinglan Yu, Lei Shi, Jiasheng Tu

    Gene therapy requires successful delivery of therapeutic nucleic acids into target cells; thus, efficient and safe gene delivery carriers are crucial to its success. Although many polymeric materials have shown their potential as effective nucleic acid carriers, the inherent heterogeneity and polydispersity of these polymers hinder their application in clinical studies because of difficulties in their further precise modification, structure–activity relationship study, as well as consistent manufacturing. Therefore, precisely defined polymers, with potential for site-specific optimization according to structure–activity relationship information and highly controllable production, have been extensively investigated. In this review, we focus on the design and development of precisely defined polymers for efficient gene delivery, illustrated with examples including dendrimers, peptide-based polymers, and sequence-defined oligoaminoamide oligomers.

  • Photo- and Electrochemical Valorization of Carbon Dioxide Using Earth-Abundant Molecular Catalysts
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-12-06
    Alonso Rosas-Hernández, Christoph Steinlechner, Henrik Junge, Matthias Beller

    The dramatic increase in anthropogenic carbon dioxide emissions in recent decades has forced us to look for alternative carbon-neutral processes for the production of energy vectors and commodity chemicals. Photo- and electrochemical reduction of CO2 are appealing strategies for the storage of sustainable and intermittent energies in the form of chemical bonds of synthetic fuels and value-added molecules. In these approaches, carbon dioxide is converted to products such as CO, HCOOH and MeOH through proton-coupled electron transfer reactions. The use of earth-abundant elements as components of the catalytic materials is crucial for the large-scale applicability of this technology. This review summarizes the most recent advances related to this issue, with particular focus on studies where molecular metal complexes are used as catalysts. In addition, with the aim of aiding in the design of more robust and efficient non-noble metal-based catalysts, we discuss the lessons learned from the corresponding mechanistic studies.

  • Recent Developments in Single-Walled Carbon Nanotube Thin Films Fabricated by Dry Floating Catalyst Chemical Vapor Deposition
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-11-27
    Qiang Zhang, Nan Wei, Patrik Laiho, Esko I. Kauppinen

    Transparent conducting films (TCFs) are critical components of many optoelectronic devices that pervade modern technology. Due to their excellent optoelectronic properties and flexibility, single-walled carbon nanotube (SWNT) films are regarded as an important alternative to doped metal oxides or brittle and expensive ceramic materials. Compared with liquid-phase processing, the dry floating catalyst chemical vapor deposition (FCCVD) method without dispersion of carbon nanotubes (CNTs) in solution is more direct and simpler. By overcoming the tradeoff between CNT length and solubility during film fabrication, the dry FCCVD method enables production of films that contain longer CNTs and offer excellent optoelectronic properties. This review focuses on fabrication of SWNT films using the dry FCCVD method, covering SWNT synthesis, thin-film fabrication and performance regulation, the morphology of SWNTs and bundles, transparency and conductivity characteristics, random bundle films, patterned films, individual CNT networks, and various applications, especially as TCFs in touch displays. Films based on SWNTs produced by the dry FCCVD method are already commercially available for application in touch display devices. Further research on the dry FCCVD method could advance development of not only industrial applications of CNTs but also the fundamental science of related nanostructured materials and nanodevices.

  • Integration of Waste Valorization for Sustainable Production of Chemicals and Materials via Algal Cultivation
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-11-27
    Yong Chen, Li-ping Sun, Zhi-hui Liu, Greg Martin, Zheng Sun

    Managing waste is an increasing problem globally. Microalgae have the potential to help remove contaminants from a range of waste streams and convert them into useful biomass. This article presents a critical review of recent technological developments in the production of chemicals and other materials from microalgae grown using different types of waste. A range of novel approaches are examined for efficiently capturing CO2 in flue gas via photosynthetic microalgal cultivation. Strategies for using microalgae to assimilate nitrogen, organic carbon, phosphorus, and metal ions from wastewater are considered in relation to modes of production. Generally, more economical open cultivation systems such as raceway ponds are better suited for waste conversion than more expensive closed photobioreactor systems, which might have use for higher-value products. The effect of cultivation methods and the properties of the waste streams on the composition the microalgal biomass is discussed relative to its utilization. Possibilities include the production of biodiesel via lipid extraction, biocrude from hydrothermal liquefaction, and bioethanol or biogas from microbial conversion. Microalgal biomass produced from wastes may also find use in higher-value applications including protein feeds or for the production of bioactive compounds such as astaxanthin or omega-3 fatty acids. However, for some waste streams, further consideration of how to manage potential microbial and chemical contaminants is needed for food or health applications. The use of microalgae for waste valorization holds promise. Widespread implementation of the available technologies will likely follow from further improvements to reduce costs, as well as the increasing pressure to effectively manage waste.

  • Biogenesis of Selenium Nanoparticles Using Green Chemistry
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-11-09
    Sara Shoeibi, Paul Mozdziak, Afsaneh Golkar-Narenji

    Selenium binds some enzymes such as glutathione peroxidase and thioredoxin reductase, which may be activated in biological infections and oxidative stress. Chemical and physical methods for synthesizing nanoparticles, apart from being expensive, have their own particular risks. However, nanoparticle synthesis through green chemistry is a safe procedure that different biological sources such as bacteria, fungi, yeasts, algae and plants can be the catalyst bed for processing. Synthesis of selenium nanoparticles (SeNPs) by macro/microorganisms causes variation in morphology and shape of the particles is due to diversity of reduction enzymes in organisms. Reducing enzymes of microorganisms by changing the status of redox convert metal ions (Se2−) to SeNPs without charge (Se0). Biological activity of SeNPs includes their protective role against DNA oxidation. Because of the biological and industrial properties, SeNPs have wide applications in the fields of medicine, microelectronic, agriculture and animal husbandry. SeNPs can show strong antimicrobial effects on the growth and proliferation of microorganisms in a dose-dependent manner. The objective of this review is to consider SeNPs applications to various organisms.

  • Two-Dimensional Resonance Raman Signatures of Vibronic Coherence Transfer in Chemical Reactions
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-11-02
    Zhenkun Guo, Brian P. Molesky, Thomas P. Cheshire, Andrew M. Moran

    Two-dimensional resonance Raman (2DRR) spectroscopy has been developed for studies of photochemical reaction mechanisms and structural heterogeneity in condensed phase systems. 2DRR spectroscopy is motivated by knowledge of non-equilibrium effects that cannot be detected with traditional resonance Raman spectroscopy. For example, 2DRR spectra may reveal correlated distributions of reactant and product geometries in systems that undergo chemical reactions on the femtosecond time scale. Structural heterogeneity in an ensemble may also be reflected in the 2D spectroscopic line shapes of both reactive and non-reactive systems. In this chapter, these capabilities of 2DRR spectroscopy are discussed in the context of recent applications to the photodissociation reactions of triiodide. We show that signatures of “vibronic coherence transfer” in the photodissociation process can be targeted with particular 2DRR pulse sequences. Key differences between the signal generation mechanisms for 2DRR and off-resonant 2D Raman spectroscopy techniques are also addressed. Overall, recent experimental developments and applications of the 2DRR method suggest that it will be a valuable tool for elucidating ultrafast chemical reaction mechanisms.

  • Ultrafast structural molecular dynamics investigated with 2D infrared spectroscopy methods
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-10-25
    Jan Philip Kraack

    Ultrafast, multi-dimensional infrared (IR) spectroscopy has been advanced in recent years to a versatile analytical tool with a broad range of applications to elucidate molecular structure on ultrafast timescales, and it can be used for samples in a many different environments. Following a short and general introduction on the benefits of 2D IR spectroscopy, the first part of this chapter contains a brief discussion on basic descriptions and conceptual considerations of 2D IR spectroscopy. Outstanding classical applications of 2D IR are used afterwards to highlight the strengths and basic applicability of the method. This includes the identification of vibrational coupling in molecules, characterization of spectral diffusion dynamics, chemical exchange of chemical bond formation and breaking, as well as dynamics of intra- and intermolecular energy transfer for molecules in bulk solution and thin films. In the second part, several important, recently developed variants and new applications of 2D IR spectroscopy are introduced. These methods focus on (i) applications to molecules under two- and three-dimensional confinement, (ii) the combination of 2D IR with electrochemistry, (iii) ultrafast 2D IR in conjunction with diffraction-limited microscopy, (iv) several variants of non-equilibrium 2D IR spectroscopy such as transient 2D IR and 3D IR, and (v) extensions of the pump and probe spectral regions for multi-dimensional vibrational spectroscopy towards mixed vibrational-electronic spectroscopies. In light of these examples, the important open scientific and conceptual questions with regard to intra- and intermolecular dynamics are highlighted. Such questions can be tackled with the existing arsenal of experimental variants of 2D IR spectroscopy to promote the understanding of fundamentally new aspects in chemistry, biology and materials science. The final part of the chapter introduces several concepts of currently performed technical developments, which aim at exploiting 2D IR spectroscopy as an analytical tool. Such developments embrace the combination of 2D IR spectroscopy and plasmonic spectroscopy for ultrasensitive analytics, merging 2D IR spectroscopy with ultra-high-resolution microscopy (nanoscopy), future variants of transient 2D IR methods, or 2D IR in conjunction with microfluidics. It is expected that these techniques will allow for groundbreaking research in many new areas of natural sciences.

  • Thiophene-Based Organic Semiconductors
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-10-24
    Gulsen Turkoglu, M. Emin Cinar, Turan Ozturk

    Thiophene-based π-conjugated organic small molecules and polymers are the research subject of significant current interest owing to their potential use as organic semiconductors in material chemistry. Despite simple and similar molecular structures, the hitherto reported properties of thiophene-based organic semiconductors are rather diverse. Design of high performance organic semiconducting materials requires a thorough understanding of inter- and intra-molecular interactions, solid-state packing, and the influence of both factors on the charge carrier transport. In this chapter, thiophene-based organic semiconductors, which are classified in terms of their chemical structures and their structure–property relationships, are addressed for the potential applications as organic photovoltaics (OPVs), organic field-effect transistors (OFETs) and organic light emitting diodes (OLEDs).

  • Towards Rectifying Performance at the Molecular Scale
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-10-24
    Guang-Ping Zhang, Zhen Xie, Yang Song, Gui-Chao Hu, Chuan-Kui Wang

    Molecular diode, proposed by Mark Ratner and Arieh Aviram in 1974, is the first single-molecule device investigated in molecular electronics. As a fundamental device in an electric circuit, molecular diode has attracted an enduring and extensive focus during the past decades. In this review, the theoretical and experimental progresses of both charge-based and spin-based molecular diodes are summarized. For the charge-based molecular diodes, the rectifying properties originated from asymmetric molecules including D–σ–A, D–π–A, D–A, and σ–π type compounds, asymmetric electrodes, asymmetric nanoribbons, and their combination are analyzed. Correspondingly, the rectification mechanisms are discussed in detail. Furthermore, a series of strategies for modulating rectification performance is figured out. Discussion on concept of molecular spin diode is also involved based on a magnetic co-oligomer. At the same time, the intrinsic mechanism as well as the modulation of the spin-current rectification performance is introduced. Finally, several crucial issues that need to be addressed in the future are given.

  • Benzenoid Quinodimethanes
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-10-17
    Akihito Konishi, Takashi Kubo

    Reactivity and physical properties of π-conjugated hydrocarbon systems depend predominantly on the topology of π-electrons array. Quinoidal conjugations serve as giving diradical character to molecules, leading to unique chemical behaviors. The simplest member of quinodimethanes are o-, m-, and p-quinodimethanes, which are very reactive due to diradical character and cannot be isolated under normal experimental conditions. However, chemical modifications, such as π-extension or introduction of substituent groups, of quinodimethanes imparts stabilities to quinodimethanes that can be handled under ambient conditions. This chapter offers an overview of reactivity and magnetic properties of benzenoid o-, m-, and p-quinodimethanes.

  • Sulfur-Containing Agrochemicals
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-10-09
    Ponnam Devendar, Guang-Fu Yang

    Modern agricultural chemistry has to support farmers by providing innovative agrochemicals. In this context, the introduction of sulfur atoms into an active ingredient is still an important tool in modulating the properties of new crop-protection compounds. More than 30% of today’s agrochemicals contain at least one sulfur atom, mainly in fungicides, herbicides and insecticides. A number of recently developed sulfur-containing agrochemical candidates represent a novel class of chemical compounds with new modes of action, so we intend to highlight the emerging interest in commercially active sulfur-containing compounds. This chapter gives a comprehensive overview of selected leading sulfur-containing pesticidal chemical families namely: sulfonylureas, sulfonamides, sulfur-containing heterocyclics, thioureas, sulfides, sulfones, sulfoxides and sulfoximines. Also, the most suitable large-scale synthetic methods of the recently launched or provisionally approved sulfur-containing agrochemicals from respective chemical families have been highlighted.

  • Cell Concepts of Metal–Sulfur Batteries (Metal = Li, Na, K, Mg): Strategies for Using Sulfur in Energy Storage Applications
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-09-29
    Lukas Medenbach, Philipp Adelhelm

    There is great interest in using sulfur as active component in rechargeable batteries thanks to its low cost and high specific charge (1672 mAh/g). The electrochemistry of sulfur, however, is complex and cell concepts are required, which differ from conventional designs. This review summarizes different strategies for utilizing sulfur in rechargeable batteries among membrane concepts, polysulfide concepts, all-solid-state concepts as well as high-temperature systems. Among the more popular lithium–sulfur and sodium–sulfur batteries, we also comment on recent results on potassium–sulfur and magnesium–sulfur batteries. Moreover, specific properties related to the type of light metal are discussed.

  • 1,3-Diphenylisobenzofuran: a Model Chromophore for Singlet Fission
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-09-11
    Justin C. Johnson, Josef Michl

    In this review we first provide an introductory description of the singlet fission phenomenon and then describe the ground and electronically excited states of the parent 1,3-diphenylisobenzofuran chromophore (1) and about a dozen of its derivatives. A discussion of singlet fission in thin polycrystalline layers of these materials follows. The highest quantum yield of triplet formation by singlet fission, 200% at 80 K, is found in one of the two known crystal modification of the parent. In the other modification and in many derivatives, excimer formation competes successfully and triplet yields are low. A description of solution photophysics of covalent dimers is described in the next section. Triplet yields are very low, but interesting phenomena are uncovered. One is an observation of a separated-charges (charge-transfer) intermediate in highly polar solvents. The other is an observation of excitation isomerism in both singlet and triplet states, where in one isomer the excitation is delocalized over both halves of the covalent dimer, whereas in the other it is localized on one of the halves. In the last section we present the operation of a simple device illustrating the use of triplets generated by singlet fission for charge separation.

  • Nonlinear and Nonsymmetric Single-Molecule Electronic Properties Towards Molecular Information Processing
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-09-05
    Takashi Tamaki, Takuji Ogawa

    This review highlights molecular design for nonlinear and nonsymmetric single-molecule electronic properties such as rectification, negative differential resistance, and switching, which are important components of future single-molecule information processing devices. Perspectives on integrated “molecular circuits” are also provided. Nonlinear and nonsymmetric single-molecule electronics can be designed by utilizing (1) asymmetric molecular cores, (2) asymmetric anchoring groups, (3) an asymmetric junction environment, and (4) asymmetric electrode materials. This review mainly focuses on the design of molecular cores.

  • Lewis Acidic Ionic Liquids
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-08-21
    Lucy C. Brown, James M. Hogg, Małgorzata Swadźba-Kwaśny

    Until very recently, the term Lewis acidic ionic liquids (ILs) was nearly synonymous with halometallate ILs, with a strong focus on chloroaluminate(III) systems. The first part of this review covers the historical context in which these were developed, speciation of a range of halometallate ionic liquids, attempts to quantify their Lewis acidity, and selected recent applications: in industrial alkylation processes, in supported systems (SILPs/SCILLs) and in inorganic synthesis. In the last decade, interesting alternatives to halometallate ILs have emerged, which can be divided into two sub-sections: (1) liquid coordination complexes (LCCs), still based on halometallate species, but less expensive and more diverse than halometallate ionic liquids, and (2) ILs with main-group Lewis acidic cations. The two following sections cover these new liquid Lewis acids, also highlighting speciation studies, Lewis acidity measurements, and applications.

  • Functional Organometallic Poly(arylene ethynylene)s: From Synthesis to Applications
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-08-17
    Jie Zhang, Linli Xu, Cheuk-Lam Ho, Wai-Yeung Wong

    This review focuses on the recent development in the rigid-rod metallopolymers of late transition metals based on triple-bond building blocks. The synthesis, structure–property relationships and potential applications of organometallic poly(arylene ethynylene)s will be discussed in detail. These functional metal-based polymers can exhibit intriguing optical, electronic and magnetic properties. Considerable focus is placed on the design strategies towards tuning the optical bandgap and emission color (spanning almost the whole visible spectrum) of this class of metallopolymers, and the investigation of their use as active materials for light/electrical energy conversion and energy and information storage. The ongoing scientific challenges and future prospects of this research field are also highlighted.

  • Recent Trends in Sustainable Textile Waste Recycling Methods: Current Situation and Future Prospects
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-08-16
    Nattha Pensupa, Shao-Yuan Leu, Yunzi Hu, Chenyu Du, Hao Liu, Houde Jing, Huaimin Wang, Carol Sze Ki Lin

    In recent years, there have been increasing concerns in the disposal of textile waste around the globe. The growth of textile markets not only depends on population growth but also depends on economic and fashion cycles. The fast fashion cycle in the textile industry has led to a high level of consumption and waste generation. This can cause a negative environmental impact since the textile and clothing industry is one of the most polluting industries. Textile manufacturing is a chemical-intensive process and requires a high volume of water throughout its operations. Wastewater and fiber wastes are the major wastes generated during the textile production process. On the other hand, the fiber waste was mainly created from unwanted clothes in the textile supply chain. This fiber waste includes natural fiber, synthetic fiber, and natural/synthetic blends. The natural fiber is mostly comprised of cellulosic material, which can be used as a resource for producing bio-based products. The main challenge for utilization of textile waste is finding the method that is able to recover sugars as monosaccharides. This review provides an overview of valorization of textile waste to value-added products, as well as an overview of different strategies for sugar recovery from cellulosic fiber and their hindrances.

  • Review of Electronics Based on Single-Walled Carbon Nanotubes
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-08-14
    Yu Cao, Sen Cong, Xuan Cao, Fanqi Wu, Qingzhou Liu, Moh. R. Amer, Chongwu Zhou

    Single-walled carbon nanotubes (SWNTs) are extremely promising materials for building next-generation electronics due to their unique physical and electronic properties. In this article, we will review the research efforts and achievements of SWNTs in three electronic fields, namely analog radio-frequency electronics, digital electronics, and macroelectronics. In each SWNT-based electronic field, we will present the major challenges, the evolutions of the methods to overcome these challenges, and the state-of-the-art of the achievements. At last, we will discuss future directions which could lead to the broad applications of SWNTs. We hope this review could inspire more research on SWNT-based electronics, and accelerate the applications of SWNTs.

  • Ionic Liquid–Liquid Chromatography: A New General Purpose Separation Methodology
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-08-10
    Leslie Brown, Martyn J. Earle, Manuela A. Gîlea, Natalia V. Plechkova, Kenneth R. Seddon

    Ionic liquids can form biphasic solvent systems with many organic solvents and water, and these solvent systems can be used in liquid–liquid separations and countercurrent chromatography. The wide range of ionic liquids that can by synthesised, with specifically tailored properties, represents a new philosophy for the separation of organic, inorganic and bio-based materials. A customised countercurrent chromatograph has been designed and constructed specifically to allow the more viscous character of ionic liquid-based solvent systems to be used in a wide variety of separations (including transition metal salts, arenes, alkenes, alkanes, bio-oils and sugars).

  • Para -Quinodimethanes: A Unified Review of the Quinoidal-Versus-Aromatic Competition and its Implications
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-07-31
    Juan Casado

    In this article, some quinoidal p-quinodimethanes compounds that convert partially or completely to diradicals or biradicaloids are analyzed. The aromatic/quinoidal balance is revisited with the objective of providing a common interpretation for most of them. For that purpose, important structural and energetic parameters such as the bond length alternation pattern and the singlet–triplet gaps are analyzed and interpreted in the framework of double spin polarization and π-conjugation. p-Quinodimethanes based in oligothiophenes, polycyclic aromatic hydrocarbons, oligophenylenes, thienothiophenes, charged dications and cyclic conjugated molecules are discussed. There are excellent reviews in the field of singlet diradicals; however, a revision similar to that proposed here can help the reader to have another perspective on these promising new functional materials. The focus has been put on molecules which are well known by the author and another of relevance in the field. In this regard, the article finishes with a discussion of some important applications of these diradicals in organic electronics. New chemical systems based on the p-quinodimethane building blocks are waiting us around the corner, bringing us new and challenging structures and fascinating novel properties, which describe a very rich field of research in chemistry and in physics with an excellent present and a bright future.

  • Helical Polyacetylenes Induced via Noncovalent Chiral Interactions and Their Applications as Chiral Materials
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-07-20
    Katsuhiro Maeda, Eiji Yashima

    Construction of predominantly one-handed helical polyacetylenes with a desired helix sense utilizing noncovalent chiral interactions with nonracemic chiral guest compounds based on a supramolecular approach is described. As with the conventional dynamic helical polymers possessing optically active pendant groups covalently bonded to the polymer chains, this noncovalent helicity induction system can show significant chiral amplification phenomena, in which the chiral information of the nonracemic guests can transfer with high cooperativity through noncovalent bonding interactions to induce an almost single-handed helical conformation in the polymer backbone. An intriguing “memory effect” of the induced macromolecular helicity is observed for some polyacetylenes, which means that the helical conformations induced in dynamic helical polyacetylene can be transformed into metastable static ones by tuning their helix-inversion barriers. Potential applications of helical polyacetylenes with controlled helix sense constructed by the “noncovalent helicity induction and/or memory effect” as chiral materials are also described.

  • Potential of Casein as a Carrier for Biologically Active Agents
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-07-15
    Tomasz Konrad Głąb, Janusz Boratyński

    Casein is the collective name for a family of milk proteins. In bovine milk, casein comprises four peptides: αS1, αS2, β, and κ, differing in their amino acid, phosphorus and carbohydrate content but similar in their amphiphilic character. Hydrophilic and hydrophobic regions of casein show block distribution in the protein chain. Casein peptides carry negative charge on their surface as a result of phosphorylation and tend to bind nanoclusters of amorphous calcium phosphate. Due to these properties, in suitable conditions, casein molecules agglomerate into spherical micelles. The high content of casein in milk (2.75 %) has made it one of the most popular proteins. Novel research techniques have improved understanding of its properties, opening up new applications. However, casein is not just a dietary protein. Its properties promise new and unexpected applications in science and the pharmaceutical and functional food industries. One example is an encapsulation of health-related substances in casein matrices. This review discusses gelation, coacervation, self-assembly and reassembly of casein peptides as means of encapsulation. We highlight information on encapsulation of health-related substances such as drugs and dietary supplements inside casein micro- and nanoparticles.

  • Recent New Methodologies for Acetylenic Polymers with Advanced Functionalities
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-06-27
    Zijie Qiu, Ting Han, Jacky W. Y. Lam, Ben Zhong Tang

    Polymers synthesized from acetylenic monomers often possess electronically unsaturated fused rings and thus show versatile optoelectronic properties and advanced functionalities. To expand the family of acetylenic polymers, development of new catalyst systems and synthetic routes is critically important. We summarize herein recent research progress on development of new methodologies towards functional polymers using alkyne building blocks since 2014. The polymerizations are categorized by the number of monomer components, namely homopolymerizations, two-component polymerizations, and multicomponent polymerizations. The properties and applications of acetylenic polymers, such as aggregation-induced emission, fluorescent photopatterning, light refraction, chemosensing, mechanochromism, chain helicity, etc., are also discussed.

  • Poly(aryleneethynylene)s: Properties, Applications and Synthesis Through Alkyne Metathesis
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-06-26
    Michael Ortiz, Chao Yu, Yinghua Jin, Wei Zhang

    Functional polymeric materials have seen their way into every facet of materials chemistry and engineering. In this review article, we focus on a promising class of polymers, poly(aryleneethynylene)s, by covering several of the numerous applications found thus far for these materials. Additionally, we survey the current synthetic strategies used to create these polymers, with a focus on the emerging technique of alkyne metathesis. An overview is presented of the most recent catalytic systems that support alkyne metathesis as well as the more useful alkyne metathesis reaction capable of synthesizing poly(aryleneethynylene)s.

  • Heterocyclic Quinodimethanes
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-06-20
    Xueliang Shi, Chunyan Chi

    This chapter describes a series of heterocyclic quinodimethanes mainly containing O, N, S and Si atoms in their frameworks with either closed- or open-shell electronic structures in the ground state. Their syntheses, structural characterizations and chemical and physical properties are comprehensively reviewed. Some of them are used as materials for dyes/pigments and semiconductors for organic electronics. Some of them show an open-shell singlet diradical character with unusual properties. The purpose of this chapter is to provide fundamental understanding on the structure-property relationships of quinoidal π-conjugated compounds and give some insight into the rational design of such molecules with desirable properties.

  • Chemical Tongues and Noses Based upon Conjugated Polymers
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-06-19
    Jan Freudenberg, Felix Hinkel, Daniel Jänsch, Uwe H. F. Bunz

    We report the uses of conjugated polymers in multisensory applications and in chemical and optoelectronic tongues. We look at the potential of single polymers to discriminate multiple analytes and into small libraries of conjugated polymers that represent sensors. These small libraries combine several barely selective, promiscuous sensor elements and react with the analytes in a fairly non-selective fashion by change of color, emission wavelength, or emission intensity. In such optoelectronic noses and tongues, response of a single element is not specific or particularly useful at all, but the response pattern after the combination of several sensor elements is often specific for an analyte and allows discrimination and identification without any problem. These types of tongues and noses are well suited for quality control of foodstuff, beverages, and biological species such as proteins or cells. The discriminative process is often not well understood but it is powerful, particularly if the obtained data are analyzed by sophisticated statistical methods, i.e., linear discriminant analysis and/or principal component analysis. This added layer of analysis extracts the hidden information/patterns out of the data and allows visualization of the results.

  • An Update on Isocyanide-Based Multicomponent Reactions in Polymer Science
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-06-12
    Audrey Llevot, Andreas C. Boukis, Stefan Oelmann, Katharina Wetzel, Michael A. R. Meier

    Developments and progress in polymer science are often inspired by organic chemistry. In recent years, multicomponent reactions—especially the Passerini and Ugi reactions—have become very important tools for macromolecular design, mainly due to their modular character. In this review, the versatility of the Passerini and Ugi reactions in polymer science is highlighted by discussing recent examples of their use for monomer synthesis, as polymerization techniques, and for postpolymerization modification, as well as their suitability for architecture control, sequence control, and sequence definition.

  • Metal Nanoparticles in Ionic Liquids
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-06-06
    Susann Wegner, Christoph Janiak

    During the last years ionic liquids (ILs) were increasingly used and investigated as reaction media, hydrogen sources, catalysts, templating agents and stabilizers for the synthesis of (monometallic and bimetallic) metal nanoparticles (M-NPs). Especially ILs with 1,3-dialkyl-imidazolium cations featured prominently in the formation and stabilization of M-NPs. This chapter summarizes studies which focused on the interdependencies of the IL with the metal nanoparticle and tried to elucidate, for example, influences of the IL-cation, -anion and alkyl chain length. Qualitatively, the size of M-NPs was found to increase with the size of the IL-anion. The influence of the size of imidazolium-cation is less clear. The M-NP size was both found to increase and to decrease with increasing chain lengths of the 1,3-dialkyl-imidazolium cation. It is evident from such reports on cation and anion effects of ILs that the interaction between an IL and a (growing) metal nanoparticle is far from understood. Factors like IL-viscosity, hydrogen-bonding capability and the relative ratio of polar and non-polar domains of ILs may also influence the stability of nanoparticles in ionic liquids and an improved understanding of the IL-nanoparticle interaction would be needed for a more rational design of nanomaterials in ILs. Furthermore, thiol-, ether-, carboxylic acid-, amino- and hydroxyl-functionalized ILs add to the complexity by acting also as coordinating capping ligands. In addition imidazolium cations are precursors to N-heterocyclic carbenes, NHCs which form from imidazolium-based ionic liquids by in situ deprotonation at the acidic C2-H ring position as intermediate species during the nanoparticle seeding and growth process or as surface coordinating ligand for the stabilization of the metal nanoparticle.

  • Towards Microcapsules with Improved Barrier Properties
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-05-31

    Microencapsulation is the generic term for numerous technologies, which are often used when the release rate of an active substance in a medium has to be controlled and/or contact between the active substance and the medium has to be prevented. This is achieved by wrapping the tiny particles or droplets of the active substance (capsule core) with a thin layer, or membrane, of another material (capsule shell). The permeability of the membrane determines whether, how fast and under which conditions the active material will be released and/or the components of the medium will enter the inner part of the capsule. Insofar as application is concerned, premature release of an active substance from microcapsules during storage is a very common problem. Prevention of diffusion of an active component or components of the outer medium through the capsule membrane is a complex challenge, which so far cannot be considered as solved. This review briefly covers the theoretical aspects of release kinetics from microcapsules and discusses how such parameters as capsule average size, capsule shell thickness as well as the chemical composition of active material and medium can influence the release profiles. All theoretical considerations are based on the dissolution-diffusion mechanism classically used for the explanation of diffusion trough flat membranes/films. In the second part of the manuscript it is discussed, which strategies have been used for the improvement of the barrier properties of microcapsules up to date and to which extent those strategies were successful.

  • Ionic Liquids for Supercapacitor Applications
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-05-30

    Supercapacitors are electrochemical energy storage devices in which the charge is accumulated through the adsorption of ions from an electrolyte on the surface of the electrode. Because of their large ionic concentrations, ionic liquids have widely been investigated for such applications. The main properties that have to be optimized are the electrochemical window, the electrical conductivity, and the interfacial capacitances. Ionic liquids allow a significant improvement of the former, but they suffer from their high viscosity. In this review, I will discuss the advantages and the inconvenience of using ionic liquids in supercapacitors. Some innovative approaches using mixtures of ionic liquids or redox-active ions will also be critically addressed.

  • Fabrication of Low-Generation Dendrimers into Nanostructures for Efficient and Nontoxic Gene Delivery
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-05-29

    Dendrimers with well-defined molecular structure and high monodispersity have gained tremendous interest in gene delivery. However, current gene carriers based on dendrimers are either not effective or are too toxic on the transfected cells. The efficacy and cytotoxicity of dendrimers are strongly correlated with their molecular weight or generation. High-generation dendrimers are reported with relatively high transfection efficacy but serious cytotoxicity due to the excess positive charges on the polymers, while low-generation dendrimers with minimal toxicity have poor polyplex stability and thus weak transfection efficacy. To break up the correlation between efficacy and toxicity, low-generation dendrimers were fabricated into various nanostructures by several strategies to improve their gene-binding capacity, polyplex stability, and transfection efficacy without inducing additional toxicity. In this review article, we will highlight recent advances in the development of assembled dendrimer nanostructures for efficient and non-toxic gene delivery. Specifically, the principles and strategies in the fabrication of dendrimer nanostructures are intensively reviewed.

  • Advance of Mechanically Controllable Break Junction for Molecular Electronics
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-05-24

    Molecular electronics stands for the ultimate size of functional elements, keeping up with an unstoppable trend over the past few decades. As a vital component of molecular electronics, single molecular junctions have attracted significant attention from research groups all over the world. Due to its pronounced superiority, the mechanically controllable break junctions (MCBJ) technique has been widely applied to characterize the dynamic performance of single molecular junctions. This review presents a system analysis for single-molecule junctions and offers an overview of four test-beds for single-molecule junctions, thus offering more insight into the mechanisms of electron transport. We mainly focus on the development of state-of-the-art mechanically controlled break junctions. The three-terminal gated MCBJ approaches are introduced to manipulate the electron transport of molecules, and MCBJs are combined with characterization techniques. Additionally, applications of MCBJs and remarkable properties of single molecules are addressed. Finally, the challenges and perspective for the mechanically controllable break junctions technique are provided.

  • Construction of Polyarylenes with Various Structural Features via Bergman Cyclization Polymerization
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-05-22

    Synthetic polymer chemistry is a fundamental part of polymer science, and highly efficient polymerization reactions are essential for the synthesis of high-performance polymers. Development of new synthetic methods for emerging polymer science is of great importance in this regard. Bergman cyclization is a chemical process in which highly reactive aryl diradicals form from enediyne precursors, having a strong impact in a number of fields including pharmaceutics, synthetic chemistry, and materials science. Diradical intermediates stemming from enediynes can cause DNA cleavage under physiological conditions, leading to the strong cytotoxicity of many naturally occurring enediyne antibiotics. Meanwhile, diradical intermediates can quickly couple with each other to construct polyarylenes, providing a novel method to synthesize these conjugated polymers with the advantages of facile and catalyst-free operation, high efficiency, and tailored structure. Moreover, conjugated polymers generated by Bergman cyclization exhibit many remarkable properties, such as excellent thermal stability and good solubility and processability, enabling their further processing into carbon-rich materials. This review presents a brief overview of the trajectory of Bergman cyclization in polymer science, followed by an introduction to research advances, mainly from our group, in developing polymerization methods based on Bergman cyclization, taking advantages of its catalyst-free, byproduct-free, in situ polymerization mechanism to synthesize new polymeric materials with various structures and morphologies. These synthetic strategies include fabrication of rod-like polymers with polyester, dendrimer, and chiral imide side chains, functionalization of carbon nanomaterials by surface-grafting conjugated polymers, formation of nanoparticles by intramolecular collapse of single polymer chains, and construction of carbon nanomembranes on the external and internal surface of inorganic nanomaterials. These polymers with novel structural features have been used in a variety of fields, such as energy transformation, energy storage, catalyst support, and fluorescent detection. Finally, the outlook for future developments of Bergman cyclization in polymer science is presented.

  • Quantum Chemical Modeling of Hydrogen Bonding in Ionic Liquids
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-05-18

    Hydrogen bonding (H-bonding) is an important and very general phenomenon. H-bonding is part of the basis of life in DNA, key in controlling the properties of water and ice, and critical to modern applications such as crystal engineering, catalysis applications, pharmaceutical and agrochemical development. H-bonding also plays a significant role for many ionic liquids (IL), determining the secondary structuring and affecting key physical parameters. ILs exhibit a particularly diverse and wide range of traditional as well as non-standard forms of H-bonding, in particular the doubly ionic H-bond is important. Understanding the fundamental nature of the H-bonds that form within ILs is critical, and one way of accessing this information, that cannot be recovered by any other computational method, is through quantum chemical electronic structure calculations. However, an appropriate method and basis set must be employed, and a robust procedure for determining key structures is essential. Modern generalised solvation models have recently been extended to ILs, bringing both advantages and disadvantages. QC can provide a range of information on geometry, IR and Raman spectra, NMR spectra and at a more fundamental level through analysis of the electronic structure.

  • Mesoscopic organization in ionic liquids
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-05-17

    We discuss some published results and provide new observations concerning the high level of structural complexity that lies behind the nanoscale correlations in ionic liquids (ILs) and their mixtures with molecular liquids. It turns out that this organization is a consequence of the hierarchical construction on both spatial (from ångström to several nanometer) and temporal (from fraction of picosecond to hundreds of nanosecond) scales, which requires joint use of experimental and computational tools.

  • Recent Developments in the Synthesis of Cyclic Carbonates from Epoxides and CO 2
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-04-24

    The use of CO2 as a C1 building block will be of essential importance in the future. In this context the synthesis of cyclic carbonates from epoxides and CO2 gained great attention recently. These products are valuable compounds in a variety of chemical fields. The development of new catalysts and catalytic systems for this atom-economic, scalable, and industrially relevant reaction is a highly active research field. Over the past 17 years great advances have been made in this area of research. This chapter covers the survey of the important known classes of homogeneous catalysts for the addition of CO2 to epoxides. Besides pioneering work, recent developments and procedures that allow this transformation under mild reaction conditions (reaction temperatures of ≤100 °C and/or CO2 pressures of 0.1 MPa) are especially emphasized.

  • New Synthetic Methods for Phosphate Labeling
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-04-25

    The complexity of phosphorylation pathways and their downstream effects is vast. Synthetic chemistry has been working side by side with biology to develop phosphate labels for biological processes involving phosphorylated compounds. This chapter discusses recently employed methods for the preparation of several phosphate labels. Synthesis of biomolecules and their analogs and other useful or potentially useful phosphate derivatives is discussed.

  • Hydrogen Sulfide and Ionic Liquids: Absorption, Separation, and Oxidation
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-04-26

    Economical and environmental concerns are the main motivations for development of energy-efficient processes and new eco-friendly materials for the capture of greenhouse gases. Currently, H2S capture is dominated by physical and/or chemical absorption technologies, which are, however, energy intensive and often problematic from an environmental point of view due to emission of volatile solvent components. Ionic liquids have been proposed as a promising alternative to conventional solvents because of their low volatility and other interesting properties. The aim of the present review paper is to provide a detailed overview of the achievements and difficulties that have been encountered in finding suitable ionic liquids for H2S capture. The effect of ionic liquid anions, cations, and functional groups on the H2S absorption, separation, and oxidation are highlighted. Recent developments on yet scarcely available molecular simulations and on the development of robust predictive methods are also discussed.

  • Valorization of Proteins from Co- and By-Products from the Fish and Meat Industry
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-05-02

    Large volumes of protein-rich residual raw materials, such as heads, bones, carcasses, blood, skin, viscera, hooves and feathers, are created as a result of processing of animals from fisheries, aquaculture, livestock and poultry sectors. These residuals contain proteins and other essential nutrients with potentially bioactive properties, eligible for recycling and upgrading for higher-value products, e.g. for human, pet food and feed purposes. Here, we aim to cover all the important aspects of achieving optimal utilization of proteins in such residual raw materials, identifying those eligible for human consumption as co-products and for feed applications as by-products. Strict legislation regulates the utilization of various animal-based co- and by-products, representing a major hurdle if not addressed properly. Thorough understanding and optimization of all parts of the production chain, including conservation and processing, are important prerequisites for successful upgrading and industrial implementation of such products. This review includes industrially applied technologies such as freezing/cooling, acid preservation, salting, rendering and protein hydrolysis. In this regard, it is important to achieve stable production and quality through all the steps in the manufacturing chain, preferably supported by at- or online quality control points in the actual processing step. If aiming for the human market, knowledge of consumer trends and awareness are important for production and successful introduction of new products and ingredients.

  • Challenges Considering the Degradation of Cell Components in Commercial Lithium-Ion Cells: A Review and Evaluation of Present Systems
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-05-03

    Owing to the high energy and power density of lithium-ion cells (1200 Wh kg−1 and 200 Wh kg−1) and due to their compact design, they are used as energy storage devices in many contemporary mobile applications such as telecommunication systems, notebooks and domestic appliances. Meanwhile their application is not limited only to consumer electronics, they are also standard in hybrid electric (HEVs) and electric vehicles (EVs). However, the profitable application of lithium-ion cells in the automobile industry requires lower costs, lower safety risks, a higher specific energy density and a longer lifetime under everyday conditions. All these aspects are directly or indirectly related to the degradation of the materials in a lithium-ion cell. One possibility for reducing the costs is a second life application of the cells after their usage in (H)EVs. In order to enable this, the safety risks at the end of life of a cell operated in a vehicle have to be reliably predicted. This requires a fundamental knowledge about underlying material degradations during operation. The safety risk of a lithium-ion cell increases during operation because the voltage windows in which the electrodes are cycled shift, resulting in a higher possibility that at least one electrode is operated in a meta- or unstable state. Furthermore, higher impedances due to material degradations lead to increasing heat generation and therefore to an increase in the risk of failure. Higher energy densities can be achieved by raising the end of charge voltage of a cell, causing additional safety risks because many cathode materials tend to decompose at high voltages. Another possibility for achieving higher energy densities is to use nickel-rich or lithium-excess cathode materials, since cathodes are currently limiting the capacity of lithium-ion cells. But these systems show a poor cycling stability (a higher degradation rate). The lifetime of a lithium-ion cell is limited by the degradation of the individual cell components. Although the degradation of materials is the key consideration in achieving lower costs, a higher safety standard, higher energy densities and a longer lifetime, the degradation of the individual cell components in dependence on the operation conditions has hardly been investigated and is poorly understood. The present work reviews known material degradations in commercial lithium-ion cells, shows a way to analyze such degradations in dependence on the operation conditions and describes how these degradation processes lead to observed performance drops.

  • Modeling the Growth of Single-Wall Carbon Nanotubes
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-05-08

    More than 20 years after their discovery, our understanding of the growth mechanisms of single-wall carbon nanotubes is still incomplete, in spite of a large number of investigations motivated by potential rewards in many possible applications. Among the many techniques used to solve this challenging puzzle, computer simulations can directly address an atomic scale that is hardly accessible by other experiments, and thereby support or invalidate different ideas, assumptions, or models. In this paper, we review some aspects of the computer simulation and theoretical approaches dedicated to the study of single-wall carbon nanotube growth, and suggest some ways towards a better control of the synthesis processes by chemical vapor deposition.

  • Switching Effects in Molecular Electronic Devices
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-05-10

    The creation of molecular electronic switches by using smart molecules is of great importance to the field of molecular electronics. This requires a fundamental understanding of the intrinsic electron transport mechanisms, which depend on several factors including the charge transport pathway, the molecule–electrode coupling strength, the energy of the molecular frontier orbitals, and the electron spin state. On the basis of significant progresses achieved in both experiments and theory over the past decade, in this review article we focus on new insights into the design and fabrication of different molecular switches and the corresponding switching effects, which is crucial to the development of molecular electronics. We summarize the strategies developed for single-molecule device fabrication and the mechanism of these switching effects. These analyses should be valuable for deeply understanding the switching effects in molecular electronic devices.

  • Synthesis of Ureas from CO 2
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-04-10

    Ureas are an important class of bioactive organic compounds in organic chemistry and exist widely in natural products, agricultural pesticides, uron herbicides, pharmaceuticals. Even though urea itself has been synthesized from CO2 and ammonia for a long time, the selective and efficient synthesis of substituted ureas is still challenging due to the difficulty of dehydration processes. Efficient and economic fixation of CO2 is of great importance in solving the problems of resource shortages, environmental issues, global warming, etc. During recent decades, chemists have developed different catalytic systems to synthesize ureas from CO2 and amines. Herein, we focus on catalytic synthesis of ureas using CO2 and amines.

  • Brain-Targeted Polymers for Gene Delivery in the Treatment of Brain Diseases
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-04-10

    Gene therapies have become a promising strategy for treating neurological disorders, such as brain cancer and neurodegenerative diseases, with the help of molecular biology interpreting the underlying pathological mechanisms. Successful cellular manipulation against these diseases requires efficient delivery of nucleic acids into brain and further into specific neurons or cancer cells. Compared with viral vectors, non-viral polymeric carriers provide a safer and more flexible way of gene delivery, although suffering from significantly lower transfection efficiency. Researchers have been devoted to solving this defect, which is attributed to the multiple barriers existing for gene therapeutics in vivo, such as systemic degradation, blood–brain barrier, and endosome trapping. This review will be mainly focused on systemically administrated brain-targeted polymers developed so far, including PEI, dendrimers, and synthetic polymers with various functions. We will discuss in detail how they are designed to overcome these barriers and how they efficiently deliver therapeutic nucleic acids into targeted cells.

  • Electronic Structure of Open-Shell Singlet Molecules: Diradical Character Viewpoint
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-04-04

    This chapter theoretically explains the electronic structures of open-shell singlet systems with a wide range of open-shell (diradical) characters. The definition of diradical character and its correlation to the excitation energies, transition properties, and dipole moment differences are described based on the valence configuration interaction scheme using a two-site model with two electrons in two active orbitals. The linear and nonlinear optical properties for various polycyclic aromatic hydrocarbons with open-shell character are also discussed as a function of diradical character.

  • Valorisation of Biowastes for the Production of Green Materials Using Chemical Methods
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-04-03

    With crude oil reserves dwindling, the hunt for a sustainable alternative feedstock for fuels and materials for our society continues to expand. The biorefinery concept has enjoyed both a surge in popularity and also vocal opposition to the idea of diverting food-grade land and crops for this purpose. The idea of using the inevitable wastes arising from biomass processing, particularly farming and food production, is, therefore, gaining more attention as the feedstock for the biorefinery. For the three main components of biomass—carbohydrates, lipids, and proteins—there are long-established processes for using some of these by-products. However, the recent advances in chemical technologies are expanding both the feedstocks available for processing and the products that be obtained. Herein, this review presents some of the more recent developments in processing these molecules for green materials, as well as case studies that bring these technologies and materials together into final products for applied usage.

  • Determination of Relative Counterion Binding Constant to Cationic Micelles
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-03-29

    The efficiency of counterion affinity towards ionic micelles is often described in terms of the degree of counterion binding (β X ) to ionic micelles or the conventional ion-exchange constant ( \(K_{X}^{\text{Br}}\) ) or relative binding constant ( \(R_{X}^{\text{Br}}\) ) of X − and Br− counterions. This review describes the use of ionized phenyl salicylate ions, PSa−, as a new probe to determine \(K_{X}^{\text{Br}}\) values using a semiempirical spectrophotometric method. The value of \(K_{X}^{\text{Br}}\) is found to be comparable to reported values obtained using different probes by the semiempirical kinetic method as well as different physical methods. Application of semiempirical methods for calculation of \(K_{X}^{\text{Br}}\) or \(R_{X}^{\text{Br}}\) values involves an inherent assumption that these values are independent of the physicochemical characteristics of the probe molecule.

  • Polymer–Nucleic Acid Interactions
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-03-29

    Gene therapy is an important therapeutic strategy in the treatment of a wide range of genetic disorders. Polymers forming stable complexes with nucleic acids (NAs) are non-viral gene carriers. The self-assembly of polymers and nucleic acids is typically a complex process that involves many types of interaction at different scales. Electrostatic interaction, hydrophobic interaction, and hydrogen bonds are three important and prevalent interactions in the polymer/nucleic acid system. Electrostatic interactions and hydrogen bonds are the main driving forces for the condensation of nucleic acids, while hydrophobic interactions play a significant role in the cellular uptake and endosomal escape of polymer-nucleic acid complexes. To design high-efficiency polymer candidates for the DNA and siRNA delivery, it is necessary to have a detailed understanding of the interactions between them in solution. In this chapter, we survey the roles of the three important interactions between polymers and nucleic acids during the formation of polyplexes and summarize recent understandings of the linear polyelectrolyte–NA interactions and dendrimer–NA interactions. We also review recent progress optimizing the gene delivery system by tuning these interactions.

  • Waste Printed Circuit Board (PCB) Recycling Techniques
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-03-28

    With the development of technologies and the change of consumer attitudes, the amount of waste electrical and electronic equipment (WEEE) is increasing annually. As the core part of WEEE, the waste printed circuit board (WPCB) is a dangerous waste but at the same time a rich resource for various kinds of materials. In this work, various WPCB treatment methods as well as WPCB recycling techniques divided into direct treatment (landfill and incineration), primitive recycling technology (pyrometallurgy, hydrometallurgy, biometallurgy and primitive full recovery of NMF-non metallic fraction), and advanced recycling technology (mechanical separation, direct use and modification of NMF) are reviewed and analyzed based on their advantages and disadvantages. Also, the evaluation criteria are discussed including economic, environmental, and gate-to-market ability. This review indicates the future research direction of WPCB recycling should focus on a combination of several techniques or in series recycling to maximize the benefits of process.

  • Polysaccharide-based Nanoparticles for Gene Delivery
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-03-01

    Nanoparticles based on nanotechnology and biotechnology have emerged as efficient carriers for various biopharmaceutical agents including proteins and genes. In particular, polysaccharides have attracted interest of many researchers in the drug delivery field due to their advantages such as biocompatibility, biodegradability, low toxicity, and ease of modification. A number of polysaccharides including chitosan, hyaluronic acid, and dextran, and their derivatives have been widely used as polymeric backbones for the formation of nanoparticles, which can be provided as valuable gene delivery carriers. In this review, we introduce the chemical and physical natures of different polysaccharides particularly used in biomedical applications, and then discuss recent progress in the development of polysaccharide-based nanoparticles for gene delivery.

  • Metallic Catalysts for Structure-Controlled Growth of Single-Walled Carbon Nanotubes
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-03-01

    Single-walled carbon nanotubes (SWNTs) have shown great potential in various applications attributed to their unique structures and outstanding structure-dependent properties. The structure-controlled growth of SWNTs is a crucial issue for their advanced applications and has been a great challenge in this field for two decades. Metal catalyst-mediated SWNT growth is believed to be very efficient. In this review, progresses in diameter and chirality controlled growth of SWNTs with metal catalysts is summarized from several aspects, including growth mechanism and theory, effects of catalysts, and the chemical vapor deposition conditions. The design, preparation, handling and dispersion, and the size evolution of metal catalysts are all discussed. The influences of growth environment including the type, composition, and pressure/concentration of the carbon source as well as the temperature on the selectivity toward the nanotube structure are analyzed. We also discuss some of the challenges and trends in this field.

  • Fluorescence Sensing of Inorganic Phosphate and Pyrophosphate Using Small Molecular Sensors and Their Applications
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-03-01

    The aim of this contribution is to provide an introduction and a brief summary of the principle of fluorescence molecular sensors specific to inorganic phosphate (Pi) and inorganic pyrophosphate (PPi) as well as their applications. In our introduction we describe the impact of both Pi and PPi in the living organism and in the environment, followed by a description of the principle of fluorescence molecular sensors and the sensing mechanism in solution. We then focus on exciting research which has emerged in recent years on the development of fluorescent sensors specific to Pi and PPi, categorized by chemical interactions between the sensor and the target molecule, such as hydrogen bonding, coordination chemistry, displacement assay, aggregation induced emission or quenching, and chemical reactions.

  • Phosphate-Modified Nucleotides for Monitoring Enzyme Activity
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-03-01

    Nucleotides modified at the terminal phosphate position have been proven to be interesting entities to study the activity of a variety of different protein classes. In this chapter, we present various types of modifications that were attached as reporter molecules to the phosphate chain of nucleotides and briefly describe the chemical reactions that are frequently used to synthesize them. Furthermore, we discuss a variety of applications of these molecules. Kinase activity, for instance, was studied by transfer of a phosphate modified with a reporter group to the target proteins. This allows not only studying the activity of kinases, but also identifying their target proteins. Moreover, kinases can also be directly labeled with a reporter at a conserved lysine using acyl-phosphate probes. Another important application for phosphate-modified nucleotides is the study of RNA and DNA polymerases. In this context, single-molecule sequencing is made possible using detection in zero-mode waveguides, nanopores or by a Förster resonance energy transfer (FRET)-based mechanism between the polymerase and a fluorophore-labeled nucleotide. Additionally, fluorogenic nucleotides that utilize an intramolecular interaction between a fluorophore and the nucleobase or an intramolecular FRET effect have been successfully developed to study a variety of different enzymes. Finally, also some novel techniques applying electron paramagnetic resonance (EPR)-based detection of nucleotide cleavage or the detection of the cleavage of fluorophosphates are discussed. Taken together, nucleotides modified at the terminal phosphate position have been applied to study the activity of a large diversity of proteins and are valuable tools to enhance the knowledge of biological systems.

  • Peptide-Based and Polypeptide-Based Gene Delivery Systems
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-03-09

    Peptide-based and polypeptide-based gene carriers are emerging as the most potentially useful agents in the field of gene therapy. Here we summarize the methods used for the preparation of peptides and polypeptides, address the primary types of peptide-based gene delivery systems, demonstrate their applications in gene therapy, and attempt to propose possible future directions in the development of peptide-based and polypeptide-based gene carriers for specific applications.

  • Applications and Advantages of Stable Isotope Phosphate Labeling of RNA in Mass Spectrometry
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-03-11

    Mass spectrometry (MS) has become an enabling technology for the characterization of post-transcriptionally modified nucleosides within ribonucleic acids (RNAs). These modified RNAs tend to be more challenging to completely characterize using conventional genomic-based sequencing technologies. As with many biological molecules, information relating to the presence or absence of a particular compound (i.e., qualitative measurement) is only one step in sample characterization. Additional useful information is found by performing quantitative measurements on the levels of the compound of interest in the sample. Phosphate labeling of modified RNAs has been developed by our laboratory to enhance conventional mass spectrometry techniques. By taking advantage of the mechanism of action of many ribonucleases (RNases), digesting RNA samples in the presence of 18O-labeled water generates an 18O-labeled 3′-phosphate in each digestion product. We describe the historical development of this approach, contrast this stable isotope labeling strategy with others used in RNA mass spectrometry, and provide examples of new analytical mass spectrometry methods that are enabled by phosphate labeling in this fashion.

  • Polymeric Nanoparticle-Mediated Gene Delivery for Lung Cancer Treatment
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-03-13

    In recent years, researchers have focused on targeted gene therapy for lung cancer, using nanoparticle carriers to overcome the limitations of conventional treatment methods. The main goal of targeted gene therapy is to develop more efficient therapeutic strategies by improving the bioavailability, stability, and target specificity of gene therapeutics and to reduce off-target effects. Polymer-based nanoparticles, an alternative to lipid and inorganic nanoparticles, efficiently carry nucleic acid therapeutics and are stable in vivo. Receptor-targeted delivery is a promising approach that can limit non-specific gene delivery and can be achieved by modifying the polymer nanoparticle surface with specific receptor ligands or antibodies. This review highlights the recent developments in gene delivery using synthetic and natural polymer-based nucleic acid carriers for lung cancer treatment. Various nanoparticle systems based on polymers and polymer combinations are discussed. Further, examples of targeting ligands or moieties used in targeted, polymer-based gene delivery to lung cancer are reviewed.

  • Degradable Polyethylenimine-Based Gene Carriers for Cancer Therapy
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-03-13

    Gene therapy using recombinant DNA or gene silencing using siRNA have become a prominent area of research in cancer therapy. However, their use in clinical applications is limited due to overall safety concerns and suboptimal efficacy. Although non-viral vectors such as polycationic polymers do not offer the same level of transfection efficiency as their viral counterparts, they still demonstrate immense potential as alternatives to viral vectors, given their versatility, low immunogenicity, ease of large-scale production, and ability to accelerate gene transfer with well-designed delivery platforms. Among these polymers, polyethylenimine (PEI) is considered a state-of-the-art gene carrier, owing to its ability to improve gene transfer capacity and intracellular delivery. Nonetheless, PEI suffers from the critical shortcoming of non-degradability that can lead to severe cytotoxic effects, despite the fact that the level of this toxicity decreases with molecular weight (MW). As a result, a considerable amount of effort has been devoted to designing low-MW PEI derivatives with degradable linkages. This review will categorize the recent advances in these degradable PEI derivatives based on their degradable chemistries, including ester, disulfide, imine, carbamate, amide, and ketal linkages, and summarize their application in gene therapies against various major cancer malignancies.

  • Synergistic Effect of Blended Components in Nonaqueous Electrolytes for Lithium Ion Batteries
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-03-15

    Application of different electrolyte components as blends in nonaqueous electrolyte formulations represents a viable approach towards improving the overall performance and reliability of a lithium ion battery cell. By combining the advantages of different electrolyte constituents, cell chemistry can be optimized and tailored for a specific purpose. In this paper, the current progress on possibilities, advantages, as well as limitations of blended nonaqueous electrolyte formulations, including solvent, salt and additive blends is reviewed and discussed. Emphasis is set on the physicochemical, electrochemical, and safety aspects. In addition, the aim of this review is to provide perspective and possible strategy for further and future development of blended nonaqueous electrolytes with long life, high energy density, high power, and adequate safety at competitive manufacturing costs. The provided overview and perspective on blended nonaqueous electrolyte formulations should encourage researchers to proceed with further and deeper investigations in this promising field of advanced batteries.

  • Metal Fluorides: Tools for Structural and Computational Analysis of Phosphoryl Transfer Enzymes
    Top. Curr. Chem. (IF 4.033) Pub Date : 2017-03-15

    The phosphoryl group, PO3 –, is the dynamic structural unit in the biological chemistry of phosphorus. Its transfer from a donor to an acceptor atom, with oxygen much more prevalent than nitrogen, carbon, or sulfur, is at the core of a great majority of enzyme-catalyzed reactions involving phosphate esters, anhydrides, amidates, and phosphorothioates. The serendipitous discovery that the phosphoryl group could be labeled by “nuclear mutation,” by substitution of PO3 – by MgF3 – or AlF4 –, has underpinned the application of metal fluoride (MF x ) complexes to mimic transition states for enzymatic phosphoryl transfer reactions, with sufficient stability for experimental analysis. Protein crystallography in the solid state and 19F NMR in solution have enabled direct observation of ternary and quaternary protein complexes embracing MF x transition state models with precision. These studies have underpinned a radically new mechanistic approach to enzyme catalysis for a huge range of phosphoryl transfer processes, as varied as kinases, phosphatases, phosphomutases, and phosphohydrolases. The results, without exception, have endorsed trigonal bipyramidal geometry (tbp) for concerted, “in-line” stereochemistry of phosphoryl transfer. QM computations have established the validity of tbp MF x complexes as reliable models for true transition states, delivering similar bond lengths, coordination to essential metal ions, and virtually identical hydrogen bond networks. The emergence of protein control of reactant orbital overlap between bond-forming species within enzyme transition states is a new challenging theme for wider exploration.

Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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