The symbol ϖ appears erroneously in thirteen places in the text of this article. It should be replaced in each case by the symbol π.

Abstract We present a spectroscopic overview of the C–H···Y (Y = hydrogen bond acceptors) hydrogen bonded (HB or H-bond) complexes in this article. Although C–H···Y interactions have been recognized as H-bonding interactions for quite some time, they have not been investigated spectroscopically until recently. Recent results indicated that unlike the conventional hydrogen bond, C–H···Y H-bond has interesting

Abstract Studies on hydrogen bonding interaction in various systems, involving phenylacetylene (PhAc), propargyl alcohol (PA), borazine (BNH), propargyl amine (PAm) were performed using matrix isolation infrared spectroscopy and supported by ab initio computations. Weak intermolecular interactions of the above mentioned precursors with water, methanol, ether, acetylene and benzene were studied. These

Abstract Mapping of charge densities in molecular crystals has been contemplated ever since it was recognized that X-rays are scattered by the electron density in the crystal. The methodology both from the experimental and theoretical perspective was standardized and applied extensively only during the last few decades, as technological advances were a prerequisite in both data collection and computation

Abstract Molecular electrostatic potentials, in conjunction with polarization, provide the key to understanding hydrogen bonding. As required by the Hellmann–Feynman theorem, hydrogen bonding is a Coulombic interaction between (a) a positive electrostatic potential associated with a region of lower electronic density on the hydrogen (a σ-hole), and (b) a negative site on the hydrogen-bond acceptor

Abstract We review the variation of X–Z stretching frequency in the formation of Z-bonds (X–Z···Y, Z = H, or other main group element). Majority of hydrogen bonds (H-bonds) occur between a strongly polar X–H bond and an electron pair donor (H-bond acceptor) Y and show a red shift in the X–H stretch. In very weak H-bonds, there are several instances where the X–H bond is blue shifted. We show that X–H

Abstract This brief review presents an overview and analysis of the experimental studies performed recently in the laboratory of the authors demonstrating the role of hydrogen bonding as a promotional factor for intermolecular vibrational energy relaxation, and as a driving force for the occurrences of specific reaction channels in binary molecular complexes. Both vibrational and electronic spectroscopic

Abstract Life makes extensive use of non-covalent interactions, as they are a convenient way to build complex structures that can be assembled or disassembled quickly, with a minimum energy consumption. Among the inter-molecular interactions, hydrogen bond plays a central role, and it is the main responsible of the structure of proteins, DNA, and several other superstructures in the cell. Characterization

Abstract Halogen bonding (XB) is an attractive interaction between a halogen atom and an electron donor. Although halogens are electron-rich atoms, they act as electrophiles in these types of interactions. This is due to the presence of a significant positive charge (σ-hole) on the halogen atoms in organic halides along the R-X (R = carbon, nitrogen, halogen) bond. With an increase in the polarizability

Abstract The hydrogen bond has justifiably been termed the ‘master key of molecular recognition’. It is an interaction that is weaker than the covalent bond and stronger than the van der Waals interaction. The ubiquity and flexibility of hydrogen bonds make them the most important physical interaction in systems of biomolecules in aqueous solution. Hydrogen bonding plays a significant role in many

Abstract Formic acid dimer as the prototypical doubly hydrogen-bonded gas-phase species is discussed from the perspective of the three translational and the three rotational degrees of freedom which are lost when two formic acid molecules form a stable complex. The experimental characterisation of these strongly hindered translations and rotations is reviewed, as are attempts to describe the associated

Abstract The field of intra- and intermolecular interactions has received a major boost in the past one decade. Significant advances in both instrumentation (for experimental purposes) and computational resources (development of theoretical models) have provided strong impetus to this area of research. The understanding of the nature, energetics and the topological characteristics of these interactions

Abstract This article is a personal, chronological account of experimental work carried out on the hydrogen bond, the halogen bond and other non-covalent interactions by my research group using (mainly) rotational spectroscopy since 1974. It is not intended to be comprehensive, and therefore does not include contributions made by many groups in the last 40 years or so.

Abstract Latimer and Rodebush (J Am Chem Soc 42: 1419–1433, 1920) discussed the ways a Lewis dot structure could be drawn for liquid water and proposed that the H held between two octets constitutes a bond in 1920. When it was realized that the other molecule of life, DNA, owes its double helix structure to specific hydrogen bonds between A–T (two) and C–G (three) base pairs, the interest in hydrogen

Abstract Since its original inception, a great deal has been learned about the nature, properties, and applications of the H-bond. This review summarizes some of the unexpected paths that inquiry into this phenomenon has taken researchers. The transfer of the bridging proton from one molecule to another can occur not only in the ground electronic state, but also in various excited states. Study of

Abstract Molecular dynamics simulations of benzene and 12 fluorobenzenes with various degrees of fluorine substitution in water reveal that the accumulation of water in the first solvent shell decreases with increase in number of fluorine atoms relative to benzene, with an exception of hexafluorobenzene. Further, the solute–solute radial density function indicates that partially substituted fluorobenzenes

Abstract Compared to conventional hydrogen bonds like (O–H···N, N–H···O, O–H···O, N–H···N), hydrogen bonds involving heavier chalcogens like sulfur, selenium, and tellurium have been considered weaker owing to less electronegativity of these elements. However, various instances exist to prove that these hydrogen bonds (H bonds) are of similar strength of conventional hydrogen bonds, although the nature

Cell membranes, despite providing a barrier to protect intracellular constituents, require selective gating for influx of important metabolites including ions, sugars, amino acids, neurotransmitters and efflux of toxins and metabolic end-products. The machinery involved in carrying out this gating process comprises of integral membrane proteins that use ionic electrochemical gradients or ATP hydrolysis

Sensory systems adapt to environmental change. It has been argued that adaptation should have the effect of optimizing sensitivity to the new environment. Here we consider a framework in which this premise is made concrete using an economic normative theory of visual motion perception. In this framework, visual systems adapt to the environment by reallocating their limited neural resources. The allocation

Animals depend on navigation to find food, water, mate(s), shelter, etc. Different species use diverse strategies that utilise forms of motion- and location-related information derived from the environment to navigate to their goals and back. We start by describing behavioural studies undertaken to unearth different strategies used in navigation. Then we move on to outline what we know about the brain

Attention is a process of selection that allows us to intelligently navigate the abundance of information in our world. Attention can be either directed voluntarily based on internal goals-"top-down" or goal-directed attention-or captured automatically, by salient stimuli-"bottom-up" or stimulus-driven attention. Do these two modes of attention control arise from same or different brain circuits? Do

For almost all cells, nutrient availability, from glucose to amino acids, dictates their growth or developmental programs. This nutrient availability is closely coupled to the overall intracellular metabolic state of the cell. Therefore, cells have evolved diverse, robust and versatile modules to sense intracellular metabolic states, activate signaling outputs and regulate outcomes to these states