Elsevier

Thermochimica Acta

Volume 683, January 2020, 178443
Thermochimica Acta

Synthesis, characterization, and thermoanalytical study of aceclofenac of light lanthanides in the solid state (La, Ce, Pr, and Nd)

https://doi.org/10.1016/j.tca.2019.178443Get rights and content

Highlights

  • Lighter lanthanide complexes with aceclofenac have been synthesized.

  • Thermogravimetry (TG) allowed the determination of the stoichiometry of the synthesized compounds.

  • The TG–DSC curves provided previously unreported information about thermal behavior.

  • The gaseous products released were detected by EGA (TG–DSC coupled to FTIR).

Abstract

Lanthanide aceclofenac compounds were synthesized by the addition of lanthanide nitrate aqueous solution to aceclofenac–acetone solution. The compounds obtained in the solid state were characterized by thermal and spectroscopic studies, as well as by complementary x-ray diffraction data. The metal–ligand stoichiometric ratio was defined by simultaneous thermogravimetry and differential scanning calorimetry (TG-DSC) as [Ln(Acec)3·nH2O], where Ln represents the metal centre (La, Ce, Pr, or Nd) and Acec represents the ligand, with n = 4(La), 3(Ce), and 2.5(Pr, Nd). TG-DSC and Fourier transform infrared spectroscopy (FTIR) data also allowed for determination of the thermal behaviour and possible coordination modes between the metal and the ligand.

Introduction

Considering the variety and design of complexes that can be formed with ions lanthanides, the anti-inflammatory compound aceclofenac (Acec) was used as a monocarboxylate ligand for the synthesis of compounds in the solid state, which can be isolated and characterized by thermal analysis techniques [[1], [2], [3]]. The Acec ligand is a non-steroidal anti-inflammatory drug mainly used to relieve pain in chronic diseases, such as rheumatoid arthritis, osteoarthritis, sprain, muscular pain, and spondylitis, besides having antipyretic effects. Acec is practically insoluble in water, consequently having low bioavailability after oral administration [4]. Aceclofenac (C16H13Cl2NO4) has a molecular weight of 354.18 g mol–1, and its chemical name is 2-[2-[2-[(2,6-dichlorophenyl)amino]phenyl]oxyacetic acid, according to International Union of Pure and Applied Chemistry IUPAC. Some important properties of this drug include a pKa value of 4.7, a melting point of 149–153 °C, and solubility in acetone and ethanol. The appearance of the solid-state drug is a crystalline white powder with light yellowish colour [5].

Lanthanide (III) compounds have already been tested in several biological applications, such as use as antitumor, cytotoxic, and antibacterial agents, as well as use as radiopharmaceuticals in oncological therapy. Cerium and neodymium trivalent compounds have also been investigated for their biological potential for the treatment of cancers. Pharmacological applications of lanthanide complexes in the clinical study phase of the treatment of lung cancer are related to neodymium compounds [[6], [7], [8], [9], [10]].

Structural investigations of the complexes formed with lanthanide ions are important for possible future biological applications due to the new physical and chemical properties that the interactions of these substances can provide, such as solubility and thermal stability [11,12].

For these reasons, we were led to develop and characterize these materials using spectroscopic data and thermoanalytical and X-ray diffraction techniques as reliable means for the elucidation of the structural and thermal behaviour of the complexes. Studies of this nature have not yet been published with trivalent light lanthanide ions; therefore, the objective was to synthesize and characterize the compounds obtained.

Section snippets

Synthesis of the complexes

The lanthanide complexes of aceclofenac were synthesized by reacting the ligand solution with a lanthanide nitrate solution. Aceclofenac (2.4 mmol) was dissolved in acetone (30 mL), while sodium hydrogen carbonate (2.4 mmol) was dissolved in water (20 mL). The two solutions were mixed in a magnetic stirrer until effervescence ceased, following a procedure described in the literature [13].

Lanthanide nitrate solutions (0.8 mmol) were prepared from their respective oxides, except for cerium (III)

Aceclofenac

The aceclofenac TG-DSC curves in an oxidizing atmosphere are shown in Fig. 1. The first sharp peak (DSC) is due to melting at 160 °C. After this physical event, the TG curve shows 95% mass loss between 165 and 290 °C, corresponding to a low-intensity endothermic peak (DSC) at 295 °C, which can be attributed to degradation followed by evaporation of part of the organic matter. The last step, a 4.85% mass loss, between 490 and 516 °C (TG) with an exothermic peak at 520 °C is due to decomposition

Conclusions

The results of the TG curves allowed for determination of the molecular formula of the compounds synthesized as Ln(Acec)3, where Ln = lanthanides (La, Ce, Pr, and Nd) and Acec = aceclofenac. This analysis also provided information about the hydration of the compounds, with lanthanum having 4 H2O, whereas the cerium compound had three, and praseodymium and neodymium had 2.5 H2O. Simultaneous TG-DSC curves provided information about the thermal behaviour of these compounds (dehydration,

Declaration of competing interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

Acknowledgements

The authors gratefully acknowledge the financial support provided by the Brazilian funding agencies: Financiadora de Estudos e Projetos (FINEP contract: 04.13.0448.00/2013), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq contracts: 303129/2016-6, 451541/2019-7), Federal University of Grande Dourados (UFGD contracts: 23005.005816/2017-31, 23005.003956/2017-75, 23005.002551/2008-29), Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP contracts: 2006/06951-3,

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