Spectroscopic, thermal and structural studies of new l-leucine and d-leucine complexes with chloranilic acid

Abstract

New molecular complexes of l-leucine and d-leucine with chloranilic acid have been synthesized. Crystal structures of these crystals have been solved; they crystallize in non-centrosymmetric monoclinic P21 space group. In the crystal, leucine molecules exist in protonated form (C6NO2H14+) and chloranilic acid molecules in deprotonated form (C6HCl2O4−). Electronic (UV–Vis) and vibrational absorption (VA) spectra for both materials were collected. Circular dichroism methods such as electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) were used to determine the absolute configuration of new complexes. In both methods a characteristic (−,+) Cotton patterns are observed. In ECD spectra absorption bands are observed at 212 nm for acetonitrile solution and at 202 nm for aqueous solution. VCD spectra (in DMSO-d6 solution) show (−,+) Cotton pattern with strong peaks at 1323 cm−1 (CH rocking mode). Differential scanning calorimetry (DSC) and thermogravimetric (TG) investigations were performed to explore thermal properties of new materials. In DSC curve the decomposition and combustion processes are observed in 220–227 °C. The decomposition process was described by use of TG method and quadruple mass spectrometer (QMS). NMR spectra of pure l-leucine and chloranilic acid as well as l-leucine – chloranilic acid complex in solutions (D2O and DMSO) and in solid state confirm the geometry of molecules in complex both in solution and in solid state.