Search

Two novel hydrogensquarates of 3-nicotinoyl (1) and 3-isonicotinoyl (2) coumarin have been synthesized and their structures and properties elucidated spectroscopically and structurally, using single crystal X-ray diffraction, linear-polarized solid-state IR-spectroscopy, UV-spectroscopy and negative ESI MS. Quantum chemical calculations were used to obtain the electronic structure, vibrational data and electronic spectra. The IR-spectroscopic elucidation is carried out by a comparison with the characteristics of corresponding neutral 3-nicotinoyl and 3-isonicotinoyl coumarins.

The self-assembly of the hydrogensquarates is elucidated by means of linear-polarized infrared (IR-LD) spectroscopy of oriented colloids in nematic host and the so-called reducing-difference procedure for polarized IR-LD spectra interpretation. The scopes and limitation are discussed on five novel derivatives of squaric acid and its anions, that is, 2-chloro-3-aminopyridinium hydrogensquarate (1), bis (1,2,3,4-tetrahydroquinolinium) squarate (2), bis hydrogensquarate dihydrate salt of 4-(aminomethyl)pyridine (3), N-(2-ammoniumethyl)-piperazinium monohydrate hydrogensquarate squarate (4), and 3-nitropyridinium hydrogensquarate monohydrate (5), respectively. The structures of these compounds 1-5 were solved by means of single-crystal X-ray diffraction, and the crystallographic data were used for the experimental elucidation of the corresponding IR spectra of crystals with respect to studying Fermi-resonance (FR), Davydov splitting (DS), and Fermi-Davydov (FD) as well as Evans' hole effects. The various motifs for self-assembly of squaric acid and its anions in the organic crystals are discussed together with their IR-spectroscopic properties.

Hydrogensquarates of dipeptide L-threonyl-L-serine (H-Thr-Ser-OH) and L: -serine (HSq x Ser) have been synthesized, isolated and spectroscopic characterized by solid-state linear-polarized IR-spectroscopy, 1H- and 13C-NMR, ESI-MS and HPLC with tandem masspectrometry (MS-MS) methods. The structures of the salts and neutral dipeptide have been predicted theoretically by ab initio calculations. In the case of H-Thr-Ser-OH the theoretical data are supported by IR-LD ones. The hydrogensquarates consist in positive charged dipeptide or amino acid moiety and negative hydrogensquarate anion (HSq) stabilizing by strong intermolecular hydrogen bonds. The data about the L-serine hydrogensquarate are compared with known crystallographic data thus indicating a good correlation between the theoretical predicted structures and experimentally obtained by single crystal X-ray diffraction.