Spectroscopic (FT-IR, FT-Raman, UV absorption, 1H and 13C NMR) and theoretical (in B3LYP/6-311++G** level) studies on alkali metal salts of caffeic acid

Synthesis, chemical characterization, computational studies and biological activity of new DNA methyltransferases (DNMTs) specific inhibitor. Epigenetic regulation as a new and potential approach to cancer therapy

“…There is a small upfield shift of the aromatic protons resonances of the ligands upon chelation with the dibutyltin(IV) moiety. The same effect has been reported previously [22]. These shifts may be attributed to decreased electron density in the catechol ring due to electron withdrawing ability of the organotin(IV), which in turn decreases the ring current and deshielding of the ring protons.…”

“…The very small modification in frequency of the C_O stretching confirms that organotin(IV) moiety does not coordinate with the carboxylate group, because in this case, the coupling of the two C-O stretching modes of the carboxylate group would occur and greatly modify the related frequencies. The modifications observed between the free and complexed ligand spectra have, to some extent, essentially two origins, as previously reported [19][20][21][22]: (i) mechanical coupling between vibrators change due to the low, but non-negligible, structural modifications of the ligand engineered by the complexation and (ii) in caffeic acid, the C-O-H in plane bending modes of hydroxyls of catechol group are largely mixed with ring vibrations; the deprotonation of hydroxyls, occurring with chelation, eliminates the C-O-H bending and, consequently, modifies both frequencies and coupling of benzene ring mode in complex. Characteristics bands of ν(Sn-C) and ν(Sn-O) are present near 600 cm −1 in the complex spectrum [24,25].…”

“…The absence of strong peaks at 1660 ν(C_O) and 1440 cm −1 ν(C-O) indicate the absence of O-quinone and O-semiquinone species relatively [19]. Persistence of 3058 cm −1 ascribed to the stretching ν(OH) of carboxylic function allows to rule out the involvement of -COOH in coordination around the organotin(IV) moiety [20][21][22][23]. The C_O stretching of the carboxyl group at 1645 cm −1 appears at 1633 cm −1 in the complex.…”

Spectroscopic features of caffeic acid: Theoretical study

“…There are a few experimental studies devoted to vibrational, NMR and UV spectra of CA (WANG et al, 2004;EUN et al, 2010;ŚWISŁOCKA, 2013). The goal of the present study is to investigate spectroscopic properties of CA by theoretical means.…”

A combined experimental and theoretical analysis on molecular structure and vibrational spectra of 2,4-dihydroxybenzoic acid

“…To improve the agreement, the computed harmonic frequencies are usually scaled for comparison. Many studies [26,27] show that the scaled quantum mechanical (SQM) method provides calculated frequencies well matched to the experimental. In this paper, the scaling calculation and potential energy distribution (PED) for each normal mode were done with the MOLVIB program (Version 7.0-G77) by Sundius [28,29].…”