Vibrational spectra of racemic and enantiomeric malic acids

Abstract

The IR and Raman spectra of racemic (DL-) and both enantiomeric (L-and D-) forms of malic acids and also their silver salts and deuterated analogues were measured in the polycrystalline state in the range 4000-100 cm −1 . Significant differences in the spectra of the racemic and enantiomeric forms of malic acid were described for the first time and are discussed in relation to the structural features, including crystal symmetry, geometric parameter distinctions and hydrogen bonding. The most significant spectral differences were noted in the ranges 3000-2800 and 1740-1630 cm −1 . In the n(CH) stretching region distinctions were strongly pronounced in the Raman spectra and the observed pattern was ascribed to crystal symmetry differences. In the second region differences were visible in both the IR and Raman spectra and they were explained as a result of distinctions in the geometric properties of carboxyl-dimer rings of the L-and DL-forms, namely two non-equivalent types of H-bonded carboxyl-dimer rings are present in the crystal of DL-form, which results in a doublet in the n(C O) stretching region. In the case of the enantiomeric form, all H-bonded carboxyl-dimer rings are equivalent, so a single n(C O) band is observed in their spectra. Other differences in the spectra of these species were observed in the region below 1500 cm −1 but their explanation is less straightforward.

ADP‐evoked phospholipase C stimulation and adenylyl cyclase inhibition in glioma C6 cells occur through two distinct nucleotide receptors, P2Y1 and P2Y12

“…We have previously characterized P2Y 1 and P2Y 2 receptors in glioma C6 cells using measurements of [Ca 2+ ] i and demonstrated that ADP, ATP and UTP initiated a large Ca 2+ response consistent with the typical capacitative model of Ca 2+ entry, associated with the stimulation of PLC and depletion of intracellular Ca 2+ stores [15]. In this process, the initial rise in [Ca 2+ ] i results from the direct effect of InsP 3 on the endoplasmic reticulum and can be observed even in the absence of extracellular Ca 2+ [28]. Our previous study showed that such Ca 2+ responses were observed for all three nucleotides [15].…”

Non-equimolar discrete compounds in binary chiral systems of organic substances

“…The results for the known racemic and enantiomer phases agree with data reported in the works 26,63 and do not contradict other literature findings. 67 Phase relationships in the (S)-malic acid-(R)-malic acid system. The TRPXRD method showed that the racemic phases RSI and RSIII do not undergo polymorph transformations until the substances reached their melting points at 124°C and 123°C, respectively.…”

Adsorption of malic acid at the hydroxyapatite/aqueous NaCl solution interface

“…An increase in pH from 6 to 11 causes a decrease in the adsorption of malate ions on hydroxyapatite and indicates a competitive exchange of malate ions for hydroxyl ions in hydroxyapatite. This mechanism is confirmed by the increase (Baranska et al 2003) Fig. 9 Effect of malate ion adsorption on HAp on the zeta potential as a function of solution pH in acidity of the groups on the surface of hydroxyapatite due to the adsorption of malate ions.…”

“…The analysis of absorption bands in the spectrum presented in Fig. 8 to DL malic acid (Baranska et al 2003). A spectrum of carbonate characteristic band appears at 1484 cm −1 that may have caused CO 2 adsorption during the sample preparation.…”