Evidence of Polaron Excitations in Low Temperature Raman Spectra of Oxalic Acid Dihydrate

Low temperature Raman spectra of oxalic acid dihydrate (8K - 300 K) both for polycrystalline and single crystal phase show strong variation with temperature in the interval from 1200 to 2000 cm-1. Previous low temperature diffraction studies all confirmed the stability of the crystal P21/n phase with no indications of any phase transition, reporting the existence of a strong hydrogen bond between the oxalic acid and a water molecule. A new group of Raman bands in the 1200 – 1300 cm-1 interval below 90 K is observed, caused by possible loss of the centre of inversion. This in turn could originate either due to disorder in hydroxyl proton positions, or due to proton transfer from carboxylic group to water molecule. The hypothesis of proton transfer is further supported by the emergence of new bands centered at 1600 cm-1 and 1813 cm-1, which can be explained with vibrations of H3O+ ions. The broad band at 1600 cm-1 looses intensity, while the band at 1813 cm-1 gains intensity on cooling. The agreement between quantum calculations of vibrational spectra and experimentally observed Raman bands of hydronium ions in oxalic acid sesquihydrate crystal corroborate this hypothesis

Locating the Binding Sites of Pb(II) Ion with Human and Bovine Serum Albumins

Lead is a potent environmental toxin that has accumulated above its natural level as a result of human activity. Pb cation shows major affinity towards protein complexation and it has been used as modulator of protein-membrane interactions. We located the binding sites of Pb(II) with human serum (HSA) and bovine serum albumins (BSA) at physiological conditions, using constant protein concentration and various Pb contents. FTIR, UV-visible, CD, fluorescence and X-ray photoelectron spectroscopic (XPS) methods were used to analyse Pb binding sites, the binding constant and the effect of metal ion complexation on HSA and BSA stability and conformations. Structural analysis showed that Pb binds strongly to HSA and BSA via hydrophilic contacts with overall binding constants of KPb-HSA = 8.2 (±0.8)×104 M−1 and KPb-BSA = 7.5 (±0.7)×104 M−1. The number of bound Pb cation per protein is 0.7 per HSA and BSA complexes. XPS located the binding sites of Pb cation with protein N and O atoms. Pb complexation alters protein conformation by a major reduction of α-helix from 57% (free HSA) to 48% (metal-complex) and 63% (free BSA) to 52% (metal-complex) inducing a partial protein destabilization

Implementation of Selective Heteronuclear 2D J-Resolved Method on Standard NMR Spectrometers and Selective Proton Pulse Calibration

Some currently used methods for determining the long-range carbon-proton coupling constants are discussed. We chose the selective heteronuclear 2D J-resolved method because of its good sensitivity and resolution in Fi dimension. We implemented the method on a standard NMR spectrometer with transmitter working at fixed power and no facilities for shaped pulse generation. Selective proton pulse was achieved by using suitable attenuators for the decoupler output power attenuation. The selective proton pulse was calibrated by the indirect method for resonance observation, which allows precise determination of the pulse length. The proposed methodology can be applied to any NMR spectrometer provided that the decoupler output power can be switched by computer at least between two levels in few ,usec. The implementation was tested on a sample of 5-Me-8-OH-quinoline, for which long-range carbon-proton coupling constants have not yet been determined

Conformation of the choline chain of phosphatidylcholines - A FTIR study of the symmetric C-N (CH

Infrared spectra of phosphatidylcholines in various forms of aggregation (multilamellar films, liposomes, unilamellar vesicles, micelles) exhibit a composite band in the 931-904cm-1 region which is ascribed to the C-N(CH3)3 stretching of the choline terminal. Mathematical resolution enhancements yields three components that can be associated with isomers concerning the rotation about the PO-CH2 bond (α4 torsion). The assignment of the components is based on single bands appearing in the spectra of the dry phosphatidylcholine-EuCl3 complex (931 cm-1, antiplanar), two crystalline phosphatidylcholine hydrates (916 cm-1, anticlinal) and Fringeli's crystalline C phase (904 cm-1, synclinal). These assignments are supported by the published normal coordinate analysis of acetylcholine halides. Integrated absorptions of the resolved components permit the estimation of rotamer population. The effect of temperature variation on the latter is very small indicating that rotamers differ very little in energy. Hydration effects are more drastic. This demonstrates the general usefulness of the C-N(CH3)3 stretching bands for conformational studies of the choline chain of phosphatidylcholines

Revealing the astragalin mode of anticandidal action.

Due to limited arsenal of systemically available antifungal agents, infections caused by Candida albicans are difficult to treat and the emergence of drug-resistant strains present a major challenge to the clinicians worldwide. Hence further exploration of potential novel and effective antifungal drugs is required. In this study we have explored the potential of a flavonoid, astragalin, in controlling the growth of C. albicans, in both planktonic and biofilm forms by microdilution method; and in regulating the morphological switch between yeast and hyphal growth. Astragalin ability to interfere with membrane integrity, ergosterol synthesis and its role in the regulation of genes encoding for efflux pumps has been addressed. In our study, astragalin treatment produced good antimicrobial and significant antibiofilm activity. Anticandidal activity of astragalin was not related to ERG11 downregulation, neither to direct binding to CYP51 enzyme nor was linked to membrane ergosterol assembly. Instead, astragalin treatment resulted in reduced expression of CDR1 and also affected cell membrane integrity without causing cytotoxic effect on human gingival fibroblast cells. Considering that astragalin-mediated decreased expression of efflux pumps increases the concentration of antifungal drug inside the fungal cells, a combinatorial treatment with this agent could be explored as a novel therapeutic option for candidiasis