No abstract

The orientational order as determined by 2H NMR and the infrared frequencies of the C-H stretching modes of the methylene groups have been measured for several systems (POPC, POPC/cholesterol and POPE), all in the fluid phase, and then were compared; this work reveals an unexpected linear correlation between them. This experimental result shows that both measurements are essentially sensitive to a common motion, most likely trans/gauche isomerisation. This new correlation with those already found in the literature suggest that several measurements related to the hydrophobic core of the fluid bilayer describe different aspects of a universal behavior. The correlation presented here does not extend to the lipid in gel phase where slower motions affect the NMR lineshape.

Optical spectroscopy and reverse-phase HPLC were used to investigate the binding of Hg(II) to plant metal-binding peptides (phytochelatins) with the structure (gammaGlu-Cys)2Gly, (gammaGlu-Cys)3Gly and (gammaGlu-Cys)4Gly. Glutathione-mediated transfer of Hg(II) into phytochelatins and the transfer of the metal ion from one phytochelatin to another was also studied using reverse-phase HPLC. The saturation of Hg(II)-induced bands in the UV/visible and CD spectra of (gammaGlu-Cys)2Gly suggested the formation of a single Hg(II)-binding species of this peptide with a stoichiometry of one metal ion per peptide molecule. The separation of apo-(gammaGlu-Cys)2Gly from its Hg(II) derivative on a C18 reverse-phase column also indicated the same metal-binding stoichiometry. The UV/visible spectra of both (gammaGlu-Cys)3Gly and (gammaGlu-Cys)4Gly at pH 7.4 showed distinct shoulders in the ligand-to-metal charge-transfer region at 280-290 mm. Two distinct Hg(II)-binding species, occurring at metal-binding stoichiometries of around 1.25 and 2.0 Hg(II) ions per peptide molecule, were observed for (gammaGlu-Cys)3Gly. These species exhibited specific spectral features in the charge-transfer region and were separable by HPLC. Similarly, two main Hg(II)-binding species of (gammaGlu-Cys)4Gly were observed by UV/visible and CD spectroscopy at metal-binding stoichiometries of around 1.25 and 2.5 respectively. Only a single peak of Hg(II)-(gammaGlu-Cys)4Gly complexes was resolved under the conditions used for HPLC. The overall Hg(II)-binding stoichiometries of phytochelatins were similar at pH 2.0 and at pH 7.4, indicating that pH did not influence the final Hg(II)-binding capacity of these peptides. The reverse-phase HPLC assays indicated a rapid transfer of Hg(II) from glutathione to phytochelatins. These assays also demonstrated a facile transfer of the metal ion from shorter- to longer-chain phytochelatins. The strength of Hg(II) binding to glutathione and phytochelatins followed the order: gammaGlu-Cys-Gly<(gammaGlu-Cys)2Gly<(gammaGlu-Cy s)3Gly<(gamma Glu-Cys)4Gly.

Kidney stones of the uric acid type were examined by Raman spectroscopy. The fingerprint pattern of the Raman spectra of these stones matched those of uric acid better than those of sodium urate. Although the Raman spectra of most stones were masked by the high fluorescence of the stones, with the use of a computer to correct the baseline, the Raman scattering bands became distinct. Uric acid has distinct Raman bands at 472, 562, 627, 784, 885, 999, 1039, 1122, 1234, 1288, 1046, 1499, 1595, and 1652 cm−1. The kidney stones examined also showed these bands, indicating that the stones were the uric acid type. Raman spectroscopy is a useful analytical tool for identifying the composition of kidney stones without much sample preparation.

Phosphate-type kidney stones have been examined by the Raman spectroscopic technique by merely focusing laser light on the cut surface of the stones. Before examination of the kidney stones, Raman spectra of several standard phosphate compounds—such as calcium monobasic phosphate [Ca(H2PO4)2], calcium dibasic phosphate (CaHPO4), calcium tribasic phosphate [Ca10(PO4)6(OH)2], calcium orthophosphate [Ca3(PO4)2], brushite (CaHPO·2H2O), struvite (MgNH4PO4·6H2O), and hydroxyapatite [Ca10(PO4)6(OH)9]—were obtained. Hydroxyapatite has a distinctive line at 961 cm−1, and one kidney stone examined showed a comparable band. It was concluded that one stone is primarily hydroxyapatite and another one is brushite. The analysis of the kidney stones by Raman spectroscopy is direct, fast, and nondestructive, and does not require tedious sample preparation.