No abstract

Sphingomyelin (SM) is a major sphingolipid in mammalian cells that forms specific lipid domains in combination with cholesterol (Chol). Using molecular-dynamics simulation and density functional theory calculation, we identified a characteristic Raman band of SM at ∼1643 cm(-1) as amide I of the SM cluster. Experimental results indicate that this band is sensitive to the hydration of SM and the presence of Chol. We showed that this amide I Raman band can be utilized to examine the membrane distribution of SM. Similarly to SM, ceramide phosphoethanolamine (CerPE) exhibited an amide I Raman band in almost the same region, although CerPE lacks three methyl groups in the phosphocholine moiety of SM. In contrast to SM, the amide I band of CerPE was not affected by Chol, suggesting the importance of the methyl groups of SM in the SM-Chol interaction.

Durch Zugabe von CsNO3‐ bzw. KNO3‐Lösungen zu RuC13/ Al2O3 und anschließende Reduktion mit H, werden Alkalimetallhydroxid‐verstärkte Ru/Al2O3‐Katalysatoren hergestellt und mit XPS, TPR (temperature‐programmed reduction), DTG und DTA untersucht.

Intermolecular photoinduced electron transfer between Rhodamine 3B cation (R3B + ), and dimethylanaline (DMA) is studied in a variety of solvents using pump-probe spectroscopy from ultrashort times (∼100 fs) to long times (∼10 ns). Excitation of R3B + results in the transfer of an electron from DMA and the production of the neutral radical R3B and the DMA + radical cation. Using a very broadband continuum probe, the generation of the R3B neutral radical is observed (430 nm) as well as the ground state bleach (550 nm), an excited state absorption (445 nm), and stimulated emission (620 nm). A good spectrum of the R3B radical is obtained by removing the overlapping excited state absorption. The forward electron transfer is examined by monitoring the time dependence of the stimulated emission. The data are analyzed with a previously presented detailed theory of through-solvent electron transfer for diffusing donors and acceptors, which includes the influences solvent structure and the hydrodynamic effect. Previous studies have shown that the theory works well for times >100 ps. It is found that in a non-hydrogen-bonding solvent (acetonitrile) and in mixtures of hydrogen-bonding solvents, the theory works well down to a few hundred femtoseconds with only one adjustable parameter, the contact electronic coupling matrix element. However, in pure hydrogen-bonding solvents, it is necessary to increase the solvent hard sphere radius used in the radial distribution to theoretically describe the data, which suggest a larger solvent structural unit than a single solvent molecule.

Infrared (IR) and Raman spectra of a sphingomyelin (SM) bilayer have been calculated for the amide I, II and A modes and the double-bonded CC stretching mode by a weight averaged approach, based on an all-atom molecular dynamics (MD) simulation and a vibrational structure calculation. Representative structures and statistical weights of SM clusters connected by hydrogen bonds (HBs) are observed in MD trajectories. After constructing smaller fragments from the SM clusters, the vibrational spectra of the target modes were calculated by normal mode analysis with a correction for anharmonicity, using density functional theory. The final IR and Raman spectra of a SM bilayer were obtained as the weight averages over all SM clusters. The calculated Raman spectrum is in excellent agreement with a recent measurement, providing a clear assignment of the peak in question observed at 1643 cm(-1) to the amide I modes of a SM bilayer. The analysis of the IR spectrum has also revealed that the amide bands are sensitive to the water content inside the membrane, since their band positions are strongly modulated by the HB between SM and water molecules. The present study suggests that the amide I band serves as a marker to identify the formation of SM clusters, and opens a new way to detect lipid rafts in the biological membrane.