Characterization of the weak SS bonds in the OSSSO and O2SSSO2 molecules.

The weak S1-S3 bonds in the OSSSO trans-disulfoxide and the corresponding sulfone, O(2)SSSO(2), are readdressed at the B3LYP/6-31+G(d) level using both the atoms-in-molecules (AIM) and the electron localization function (ELF) approaches. The S1-S3 bonds are clearly characterized as fractional (i.e., with a bond number or bond order which is less than unity) or protocovalent and are very similar in nature to the weak N-N bond in O(2)NNO(2). These results are in accord with what is obtained by inspection of valence bond structures of the increased-valence type.

A theoretical study of 31P NMR chemical shielding models for concentrated phosphoric acid solution.

Calculations on the hydrates, dimer, and trimer of phosphoric acid were carried out in an effort to obtain a viable model of the phosphorus NMR chemical shielding in 85% phosphoric acid solution. The theoretical approaches used the gauge-including-atomic-orbital (GIAO) 6-311+G(nd,p) basis set at both scaled density functional theory (sB3LYP) and estimated infinite order Møller-Plesset (EMPI) approaches and with the aug-cc-pvtz basis in the sB3LYP approach. Shieldings and hydrogen bonding stabilization energies are similar in the three approaches and indicate that the faster sB3LYP/6-311+G(nd,p) approach can be used with larger systems. The changes in shielding compared to the isolated species are small and suggest that the undissociated acid dihydrate could serve as a model entity for modeling the phosphorus shielding in concentrated phosphoric acid solution.

Nature of bonding in the sulfuryl group.

The SO sulfuryl bond in a number of representative sulfoxides and sulfones has been studied at the B3LYP/6-311+G(d,p) level in the atoms-in-molecules (AIM) approach involving the AIM delocalization index and the Cioslowski-Mixon localized orbitals and associated covalent bond order. The sulfur-oxygen covalent bond is strongly polarized toward oxygen and the oxygen lone pairs provide significant backbonding to create short and strong SO bonds, similar in nature to those found in the analogous phosphoryl (PO) bond. Although the sulfoxides in general have larger delocalization indices than the sulfones, there is no correlation between these quantities and the bond dissociation energies.

Methamphetamine toxicity is attenuated in mice that overexpress human manganese superoxide dismutase.

We have investigated methamphetamine (MA) toxicity in transgenic mice that overexpress the human form of mitochondrial manganese superoxide dismutase (MnSOD). Our results reveal a significant reduction in the long-term depletion of striatal dopamine and protein oxidation following repeated administration of MA in transgenic vs. non-transgenic littermates. These findings support the notion that ROS contribute to MA-induced brain damage and suggest that mitochondria may play an important role in this form of neurodegeneration.

A spin label study of the urinary bladder luminal membrane.

Spin label experiments have been carried out on the urinary bladder luminal membrane of the bovine transitional epithelium employing the 5-, 7-, 12-, and 16-doxyl substituted stearic acid methyl esters, and compared for reference to similarly labeled bovine erythrocytes. The bladder membranes are significantly different from the bovine red blood cell membranes and show a lower order and polarity near the membrane surface. This fact and the general similarity of results for the bladder and isolated plaque membranes suggests that the highly organized proteins of the bladder membrane may act as a coat on the lipid bilayer and, while intrinsic in nature, do not significantly perturb the hydrophobic core of the lipid bilayer.

On the use of the spin labeling technique in the study of erythrocyte membranes.

ESR spectra and scanning electron micrographs of human erythrocytes spin labeled with the conventional stearic acid nitroxide substituted at the 5-position have been obtained over a range of label-to-lipid ratios. While morphological changes as previously reported (Bieri, V. G., Wallach, D. F. H. and Lin, P. S. (1974) Proc. Natl. Acad. Sci. U.S. 71, 4797-4801) are reproduced, it is shown that at label-to-lipid ratios of 1:10 or less the basic ESR spectrum is not significantly affected. At low label concentrations the spin labeling technique is a viable one and can be used to investigate membrane properties.

Electron spin resonance studies of erythrocytes from patients with myotonic muscular dystrophy.

Electron magnetic resonance experiments have demonstrated that spin-labeled myotonic erythrocyte membranes have spectra that are recognizably different from those of normal erythrocytes. The spin label incorporated in the erythrocyte membranes of patients having myotonic muscular dystrophy is apparently located in a less polar and somewhat more fluid region than the label in a normal membrane. Although the mechanisms of molecular interaction and their relationship to enzymatic differences is unclear, the results lend confirmation to the suggestion that myotonic muscular dystrophy may be a disease resulting from a basic membrane abnormality.