The effects of dehydroepiandrosterone (DHEA) as well as its sulfate and fatty acid ester derivatives on rat brain membrane fluidity was investigated by fluorescence depolarization of a lipid probe 1,6-diphenyl-1,3,5-hexatriene and compared to its effect on phospholipid conformation investigated by Fourier transform infrared spectroscopy. In rat brain, membrane fluidity varied rostro-caudally, the frontal cortex showing the highest fluidity compared to the hypothalamus, hippocampus, striatum, thalamus, and hindbrain. As previously reported, it was observed that cholesteryl hemisuccinate and stearic acid rigidify striatal membrane whereas linoleic acid and l-α-phosphatidylcholine increase the membrane fluidity. Striatal fluidity was increased in vitro with increasing concentrations of DHEA, this effect was greater with the DHEA fatty acid ester derivatives (DHEA-L), DHEA-undecanoate, and DHEA-stearate, whereas no effect was observed with DHEA-sulfate (DHEA-S). In the frontal cortex only the two DHEA-L derivatives increased membrane fluidity, whereas DHEA and DHEA-S were without effect. The effect of DHEA-L on synthetic dimyristoylphosphatidylcholine-d54 phospholipid membranes indicates a disordering effect of DHEA-undecanoate and DHEA-stearate as reflected by increased trans-gauche isomerization of the acyl chains of the lipid. Hence, DHEA-L increase the disorder and/or fluidity of brain membranes; interestingly, these compounds are abundant in the brain where they are generally considered as storage compounds that slowly release the active unconjugated steroid hormone.

Nongenomic effects of steroids on rat brain neurotransmitter transporters and receptors have been reported in several laboratories. In the present study, we have investigated possible membrane effects of 17alpha- and 17beta-estradiol, as well as tamoxifen, by studying their interactions with synthetic phospholipid membranes using Fourier transform infrared spectroscopy. We have also used the fluidity of rat striatal and frontal cortex membranes, as determined by fluorescence depolarization of the probe 1,6-diphenyl-1,3,5-hexatriene (DPH), to probe the effects of these drugs on membranes. Our results show that tamoxifen induces conformational disorder along the acyl chains of deuterated dimirystoylphosphatidylcholine and decreases the gel to liquid-crystalline phase transition temperature by approximately 10 degrees C. Similar effects, although less pronounced, were observed with 17beta-estradiol, whereas 17alpha-estradiol had no significant effect. The DPH fluorescence anisotropy of striatum and frontal cortex membranes was decreased in vitro with 17beta-estradiol or tamoxifen and also with 17alpha-estradiol, but to a lesser extent. These results suggest a stereospecific estradiol effect on membranes and that the effects of these compounds are not related to their activity on estrogen receptors. These observations support a different mechanism of action of steroids that could be implicated in their neuroprotective activity.

A parallel investigation of the conformational changes of dipalmitoylphosphatidylglycerol (DPPG) monolayers induced by surface pressure has been studied in situ at the air water interface using polarization modulation external infrared reflection absorption spectroscopy (PM-IRRAS) and on solid substrate by attenuated total reflection (ATR) spectroscopy. For both the ATR and PM-IRRAS spectra of DPPG, the non-linear increase of the intensity of the antisymmetric methylene stretching band of DPPG with molecular surface density, indicates that the compression of the DPPG monolayer induces a change of the conformation and/or orientation of the acyl chains of the phospholipid. At surface pressures between 7 and 20 mN/m, the acyl chains of the DPPG monolayer are found to be more ordered on the germanium substrate than at the air–water interface. At higher surface pressures, the conformation of the lipid acyl chains of DPPG on both substrates are almost similar. In the liquid-condensed phase, the acyl chains are in all-trans conformation and their tilt angle with respect to the normal of the film is approximately 30°. Our results also suggest the presence of DPPG solid domains in the liquid-expanded phase. Investigation of polar head group region indicates that at low surface pressures, the carbonyl groups were more oriented on the water surface than the acyl chains. Finally, the present study shows that intermolecular hydrogen bonding probably occur between the glycerol hydroxyl and the phosphate or carbonyl groups of the phospholipid.

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Ti-MCM-41 and Ti-HMS were prepared. Characterization techniques included N 2 adsorption FTIR spectroscopy, XPS and transmission electron microscopy. Catalytic experiments were carried out

Temperature programmed reduction, X-ray photoelectron spectroscopy, and X-ray diffraction were used for comparative characterization of Pt on sulfated and nonsulfated zirconia catalysts calcined both in situ and ex situ at different temperatures in the range 25-800°C. The effect of sulfur species on the state of Pt was twofold. They decreased the interactions between Pt oxide and the support, thus leading to large particles easy to decompose into large metallic Pt particles that resisted reoxidation in air. In the absence of sulfur species, up to a calcination temperature of 650°C, Pt oxide and metallic Pt particles remained small. Such samples underwent almost complete reoxidation during storage in air. Sulfur species also had a direct effect on the state of Pt. Sulfur dioxide produced by decomposition of sulfate played the role of a reducing agent. Under temperature programmed reduction conditions, two sulfate reduction peaks were obtained regardless of the presence of Pt. The occurrence of two different sulfate species was suggested and a tentative assignment proposed.

Ti modified large Pore {beta} zeolite and mesoporous MCM-41 molecular sieve were synthesized using hydrothermal procedures. Several other Ti-{beta} zeolites were prepared by treating a {beta} zeolite (Si/Al = 100) with ammonium titanyl oxalate solution. All samples were characterized by atomic absorption, XRD, IR, UV-Vis, Raman and XPS. The presence of tetrahedral Ti was evidenced particularly by the presence of a 212 nm absorption band in the UV-Vis spectra and a Ti(2p{sub 3/2}) binding energy of 459.5 eV. All samples were tested for the hydroxylation of hexane, benzene and phenol, and also for the epoxidation of 1-hexene. High catalytic activity was found only for the epoxidation reaction. Previous reports showed that, contrary to TS-1 and TS-2 zeolites, Ti modified {beta} (M.E. Davis et al. Prepr. Div. Petrol. Chem. 1993, p.769) and ZSM-48 (A. Sayari et at Catal. Lett. 23 (1994) 175) zeolites are poor hydroxylation catalysts in the presence of H{sub 2}O{sub 2}. In a paper devoted to Ti-MCM-41, Corma et al. (Chem. Commun. 1994, 147) reported only on the 1-hexene epoxidation. However, in the presence of excess H{sub 2}O{sub 2}, Pinnavaia et al. (Nature 368 (1994) 321) found that Ti-MCM-41 exhibits significant catalytic activity in the hydroxylation of benzenemore » and substituted phenol. This behavior may indicate that in TS-1 and TS-2, Ti has a different local environment.« less

X-ray photoelectron spectroscopy, X-ray diffraction, and temperature-programmed reduction were used to characterize Pt on both sulfated and nonsulfated zirconia. Upon air calcination of the sulfated sample at 600°C, Pt was reduced to the metallic state. In the case of nonsulfated samples, Pt remained in an oxidized form. It is proposed that SO2 produced by the decomposition of sulfate ions reduces Pt.