Monday, March 22, 2010

J. Phys. Chem B and C, vol. 114, issues 11

Chemisorbed Thiols on Silica Particles: Characterization of Reactive Sulfur Species

Paula Caregnato*†, Malcolm D. E. Forbes‡, Delia B. Soria§, Daniel O. Mrtire† and Mnica C. Gonzalez†
J. Phys. Chem. C, 2010, 114 (11), pp 5080–5087
DOI: 10.1021/jp911253f

Abstract: Silica particles with surface thiol groups (Sil−SH) were prepared by silylation of silanol groups using 3-mercaptopropyltrimethoxysilane. The particles were characterized by FTIR, Raman, and XPS spectroscopies; thermogravimetry; and solid state 13C and 29Si NMR spectroscopy. Laser flash excitation at 266 nm of Sil−SH water suspensions in the presence of sodium peroxodisulfate generated sulfur-centered radicals that were attached to the silica surface. These radicals were detected at their absorption maxima (330 nm) by transient optical techniques. Absorbance decay signals were fit to first- and second-order decay kinetics and were assigned to thiyl radicals. Formation of disulfide radicals, a major decay channel for free thiyl radicals in solution, was not observed for surface-grafted thiyl radicals.

Reversibility and Improved Hydrogen Release of Magnesium Borohydride

Rebecca J. Newhouse†‡, Vitalie Stavila*‡, Son-Jong Hwang§, Leonard E. Klebanoff‡ and Jin Z. Zhang†
J. Phys. Chem. C, 2010, 114 (11), pp 5224–5232
DOI: 10.1021/jp9116744

Abstract: Desorption and subsequent rehydrogenation of Mg(BH4)2 with and without 5 mol % TiF3 and ScCl3 have been investigated. Temperature programmed desorption (TPD) experiments revealed a significant increase in the rate of desorption as well as the weight percentage of hydrogen released with additives upon heating to 300 °C. Stable Mg(BxHy)n intermediates were formed at 300 °C, whereas MgB2 was the major product when heated to 600 °C. These samples were then rehydrogenated and subsequently characterized with powder X-ray diffraction (pXRD), Raman, and NMR spectroscopy. We confirmed significant conversion of MgB2 to fully hydrogenated Mg(BH4)2 for the sample with and without additives. TPD and NMR studies revealed that the additives have a significant effect on the reaction pathway during both dehydrogenation and rehydrogenation reactions. This work suggests that the use of additives may provide a valid pathway for improving intrinsic hydrogen storage properties of magnesium borohydride.

Comparison of Different Theory Models and Basis Sets in the Calculations of Structures and 13C NMR Spectra of [Pt(en)(CBDCA−O, O′)], an Analogue of the Antitumor Drug Carboplatin

Hongwei Gao*, Xiujuan Wei, Xuting Liu and Tingxia Yan
J. Phys. Chem. B, 2010, 114 (11), pp 4056–4062
DOI: 10.1021/jp912005a

Abstract: Comparisons of various density functional theory (DFT) methods at different basis sets in predicting the molecular structures and 13C NMR spectra for [Pt(en)(CBDCA−O, O′)], an analogue of the antitumor drug carboplatin, are reported. DFT methods including B3LYP, B3PW91, mPW1PW91, PBE1PBE, BPV86, PBEPBE, and LSDA are examined. Different basis sets including LANL2DZ, SDD, LANL2MB, CEP-4G, CEP-31G, and CEP-121G are also considered. It is remarkable that the LSDA/SDD level is clearly superior to all of the remaining density functional methods in predicting the structure of [Pt(en)(CBDCA−O, O′)]. The results also indicate that the B3LYP/SDD level is the best to predict 13C NMR spectra for [Pt(en)(CBDCA−O, O′)] among all DFT methods.

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