Gerry W. Zajac

Re-investigation of titanium silicalite by X-ray absorption spectroscopy: Are the novel titanium sites real?

EXAFS studies have been carried out on titanium silicalite-1 (TS-1). The titanium atom is coordinated to four oxygen atoms at the distance of 1.80(1) Å. There is no evidence for the presence of 5- and 6-coordinated titanium species or the novel 4-coordinated titanium species involving [TiOx] units sharing edges with [SiO4] units. The EXAFS spectrum of TS-1 appears to be consistent with the model that titanium resides at the tetrahedral sites of the framework.

Structural Studies of Bleached Melanin by Synchrotron Small-angle X-ray Scattering¶

Abstract Small-angle X-ray scattering was used to measure the effects of chemical bleaching on the size and morphology of tyrosine-derived synthetic melanin dispersed in aqueous media. The average size as measured by the radius of gyration of the melanin particles in solution, at neutral to mildly basic pH, decreases from 16.5 to 12.5 Å with increased bleaching. The melanin particles exhibit scattering characteristic of sheet-like structures with a thickness of approximately 11 Å at all but the highest levels of bleaching. The scattering data are well described by the form factor for scattering from a pancake-like circular cylinder. These data are consistent with the hypothesis that unbleached melanin, at neutral to mildly basic pH, is a planar aggregate of 6- to 10-nm-sized melanin protomolecules, hydrogen bonded through their quinone and phenolic perimeters. The observed decrease in melanin particle size with increased bleaching is interpreted as evidence for deaggregation, most probably the result of oxidative disruption of hydrogen bonds and an increase in the number of charged, carboxylic acid groups, whereby the melanin aggregates disassociate into units composed of decreasing numbers of protomolecules.

Direct conversion of methane to higher hydrocarbons via an oxygen free, low-temperature route

AbstractThe direct conversion of methane to higher hydrocarbons over a silica-supported Ru catalyst has been investigated via an oxygen free, two-step route. The reaction consists of decomposition of methane over a 3% silica-supp orted Ru catalyst at temperatures

Electron energy loss studies of propylene interactions in US-Y faujasites

(T_{CH_4 } )

Interlaboratory study of adhesion using voltage contrast XPS

between 400 and 800 K to produce surface carbonaceous species followed by rehydrogenation of these species to higher hydrocarbons at

Spectroscopic Study and Simulation from Recent Structural Models for Eumelanin: I. Monomer, Dimers

T_{H_2 }