Photodissociation of high molecular weight peptides and proteins in a two-stage linear time-of-flight mass spectrometer

A two-stage linear time-of-flight mass spectrometer is used to investigate the requirements for performance of laser photodissociation of peptide and protein ions. Results are presented that demonstrate that desorption and dissociation laser pulses can be synchronized to irradiate ions that travel at high velocities down the drift tube of a time-of-flight mass spectrometer. For example, 193-nm photodissociation of bovine insulin and doubly charged lysozyme is demonstrated, and laser power studies suggest that dissociation is initiated by the absorption of a single 193-nm photon. These results are encouraging because they suggest that laser photodissociation of high molecular weight proteins can lead to fragmentation on time scales compatible with time-of-flight mass spectrometry.     

Efficient Preparation of γ-Hydroxynitriles via Nitrile Enolate-Epoxide Reactions: Scope and Diastereoselectivity

The nucleophilic opening of epoxides by nitrile enolates using an efficient, convenient protocol is described. The diastereoselectivity of this reaction was explored and found to give syn:anti ratios ranging from 1.1:1.0 to 4.8:1.0.

     

Cultural influences on sex differentials in mathematics aptitude and achievement

Results of mathematics testing of 14‐year‐olds and college freshmen in the West Bank indicate more substantial variation on the basis of cultural factors than on the basis of gender. In particular, no significant difference in the mathematical abilities of men and women appeared in the college group.     

Interfacial electronic structure of vanadyl naphthalocyanine on highly ordered pyrolytic graphite

We present a core and valence region spectroscopic analysis of the interfacial electronic structure of thin films of vanadyl naphthalocyanine (VONc) deposited onto highly oriented pyrolytic graphite (HOPG). X-ray photoelectron spectroscopy indicates the predominantly ionic character of the vanadyl metal center coordinated by the heterocycle and affords the bandgap in the thin VONc films. Valence band photoelectron spectroscopy points to the existence of three different adsorption geometries of VONc on the HOPG surface. The distribution of the different geometries can be systematically influenced in a simple post-deposition processing step, with an immediate effect on the interfacial electronic environment. We find spectroscopic evidence in the valence levels that VONc grows on HOPG most likely in a 2D-gas fashion rather than by nucleation and growth of islands. These data allow us to predict accurately the interface dipole in the case of a broad class of dipolar organic semiconductors, based simply on molecular dipole moment, polarizability and molecular diameter. This ability provides an important step towards rational optimization of energy level alignment in organic electronics.     

Rapid initiation of reactions in Al/Ni multilayers with nanoscale layering

Research into nanoenergetic materials is enabling new capabilities for controlling exothermic reaction rates and energy output, as well as new methods for integrating these materials with conventional electronics fabrication techniques. Many reactions produce primarily heat, and in some cases it is desirable to increase the rate of heat release beyond what is typically observed. Here we investigate the Al-Ni intermetallic reaction, which normally propagates across films or foils at rates lower than 10 m/s. However, models and experiments indicate that local heating rates can be very high (10⁷ K/s), and uniform heating of such a multilayer film can lead to a rapid, thermally explosive type of reaction. With the hopes of using a device to transduce electrical energy to kinetic energy of a flyer plate in the timescale of 100's of nanoseconds, we have incorporated a Ni/Al nanolayer film that locally heats upon application of a large electrical current. We observed flyer plate velocities in the 2-6 km/s range, corresponding to 4-36 kJ/g in terms of specific kinetic energy. Several samples containing Ni/Al films with different bilayer thicknesses were tested, and many produced additional kinetic energy in the 1.1-2.3 kJ/g range, as would be expected from the Ni-Al intermetallic reaction. These results provide evidence that nanoscale Ni/Al layers reacted in the timescale necessary to contribute to device output.     

Computational investigation of the role of fluoride in Tamao oxidations

The Tamao oxidation of alkoxysilanes was investigated computationally to determine the role of fluoride, a key additive, in this reaction. A sequence of fluoride equilibria as well as possible transition states, mediated by basic and neutral peroxide, respectively, were examined, and a potential energy surface was calculated which was consistent with the typical synthetic methods required for the conversion of alkoxysilanes to alcohols.     

Surface characterization of synthetic and mineral carbonate fluoroapatites

As part of a larger project concerning the sorption capacities of carbonate fluoroapatites, the physical and surface properties of the synthetic carbonate fluoroapatite and mineral francolite retained for this work have been carefully examined. The average particle size of the powdered samples, determined by laser granulometry, is around 30 microm. Their specific surface areas, measured according to the N(2) BET method, are 8.8+/-0.1 and 13.9+/-0.1 m(2).g(-1), respectively, for the synthetic and the mineral compound. The solubility of both solids has been studied under undersaturation initial conditions. The synthetic compound has a solubility product of 10(-103+/-2), but the mineral francolite, which is highly substituted and poorly crystalline, is more soluble and dissolves incongruently. The amphoteric properties of the hydrous carbonate fluoroapatites surfaces have also been investigated through zeta-potential measurements and potentiometric titrations in KNO(3) medium at 25 degrees C. The experimental data have been interpreted using the computer program FITEQL 3.2, applying either the nonelectrostatic or the constant capacitance model. For both solids, the values of the surface acidity constants determined with the two models are very close, suggesting a weak contribution of the electrostatic interactions. Moreover, the more acidic surface of the synthetic compound compared to that of the mineral one is assigned to the differences in crystallinity and chemical composition between the two solids.     

S-pixyl analogues as photocleavable protecting groups for nucleosides

Several analogues of the 9-phenylthioxanthyl (S-pixyl) photocleavable protecting group have been synthesized, containing substituents on the 9-aryl ring and on the thioxanthyl backbone. Each analogue protected the 5'-hydroxy moiety of thymidine in good to excellent yield. The protected substrates were deprotected in 1:1 water:acetonitrile with irradiation at 300 nm, resulting in recovered thymidine in excellent yield, except for the nitro-substituted analogues which gave substantially lower yields. Substrates with 2,7-dibromo or 3-methoxy substitution on the thioxanthyl backbone were also deprotected efficiently with irradiation at 350 nm. Shorter irradiation times were observed in the less nucleophilic solvent mixture of 1:9 trifluoroethanol:acetonitrile, with no formation of secondary photooxidation products. Photodeprotection with high yields was also achieved in the absence of solvent, with no secondary photoproducts.