Simulation of the electronic and vibrational structure of hydrogenated amorphous silicon using cluster models

A set of simple models of hydrogenated amorphous silicon (a-Si:H) consisting of hypothetical silane molecules with diamond or similar lattices was studied by the semiempirical AM1 method. Densities of states and infrared spectra were calculated for the silane molecules and similar molecules with dangling bonds disorder, and with boron or phosphorus substitution to simulate doping. Some examples are presented, and a comparison is made with experimental properties of a-Si:H. It is proposed to use these models in a study of the Staebler–Wronski photodegradation of a-Si:H and other aspects of amorphous silicon technology. © John Wiley & Sons, Inc.     

LIFETIME AND ACTIVATION ENERGY OF THE PHOTOINDUCED QUINOID INTERMEDIATE IN PYRIDOXAL CATALYSIS

Abstract— The lifetime of the p -quinoid intermediate of transamination was determined through photoinduction in the metal-ion model system. From the dependence of the lifetime on temperature, the Arrhenius activation energy for proton transfer was 4.2–8.4 kJ/mol (1-2 kcal/mol). The activation energy correlated well with the R group of the amino acid and demonstrated that native substrates have a very labile proton.     

Miniature time-of-flight mass spectrometer using a flexible circuitboard reflector

An innovative design for a miniature time-of-flight mass spectrometer has been developed employing several newly designed components. These include: (1) a gridless, focusing ion source allowing for the use of very high extraction energies in a maintenance-free design, (2) a new method of construction for an ion reflector using rolled flexible circuitboard material, and (3) an improved center-hole microchannel plate detector assembly that significantly reduces the noise (or 'ringing') inherent in the coaxial design. A prototype time-of-flight instrument was constructed and used to evaluate the performance of these components. Compared to previous designs, results indicate that background noise for data acquired on this instrument is substantially reduced, resolution is improved, and the potential for mass producing this instrument in an inexpensive and rugged package for field-portable and remote installations is significantly enhanced. Copyright 2000 John Wiley & Sons, Ltd.     

Improved RP‐HPLC method for determination of bovine lactoferrin and its proteolytic degradation in simulated gastrointestinal fluids

The objective of this study was to qualitatively and quantitatively evaluate bovine lactoferrin (bLf) and its stability using a rapid RP‐HPLC method. bLf could be rapidly detected within 20 min and quantitated at levels down to 5 µg/mL, and the equation of linearity was y = 86.10x + 178.31 with the correlation coefficient (r²) 0.9997. Quantitative data obtained in the present study proved the improved RP‐HPLC method to be a sensitive and accurate analytical tool for bLf determination. The proteolytic cleavage of bLf in simulated human gastrointestinal fluids was further analyzed by RP‐HPLC, and found to follow pseudo‐first‐order kinetics. The typical equation obtained by pepsin was log₁₀ [A_t]/[A₀] = ?0.03x (r² = 0.85), and log₁₀ [A_t]/[A₀] = ?0.01x (r² = 0.81) for trypsin and chymotrypsin combination. Pepsinolysis of bLf in simulated gastric fluid was relatively fast with the half‐life t_1/2 23.1 min. The digestion of bLf in simulated intestinal fluid was slower with about a 3‐fold increase in half‐life (69.3 min). After the complete proteolysis of bLf, small cleaved peptide fragments were fully separated and identified by RP‐HPLC. The proteolytic study indicated that this validated RP‐HPLC was able to evaluate bLf stability though monitoring the derivatization products. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and biological evaluation of the osteoblast proliferating cyclic peptides dianthins G and H

The first synthesis and osteoblast proliferative activity of the naturally occurring cyclic peptides dianthins G and H is described. The greater potency of naturally occurring dianthin G over dianthin H at physiological concentrations mirrored the osteoblast proliferative activity observed for synthetic dianthins G and H. Six alanine-scan analogues of the more potent dianthin G were also synthesised and osteoblast assays revealed that four of the six residues can be further modified for improved activity. We also confirmed by variable temperature ¹H NMR spectroscopic analysis that the sets of major and minor signals observed for dianthins G and H in DMSO-d₆ are in fact due to cis–trans rotational isomers of the proline ring.