Boronate functionalised polymer monoliths for microscale affinity chromatography

Novel macroporous monolithic stationary phase materials suitable for microscale boronate affinity chromatography were developed.     

Ultracold Rb-OH collisions and prospects for sympathetic cooling

We compute ab initio cross sections for cold collisions of Rb atoms with OH radicals. We predict collision rate constants of order 10(-11) cm3/s at temperatures in the range 10-100 mK at which molecules have already been produced. However, we also find that in these collisions the molecules have a strong propensity for changing their internal state, which could make sympathetic cooling of OH in a Rb buffer gas problematic in magnetostatic or electrostatic traps.     

Magnesium coordination-directed n-selective stereospecific alkylation of 2-pyridones, carbamates, and amides using α-halocarboxylic acids

A general inversion-stereospecific, N-selective alkylation of substituted 2-pyridones (and analogues), amides, and carbamates using chiral α-chloro- or bromocarboxylic acids in the presence of KOt-Bu (or KHMDS) and Mg(Ot-Bu)(2) is reported. The resulting α-chiral carboxylic acid products were isolated by crystallization in good chemical yields and in high ee (>90% ee). Mechanistic evidence suggests that the reaction proceeds through 2-pyridone O-coordinated Mg carboxylate intermediates, which afford the product through an intramolecular S(N)2 alkylation.     

H.323 — A Key to the Multimedia Future

The advent of the Internet has created a revolution in the telecommunications and computing industries. The rapid growth in the use of personal computers plus their ubiquity, combined with easy access to the Internet in both the office and at home, has led to the development of standard protocols that can support voice and video communication over the same data networks used for the Internet. This paper describes one such standard developed by the International Telecommunications Union — H.323. The paper describes the origin of the standard and the processes and drivers from which it has been developed. It then overviews the standard and the capabilities in each version and describes the future direction.     

Microbial dynamics in oil-impacted prairie soil

A remote site in the Tallgrass Prairie Preserve (Osage County, OK) was contaminated with crude oil by a pipeline break in 1992. In 1996, the contaminated soil was bioremediated by blending with uncontaminated soil, prairie hay, buffalo manure, and commercial fertilizers, and spreading in a shallow layer over uncontaminated soil to create a landfarm. The landfarm was monitored for two years for aerobic and anaerobic bacteria, soil gases indicative of microbial activity, and for changes in the concentration of total petroleum hydrocarbons (TPH). Levels of hydrocarbon degraders and soil gas indicators of aerobic degradation were stimulated in the landfarm during the first warm season relative to uncontaminated prairie soil. However, these same indicators were less conclusive during the second warm season, indicating depletion of the more easily degradable hydrocarbons, although the landfarm still contained 6,800 mg/kg TPH on the average at the beginning of the second warm season. Methane formation and methanogen counts were clearly stimulated in the first warm season relative to uncontaminated prairie soil, in dicating that methanogenesis plays an important role in the mineralization of hydrocarbons even in these shallow soils.     

Optimization of low temperature silicon nitride processes for improvement of device performance

This paper gives some insights in the applications where PECVD nitrides can be introduced to replace the LPCVD layers and how the process parameters need to be varied to obtain the desired properties. Film properties like stress, hydrogen content, wet etch rate and deposition rate are reported. The nitrides are optimized for specific applications and examples on the influence of nitride properties on device performance are given. It is important to investigate that the advantage of the high film integrity of nitride layers used in the past is not lost due to the strong demand for developing new process schemes with low thermal budget layers. We show that PECVD films are a valid alternative for LPCVD and that the majority of the film properties satisfy the criteria to use PECVD films as contact-etch-stop layers, silicidation blocking films and spacer materials.     

First enzymatic synthesis of an N1-cyclised cADPR (cyclic-ADP ribose) analogue with a hypoxanthine partial structure: discovery of a membrane permeant cADPR agonist

Nicotinamide 8-Br-hypoxanthine dinucleotide (8-Br-NHD+) was cyclised at the N1 position by the ADP-ribosyl cyclase from Aplysia californica to give cyclic 8-Br-inosine diphosphoribose (8-Br-N1-cIDPR), a novel membrane-permeant agonist of Ca2+ release in human T cells.     

Structure, absolute configuration, and conformation of the antimalarial compound, Artemisinin

The crystal and molecular structure of the antimalarial compound Artemisinin (formerly known as Qinghaosu), C₁₅H₂₂O₅ has been determined by direct methods. Crystals are orthorhombic colorless needles, space group P2₁2₁2₁, Z = 4. D _c = 1.299 g cm ^–3, with unit cell parameters a = 6.3543(9), b = 9.439(3), c= 24.066(4) Å. The molecule incorporates a fused ring system containing a six-membered ring C which includes an oxygen bridge and a peroxy-bridge. The ring C has a distorted boat conformation and the C - O - O - C torsion angle is 47.8(2)°. Rings A and D have symmetrical chair and distorted chair conformations, repectively. Ring junctions A/B, A/D, and C/D are cis, junction B/D is trans. All inter-molecular contacts are van der Waals. The absolute configuration of Artemisinin was determined from the refined value of the Flack x parameter. [The atomic coordinates given in a previous structure analysis, Crystal Structure and Absolute Configuration of Qinghaosu, Qinghaosu Research Group, Institute of Biophysics, Academica Sinica, Scientia Sinica, Vol. XXIII No. 3, 380 (1980), do not display the molecule in its absolute configuration.]     

Biomimetic and microbial reduction of nitric oxide

The biomimetic reduction of nitric oxide (NO) to nitrous oxide (N₂O) by dithiothreitol in the presence of cyanocobalamin and cobaltcentered porphyrins has been investigated. Reactions were monitored directly using Fourier Transform Infrared (FTIR) Spectroscopy vapor-phase spectra. Reaction rates were twofold faster for the corrin than for the cobalt-centered porphyrins. The stoichiometry showed the loss of two molecules of NO per molecule of N₂O produced. We have also demonstrated that the facultative anaerobe and chemoautotroph,Thiobacillus denitrificans, can be cultured anoxically in batch reactors using NO as a terminal electron acceptor with reduction to elemental nitrogen (N₂). We have proposed that the concentrated stream of NO_x, as obtained from certain regenerable processes for the gas desulfurization and NO_x removal, could be converted to N₂ for disposal by contact with a culture ofT. denitrificans. Four heterotrophic bacteria have also been identified that may be grown in batch cultures with succinate, yeast extract, or heat and alkali pretreated sewage sludge as carbon and energy sources and NO as a terminal electron acceptor. These areParacoccus dentrificans, Pseudomonas denitrificans, Alcaligens denitrificans, andThiophaera pantotropha.     

Simultaneous purification of the neuroproteins synapsin I and synaptophysin.

A procedure for the simultaneous purification of synapsin I and synaptophysin from calf brain was developed. Demyelinated membranes were extracted with 2% Triton X-100 and 2 M KCl. The extracted proteins were separated by weak cation-exchange chromatography on carboxymethyl-Sepharose Fast Flow. Synaptophysin was finally purified by preparative sodium dodecyl sulphate-polyacrylamine gel electrophoresis and synapsin I by affinity chromatography using a calmodulin-Sepharose column. The recovery obtained was 40 micrograms/g in brain for synaptophysin and 25 micrograms/g in brain for synapsin I.