Electron spin echo envelope modulation from trapped electrons in a glassy medium

An amplitude modulation of the electron spin echo envelope has been observed for radiation-produced trapped electrons in 10 M NaOD/D₂O at 77°K but not in 10 M N₂OH/H₂O. The modulation has been simulated theoretically by generalizing the single crystal model of Rowan et al. to disordered systems. The modulation has been interpreted as due to dipolar interactions with deuterons in molecules of the second solvation shell around the trapped electrons.     

Synergism in binary mixtures of Thermobifida fusca cellulases Cel6B,Cel9A,and Cel5A on BMCC and Avicel

In an earlier binding study conducted in our laboratory using Thermobifida fusca cellulases Cel6B, Cel9A, and Cel5A (formally Thermomonospora fusca E₃, E₄, and E₅), it was observed that binding capacities for these three cellulases were 18–30 times higher on BMCC than on Avicel. These results stimulated an interest in how the difference in accessibility between the two cellulosic substrates would affect synergism observed with cellulase mixtures. To explore the impact of substrate, accessibility on the extent of conversion and synergism, three binary T. fusca cellulase mixtures were tested over a range of cellulase ratios and total molar cellulase concentrations on Avicel and BMCC. Higher extents of conversion were observed for BMCC due to the higher enzyme to substrate ratio resulting from the higher binding The processive endoglucanase, Cel9A, had four times the extent of conversion of the end endocellulase Cel5A, while the exocellulase Cel6B had three times the extent of conversion of Cel5A. Approximately 500 nmol/g of the cel9A+Cel6B mixture was needed to obtain 80% conversion, while the Cel6B+Cel5A and Cel9A+Cel5A mixtures required 1500 and 1250 nmol/g, respectively, to obtain 80% conversion. Thus, it appears that the more accessible structure of BMCC, as reflected by its binding capacity, results in relative higher processive activity.     

Maleation of poly(3,4‐epoxy‐1‐butene) for accelerated crosslinking in the presence of a redox catalyst

Accelerated crosslinking of novel poly(3,4‐epoxy‐1‐butene) (3,4‐PEPB) oligomers in the presence of a cobalt‐based redox catalyst was investigated. Previous studies using model compounds, 3,4‐dimethoxy‐1‐butene and 1,4‐dimethoxy‐2‐butene, suggested that maleation of hydroxyl‐terminated 3,4‐PEPB oligomers would result in more rapid crosslinking in thin films. Novel maleated oligomers offered a unique combination of both electron‐rich and electron‐poor olefinic sites, and quantitative maleation significantly increased the crosslinking rate of 3,4‐PEPB. Efficient copolymerization between terminal maleate groups and olefinic groups in the repeating unit was proposed to account for accelerated crosslinking rates. Furthermore, the addition of novel reactive diluents, such as maleic acid mono‐ethyl ester, also effectively improved the 3,4‐PEPB crosslinking rate. Sol fraction measurements as a function of coating thickness revealed that the crosslinking rate versus oxygen diffusion was less significant for the maleated oligomers because of the presence of reactive electron‐poor olefins. Sol fractions were constant for catalyst concentrations greater than 0.25–0.50 wt % (as compared with oligomer feed). This observation suggested that a redox process was not a dominant factor in determining crosslinking rates at various experimental conditions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2789–2798, 2002     

Predicting the shape and structure of face-centered cubic gold nanocrystals smaller than 3 nm.

Although a number of computational studies have examined the relative stability of icosahedral and decahedral gold clusters from 1 to 3 nm in size, few studies have focussed on the variety of face-centered cubic (fcc) nanoparticles in this size regime. In most cases small fcc gold particles are assumed to adopt the truncated octahedral shape, but in light of the fact that the shape and structure of gold nanoparticles is known to vary, the relative stability of fcc polyhedra may change with size. Presented here are results of first-principles calculations investigating the preferred shape of gold particles less than 3 nm in size. Our results indicate that the equilibrium shape of fcc gold nanoparticles less than 1 nm is the cuboctahedron, but this shape rapidly becomes energetically unstable with respect to the truncated octahedron, octahedron and truncated cube shapes as the size increases.     

Open-access liquid chromatography/mass spectrometry in a drug discovery environment

The use of open-access mass spectrometry to monitor synthetic chemistry reactions, and also the integrity and purity of new chemical entities, has been a part of the medicinal chemist's tool-box for more than 5 years. Originally in our group at Wyeth Research there were two open-access methods available to the chemists, flow injection analysis (FIA) and liquid chromatography/mass spectrometry (LC/MS). The FIA method was approximately 3 min long, while the LC/MS method was approximately 20 min long (including an 8 min gradient). Within the first 2 years, the total number of open-access analyses increased by approximately 125%. It is interesting, however, that the number of LC/MS analyses increased by more than 285%. This is attributed to the fact that the chemists began using the LC/MS data to monitor reactions and also to check final product integrity and purity. In addition, the number of chemists performing parallel synthesis reactions has increased; thus, individual chemists can produce sample sets of up to 100 vials. This paper describes the implementation of new methodology, which accommodates the need for much faster run times and also the ability to acquire alternating positive and negative ion spectra within the same run. In addition, the instrument has been configured to e-mail the resulting processed data report to the submitting chemist. Several methods have been developed, including structure elucidation using in-source collision-induced dissociation (CID) and night-time analysis. The LC/MS methods for this system are described herein and are applicable to both industrial and academic synthetic chemistry optimization efforts.     

ENHANCED SUSCEPTIBILITY TO HPD-SENSITIZED PHOTOTOXICITY AND CORRELATED RESISTANCE TO TRYPSIN DETACHMENT IN SV-40 TRANSFORMED IMR-90 CELLS

Abstract— The response of a normal human cell strain, IMR-90 and a line derived from it by SV40 transformation were compared after treatment in vitro with hematoporphyrin derivative (HPD) and red light. Transformed cells were inactivated at a significantly higher rate than normal cells when assayed by clonogenic survival. Co-treatment with HPD and light also induces cellular resistance to enzymatic cleavage by trypsin; transformed cells exhibit a greater resistance than the normal cells to detachment from the growing surface. These data indicate that transformed cells may possess intrinsic characteristics that render them more sensitive than normal cells to HPD-induced phototoxicity and that the plasma membrane may be the site of differential toxicity.     

Complex 2 plane bundles over CP(n)

The purpose of this note is to construct examples of non-trivial rank 2 complex bundles over CP(n) with vanishing Chern classes for all n5.     

A critical evaluation of high performance liquid chromatography-electrospray ionisation-mass spectrometry and capillary electrophoresis-electrospray-mass spectrometry for the detection and determination of small molecules of significance in clinical and forensic science

A critical review of applications for the period 2000-2003, taken from the Web of Knowledge database, of the techniques high performance liquid chromatography-electrospray ionisation-mass spectrometry (HPLC-ESI-MS) and capillary electrophoresis-electrospray ionisation-mass spectrometry (CE-ESI-MS) to the detection and determination of small molecules of significance in clinical and forensic science is presented. The molecules of mass less than 500 Da are chosen according to selected structural classes in which they give ESI signals primarily as [M+H](+) ions although other ions such as [M-H](-), [M+Na](+) and [M+NH(4)](+) are also reported. The structural classes are drugs with amine-containing side chains, drugs with N-containing saturated ring structures, 1,4-benzodiazepines, carbohydrates, benzimidazoles, other heterocycles, sulphonylureas, anthracyclines, sulphonamides, penicillins, cephalosporins, tetracyclines, nitrocatechols, steroids, flavonoids, oxazaphosphorines, cannabinols, and miscellaneous molecules. Details are given on the fragmentations, where available, that these ionic species exhibit in-source and in ion-trap, triple quadrupole and time-of-flight mass spectrometers. The review then gives a critical evaluation of these recent HPLC-ESI-MS and CE-ESI-MS analytical methods for the detection and determination of small molecules of clinical and forensic significance. Analytical information on, for example, sample concentration techniques, HPLC and CE separation conditions, recoveries from biological media and limits of detection (LODs) are provided.     

Synthesis of a digermane-containing tricylic nonadecadienedione incorporating an equivalent of ring-opened THF

The combination of 2 equiv of bis[bis(trimethylsilyl)amide]germylene (5) with 2 equiv of 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) in tetrahydrofuran (THF) results in the ring-opening of 1 equiv of THF to form 2,2,8,8-tetrakis(1,1,1,3,3,3-hexamethyl-disilazan-2-yl)-5,16-diphenyl-7,9,14-trioxa-1,3,5,16,18,19-hexaaza-2,8-digerma-tricyclo[13.2.1.13,6]nonadeca-6(19),15(18)-diene-4,17-dione (6). This fast and nearly quantitative reaction builds a 15-membered ring from five different molecules. The new ring, structurally assigned by X-ray crystallography, contains a flexible methylene chain that moves rapidly on the NMR time scale.     

Preparation,properties and x-ray crystal structure of a complex of bis(triphenylphosphoranylidene)ammonium iodide with 7,7,8,8-tetracyano-P-quinodimethane: (PPN)2(TCNQ)3(CH3CN)2

Bis(triphenylphosphoranylidene)ammonium iodide (PPN⁺I^?) forms a 2:3 complex with TCNQ [(PPN)₂(TCNQ)₃(CH₃CN)₂] that provides an example of a TCNQ complex containing acetonitrile in the crystal lattice; the material is a semi-conductor with trimerised TCNQ stacks.