Colin G. Pitt

The enzymatic surface erosion of aliphatic polyesters

Abstract The rates and mechanisms of biodegradation of a series of homo- and copolymers of ϵ caprolactone, crosslinked to varying degrees with 2,2-bis(e-caprolacton-4-yl)propane (BCP), were determined in rabbit and rat. These polymers were elastomeric, with little or no crystallinity. In contrast to the uncrosslinked crystalline homopolymer, which is subject to long induction periods prior to weight loss, poly(e-caprolactone) crosslinked with 6 mole % BCP was bioabsorbed by an enzymatic surface erosion process which was detectable within two weeks in rabbit and was 80% complete after 100 weeks. The bioabsorption of crosslinked 1:1 copolymers of e-caprolactone and δ-valerolactone was proportional to the crosslink density, ρ, and, for ρ

Synthesis and crystal structure of tris(dimesitylarsino)gallane, a monomeric tricoordinate gallium-arsenic compound

Abstract : The gallium-arsenic bond, in polymeric form is expected to exhibit anisotropic conductivity by virtue of an extended p-pi system, isoelectronic with polyacetylene. Four mono-, bis-, and trisarsinogallanes were prepared from the reaction of lithium dimesitylarsenide with gallium chlorides. One of these, tris(dimesitylarsino) gallane, (Mes2As)3Ga(1), was characterized by single crystal x-ray analysis and shown to be the first example of a monomeric tricoordinate gallium-arsenic compound. Orange crystals of 1 belong to the triclinic system space group P1. The gallium atom is bonded to the three arsenic atoms in a trigonal planar configuration. The color of 1 is the result of tailing of a 276 nm CT band into the visible.

Isolation and characterization of an organogallium–arsenic cluster: crystal structure of [(PhAsH)(R2Ga)(PhAs)6(RGa)4](R = Me3SiCH2)

[(PhAsH)(R2Ga)(PhAs)6(RGa)4](R = Me3SiCH2) has been isolated as a product of the reaction of PhAsH2 with (Me3SiCH2)3Ga and determined by X-ray crystallographic analysis to be a cluster containing an As7Ga5 core.

The first gallium–arsenic compound containing a single Ga3As unit: isolation and crystal structure of [(thf)Br2Ga]3As (thf = tetrahydrofuran)

[(thf)Br2Ga]3As (thf = tetrahydrofuran), isolated from the products of the reaction of (Me3Si)3As with GaBr3, has been shown by X-ray crystallographic analysis to be the first example of a compound containing a single Ga3As unit.

Some gas phase reactions of silicenium ions derived from sym-tetramethyldisiloxane

Abstract Ion cyclotron resonance spectroscopy has been used to study reactions of the silicenium ions, Me2HSiO S + iMeR (R = H and Me), generated from sym-tetramethyldisiloxane in the gas phase. These silicenium ions react with neutral sym-tetramethyldisiloxane by an addition—elimination process, to form the homologous silicenium ions, H(Me2SiO ) + nSiMeR (n = 2 and 3). Analogous addition—elimination products, MeO(Me2SiO)nSiMeR, are derived from their reaction with methanol. Bimolecular adducts are observed in the presence of benzene and anisole, while oxygen abstraction occurs in the presence of anisole and acetone.

The Use of Tris(trimethylsilyl)arsine to Prepare AlAs, GaAs and InAs. The X-Ray Crystal Structure of (Me3Si)3AsAlCl3.C7H8.

Abstract : The reactions of (Me3Si)3As with group III halides have been utilized to prepare A1As, GaAs and InAs. The adduct (Me3Si)3AsA1C13 has been isolated as an intermediate in the formation of A1As from (Me3Si)3As and A1C13. The crystal structure of its toluene solvate has been determined. Keywords: Aluminum arsenide, Gallium arsenide, Indium arsenide, Preparation, Crystal structure, Silyl radicals. (MJM)

Synthesis, crystal and molecular structure of a 1,11-etheno-steroid: 3-methoxy-1,11-ethenoestra-1,3,5(10),9(11)-tetraen-17-one

Methods of construction of a two carbon bridge between C(1) and C(11) of the steroid skeleton have been studied. Treatment of 17,17-ethylenedioxy-11α-ethynyl-3-methoxyestra-1,3,5(10)-trien-11β-ol (2) with toluene-p-sulphonic acid in benzene gave a mixture of 3-methoxy-1′ξ-methyl-1,11ξ-methanoestra-1,3,5(10),6,8,-pentaen-17-one (7) and the title compound (8). The latter was also obtained in poor yield from 17,17-ethylenedioxy-3-methoxy-11α-(2-oxoethyl)estra-1,3,5(10)-trien-11β-ol (4) in hydrogen fluoride and in better yield (76%) from treatment of (2) with tris(triphenylsilyl) vanadate. Crystals of (8) are orthorhombic, space group P212121, a= 7.867(5), b= 30.036(20), c= 6.838(5)A, Z= 4. The structure was solved by direct methods and refined by full-matrix least-squares calculations to R 0.044 over 1 283 statistically significant reflections from diffractometer measurements. The modified steroid skeleton is very flat, the maximum deviation of any ring atom from the naphthalene plane being 0.635 A. Ring B approximates to a C(7)α-envelope form, ring C adopts a half-chair conformation, and ring D has a C(14)α-envelope form.

The relative gas-phase proton affinities and polarisabilities of alkyl and silyl ethers

The relative gas-phase proton affinities of a number of alkyl and silyl ethers have been determined by ion cyclotron resonance spectroscopy and compared with the relative basicities toward weaker protic and Lewis acids. The basicities of the silyl ethers are enhanced by the stronger acid, but are still weaker than the isostructural carbon ethers. The CNDO/2 method has been used to estimate the extent of eletron redistribution in charged silyl and alkyl derivatives.