The arsonomethyl group as an analogue of phosphate. An X-ray investigation

The X-ray structure analysis of three compounds of interest as enzyme substrates is reported. They are the hydrated forms of (I) DL-2-amino-4-arsonobutanoic acid [HO–AsO2-–CH2–CH2–CH(NH3+)–CO2H], (II) DL-2-amino-4-phosphonobutanoic acid [HO–PO2-–CH2–CH2–CH(NH3+)–CO2H] and the hydrated barium salt of (III) D-3-phosphoglycerate [HO–PO2-–O–CH2–CH(OH)–CO2-]. The structures were fully refined to R factors of 0.033, 0.053 and 0.046. For the compounds (I) and (II) the charge distribution was directly determined by locating all H atoms. The co-ordination around As and P is approximately tetrahedral, with the valency angle between the two charged O atoms enlarged to 112 degrees in compound (I), 166 degrees in compound (II) and 122 degrees in compound (III). The As-X bond distances are increased relative to P-X to accommodate the increased atomic radius. The analysis establishes that the compounds are structural analogues. Tables of co-ordinates for H atoms, anisotropic thermal parameters, bond lengths and bond angles for the three compounds have been deposited as Supplementary Publication SUP 50122 (5 pages) with the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained directly [see Biochem J. (1983) 209, 5].

STEREOCHEMISTRY OF ARSENIC: PART XII. BIS(DIPHENYLARSENIC) OXIDE

Crystals of bis(diphenylarsenic) oxide are monoclinic, with four molecules in a unit cell of dimensions a = 11.48, b = 30.2, c = 5.97 Å, β = 93.8°, space group P21/n. The structure has been determined from projections along the a and c axes, using Fourier and difference syntheses. The As—O—As angle is 137°, the increase from the normal oxygen valency angle probably being a result of pπ—dπ bonding involving arsenic 4d orbitals. The As—O distance is 1.67 Å, and all the other bond lengths and angles are normal. The orientations of the substituent phenyl groups have been determined.

The use of polarized infra-red radiation in the study of doubly oriented long-chain polymers

The use of polarized infra-red radiation in examining the structure and orientation of high polymers has been investigated quantitatively. It is shown that infra-red spectroscopy can furnish evidence for double orientation in rolled sheets of nylon 66, polyvinyl alcohol and (with less certainty) polythene. In the case of polyvinyl formate, acetate, chloride and polyvinylidene chloride such double orientation could not be detected. Evidence is given to show that in nylon the N -H bond is bent by hydrogen bonding forces, the angle between this bond and the plane of the skeleton being thereby reduced from 39° (the valency angle) to 22°. The structure of polyvinyl alcohol recently proposed by Bunn receives strong support from the absence of dichroism in the O-H frequency in the spectrum of that material, when a doubly oriented specimen is examined.