Brian K. Hunter

The elasticity of spiders' webs is due to water-induced mobility at a molecular level

13C nuclear magnetic resonance (NMR) spectroscopy of intact webs from the common garden spider Araneus diadematus has been used to demonstrate that: (i) water retention is an important role for the viscid coating of capture thread; (ii) the elasticity of capture thread results from water-induced mobility at a molecular level, (iii) the organization and composition of structural and capture thread are different, even in the absence of coating; and (iv) glycoproteins may have a more important presence and structural role than previously realized. Different 13C-labelling patterns of webs were achieved by feeding spiders either with [13C]glucose or with [13C ]amino acids.

The crystal and molecular structure of bis(biscyclopentadienylchlorotitanium) oxide

Abstract Bis(biscyclopentadienylchlorotitanium) oxide, Cp 2 TiCl) 2 O, crystallizes in the enantiomorphic space groups P 3 1 21 and P 3 2 21 with a 7.742(1), c 27.177(7) A. In this study only twins were obtained. On the basis of intensity data for 1106 independent reflections, the structure is described in P 3 1 21 with final residuals of R F = 3.27% and R WF = 2.53%. The molecule is very similar to that of the analogous zirconium compound. Mean bond lengths are CpTi(π), 2.09; ClTi, 2.41; and TiO, 1.84 A. The TiOTi bond angle is 173.8°.

Crystallization of side chains in copolymers of ethylene and 1‐alkenes

The phase structure of random copolymers of ethylene and ethylene-d4 with 1-octadecene and other 1-alkenes has been investigated. CPMAS 13C NMR spectra show that a fraction of the central sections of C16H33 side chains in ethylene-d4 copolymers are in ordered environments at 298 K. They give rise to resonances from 32.9 ppm to 33.8 ppm, which show that they are in trans conformations; T1C values for this group of resonances range from 1 s to 7 s. The remaining side chains are in an amorphous environment, the internal methylenes having a chemical shift of 30.8 ppm and a T1C close to 0.4 s. A Raman band at 1062 cm−1 in the spectrum of an ethylene-d4-1-octadecene copolymer is consistent with partial crystallization of side chains. Some side-chain crystallization also occurs in a 1-tetradecene copolymer. X-ray diffraction studies suggest that smaller side chains do not crystallize to a significant extent at 298 K.

Stable and convenient alkyltitanium reagents for organic synthesis

Abstract Monocyclopentadienyl titanium alkyls perform similarly to other alkyltitanium reagents in reactions with carbonyl groups while possessing significantly greater thermal stability.

Reactions of a chelated alkylpalladium compound

Abstract The chemistry of the compound [P d(CH 2 CHRCH 2 N Me 2 )Cl] 2 (V. R.  CH(CO 2 Et) 2 ) with nucleophilic (PPh 3 , pyridine, CO) and electrophilic (H 2 , HCl) reagents is studied. Although the nucleophiles cleave the chloride bridges, they do not readily disrupt the PdN bond, and both V and its adduct are very stable with respect to decomposition via olefin elimination. As expected, however, H 2 and HCl cleave the PdC bond to give CH 3 CHRCH 2 NMe 2 and either Pd metal or a palladium chloride complex, respectively.

Synthesis and properties of a thermally stable methyltitanium(IV) compound: Cyclopentadienylmethyldichlorotitanium(IV)

Abstract η5C5H5Ti(CH3)Cl2 and η5-C5H5Ti(C2H5TiCl2 have been synthesized. The reactivity of the methyl compound is much greater than that of the closely related sandwich compound, (η5-C5H5)2Ti(CH3)Cl, but the thermal stability is comparable.

15,17-Butano-3,8-diethyl-2,7,12,18-tetramethylporphyrin - a novel naturally occurring tetrapyrrole

The title compound (2) has been isolated from a Triassic oil shale and its structure determined by nuclear Overhauser effect difference studies.

Polyethylenes revisited: Waxs and the phase structure

Abstract The use of multiple Cauchy/Gauss envelopes to describe crystalline and amorphous reflections in the deconvolution of X-ray diffraction patterns is examined. Crystallinities were estimated for a number of ethylene polymers and copolymers with a variety of sample configurations and of band inputs. These are compared with crystallinities estimated from density and enthalpy of fusion data. The significance of the extra bands required to give an optimum fit with the diffraction pattern is discussed briefly.

Relaxation in calcium hexachlorostannate hexahydrate

Abstract Measurements of 1 H and 35 Cl relaxation times in [Ca·6H 2 O][SnCl 6 ] are reported. The 35 Cl quadrupolar T 1 indicates anion reorientation at temperatures above 250 K, with an activation energy of 29.5 ± 1.0 kJ mol −1 . Measurements at high pressure were also carried out, and the volume of activation for anion reorientation was found to be 8.5 ± 0.2 cm 3 mol −1 . Proton T 1 and T 1 ϱ measurements show the presence of three motions associated with the cation. The first is a 180° flipping motion of the water molecules with an activation energy of 13.7 ± 0.4 kJ mol −1 . The other two motions are derived from an asymmetrical double minimum in T 1 ϱ , and reflect uniaxial ( C 3 or C 4 ) reorientation and isotropic tumbling of the entire cation. The activation energies are 38.1 ± 0.4 and 48 ± 2 kJ mol −1 , respectively.

Proton nuclear magnetic resonance and line shape analysis in the alkali metal hydroxides: LiOH, NaOH, KOH, and RbOH

The proton NMR line shapes of the anhydrous alkali metal hydroxides at 27 and 200 MHz are presented. The structure in the proton resonances of NaOH, KOH, and RbOH is explained using a four‐spin planar zig–zag chain model calculation. Second moment calculations show that the observed line shapes are consistent with known crystal structures. The crystal structures of KOH and RbOH, as determined by x‐ray powder diffraction, are confirmed.