Parabolic focal conics in self-assembled solid films of cellulose nanocrystals

Suspensions of cellulose nanocrystals form colloidal chiral nematic phases. The liquid crystalline order in these suspensions can be captured in solid films by slow evaporation of the liquid. Studies of the microstructure of such chiral nematic solid films revealed parabolic focal conic (PFC) defects, a symmetric form of focal conic defects in which the line defects form a pair of perpendicular, antiparallel, and confocal parabolas. The cellulose films with PFC defects were characterized by polarized-light and atomic force microscopy. The film surface showed a regular array of large and small elevations resulting from the displacement of the structural layers. Film fracture lines showed a series of layered half-cones. The microstructure of the films was modeled by computer. The model revealed that many structural layers terminate at the film surface.     

Radical addition to vinyl sulphones and vinyl phosphonium salts

Alkyl radicals, derived from decarboxylation of carboxylic acids, add readily to phenyl vinyl sulphone and vinyl phosphonium bromide. The adducts may be further converted into a variety of useful synthetic intermediates.     

An electron microscopic and enzymic study of rat liver peroxisomal nucleoid core and its association with urate oxidase

The appearance of the characteristic crystalloid core of rat liver peroxisomes is emulated by the electron microscopic (EM) appearance of highly purified urate oxidase prepared from the same tissue. The purity of the enzyme preparation was established by gel electrophoresis under various conditions and the specific enzyme activity was at least as high as any previously reported. The amino acid composition of urate oxidase was determined. As additional evidence for close association of the peroxisomal core with urate oxidase, it was demonstrated that the biphasic changes in rat liver urate oxidase activity in response to prolonged starvation were paralleled by changes in the EM appearance of peroxisomes. Under comparable conditions catalase, another peroxisomal enzyme, did not show the same changes in activity as did urate oxidase. Evidence for the possible identity of urate oxidase with the peroxisomal crystalloid of rat liver has been presented, all materials having been obtained from, and experiments performed with, the rat.     

Hydrogen-bonded networks through second-sphere coordination

The reaction of 4, 7-phenanthroline (1) with aqueous transitionmetal complexes [Mn(H2O)6][NO3]2, [Co(H2O)6][NO3]2, [Ni(H2O)6[NO3]2, [Mn(H2O)6][ClO4]2, and [Co(H2O)6][ClO4]2 does not produce coordination complexes between these metal cations and the N-donor ligand as expected. Instead, supramolecular hydrogenbonded networks are formed between the nitrogen donor atoms of 4, 7-phenanthroline and the OH groups of coordinated water molecules: M-O-H...N interactions. This motif of second-sphere coordination for 1 can be exploited as a tool for crystal engineering. As a demonstration of the generality of this new interaction as a supramolecular building block, five X-ray crystal structures are reported that utilise this hydrogen bonding scheme; [Co(H2O)4(NO3)2].(1)2 (2a), [Co(MeCN)2(H2O)4][ClO4]2.(1)2 (2b), [Ni(H2O)4(NO3)2].(1)2 (3a), [Mn(H2O)4(NO3)2].(1)2 (4a), and [Mn(H2O)6][ClO4]2.(1)(4).4H2O (4b). Each network involves complete saturation of the hydrogen-bond donor sets between the aqua complex and 1 using primarily M-O-H...N(1) and M-O-H...O(anion), interactions. Thermogravimteric analysis shows these materials to have stabililities similar to coordination polymers involving metal-ligand bonds; this demonstrates that second-sphere hydrogen bonding has potential for the construction of polymeric metal-containing materials.     

The synthesis of N-substituted ketimines from oxazirdines

N-Unsubstituted diaryl, alkyl aryl and dialkyl ketimines are prepared in good yield at ambient temperature by the reaction of KOBu^t on oxaziridines having an α-hydrogen atom on the N-alkyl substituent; the mechanism and stereochemistry of the reaction are discussed.     

Oxidation reactions of an anionic gallium(I) N-heterocyclic carbene analogue with group 16 compounds

The reactivity of an anionic gallium(I) heterocycle, [K(tmeda)][:Ga([N(Ar)C(H)]2)], Ar = C6H3Pr(i)2-2,6, towards sources of elemental chalcogens and diorgano-dichalcogenides has been investigated and comparisons drawn with the reactivity of the valence isoelectronic N-heterocyclic carbene class of ligand. The reactions of the heterocycle with N2O or (Te)PEt3 yielded the dimeric, dianionic gallium(III) complexes, [K(L)]2[(mu-E)Ga([N(Ar)C(H)]2)]2, E = O, L = tmeda; E = Te, L = THF. Treatment of [K(tmeda)][:Ga([N(Ar)C(H)]2)] with the diphenyl dichalcogenides, PhEEPh, E = Se or Te, gave the one dimensional polymer, [K[(PhSe)2Ga([N(Ar)C(H)]2)]]infinity and the monomeric complex, [K(OEt2)3][(PhTe)2Ga([N(Ar)C(H)]2)], respectively. The X-ray crystal structures of the four complexes are reported.     

The chemistry of electrogenerated transition metals species - the insertion of olefins into a nickelcarbon bond

The nickel(1) complex, Ni(teta)⁺, formed by cathodic reduction of the corresponding nickel(11) complex, reacts rapidly with alkyl bromides to form an unstable intermediate containing a nickelcarbon bond. When the electrolysis medium also contains an activated olefin an insertion reaction occurs. The new metalcarbon bond is cleaved by further reduction and overall the reduction of Ni(teta)²⁺ in the presence of RBr and CH₂CHY leads to high yiels of RCH₂CH₂Y.     

Syntheses of 3,7-dimethylpentadecan-2-ols from intermediates formed from co-oligomerisation reactions of butadiene with diethyl malonate and acetaldehyde

The products of the reaction of butadiene with diethyl malonate catalysed by a palladium complex and of butadiene with acetaldehyde catalysed by a nickel(0) complex have been used in two syntheses of 3,7-dimethylpentadecan-2-ol.     

Kinetics and mechanism of the grafting of 2-(dimethylamino)ethyl methacrylate onto hydrocarbon substrates

The kinetics of grafting a basic monomer, 2-(dimethylamino)-ethyl methacrylate (DMAEMA) to hydrocarbon substrates have been investigated. These systems were chosen as models for the grafting of a homopolymerizable monomer to polyolefins such as polyethylene. The reactions with squalane and n-eicosane were initiated by an organic peroxide, 2,5-dimethyl 2,5 dit-butylperoxy)-3-hexyne; grafting yields become significant at high reaction temperatures and low monomer concentrations. In squalane, the order of reaction with respect to monomer increased from about 1.1 for 0.22?0.44M DMAEMA to almost 2 at 0.69M DMAEMA; the order with respect to initiator was 0.56. The overall activation energy in the 130?160°C temperature range was, however, surprisingly low, 42±5 kJ mol^?1. When analytical data were used to separate the overall rate into those for grafting and homopolymerization, different kinetic paths were observed for the competing reactions. These results are interpreted in terms of two different mechanisms; intramolecular chain transfer plays an important role in grafting, while depropagation becomes a major factor in homopolymerization at temperatures above 150°C. © 1995 John Wiley & Sons, Inc.     

Comparison of the Diffusion of Aqueous Glycine Hydrochloride and Aqueous Glycine

A Taylor dispersion tube has been used to measure mutual diffusion in aqueous solutions of glycine hydrochloride at 25°C and concentrations from 0.0005 to 0.5 M. Analysis of the dispersion profiles shows that the diffusion of glycine hydrochloride (GlyHCl) produces a subtantial additional flow of hydrochloric acid that is liberated by the dissociation: GlyH⁺ + Cl^- Gly + H⁺ + Cl^-. Diffusion in this system is, therefore, a ternary process described by the equations J ₁(GlyHCl) = – D ₁₁C ₁ – D ₁₂C ₂ and J ₂(HCl) = –D ₂₁C ₁ – D ₂₂C ₂ for the coupled fluxes of total glycine hydrochloride (1) and hydrochloric acid (2) components. The ratio D ₂₁/D ₁₁ of measured diffusion coefficients indicates that up to two moles of HCl are cotransported per mole of GlyHCl. Although protonated glycine diffuses with relatively mobile Cl^– counterions, the main diffusion coefficient of glycine hydrochloride, D ₁₁, is lower than or nearly identical to the diffusion coefficient of aqueous glycine. A model for the diffusion of protonated solutes is developed to interpret this result and the large coupled flows of HCl. Diffusion coefficients are also reported for the aqueous hydrochlorides of 3- and 4-aminobenzoic acids.