Small Molecule Model Compounds Research Articles

Poly(organophosphazenes) Containing Allyl Side Groups: Crosslinking and Modification by Hydrosilylation

Poly(organophosphazenes) containing 4-(allyloxy)phenoxy and 4-[4'-(allyloxy)phenyl]phenoxy side groups were synthesized and modified by hydrosilylation reactions. A small-molecule model compound, pentaphenoxy[4-(allyloxy)phenoxy]cyclotriphosphazene, underwent platinum-catalyzed hydrosilylation reactions with heptamethyltrisiloxane and dimethylethoxysilane. The product of the second reaction, containing one dimethylethoxysilane group, underwent hydrolysis and self-condensation reactions in the presence of acid. Transposition of this chemistry to the high-polymer level was then accomplished

Photogeneration of polymeric amines: synthesis, photocrosslinking and photoimaging of copolymers containing photoactive carbamate pendant groups

Two families of copolymers containing 4-[(2-nitrobenzyloxy)carbamoyl]styrene as the photoactive component, with styrene or methyl methacrylate as the other component are described. The polymers are prepared by chemical modification of copolymers of 4-aminostyrene with styrene and methyl methacrylate, respectively, using 2-nitrobenzyl chloroformate. The photoactive carbamate groups of both copolymers can be removed by irradiation with UV light below 320 nm. Quantum-yield measurements and comparisons with small-molecule model compounds confirm that attachment to the polymer has no effect on the photolability of the 2-nitrobenzylcar-bamoyl protecting group. Quantum-yield values near 0.10 also compare favourably with those obtained for related small molecules. The photoactive polymers have been tested successfully in the UV-induced crosslinking of formulations containing epoxy groups.

A predictive theoretical model for electron tunneling pathways in proteins

A practical method is presented for calculating the dependence of electron transfer rates on details of the protein medium intervening between donor and acceptor. The method takes proper account of the relative energetics and mutual interactions of the donor, acceptor, and peptide groups. It also provides a quantitative search scheme for determining the important tunneling pathway(s) [specific sequence(s) of localized bonding and antibonding orbitals of the protein which dominate the donor–acceptor electronic coupling] in native and tailored proteins, provides a tool for designing new proteins with prescribed electron transfer rates, and provides a consistent description of observed electron transfer rates in existing redox labeled metalloproteins and small molecule model compounds.

Hydrophilic polyphosphazenes as hydrogels: radiation cross-linking and hydrogel characteristics of poly [ bis (methoxyethoxyethoxy)phosphazene

The water-soluble polyphosphazene, [NP(OCH 2CH 2OCH 2CH 2OCH 3) 2] n, cross-links when exposed to γ rays to form hydrophilic, water-swellable membranes and hydrogels. The degree of cross-linking increases with irradiation dose in a manner that can be utilized to change the properties, γ irradiation studies of the small molecule model compound, [NP(OCH 2CH 2OCH 2CH 2OCH 3) 2] 4, were also carried out to probe the relationship between irradiation dose and cross-link density.

Hydrogen-bonded structure of the complex N-linked fetuin glycopeptide.

The conformation of the N-linked complex glycopeptide of fetuin was examined with hydrogen-exchange techniques. The glycopeptide molecule contains eight acetamido hydrogens stemming from five N-acetylglucosamine residues and three N-acetylneuraminic acid residues and also one from the remaining sugar-peptide linkage. The hydrogen-exchange rates of these secondary amides were compared with small molecule model compounds having identical primary structures at their exchangeable hydrogen sites. Differences between the model rates and glycopeptide rates therefore cannot be accounted for by primary structure effects but reflect conformational features of the glycopeptide. Two glycopeptide hydrogens exhibit significantly hindered exchange; the rest exchange at the model rates. Removal of the three N-acetylneuraminic acid residues from terminal positions on the three branches of the glycopeptide removes the slowed hydrogens. The remaining ones continue to exchange at the model rate. These results indicate that two of the eight sugar acetamido hydrogens are involved in intramolecular hydrogen bonds. A likely structure includes two hydrogen bonds between the three N-acetylneuraminic acid residues. These two hydrogens, slowed to a moderate degree, reflect a preferred conformation stabilized by about 1 kcal/mol in free energy. The solution conformation of the glycopeptide suggested by these results is one that is partially ordered and can be easily modulated, owing to the relatively small amount of energy stabilizing the preferred conformation.

The infrared spectra of crystalline polysaccharides. VIII. Xylans

AbstractOriented films of 4‐O‐methylglucuronoxylan from several sources were prepared by hot stretching acetyl derivatives. The resulting oriented samples could be converted to crystalline xylans without destroying the orientation. Infrared spectra of the oriented samples were recorded using polarized radiation. Band assignments were made on the basis of empirically known group frequencies, the spectra of the deuterated analogs (OH → OD), and comparison with the spectra of small molecule model compounds. The dichroic ratios observed for the carbon hydrogen modes in the polarized spectrum along with the observed 15 A. fiber repeat of crystalline xylan “hydrate” are interpreted in terms of a threefold screw polymer conformation. Finally, by comparison of the polarized spectrum of an oriented hardwood xylan with that derived from a radial section of hardwood it was deduced that the xylan is oriented in the fiber direction in the tree.