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The structure of Gd-DTPA-polylysine, Gd-DOTA-polylysine, Gd-SCN-Bz-DOTA-polylysine, and Gd-DTPA-poly(glu:lys) was investigated with circular dichroism, gel permeation chromatography, low angle light scattering, and proton longitudinal relaxivity. Molecular modeling calculations were performed and predicted helical secondary structure for charged Gd-chelator residues, i.e., Gd-DTPA, when the DTPA conjugation levels reached 90% and higher. This helical secondary structure was observed with circular dichroism. The conformational transition from coiled to extended linear was observed also by gel permeation chromatography and by proton relaxivity measurements. The helical secondary structure was not observed when the chelator was changed to DOTA. The residue charge interactions were eliminated in this case since the Gd-DOTA complex had no net charge. For this construct, the gel permeation and relaxivity measurements indicated a coiled conformation. An extended linear conformation was regained when the chelator complex was changed to Gd-SCN-Bz-DOTA, which had a net negative charge. The functional aspects of these structures were investigated by MR imaging of an animal tumor model. The linear extended polymer constructs gave 10-fold higher tumor signals then the coiled-collapsed constructs, indicating a much higher degree of trans-endothelial transport in the tumors.

A method for measuring composition and sequence lengths in poly(dimethylsiloxane) /poly-(tetramethyl-p-silphenylenesiloxane) copolymers by MSi NMR is presented. The technique has been used to study the relationship between the block length in the copolymer and the degree of oligomerization of the starting disiloxanol, and to study the redistribution reaction of the polymer. It has been shown from ^Si NMR studies of the polymerization reaction that efficient water removal is necessary to minimize redistribution of siloxane bonds in the polymer.

Pent-l-en-3-ol and pent-l-en-3-one were isolated in approximately equal amounts from buttermilk obtained from oxidized cream. The two vinyl compounds were identified by combined gas chromatography and mass spectrometry. The flavour of pent-l-en-3-ol is comparatively mild being detectable in water, skim-milk, butter oil and butter at 3 pts in 10 6 , 3 pts in 10 6 , 1 pt in 10 5 and 1 pt in 10 5 , respectively. The flavour of pent-l-en-3-one is approximately 1000 times stronger being detectable in water, skim-milk, butter oil and butter at 1 pt in 10 9 , 3 pts in 10 9 , 5 pts in 10 9 and 5 pts in 10 9 , respectively: these concentrations are of the same order of magnitude as for the compound responsible for metallic flavour, oct-l-en-3-one.The formation of pent-l-en-3-ol and pent-l-en-3-one is discussed. EXPERIMENTAL Control (normal) and oxidized (copper and ascorbic acid) butters were prepared, and the volatile compounds isolated as previously described (Stark & Forss, 1966). Control and oxidized buttermilks were obtained from the churning of normal and oxidized (copper and ascorbic acid) cream held for 5 days at 2°C. By vacuum sub-J Present address:

SYNOPSISSilicone-release coatings are used by the pressure-sensitive adhesive industry for labeling applications. Typical release coatings are prepared by the platinum-catalyzed addition reaction of a silicone hydride fluid with a silicone vinyl polymer. Methodology has been developed to determine the network structure of cured release coatings, which involves degradation of the network with trifluoromethane sulfonic acid in excess hexamethyldisiloxane. Gas chromatography-mass spectrometry (GC-MS) and gas chromatography (GC) were employed to identify and quantify residual functionality and cross-links. Residual hydride functionality was also determined by attenuated total reflectance-Fourier transform infrared spectroscopy ( ATR-FTIR) . The observation of network structure by solid-state ?3i-NMR using cross polarization ( C P ) and magic angle spinning (MAS) is also discussed. The networks underwent a postcure as evidenced by a decrease in residual hydride functionality and an increase in silane content and/or cross-links. 0 1993 John Wiley & Sons, Inc.

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Ru complexes containing ortho‐metalated triphenyl phosphite linkages react with ethylene to give ortho‐alkylation on the triphenylphosphite ligands.