No abstract

Thin sections of heat‐set protein gels formed from bovine serum albumin, insulin, lysozyme, ribonuclease, and alpha‐chymotrypsin, have been studied by transmission electron microscopy. Micrographs have been interpreted as showing protein networks with strands between one and two times as thick as the native protein diameters. Considerable differences in the persistence characteristics, and frequencies of cross‐linking, of the strands are observed, and there are variations in network homogeneity over long distances which correlate well with changes in gel opacity caused by alterations in pH and ionic strength. Evidence that arte facts are unlikely to have influenced these interpretations has been obtained in the BSA case in particular, by studying the aggregation process in solution, using alternative microscope approaches such as heavy‐metal shadowing and negative staining. Assuming that artefacts are absent, gel section micrographs have been simulated by a computer procedure, and the results suggest that, in most cases, the simplest interpretation of the microscope data is in terms of a “string of beads” model for the aggregation process, involving only moderately unfolded, and still globular, protein molecules. Other structural interpretations cannot be ruled out, however, as the degree of protein unfolding, and the exact mode of incorporation of the monomers into the network filaments, cannot be established by the microscope technique alone.

[Ru­(Cp)­(PPh 2NBn 2)­(MeCN)]­PF6 (1; PPh 2NBn 2 = 1,5-benzyl-3,7-phenyl-1,5-diaza-3,7-diphosphacyclooctane) and [Ru­(Cp)­(dppp)­(MeCN)]­PF6 (2; dppp = 1,3-bis­(diphenylphosphino)­propane) are both active toward the acceptorless dehydrogenation of benzylamine (BnNH2) and N-heterocycles. The two catalysts have similar activities but different selectivities for dehydrogenation products. Independent synthesis of a [Ru­(Cp)­(PPh 2NBn 2)­(NH2Bn)]­PF6 adduct (3) reveals the presence of a hydrogen bond between the bound amine and the pendent base of the PPh 2NBn 2 ligand. Preliminary mechanistic studies reveal that the benzylamine adduct is not an on-cycle catalyst intermediate.

The first successful use of the PN (1,5-R'-3,7-R-1,5-diaza-3,7-diphosphacyclooctane) ligand family toward an organic synthesis is described. The precatalysts [Ru(Cp)(PN)(MeCN)]PF are active toward cyclization of 2-ethynylbenzyl alcohol at low catalyst loading and mild temperatures. Catalyst performance however is limited by both low conscription and by competitive deactivation.