Enzymatics synthesis and use of new fluorigenic substrates for a novel approach to the study of bacterialpeptidoglycan degradation

Two complex new fluorigenic substrates were synthesized enzymatically. Their use is demonstrated in the study of specific hydrolases concerned in the degradation of bacterial peptidoglycans. The substrates operate according to the “sequential fluorigenic enzyme assay” principle. Results are presented to illustrate the fluorigenic method for the estimation of lysozyme activities. The limitations of simple fluorigenic substrates in studies on the degradation of inter-sugar linkages in complex natural substances are demonstrated.     

Spin diffusion in semiconductors

The behavior of spin diffusion in doped semiconductors is shown to be qualitatively different than in undoped (intrinsic) ones. Whereas a spin packet in an intrinsic semiconductor must be a multiple-band disturbance, involving inhomogeneous distributions of both electrons and holes, in a doped semiconductor a single-band disturbance is possible. For n-doped nonmagnetic semiconductors the enhancement of diffusion due to a degenerate electron sea in the conduction band is much larger for these single-band spin packets than for charge packets-this explains the anomalously large spin diffusion recently observed in n-doped GaAs at 1.6 K. In n-doped ferromagnetic and semimagnetic semiconductors the motion of spin packets polarized antiparallel to the equilibrium carrier spin polarization is predicted to be an order of magnitude faster than for parallel polarized spin packets. These results are reversed for p-doped semiconductors.     

A Simple,Selective, and General Catalyst for Ring Closing Depolymerization of Polyesters and Polycarbonates for Chemical Recycling

The ability to efficiently and selectively process mixed polymer waste is important to address the growing plastic waste problem. Herein, we report that the combination of ZnCl₂ and an additive amount of poly(ethylene glycol) under vacuum can readily and selectively depolymerize polyesters and polycarbonates with high ceiling temperatures (T_c>200 °C) back to their constitute monomers. Mechanistic experiments implicate a random chain scission mechanism and a catalyst structure containing one equivalent of ZnCl₂ per ethylene glycol repeat unit in the poly(ethylene glycol). In addition to being general for a wide variety of polyesters and polycarbonates, the catalyst system could selectively depolymerize a polyester in the presence of other commodity plastics, demonstrating how reactive distillation using the ZnCl₂/PEG600 catalyst system can be used to separate mixed plastic waste.     

An efficient synthesis of tertiary amines from nitriles in aprotic solvents

Tertiary amines are utilized extensively as non-nucleophilic proton scavengers for a number of organic transformations. Herein we report the efficient syntheses of tertiary alkyl amines from their corresponding alkyl nitriles in the presence of a heterogeneous palladium catalyst and a source of dihydrogen in aprotic solvents. The reaction is atom economic, the conditions are mild, and the isolated yields are virtually quantitative. The degree of amine alkylation shows some solvent dependency; in polar protic solvents such as ethanol or methanol, the reaction affords a mixture of products with the secondary alkyl amine as the major product.     

Radical additions to (eta6-styrene) chromium tricarbonyl

[reaction: see text] Alkyl radical addition reactions to styrene chromium tricarbonyl can be accomplished using alkyl halides and tris(trimethylsilyl)silane in the presence of AIBN in refluxing benzene. The ketyl generated from acetone with SmI2 in THF/HMPA also underwent successful addition. These addition reactions are believed to proceed through intermediates in which the radical is interacting with an adjacent arene chromium tricarbonyl functionality and do not appear to be complicated by polymerization.     

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