MODULATION OF BALLISTIC PHONON FLUXES IN Ge BY A He GAS FILM AT A SOLID/SUPERFLUID INTERFACE

A He gas bubble may be formed at the surface of a sample which is immersed in a superfluid He cooling bath and subject to intense optical excitation. We have discovered that this bubble oscillates at 1-10 KHz, under steady state optical excitation, and this leads to a modulation of the ballistic phonon flux intensity into the sample

Studies on Arginine Peptides. I. Intermediates in the Synthesis of N-Terminal and C-Terminal Arginine Peptides

Tricarbobenzoxy-L-arginine, as its sodium salt, was prepared in strongly alkaline medium via the carbobenzoxylation of L-arginine. This sodium salt, which was in fact a mixture of at least two different isomeric forms, was converted into a mixture of NαN,ω-dicarbobenzoxy-L-arginine and a single pure isomer of sodium tricarbobenzoxy-L-argininate upon treatment with boiling ethanol. Fractionation of these compounds, followed by acidification of the latter material, yielded pure tricarbobenzoxy- L-arginine wherein the basic properties of the guanido group were completely masked. The utility of this compound in the preparation of N-terminal arginine peptides was demonstrated upon its condensation with amino acid benzyl esters, via the mixed carbonic-carboxylic acid anhydride procedure, followed by catalytic hydrogenolysis of the condensation product. In addition, the N-carboxyanhydride procedure was utilized to effect the transformation of tricarbobenzoxy-L-arginine into NωN,ω -dicarbobenzoxy-L-arginine, and of NαN,ω -dicarbobenzoxy-L-arginine into Nω-carbobenzoxy-L-arginine, as well as the benzyl and methyl ester derivatives of the latter. All of these products are of potential value in the synthesis of C-terminal arginine peptides. In this connection, the esters of Nω-carbobenzoxy-L-arginine were employed in the synthesis of the benzyl and methyl esters of tricarbobenzoxy-L-arginyl-Nω-carbobenzoxy-L-arginine. © 1957, American Chemical Society. All rights reserved

Studies on Arginine Peptides. III. On the Structure of Tricarbobenzoxy-L-arginine

The structural elucidation of Nα,Nω,Nω-tricarbobenzoxy-l-arginine has been achieved. Thus, conversion of this compound to the p-nitrobenzyl ester, followed by the treatment with propionic anhydride, led to Nα,Nω,Nω-tricarbobenzoxy-Nω-propionyl-l-arginine p-nitrobenzyl ester. Catalytic hydrogenolysis of the latter yielded Nω-propionyl-l-argmine which, when subjected to the action of acetic anhydride, was converted to Nα,Nω-diacetyl-Nω-propionylanhydroarginine. Cleavage of the latter with water led to N-acetyl-N′-propionylurea and dl-α-acetylaminopiperidone which, upon identification, established the structure of the starting material. The relation of the structure of tricarbobenzoxyarginine to its utility as a peptide intermediate is considered. © 1961, American Chemical Society. All rights reserved

Studies on Arginine Peptides. II. Synthesis of L-Arginyl-L-arginine and other N-Terminal Arginine Dipeptides

Dicarbobenzoxy-L-arginine and tricarbobenzoxy-L-arginine have been utilized for the preparation of a variety of dipeptides containing an N-terniinal arginine residue. The former compound, either as its acid chloridehydrochloride derivative or under the condensing action of dicyclohexylcarbodiimide, was coupled with diethyl L-glutamate and the condensation product subsequently converted to the corresponding free peptide via successive saponification and catalytic hydrogenolysis; the formation of Nα,Nπ-dicarbobenzoxyanhydro-L-arginine accompanied the coupling reaction, an occurrence presumably attributable to the fact that the basicity of the guanido moiety of Nα,Nπdiacylated arginines is not completely masked. No analogous evidence of intramolecular cyclization was revealed in the case of the more exhaustively protected tricarbobenzoxy-L-arginine upon like condensation, via its mixed carbonic-carboxylic acid anhydride derivative, with the benzyl ester derivatives of L-alanine, L-aspartic acid, L-glutamic acid, glycine, L-isoleucine, D-alloisoleucine, 1,-leucine, L-phenylalanine, L-tyrosine and L-valine. Catalytic hydrogenolysis of the tricarbobenzoxy-L-arginylammo acid benzyl esters so procured led to the corresponding dipeptides, which were isolated in high over-all yield. A comparable condensation between tricarbobenzoxy-L-arginine and benzyl Nπ-carbobenzoxy-L-argininate permitted the ultimate synthesis of L-arginyl-L-arginine, which was isolated and characterized as its diflavianate and dipicrolonate derivatives. © 1959, American Chemical Society. All rights reserved

Preparation and Disulfide Interchange Reactions of Unsymmetrical Open-chain Derivatives of Cystine

Preparation of mono-(carbobenzoxyglycyl)-L-cystine was achieved by treatment of an excess of L-cystine in aqueous alkali with carbobenzoxyglycyl chloride. Decarbobenzoxylation of the compound by the action of hydrogen bromide in glacial acetic acid permitted the subsequent isolation of pure, crystalline monoglycyl-L-cystine. The bis-methyl, bis-benzyl, monomethyl and monobenzyl ester derivatives of monocarbobenzoxy-L-cystine were prepared by the usual esterification procedures. Conversion of the first-mentioned derivative to Nα-carbobenzoxy-Nα'-trityl-L-cystine bis-methyl ester was effected by the action of trityl chloride in chloroform containing triethylamine. Treatment of such product with hydrazine did not lead to the expected α-monohydrazide but rather induced a rapid disulfide interchange with the formation of the symmetrical bis-trityl-L-cystine bis-methyl ester and bis-carbobenzoxy-L-cystine bis-hydrazide as the only isolable products. Comparable disulfide interchange of this same compound as well as of monocarbobenzoxy- and monoglycyl-L-cystine was catalyzed by alkali in both aqueous and methanolic solution. The rate and extent of such interchange in basic solution was shown to increase with an increase in pH. © 1959, American Chemical Society. All rights reserved