SynopsisThe complexes of cyclodisarcosyl (N,N'-dimethyldiketopiperazine) have been synthesized with copper perchlorate, lithium perchlorate, barium perchlorate, silver perchlorate, silver nitrate, and boron trifluoride. It has been shown by infrared absorption spectra that the metal cations coordinate to carbonyl groups of the peptide to form insoluble complexes. It has been suggested that the complexation takes place by iondipole interaction. Since a linear analog of the peptide formed no insoluble complex with the metal salts, conformation of cyclodisarcosyl seems to play an important role in the complex formation. Examination of the molecular model and X-ray analysis suggest that the copper perchlorate complex of the cyclic peptide has a "2: 1-sandwich" structure.
SynopsisA histidine-containing cyclic dipeptide, c~c~o(D-L~u-L-H~s), was almost 20 times as efficient a catalyst as imidazole in the hydrolysis of p-nitrophenyl laurate. The effect of dioxane on the hydrolysis showed that hydrophobic interaction between the cyclic dipeptide and the ester is very important. This reaction obeyed the Michaelis-Menten kinetics, and the Michaelis constant K , was as low as 9.98 X 10-5M. Since the linear dipeptide having D-Leu-L-His sequence was nearly inactive in the hydrolysis, the functional groups of cyclo(D-Leu-L-His) in a specific arrangement held by the rigid backbone must have cooperated in the fast hydrolysis. Very weak catalysis by the diasteremeric cyclic dipeptide, cyclo(L-Leu-L-His), in the hydrolysis supported the above view.
SynopsisCyclic peptides containing sarcosine, cyclo-(Pro-Sar-Gly)*, cyclo-(Sar-Sar-Gly)?, cyclo-(Sarc), and cyclo-(Sar6) have been synthesized by the cyclization of the p-nitrophenyl ester of linear peptides. The tert-butoxycarbonyl group was used as the Naprotecting group, which was removed by acid. Benzyl ester was used to protect the Cterminal. tert-butoxycarbonylpeptide was obtained by the stepwise elongation of the peptide bond by the carbodiimide method. 1)ebloeking and cyclization of the linear peptides gave the cyclic peptides.
We have found that the visible absorption maximum (λmax) of retinal Schiff’s base in fluoro alcohols is considerably red-shifted. The C=N stretching Raman line exhibits a frequency shift in deuterated fluoro alcohols, indicating that the Schiff’s base is protonated. Frequencies of the in-phase C=C stretching Raman lines (νC=C) changed linearly with λmax, and the νC=C vs. λmax correlation coincides with that observed for retinoid proteins.
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