Quantitative gas-liquid chromatography of non-protein amino acids.

The quantitative gas--liquid chromatographic analysis of non-protein amino acids, in the presence of protein amino acids, is described. The amino acids were determined as their N-trifluoroacetyl n-butyl esters on an ethylene glycol adipate column. The relative molar responses of 38 amino acids are reported.     

CE methods for the determination of non-protein amino acids in foods

In addition to the 20 amino acids universally distributed as protein constituents in living organisms, there are other amino acids of non-protein origin that can be found in foods. The determination of these non-protein amino acids is interesting since they can be indicative of the quality and safety of foods. This work presents for the first time an updated and comprehensive review devoted to show the possibilities of capillary electrophoresis for the determination of non-protein amino acids in food samples. The results reported have been classified according to the chemical structure of the non-protein amino acid studied. Separation conditions as well as detection systems used have been detailed since most of these amino acidic compounds do not possess chromophore groups detectable by conventional UV-Vis detection, being in this case necessary a previous derivatization step. Finally, the application of microchip electrophoresis to the determination of non-protein amino acids in foodstuffs is also included in this review.     

Resolution of non-protein amino acids via Carica papaya lipase-catalyzed enantioselective transesterification

Carica papaya lipase-catalyzed transesterification of the 2,2,2-trifluoroethyl esters of N-benzyloxycarbonylated dl-amino acids carrying aliphatic side chains proceeded smoothly and, in almost all the cases, enantiospecifically (E = >200), affording the l-methyl esters and leaving the d-trifluoroethyl esters intact.     

Selective racemization of amino acid amides in the presence of amino acids

Conclusions The significant differences in the racemization rates of amino acids and the corresponding amides make it possible to carry out selective racemization of amides in the presence of optically active amino acids.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1593–1596, July, 1986.     

High resolution capillary gas chromatography and gas chromatography–mass spectrometry of protein and non-protein amino acids,amino alcohols,and hydroxycarboxylic acids as their tert-butyldimethylsilyl derivatives

A simple, single-step derivatization technique is presented for capillary GC-FID and GC-MS separation and identification of common protein and non-protein constituents of natural peptides as their tert-butyldimethylsilyl (TBDMS) derivatives. The tert-butyldimethyl-silylation of more than sixty compounds was accomplished with high yields and a single peak observed for each component. The TBDMS derivatives of both the protein and non-protein substances, moreover, exhibit excellent separation on apolar capillary columns and can be resolved completely using a polydimethylsiloxane or 5 % phenyl polydimethylsiloxane column and, complementarily, a 50 % phenyl polydimethylsiloxane column. Retention data and molar responses of the TBDMS derivatives on the polydimethylsiloxane column are compiled. Direct coupling of the 5 % phenyl polydimethylsiloxane column to an ion trap mass spectrometer enabled fast separation and identification of the investigated components, at nanomole to picomole levels, on the basis of retention and mass spectral data. The general usefulness of the method is demonstrated by research into new biologically active peptides isolated from entomopathogenic fungi.     

Resolution of non-protein amino acids via the microbial protease-catalyzed enantioselective hydrolysis of their N-unprotected esters

In the Aspergillus oryzae protease-catalyzed ester hydrolysis, substitution of N-unprotected amino acid esters for the corresponding N-protected amino acid esters resulted in a large enhancement of the hydrolysis rate, while the enantioselectivity was deteriorated strikingly when the substrates employed were the conventional methyl esters. This difficulty was overcome by employing esters bearing a longer alkyl chain such as the isobutyl ester. Utilizing this ester, amino acids carrying an aromatic side chain were resolved with excellent enantioselectivities (E=50 to >200). With amino acids bearing an aliphatic side chain also, good results in terms of the hydrolysis rate and enantioselectivity were obtained by employing such an ester as the isobutyl ester. Moreover, the enantioselectivity proved to be enhanced further by conducting the reaction at low temperature. This procedure was applicable to the case where the enantioselectivity was not high enough even by the use of the isobutyl ester.     

非蛋白氨基酸对生物活性多肽的修饰及其构效关系的研究进展

简述了非蛋白氨基酸的结构特征和生理活性。介绍了某些天然存在的含非蛋白氨基酸的生物活性肽及非蛋白氨基酸残基在相应活性肽中的重要作用。着重总结了非蛋白氨基酸对生物活性肽进行修饰的方式和构效关系研究的进展。     

One-electron reduction of excited NMN and NADP in the presence of amino acids

Excitation of oxidized forms of nicotinamide coenzymes (NADP⁺, NMN⁺) at 254 nm under anaerobic conditions in the presence of EDTA, lysine, serine, glycine leads, in the initial stage of irradiation, to photoreduction of coenzyme. Formation of the photoreduction products was observed by polarographic, spectrophotometric and enzymatic methods. Quantum yields for NMN⁺ and NADP⁺ photoreduction have been calculated and a mechanism proposed. No photoreduction was observed with histidine. Long-term irradiation leads to further reduction of the nicotinamide ring to tetrahydroderivatives absorbing at 280–290 nm. The photochemically generated dimers undergo phototransformation to the parent monomers on irradiation at 365 nm either in the presence or absence of oxygen. The biological significance of the results is discussed.     

Extended Hückel MO calculations of the conformation of several amino acids

The conformation of the amino acid residues, glycine, alanine, proline, and phenylalanine have been predicted from molecular orbital calculations of appropriate model compounds. Using the current main chain rotation convention (, ) the principle conformations were found to be glycine (0, 0), alanine (240, 240), proline (120, 330) and phenylalanine (30, 330). Several secondary conformations were also found for glycine. A comparison of the predicted conformations is in good agreement with experimental data on comparable residues or model compounds.Supported by National Institutes of Health Grants No. FR 5409-07 and GM 16312-01.Recipient of a Public Health Service Research Career Development Award AM 1159-01.     

Fluorinated amino acids in protein design and engineering

Selective incorporation of unnatural amino acids into proteins is a powerful tool for illuminating the principles of protein design. In particular, fluorinated amino acids have recently emerged as valuable building blocks for designing hyperstable protein folds, as well as directing highly specific protein-protein interactions. We review the collagen mimetic and coiled coil peptide systems that exemplify generalizable paradigms for future design. The unique electronic and phase properties of fluorocarbons are discussed, and protein synthesis using unnatural amino acids is briefly reviewed.     

Heat-capacity changes and partial molal heat capacities of several amino acids in water

Integral enthalpies of solution of several amino acids in water at low concentrations have been determined at 25 and 35°C. These data have been used to derive the heat-capacity change C _p ^o on dissolution at 30°C. Partial molal heat capacities C _p2 ^o have been obtained by combining C _p ^o with C _p2 ^o (heat capacity of pure solid amino acids). The results indicate that the increments in C _p ^o and C _p2 ^o values per CH₂ group increment in the homologous series of -amino acids are constant and in agreement with those found for other homologous series of compounds containing monofunctional groups. However, this is not the case with amino acids having the NH ₃ ⁺ group at the terminal position. The present work also indicates that, as the NH ₃ ⁺ group is shifted away from the COO^– group, hydrophobic hydration decreases, as indicated by a decrease in C _p ^o and C _p2 ^o . the results on various isomers of amino acids show that branching of alkyl groups has no effect on C _p ^o and C _p2 ^o , indicating that hydrophobic hydration is unaffected by branching. The effect of substitution of H by OH and of CH₃ by groups in some amino acids has also been studied and discussed.     

Thermogravimetric study of some divalent transition metal chelates of several amino acids

Thermogravimetric studies of divalent metal chelates of eight common amino acids have revealed that no relationship exists between thermal stability orders of the chelates and hydrolytic stability orders, infrared band shifts or force constants. An attempt is made to relate thermal stability order to relative heats of formation and stereochemistry.

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Zusammenfassung Die thermogravimetrische Untersuchung der Chelatkomplexe von acht gewöhnlichen AminosÄuren mit zweiwertigen Metallen zeigte, da\ keine Beziehung zwischen der Reihenfolge der ThermostabilitÄt und der hydrolytischen StabilitÄt, der Verschiebung der infraroten BÄnder oder den StabilitÄtskonstanten besteht. Es wurde versucht, die thermische StabilitÄt mit den relativen BildungswÄrmen und mit stereochemischen Deutungen in Beziehung zu bringen.

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Résumé L'étude thermogravimétriques des chélates de huit acides aminé communs avec des métaux divalents a montré qu'il n'exitait pas de relation entre l'ordre de stabilité thermique et l'ordre de la stabilité hydrolytique, ni avec le déplacement des bandes infrarouges ou constantes de stabilité. On a essayé de constater une corrélation entre l'ordre de la stabilité thermique et la chaleur de formation et structure stereochimique.

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Taken in part from a thesis submitted by R. G. Schneggenburger to the Graduate School of the University of Notre Dame in partial fulfillment for the Ph.D. degree.

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The Radiation Laboratory is operated under contract with the U.S. Atomic Energy Commission. This is AEC Document COO-38-685.     

One-electron reduction of excited NMN+ and NADP+ in the presence of amino acids

Excitation of oxidized forms of nicotinamide coenzymes (NADP⁺, NMN⁺) at 254 nm under anaerobic conditions in the presence of EDTA, lysine, serine, glycine leads, in the initial stage of irradiation, to photoreduction of coenzyme. Formation of the photoreduction products was observed by polarographic, spectrophotometric and enzymatic methods. Quantum yields for NMN⁺ and NADP⁺ photoreduction have been calculated and a mechanism proposed. No photoreduction was observed with histidine. Long-term irradiation leads to further reduction of the nicotinamide ring to tetrahydroderivatives absorbing at 280–290 nm. The photochemically generated dimers undergo phototransformation to the parent monomers on irradiation at 365 nm either in the presence or absence of oxygen. The biological significance of the results is discussed.