Silicon amino acids

The existence and gas phase stability of silicon analogues of three natural amino acids (i.e., silicon glycine, silicon alanine, and silicon valine) belonging to the novel class of compounds termed silicon amino acids (SiAA) are investigated theoretically on the basis of ab initio QCISD/aug‐cc‐pVTZ and MP2/aug‐cc‐pVTZ calculations. All molecules studied (in their gas phase canonical forms) are structurally comparable to their proteinogenic counterparts (i.e., glycine, l ‐alanine, and l ‐valine) and capable of forming several structural isomers as such. These higher energy isomers are characterized by small relative energies (not exceeding 4 kcal mol⁻¹). The simulated IR spectra of the Si‐Gly, Si‐Ala, and Si‐Val global minima are also presented and discussed.     

Methylthiohydantoin amino acids: chromatographic separation and comparison to phenylthiohydantoin amino acids

Most phenylthiohydantoin (PTH) amino acids and most methylthiohydantoin (MTH) amino acids may be separated from one another by thin-layer chromatography (TLC) using the same sequential development technique with the same two solvents. Similarly, a single solvent system may be used in high-performance liquid chromatography (HPLC) to separate most PTH-amino acids and most MTH-amino acids. When both TLC and HPLC separations are performed on a sample, all MTH-and PTH-amino acids can be uniquely identified. Since many solid-phase protein sequencing techniques generate both MTH-and PTH-amino acids, these analytical systems simplify identification of the amino acid derivatives. Although the chromatographic properties of MTH-and PTH-amino acids are similar, they are not identical (contrary to a previous report).     

Helix-forming carbohydrate amino acids

[reaction: see text] The solution-phase conformational properties of tetrameric and octameric chains of C-glycosyl alpha-d-lyxofuranose configured tetrahydrofuran amino acids (where the C-2 and C-5 substituents on the tetrahydrofuran ring are trans to each other) were examined using NMR and IR and CD in organic solvents. Studies by NMR and IR demonstrated that in chloroform solution, the tetramer 7 does not adopt a hydrogen-bonded conformation whereas the octamer 10 populates a well-defined helical secondary structure stabilized by 16-membered (i, i - 3) interresidue hydrogen bonds, similar to a pi-helix. Circular dichroism studies in trifluoroethanol are consistent with this conformation for the octamer 10, and also indicate that the tetramer 7 adopts a rigid conformation not stabilized by hydrogen bonds.     

Prevalent intrinsic emission from nonaromatic amino acids and poly(amino acids)

Nonaromatic amino acids are generally believed to be nonemissive, owing to their lack of apparently remarkable conjugation within individual molecules. Here we report the intrinsic visible emission of nonaromatic amino acids and poly(amino acids) in concentrated solutions and solid powders. This unique and widespread luminescent characteristic can be well rationalized by the clustering-triggered emission(CTE) mechanism, namely the clustering of nonconventional chromophores(i.e. amino, carbonyl,and hydroxyl) and subsequent electron cloud overlap with simultaneous conformation rigidification. Such CTE mechanism is further supported by the single crystal structure analysis, from which 3 D through space electronic communications are uncovered.Besides prompt fluorescence, room temperature phosphorescence(RTP) is also detected from the solids. Moreover, persistent RTP is observed in the powders of exampled poly(amino acids) of ε-poly-L-lysine(.-PLL) after ceasing UV irradiation. These results not only illustrate the feasibility of employing the building blocks of nonaromatic amino acids in the exploration of new luminescent biomolecules, but also provide significant implications for the emissions of peptides and proteins at aggregated or crystalline states. Meanwhile, they may also shed lights on further understanding of autofluorescence from biological systems.     

Arylhydroxyacetic acids and amino acids derived from ethinylphenols

Conclusions A method of synthesis of arylhydroxyacetic acids and ammo acids derived from ethinylphenols has been developed in view of possible physiological activity of these compounds.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1170–1172, May, 1970.     

Enantiomeric separation of amino acids and nonprotein amino acids using a particle-loaded monolithic column

A solution is prepared of 5 microm silica particles modified with (S)-N-3,5-dinitrobenzoyl-1-naphthylglycine (particle 1) or (S)-N-3,5-dinitrophenylaminocarbonyl-valine (particle 2) suspended in liquid tetraethylorthosilicate, ethanol, and aqueous hydrochloric acid. This solution is injected under pressure into a 30 cm long, 75 microm inner diameter capillary column and heated for 1 h at 120 degrees C after which the modified particles are embedded in a monolithic column of sol gel. The packed column measures approximately 15 cm from the inlet to the window used to view the laser-induced fluorescence. Thirteen different amino acids and three nonprotein amino acids are derivatized with the fluorogenic reagent 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) before injection onto the column for capillary electrochromatographic separation. The enantiomeric separation of the monolithic column packed with particle 1 results in a resolution ranging from 1.14 to 4.45, whereas that packed with particle 2 results in a resolution ranging from 0.79 to 1.17. On the basis of resolution and amount of chiral packing material the enantiomeric separation obtained by capillary electrochromatography is judged to be superior to that obtained previously with high performance liquid chromatography (HPLC).     

Cyclization of N-diacetic amino acids

Cyclization of a number of N-diacetic amino acids has been carried out. The dependence of the cyclization products — 3,5-dioxopiperazinoalkanecarboxylic acids and/or their amides—on the temperature, ratio of components, and the presence of solvent has been established. Institute of Biochemistry of the Lithuanian Republic, Vilnius 2600. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1392–1396, October, 1998.     

Bend ribbon-forming tetrahydrofuran amino acids

Short oligomeric chains of C-glycosyl beta-D-arabinofuranose configured tetrahydrofuran amino acids (where the C-2 and C-5 substituents of the tetrahydrofuran ring are cis to each other) exhibit a well-defined repeating turn secondary structure stabilised by (i, i - 2) inter-residue hydrogen bonds. This is in contrast to the epimeric alpha-D-arabinofuranose oligomer (where the C-2 and C-5 substituents of the tetrahydrofuran ring are trans to each other) in which there is no indication of any secondary structure in solution.     

Optical activity of amino acids

Journal of Structural Chemistry -     

Desulfolanylation of N-sulfolanyl amino acids

N-Sulfolanyl amino acids are cleaved at the C-N bond in ammonium hydroxide and aqueous solutions of amines to give the corresponding aminosulfolanes and amino acids.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1340–1341, October, 1973.     

Separation of acetylated amino acids

Acetylated amino acids (Nac-AA) are separated as anions on a reversed stationary phase from a mobile phase containing a quaternary ammonium (R₄N⁺) salt as a mobile phase additive. If the counteranion accompanying the R₄N⁺ or ionic strength salt is detector active than the separated NAc-AA derivatives can be detected by an indirect detection strategy. Variables influencing the separations are NAc-AA side chain structure and the mobile phase parameters such as hdyrophobicity of the alkyl groups in the R₄N⁺ salt, R₄N⁺ salt concentration, counteranion eluent strength, counteranion concentration, solvent composition, and pH. Indirect detection is influenced by these same mobile phase parameters as well as the properties of the detector active counteranion. The detection limit for indirect photometric detection at 287 nm using a tetrapentylammonium salt with a disodium 1,5-naphthalenedisulfonate—sodium benzoate counteranion mixture was about 70 pmol of NAc-AA depending on the amino acid injected as a 10-μ1 sample.     

Solvation parameters for amino acids

Atomic radii have been derived for the common amino acid side chains using a solvent interaction potential (SIP) based on quantum mechanically derived charges. Solvation energies calculated using these parameters are compared with those obtained using other sets of radii and charges, and from alternative methods. The differences from the experimental solvation energies for the nonionizable residues are all less than 10 kJ mol⁻¹. The largest error in the solvation energy occurs for acetic acid (−16.0 kJ mol⁻¹). For the charged side chain systems the difference from experiment are all less than 10 kJ mol⁻¹. SIP parameters for the aminoacetaldehyde derivatives of the common amino acids are presented. These are used in the calculation of the relative binding energies of six benzamidine inhibitors with trypsin. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 428–442, 1999     

Electrochemical detection of amino acids

Conclusion A method for the separation and the quantification of amino acids by high performance liquid chromatography and electrochemical detection using an isocratic mobile phase is possible and satisfactory.

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Elektrochemischer Nachweis von Aminosäuren