Amino acids perchlorate

Cucurbitine (47) is the active principle from the seeds of Cucurbita moschata Duch., which are used in Chinese folk medicine. The structure of this unique a-amino acid was established through a combination of chemical and spectroscopic techniques (81, 82). A single-crystal X-ray analysis of the perchlorate of cucurbitine has confirmed the original hypothesis and has established the absolute configuration of 47 (83). 

With amino-acid salts the effect of the medium is considerably larger. Peacock and Cram (1976) reported that the degree of chiral recognition of DL-phenylglycine perchlorate by crown ether [285] depends on the ratio of acetonitrile and chloroform. The observed EDC values vary from 6 to 52, which corresponds to a difference in free energy of —1.15 kcal mol-1 (Table 72). The optimum is very sharply defined (23.1% of acetonitrile) and is... 

Amino acids, peptides, and proteins have been analyzed, using hetaerons. Hiosphoric acid or perchlorate salts in the mobile phase de-... 

E. Write the chemical reactions (including structures of reactants and products) that occur when the amino acid histidine is titrated with perchloric acid. (Histidine is a molecule with no net charge.) A solution containing 25.0 mL of 0.050 0 M histidine was titrated with 0.050 0 M HC104. Calculate the pH at the following values of Ve 0, 4.0, 12.5, 25.0, 26.0, and 50.0 mL. 

Having accomplished the homogenization of the sample, extraction of free amino acids is usually a simple process of stirring the sample in an appropriate solvent. This is typically a dilute solution (0. IN) of hydrochloric acid (2,7). Elevated temperatures may be used to assist dissolution, but care must be taken not to damage the more acid-labile amino acids. More recently, Moret and Conte (8) report that 0.1N HC1 was not a suitable solvent for all types of food samples. For some types of meat samples, 5% trichloroacetic acid is reported to afford superior performance (for biogenic amines, also amino acids ). It is not unusual to see perchloric acid employed for extraction from meat tissues (also more commonly for biogenic amines). 

The kinetics of oxidation of selected 7-amino acids125 and aliphatic aldehydes126 by trichloroisocyanuric acid (TCICA) in aqueous acetic acid-perchloric acid is first order in both TCICA and substrate. The kinetics of Ru(IH)-catalysed oxidation of aliphatic alcohols by TCICA in aqueous H0Ac-HCI04 are zero order in [TCICA], fractional order in alcohol and first order in Ru(IH).127... 

Polar biomarkers have also been investigated by NMR (SO) in postmortem BT samples. These samples were treated with perchloric acid, and metabolic extracts were analyzed to compare AD with amyotrophic lateral sclerosis (ALS) (80). After multivariate statistical analysis of the 8 AD and the 11 ALS samples, a high score in the statistical parameters of OPLS was obtained with the exclusion of 1 AD sample. Increased concentration of branched amino acids, alanine, acetate, glutamine, glutamate, and glyceropho-sphocholine in AD patients was observed when compared to ALS (80). 

Metal ions can enhance the resolution of nucleic acids and amino acids in MECC. Zinc perchlorate (0-30 mM) has been found useful as a complexing reagent for histidine-containing peptides. 

Courderot, C.M. et al. Chiral discrimination of dansyl-amino-acid enantiomers on tei-coplanin phase sucrose-perchlorate anion dependence. Anal. Chim. Acta 2002, 457, 149-155. 

In order to be able to predict the retention behavior of peptides of different composition, of peptides of the same composition but different sequence (positional isomers), and of diastereoisomeric peptides, a knowledge of the incremental contribution of each amino acid to the overall contact area term is required not only for each well-defined stationary phase but also for each mobile-phase condition. Group retention coefficient summation approaches based on the assumption that selectivity differences can be ascribed predominantly to amino acid sequence differences, have been developed by Meek (46a, 52b) and Su et al. (45a). These treatments have subsequently been applied to a number of different elution systems (52c-52e). A comparative analysis of the different amino acid group contribution coefficients derived for phosphate, perchlorate, pyridine/acetate, trifluoroacetate, and bicarbonate buffer systems has been reported (52f). 

The classical method for tert-butyl esterification involves nnineral add catalyzed addition of the amino acid to isobutene. Both, N-protected, e.g. Z-Xaa-OH, and unprotected amino acids form tert-butyl esters with isobutene in the presence of catalytic amounts of sulfuric acid or TosOH. " Another efficient method is the transesterification of an acetic acid tert-bvXy ester catalyzed by perchloric acid. " Amide tert-butylation was recognized as a side reaction in the presence of perchloric acid, but could be completely suppressed by using sulfuric acid. Both methods, acid-catalyzed addition to isobutene and the transesterification of acetic add terf-butyl esters, result in simultaneous terf-butyl-ation of hydroxy and sulfanyl groups. A synthetic route to Z-Thr-OtBu, Z-Ser-OtBu, and Z-Hyp-OtBu without conconnitant O-alkylation involves the hydroxy protection by the acetoacetyl group, which is readily cleaved by treatment with 2 equivalents of hydrazine in EtOH for 30 minutes. ... 

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