Amino acids separation direct

The use of pH-sensitive fluorescent indicators as spray reagents has been recently examined for the determination of sulphur-containing pesticides and amino acids separated by TLC [158,159]. The procedure is adapted from a ligand-exchange method of Frei and Mallet [160]. The separated pesticides are brominated directly on the TLC plate. This treatment oxidizes the pesticides and liberates hydrobromic acid as a side product. On... 

Two types of crosslinking domains exist in tropoelastin those rich in alanine (KA) and those rich in proline (KP). Within the KA domains, lysine residues are typically found in clusters of two or three amino acids, separated by two or three alanine residues. These regions are proposed to be Q-helical with 3.6 residues per turn of helix, which has the effect of positioning two lysine sidechains on the same side of the helix, although there is no direct structural evidence (Brown-Augsburger et al., 1995 Sandberg et al, 1971), and facilitating the formation of desmosine crosslinks. Desmosine crosslinks are formed by the condensation of two allysine... 

After separation of the L-amino acid through ion exchange or by a crystallization step, the remaining N-acetyl-D-amino acid is recycled by thermal racemization under drastic conditions or by a racemase to achieve an overall yield of around 45% of L-amino acid (50% is the theoretical maximum) (Figure 7.11). D-Amino acids are also accessible by chemical hydrolysis of the N-acetyl-D-amino acid or directly by use of D-selective acylases. 

Other hand visible light serves as the coupling reagent. This opens up a possibility for the direct incorporation of various (even very unusual) amino acids into peptides without the requirement to synthesize the amino acid separately. 

The a tz-adduct 15 is generally the major one (compare theazidation reaction, Section 7.1.1.1.). After separation from the minor adduct 16 by chromatography, the different ester groups are saponified, giving /i-hydroxy-a-hydrazino acids 17 in reasonably good yields. The hydrochlorides of 17 can be reduced to the corresponding a-amino acids 18. The optical purity of these amino acids is directly related to the optical purity of the esters 1419. 

The DNP-amino acids, after separation into individual spots on the chromatographic plate, can be eluted from the scraped off area by adding 4 ml of water to the material in a small tube. The tube is heated at 50° in a water bath for 15 minutes and centrifuged to clear the solution. The color is read against known standards at 360 nm. Direct estimation of DNP-, PTH-, and DANS-amino acids separated on the thin-layer plate can be performed by fluorescence and fluorescence quenching techniques (P8). It is also possible to convert unmodified amino acids, separated on a silica gel G chromatographic plate, into DNP-amino acids by in situ conversion as was described in Section 4.7.18. The DNP-derivatives can then be developed in the second dimension and the spots analyzed quantitatively. 

First, they compared CSPs 1 and 3 prepared by the two-step solid-phase methodology with their commercially available counterparts (CSPs 2 and 4) obtained by direct reaction of the preformed selector with a silica support. Although no exact data characterizing the surface coverage density for these phases were reported, all of the CSPs separated all four racemates tested equally. These results shown in Table 3-3 subsequently led to the preparation of a series of dipeptide and tripeptide CSPs 5-10 using a similar synthetic approach. Although the majority of these phases exhibited selectivities lower or similar to those of selectors built around a single amino acid (Table 3-3), this study demonstrated that the solid-phase synthesis was a... 

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