Carboxylic group terminal determination

Determination of Carboxylic Group Terminals. The carboxylic group terminals were determined by alkali titration (12.). After 200 mg of the sample was dissolved in T.5 ml of benzyl alcohol in a nitrogen atmosphere at 110 °C, the solution was titrated with 0.05N potasL- Vum hydroxide using phenolphthalein as an indicator. A blank test was carried out by the same method but omitting the sample. 

These two selectors terminated with a glycine were then prepared on a larger scale, their carboxyl groups reacted with 3-aminopropyltriethoxysilane, and the conjugate immobilized onto silica. Each CSP was packed into columns and used for the separation of racemic (l-naphthyl)leucine ester 17. Separation factors of 6.9 and 8.0 were determined for the columns with DNB-ala-gly and DNB-leu-gly selector respectively. These were somewhat lower than those found for similar CSPs using the parallel synthesis and attached through a different tether [87]. 

For carboxyl terminal determination of peptides by means of CDI the terminal carboxylic acid group of the peptide is selectively reduced with sodium dihydrobis(2-methoxy-ethoxy)aluminate to an alcohol. Subsequent conversion of the amino alcohol moiety with CDI yields an 7V-acyl-2-oxazolidone derivative, from which the oxazolidone unit can be easily removed and characterized.[56]... 

The first four facets are rotationally equivalent to each other as are the final four. The two sets are related by reflectional symmetry to each other. When a chiral adsorbate, for example, S-lysine, is used, the reflectional symmetry is no longer valid and only rotationally equivalent facets should be formed. This was demonstrated elegantly by Zhao with STM [53], The driving force for facet formation is proposed to be a three-point interaction involving the carboxylate group, the a-amino group, and the amino-terminated side chain. The simultaneous optimization of adsorbate-adsorbate and adsorbate-substrate interactions determines the stereochemistry of the facet. 

The acid-base behavior of peptides (10) is determined by the free a-amino group on the N-terminal residue, by the free a-carboxyl group on the C-terminal residue, and by the ionizable R groups located at intermediate positions. The pK values of the terminal a-carboxyl groups are somewhat higher and those of the a-amino groups somewhat lower than those of the corresponding free amino acids (Table 1) (11). 

The assembly of the carbon skeletons of these unusual hydrocarbons was first studied in Carpophilus freemani Dobson, through careful GC-MS and Nuclear Magnetic Resonance (NMR) studies of the incorporation of 2H or 13C-labeled precursors (Petroski et al., 1994). Assembly of the carbon skeleton of the aggregation pheromone of C. freemani, (2 , 4 , 6ii)-5-ethyl-3-methyl-2,4,6-nonatriene, involves initiation with acetate elongation with first propionate (to provide the methyl branch), then butyrate (to provide the ethyl branch) and chain termination with a second butyrate (Figure 6.7). At some point, loss of C02 from one of the butyrate units occurs to yield the appropriate hydrocarbon, but Petroski et al. (1994) were unable to determine which of the butyrate units loses its carboxyl group. Bartelt and Weisleder (1996) studied the biosynthesis of 15 additional methyl- and/or ethyl-branched, tri- and tetraenes in the related... 

This procedure was chosen by Waite 91> to synthesize polyester macromonomers starting from 12-hydroxystearic acid. The self-condensation of this compound was carried out to the desired conversion p which also determines the average degree of polymerization thereafter, the terminal carboxylic groups were reacted with glycidyl methacrylate, thus yielding the macromonomer ... 

All peptides and proteins, unless they are cyclic, contain the so-called N- and C-terminal residues a free a-amino group at one end and a free a-carboxyl group at the other. The identity of such groups may be determined by various chemical and enzymatic means. One of the first such methodologies utilized fluorodinitrobenzene (FDNB) for N-terminal group analysis ... 

Dinitrophenyl (DNP) derivatives of amino acids are used to identify terminal amino acids in proteins. They are determined by GC after the conversion of free carboxyl groups into methyl esters [283—285] with the aid of either diazomethane or BF3—methanol. 

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