Amino group detection

Colorimetric and Fluorimetric Analysis. The functional groups of amino acids exhibit Htde absorption of uv light from 210 to 340 nm where uv absorption spectrometry is most conveniently conducted. Thus color or fluorescence formation reactions are employed for amino acid detection (128). 

The amino group is readily dia2oti2ed in aqueous solution, and this reaction forms a basis for the assay of sulfas. Aldehydes also react to form anils, and the yellow product formed with 4-(dimethylamino)hen2a1dehyde can be used for detection in thiu-layer and paper chromatography. Chromatographic retention values have been deterrnined in a number of thiu layer systems, and have been used as an expression of the lipophilic character of sulfonamides (23). These values have corresponded well with Hansch lipophilic parameters determined in an isobutyl alcohol—water system. 

Benzoylate the amino groups by overspotting at [103] the start This makes detection with Gibbs reagent possible... 

An amino group may take any of three possible positions in the five-membered isoxazole ring, giving rise to three tautomeric forms for 70 and 71 and four forms for 72 [76AHC(S1), pp. 416, 444, 445 84CHEC-I(5)1]. However, only amino structures 70a-72a have been detected using IR- or NMR-spectroscopic techniques (Scheme 33). 

Reports on the use of fluorescent derivatives abound (5). Some reagents have become widely used. The dansyl group is probably the most thoroughly studied. Dansyl chloride has been widely used as a fluorescent derivatizing reagent for HPLC (6,7). It reacts readily with primary and secondary amino groups (7) and with phenols (8), but forms derivatives of alcohols very slowly (9). The lower detection limit for dansyl derivatives of aliphatic amines is in the range of 300 femtomoles per injection. 

Fig. 21 Reaction scheme for the detection of aromatics, by means of the reaction sequence, nitration, reduction, diazotization and coupling to an azo dye, and of aliphatic nitro compounds by detection of the primary amino group produced on reduction.

The specific detection of aromatic nitro compounds is a second example. These can be converted by reduction to primary amines, which are then diazotized and coupled to yield azo dyes (cf. reagent sequence Titanium(III) chloride — Bratton-Marshall reagent ). Sodium nitrite —naphthol reagent, diazotized sulfanilic acid and other reagents specific for amino groups (e.g. ninhydrin, fluorescamine, DOOB, NBD chloride [9]) can also be used in the second stage of the reaction (Fig. 21). 

In contrast to the lability of certain dN adducts formed by the BHT metabolite above, amino acid and protein adducts formed by this metabolite were relatively stable.28,29 The thiol of cysteine reacted most rapidly in accord with its nucleophilic strength and was followed in reactivity by the a-amine common to all amino acids. This type of amine even reacted preferentially over the e-amine of lysine.28 In proteins, however, the e-amine of lysine and thiol of cysteine dominate reaction since the vast majority of a-amino groups are involved in peptide bonds. Other nucleophilic side chains such as the carboxylate of aspartate and glutamate and the imidazole of histidine may react as well, but their adducts are likely to be too labile to detect as suggested by the relative stability of QMs and the leaving group ability of the carboxylate and imidazole groups (see Section 9.2.3). 

The synthesis of urea-formaldehyde resin takes place in two stages. In the first stage, urea is hydroxymethylolated by the addition of formaldehyde to the amino groups of urea (Figure 19.1). This reaction is in reality a series of reactions that lead to the formation of mono-, di-, and trimethy-lolureas. Tetramethylolurea does not appear to be produced, at least not in a detectable quantity. The addition of formaldehyde to urea takes place over the entire pH range, but the reaction rate is dependent on the pH. 

Detection powders and fingerprint development kits commonly contain cream- or yellow-colored ninhydrin crystals or a solution of dissolved ninhydrin. Ninhydrin (also known as 1,2,3-indantrione, monohydrate 2,2-dihydroxy-1,3-indandione triketohydrindene, monohydrate and triketohydrinden hydrate) has the structure presented in Fig. 13.3.1. Ninhydrin will react with a free a-amino group, -NH2. This group is contained in all amino acids, and analysis with ninhydrin is often performed to verify the presence of amino acids. When a-amino acids (i.e., amino acids with the structure NH2-CHR-COOH) react with ninhydrin, a characteris-... 

Several of the compounds identified in ISM have not so far been synthesized in the laboratory however, two of them have now been obtained. The cyclic compound cyclopropylidene (C3H2), first detected in ISM in 1985 and later more frequently, was considered to be too unstable to exist on Earth under laboratory conditions. A derivative of this carbocycle, stabilized by amino groups which serve as -donors, has now been reported. X-ray crystallography shows that the presence of the amino groups has little effect on the molecular geometry as calculated for the unsubstituted cyclopropylidene (Lavallo et al., 2006). 

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