Amino acids ultraviolet spectra

Attempts to prepare 6-hydroxybenzofuroxan by demethylation of 5-methoxybenzofuroxan, by pyrolysis of 4-azido-3-nitrophenol, and by hypochlorite oxidation of 4-amino-3-nitrophenoD failed. This rather unstable compound was finally prepared by hydrolysis of 5-acetoxybenzofuroxan its tautomeric possibilities are numerous, but from the similarity of its ultraviolet spectrum to that of 5-methoxybenzofuroxan it was considered to be largely in the hydroxy form. It is a fairly strong acid, of pK 6.76 (cf. 5-hydroxybenzo-furazan, pK 7.28). 7-Hydroxy-4,6-dinitrobenzofuroxan has been reported as arising from oxidation and nitration of dinitrosoresorcinol monooxime (tetraoxocyclohexene trioxime). ... 

The enolic form of 2 was confirmed by a ferric chloride color reaction and by its acidity and ultraviolet spectrum, A-Aroyl derivatives of amino acids other than glycine fail to form such azlactones, probably because the stabilization afforded by enolization cannot occur. 

In the preceding Section (5.3) the CD bands in the near ultraviolet region are assigned to those of tyrosyl and phenylalanyl residues, whose thermal motions are restricted sterically keeping their geometry constant around the main chain in the proteins. The CD spectrum of aromatic moieties provides a good measure for the analysis of motional freedom around a given amino acid residue. Better examples have been reported on several kinds of amino acids and their polymers. 

Side chains of the three aromatic amino acids phenylalanine, tyrosine, and tryptophan absorb ultraviolet light in the 240- to 300-nm region, while histidine and cystine absorb to a lesser extent. Figure 3-13 shows the absorption spectrum of a "reference compound" for tyrosine. There are three major absorption bands, the first one at 275 nm being a contributor to the well-... 

Protein has a secondary structure a-helix, -structure or random chain. The contents of these components in the protein structure can be calculated on the basis of circular dichroism spectrum in the region of far-ultraviolet wavelength (around 220 nm),46 or amino acid sequences.47 Although these methods do not always reflect a secondary structure of protein, they are applicable to research on the structure of proteins, especially homologous proteins whose three-dimensional structures have not been shown. 

Physical Chemical Characterization. Thiamine its derivatives, and its degradation products have been fuUy characterized by spectroscopic methods (9,10). The ultraviolet spectrum of thiamine shows pH-dependent maxima (11). H, and nuclear magnetic resonance spectra show protonation occurs at the 1-nitrogen, and not the 4-amino position (12—14). The H spectmm in D2O shows no resonance for the thiazole 2-hydrogen, as this is acidic and readily exchanged via formation of the thiazole jlid (13) an important intermediate in the biochemical functions of thiamine. Recent work has revised the pTC values for the two ionization reactions to 4.8 and 18 respectively (9,10,15). The mass spectmm of thiamine hydrochloride shows no molecular ion under standard electron impact ionization conditions, but fast atom bombardment and chemical ionization allow observation of both an intense peak for the parent cation and its major fragmentation ion, the pyrimidinylmetbyl cation (16). 

Plastocyanin contains two copper atoms per molecule. Plastocyanin in photosystem I is soluble in the lumen region and can be readily released in a hypotonic medium and purified by DEAF chromatography. In the oxidized form the copper protein is blue with a major absorption band at 597 nm = 4.7 mM two weaker absorption bands at 460 and 770 nm, and one band with vibrational structure characteristic of amino acids in the ultraviolet region (see Fig. 2). Plastocyanin in the reduced state does not absorb in the visible region. The low-temperature EPR spectrum of oxidized PC has characteristic g-values at 2.05 and 2.23. 

This ring system has also been called pyrazolo[2,3-a]quinoxaline and pyrazolo[a]quinoxaline. Little work has however been done on this heterocycle. Catalytic reduction of the o-nitrophenylpyrazole 1 results in ring closure to give the pyrazolo[l,5-a]quinoxaline 2. Sequential decarboxylation, treatment with phosphoryl chloride, and catalytic hydrogenation give the parent heterocycle 3. The unsubstituted compound is reported to have a broad band at 240-245 nm in its ultraviolet spectrum in 95% ethanol. A recent patent describes several 4-substituted amino derivatives of pyrazolo[l,5-a]quinoxaline-3-carboxylic acid as possessing antiinflammatory properties. ... 

Phenylalanine s phenyl side chain classifies it as an aromatic amino acid. The aromatic amino acids, like most compounds carrying conjugated rings, exhibit strong absorption of light in the near-ultraviolet region of the spectrum (Figure 5.6). This absorption is frequently used for the analytical detection of proteins. 

The application of low-temperature techniques to the investigation of protein spectra in the ultraviolet region was initiated by Lavin and Northrop (1935) who investigated the ultraviolet absorption spectra of pepsin, serum albumin, and ovalbumin in glycerol, and showed that the fine structure of the protein spectrum was enhanced at — 100°C. Preliminary reports of similar work have been published by Randall and Brown (1949) on thin films of sublimed tryptophan and phenylalanine at 90°C., and by Sinsheimer et al. (1949) for tryptophan at 77.6°K. Loof-bourow and his coworkers (Sinsheimer et al., 1950) have begun publication of a series of papers reporting much more comprehensive work on the influence of low temperature on the spectra of amino acids and proteins in thin films and in solid solution. Beaven et al. (1950) have reported a few results on thin Aims of the aromatic amino acids. 

Following trends in die pH dependence of its ultraviolet spectrum, the dissociation constant of the amino group (pXa2) in 5-aminosalicylic acid was determined to be 5.69. The dissociation constant of die carboxyl group pJCai was obtained through studies of die compound solubility at pH values between 1.0 and 2.5, and was reported to be 2.30 [15]... 

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