Decomposition acid amino acids

The crude product is dissolved in five times its weight of water, and after clearing with a little Norite the solution is diluted with one and one-half volumes of 95 per cent alcohol. The product separates in well-formed, snow-white crystals, and after standing for several days in an ice chest is collected with suction on a Buchner funnel. The yield of purified histidine monohydrochloride is 75-80 g. (Note 5). The compound melts at 251-2520, with decomposition. The amino acid is not race-mized by the procedure employed, and shows the characteristic optical activity, [a]n6° = +8.00, in the presence of three moles of... 

Lee, C., and C. Cronin. 1982. The vertical flux of particulate organic nitrogen in the sea decomposition of amino acids in the Peru upweUing area of the equatorial Atlantic. Journal of Marine Research 40 227-251. 

E. J. Mclntee, R. P. Remmel, R. F. Schinazi, T. W. Abraham, C. R. Wagner, Probing the Mechanism of Action and Decomposition of Amino Acid Phosphomonoester Amidates of Antiviral Nucleoside Prodrugs , J. Med. Chem. 1997, 40, 3323-3331. 

Fig. 4.5. Rhodium(II) acetate-catalyzed decomposition of amino acid-derived diazoamides...

Amides and Nitriles. Primary amines or ammonia, from the thermal decomposition of amino acids, can be acylated by carboxylic acids to produce amides (30). 

From Amino Benzoic Acid.—Amino acids by the diazo reaction and decomposition with water will yield the corresponding phenol acids. In such cases also if we start with benzoic acid, nitrate directly and reduce this to the amino compound, the final product of the diazo reaction will be the meta hydroxy acid. If we start with toluene and nitrate it and then proceed as in the foregoing and oxidize the amino toluene to amino benzoic acid our product will be the ortho and para hydroxy acids. 

The thiobarbituric acid (TBA) value test is a popular way of measuring rancidity in certain foods and oxidation products in biological systems. It is based on the formation of a colored complex between two molecules of TBA and one molecule of malonaldehyde resulting from thermal decomposition of polyunsaturated peroxides. This reaction is not specific due to the presence of many TBA-reactive substances (TBARS), such as browning reaction products, protein and sugar decomposition products, amino acids, nucleic acids and nitrite. 

In the case of faeces, partic arly lipids, proteins, polysaccharides and products of their decomposition (e.g. aliphatic acids, amino acids, amines, etc.) are concerned in the case of urine the highest amount of organic compounds is due to nitrogen substances, particularly urea to a lesser extent amino acids, ammonia nitrogen, uric acid, etc. are present. Urine contains a considerably lower amount of nitrogen-free organic matters (e.g. oxalic acid, glycides, phenols, etc.). 

It is probable that the oxyacids formed in die organism come from the decomposition of amino-acids, in consequence of the intervention of a special amidase. 

Sumner s analytical studies convinced him that urease was a protein. This conclusion was resisted by the chemical community but John H. Northrop s (1891-1987) crystallization of pepsin in 1930 at the Rockefeller Institute in New York City and its unambiguous decomposition into amino acids fully vindicated Sumner. Sumner and Northrop were able to make use of the ultracentrifiige developed by Svedberg and the electrophoresis technique developed by his student Tiselius to fully establish purities and molecular weights of their enzymes. Sumner and his coworkers then crystallized trypsin and chymotrypsin. Sumner and Northrop shared the 1946 Nobel Prize in chemistry with Wendell M. Stanley (1904—71), who in 1935 crystallized the tobacco mosaic virus in his laboratory at the Rockefeller Institute. 

Kamimura [100], Shida et al. [101,102], and Kubo et al. [103] conducted extensive studies on biodegradability and found that A-acylamino acids are readily biodegradable through decomposition into amino acid and fatty acid. Thus they are desirable surfactants compatible with the environment [Fig. 22],... 

Decomposition Products. — Among the products of decomposition are amino-acids, such as glycocoll, leucin, asparaginic and glutaminic acids, alanin, phenylalanin, a-prolin, etc. Tyrosin is not present. 

Another important reaction is decomposition of amino acid derived ketosamines in the presence of oxygen, which is catalysed by transition metal ions. Products of this decomposition are glycos-2-uloses. For example, n-fructosamine yields D-arahino-hexos-2-ulose and in addition to other products, this reaction produces the corresponding Strecker aldehyde (Figure 4.88). 

To study the photocatalytic decomposition of amino acids by TiOi, Dolamic and Buergi modulated UV light on and off while flowing l-G1u and L-Asn over the catalyst surface in an ATR-IR cell [22], The demodulation of the data with PSD removed any signals not oscillating with the UV light frequency, allowing them to observe cyanide on the catalyst surface, which was not observed in other more conventional studies. 

The amino-acids are colourless, crystalline substances which melt with decomposition. They are mostly soluble in water and insoluble in alcohol. 

The melting points of the derivatives of a number of amino acids are collected in Table 111,132. Most a-amino acids decompose on heating so that the melting points would be more accurately described as decomposition points the latter vary somewhat with the rate of heating and the figures given are those obtained upon rapid heating. 

The deterruination of amino acids in proteins requires pretreatment by either acid or alkaline hydrolysis. However, L-tryptophan is decomposed by acid, and the racemi2ation of several amino acids takes place during alkaline hydrolysis. Moreover, it is very difficult to confirm the presence of cysteine in either case. The use of methanesulfonic acid (18) and mercaptoethanesulfonic acid (19) as the protein hydroly2ing reagent to prevent decomposition of L-tryptophan and L-cysteine is recommended. En2ymatic hydrolysis of proteins has been studied (20). 

The principal pathway for the decomposition of aspartame begins with the cleavage of the ester bond, which may or may not be accompanied by cyclization (Eig. 2). The resultant diketopipera2ine and/or dipeptide can be further hydroly2ed into individual amino acids (qv). 

Fig. 2. Decomposition of aspartame to diketopipera2ine and/or aspartyl-phenylalanine and then to the amino acids aspartic acid and phenylalanine (22).

A significant difference between pseudoirreversible inhibitors and mechanism-based inactivators is the reversibiUty of the inactivation. A complete evaluation of the mechanism involved would require evidence not only for the covalent enzyme-inhibitor complex, but also for its decomposition products and its rate of reactivation. It is often difficult to identify the active site amino acid residue covalently linked to the inhibitor because of the instabiUty of the complex. 

Amino acids have high melting or decomposition points and are best examined for purity by paper or thin layer chromatography. The spots are developed with ninhydrin. Customary methods for the purification of small quantities of amino acids obtained from natural sources (i.e. l-5g) are ion-exchange chromatography (see Chapter 1). For general treatment of amino acids see Greenstein and Winitz [The Amino Acids, Vols 1-3, J.Wiley Sons, New York 1961] and individual amino acids in Chapters 4 and 6. 

Benzyioxycarbonyi chioride (Cbz-Ci, benzyi cbioroformate) [501-53-1] M 170.6, b 103 /20mm, d 1.195, n 1.5190. Commercial material is better than 95% pure and may contain some toluene, benzyl alcohol, benzyl chloride and HCl. After long storage (e.g. two years at 4 , Greenstein and Winitz [The Chemistry of the Amino Acids Voi 2 p. 890, J Wiley and Sons NY, 1961] recommended that the liquid should be flushed with a stream of dry air, filtered and stored over sodium sulfate to remove CO2 and HCl which are formed by decomposition. It may further be distilled from an oil bath at a temperature below 85 because Thiel and Dent [Annalen 301 257 1898] stated that benzyioxycarbonyi chloride decarboxylates to benzyl chloride slowly at 100 and vigorously at 155 . Redistillation at higher vac below 85 yields material which shows no other peaks than those of benzyioxycarbonyi chloride by NMR spectroscopy. LACHRYMATORY and TOXIC. 

---