Amino glycine

The positions of the three amino-acids are shown clearly by the colour of their zones or spots, the proline being yellow and the glycine and phenylalanine being blue. Note the Rp value for each amino-acid ... 

Some amino-acids, e.g, glycine, can also be acetylated by this method. 

Glycine is the simplest member of a large and very important class of compounds, the a-amino-carboxylic acids. TTiere are many different methods available for the synthesis of amino-acids, but glycine can be readily prepared by the action of an excess of ammonia on chloroacetic acid ... 

Note that the amino-acids, because of their salt-like nature, usually decompose on heating, and therefore seldom have sharp melting-points. Furthermore, all naturally occurring amino-acids are a-amino-acids, and consequently, with the exception of glycine, can exist in optically active forms. 

A) Amino-aliphatic carboxylic acids. Glycine, tyrosine cystine. ... 

Acetamide CH3CONH2 Urea H3NCONH2 Glycine HgNCHjCOOH Amino-carboxylic... 

Note. When this test is applied to amino-acids, e.g. glycine, anthranilic acid, ulphanilic acid, no odour is detected owing to the non-volatility of the acidic isocyanide in the alkaline solution. 

Glycine or amino-acetic acid, NHjCHjCOOH tyrosine, />-HOC<.H4CH2CH(NH2)COOH cystine, [ SCH2CH(NH2)COOH]2. 

A) AMINO-ALIPHATIC CARBOXYLIC ACIDS. Glycine, tyrosine, cystine. 

Physical Properties. Glycine is a colourless crystalline solid soluble in water. Owing to the almost equal opposing effects of the amino and the carboxylic groups. its aqueous solution is almost neutral (actually, slightly acidic to phenolphthalein) and glycine is therefore known as a neutral ampholyte. f It exhibits both acidic and basic properties. 

All the amino-acids of physiological importance are a-amino-acids, e.g. (in addition to the above compounds), alanine or a-amino-propionk acid, CHaCH(NH,)COOH, and leucine or a-amino-Y-dimethyl-rt-butyric acid, (CH,)aCHCH,CH(NHa)COOH, and naturally occurring samples (except glycine) are therefore optically active. 

Method. An amino-acid such as glycine, NHjCH,COOH, cannot be estimated by direct titration with standard alkali solution, owing to the opposing effects of the basic and the acidic groups. If, however, the amino-acid is first... 

Since formaldehyde solutions almost invariably contain formic acid, and amino-acids themselves are seldom exactly neutral, it is very important that both the formaldehyde solution and the glycine solution should before mixing be brought to the same pH (see footnote, p. 509), and for this purpose each solution is first madejWl alkaline to phenolphthalein by means of dilute sodium hydroxide solution. This preliminary neutralisation must not be confused with... 

Glycine itself is almost neutral, and requires very little sodium hydroxide to give a pink colour with phenolphthalein some other amino-acids, e.g., glutamic acid, aspartic acid, etc., are definitely more acidic and consequently require more alkali for this purpose cf. footnote, p. 380). 

The calculation depends simply on the fact that 1000 ml. M.NaOH 1 g. mol. of glycine. The method can clearly be used either to deter mine the molecular weight of an amino-acid of known basicity, or to estimate an amino-acid of known molecular weight. 

The influence of a large number of oc-amino acids on the values of and k at have been determined. These a-amino acids included glycine, L-valine, L-leucine, L-phenylalanine, L-tyrosine, L-tryptophan, NOrmethyl-L-tryptophan (L-abrine), N-methyl-L-tyrosine, N,N-dimethyl-L-tyrosine and p -me thoxy-N-me thyl -L -phenyl al anine. 

Simple esters cannot be allylated with allyl acetates, but the Schiff base 109 derived from o -amino acid esters such as glycine or alanine is allylated with allyl acetate. In this way. the o-allyl-a-amino acid 110 can be prepared after hydrolysis[34]. The Q-allyl-o-aminophosphonate 112 is prepared by allylation of the Schiff base 111 of diethyl aminomethylphosphonates. [35,36]. Asymmetric synthesis in this reaction using the (+ )-A, jV-dicyclohex-ylsulfamoylisobornyl alcohol ester of glycine and DIOP as a chiral ligand achieved 99% ec[72]. 

The physical properties of a typical amino acid such as glycine suggest that it is a very polar substance much more polar than would be expected on the basis of its formula tion as H2NCH2CO2H Glycine is a crystalline solid it does not melt but on being heated It eventually decomposes at 233°C It is very soluble m water but practically insoluble m nonpolar organic solvents These properties are attributed to the fact that the stable form of glycine is a zwittenon, or inner salt... 

Example Jensen and Gorden calculated the potential energy surface of glycine using ab initio and semi-empirical methods.This study is of special interest to developers of molecular mechanics force fields. They frequently check their molecular mechanics methods by comparing their results with ab initio and semi-empir-ical calculations for small amino acids. 

For amino acids having trivial names ending in -ine, the suffix -amide is added after the name of the acid (with elision of e for monoamides). For example, HjN—CHj—CO—NHj is glycin-amide. 

The sequence of each different peptide or protein is important for understanding the activity of peptides and proteins and for enabling their independent synthesis, since the natural ones may be difficult to obtain in small quantities. To obtain the sequence, the numbers of each type of amino acid are determined by breaking down the protein into its individual amino acids using concentrated acid (hydrolysis). For example, hydrolysis of the tetrapeptide shown in Figure 45.3 would give one unit of glycine, two units of alanine, and one unit of phenylalanine. Of course, information as to which amino acid was linked to which others is lost. 

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