Amino acids alkaline conditions

Amphoteric Detergents. These surfactants, also known as ampholytics, have both cationic and anionic charged groups ki thek composition. The cationic groups are usually amino or quaternary forms while the anionic sites consist of carboxylates, sulfates, or sulfonates. Amphoterics have compatibihty with anionics, nonionics, and cationics. The pH of the surfactant solution determines the charge exhibited by the amphoteric under alkaline conditions it behaves anionically while ki an acidic condition it has a cationic behavior. Most amphoterics are derivatives of imidazoline or betaine. Sodium lauroamphoacetate [68647-44-9] has been recommended for use ki non-eye stinging shampoos (12). Combkiations of amphoterics with cationics have provided the basis for conditioning shampoos (13). 

Hydrolysis. Although hydantoins can be hydroly2ed under strongly acidic conditions, the most common method consists of heating ia an alkaline medium to give iatermediate ureido acids (the so-called hydantoic acids), which are finally hydroly2ed to a-amino acids. 

Paraformaldehyde [30525-89-4] is a mixture of polyoxymethylene glycols, H0(CH20) H, with n from 8 to as much as 100. It is commercially available as a powder (95%) and as flake (91%). The remainder is a mixture of water and methanol. Paraformaldehyde is an unstable polymer that easily regenerates formaldehyde in solution. Under alkaline conditions, the chains depolymerize from the ends, whereas in acid solution the chains are randomly cleaved (17). Paraformaldehyde is often used when the presence of a large amount of water should be avoided as in the preparation of alkylated amino resins for coatings. Formaldehyde may also exist in the form of the cycHc trimer trioxane [110-88-3]. This is a fairly stable compound that does not easily release formaldehyde, hence it is not used as a source of formaldehyde for making amino resins. 

A troublesome side reaction encountered ia the manufacture and use of amino resias is the conversion of formaldehyde to formic acid. Often the reaction mixture of amino compound and formaldehyde must be heated under alkaline conditions. This favors a Canni22aro reaction ia which two molecules of formaldehyde iateract to yield one molecule of methanol and one of formic acid. 

Dicyandiamide may be treated with formaldehyde (49) to produce resiaous compositions of varyiag properties (see Amino resins and plastics), under either acid or alkaline conditions. The reaction can be controlled to give mainly monomethyloldicyandiamide, a very water-soluble compound ... 

Amino groups a to nitrogen are hydrolyzed to the corresponding oxo compounds (as in the purines and pteridines) in bo h acid and alkaline conditions. Schiff bases are reduced to benzylamino derivatives with borohydride. 

FIGURE 5.19 N-Tertninal analysis using Edman s reagent, phenylisothiocyanate. Phenylisothiocyanate combines with the N-terminus of a peptide under mildly alkaline conditions to form a phenylthiocarbamoyl substitution. Upon treatment with TFA (trifluo-roacetic acid), this cyclizes to release the N-terminal amino acid residue as a thiazolinone derivative, but the other peptide bonds are not hydrolyzed. Organic extraction and treatment with aqueous acid yield the N-terminal amino acid as a phenylthiohydantoin (PTH) derivative. 

A 0-9% salt solution is considered to be isotonic with blood. Other electrolytes present include bicarbonate ions (HCOj ) and small amounts of potassium, calcium, magnesium, phosphate, sulphate and organic acid ions. Included among the complex compounds and present in smaller amounts are phospholipids, cholesterols, natural fats, proteins, glucose and amino acids. Under normal conditions the extracellular body fluid is slightly alkaline with a pH of 7-4. ... 

More recently, Stepanov et al. (1989) investigated the acid-base properties of the zwitterion 3.22 which is obtained in the diazotization of 5-amino-3-nitro-l,2,4-triazole. Under alkaline conditions the (Z)-diazoate dianion 3.23 is formed. It can be isomerized thermally to give the (E)-diazoate dianion 3.24. If the solution of this compound is acidified, the primary addition of a proton takes place at the anionic ring nitrogen yielding 3.25, and subsequently the hydrogen-bond-stabilized (Z)-iso-mer (3.26). Further acidification gives the nitrosoamine (3.27). 

Another important N-donor group is the amide group. Contrary to the basic amino groups, the more acidic amide functions tend to be deprotonated in the complex and therefore operate as a monoanionic donor. Alkaline conditions promote the deprotonation and subsequent complex formation. The amide group is a very useful component of mixed donor sets, such as N2S2 or N3S, as discussed in the next chapter. Whether a pure amide coordination may occur in M(V) complexes has not yet been proved. Tetrapeptides do form Tc(V) complexes [68], apparently without involvement of the carboxyl group. The N-donor atom provided by Schiflf bases plays only a role in mixed donor sets and will be discussed below. 

The iodoacetyl group of both isomers reacts with sulfhydryls under slightly alkaline conditions to yield stable thioether linkages (Figure 9.7). They do not react with unreduced disulfides in cystine residues or with oxidized glutathione (Gorman et al., 1987). The thioether bonds will be hydrolyzed under conditions necessary for complete protein hydrolysis prior to amino acid analysis. 

Introduction of microbiological methods for the determination of amino acids made possible the estimation of the amount of both free and combined amino acids in urine. Dunn et al. (D4), Thompson and Kirby (Tl), Eckhard and Davidson (El), and Woodson et al. (W3) estimated the amount of amino acids liberated in the course of acid or, as in the case of tryptophan determination, alkaline hydrolysis. Microbiological and colorimetric methods used for the determination of certain amino acids present very little opportunity for evaluating the proper quantitative relations between free and combined amino acids, since under the applied condition both combined and free amino acids are equally involved in the reaction. In 1949 Albanese et al. (A3) applied such methods to the quantitative determination of free and combined amino acids in the nondiffusible fraction of urine, and subjected the procedures to broad criticism from just this point of view. 

PITC has been used extensively in the sequencing of peptides and proteins and reactions under alkaline conditions with both primary and secondary amino acids. The methods of sample preparation and derivatization follow a stringent procedure which involves many labour-intensive stages. However, the resulting phenylthio-carbamyl-amino acids (PTC-AA s) are very stable, and the timing of the derivatization step is not as critical as when using OPA. 

The pH of the water can affect the adsorptive capacity. Organic acids adsorb better under acidic conditions, whereas amino compounds favor alkaline conditions. 

Hydrolysis reactions occur by nucleophilic attack at a carbon single bond, involving either the water molecule directly or the hydronium or hydroxyl ion. The most favorable conditions for hydrolysis, e.g. acidic or alkaline solutions, depend on the nature of the bond which is to be cleaved. Mineral surfaces that have Bronsted acidity have been shown to catalyze hydrolysis reactions. Examples of hydrolysis reactions which may be catalyzed by the surfaces of minerals in soils include peptide bond formation by amino acids which are adsorbed on clay mineral surfaces and the degradation of pesticides (see Chapter 22). 

These stabilizing interactions are destroyed if an enzyme is exposed to conditions much harsher than its natural ones. Thrown into industrial processes where temperatures are too high or a mixture is too acidic or too alkaline, enzymes will unfold and immediately lose the shapes necessary for their catalytic activity the chain of amino acids has not necessarily broken, but the stabilizing interactions are lost and the unfolding molecule becomes a messy conglomeration of disordered, catalytically useless arrangements. Once this happens, many enzymes cannot be coaxed to refold into their catalytically active form. This sensitivity limits industrial use of enzymes to processes carried out under suitably mild conditions. 

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