Amino acid acid-base properties

CHEMICAL PROPERTIES OF AMINO ACIDS ACID-BASE (AMPHOTERIC) PROPERTIES... 

Acid-Base Properties of Amino Acids with Neutral Side Chains... 

Aminopyridines, aminopyridine oxides, and 3-aminoquinoline are obviously diazotized by analogous mechanisms. Kalatzis (1967 b) studied the diazotization of 4-aminopyridine over a very large range of acid concentrations (0.0025-5.0 m HC104). This compound is comparable to 2-aminothiazole in its acid-base properties the heterocyclic nitrogen is easily protonated at pH 10, whereas the amino group is a very weak base (pKa = -6.5). Therefore, the kinetics indicate that the (mono-protonated) 4-aminopyridinium ion reacts with the nitrosyl ion. The... 

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). 

Mu, Pi, Theta-Omega and Zeta, based on their amino acid sequences, immunological properties and substrate specificities [37,38]. The Alpha, Mu and Pi classes are the most abundantly expressed GSTs. 

ACiD-BASE PROPERTIES OF AMINO ACIDS AND PROTEINS... 

Formation of a broad range of materials with a wide variety of general or specific properties and function (such as proteins and enzymes) through a controlled sequence assembly from a fixed number of feedstock molecules (proteins about 20 different amino acids, five bases for nucleic acids, and two sugar units)... 

In this section, enzymes in the EC 2.4. class are presented that catalyze valuable and interesting reactions in the field of polymer chemistry. The Enzyme Commission (EC) classification scheme organizes enzymes according to their biochemical function in living systems. Enzymes can, however, also catalyze the reverse reaction, which is very often used in biocatalytic synthesis. Therefore, newer classification systems were developed based on the three-dimensional structure and function of the enzyme, the property of the enzyme, the biotransformation the enzyme catalyzes etc. [88-93]. The Carbohydrate-Active enZYmes Database (CAZy), which is currently the best database/classification system for carbohydrate-active enzymes uses an amino-acid-sequence-based classification and would classify some of the enzymes presented in the following as hydrolases rather than transferases (e.g. branching enzyme, sucrases, and amylomaltase) [91]. Nevertheless, we present these enzymes here because they are transferases according to the EC classification. 

As we will see in Chapter 8, the delocalization of the unshared electron pair in aniline has an important impact on the acid/base properties of anilines as compared to aliphatic amino compounds. 

Of the substances studied the most abundant in the Paleozoic rocks of the area are furfurals presumably derived from carbohydrates, higher molecular weight hydrocarbons, and in a few samples, amino acids. Acid and base soluble, low boiling substances having some properties of heterocyclic compounds, phenols, and organic acids exist in smaller amounts. 

The acid-base properties, and hence ionic character, of peptides and proteins also can be used to achieve separations. Ion-exchange chromatography, similar to that described for amino acids (Section 25-4C), is an important separation method. Another method based on acid-base character and molecular size depends on differential rates of migration of the ionized forms of a protein in an electric field (electrophoresis). Proteins, like amino acids, have isoelectric points, which are the pH values at which the molecules have no net charge. At all other pH values there will be some degree of net ionic charge. Because different proteins have different ionic properties, they frequently can be separated by electrophoresis in buffered solutions. Another method, which is used for the separation and purification of enzymes, is affinity chromatography, which was described briefly in Section 9-2B. 

Acid-base properties can also be used to orient amino-functional silanes on glass surfaces with strong effects on performance of the coupling agent in... 

Separation of proteins based on differences in their electrical charge depends on their acid-base properties, which are mostly determined by the number and type of ionizable side groups in the peptide chain. Since proteins are different from each other with respect to their composition and amino acid sequence, they also have distinct acid-base properties. Information on these properties allows a prediction of the behavior of a given protein when exposed to an electrical field. 

Even though 4a and its analogues are relatively simple compounds, they come to assume an importance which is quite disproportionate, when their origin is considered. Their two parts are derived differently the furfural resulting from 1,2-enolisa-tion of the Amadori compound and the furanone from 2,3-enolisation (see Chapter 2), the former being favoured by low pH and the latter by moderate pH. This means that for both components to be available for interaction, the reaction conditions, including pH, need to be carefully balanced. pH optimisation of the reaction will also be affected by the acid/base properties of the amino acid moiety of the Amadori compound. 

To study the acid-base properties, one can perform a simple titration. We start our titration with the amino acid being in its acidic form at a low pH ... 

Acid-base properties of amino acids Special Equipment... 

A mammalian cell may contain as few as 2000 different proteins and as many as 50,000 at any given time. Each of these is uniquely suited to the function it performs, and this in turn depends on its size, shape, solubility in aqueous media, acid-base properties, propensity to form fibers, and numerous other physical and chemical properties. The component amino acids are largely responsible for the ability of proteins to perform their biologic roles. The properties of amino acids are therefore of paramount importance in determining how proteins work. 

Acid-Base Properties of Amino Acids 1160 24-4 Isoelectric Points and Electrophoresis 1162 24-5 Synthesis of Amino Acids 1164... 

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