Carboxyl groups chemical structure

When arranged according to their chemical composition the fatty acids form a homologous series. The first member in the series has the composition represented by the formula CH2O2. It is known as formic acid. As it contains the carboxyl group, its structural formula is H.COOH. The second member in the series is acetic acid, CH3.COOH, the third propionic acid, C2H5.COOH, etc. A few of the more important acids will be considered in some detail. 

The primary oxidation product of 3-hydroxyanthranilic acid is the precursor of two pyridine compounds, quinolinic and picolinic acids (Mehler, 1956). The structure of the oxidation product is supported by this information, since a chemically plausible mechanism can be devised to acccount for these reactions. The formation of quinolinic acid is a nonenzymic, first-order reaction. The reaction rate is a function of temperature but not of the composition of the medium except for low pH. At low pH values a rapid, irreversible elimination of ammonia and carbon dioxide competes with quinolinic acid formation. At higher pH values the reaction may be considered as beginning with an isomerization of the double bond, leading to the formation of a compound with cu-carboxyl groups. This structure would ordinarily be the less favorable form. 

The primary structure of a polypeptide is its sequence of amino acids. It is customary to write primary structures of polypeptides using the three-letter abbreviation for each amino acid. By convention, the structure is written so that the amino acid on the left bears the terminal amino group of the polypeptide and the amino acid on the right bears the terminal carboxyl group. Figure 13-35 shows the two dipeptides that can be made from glycine and serine. Although they contain the same amino acids, they are different molecules whose chemical and physical properties differ. Example shows how to draw the primary stmcture of a peptide. 

There are many ligands and group-specific reagents that have been demonstrated to alter the properties of H,K-ATPase, and which are not clinically useful. For example, there is a variety of chemicals that have been used in studies on structure-function relations of H,K-ATPase and that inhibit the enzyme in vitro by modification of its amino [49,67,158], sulfhydryl [95,165,166] or carboxyl groups [140]. 

Fig. 6.2. Chemical structures of fluorescein and some commonly used derivatives. The carboxylic acid groups are used for forming conjugates with other molecules.

Several studies have dealt with the problem of discriminating between mastic and dammar, and three marker compounds of mastic have been identified moronic, masticadienonic and acetyl masticadienolic acids [42], The chemical structure of (iso)masticadienonic acid and 3-0-acetyl-3-epi(iso)masticadienonic acid is characterized by a side chain, as for dammarane molecules, but with a carboxylic acid end group (Table 12.1). Under pyrolysis conditions this side chain is susceptible to cleavage as demonstrated by the presence, among the pyrolysis products of mastic, of 2-methyl-pent-2,4-dienoic acid, that perfectly matches with the chemical structure of the side chain end. In addition 3-(9-acetyl-3-epi-(iso)masticadienolic acid also loses the acetyl group and, in contrast to masticadienonic acid, is not detected at all. 

The chemical structures of polymers will be changed by the evolution of small molecule products. The formation of C=C bonds in the polymer backbone by loss of H2 from hydrocarbon polymers, or HC1 from PVC, is well established and leads to colouration of the polymer, especially with increasing sequence lengths of conjugated unsaturation. Carboxylic acid groups are... 

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