Aliphatic hydroxylic acids

MaX, Jian R, Chang PR, Yu J (2008) Fabrication and characterization of citric acid-modified starch nanoparticles/plasized-starch composites. Biomacromol 9 3314-3320 Molnar-Perl I, Morvai M (1987) Esterification of aliphatic hydroxyl acids to n-propyl esters in aqueous solutions for their gas chromatographic analysis. Chromatographia 23 760-763 Bouchard EF, Meritt EG (1984) Citric acid. In Kirk-Othmer Encyclopedia of Chemical Technology, 3rd edn, vol 6. Wiley-Interscience, New York, pp 150-176 Prokop M, Milewska MJ (2009) An improved synthesis of trisodium -homocitrate from citric acid. Polish J Chem 83 1317-1322... 

Many of the aliphatic hydroxylic acids ionize in a > remote part of the pK scale where accurate result have not long been accessible. 

The epoxidation is generally conducted in two steps (/) the polyol is added to epichlorohydrin in the presence of a Lewis acid catalyst (stannic chloride, boron triduoride) to produce the chlorohydrin intermediate, and (2) the intermediate is dehydrohalogenated with sodium hydroxide to yield the aliphatic glycidyl ether. A prominent side-reaction is the conversion of aliphatic hydroxyl groups (formed by the initial reaction) into chloromethyl groups by epichlorohydrin. The aliphatic glycidyl ether resins are used as flexibilizers for aromatic resins and as reactive diluents to reduce viscosities in resin systems. 

Serine (Ser or S) ((S)-2-amino-3-hydroxypropanoic acid) is a polar, neutral, uncharged amino acid with the formula H00CCH(NH2)CH20H. It has an aliphatic hydroxyl side chain and can be seen as a hydroxylated version of Ala. Ser participates in the biosynthesis of purines and pyrimidines and is also the precursor to several amino acids including Gly, Cys, and Trp (in bacteria). In addition, it is the precursor to numerous other metabolites, including sphingolipids and is present in enzymes such as a-chymotrypsin. Ser, Asn, and aspartate disrupt a helices. 

Threonine (Thr or T) ((2S,31( )-2-amino-3-hydroxybutanoic acid) has an aliphatic hydroxyl side chain and is classified as a polar, uncharged amino acid with the formula HOOCCH(NH2)CHOHCH3. Together with Ser and Tyr, Thr is one of the three proteinogenic amino acids bearing an alcohol group. Thr can be seen as a hydroxylated version of Val. With two chiral centers, Thr can exist in four possible stereoisomers, or two possible diastereomers of L-Thr. However, the name L-Thr is used for one single enantiomer, (2S, 3if)-2-amino-3-hydroxybutanoic acid. The second diastereomer (2S,3S), which is rarely present in nature, is called L- //o-Thr. 

You can use analogies to put adipic acid in its right place. Acetic acid is the most important aliphatic monocarboxylic acid adipic is the most important aliphatic dicarboxylic acid. (You remember, of course, that carboxylic is the contraction for carbonyl and hydroxyl, -C-O and -OH, or together, -COOH. Right ) Also, adipic acid is to Nylon 66 what cumene is to phenol. About 95% of the adipic acid ends up as Nylon 66, which is used for tire cord, fibers, and engineering plastics. 

Composition. Shellac is primarily a mixture of aliphatic polyhydroxy acids in the form of lactones and esters. It has an acid number of ca 70, a saponification number of ca 230, a hydroxyl number of ca 260, and an iodine number of ca 15. Its average molecular weight is ca 1000. Shellac is a complex mixture, but some of its constituents have been identified. Aleuritic acid, an optically inactive 9,10,16-trihydroxypalmitic acid, has been isolated by saponification. Related carboxylic acids such as 16-hydroxy- and 9,10-dihydroxypalmitic acids, also have been identified after saponification. These acids may not be primary products of hydrolysis, but may have been produced by the treatment. Studies show that shellac contains carboxylic acids with long methylene chains, unsaturated esters, probably an aliphatic aldehyde, a saturated aliphatic ester, a primary alcohol, and isolated or unconjugated double bonds. 

Other than water, protein is the major constituent of meat averaging nearly 21% in heef or chicken meat, with fat varying fiom 4.6 to 11.0% in beef and fiom 2.7 to 12.6% in chickoi. The principal radiolytic reactions of aqueous solutions of aliphatic amino acids are reductive deamination and decarboxylation. Alanine yields NH3, pyruvic add, acetaldehyde, propionic acid, CO2, H2, and ethylamine (6). Sulfur-containing amino adds are espedally sensitive to ionizing radiation. Cysteine can be oxidized to cystine by the hydroxyl radical or it can react with the hydrated electron and produce... 

Aliphatic hydroxyl groups cannot normally be selectively modified except in certain special cases such as the serine proteinases. In anhydrous formic acid, the A,O-acyl migration that occurs in strong sulfuric or phosphoric acid apparently does not occur. Instead there is formylation of the serine and threonine residues (208). Enzymically inactive aggregates are produced, but the reaction is reversed in aqueous solution at neutral pH and the activity returns. Josefsson reported the introduction of 29 formyl groups in RNase (209) as compared to the total of 25 Ser and Thr residues. This identification of reaction sites is not clear, however, since the number of formyl groups introduced into lysozyme far exceeded the Ser-Thr total. 

Concepts of the compositions of coals influenced many in considerations of the structures of soil HS. For example, the proposal of Fuchs (1931) for structures of coal HAs (Figure 1.1) influenced soil humic scientists. The proposed structure is composed of heterocyclic aliphatic functionalities, some phenol-derived units, and considerable amounts of carboxylic and hydroxyl acidic functionalities. It may be possible that such structures could arise under conditions of elevated temperature and pressure, with oxidation taking place subsequently. Whereas such conditions might prevail during the synthesis of coals, they would be most unlikely to take place during the transformations of organic materials in the soil environment. 

One feature of the hydroxypyranones that presented a major challenge was the poor translation of high intrinsic inhibitory potency against the enzyme into antiviral activity in cell culture (Prasad et al., 1996). The acidic character of the enolic hydroxy group (pAa 4.2-6.5) as compared with aliphatic hydroxyl groups found in other classes of inhibitors did not appear to offer an explanation in as much as inhibitors of the pyranone class penetrate cells efficiently (Vara Prasad et al, 1995). Empirically,... 

Immobilization of enzymes. Enzymes consist of amino acids which contain reactive groups such as amino(lysine, c-terminus), thiol (cysteine), carbonyl (aspartate, glutamate and c-terminus), aromatic hydroxyl (tyrosine) and aliphatic hydroxyl (serine and threonine). Chemical, ionic or chelation reactions with such groups can enable us to attach the amino acids and hence proteins to insoluble, inert supports. Immobilization is one of the best ways of stabilizing enzymes. There is a vast literature on this subject and the reader is directed to Barker (9) and Goughian et al (10) for further reading on specific systems, techniques and applications of immobilization. 

In relation to the aromas produced on exposure to microwave radiation, Yaylayan et al.2S1 examined many combinations of sugars and amino acids, grouping the latter into aliphatic, hydroxylated, aromatic, secondary, basic, amide, acid, and sulfur-containing ones. The odours observed were grouped into eight and they have been assigned to the above groups, as far as possible, below ... 

Fig ( 18 ) A series of reactions are carried out for the conversion of dehydroabietic acid to ketone (155) to hydroxymethyiation, protection of aliphatic hydroxyl group, addition of an -benzyloxymethyl group and acid treatment provides (156) which is con verted to (158). The butenolide function is constructed by successive oxidation and debenzylation to yield (159) which is converted to triptolide (149) by conventional methods. 

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