Carboxylic functional groups

Because lactic acid has both hydroxyl and carboxyl functional groups, it undergoes iatramolecular or self-esterificatioa and forms linear polyesters, lactoyUactic acid (4) and higher poly(lactic acid)s, or the cycUc dimer 3,6-dimethyl-/)-dioxane-2,5-dione [95-96-5] (dilactide) (5). Whereas the linear polyesters, lactoyUactic acid and poly(lactic acid)s, are produced under typical condensation conditions such as by removal of water ia the preseace of acidic catalysts, the formation of dilactide with high yield and selectivity requires the use of special catalysts which are primarily weakly basic. The use of tin and ziac oxides and organostaimates and -titanates has been reported (6,21,22). 

If the carboxylic acid has two carboxyl functional groups (a dicarboxylic acid) and if the alcohol has two hydroxyl functional groups (a diol), a polyester will result nHOOC—R—COOH + nHO—R —OH —> +OOC—R—COO—R +n + nH20. 

As an example, bulk modification by the organic reaction of unsaturated PHA with sodium permanganate resulted in the incorporation of dihydroxyl or carboxyl functional groups [106]. Due to the steric hindrance of the isotactic pendant chains, complete conversion could not be obtained. However, the solubility of the modified polymers was altered in such a way that they were now completely soluble in acetone/water and water/bicarbonate mixtures, respectively [106]. Solubility can play an important role in certain applications, for instance in hydrogels. Considering the biosynthetic pathways, the dihydroxyl or carboxyl functional groups are very difficult to incorporate by microbial synthesis and therefore organic chemistry actually has an added value to biochemistry. 

In all cases, in order to make polar molecules volatile so that they can be separated by GC, derivatizing reactions on polar functional groups are usually performed. Carboxylic functional groups can be transformed into the corresponding 2-propyl esters [35], methyl esters [18], ethylchloroformate derivatives [36], f-butyldimethylsilyl esters [9] and tri-methylsilyl ester derivatives [3,12,30],... 

A protocol for the use of carbohydrazide in the modification of aldehyde or carboxylate functional groups can be found in Chapter 1, Section 4.5. 

Fowle et al. (2000) have measured the sorption by a soil bacterium (B. subtilis) of uranyl in 0.1 M NaC104 at 25°C as a function of pH, time, and solid solute ratio, using a batch technique. The stoichiometiy and thermodynamic stability of the important uranyl-surface complexes indicated that uranyl formed two different surface complexes, one involving neutral phosphate functional groups, and another with deprotonated carboxyl functional groups, on the bacterial cell wall ... 

Triacylglycerols, commonly refered to as fats and oils, consist of three fatty acids linked to a molecule of glycerol, a three-carbon alcohol. Fatty acids are long-carbon-chain molecules, each with a single carboxyl functional group. Common examples are stearic acid and palmitic acid, shown in Figure 16.3. 

The improvement in liquefaction behavior appears to be due to loss of the carboxyl functional groups usualfy responsible for crosslinking without the associated crosslink formation. 

Carboxylic acids are organic acids that contain the carboxyl functional group, —COOH—. The carboxyl group is a combination of the carbonyl group and the hydroxyl group ... 

Carbonyl a carbon atom and oxygen atom joined by a double bond C=0, present in aldehydes and ketones Carboxyl Functional Group a carbonyl with a hydroxyl (-OH) attached to the carbon atom... 

Indeed, increased water concentration affects transesterification more than it affects esterification." This is due to the presence of polar carboxylic functional groups in FFAs that allows FFAs to more easily interact with polar compounds, facilitating the alcoholysis reaction. 

A more challenging example of an unsaturated nitrile reduction that lacks the carboxylate functional group is the asymmetric reduction of the nitrile shown in Figure 1.15. The product was required in the synthesis of chiral... 

Sulfonic and phosphonic acids contain sulfur and phosphorus in their structures, substituting for carbon in the carboxyl function group. They are fairly abundant, but have not been studied extensively. 

Figure 10 Possible anchoring modes for a sensitizer (22) using the carboxylate functional group.

Humic materials absorbed in the UV-vis spectral region because of an aromatic structure containing phenolic and carboxylic functional groups. 

Molecules modified with succinic anhydride to create terminal carboxylate functional groups may be further conjugated to amine-containing molecules by use of amide bond-forming reagents such as carbodiimides (Chapter 3, Section 1). 

The relative reactivity of a-haloacetates toward protein functionalities is sulfhydryl > imidazolyl > thioether > amine. Among halo derivatives the relative reactivity is I > Br > Cl > F, with fluorine being almost unreactive. The a-haloacetamides have the same trend of relative reactivities, but will obviously not create a carboxylate functional group. The acetamide derivatives typically are used only as blocking reagents. 

Chemical groups that specifically react with carboxylic acids are limited in variety. In aqueous solutions, the carboxylate functional group displays rather low nucleo-philicity. For this reason, it is unreactive with the great majority of bioconjugate reagents that couple through a nucleophilic addition process. 

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