Small organic acids

Scheme 2.1. Lewis-acid catalysed organic reactions that are promoted by small amounts ofwater in organic solvents.

Sulphuric acid catalysed nitration in concentrated nitric acid, but the effect was much weaker than that observed in nitration in organic solvents ( 3.2.3). The concentration of sulphuric acid required to double the rate of nitration of i-nitroanthraquinone was about 0-23 mol 1, whereas typically, a concentration of io mol 1 will effect the same change in nitration in mixtures of nitric acid and organic solvents. The acceleration in the rate was not linear in the concentration of catalyst, for the sensitivity to catalysis was small with low concentrations of sulphuric acid, but increased with the progressive addition of more catalyst and eventually approached a linear acceleration. 

In mixtures of nitric acid and organic solvents, nitrous acid exists mainly as un-ionised dinitrogen tetroxide. The heterolysis of dinitrogen tetroxide is thus complete in sulphuric acid ( 4 i), considerable in nitric acid, and very small in organic solvents. 

Molecular Interactions. Various polysaccharides readily associate with other substances, including bile acids and cholesterol, proteins, small organic molecules, inorganic salts, and ions. Anionic polysaccharides form salts and chelate complexes with cations some neutral polysaccharides form complexes with inorganic salts and some interactions are stmcture specific. Starch amylose and the linear branches of amylopectin form inclusion complexes with several classes of polar molecules, including fatty acids, glycerides, alcohols, esters, ketones, and iodine/iodide. The absorbed molecule occupies the cavity of the amylose helix, which has the capacity to expand somewhat to accommodate larger molecules. The starch—Hpid complex is important in food systems. Whether similar inclusion complexes can form with any of the dietary fiber components is not known. 

In 1932 Krebs was studying the rates of oxidation of small organic acids by kidney and liver tissue. Only a few substances were active in these experiments —notably succinate, fumarate, acetate, malate, and citrate (Figure 20.2). Later it was found that oxaloacetate could be made from pyruvate in such tissues, and that it could be further oxidized like the other dicarboxylic acids. 

Interest in fuel cells has stimulated many investigations into the detailed mechanisms of the electrocatalytic oxidation of small organic molecules such as methanol, formaldehyde, formic acid, etc. The major problem using platinum group metals is the rapid build up of a strongly adsorbed species which efficiently poisons the electrodes. 

Supramolecular Entities of Trinuclear Cold(l) Complexes Sandwiching Small Organic Acids... 

Rawashdeh-Omary, M.A., Omary, M.A., Fackler, J.P. Jr, Galassi, R., Pietroni, B.R. and Burini, A. (2001) Chemistry and optoelectronic properties of stacked supramolecular entities of trinuclear Gold(I) complexes sandwiching small organic acids. Journal of the American Chemical Society, 123, 9689. 

CE is widely used for separation and quantification of organic acids (Stover, 1997). Many CE studies were performed to quantify organic acids in some food matrices (Erazier, 2001 Galli et al., 2003 Klampfl et al., 2000 Lindeberg, 1996). Many small organic acids can be well separated with CE (Boden et al., 2000 Mato et al., 2006a,b Navarrete et al., 2005). Those acids include acetic, citric, fumaric, lactic, maleic, malic, oxalic, pyruvic, succinic, and gluconic acids which can be separated by CE in a short time. 

If the analyte contains either an acidic or a basic functionality, adjusting the pH of the extraction solvent to make the analyte either ionic or nonionic may be advantageous. To make an analyte that contains an acidic or basic functionality nonionic for extraction into a nonpolar solvent, a small amount (5% or less) of an organic acid (such as acetic acid or trifluoroacetic acid) or organic base (triethylamine) along with methanol (about 10%) can be added to diethyl ether or ethyl acetate. Conversely, buffered solutions can be used to control the pH precisely in such a way as to control the charge on an analyte and thus improve its extraction efficiency into polar solvents. 

Recent developments in drug discovery and drug development spurred the need for novel analytical techniques and methods. In the last decade, the biopharmaceutical industry set the pace for this demand. The nature of the industry required that novel techniques should be simple, easily applicable, and of high resolution and sensitivity. It was also required that the techniques give information about the composition, structure, purity, and stability of drug candidates. Biopharmaceuticals represent a wide variety of chemically different compounds, including small organic molecules, nucleic acids and their derivatives, and peptides and proteins. 

He Y. and Lee H.K., Large-volume sample stacking in acidic buffer for analysis of small organic and inorganic anions by capillary electrophoresis, Anal. Chem. 71, 995, 1999. 

In addition to small organic molecules or metal ions, proteins may have other components tightly associated with them. Nucleoproteins, for instance, contain noncovalently bound DNA or RNA, as in some of the structural proteins of viruses. Lipoproteins contain associated lipids or fatty acids and may also carry cholesterol, as in the high-density and low-density lipoproteins in serum. 

One of the important purposes for the study of the direct electron transfer of protein is to construct the mediator-free protein-based biosensors. These biosensors can determine many small molecules like H202, 02, NO, nitrite, small organic peroxide, and so on. They also can determine glucose, alcohol, and amino acids by... 

Lewis add catalysis has been and continues to be of great interest in organic synthesis.111 While various kinds of Lewis add-promoted reactions have been developed and many have been applied in industry, these reactions must generally be carried out under stridly anhydrous conditions. The presence of even a small amount of water stops the reaction because most conventional Lewis adds read immediately with water, rather than with the substrates, and decompose. This destrudive reaction has restrided the use of Lewis acids in organic synthesis. From a viewpoint of today s environmental consciousness, however, it is desirable to use water instead of organic solvents as a reaction solvent.1231... 

Uptake of small organic metal complexes over transport systems of organic metabolites may be possible, for example, of small organic acids like citrate or amino acids. However, only few examples of such processes have been studied so far. Increased uptake of cadmium by an alga has been observed in the presence of citrate and has been attributed to accidental transport of the metal-citrate complex over a citrate transporter [212]. Transport systems of inorganic anions may also play a role in metal transport. Silver uptake by algae was enhanced in the presence of thiosulfate. In this case, the silver thiosulfate complex was transported over a sulfate uptake system [213]. It remains to be demonstrated how widespread these processes may be for metal uptake in the aquatic environment [12]. 

---