Organic acids citric acid transformation

The osmium-catalyzed dihydroxylation reaction, that is, the addition of osmium tetr-oxide to alkenes producing a vicinal diol, is one of the most selective and reliable of organic transformations. Work by Sharpless, Fokin, and coworkers has revealed that electron-deficient alkenes can be converted to the corresponding diols much more efficiently when the pH of the reaction medium is maintained on the acidic side [199]. One of the most useful additives in this context has proved to be citric acid (2 equivalents), which, in combination with 4-methylmorpholine N-oxide (NMO) as a reoxidant for osmium(VI) and potassium osmate [K20s02(0H)4] (0.2 mol%) as a stable, non-volatile substitute for osmium tetroxide, allows the conversion of many olefinic substrates to their corresponding diols at ambient temperatures. In specific cases, such as with extremely electron-deficient alkenes (Scheme 6.96), the reaction has to be carried out under microwave irradiation at 120 °C, to produce in the illustrated case an 81% isolated yield of the pure diol [199]. 

The citric acid cycle is the central metabolic hub of the cell. It is the gateway to the aerobic metabolism of any molecule that can be transformed into an acetyl group or dicarboxylic acid. The cycle is also an important source of precursors, not only for the storage forms of fuels, but also for the building blocks of many other molecules such as amino acids, nucleotide bases, cholesterol, and porphyrin (the organic component of heme). 

Pitta-Alvarez, S. 1. and Giulietti, A. M. (1999) Influence of chitosan, acetic acid and citric acid on growth and tropane alkaloid production in transformed roots of Brugmansia Candida. Effect of medium pH and growth phase. Plant Cell Tissue and Organ Culture. 59, 31-38. 

Occasionally the synthesis of a microbial product, for example that of ethanol from glucose, is catalysed by non-viable cells (section 6.2.1.1). Then the process is properly catalytic because the Saccharomyces cerevisiae cells do not change, for a time at least. However there are some industrially important reactions in which micro-organisms are first grown to a high biomass and are then added to a substrate which is almost quantitatively converted to a product. These are effectively catalytic processes in which one or a few enzymes in the organism transform an added substrate into a useful product. These transformations are divorced from cell growth, in contrast to syntheses such as those in which carbohydrates are converted into citric acid or complex feedstocks into secondary metabolites. 

A SIA system with attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) detection has been studied for sugar and organic acid analysis of Belgian tomato samples (Vermeir et al., 2009). Prediction models for D-glucose, D-fructose, citric acid, and L-glutamic acid concentrations in tomato samples were successful. 

Fig. 10.7 Effects of various organic acids on growth of A. aceti strains. (Figure fiom Nakano et al. 2006) The A. aceti transformants were cultured at 30 °C in the presence of acetic acid (A), lactic acid, citric acid, formic acid, and propionic acid (B) in YPG medium for 120 h. The growth of the strains was followed by measuring optical density at 660 nm (OD eo)- Solid circles wild-type strain carrying the vector, open circles transformant harboring multiple copies of the aconitase gene...

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