Studies using Ascorbic Acid

STUDIES USING ASCORBIC ACID 18.13.1 Stability of ascorbic acid solutions... 

Levin ED, Behm F, Carnahan E, LeClair R, Shipley R, Rose JE (1993) Clinical trials using ascorbic acid aerosol to aid smoking cessation. Drug Alcohol Depend 33 211-223 Lorillard (1973) Research 1-3-5 year projection of major projects, 02 Nov 1973, Bates 83250679-83250693, http //tobaccodocuments,org/lor/83250679-0693,html Madyastha KM, Siivatsan V (1988) Studies on the metabolism of 1-menthol in rats. Drug Metab Dispos 16 765-772... 

A number of enzymes have been characterized that catalyze reactions involving DHA. In addition, other aspects of DHA biochemistry can be deduced from metabolic studies of ascorbic acid. Experiments demonstrating the biological oxidation of AA and reduction of DHA were first made in 1928 (10) and during the next decade several groups studied these reactions. By 1941 Crook (62) was able to separate the ascorbic acid oxidase and DHA reductase activities and to show that glutathione was used in the reductase reaction. 

Similar reports have appeared in the technology of polymerizing acrylic monomers such as acrylonitrile (753-759) or acrylamide (760-763), Korolev et al. (764) have used ascorbic acid as a reducing agent in the mixture to increase the polymerization rate. The kinetics of polymerization in the presence of oxygen has been studied in systems containing ascorbic acid (765), Recent patents (766,767) have been issued with ascorbic acid in the dispersion of acrylic aqueous resins. 

Orr (43) used dimethyl sulfoxide as a free radical sink to inhibit the effect of Cu and ascorbic acid on catalase and 8-glucuronidase as well as the degradation of hyaluronic acid. The formation of a radical from ascorbic acid and Cu in water was detected by EPR (44). Based on an EPR spectroscopic study of ascorbic acid during oxidation of methyl-arachidonate-enriched liposomes, ascorbic acid may be important in preventing free radical damage in the central nervous system (45). 

The field studies indicated that all of the dechlorination chemicals were effective in neutralizing free and combined chlorine to below 0.1 mg/L. In most cases the stoichiometric amount of dechlorination chemicals removed more than 90% of the chlorine. However, the reaction rates and the water quality impacts varied with the type, amount, and form of the chemicals used. In general, the rates of dechlorination using sodium/calcium thiosulfate were slower than those using the other chemicals. However, studies by others indicated that dechlorination of wastewater samples using sodium thiosulfate was more rapid that using ascorbic acid (24). 

Increased effectiveness of organic acids may be achieved when used in lower concentrations, but in combination with additional inhibitors. For example, combining nisin with reduced organic acid concentrations may decrease potential flavor flaws in meat products (Samelis et al., 2005). Citric and ascorbic acids, in combination, are effective in inhibiting growth and toxin production of C. botulinum type B in vacuum-packed foodstuffs (Barbosa-Canovas et al., 2003 Samelis et al., 2005). In other studies, a combination of equal amounts of ascorbic acid and citric acid did not have additional benefits, compared with using ascorbic acid alone (Mancini et al., 2007). 

Sakurai and coworkers developed a novel pharmacokinetic method for the real-time tracking of the blood distribution of paramagnetic species through EPR. Termed blood-circulation monitoring EPR (BCM-EPR), the method was initially developed for study of ascorbic acid radicals [89] and chromium carcinogens [90]. It has proven, however, to be useful for the study of the distribution and elimination of vanadium(rV) species from the bloodstream of live animals following i.v. injection [83]. 

Ascorbic acid also forms soluble chelate complexes with iron (142—145). It seems ascorbic acid has no effect on high iron levels found in people with iron overload (146). It is well known, in fact, that ascorbic acid in the presence of iron can exhibit either prooxidant or antioxidant effects, depending on the concentration used (147). The combination of citric acid and ascorbic acid may enhance the iron load in aging populations. Iron overload may be the most important common etiologic factor in the development of heart disease, cancer, diabetes, osteoporosis, arthritis, and possibly other disorders. The synergistic combination of citric acid and ascorbic acid needs further study, particularly because the iron overload produced may be correctable (147). 

Solid-phase basic dyes ai e also used for the study of their interaction with medical products nicotinic, aminocaproic, acetylsalicylic and ascorbic acids and for the establishing of the new methods of SPS determination in known medical products. 

A. Pentoses.—t-Ascorbic acid 2- and 3-phosphates, together with their phosphate esters, give a characteristic colour with ferric chloride and this colour reaction has been used in a study of the hydrolysis of L-ascorbic acid 3-phosphate (58). The acid-catalysed, pseudo-firsi-order hydrolysis proceeds with P—O bond fission, as does the bromine oxidation of its phenyl ester. Both of these observations can be rationalized if (58) is... 

N-Nitrosamine inhibitors Ascorbic acid and its derivatives, andDC-tocopherol have been widely studied as inhibitors of the N-nitrosation reactions in bacon (33,48-51). The effect of sodium ascorbate on NPYR formation is variable, complete inhibition is not achieved, and although results indicate lower levels of NPYR in ascorbate-containing bacon, there are examples of increases (52). Recently, it has been concluded (29) that the essential but probably not the only requirement for a potential anti-N-nitrosamine agent in bacon are its (a) ability to trap NO radicals, (b) lipophilicity, (c) non-steam volatility and (d) heat stability up to 174 C (maximum frying temperature). These appear important requirements since the precursors of NPYR have been associated with bacon adipose tissue (15). Consequently, ascorbyl paImitate has been found to be more effective than sodium ascorbate in reducing N-nitrosamine formation (33), while long chain acetals of ascorbic acid, when used at the 500 and lOOO mg/kg levels have been reported to be capable of reducing the formation of N-nitrosamines in the cooked-out fat by 92 and 97%, respectively (49). 

Since many essential nutrients (e.g., monosaccharides, amino acids, and vitamins) are water-soluble, they have low oil/water partition coefficients, which would suggest poor absorption from the GIT. However, to ensure adequate uptake of these materials from food, the intestine has developed specialized absorption mechanisms that depend on membrane participation and require the compound to have a specific chemical structure. Since these processes are discussed in Chapter 4, we will not dwell on them here. This carrier transport mechanism is illustrated in Fig. 9C. Absorption by a specialized carrier mechanism (from the rat intestine) has been shown to exist for several agents used in cancer chemotherapy (5-fluorouracil and 5-bromouracil) [37,38], which may be considered false nutrients in that their chemical structures are very similar to essential nutrients for which the intestine has a specialized transport mechanism. It would be instructive to examine some studies concerned with riboflavin and ascorbic acid absorption in humans, as these illustrate how one may treat urine data to explore the mechanism of absorption. If a compound is... 

Figure 15.14 illustrates a typical voltammetric result for the determination of dopamine in the presence of ascorbic acid with a CNT-modified electrode. The selective voltammetric detection of uric acid [82] or norepinephrine [83] in the presence of ascorbic acid has been demonstrated with a (3-cyclodextrin-modified electrodes incorporating CNTs. Ye et al. [84] have studied the electrocatalytic oxidation of uric acid and ascorbic acid at a well-aligned CNT electrode, which can be used for the selective determination of uric acid in the presence of ascorbic acid. The simultaneous determination of dopamine and serotonin on a CNT-modified GC electrode has also been described [85],... 

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