Vitamin chemical modification

Fumed silica A-200 (Pilot plant at the Institute of Surface Chemistry, Kalush, Ukraine specific surface area Ascorbic acid (vitamin C) and all-rac-a-Tocopheryl acetate (vitamin E acetate) were used as adsorbates. Folin-Ciocalteu s phenol reagent (Merck) was used to measure the total polyphenolic index. Silica samples with different degree of surface silylation were obtained using gas-phase chemical modification of highly disperse silica (A-200) surface by trimethylchlorosilane.6... 

Hydroxyproline and hydroxylysine occur most noticeably in collagen. These are formed by modification of proline and lysine residues by specific enzymes after synthesis of the collagen chains. It is interesting to note that proly/hydroxylase, which hydroxylates proline, requires ascorbate (vitamin C) as a coreactant. Other chemical modifications known to occur commonly are the attachment of sugars (glycosylation) to asparagine, serine, and threonine residues and the phosphorylation of serine. Chemical modifications are also associated with the transport of proteins out of the cells in which they are synthesized. 

Seetharam B. Receptor-mediated endocytosis of cobalamin (vitamin B12). Annu. Rev. Nutr. 1999 19 173-195. Boonyarattanakalin S, Martin SE, Sun Q, Peterson BR. A Synthetic Mimic of Human Fc Receptors Defined Chemical Modification of Cell Surfaces Enables Efficient Endocytic Uptake of Human Immunoglobulin-G. J. Am. Chem. Soc. 2006 128 11463-11470. 

The water-soluble vitamins are organic substances needed in small amoimts in the diet because they are required for a variety of essential enz)unatic reactions in cells. The water-soluble vitamins are components of many coenz)unes that are required by enz)unes to carry out a variety of important biochemical reactions. Once ingested, these vitamins undergo chemical modifications that convert them into coenz)unes. However, it serves no purpose to consume vast quantities of water-soluble vitamins by taking enormous doses of vitamin tablets because they are not stored in the body. Because they are soluble in water, the excess is simply excreted in the urine. Table 20.1 lists the coenz)unes derived from the water-soluble vitamins and their chemical functions. Table F.l provides the major nutritional sources of the water-soluble vitamins and the clinical conditions that result from their deficiency. 

All photosynthetic tissues, as well as some nonphotosynthetic tissue and Protista, contain carotenoids. It is said that over 400 carotenoids have been identified, but that most are xanthophylls. As noted above, xanthophylls are carotenoid derivatives with oxygen substitutions in the ring or side chain and have reduced or no vitamin A activity (Simpson and Chichester, 1981). Vitamin A activity for vertebrates requires that a carotenoid have at least the unaltered p-ionone ring with an attached polyene side chain containing 11 carbon atoms. Although some compounds with chemical modifications in the P-ionone ring still... 

A form of ascorbic acid (vitamin C C, H,o O,) which has one minor chemical modification. It does not act like vitamin C. Rather, it is an antagonist to the vitamin and can be used experimentally to produce scurvy in animals. 

Most current industrial vitamin C production is based on the efficient second synthesis developed by Reichstein and Grbssner in 1934 (15). Various attempts to develop a superior, more economical L-ascorbic acid process have been reported since 1934. These approaches, which have met with htde success, ate summarized in Crawford s comprehensive review (46). Currently, all chemical syntheses of vitamin C involve modifications of the Reichstein and Grbssner approach (Fig. 5). In the first step, D-glucose (4) is catalytically (Ni-catalyst) hydrogenated to D-sorbitol (20). Oxidation to L-sotbose (21) occurs microhiologicaRy with The isolated L-sotbose is reacted with acetone and sulfuric acid to yield 2,3 4,6 diacetone-L-sorbose,... 

Reichsteia and Grbssner s second L-ascorbic acid synthesis became the basis for the iadustrial vitamin C production. Many chemical and technical modifications have improved the efficiency of each step, enabling this multistep synthesis to remain the principal, most economical process up to the present (ca 1997) (46). L-Ascorbic acid is produced ia large, iategrated, automated faciUties, involving both continuous and batch operations. The process steps are outlined ia Figure 7. Procedures require ca 1.7-kg L-sorbose/kg of L-ascorbic acid with ca 66% overall yield ia 1977 (55). Siace 1977, further continuous improvement of each vitamin C production step has taken place. Today s overall ascorbic acid yield from L-sorbose is ca 75%. In the mid-1930s, the overall yield from L-sorbose was ca 30%. 

All of the studies were conducted with weanling, male albino rats of the Sprague-Dawley strain (Holtzman company). The basal diet used for these studies consisted of casein, starch, vegetable oil, vitamin and mineral mixtures, and cellulose. The Wesson Modification of the Osborne-Mendel mineral mixture was used in all studies. This mineral mixture contained no zinc, but it was adequate in the other minerals required by the rat. Most of the non-zinc-supplemented diets used in the various experiments contained approximately 7 ppm zinc. The level of mineral mixture used in the basal diets was 4%, and based on the chemical composition of the mixture, the basal diets contained approximately 0.57% calcium and 0.41% phosphorus ... 

Little data is available on the interaction of protein modification for improved functionality and vitamin bioavailability from modified food-stuffs. Some water-soluble and fat-soluble vitamins are protein-bound in their transport, storage and/or active forms. Therefore, methods used to cause dramatic alteration of protein conformation or chemical structure can be assumed to alter some vitamins as well. 

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