Hydrophobic vitamin

Natural antioxidants may be classified according to their nutritive value or according to their solubility. The hydrophobic vitamin E and the hydrophilic vitamin C are thus important both as nutrients and as antioxidants. The nonnutritive antioxidants may similarly be divided into lipid-soluble and water-soluble antioxidants, as shown in Fig. 16.3, which will also form the basis for a discussion of exploitation of combinations of anhoxidants in order to improve protective effects. 

The electroreductive dehalogenation of a-haloacetic acids has been achieved with cobalamin [387]. The hydrophobic vitamin B12 Co complex immobilized on a glassy carbon electrode (252) may catalyze the electrochemical carbon-skeleton rearrangements of... 

In this paper, we report the development of ISEs that have been designed by using molecular recognition principles. Specific examples include the development of polymer membrane anion-selective electrodes based on hydrophobic vitamin B12 derivatives and a cobalt porphyrin. The selectivity patterns observed with these electrodes can be related to differences in the structure of the various ionophores, and to properties of the polymer film. 

Anion-Selective Electrodes Based on Hydrophobic Vitamin B12 Derivatives... 

ISE Based on a Hydrophobic Cobalamin. Cobalamin 4 (Figure 2) is a hydrophobic vitamin B12 derivative that retains a proximal base (an imidazole ring), which provides the molecule with a resemblance to the original vitamin (Figure 1). The selectivity pattern of electrodes prepared with ionophore 4 at pH 5.5 is shown in Figure 4. These electrodes exhibit an anion selectivity pattern that differs from that of the Hofmeister series and from that of the previously reported cobyric acid derivatives (see section above). Indeed, electrodes based on 4 are selective for... 

In summary, it has been demonstrated that ISEs can be designed by employing molecular recognition principles. In particular, the feasibility of using hydrophobic vitamin B12 derivatives and electropolymerized porphyrin films in the development of polymer membrane anion-selective electrodes has been demonstrated. The studies indicated that the changes in the selectivity of these ISEs can be explained by the difference in structure of the ionophores. In addition, it was shown that by electropolymerization of a cobalt porphyrin, anion-selective electrodes can be prepared that have extended lifetimes compared with PVC-based ISEs, which use a similar compound as the ionophore. 

Fig. 4. Redox cooperation of hydrophobic vitaminE and hydrophilic vitaminC. Ascorbate (AH-) acts as an electron-transfer agent at the water/membrane interface. Note that one molecule of lipid hydroperoxide LOOH is produced for each termination reaction by vitamin E. See the discussion in...

On the other hand, Hisaeda and coworkers [504] found that the vitamin Bi2-mediated electroreductive optical resolution was accompanied by rearrangement Electroreduction of racemic 3-bromo-2-methoxy-2-phenylpropionate using a hydrophobic vitamin Bi2 mediator afforded ethyl (S)-2-methoxy-2-phenylpropionate in 55% ee, while a novel hydrophobic vitamin Bj2 modified by introducing a 1,3-phenylene diacetyl moiety into the peripheral site around the corrin s B ring, a so-called strapped hydrophobic vitamin B12, provided the corresponding R-enantiomer in 26% ee. 

A recently proposed method (314) for the separation of fat-soluble vitamins by electrokinetic chromatography was further developed (315). The separation medium consisted of acetonitrile water (80 20 v/v) and contained tetradecylam-monium bromide as a pseudostationary phase. The high acetonitrile content was necessary to keep the hydrophobic vitamins in solution during electrophoresis. With the cathode placed at the capillary outlet, the fat-soluble vitamins were separated based on different hydrophobic interactions with the pseudo-stationary phase. The vitamins migrated in order of decreasing hydrophobicity prior to the electroosmotic flow. 

A hydrophobic vitamin B12 derivative (111) is synthesized from monocyano-cobyrinic acid hexamethyl ester (110) using DEPC.43 The cyanide ion from DEPC is trapped by the cobalt complex as an axial ligand.43 In this condensation reaction DEPC is a superior coupling agent compared to DCC 43... 

Fig. 3 An example of artificial holoenzyme formed with the octopus cyclophane (6) and the hydrophobic vitamin derivative (7).

Preparation and characterization of liposomes formed with natural phospholipids were well established. However, in using liposomes for simulation of enzymatic functions, especially in acid-base catalysis, difficulties would be encountered due to their chemicai and morphological instabilities. Thus, bilayer membranes composed of synthetic amphiphiles are more favorable candidates for enzyme mimics. For example, artificial vitamin Bg-dependent enzymes were constructed from catalytic bilayer membranes in combination with a bilayer-forming peptide lipid (10), a hydrophobic vitamin derivative (11), and metal ions (Fig. 5). The catalyst acts as an artificial aminotransferase, showing marked substrate specificity, high enantioselectivity, and turnover behavior for the transamination of a-amino acid with a-keto acids. In addition, the reaction fields provided by the catalytic bilayer membranes are suitable to establish multienzyme systems through functional ahgnments of artificial enzymes and natural ones in a sequential manner. 

Fig. 5 An example of an artificial holoenzyme formed with the bilayer-forming peptide lipid (10). the hydrophobic vitamin 65 derivative (11), and metal ions..(View thii art in color at WWW. dekker. com.)...

Murakami, Y. Hisaeda, Y. Kajihara. A. Ohno, T. Hydrophobic vitamin B,2. Coordination geometry and redox behavior of heptamethyl cobyrinate in non-aqueous media. Bull. Chem. Soc. Jpn. 1984. 57 (2). 405-411. 

Vitamins are organic compounds that have biochemical and physiological proprieties. Because of these qualities, they have been the subject of numerous scientific investigations. Vitamins are classified according to their solu-biUty in water and in fats. Lipophilic (hydrophobic) vitamins are vitamins A, D, E, and K. Chromatography is useful in the identification and determination of vitamins in pharmaceutical preparations, the identification and determination of vitamins and related substances in natural materials and foodstuffs, and the chemical and biochemical determination of vitamins and their metabolites in fats and tissues. 

Table 3 i p values of hydrophobic vitamins separated on various supports. 

Perisic-Janjic, Petrovic, and Hadzic described a method for the quantitative analysis of hydrophobic vitamins K3, K4, and K5 by thin-layer chromatography on starch, cellulose impregnated with paraffin oil, and talc (unimprcgnated) using a mixture of water-dioxane-acetone—formaldehyde (85 20 15 25, v/v/v/v) as the mobile phase (Table 1). 

SEPARATION OF MIXTURES OF HYDROPHOBIC VITAMINS AND OF HYDROPHOBIC VITAMINS FROM OTHER COMPOUNDS... 

Chromatographic systems have been developed for RPTLC separation of hydrophobic vitamins on RP-18 as the stationary phase by Baranowska and Kadziolka. A mixture of hydrophobic vitamins (A acetate, E, E acetate, and D3) was separated using acetonitrile-benzene-chloroform (10 10 1, v/v) as the mobile phase (Table 1). Applied chromatographic conditions do not permit the separation of vitamin E and vitamin E acetate. Derivative spectrometry was used to determine vitamin A acetate in mixtures with other hydrophobic or water-soluble vitamins. Spectrodensitometric analysis of hydro-phobic vitamins enables determination of vitamin A-acetate in the presence of vitamins E, E-acetate, and D3 as well as Iso of C, Bi, and nicotinamide, as earlier presented. 

This entry has discussed the use of TLC in the investigation of hydrophobic vitamins. In earlier articles, Pyka referenced the full scientific literature for analysis of hydrophobic vitamins investigated by the TLC... 

CCI4 in male Wistar rats induce oxidative stress mainly in the aqueous phase of the liver cell as ascorbic acid concentration was significantly decreased, while hydrophobic vitamin E was not influenced significantly (Sun et al. 2001). 

Murakami Y, Hisaeda Y, Tashiro T, Matsuda Y (1985) Electrochemical carbon-slmletai rearrangeinent as catalyzed by hydrophobic vitamin B12 in nonaqueous media. Chem Lett 14 1813-1816... 

Hisaeda Y, Takenaka J, Murakami Y (1997) Hydro-phobic vitamin B12. Part 14. Ring-expansion reactions catalyzed by hydrophobic vitamin B12 under electrochemical conditions in nonaqueous medium. Electrochimca Acta 42 2165—2172... 

Shimakoshi H, Nakazato A, Hayashi T, Tachi Y, Naruta Y, Hisaeda Y (2001) Electroorganic syntheses of macrocyclic lactraies mediated by vitamin B12 model cranplexes. Part 17. Hydrophobic vitamin B]2. j Electroanal Chem 507 170-176... 

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