Using N•3 species as specific electron acceptor a defined ascorbate radical: AH•↔A•−+H+ (λmax=360 nm, =3400 dm3 mol−1 cm−1) is observed. The attack of DMSO•+ on vit.E results in a vit.E• radical (k=1×109 dm3 mol−1 s−1; λmax=425 nm, =2400 dm3 mol−1 cm−1; 2k=4.7×108 dm3 mol−1 s−1). Vit.E-acetate leads to the formation of a radical cation (vit.E-ac•+). β-carotene reacts also with DMSO•+ forming a radical cation, β-car•+ (k=1.75×108 dm3 mol−1 s−1; λmax=942 nm, =14 600 dm3 mol−1 cm−1), which probably leads to the formation of a dimer radical cation, (β-car)•+2 (k=2.5×107 dm3 mol−1 s−1).
Using E.coli bacteria (AB1157) as a model system in vitro it was found that all three vitamins are rather efficient radiation protecting agents. They can also increase the activity of cytostatica, e.g., mitomycin C (MMC), by electron transfer process. The mixture of vit.E-ac and β-car acts contradictory, but adding vit.C to it a strong cooperative enhancement of the MMC activity is observed once again. A relationship between the pulse radiolysis and the radiation biological data is found and discussed. A possible explanation of the previously reported trials concerning the role of vit.E and β-car on the increased occurence of lung and other types of cancer in smokers and drinkers is presented. 相似文献
Simple corrins such as vitamin B12 and vitamin B12 coenzyme catalyze a variety of unusual enzymatic reactions of which some are still without analogy in organic or organometallic chemistry. The mechanisms of these reactions are currently the subject of lively discussion. The present review focuses attention on new ideas about the mode of action of vitamin B12 coenzymes in enzymatic reactions. 相似文献
The direct on-line coupling between capillary high-performance liquid chromatography (capillary HPLC) and proton high-field nuclear magnetic resonance (NMR) spectrometry has been used to derive structural information about constituents of a mixture of vitamin A derivatives. 1H NMR spectra were recorded in the stopped-flow and continuous-flow mode within a 180 μm I.D. capillary column mounted in a micro probe on a 600 MHz NMR spectrometer. The resolution of the 1H NMR spectra obtained in capillary HPLC-NMR coupling experiments is sufficient to determine coupling constants in the order of 1.5 Hz. The detection limit is in the lower nanogram range. A stopped-flow 2D-TOCSY experiment of a 1% solution of vitamin A acetate acquired within 4 h reveals that the acquisition of 2D NMR spectra is possible in the nanoliter detection scale without any loss of structural information. 相似文献
3-Hydroxy-2-methyl-1,4-naphthoquinone-immobilized silica gel has been used for the adsorption and estimation of copper, cobalt, iron and zinc by both batch and column techniques. The distribution coefficient D determined for each metal ion was as follows (ml g1): Fe, 3.6 × 102; Cu, 3.9 × 102; Co, 3.8 × 102; Zn, 4.1 × 102. Methods have been developed to estimate zinc, copper and cobalt in milk, steel and vitamin samples respectively. 相似文献
The introduction of a polymeric C30 liquid chromatographic column by Sander et al. [Anal. Chem., 66 (1994) 1667] designed for the separation of carotenoid isomers, has led to the development of improved analytical methods for these compounds. Subsequent commercial availability of polymerically bonded C30 columns has facilitated these advances, and applications to a wide variety of separation problems with biological samples have been described. This report provides a comprehensive review of applications of polymeric C30 columns, utilized in the determination of carotenoids, retinoids, and other nutrients and related compounds in complex, natural-matrix samples. 相似文献
The introduction of a polymeric C30 liquid chromatographic column by Sander et al. [Anal. Chem., 66 (1994) 1667] designed for the separation of carotenoid isomers, has led to the development of improved analytical methods for these compounds. Subsequent commercial availability of polymerically bonded C30 columns has facilitated these advances, and applications to a wide variety of separation problems with biological samples have been described. This report provides a comprehensive review of applications of polymeric C30 columns, utilized in the determination of carotenoids, retinoids, and other nutrients and related compounds in complex, natural-matrix samples. 相似文献
Multiple response simultaneous optimization by using the desirability function was used for the development of a capillary electrophoresis method for the simultaneous determination of four active ingredients in pharmaceutical preparations: vitamins B6 and B12, dexamethasone and lidocaine hydrochloride. Five responses were simultaneously optimized: the three resolutions, the analysis time and the capillary current. This latter response was taken into account in order to improve the quality of the separations. The separation was carried out by using capillary zone electrophoresis (CZE) with a silica capillary and UV detection (240 nm). The optimum conditions were: 57.0 mmol l−1 sodium phosphate buffer solution, pH 7.0 and voltage = 17.2 kV. Good results concerning precision (CV lower than 2%), accuracy (recoveries ranged between 98.5 and 102.6%) and selectivity were obtained in the concentration range studied for the four compounds. These results are comparable to those provided by the reference high performance liquid chromatography (HPLC) technique. 相似文献