Crystallography of vitamin B12 proteins

This review deals with results from crystallographic studies on proteins that interact with the essential micronutrient cobalamin (vitamin B12). Both B12-dependent enzymes and B12-transport proteins are described with an emphasis on structural aspects of cobalamin and its protein environment.     

Radiolysis of cyanocobalamin (vitamin B12)

Research on the radiolysis of vitamins is of considerable interest since these compounds are important nutritional constituents in foods and in dietetic supplements. In spite of these considerations there are few data and very often difficult to compare for the radiolytic behavior of vitamins. In this work we focused our attention on to the study of the radiolysis of cyanocobalamin (vitamin B₁₂) in solid state and in aqueous solutions. The procedure was followed by HPLC and UV-spectroscopy. The results obtained in aqueous solutions showed a dependence of the decomposition as a linear function of the dose. The G of decomposition for a 1×10⁻⁵ M solution was 3.3. In the solid state the vitamin was very stable towards the irradiation in the conditions used in this study with a G=2.1×10⁻³. A study made with Serratia marcescens as a microbiological contaminant showed that at the sterilization dose there is a destruction of the vitamin in aqueous solution. In the solid state the degree of decomposition was 7%.     

维生素B6在维生素B12修饰电极上的电化学行为及其分析应用

采用循环伏安法研究了维生素B6在维生素B12修饰玻碳电极上的电化学行为,建立了测定痕量维生素B6的新方法.在pH 8.6的NH3-NH4Cl缓冲溶液中,维生素B6在修饰电极上产生一个灵敏的氧化峰,采用差分脉冲伏安法测定,其氧化峰电流与维生素B6的浓度在8.0×10-7～2.0×10-4 mol/L范围内呈良好的线性关系,检出限为2.0×10-7 mol/L.该修饰电极具有良好的选择性、灵敏度及稳定性,用于片剂中维生素B6的定量分析,结果令人满意.     

Iodination of cisplatin adduct of Vitamin B12 [{B12}-CN-{cis-PtCl(NH3)2}]

The cisplatin adduct of vitamin B₁₂, [{B₁₂}-CN-{cis-PtCl(NH₃)₂}]⁺ (1), reacts with iodide in aqueous solution to form [{B₁₂}-CN-{trans-PtI₂(NH₃)}] (3) in good yield. Mono-substitution of chloride was not observed since a subsequent replacement of one NH₃ by a second iodide is very fast as compared to the Cl⁻ → I⁻ exchange. The same reaction conditions allowed to introduce radioiodide ¹³¹I. Vitamin B₁₂ can therefore be labeled with radionuclides via binding to the Pt(II) center.     

Synthesis and characterization of vitamin B12-hyperbranched polymer

Vitamin B₁₂-hyperbranched polymer was synthesized and characterized by UV-vis and NMR spectroscopy as well as DLS. The shape of hybrid polymer was also directly observed by TEM. Microenvironmental polarity around vitamin B₁₂ derivative on the polymer was evaluated by UV-vis absorption peak with α-band of vitamin B₁₂ chromophore.     

Li修饰B12N12储氢行为的密度泛函理论研究

采用基于密度泛函理论(DFT)的第一性原理投影缀加波方法, 研究了Li 修饰的B₁₂N₁₂笼子的储氢行为.计算结果表明: Li 原子吸附在B₁₂N₁₂笼子的四元环和六元环相交的B－N桥位上, 相对于其它六个高对称吸附位置更稳定, B₁₂N₁₂笼子周围最多可以吸附3 个Li 原子, 最稳定的构型是三个Li 原子同时吸附在N原子顶位(Top-N site). 每个Li 原子的周围能吸附三个氢分子, 笼子外侧还可以吸附两个氢分子, 内部最多可以吸附5 个氢分子. 考虑到笼内和笼外的吸附, B₁₂N₁₂笼子总的储氢量(氢分子)达到9.1% (w).     

Dipstick based immunochemiluminescence biosensor for the analysis of vitamin B12 in energy drinks: A novel approach

In this article, we describe a dipstick based immunochemiluminescence (immuno-CL) biosensor for the detection of vitamin B₁₂ in energy drinks. The method is a direct competitive type format involving the immobilization of vitamin B₁₂ antibody on nitrocellulose membrane (NC) followed by treatment with vitamin B₁₂ and vitamin B₁₂–alkaline phosphatase conjugate to facilitate the competitive binding. The dipstick was further treated with substrate disodium 2-chloro-5-(4-methoxyspiro {1,2-dioxetane-3,2¢-(5¢-chloro)tricyclo[3.3.1.13,7]decan}-4-yl)-1-phenyl phosphate (CDP-Star) to generate chemiluminescence (CL). The number of photons generated was inversely proportional to the vitamin B₁₂ concentration. After systematic optimization, the limit of detection was 1 ng mL⁻¹. The coefficient of variation was below 0.2% for both intra- and inter-assay precision. Vitamin B₁₂ was extracted from energy drinks with recovery ranged from 90 to 99.4%. Two different energy drinks samples were analyzed, and a good correlation was observed when the data were compared with a reference enzyme linked immuno sorbent assay (ELISA) method. The developed method is suitable for an accurate, sensitive, and high-throughput screening of vitamin B₁₂ in energy drinks samples. The dipstick technique based on immuno-CL is suitable for the detection of several analyte in food and environmental samples.     

Effect of gamma irradiation on the thiamine, riboflavin and vitamin B6 content in two varieties of Brazilian beans

The effect of ⁶⁰Co gamma rays on the content of several B-vitamins in two varieties of Brazilian beans has been studied. Carioca (Phaseolus vulgaris L. var. Carioca) and Macaçar beans (Vigna unguiculata L. Walp, var. Macaçar) were irradiated at doses of 0, 0.5, 1.0, 2.5, 5.0 and 10 kGy, and subsequently stored at ambient temperature for 6 months. The content of vitamin B₁, B₂ and B₆ was analysed by HPLC. In addition, the optimum cooking time was established for each dose and bean variety. A taste panel evaluated sensory properties. Only slight changes were measured for thiamine and riboflavin, whereas a dose-dependent decrease was noted for pyridoxine, which, however, was significant only at the highest doses of 5 and 10 kGy. Cooking time was considerably reduced with increasing radiation dose, but accompanied by a loss of the sensory quality. However, at the disinfestation dose up to 1 kGy, acceptable ratings were obtained for the sensory evaluation. In conclusion, for insect disinfestation of Brazilian beans radiation processing is a promising technology.     

Simultaneous determination of antioxidants at a chemically modified electrode with vitamin B12 by capillary zone electrophoresis coupled with amperometric detection

In the paper, a new kind of vitamin B₁₂ (acquo-cobalamine) chemically modified electrode was fabricated and applied in capillary zone electrophoresis coupled with amperometric detection (CZE-AD) for simultaneous determination of six antioxidants in fruits and vegetables. The catalytic electrochemical properties of the chemically modified electrode could obviously enhance oxidation peak heights responses by about five times to glutathione, ascorbic acid, vanillic acid, chlorogenic acid, salicylic acid, and caffeic acid compared with common carbon disk electrode. Furthermore, the effects of working electrode potential, pH and concentration of running buffer, separation voltage and injection time on CZE-AD were investigated. Under the optimum conditions, the six analytes could be completely separated and detected in a borate-phosphate buffer (pH 8.4) within 15 min. Their linear ranges were from 2.5 × 10⁻⁷ to 1.0 × 10⁻⁴ mol L⁻¹ and the detection limits were as low as 10⁻⁸ mol L⁻¹ magnitude (S/N = 3). The proposed method has been successfully employed to monitor the six analytes in practical samples with recoveries in the range 96.0-106.0% and RSDs less than 5.0%. Above results demonstrate that capillary zone electrophoresis coupled with electrochemical detection using vitamin B₁₂ modified electrode as detector is of convenient preparation, high sensitivity, good repeatability, and could be used in the rapid determination of practical samples.     

由M0.02Cu0.4Mg5.6Al1.98(OH)16CO3 (M=Ru,Re)水滑石为前驱体制备的双金属固体碱催化甘油氢解

采用共沉淀法合成了M_0.02Cu_0.4Mg_5.6Al_1.98(OH)₁₆CO₃ (M = Ru,Re)水滑石前驱体,然后经焙烧和还原制备了铜分散度较高的双功能M-Cu/固体碱催化剂.这些双功能催化剂在粗甘油氢解制备丙二醇反应中表现出了很好的催化活性.表征结果证明,M的加入增强了催化剂表面氢的吸附和活化,进而促进了甘油的转化.     

Epoxidation of alkenes with molecular oxygen and isobutyraldehyde catalyzed by immobilized vitamin B12 within Al-MCM-41

Vit-B₁₂/ Al-MCM-41 catalyzed successfully the epoxidation either of cis or trans — stilbene with O₂ as oxidant and isobutyraldehyde as co-reductant with 86–98% reactivity and 97–100% selectivity. Other olefins such as norbornene and styrene undergo epoxidation reaction under similar conditions with good to fair selectivity. Details of the reactions will be presented in this article.     

Vitamin B12-catalyzed conversion of some γ- and δ-bromoalkanols to polyhydroxy alkanols

Vitamin B₁₂-catalyzed allylic dimerization of some γ- and δ-bromoalkanols with activated Zn-dust in mixture ethanol/water (1:1) has been studied. Investigated bromoalkanols were prepared from corresponding tertiary Δ⁴- and Δ⁵-alkenols by means of benzeneselenyl bromide and subjected to chemical reduction with vitamin B₁₂. All investigated bromoalkanols, after dehydrobromination, underwent to oxidative allylic coupling and hydratation in the presence of protic solvents to give predominantly polyhydroxy alkanols.     

Vapor-phase Beckmann rearrangement of cyclohexanone oxime over B2O3 catalysts supported on TiO2-ZrO2 mixed oxide

A novel catalyst, boria supported on titania-zirconia mixed oxide, exhibits very high catalytic activity and selectivity in vapor-phase Beckmann rearrangement of cyclohexanone oxime to e-caprolactam. It gives 99.7% oxime conversion and 97.0% lactam selectivity at 300°C.     

Sub-picogram determination of Vitamin B12 in pharmaceuticals and human serum using flow injection with chemiluminescence detection

A sensitive chemiluminescence (CL) method, based on the enhancive effect of cobalt(II) on the CL reaction between luminol and dissolved oxygen in a flow injection (FI) system, was proposed for determination of Vitamin B₁₂. The increment of the CL intensity was proportional to the concentration of Vitamin B₁₂, giving a calibration graph linear over the concentration from 2.0×10⁻¹⁰ to 1.2×10⁻⁶ g l⁻¹ (r²=0.9992) with the detection limit of 5.0×10⁻¹¹ g l⁻¹ (3σ). At a flow rate of 2.0 ml min⁻¹, a complete determination of Vitamin B₁₂, including sampling and washing, could be accomplished in 0.5 min with the relative standard deviations (R.S.D.) of less than 5.0%. The proposed method was applied successfully to the determination of Vitamin B₁₂ in pharmaceuticals, human serum, egg yolk and fish tissue.     

Effects of γ-irradiation and cooking on vitamins B6 and B12 in grass prawns (Penaeus monodon)

The effects of irradiation doses, irradiation temperature and a combined treatment of irradiation and cooking on the vitamin B₆ and B₁₂ contents of grass prawns have been studied. Grass prawns were irradiated at refrigerated (4°C) or frozen (-20°C) temperatures with different doses. A domestic cooking procedure was followed after irradiation. The changes in vitamins B₆ and B₁₂ of both raw and cooked grass prawns were evaluated. Results showed no significant changes of vitamin B₆ and B₁₂ in grass prawns with a radiation dose up to 7 kGy at either 4°C or -20°C. Irradiation at 4°C caused more destruction of vitamin B₁₂ but not vitamin B₆ than did irradiation at -20°C in grass prawns. There was significant destruction of both vitamins B₆ and B₁₂ in unirradiated samples during cooking. The introduction of the irradiation process before cooking had no effect on either vitamin. These results indicate that the loss of vitamins B₆ and B₁₂ in the combined treatments was caused mainly by thermal destruction.     

辅酶B12模型化合物生成与解离电化学研究(II)

用电化学方法研究了钴卟啉与多种直链溴代烷的相互作用，表明１价钴卟啉可以与溴代烷形成有σ钴－碳键的辅酶Ｂ１２模型化合物。计算了Ｉ价钴卟啉与各种直链溴代烷的加合速率常数。详细讨论了直链烷烃的链长与模型化合物生成速率及烷基钴卟啉负离子稳定性的关系。讨论了几种模型化合物的优劣。     

Solid-solid synthesis of a hydrophobic vitamin B12 having a benzo-18-crown-6 moiety at the C10 position of the corrin ring

A new hydrophobic vitamin B₁₂ having a benzo-18-crown-6 moiety at the C-10 position of the corrin ring was synthesized by solid-state condensation reaction. The proton NMR titration study in acetonitrile exhibits a potassium ion binding behavior of the hydrophobic vitamin B₁₂ at the benzo-18-crown-6 moiety.     

On the mechanism of propene oxidation on Bi3Mo2FeO12 and Bi2Mo2Fe2O12 catalysts

Oxidation of propene on Bi₃Mo₂FeO₁₂ and Bi₂Mo₂Fe₂O₁₂ and Bi₂(MoO₄)₃ has been compared with the interaction of allyl iodide and diallyl oxalate with these compounds. Bi₂Mo₂Fe₂O₁₂ was found to be the most active and the least selective in propene oxidation. The three compounds show at the same time the same activity in acrolein formation from allyl iodide and oxalate. The results are interpreted in terms of the two-center mechanism of propene oxidation [9, 10]. The role of iron in elementary steps of propene oxidation on Bi–Mo–Fe–O catalysts is also discussed.

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Bi₃Mo₂FeO₁₂, Bi₂Mo₂Fe₂O₁₂ Bi₂(MoO₄)₃ . Bi₂Mo₂Fe₂O₁₂ . . , . Bi–Mo–Fe–O.

     

Cyclic voltammetry at microdroplet modified electrodes. A comparison of the reaction of vicinal dibromides with vitamin B12s at the liquid/liquid interface with the corresponding homogeneous process: evidence for polar-solvent effects at the liquid/liquid interface

The electrocatalytic reactions of vitamin B_12s with three vicinal dibromides (cis-1,2-dibromocyclohexane, trans-1,2-dibromocyclohexane and 1,2-dibromobutane) are investigated in homogeneous and heterogeneous media. In the latter, cyclic voltammetry with basal plane pyrolytic graphite electrodes modified with microdroplets of dodecane + dibromide is employed to obtain kinetic parameters for the liquid/liquid reaction. The homogeneous and interfacial reactions exhibit marked differences in reactivity and the contrasting behaviour of the two systems suggests the liquid/liquid interface has a major role in the B_12s/RBr₂ reaction, consistent with a polar solvent effect.     

Group 12 metal aryl selenolates. Crystal and molecular structure of [2-(Et2NCH2)C6H4]2Se2 and [2-(Me2NCH2)C6H4Se]2M (M = Zn, Cd)

Diorganodiselenide [2-(Et₂NCH₂)C₆H₄]₂Se₂ (1) was obtained by hydrolysis/oxidation of the corresponding [2-(Et₂NCH₂)C₆H₄]SeLi derivative. The treatment of [2-(Et₂NCH₂)C₆H₄]₂Se₂ with elemental sodium in THF resulted in [2-(Et₂NCH₂)C₆H₄]SeNa (2). Reactions between alkali metal selenolates [2-(R₂NCH₂)C₆H₄]SeM′ (R = Me, Et; M′ = Li, Na) and MCl₂ (M = Zn, Cd) in a 2:1 molar ratio resulted in the [2-(R₂NCH₂)C₆H₄Se]₂M species [R = Me, M = Zn (3), Cd (4); R = Et, M = Zn (5), Cd (6)]. The new compounds were characterized by multinuclear NMR (¹H, ¹³C, ⁷⁷Se, ¹¹³Cd) and mass spectrometry. The crystal and molecular structures of 1, 3 and 4 revealed monomeric species stabilized by N → Se (for 1) and N → M (for 3 and 4) intramolecular interactions.