【作者】 顾文秀；

【导师】 夏文水；

【作者基本信息】 江南大学 ， 食品科学， 2008， 博士

【摘要】 氨基葡萄糖酸（2-氨基-2-脱氧-D-葡萄糖酸,GAA）,是构成生命活动物质的糖单元之一,具有重要的生理学功能,在食品、医药、化妆品方面有广泛的应用前景。目前国内外有关氨基葡萄糖酸合成的文献报道不多,对于其络合性质也了解不多。本研究的目的在于探索氨基葡萄糖酸高效合成的新方法及其相应的机理,并测定其与金属离子的络合性质及其相应的热力学性质。这对于氨基葡萄糖酸的开发和应用有着重要的理论意义和应用价值。首次使用双金属催化氧化法进行氨基葡萄糖酸高效合成的探索,改进传统的催化剂制备方法,以先后浸渍、新的表面氧化还原法制备负载型双金属催化剂Pd-Bi/C,以氨基葡萄糖盐酸盐为原料,以氧气作为氧化剂,进行合成氨基葡萄糖酸的研究,并用正交试验法优化了氧化反应的条件。通过催化剂微观结构和催化过程热力学的表征手段探讨了双金属催化氧化法的机理。结果表明:1)Pd-Bi/C双金属催化氧化法合成氨基葡萄糖酸,选择性高（＞90%）,反应条件温和（30℃）,反应时间较短（6h）,反应可一步、在单一的反应器中完成;催化过程环境清洁,催化剂可重复使用7次,活性基本不变。采用新型表面氧化还原方法制备的催化剂比较稳定,金属剥落程度非常小,合成产率为70%,产品可达食品和医药级,是一种非常有应用前景的氨基葡萄糖酸的合成新方法;2)探索得出双金属催化法合成氨基葡萄糖酸的“络合传递型协同催化机理”,具体的历程为:第一步,反应物在溶液中与铋离子形成络合物,该络合物在铋与钯的协同效应下很容易定位于催化剂表面的活性钯原子上,然后与水分子形成水合物,吸附的水合物在活性钯的作用下脱氢。而分子态的氧先和位于钯表面的铋结合,形成表面活性物种“Bi₂O₃”,此时的氧可认为处于晶格氧的形式,“Bi₂O₃”中的晶格氧与水合物脱下来的活性氢反应生成水,使铋重新回到Bi⁰,水合物脱氢后氧化成相应的酸,该酸在钯的协同作用下,释放出铋离子,进入溶液,而铋离子在钯的协同作用下与反应物重新络合,进入新一轮的氧化过程。该机理能很好地与实验结果吻合,是理论上的创新和突破。首次使用成对电催化氧化法进行氨基葡萄糖酸高效合成的探索,以氨基葡萄糖盐酸盐为原料,用循环伏安法研究电极表面微观反应过程及电催化动力学,探索影响电极活性的因素,进而探讨电催化的机理。用UPD修饰电极的方法来提高电极的催化性能,在修饰电极的基础上,采用成对电催化的方法进一步提高反应的时空效率。结果表明:1)金电极是催化氨基葡萄糖氧化成氨基葡萄糖酸的活性电极;2)阴离子的吸附是影响电极活性的关键因素;3)探索得到相应的电催化机理,机理的具体历程为:第一步,形成Au（OH）^1-λ-吸附物种,该物种对反应有催化活性,然后是氨基葡萄糖的C1上的结合氢解离,生成吸附自由基,这一步为反应的决速步,表现为一级反应。接着,吸附自由基氧化成中间体氨基葡萄糖酸内酯,内酯水解生成氨基葡萄糖酸;4)金电极上电催化氧化合成氨基葡萄糖酸时,在碱性介质中,产率可达99.5%;在中性介质中,产率为70.7%;5)成对电催化氧化合成氨基葡萄糖酸,平均产率为:67.5%,同时收获对电极产物乙醛酸,产率44%,且耗时少（4 h）,与双金属化学催化法（70%）相比,该法时空效率高、选择性和重复性更好,具有更广阔的应用前景。采用简便易行,准确度较高的分光光度法和pH-电位滴定法研究了氨基葡萄糖酸与金属离子的络合性质及其相应的热力学性质。结果表明:在pH=12.0的介质中,Cu（Ⅱ）与氨基葡萄糖酸的络合摩尔比为1:2,吸收波长为:630 nm,摩尔吸光系数为39.906 L·mol^-1·cm^-1,络合物的稳定常数β_n为6.24×10⁵。双系列线性回归方法计算所得的络合剂的浓度与给定的值十分吻合,这从一个侧面证实了该方法的可靠性。根据pH-电位滴定法得到了氨基葡萄糖酸与Ni（Ⅱ）、Co（Ⅱ）和Zn（Ⅱ）络合平衡的热力学函数,氨基葡萄糖酸络合物的稳定性常数与丙氨酸和己氨酸的值几乎相同,只是相应的AH值较大,而△S值较小,证实醇羟基参与了络合物的形成。这些性质对指导这些络合物的合成及将其用于食品和医药领域中均有着重要的理论指导意义。更多还原

【Abstract】 Glucosaminic acid （2-amino-2-deoxy-D-gluconic acid, GAA） is one of the carbohydrate units to manufacture various biotic substances. It has various physiological functions. It has extensive application prospects in the food, cosmetic and pharmaceutical industries.There are few literatures on the synthesis of glucosaminic acid. The coordination properties of glucosaminic acid were explored little.Therefore, one of the objects of the present investigation was to explore some novel highly efficient synthesis methods of glucosaminic acid and discover the corresponding mechanisms. The other was to study the coordination equilibria of glucosaminic acid with metal ions in order to obtain the corresponding stability constants and thermodynamic functions which had not been found in the present literatures. This investigation has the important theory significance and the practical application value to the exploitation of GAAThe bimetallic catalytical oxidation method and the electrocatalytical oxidation method were first used to explore the highly efficient synthesis of glucosaminic acid. An improved method on traditional catalyst preparation methods was applied. The supported Pd-Bi/C catalyst was prepared by successively incorporating the active components Pd and Bi into the supports by impregnation. Then a novel surface redox reaction in the liquid phase was explored to activate the catalyst. The synthesis of glucosaminic acid was done with glucosamine chloride as the material and molecular oxygen as the oxidant. Optimization of the oxidation reaction conditions was done with orthogonal method. The mechanism of the bimetallic catalytical method was discussed on the results of the microstructure of the catalyst and the thermodynamic study on the catalytical process. The result shows: 1) The bimetallic catalytical oxidation method with Pd-Bi/C has high selectivity （>90%）, mild conditions（30℃）, shorter reaction time（6h） and easy manipulation, the possibility of conducting the oxidation in one step in a single reaction vessel. Moreover, the catalytical process is environmentally clean and the catalyst can be recycled for 7 times with almost unreducing activity. The Pd-Bi/C catalyst prepared by a new surface redox reaction in the liquid phase is very stable. There is neither bismuth nor palladium was detected in the product. The product can reach food and pharmaceutical grade. The yield of the bimetallic catalytical oxidation method is 70.0% and the method is a novel synthesis for glucosaminic acid with promising application prospect. 3) A novel mechanism model as "the catalytical mechanism of coordination and transmission with synergistic effect" was proposed. The steps of the mechanism are as follows: first, the complex of Bi（Ⅲ） with the reactant was formed in the reaction solution, the complex was accurately located on Pd atom which was deposited on the surface of the catalyst with the synergistic effect of Bi and Pd. Then the complex was combined with water to form the corresponding hydrate. Successively, the adsorptive hydrate was dehydrogenated. The molecular oxygen was combined with Bi located on the surface of Pd to form "Bi₂O₃, the state of the oxygen now was proposed in the form of lattice oxygen. Water was formed by the lattice oxygen in "Bi₂O₃" with the active hydrogen from the hydrate. Thus, bismuth was regenerated to Bi⁰, The hydrate was oxidized to the corresponding acid in complex state, Bi（III） was released into the solution from the complex of the acid with the synergistic effect of Pd. Then the released Bi（Ⅲ） was recomplexed with the reactant to enter the next cycle of the oxidation process. The mechanism could give perfect interpretations on various experimental results, which provided the evidence for the rationality of it. This is an innovation and breakthrough in catalytical theory.The paired electrocatalytical method was first used to explore the highly efficient synthesis of glucosaminic acid from glucosamine chloride. The microscopic reaction process on the surface of the electrode and the reaction kinetics of the electrocatalytical oxidation were studied by cyclic voltammetry method and the factor which effects the activity of the electrodes was studied. Then the mechanism of the electrocatalytical oxidation was disclosed. The UPD modification electrode method was used to improve the catalytical performance of the electrodes. On the basis of the modification of the electrode, the paired electrocatalytical method was applied to further improve the spatiotemporal efficiency of the reaction. The result shows: 1) Gold is the active electrode material for the electrocatalytical synthesis of glucosaminic acid. 2) The adsorption of anions is the critical factor which affects the activity of the electrodes. The electrocatalytical oxidation mechanism was proposed. Under the guidance of it, the paired electrocatalytical synthesis for glucosaminic acid was successful. The spatiotemporal efficiency of the reaction was improved greatly. 3) The steps of the mechanism are as follows: firstly, the adsorptive species Au（OH）^（1-λ）- was formed, which can catalyze the oxidation reaction, then the combining hydrogen on the C1 of the glucosamine is dissociated to form the adsorptive free radical. The step is the rate-determining step of the oxidation reaction. The step shows the kinetic characteristic of a first order reaction under the experiment condition. Subsequently, the adsorptive free radical was oxidized to intermediate lactone of glucosaminic acid. Then the lactone was transformed to glucosaminic acid by hydrolysis. 4) In the electrocatalytical synthesis of glucosaminic acid in alkaline medium, the current efficiency can reach 99.5%. The value is 70.7% in neutral medium. The yield is higher and the reproducibility better compared with the enzymatic, fermentative and bimetallic catalytical synthesis. Moreover, the paired electrosynthesis of glyoxylic acid and glucosaminic acid was feasible and the better experiment results were obtained on both of the electrodes. The mean yield of glucosaminic acid is 67.5%. The reaction time is 4 h. Compared with the bimetallic catalytical oxidation method, the electrosynthesis method has brighter application prospect.Two simple and convenient methods as spectrophotometry and pH-potential titration were adopted to study the coordination properties of glucosaminic acid with metal ions and the corresponding thermodynamic functions. The results are as follows: the complexation molar ratio with Cu（Ⅱ） is 1:2, the molar adsorptivity of the complex is 39.906 L·mol^-1·cm^-1 at 630 ran, the stability constantβ_n is 6.24×10⁵. The calculated concentration of the complexing agent is in accord with the given one, which provided the evidence for the rationality of the used dual-series linear regression method. The thermodynamic functions in the formation reactions of Ni（Ⅱ）, Co（Ⅱ） and Zn（Ⅱ） with glucosaminic acid were determined by the method of pH-potential titration. The stability constants of the glucosaminic acid complexes are almost equal to the corresponding ones of the alanine and norleucine, but their enthalpy changes are larger and the entropy changes are smaller. Therefore, it was inferred that the alcoholic hydroxyl groups of glucosaminic acid might take part in the complex formation.更多还原