Density Functional Study on the Mechanism of Amadori Rearrangement Reaction

The reaction mechanism of amadori rearrangement in the initial stage of Maillard reaction has been investigated by means of density functional theory calculations in the gaseous phase and aqueous solution.Cyclic ribose and glycine were taken as the model in the amadori rearrangement.Reaction mechanisms have been proposed,and possibility for the formation of different compounds has been evaluated through calculating the relative energy changes for different steps of the reaction by following the total mass balance.The calculations reveal that the amadori rearrangement initialized via the intramolecular rearrangement,transferring one proton from N(3) to O(4) atom.In the next step,the second proton is also transferred from N(3) to O(4) atom,corresponding to the cleavage of C(4)-O(4) bond and the release of one water molecule.Then another proton is transferred from N(3) to C(5) atom via TS3 with the reaction barrier of 58.3 kcal·mol-1 after tunneling the effect correction calculated at the B3LYP/6-31+G(d) level of theory,and this step is rate limiting for the whole catalytic cycle.Ultimately,the product is generated via keto-enolic tautomerization.Present calculation could provide insights into the reaction mechanism of Maillard reaction since experimental evaluation of the role of intermediates in the Maillard reaction is quite complicated.     

氧化锌纳米颗粒增强鲁米诺-EDTA化学发光测定咖啡酸

在ZnO纳米颗粒( ZnO nanoparticles, ZnO NPs)和EDTA存在的条件下,无需外加氧化剂,鲁米诺( Luminol)即能产生很强的化学发光,由此建立了化学发光体系Luminol-EDTA-ZnO NPs。基于咖啡酸能够有效抑制Luminol-EDTA-ZnO NPs化学发光,结合流动注射技术测定了咖啡酸含量。在最佳的实验条件下,咖啡酸浓度在1.0伊10-7~1.0伊10-5 mol/L范围内,相对发光强度与咖啡酸浓度对数分段呈线性关系,检出限为1.8伊10-8 mol/L (3滓),对4.0伊10-7 mol/L咖啡酸平行测定11次,相对标准偏差(RSD)为3.5%。利用本方法测定片剂中咖啡酸的含量,回收率为97%~101%。