Carbon Atoms Speaking Out: How the Geometric Sensitivity of 13C Chemical Shifts Leads to Understanding the Colour Tuning of Phycocyanobilin in Cph1 and AnPixJ

We present a combined quantum mechanics/molecular mechanics (QM/MM) molecular dynamics–statistical approach for the interpretation of nuclear magnetic resonance (NMR) chemical shift patterns in phycocyanobilin (PCB). These were originally associated with colour tuning upon photoproduct formation in red/green-absorbing cyanobacteriochrome AnPixJg2 and red/far-red-absorbing phytochrome Cph1Δ2. We pursue an indirect approach without computation of the absorption frequencies since the molecular geometry of cofactor and protein are not accurately known. Instead, we resort to a heuristic determination of the conjugation length in PCB through the experimental NMR chemical shift patterns, supported by quantum chemical calculations. We have found a characteristic correlation pattern of 13C chemical shifts to specific bond orders within the π-conjugated system, which rests on the relative position of carbon atoms with respect to electron-withdrawing groups and the polarisation of covalent bonds. We propose the inversion of this regioselective relationship using multivariate statistics and to apply it to the known experimental NMR chemical shifts in order to predict changes in the bond alternation pattern. Therefrom the extent of electronic conjugation, and eventually the change in absorption frequency, can be derived. In the process, the consultation of explicit mesomeric formulae plays an important role to qualitatively account for possible conjugation scenarios of the chromophore. While we are able to consistently associate the NMR chemical shifts with hypsochromic and bathochromic shifts in the Pg and Pfr, our approach represents an alternative method to increase the explanatory power of NMR spectroscopic data in proteins.     

Analysis of a theoretical model for anisotropic enzyme membranes application to enzyme electrodes

A theoretical model of diffusion and reaction in an anisotropic enzyme membrane is presented with particular emphasis on the application of such membranes in enzyme electrodes. The dynamic response of systems in which the kinetics are linear, which comprises the practical operating regime for enzyme electrodes in analysis, is investigated via an analytic solution of the governing differential equations. The response is presented as a function of a single dimensionless group, Μ, that is the membrane modulus.     

化学反应限度实验的再讨论

苏教版《化学2》化学反应限度一节用“2Fe3++2I-=2Fe2++I2”的反应为例来引导学生认识可逆反应,但是用KSCN溶液真的能检验溶液中剩余的Fe3+吗？通过理论计算和实验验证得出了一致的结论,并找到一个更具有代表性的可逆氧化还原反应来引入反应限度的概念。     

Combined Cluster Quantum Chemical MINDO/3 and Ab Initio Study on Zinc Phosphate Structures

Semiempirical MINDO/3 and ab initio calculations were performed to mimic different synthesis routes of zinc phosphates (ZPO) having four-, six- and eight-member ring structures. The Zn/P ratio remained equal to unity while the ZPO followed a strict alternating tetrahedral connectivity. Two different basis sets, i.e., 3-21G* and 6-31G**, were used. It was found that the formation of the ZPO structure is energetically highly favored when the building blocks that compose the structure interacts according to a deep acid–base neutralization. The Lewis acid sites (LAS) formed from the most stable precursor ZPO structure display high activity in binding with Lewis base molecules such as CO. Both the blue-shift of the adsorbed CO stretching mode and its adsorption energy with the LAS shows that the Lewis acidity of ZPO is not less than that of pure ZnO.