Theoretical study of exchange coupling constants in an Fe19 complex

The application of theoretical methods based on density functional theory using generalized-gradient approximation functionals provides reasonable estimates of the exchange coupling constants for polynuclear transition metal complexes. Calculations for the complete, non-modeled Fe₁₉ complex have been performed and a comparison with the experimental magnetic susceptibility values using Monte Carlo simulations is presented.     

Boundary regularity, uniqueness and non-uniqueness for AH Einstein metrics on 4-manifolds

This paper studies several aspects of asymptotically hyperbolic (AH) Einstein metrics, mostly on 4-manifolds. We prove boundary regularity (at infinity) for such metrics and establish uniqueness under natural conditions on the boundary data. By examination of explicit black hole metrics, it is shown that neither uniqueness nor finiteness holds in general for AH Einstein metrics with a prescribed conformal infinity. We then describe natural conditions which are sufficient to ensure finiteness.     

温度对PSⅡCP4 7/D1/D2/Cytb559复合物荧光光谱特性的影响

采用激励光源为514.5 nm的分幅扫描单光子计数荧光光谱装置对经20℃、42℃和48℃不同温度处理后的反应中心复合物CP47/D₁/D₂/Cyt b559的荧光光谱特性进行了研究.经解析,获得不同温度处理后,CP47/D₁/D₂/Cyt b559复合物最大峰值未发生变化,均在682 nm,说明Chla670的能量都由Chla682接收,但损耗愈来愈小,在48℃时,损耗程度最小,而其荧光百分比未发生多大变化.振动副带～700 nm和～740 nm的中心波长都发生蓝移,在不同温度下分别为:20℃ 703 nm,749 nm;42℃ 697 nm,744 nm;48℃ 694 nm,740 nm.因此可以推测温度的升高,影响了CP47/D₁/D₂/Cyt b559色素蛋白的二级结构以及色素分子的空间位置,使最大峰值处的荧光强度逐渐降低,振动副带逐渐蓝移.42℃的温度已造成影响,48℃影响较大.     

1H and 13C NMR spectroscopic study of oxidation of D,L‐cystine and 3,3′‐dithiobis(propionic acid) with hydrogen peroxide in aqueous solution

The oxidation of symmetrical disulfides [D ,L ‐cystine ( 1 ) and 3,3′‐dithiobis(propionic acid) ( 2 )] with hydrogen peroxide in D₂O–NaOH solution (pH 10–11) was studied by NMR spectroscopy. Assignments of the proton and carbon NMR signals of starting materials ( 1 and 2 ) and products of oxidation are based on conventional 1D NMR methods (DEPT, selective spin decoupling). Formation of C—S bond cleavage products or, in case of 2 , partially oxidized intermediates was not detected. The accelerating effect of Cu²⁺ cations, but not Fe³⁺ cations, on the oxidation rate of 1 in basic medium was demonstrated. Copyright © 2002 John Wiley & Sons, Ltd.     

Well-dispersed gold nanowire suspension for assembly application

A method for fabricating well-dispersed nanowire suspension has been demonstrated in the paper. Thin gold nanowires were prepared by template synthesis, and then functionalized with sulphonate group-terminated thiols before suspended in different solvents. The degree of aggregation of the obtained suspension was evaluated with transmission electron microscopy (TEM) and UV-vis spectroscopy. It was found that the degree of aggregation was predominated by the solvents, and the best degree of dispersion was obtained when isopropyl alcohol (IPA) was used as the solvent. The gold nanowires from the suspension can be selectively assembled onto chemically patterned substrates. This well-dispersed nanowire suspension is potentially useful for fabricating novel nanodevices.     

Transport properties of acetone aqueous solutions: molecular dynamics simulation and NMR studies

Two quantities η_rel and are applied to study the nonideal acetone–water association mixture. An all-atom acetone model and a TIP5P water model have been adopted for molecular dynamics simulation. We study the transport properties of the system comparing the 's of strong hydrogen bond and weak contact based on transport properties, MD simulations together with NMR experimental data and find good agreement of concentration dependence, which exhibits the cooperation effect.     

The role of As2O3 on the stability and some physical properties of PbO-Sb2O3 glasses

PbO-Sb₂O₃ glasses added with different concentrations of As₂O₃ (10-55 mol%) were prepared to understand their IR spectra, elastic properties (Young's modulus E, Shear modulus G, microhardness H), optical absorption and dielectric properties (constant ε, loss tan δ, ac conductivity σ_ac over a moderately wide range of frequency and temperature and breakdown strength in air medium at room temperature). Results have indicated that the structure of the PbO-Sb₂O₃-As₂O₃ glass is more rigid when the concentration of As₂O₃ is around 40 mol%.     

Cauchy problems for linear thermoelastic systems of type III in one space variable

The goal of the paper is to analyse properties of solutions for linear thermoelastic systems of type III in one space variable. Our approach does not use energy methods, it bases on a special diagonalization procedure which is different in different parts of the phase space. This procedure allows to derive explicit representations of solutions. These representations help to prove results for well‐posedness of the Cauchy problem, L^P–L^q decay estimates on the conjugate line and results for propagation of singularities. Copyright © 2005 John Wiley & Sons, Ltd.     

Stemmosides C and D, two novel unusual pregnane glycosides from Solenostemma argel: structural elucidation and configurational study by a combined NMR-quantum mechanical strategy

Stemmosides C and D, two novel pregnane glycosides characterized by an unusual C-17 side chain were isolated from the pericarps of Solenostemma argel. In addition, stemmoside D displays an uncommon 14β proton configuration, apparently being the first pregnane isolated from plants known to have a 15 keto, cis CD ring junction. Their structures have been established by ESIMS and NMR experiments. The relative configuration of the molecules was determined using a strategy based on the simulation of ¹H, ¹³C, and J coupling NMR parameters. DFT calculations of ¹H and ¹³C chemical shifts, and of the ¹H homonuclear spin–spin coupling constants were performed with the mPW1PW91 functional using the 6-31G(d,p) basis set on the fully optimized geometries of all the possible stereoisomers.     

Synthesis and conformational investigation of tetrapeptide analogues of the fragment B23-B26 of insulin

Tetrapeptides containing one of a set of four different α,α-dialkyl glycines at the C-terminus were synthesized by conventional methods in solution and their conformational behavior investigated by ¹H NMR spectroscopy in connection with molecular mechanics calculations. The results were consistent with conformations stabilized by a γ-turn in the case of compounds with alkyl groups larger than methyl, while the corresponding Aib derivative did not exhibit intramolecular hydrogen bonding.