液态水热容的量子校正

在不同温度下对液态水进行分子动力学模拟，研究各温度下液态水中各个原子的速度自相关函数密度谱，以考察液态水热容的量子校正随温度的变化规律．研究结果表明，水分子的三个内部振动模式对热容的量子校正不随温度变化，而转动和分子距平衡位置的摆动运动模式的量子校正随温度升高而逐步减小．对于分子动力学模拟结果经温度涨落计算所得的热容进行了量子校正，校正结果与实验值能符合．     

代铬镀层的研究进展

六价铬会严重破坏环境并危害人类的健康,所以开发无六价铬的代铬镀层电镀工艺具有重要的现实意义。本文主要介绍了几种代铬镀层的研究进展,包括合金代装饰铬镀层、电镀及化学镀合金代硬铬镀层以及复合镀代铬镀层等,重点论述了其特点、典型电镀工艺及其应用,并结合其研究现状对代铬镀层的发展进行了展望。     

Isomeric Effect on H/D Exchange of Resveratrol Studied by NMR Spectroscopy

Resveratrol (3,5,4′‐trihydroxylstilbene), a phytoalexin in response to injury or fungal attack, is found in grapes and other food products. It has been well documented that the compound has beneficial effects as hypolipidemic, anticancer, antiviral, neuroprotective, antiaging, and anti‐inflammatory natural active principle. It was observed that both trans‐ and cis‐resveratrols undergo hydrogen‐deuterium (H/D) exchange at H‐2,6 and H‐4 positions of the A‐ring. The exchange rates were determined by ¹H NMR spectroscopy. The results reveal that the exchange rates are configuration and pH dependent. Derivative of 2‐O‐β‐D‐glucoside can significantly speed up the H/D exchange reactions for both isomers. The trans‐resveratrol experiences faster H/D exchanging than the cis‐resveratrol. Such isomeric effect is possibly due to the factor that the trans‐resveratrol is in favor of forming larger/super conjugative system and has less spatial interference. Theoretical calculation shows that electronegativity at these positions is in the order of H‐2,6>H‐4, which is in consistent with the exchange rates observed by NMR. The results may be of help in understanding the properties of resveratrol, and in analysis of resveratrol in natural products or body fluids using mass spectroscopy that occasionally requires stable deuterium isotope labeling.     

The excited state dynamics study of di‐2‐pyridylketone in the A‐band and B‐band absorptions by using resonance Raman spectroscopy,IR and UV–visible spectroscopy

Excitation wavelengths of 282.4, 273.9 (A band), 252.7, 239.5 and 228.7 nm (B band) resonance Raman spectra were acquired for di‐2‐pyridylketone, and density functional calculations were carried out to help in the elucidation of the photo relaxation dynamics of A‐band and B‐band electronic transitions. The resonance Raman spectra show that the intensity pattern of the A band presents great difference from that of the B band, which indicate that the short‐time A‐band (S₀→S₄) photo relaxation dynamics have substantial difference from that of B band (S₀→S₁₀) . The overall picture of short‐time dynamics and the vibronic coupling mechanisms are interpreted using Albrecht's theory. Copyright © 2012 John Wiley & Sons, Ltd.     

A Gaussian-3 investigation on the stabilities and bonding of the nine N10 clusters

A Gaussian-3 investigation has been performed to examine the stabilities of the nine N₁₀ isomers. G3 energies at 0K, enthalpies and heats of formation at 298K have been calculated. The most stable structure is VIII, which consists of three five-membered rings with a bowl-shape structure. The thermodynamic stability trend of the nine N₁₀ clusters is VIII > V > IX > VII > IV > VI > III > I > II, which is different from the previous theoretical results. Natural bond orbital (NBO) and atom in molecules (AIM) analysis have been carried out to study the bonding of these isomers.     

Prediction of the 13C NMR chemical shifts of organic species adsorbed on H-ZSM-5 zeolite by the ONIOM-GIAO method

The ONIOM-GIAO method has been used to accurately predict 13C NMR chemical shifts for a series of organic species adsorbed on H-ZSM-5 zeolite. This is useful for the spectroscopic identification of complicated catalytic systems.     

关于Weingarten超曲面的一个存在性定理

本文研究伪黎曼空间型中一类特殊的Weingarten超曲面的存在性问题.通过引入伪黎曼空间型中旋转超曲面的概念,并给出其主曲率计算公式.得到伪黎曼空间型中旋转型Weingarten超曲面的存在性定理.推广并统一了相关结果.     

Integral Formulas for Submanifolds in Enclidean Space and Their Applications to Uniqueness Theorem

In this paper, the author derives some integral formulas for a pair of submanifolds in Euclidean Space E^n+p, and applies these formulas to generalize the Christoffel theorem and the Hilbert Liebmann-Hsiung theorem.     

半欧氏空间R_v~3中的广义Weierstrass公式

本文在一种特殊的三维半氏欧空间R_v~3中定义了复微分算子和广义高斯映射。在[1]的基础上进一步把广义Weierstrass公式推广到R_v~3中。通过这个公式,只要给定二维流形M上的非零C~1级函数H以及M上的光滑映射ψ,就可以构造出R_v~3中的曲面,使得H为它的平均曲率且ψ是它的高斯映射     

Location, acid strength, and mobility of the acidic protons in Keggin 12-H3PW12O40: a combined solid-state NMR spectroscopy and DFT quantum chemical calculation study

Solid-state 13C NMR experiments and quantum chemical Density Functional Theory (DFT) calculations of acetone adsorption were used to study the location of protons in anhydrous 12-tungstophosphoric acid (HPW), the mobility of the isolated and hydrated acidic protons, and the acid strength heterogeneity of the anhydrous hydroxyl groups. This study presents the first direct NMR experimental evidence that there are two types of isolated protons with different acid strengths in the anhydrous Keggin HPW. Rotational Echo DOuble Resonance (REDOR) NMR experiments combined with quantum chemical DFT calculations demonstrated that acidic protons in anhydrous HPW are localized on both bridging (Oc) and terminal (Od) atoms of the Keggin unit. The CP/MAS NMR experiments revealed that the isolated acidic protons are immobile, but hydrated acidic protons are highly mobile at room temperature. The isotropic chemical shift of the adsorbed acetone suggested that the acid strength of the H(H2O)n+ species in partially hydrated HPW is comparable to that of a zeolite, while the acidity of an isolated proton is much stronger than that of a zeolite. Isolated protons on the bridging oxygen atoms of anhydrous HPW are nearly superacidic.