Investigation of the Variation of Unit Cell Dimensions of Crystalline Polymers with High‐Resolution FT‐IR Spectroscopy

Summary: High‐resolution FT‐IR spectroscopy has been used for the first time to characterize the variation of the unit cell dimensions of high‐density polyethylene (HDPE). In combination with the unit cell parameters of HDPE measured at different temperatures by Swan using wide‐angle X‐ray diffraction, the relationship between the rocking band shift (730 cm⁻¹) and the change of the unit cell volume of HDPE has been established.

High‐resolution variable‐temperature FT‐IR spectra of HDPE rocking bands with decreasing temperature.     

Electron‐phonon short‐range interactions mobility and p‐ to n‐type conversion in TlGaS2 crystals

The conductivity type conversion from p ‐ to n ‐type at a critical temperature of 315 K in TlGaS₂ crystals is observed through the Hall effect measurements in the temperature range of 200–350 K. The analysis of the temperature‐dependent electrical resistivity, Hall coefficient and carrier concentration data reveals the extrinsic type of conduction with donor impurity levels that behave as acceptor levels when are empty. The data analysis allowed the calculation of hole and electron effective masses of 0.36m ₀ and 0.23m ₀, respectively. In addition, the temperature‐dependent Hall mobility is found to decrease with temperature following a logarithmic slope of ∼1.6. The Hall mobility in the n ‐region is limited by the electron‐phonon short‐range interactions scattering with an electron‐phonon coupling constant of 0.21. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

5,10-CH+-THF向邻苯二胺转移一碳单元反应的理论研究

叶酸辅酶在酶催化的一碳单元转移过程中具有重要的作用,已有大量的实验及实验模拟对其生物学功能进行了研究分析.本文用PM3半经验方法对5,10-CH⁺-THF向邻苯二胺转移一碳单元的反应进行了理论研究.结果表明,5,10-CH⁺-THF中的咪唑啉环有两种开环方式,从而使得该反应可以通过两种途径实现,每一种途径都经历了6个反应步骤,其中包括限制速度的两次质子转移步骤.优化计算了每个步骤所有可能的中间体和过渡态的结构和能量,并通过比较分析得到了各反应阶段的最优中间体和过渡态结构.     

Temperature dependence of Hall electron density of GaN-based heterostructures

The theoretic calculation and analysis of the temperature dependence of Hall electron density of a sample AlGaN/GaN heterostructure has been carried out in the temperature range from 77 to 300K. The densities of the two-dimensional electron gas and the bulk electrons are solved by self-consistent calculation of one-dimensional Schr?dinger and Poisson equations at different temperatures, which allow for the variation of energy gap and structure strain, and are used for evaluation of the temperature dependence of Hall electron density. The calculated Hall electron density agrees with the measured one quite well with the appropriate bulk mobility data. Analysis revealed that for the temperature range considered, even in the heterostructures with a small bulk conductance the factors that determine the Hall mobility and electron density could be of different sources, and not just the two-dimensional electron gas as generally supposed.     

用C-1 3核磁共振谱测定高聚物中微量异种结构单元的探讨

通过高低工作频率的高分辩率核磁共振谱仪（型号分别为GX-400和FX-90Q）对含有不同微量异种结构单元的聚乙烯样品作了^13C谱测量和比较分析;结果表明^13C谱在较高磁场频率（100.4MHz)条件下可检测灵敏度达到0.5个支化点/10000个碳原子（0.5/10000C);而较低磁场频率（22.5MHz)只达到1个支化点/1000个碳原子（1/1000C）以上;综合分析所得结果,指出在用电磁体系列（谱仪频率一般为90MHz或100MHz)核磁共振谱仪检测高分子量物质时,应注意有遗漏1/1000C以下浓度结构的可能性;分析了^13C谱可检测灵敏度与磁场强度等因素的关系,得到了可检测灵敏度S/N与磁场强度（H0）间比较适合的关系式。     

One‐carbon unit transfer quantum study of 1,10‐CH+‐tetrahydroquinoxaline analog

Quantum mechanics is used in this article to study one‐carbon unit's transfer from 1,10‐tetrahydroquinoxaline analog to methylamine. The computation result shows this reaction can be completed via two paths. Each path experiences two processes of proton transferring and bond rupturing. The structures and energies of all possible stationary points have been calculated by different methods. By analyzing the result, we can find that along the reaction route the proton transfer reaction has the highest energy barrier, which indicates that a general‐acid catalysis exists in this reaction. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

Theoretical study of one‐carbon unit transfer between methyl‐AICA and N1‐methyl‐N1‐acryloyl‐formamide

The mechanism of one‐carbon unit transfer between 1‐methyl‐5‐amino‐4‐carboxamide imidazole (M‐AICA) and N¹‐methyl‐N¹‐acryloyl‐formamide (the model molecule of 10‐f‐H4F) is investigated by the Hartree–Fock and DFT methods, respectively, at the 6‐31G* basis level. There are two different channels for the proton transfer, resulting in two reaction pathways with different properties. The results indicate that both channels can complete the reaction, but path a is slightly favored due to its lower active energy barrier. Furthermore, the influence of 4‐carboxamindde in M‐AICA is also discussed. This group can stabilize the reactant and intermediates, and reduce the active energy barrier through the intermolecular hydrogen bond. The intermolecular hydrogen bond results in an enlarged conjugation system and makes the transition states more stable. Our results are in agreement with experiments. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

基于发展学生化学核心素养的教学设计——以“沉淀溶解平衡”为例

为了促进学生化学学科核心素养的形成和发展,构建了基于高中化学学科核心素养的教学设计基本思路,提出了4个方面的教学策略：设计教学单元,整体规划素养发展路径;制订教-学-评目标,监测素养达成;设置活动任务,承载素养的发展;创设真实情境,联结素养与知识。并以“沉淀溶解平衡”为主题教学单元进行教学设计,将基于核心素养发展的教学设计思路付诸应用,促进化学核心素养培养目标的达成。     

Ligand based virtual screening using SVM on GPU

In silico methods play an essential role in modern drug discovery methods. Virtual screening, an in silico method, is used to filter out the chemical space on which actual wet lab experiments are need to be conducted. Ligand based virtual screening is a computational strategy using which one can build a model of the target protein based on the knowledge of the ligands that bind successfully to the target. This model is then used to predict if the new molecule is likely to bind to the target. Support vector machine, a supervised learning algorithm used for classification, can be utilized for virtual screening the ligand data. When used for virtual screening purpose, SVM could produce interesting results. But since we have a huge ligand data, the time taken for training the SVM model is quite high compared to other learning algorithms. By parallelizing these algorithms on multi-core processors, one can easily expedite these discoveries. In this paper, a GPU based ligand based virtual screening tool (GpuSVMScreen) which uses SVM have been proposed and bench-marked. This data parallel virtual screening tool provides high throughput by running in short time. The proposed GpuSVMScreen can successfully screen large number of molecules (billions) also. The source code of this tool is available at http://ccc.nitc.ac.in/project/GPUSVMSCREEN.     

A highly selective fluorescent probe for Sn based on a new photochromic diarylethene with a phenol-containing Schiff base unit

A novel diarylethene with a phenol-containing Schiff base unit was successfully synthesized and its multi-responsive photoswitching property was investigated by the stimulation of base/acid and light. The diarylethene showed not only normal photochromism by photoirradiation, but also abnormal photochromism by base and light stimuli. By the stimulation of sodium hydroxide, the absorption maximum of its open-ring isomer showed extraordinarily large redshift of 60 nm, accompanied with a notable color change from colorless to yellow. Subsequent irradiation with 297 nm light further caused a dramatic change in its structure transformation from the deprotonated open-ring isomer to the original closed-ring isomer. Similarly, its deprotonated closed-ring isomer returned to its original open-ring isomer upon irradiation with appropriate visible light. Its deprotonated forms could be restored by the stimulation of hydrochloric acid. Moreover, the diarylethene could be served as a fluorescence probe for recognition of Sn²⁺ with high selectivity.