2-三氰基乙烯基蒽及其旋转异构体的量子化学研究

用量子化学从头算方法 ,在RHF/STO - 3G水平上 ,对 2_三氰基乙烯基蒽 (2_TCVA)分子进行了理论计算 ,优化得到了它的平衡几何构型 ,并计算了它的谐振动频率 .结果表明 :2_TCVA存在两种旋转异构体 :2_TCVA(1)和 2_TCVA(2 ) ,2_TCVA(2 )的总能量比 2_TCVA(1)的略高 .在PM3/CIS水平上计算了它们的电子光谱 ,得到了由基态到各激发态的垂直跃迁能和相应的振子强度 .研究表明 :2_TCVA(1)和 2_TCVA(2 )的强度最大的吸收波长分别为 2 4 9.72nm和 2 89.4 1nm ,2_TCVA(2 )的强度最大的吸收波长比 2_TCVA(1)的要长 .计算结果与实验结果符合得较好     

Transition state geometry in radical abstraction reactions: comparison of interatomic distances in the intersecting parabolas and Morse curves models with quantum-chemical calculations

Interatomic distances in the transition state were estimated for the reactions of radical abstraction: H^· + H₂, H^· + HCl, H^· + CH₄, N^·H₂ + NH₃, HO^· + H₂O, HO₂ ^· + HOOH, and C^·H₃ + SiH₄. The calculation was performed by the quantum-chemical density functional method or coupled clusters method (QCH), as well as by the methods of intersecting parabolas (IPM) and Morse curves (IMM), using experimental data (activation energies and reaction enthalpies). The results of the latter two methods are close to the quantum-chemical calculation and differ only by the increment a: r(IPM or IMM) = a + r(QCH), where a = –4.5·10^–12 m for IPM and a = +1.9·10^–12 m for IMM.     

Spin interaction with an ideal Fermi gas

We consider the equilibrium dynamics of a system consisting of a spin interacting with an ideal Fermi gas on the lattice , 3. We present two examples: when this system is unitarily equivalent to an ideal Fermi gas or to a spin in an ideal Fermi gas without interaction between them.     

5,7′-(亚甲胺基)-二-8-羟基喹啉的合成及其理论研究

以4-甲基苯磺酸作催化剂、用三乙胺调节pH值约为9的条件下, 由5-甲酰基-8-羟基喹啉和5-氨基-8-羟基喹啉合成了新的5,7′-(亚甲胺基)-二-8-羟基喹啉, 利用IR, UV, ¹H NMR, MS确认了分子结构, 比较研究了其光致发光特性, 运用Gaussian 98量子化学程序包, 采用B3LYP密度泛函(DFT)的方法, 在6-31G(d,p)水平上对分子的几何构型进行结构优化; 并对目标化合物的稳定结构通过计算预测其振动光谱, 计算结果与实验值基本相符.     

DNA-mediated coordinative assembly of upconversion hetero-nanostructures for targeted dual-modality imaging of cancer cells

We reported a simple and universal strategy for DNA-mediated assembly of CdTe quantum dots (QDs) and lanthanide-doped upconversion nanoparticles (UCNPs). Such DNA-QD/UCNPs heterostructures not only maintains both fluorescent properties of QDs and upconversion luminescence behaviors of UCNPs, but also offers a polyvalent DNA surface, allowing for targeted dual-modality imaging of cancer cells using an aptamer     

Molecular caps for full quantum mechanical computation of peptide-water interaction energy

We present a systematic study of numerical accuracy of various forms of molecular caps that are employed in a recently developed molecular fractionation scheme for full quantum mechanical computation of protein-molecule interaction energy. A previously studied pentapeptide (Gly-Ser-Ala-Asp-Val) or P5 interacting with a water molecule is used as a benchmark system for numerical testing. One-dimensional potential energy curves are generated for a number of peptide-water interaction pathways. Our study shows that various forms of caps all give consistently accurate energies compared to the corresponding full system calculation with only small deviations. We also tested the accuracy of cutting peptide backbone at different positions and comparisons of results are presented.     

Intramolecular charge transfer in pyrromethene laser dyes: photophysical behaviour of PM650.

Absorption and fluorescence (steady-state and time-correlated) techniques are used to study the photophysical characteristics of the pyrromethene 650 (PM650) dye. The presence of the cyano group at the 8 position considerably shifts the absorption and fluorescence bands to lower energies with respect to other related pyrromethene dyes; this is attributed to the strong electron-acceptor character of the cyano group, as is theoretically confirmed by quantum mechanical methods. The fluorescence properties of PM650 are intensively solvent-dependent. The fluorescence band is shifted to lower energies in polar/protic solutions, and the evolution of the corresponding wavelength with the solvent is analysed by a multicomponent linear regression. The fluorescence quantum yield and the lifetime strongly decrease in polar/protic solvents, which can be ascribed to an extra nonradiative deactivation, via an intramolecular charge-transfer state (ICT state), favoured in polar media.     

Atomic structure of InAs quantum dots on GaAs

In recent years, the self-assembled growth of semiconductor nanostructures, that show quantum size effects, has been of considerable interest. Laser devices operating with self-assembled InAs quantum dots (QDs) embedded in GaAs have been demonstrated. Here, we report on the InAs/GaAs system and raise the question of how the shape of the QDs changes with the orientation of the GaAs substrate. The growth of the InAs QDs is understood in terms of the Stranski–Krastanow growth mode. For modeling the growth process, the shape and atomic structure of the QDs have to be known. This is a difficult task for such embedded entities.

In our approach, InAs is grown by molecular beam epitaxy on GaAs until self-assembled QDs are formed. At this point the growth is interrupted and atomically resolved scanning tunneling microscopy (STM) images are acquired. We used preparation parameters known from the numerous publications on InAs/GaAs. In order to learn more about the self-assemblage process we studied QD formation on different GaAs(0 0 1), (1 1 3)A, and ( )B substrates. From the atomically resolved STM images we could determine the shape of the QDs. The quantum “dots” are generally rather flat entities better characterized as “lenses”. In order to achieve this flatness, the QDs are terminated by high-index bounding facets on low-index substrates and vice versa. Our results will be summarized in comparison with the existing literature.     

Luminescent Sensing with Quantum Dots

Summary This review highlights recent advances in the use of quantum dots (QD’s) as luminescent sensors. The bulk of the study concentrates on systems that possess organic ligands bound to the surface of QD’s. These ligands vary from low molecular weight thiols to larger molecules such as maltose binding protein. All have one thing in common: when a target analyte binds to the ligand/receptor, a perturbation of the system occurs, that registers itself as a change in the luminescence intensity of the QD. Two main mechanisms are prevalent in controlling the luminescent intensity in such systems. The first is Photoinduced Electron Transfer (PET) and the second energy transfer. This review looks at current sensors that operate by using these mechanisms. Two component systems are also investigated where a quencher is first added to a solution of the QD, followed by addition of the target analyte that interacts with the quencher to influence the luminescence intensity.