抗肿瘤多酸药物[Mo7O24]6-的电子结构研究

运用第一原理密度泛涵理论中的离散变分方法（ＤＦＴ－ＤＶＭ）对具有抗肿瘤活性的多酸药物三合水七钼酸异丙基胺的阴离子「Ｍｏ７Ｏ２４」＾６－进行了电子结构，获得了键级、不等价原子的电子占据数、原子净电荷，分子轨道能级以及「Ｍｏ７Ｏ２４」＾６－的ＨＯＭＯ和ＬＵＭＯ组成等数据，并对该药物的活性和作用机理从电子结构的角度进行了讨论。     

The influence of peripheral ligand bulk on nitrogen activation by three‐coordinate molybdenum complexes—A theoretical study using the ONIOM method

Electronic structure methods have been combined with the ONIOM approach to carry out a comprehensive study of the effect of ligand bulk on the activation of dinitrogen with three‐coordinate molybdenum complexes. Calculations were performed with both density functional and CCSD(T) methods. Our results show that not only is there expected destabilization of the intermediate on the pathway due to direct steric interactions of the bulky groups, but also there is significant electronic destabilization as the size of the ligand increases. This latter destabilization is due to the inability of the molecule to accommodate a rotated amide group bound to the molybdenum once the amide reaches a certain size. This destabilization also leads to a clear preference for the triplet intermediate (rather than the singlet intermediate) for bulky substituents which is in agreement with experiment. Overall, the calculated reaction profile for the bulky substituents shows a good correlation with the available experimental data. © 2009 Wiley Periodicals, Inc. J Comput Chem 2009     

Stochastic self-oscillations in an extrinsic semiconductor under intense illumination

Summary We show that an extrinsic semiconductor (n-type), containing a deep level from impurity centres, may produce stochastic self-oscillations in the electron density and in the electric field, under intense illumination which ionizes the deep traps and heats the electrons. The feedback mechanism is the dependence of the capture coefficient of the deep centres on the electron temperature and the dependence of the deep energy level on electron temperature and concentration. The conditions for the occurrence of periodic and stochastic self-oscillations are explicitly given.

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Riassunto Si mostra che in un semiconduttore estrinseco (di tipon), contenente impurezze con un livello profondo, si possono produrre auto-oscillazioni stocastiche nella densità di elettroni in modo da ionizzare le impurezze e riscaldare gli elettroni. Il meccanismo responsabile è la dipendenza della sezione di cattura degli elettroni nel livello profondo della temperatura degli elettroni e la dipendenza dell’energia del livello dalla temperatura degli elettroni e dalla loro densitá. Si danno le esplicite condizioni per l’insorgere di auto-oscillazioni periodiche e stocastiche.

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Резюме Мы показываем, что собственный полупроводник (n-типа), содержащий глубокий уровень, связанный с примесными центрами, может производить стохастические автоколебания в электронной плотности и в электрическом поле при интенсивном облучении, которое ионизует глубокие ловушки и нагревает электроны. Этот механизм обратной связи представляет зависимость коэффициента захвата для глубоких центров от электронной температуры и зависимость глубокого энергетического уровня от температуры и концентрации электронов. В явном виде приводятся условия для возникновения периодических и стохастических автоколебаний.

     

Calculation of the vibronic spectra and structure of methylstyrene in the excited state by the parametric method

Calculations of the excited-state structure and of the absorption and radiation spectra of trans-β-methylstyrene are performed by the parametric method for models of the first and second approximations. Only three of the parameters, being constant in a series of related compounds, are used for molecular fragments. In the calculation, the main regularities observed in electronic spectra are reproduced, and an analysis and interpretation of their fine vibrational structure are carried out. The use of the model of the second approximation with a single additional parameter allows more accurate reproduction of angular deformations of the molecule under excitation and of the characteristic changes observed in the low-frequency spectral region in the series of diphenyl polyenes, stilbene, styrene, and methylstyrene molecules. It is shown that the parameters of the second approximation (just as of the first one) possess the transference property in the homological series of molecules. In modeling complex molecules in excited states and their vibronic spectra, the parametric method is more efficient than the ab initio one. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 148–153, March–April, 2000.     

Quantum–Chemical Investigation of the Influence of Conformations and Extra–Ligation on Electronic Spectra of Chemical Dimers of Metalloporphyrins and Metallochlorins

We have made a theoretical analysis of the factors influencing the electronic absorption spectra of monomers of porphyrins and chlorins as well as of their chemically bound dimers in which the monomeric subunits are bound through the CH₂–CH₂ group. On the basis of quantum–chemical calculations by the semiempirical method CNDO/S it is shown that the addition of extra–ligands causes a change in the conformation of the dimers.     

Influence of Solvent Polarity and Hydrogen Bonding on the Electronic Transition of Coumarin 120: A TDDFT Study

The characteristics of the electronic transition energy of Coumarin 120 (C120) and its H‐bonded complexes in various solvents have been examined by time‐dependent density functional theory (TDDFT) in combination with a polarizable continuum solvent model (PCM). Molecular structures of C120 and its H‐bonded complexes are optimized with the B3LYP method in PCM solution, and the dihedral angle H14? N13? C7? H15 is dependent on solvent polarity and the type of H‐bond. A linear correlation of the absorption maximum of C120 with the solvent polarity function is revealed with the PCM model for all solvents except DMSO. The experimental absorption maximum of C120 in nine solvents is well described by a PCM–TDDFT scheme augmented with explicit inclusion of a few H‐bonded solvent molecules, and quantitative agreement between our calculated results and experimental measurements is obtained with an average error of less than 2 nm. H‐bonding at three different sites shifts the absorption wavelength of C120 either to the blue or to the red, that is, a significant role is played by solvent molecules in the first solvation shell in determining the electronic transition energy of C120. The dependence on the H‐bonding site and solvent polarity is examined by using the Kamlet–Taft equation for solvatochromism.     

Rotational analysis of 3664 Å band of NiCl

Nickel chloride was excited in a high frequency discharge source and the band at 3664 Å was photographed at an inverse dispersion of 0.59 Å/mm on a two metre plane grating spectrograph. The rotational analysis was carried out and the molecular constants of the upper state are reported. The rotational isotopic shifts due to³⁷Cl support the rotational analysis. The electronic transition involved is identified to beβ ²Δ_5/2 →X ₁ ²Δ_5/2.