取代基对醌的结构及电子转移能力的影响

用半经验的AM1,abinitio(HF/3-21G,HF/6-31G^*),及密度泛函[B3LYP/6-31G^*,B3LYP/6-311G(d,p)]方法对1,4-苯酯及其阴离子的结构与性质进行了研究。在此基础上用AM1及BLYP/6-31G(d,p)方法对泛醌Q~0,用AM1方法对泛醌Q~1,泛醌Q~2及其阴离子的结构与性质进行了研究。研究结果表明,由于取代基的影响,泛醌的环平面发生了扭曲,环上原子不再位于同一平面上。结构的变化导致了电子分布发生了变化,并由此导致了偶极矩随6位上取代基的增大而增大。随着6位支链的增长,泛醌的电离势逐渐减小而电子亲和势逐渐增大,泛醌传递电子的能力增强。在上述研究的基础上,对1,4-苯醌及泛醌的自交换电子转移反应过程进行了过程,计算了反应的内重组能,溶剂重组能及电子转移速率常数。结果表明内重组能的大小与取代基的长短无直接关系,而与得电子前后醌的结构变化程度密切相关。除高频振动的变化外,低频振动的变化对内重组能也有显著的贡献。计算所得1,4-苯醌自交换电子转移反应速率常数与实验值相符得很好。     

The effect of electron irradiation on the structure and mechanical properties of highly drawn polyethylene fibers

Two very different high-modulus polyethylene fiber samples, a low molecular weight melt-spun and drawn fiber, and a high molecular weight gel-spun and drawn fiber, have been subjected to electron beam irradiation to various doses in vacuum and in the presence of acetylene. The gel content after irradiation in acetylene was found to be much greater than for an equivalent dose in vacuum. The gel content–dose relationship could not be described by either Charlesby–Pinner analysis or the Inokuti equation. This is attributed to the polydispersity and the complications introduced by the unique morphologies of highly drawn fibers. Following previous studies, the tensile creep behavior was interpreted in terms of a model comprising two thermally activated processes in parallel, a low stress process relating to the amorphous network, and a high stress process relating to the continuous crystal fraction. Analysis of the creep behavior of the melt-spun, low molecular weight fiber irradiated in vacuum revealed crosslinking in the amorphous regions and chain scission in the crystal. Chain scission was found to be much reduced when irradiating in acetylene, for which a mechanism has been proposed. The creep rates and activation volumes of the high molecular weight, gel-spun fiber were found to be significantly lower, probably due to the unique morphology. In this case the dominant effect of irradiation on the mechanical properties can be attributed to chain scission rather than crosslinking.     

Impact of anionic substitutions on apatite structure and properties

A review of the results of the authors on single and coupled substitutions of F for OH, and of CO₃ and SO₄ for PO₄ in synthetic and natural apatites, their influence on apatite structure and properties, studied by peak fitting FTIR, XRD, TG/DTA and TG/EGA methods, is presented. Calcination of carbonate and sulphate substituted apatites leads to the formation of stable stoichiometric apatite.     

The effect of electron correlation on the shell structure of atoms

The effect of electron correlation on the spherically averaged electron density (r) and the radial density distribution function D(r), exhibiting the shell structure of atoms, is studied, using basis sets consisting of contracted Gaussians, for the atoms Li through Ar. These effects were shown to be of smaller importance as compared to the effect associated to basis set extension.     

Photoinduced dissociation of anionic and electron detachment of dianionic gold clusters by use of a laser pointer

Size-selected anionic and dianionic gold clusters have been stored in a Penning trap and irradiated with the green light of a laser pointer. As examples of special interest, the systems Au₇⁻ and Au₂₉²⁻ have been chosen. In particular, Au₇⁻, a small gold cluster with closed electron shell, is observed to decay into Au₆⁻ and Au₅⁻ with a decay pathway branching ratio similar to that of Au₉⁺. The dianionic cluster Au₂₉²⁻ shows electron detachment upon photoexcitation. This observation is in agreement with independent experiments [Stoermer et al., Int. J. Mass Spectrom. 201 (2001) 63], where Au₂₉²⁻ is found to be the smallest dianion produced by neutral monomer evaporation of hot dianionic gold clusters.     

The effect of electron correlation on the topological and atomic properties of the electron density distributions of molecules

The topological properties of the electron density and the properties of an atom in a molecule are calculated by means of second-order Møller-Plesset perturbation theory (MP2) and compared with the results of configuration interaction calculations (C12) which include all single and double substitutions from the Hartree-Fock reference configuration. A software package for analyzing the effects of electron correlation on the topological properties of the electron density of molecules is described. H₂CO is used to provide a numerical example and to indicate that the number of bond critical points is unaffected by the inclusion of electron correlation. Correlation leads to only a small shift in the positions of bond critical points and a small change in the electron density at bond critical points. It is further shown that the energy of an atom in a molecule can be calculated to an accuracy of 1 kcal/mol and the electron population of an atom to about 0.001e. A statistical method is used to show that the deviation of the MP2 correlation correction relative to the CI2 correlation correction for a variety of atomic properties is about 25%.     

Electronic structure analysis and electron detachment energies of polynitrogen pentagonal aromatic anions

Various decouplings of the electron propagator have been employed to provide theoretical comparison to experimental electron detachment energies for the pyrrolide, imidazolide, and pyrazolide anions. Predictions for isoelectronic anions in which CH groups are replaced by N atoms also are reported. The ab initio electron propagator results agree closely with experimental values, and the associated Dyson orbitals provide a detailed catalog of bonding changes as the number and positions of N atoms vary within the set of pentagonal aromatic anions.     

Influence of structure on electron correlation effects and electron-water dispersion interactions in anionic water clusters

Electronic structure calculations at the level of second-order M?ller-Plesset perturbation theory have been performed on anionic water clusters, (H2O)n(-), in the n = 14-33 size regime. The contribution to the electron binding energy that arises from electron correlation is found to be significantly larger for cavity-bound electrons than it is for surface-bound electrons, even for surface states with electron binding energies well above 1 eV. A decomposition of the correlation energy into interactions between pairs of Boys-localized molecular orbitals is used to demonstrate that the larger correlation energy found in the cavity isomers arises from electron-water dispersion interactions, and that the dispersion interaction is larger in cavity-bound isomers because the unpaired electron penetrates well beyond the first solvation shell. In contrast, a surface-bound electron exhibits virtually no penetration into the interior of the cavity. To obtain a qualitatively accurate picture of this phenomenon, one must plot molecular orbitals using isoprobability surfaces rather than arbitrarily-selected isocontours.     

The effect of terminal groups on the structure and properties of oligosilsesquioxanes

The interaction of oligomeric silsesquioxanes, whose organic moieties contain tertiary amino groups and primary and secondary hydroxyl groups, with monoisocyanates and phthalic and acetic anhydrides is employed to synthesize a number of their N-alkyl(aryl)urethane-, carboxyl- and acetyl-terminated derivatives with different degrees of substitution and combinations of the substituents. The obtained derivatives are studied by functional analysis, IR spectroscopy, GPC, DSC, TGA, and wide-angle X-ray scattering. The chemical nature of the incorporated functional groups is found to markedly influence the structure and properties of the synthesized compounds. Depending on the type of substituents and their combination, either the complete amorphization or ordering of the structure of the oligosilsesquioxanes is observed with corresponding changes in their properties.     

The structure and properties of functionalized cyclodextrins and complex compounds based on them

Russian Chemical Bulletin - This review presents data on advanced research on functionalized cyclodextrins. In particular, metal complexes of cyclodextrin derivatives and their possible...     

Substituent effect on the structure and properties of dialumene

In this work, we report a theoretical study on molecular structure, and electronic properties of dialumene (ArAl = AlAr, Ar = aryl) and substituted dialumene. The effects of the substituent groups on the structure, electronic properties, ionization potential (IP), electron affinity (EA), and reorganization energy were studied. Theoretical calculations were carried out by density functional theory (DFT) using the B3LYP hybrid function combined with the 6-311 + G(d) basis set. The most intensity electronic transition energy and oscillator strength of molecules were calculated by time-dependent density functional theory (TD-DFT) and shows λ_max blue-shifted in withdrawing electron substituents. Quantum theory of atom in molecules was used for explain of AlAl and AlC bonds in all molecules.     

Solvent effects on the electron donor acceptor complex properties of ferrocene and tetranitromethane

Summary Spectral investigations in the 350–800 nm range of ferrocene (FcH) and tetranitromethane [C(NO₂)₄] solutions in cyclohexane and carbon tetrachloride at concentration-constant (FcH) and variable (tetranitromethane) were made. The electron donor acceptor (EDA) complex of ferrocene and tetranitromethane and its dissociation to the ferricenium cation (FcH⁺) were studied as a function of the solvent, the initial C(NO₂)₄ concentration and reaction time.     

Interaction of 4-hydroxybiphenyl with cyclodextrins: effect of complex structure on spectroscopic and photophysical properties

The structures, spectroscopic and photophysical properties of the inclusion complexes between 4-OH-biphenyl and cyclodextrins (CD) in water were studied theoretically and experimentally. The complex structures were predicted using a dynamic Monte Carlo procedure including solvation effects and analyzed via computed and experimentally determined circular dichroism. The interpretation of the induced circular dichroism spectra indicated the formation of stable 2:2 complexes between the probe and alpha-CD, while 1:1 structures account for the circular dichroism induced by beta- and gamma-CD. Fluorescence emission quantum yields and lifetimes, measured as a function of the CD concentration, confirmed the formation of this higher order complex with alpha-CD. Prototropic equilibration in the singlet excited state was found to be depressed in 2:2 complexes due to the hydrophobic environment of the OH groups, while it remained unperturbed in 1:1 complexes, where the substituent is exposed to the aqueous environment. Triplet-triplet absorption and triplet quenching data supported this interpretation. The photophysical properties of both the 1:1 and the 2:2 complexes are characterized by a significant reduction of the nonradiative decay rates.     

Salt effect on the complex formation between cationic gemini surfactant and anionic polyelectrolyte in aqueous solution

Salt effect on the interaction of anionic polyelectrolyte sodium carboxymethylcellulose (NaCMC) with cationic gemini surfactant hexamethylene-1,6-bis(dodecyldimethylammonium bromide) [C12H25(CH3)2N(CH2)6N(CH3)2C12H25]Br2 (C12C6C12Br2) has been investigated using turbidimetric titration, steady-state fluorescence, and mobility measurement. It is found that the critical aggregation concentration(cac) for C12C6C12Br2/NaCMC complexes depends little on addition of sodium bromide (NaBr). However, in the presence of nonionic surfactant Triton X-100 (TX100), the critical ionic surfactant mole fraction for the onset of complex formation (Yc) increases markedly with increasing NaBr concentration. These salt effects are supposed as the overall result from competition between the increase of interaction and the screening of interaction. The increase of interaction is referred to as the effect that the larger micelle with higher surface charge density induced by salt has a stronger interaction with oppositely charged polyelectrolyte. The screening of interaction is referred to as the salt screening of electrostatic attraction between the polymer chain and the surfactant. For complex formation between C12C6C12Br2 and NaCMC, the increase of interaction probably compensates the screening of interaction, leading to constant cac values at different salt concentrations. For complex formation between the C12C6C12Br2/TX100 mixed micelle and NaCMC, the screening of interaction probably plays a dominant role, leading to higher suppression of electrostatic binding of micelles to polyelectrolyte.     

Vertical detachment energies of anionic thymidine: Microhydration effects

Density functional theory has been employed to investigate microhydration effects on the vertical detachment energy (VDE) of the thymidine anion by considering the various structures of its monohydrates. Structures were located using a random searching procedure. Among 14 distinct structures of the anionic thymidine monohydrate, the low-energy structures, in general, have the water molecule bound to the thymine base unit. The negative charge developed on the thymine moiety increases the strength of the intermolecular hydrogen bonding between the water and base units. The computed VDE values of the thymidine monohydrate anions are predicted to range from 0.67 to 1.60 eV and the lowest-energy structure has a VDE of 1.32 eV. The VDEs of the monohydrates of the thymidine anion, where the N(1)[Single Bond]H hydrogen of thymine has been replaced by a 2(')-deoxyribose ring, are greater by ～0.30?eV, compared to those of the monohydrates of the thymine anion. The results of the present study are in excellent agreement with the accompanying experimental results of Bowen and co-workers [J. Chem. Phys. 133, 144304 (2010)].     

The effect of pressure crystallization on structure and properties of hot-drawn polyethylene

Colloid and Polymer Science - The change of the drawing behaviour of polyethylene is studied as a function of molecular weight and crystallization pressure. The results are interpreted using the...     

DFT description on electronic structure and optical absorption properties of anionic S-doped anatase TiO2

Plane-wave-based pseudopotential density functional theory (DFT) calculations are used to characterize the doping effect of S substituting for O in anatase TiO(2). Through band structure calculation, a direct band gap is predicted in TiO(2)(-)(x)S(x). Electronic structure analysis shows that the doping S could substantially lower the band gap of TiO(2) by the presence of an impurity state of S 3p on the upper edge of the valence band. Excitations from the impurity state of S 3p to the conduction band may be responsible for the red shift of the absorption edge observed in the S-doped TiO(2). The band gap lowering and red shift of the absorption edge are found to increase as the sulfur concentration increases.     

Electronic structure and electron transport characteristics of a cobalt complex

The molecular and electronic structures and electron transport characteristics of a Co complex are investigated using first principles calculations. The Co complex belongs to the D(2d) point group, and its two ligands are perpendicular to each other. The central atom Co forms a distorted octahedron with six donor N atoms. In a low oxidation state, the bond length between Co and pyrrole nitrogen, 1.849 A, is much shorter than the distance between Co and pyridine nitrogen, 2.168 A, while, in a high oxidation state, the bond length differences between Co and pyrrole nitrogen, 1.814 A, and between Co and pyridine nitrogen, 1.990 A, are not as large as those in the Co2+ complex. The HOMO energy of the low oxidation state is very close to the Fermi level of bulk Au, allowing hole creation in the molecule. On the other hand, the LUMO energy of the high oxidation state is close to the Au Fermi level, allowing a low barrier for electron injection from the Au cathode to the molecule. These structural characteristics make the Co complex a good hole-conduction molecule. The density of states, transmission probability, and I-V characteristics are evaluated using the Green function approach.