Photo-induced Charge Separation of p-Tricyanovinyl-N,N-Dialkylanilines

In this paper,p-tricyanovinyl-N,N-dialkylanilines were synthesized as model compounds and through their spectroscopic behavior,the photo-induced electron transfer,charge separation were discussed and the aggregation in DMSO-H_2O system was investigated.     

Dynamic optimization problems with bounded terminal conditions

Bounded terminal conditions of nonlinear optimization problems are converted to equality terminal conditions via the Valentine's device. In so doing, additional unknown parameters are introduced into the problem. The transformed problems can still be easily solved using the sequential gradient-restoration algorithm (SGRA) via a simple augmentation of the unknown parameter vector . Three example problems with bounded terminal conditions are solved to verify this technique.This research was supported in part by the National Aeronautics and Space Administration under NASA Grant No. NCC 2-106.     

An Asymmetric Edge-Sharing Bioctahedral Complex: (η2-DAniF)MoIII(μ-DAniF)2(μ-O,Cl)MoVCl2 (DAniF=N,N′-di-p-anisylformamidinate)

A novel asymmetric, edge-sharing bioctahedral complex with formamidinato ligands ( ²-DAniF)Mo(-DAniF)₂(-O,Cl)MoCl₂, 1, (DAniF=N,N-di-p-anisylformamidinate) has been isolated as a byproduct from the preparation of the dimolybdenum(II,III) compound Mo₂(DAniF)₃Cl₂. An X-ray crystallographic study shows that the structure consists of edge-sharing bioctahedra, with the shared edge defined by the vector joining the: -O and -Cl ligands. Compound 1 is best formulated as a mixed-valent Mo^IIIMo^V compound, the Mo(V) ion being that with the two terminal Cl^– ligands. The cyclic voltammogram of 1 shows a reversible reduction at –0.472 V and a reversible oxidation at 1.028 V vs. the Ag/AgCl reference electrode, while the absorption spectrum of 1 reveals an intense low energy absorption at 523 nm ( _max=12 500) which is attributed to an intervalence charge transfer transition. Crystallographic data for 1 are as follows: a=13.387(1) Å, b=15.500(2) Å, c=21.855(2) Å, =98.786(2)°, V=4481.8(8) ų, P2₁/c, R1 (wR2)=0.082 (0.177).     

纳米TiO2的光生电荷迁移特性研究

利用场诱导光电压谱(简称FISPS)和瞬态光伏(简称TPV)技术研究了TiO₂的光生电荷的产生和传输机制.发现光生电荷在体块TiO₂上的迁移机制不同于在纳米TiO₂上的迁移机制，也不同于在结界面空间电荷区的迁移机制. 400 ℃处理的TiO₂颗粒表面具有大量的表面态，光生电荷被表面态捕获-释放机制控制着光伏行为的过程是慢过程. 800 ℃处理的TiO₂已经形成了完整的能带结构，光伏响应除了表现带-带跃迁外,还有一个在带边的自由激子带，光生电荷被表面自建场驱动进行传递的过程是快过程. 600 ℃处理的TiO₂混晶由锐钛矿型和金红石型两种构型组成，在两相之间存在着较低势垒的结界面．它的光伏响应受控于两种机制 ：光生电荷在两相间结界面空间电荷区的传输和在表面自建场驱动下的传输.当激发光强较小时，界面空间电荷区的光生电子由于积累的浓度较小而不能隧穿过结界面，这种场助隧穿只有在外场作用下才能发生.     

Modelling and mutation studies on the histamine H1-receptor agonist binding site reveal different binding modes for H1-agonists: Asp116 (TM3) has a constitutive role in receptor stimulation

Summary A modelling study has been carried out, investigating the binding of histamine (Hist), 2-methylhistamine (2-MeHist) and 2-phenylhistamine (2-PhHist) at two postulated agonistic binding sites on transmembrane domain 5 (TM5) of the histamine H₁-receptor. For this purpose a conformational analysis study was performed on three particular residues of TM5, i.e., Lys²⁰⁰, Thr²⁰³ and Asn²⁰⁷, for which a functional role in binding has been proposed. The most favourable results were obtained for the interaction between Hist and the Lys²⁰⁰/Asn²⁰⁷ pair. Therefore, Lys²⁰⁰ was subsequently mutated and converted to an alanine, resulting in a 50-fold decrease of H₁-receptor stimulation by histamine. Altogether, the data suggest that the Lys²⁰⁰/Asn²⁰⁷ pair is important for activation of the H₁-receptor by histamine. In contrast, analogues of 2-PhHist seem to belong to a distinct subclass of histamine agonists and an alternative mode of binding is proposed in which the 2-phenyl ring binds to the same receptor location as one of the aromatic rings of classical histamine H₁-antagonists. Subsequently, the binding modes of the agonists Hist, 2-MeHist and 2-PhHist and the H₁-antagonist cyproheptadine were evaluated in three different seven--helical models of the H₁-receptor built in homology with bacteriorhodopsin, but using three different alignments. Our findings suggest that the position of the carboxylate group of Asp¹¹⁶ (TM3) within the receptor pocket depends on whether an agonist or an antagonist binds to the protein; a conformational change of this aspartate residue upon agonist binding is expected to play an essential role in receptor stimulation.Abbreviations 2-MeHist 2-methylhistamine - 2-PEA 2-pyridyl-ethylamine - 2-PhHist 2-phenylhistamine - CHO Chinese hamster ovary - E_int interaction energy - E_str strain energy - GES global energy structure - gpH₁R guinea pig H₁-receptor - GPCR G-protein coupled receptor - Hist histamine - N proximal nitrogen - N tele nitrogen - TM transmembrane domain - WT wild type     

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.     

Isomorphic electron orbitals for vibronic flexibility in a cyclopropenyl radical molecular device

Summary The vibronic character of this molecular device has been studied using isomorphic electron orbitals. The leading role of the softest vibrational mode for the electron transport process is stressed by the quantum mechanical treatment of the rearrangement operator. The theory was used to investigate the possible function of the soliton valve, which has been suggested as a switching tip. The electronic flexibility of the cyclopropenyl radical with respect to molecular vibrations, which is important for the function of the molecular device, is well characterized by the hardness and softness of the electron structure in terms of the orbital energy-occupation number correlation diagram.     

Linear scaling local correlation approach for solving the coupled cluster equations of large systems

A linear scaling local correlation approach is proposed for approximately solving the coupled cluster doubles (CCD) equations of large systems in a basis of orthogonal localized molecular orbitals (LMOs). By restricting double excitations from spatially close occupied LMOs into their associated virtual LMOs, the number of significant excitation amplitudes scales only linearly with molecular size in large molecules. Significant amplitudes are obtained to a very good approximation by solving the CCD equations of various subsystems, each of which is made up of a cluster associated with the orbital indices of a subset of significant amplitudes and the local environmental domain of the cluster. The combined effect of these two approximations leads to a linear scaling algorithm for large systems. By using typical thresholds, which are designed to target an energy accuracy, our numerical calculations for a wide range of molecules using the 6-31G or 6-31G* basis set demonstrate that the present local correlation approach recovers more than 98.5% of the conventional CCD correlation energy.     

Elucidating Factors Manipulated the Formation of Multiply Charged Protein Homomultimeric Complexes by Electrospray Ionization

Native non‐covalently bonded protein‐protein and protein‐substrate complexes are of great interest and have been extensively studied by electrospray ionization mass spectrometry (ESI‐MS). Multiply charged protein homomultimeric complexes are shown to form by ESI‐MS. This study addresses factors that can artificially induce the formation of multiply charged protein homomultimeric complexes. Cytochrome c (Cyt c) and ubiquitin, which are monomers in solution, were found to generate (Cyt c)_mⁿ⁺ by electrospray ionization (ESI). The homomultimeric complexes were not limited to dimeric complexes but include also multiply charged trimers, tetramers, and pentamers. The observation of these homomultimeric complexes has never been revealed from a Cyt c solution at the concentration as low as 10 μM. Increasing the concentration of Cyt c enhanced the formation of (Cyt c)_mⁿ⁺ as expected; however, the protein concentration does not affect the relative intensities of monomeric and dimeric complexes. Additionally the enrichment of NH₄OH also promotes the formation of (Cyt c)_mⁿ⁺. Notably, source collision‐induced dissociations (source‐CID) of (Cyt c)_mⁿ⁺ alter the charge state distribution (CSD) and may lead to an incorrect interpretation of Cyt c conformations. Hence, extra care should be taken when using CSD to interpret the conformation of a protein derived from ESI‐MS.     

A soluble and multichromic conducting polythiophene derivative

A new soluble polythiophene derivative was synthesized by both chemical and electrochemical oxidative polymerization of 1-4-nitrophenyl-2,5-di(2-thienyl)-1H-pyrrole (SNSNO₂). Chemical method produces a polymer which is completely soluble in organic solvents. The structures of both the monomer and the soluble polymer were elucidated by ¹H and ¹³C-NMR and FTIR. The average molecular weight has been determined by GPC to be Mn = 6.3 × 10³ for the chemically synthesized polymer. P(SNSNO₂) was also synthesized via potentiostatic electrochemical polymerization. Characterizations of the resulting polymer were performed by cyclic voltammetry CV, FTIR and UV-Vis spectroscopy. Four-probe technique was used to measure the conductivities of the samples. Moreover, the spectroelectrochemical and electrochromic properties of the polymer film were investigated. In addition, dual type polymer electrochromic devices ECDs based on P(SNSNO₂) with poly3,4-ethylenedioxythiophene (PEDOT) were constructed. Spectroelectrochemistry, electrochromic switching and open circuit stability of the devices were studied. They were found to have good switching times, reasonable contrasts and optical memories.