Nonadiabatic ab initio molecular dynamics study of photoisomerization in N-salicilydenemethylfurylamine (SMFA).

The photoisomerization mechanisms of N-salicilydenemethylfurylamine upon excitation to the first singlet state are investigated by means of surface-hopping dynamics simulations based on the Zhu-Nakamura theory. Due to different orientations of the methyl-furyl part with respect to the salicylaldimine part and different orientations of hydroxy group with respect to the benzene ring, various stable structures are obtained in the optimization. The enol isomer, S0-ENOL-5a, is the most stable conformer. An ultrafast excited-state intramolecular proton transfer is observed after photoexcitation of the most stable enol conformer and then the molecule reaches the excited-state minimum. After the internal conversion around a conical intersection, the system relaxes to either the cis-keto or trans-keto region in the ground state. The potential energy profiles of the ground and the first excited singlet state are also calculated. According to full-dimensional nonadiabaticdynamics simulations and potential energy profiles, the trans-keto and cis-keto photoproducts can be responsible for the photochromic effect of N-salicilydenemethylfurylamine.

Inhibition of ovarian cancer proliferation and invasion by pachymic acid.

To determine the effect of pachymic acid (PA) on proliferation, cell cycle, and invasion in human ovarian carcinoma cell lines HO-8910 and explore some possible mechanisms, HO-8910 cells was treated with different concentrations of PA (0.5, 1, 2 µM). CCK-8 assay, propidium iodide staining, was applied to measuring the growth inhibiting rates of HO-8910 cells. Cell cycle was measured by flow cytometry. In addition, the activity of PA against HO-8910 cells invasion was evaluated in transwell assay. Western blot detected the proteins expression of E-cadherin, ß-catenin and COX-2 of different groups treated with PA in different concentrations (0.5, 1, 2 µM) for 48 h. Our results showed that PA could effectively inhibit the in vitro growth of HO-8910 cells in dose-dependent manners in 72 h, suppressed migration and invasion of HO-8910 cells in concentration-dependent manners at 24 h, caused the increased accumulation of G1 phase cells, and caused down-regulation of ß-catenin and COX-2 and up-regulation of E-cadherin expression level. Taken together, it could conclude that PA might inhibit proliferation and invasion of ovarian carcinoma cell through decreasing ß-catenin and COX-2 expression and increasing E-cadherin expression.

Non-adiabatic dynamics of isolated green fluorescent protein chromophore anion.

On-the-fly ab initio molecular dynamics calculations have been performed to investigate the relaxation mechanism of green fluorescent protein chromophore anion under vacuum. The CASSCF surface hopping simulation method based on Zhu-Nakamura theory is applied to present the real-time conformational changes of the target molecule. The static calculations and dynamics simulation results suggest that not only the twisting motion around bridging bonds between imidazolinone and phenoxy groups but the strength mode of C=O and pyramidalization character of bridging atom are major factors on the ultrafast fluorescence quenching process of the isolated chromophore anion. The abovementioned factors bring the molecule to the vicinity of conical intersections on its potential energy surface and to finish the internal conversion process. A Hula-like twisting pattern is displayed during the relaxation process and the entire decay process disfavors a photoswitching pattern which corresponds to cis-trans photoisomerization.

Nonadiabatic ab initio molecular dynamics of photoisomerization in bridged azobenzene.

The photoisomerization mechanisms of bridged azobenzene are investigated by means of surface hopping dynamics simulations based on the Zhu-Nakamura theory. In the geometry optimizations and potential energy surface calculations, four minimum-energy conical intersections between the ground state and the lowest excited state are found to play important roles in the trans-cis and cis-trans isomerization processes. The trans-cis photoisomerization proceeds through two minimum-energy conical intersections. Ultrafast pedal motion of the N atoms and twisting of phenyl rings around their N-C bonds allows the molecule to move to a minimum-energy conical intersection, after which surface hopping from S(1) to S(0) occurs. In the S(0) state, further rotation occurs around the N=N bond and two N-C bonds until the azo moiety and phenyl rings complete their isomerization. Finally, the cis form is achieved by subsequent adjustment of the ethylene bridge. In the cis-trans photodynamics, there is one rotational pathway, in the middle of which two CIs are responsible for the surface hopping to the S(0) state. After the nonadiabatic transition, the molecule reaches the trans form through a barrierless pathway and the two phenyl rings and the additional bridge complete their reorientation almost at the same time.

Theoretical study on photoisomerization effect with a reversible nonlinear optical switch for dithiazolylarylene.

DFT and TDDFT methods have been performed to investigate the photoisomerization effect for dithiazolylarylene on solution. The weak S···N interaction and CH···N hydrogen bond restrain the rotation of the side-chain thiazolyl ring in open-isomer 1a, the higher stability of which prefers to show a high quantum yield of photoisomerization. The calculated UV-Vis spectrum at around 320 nm for open-isomer 1a is bathochromically shifted to 647 nm for closed-isomer 1b, in excellent agreement with the experimental photochromic phenomenon. The electron transition in ECD (electron circular dichroism) spectra for closed-isomer 1b with two chiral carbon atoms is dominated by ICT (intramolecular charge transition) and LE (local excitation) corresponding to one positive (440 nm) and one negative Cotton effect (650 nm), respectively, where the two chiral carbon atoms play a slight role in these transitions. The PES in the S(1) and S(0) states, respectively, indicates that the cyclization reaction from open-isomer 1a to closed-isomer 1b is allowed in the photoexcited state with high-conversion quantum efficiency, while it is forbidden in the thermodynamic process. In addition, the second-order nonlinear optical response for closed-isomer 1b is nearly six times larger than that for open-isomer 1a. It is also confirmed that the photoirradiation evokes the photoisomerization character to show dramatic difference in the second-order NLO response, which can be applied to designing photochromic materials and reversible NLO switches.

[The study of vibrational spectra of 3-amino-2, 5-dichlorobenzoic acid by density functional theory].

To understand the relationship between the vibrational spectra and the geometry structure of 3-amino-2, 5-dichlorobenzoic acid (3A2, 5DBA) essentially, geometry optimizations and vibrational frequencies calculation of 3A2, 5DBA were performed at Hartree-Fock (HF) and Becke's three-parameter hybrid functional (B3) for the exchange part and the Lee-Yang-Parr (LYP) correlation function (B3LYP) level using 6-311G(d, p) basis set, respectively. The structural information and 45-complete normal vibrational modes of 3A2, 5DBA were obtained. Comparing the computational geometric parameters of 3A2, 5DBA with the values observed in experimental measurement of benzoic acid as well as the computed vibrational frequencies of 3A2, 5DBA with the reported data of pertinent literature, it was revealed that the results coming from B3LYP/6-311G(d, p) are more reasonable than those by HF/6-311G(d, p). Taking into account the difference between the computed 3A2, 5DBA molecule and the experimental measured sample, the calculated vibrational frequencies were reasonably scaled. Under the B3LYP/6-311G(d, p) method, the scale factor was 1.0013 for the vibrational frequencies with wave numbers <800 cm(-1), while the scale factor was 0.9613 for the vibrational frequencies with wave numbers >800 cm(-1). With the help of Gaussian View software package, the theoretically calculated vibrational frequencies were assigned much more accurately. In addition, the vibrational analysis of substitutive groups and main functional groups of 3A2, 5DBA was carried out. Through the comparison of the calculated vibrational frequencies with the frequencies of 3A2, 5DBA observed in FTIR experiment, the authors found that the theoretically calculated vibrational frequencies scaled reasonably were in excellent agreement with the data coming from experimental measurements. Meanwhile, according to the related literature reports, it was shown that our work done in the paper about vibrational assignments and vibrational analysis of 3A2, 5DBA turned out to be reasonable.