Reversible photochromism of a ferrocenylazobenzene monolayer controllable by a single green light source

A 3-ferrocenylazobenzene monolayer on an ITO electrode exhibits reversible azobenzene isomerization using a single green light source, assisted by electrochemical control of the ferrocene redox state.     

Cis-trans isomerization of styrylpyrroles by stray light

A series of substituted N-methylstyrylpyrroles (H, p-Br, p-CN, o,p-diCl, m-CH₃, m-CN, m-NO₂) were prepared via the Wittig reaction of 1-methylpyrrole-2-carboxaldehyde and substituted benzyltriphenylphosphonium bromides. Both cis and trans isomers were found to be present in the reaction mixture and they were separable by column chromatography in a few cases (H, p-Br, m-CN, m-NO₂). Photochemical isomerizations of cis-styrylpyrroles to trans isomers were observed when the substituents were o,p-diCl and m-NO₂, while the opposite was the case with compounds having H, p-Br, m-CH₃, m-CN. It was difficult to separate the cis and trans mixture of p-cyanostyrylpyrroles and the equilibrium ratio did not change under similar photochemical reaction conditions.     

Fast reversible isomerization of merocyanine as a tool to quantify stress history in elastomers

A mechanochemistry based approach is proposed to detect and map stress history during dynamic processes. Spiropyran (SP), a force sensitive molecular probe, was incorporated as a crosslinker into multiple network elastomers (MNE). When these mechanochromic MNEs are loaded, SP undergoes a well-known force-activated reaction to merocyanine (MC) changing its absorption in the visible range (visible blue color). This SP to MC transition is not reversible within the time frame of the experiment and the color change reports the concentration of activated molecules. During subsequent loading–unloading cycles the MC undergoes a fast and reversible isomerization resulting in a slight shift of absorption spectrum and results in a second color change (blue to purple color corresponding to the loading–unloading cycles). Quantification of the color changes by using chromaticity shows that the exact color observed upon unloading is characteristic not only of the current stress (reported by the shift in color due to MC isomerization), but of the maximum stress that the material has seen during the loading cycle (reported by the shift in color due to the change in MC concentration). We show that these two color changes can be separated unambiguously and we use them to map the stress history in the loading and unloading process occurring as a crack opens up and propagates, breaking the material. Color maps on fractured samples are compared with finite element simulations and the agreement is excellent.

A mechanochemistry based approach is proposed to detect and map stress history during dynamic processes.     

Polymeric tertiaryphosphine as a green and recyclable organocatalyst for stereoselective isomerization reaction

A green, simple and effective polymeric organocatalytic system, polymer-supported triphenylphosphine (PS-TPP), for the stereoselective isomerization of α,β-ynones to (E,E)-α,β-γ,δ-dienones is reported here. The catalyst, PS-TPP could be recovered by simple filtration and reused several times with high activity.     

E-selective isomerization of stilbenes and stilbenoids through reversible hydroboration

Hydroboration of a mixture of E and Z stilbenes and stilbenoids is followed by an elimination reaction to yield the E isomer with high stereoselectivity. The reaction tolerates aromatic substituents with varying stereoelectronic properties, occurs in one pot, and requires only commercially available reagents. An illustration of the isomerization reaction in a synthesis of resveratrol, a biologically active antioxidant, is presented.     

Strong and reversible binding of carbon dioxide in a green metal-organic framework

The efficient capture and storage of gaseous CO(2) is a pressing environmental problem. Although porous metal-organic frameworks (MOFs) have been shown to be very effective at adsorbing CO(2) selectively by dint of dipole-quadruple interactions and/or ligation to open metal sites, the gas is not usually trapped covalently. Furthermore, the vast majority of these MOFs are fabricated from nonrenewable materials, often in the presence of harmful solvents, most of which are derived from petrochemical sources. Herein we report the highly selective adsorption of CO(2) by CD-MOF-2, a recently described green MOF consisting of the renewable cyclic oligosaccharide γ-cyclodextrin and RbOH, by what is believed to be reversible carbon fixation involving carbonate formation and decomposition at room temperature. The process was monitored by solid-state (13)C NMR spectroscopy as well as colorimetrically after a pH indicator was incorporated into CD-MOF-2 to signal the formation of carbonic acid functions within the nanoporous extended framework.     

Sampling effects on observed cyclopropane isomerization in a single pulse shock tube

Cyclopropane in argon mixtures was heated in a single-pulse shock tube, and syringes were used to withdraw samples from both the central gas slug and the gas adjacent to the tube walls. Differences were observed in the measured conversion, with larger conversion found in the center location. The discrepancy increased with increasing conversion, and the results indicate that boundary-layer effects can seriously affect the results of absolute single-pulse shock-tube studies when percent conversion is large.     

A neutral state green polymer with a superior transmissive light blue oxidized state

This report highlights the synthesis of only the second green polymer in the literature, which possesses superior properties over the first: a highly transmissive light blue color in the oxidized state with high optical contrast and excellent switching properties.     

Asymmetric reversible structural switching of a diene coordination polymer promoted by UV-visible light

In natural and artificial systems,reversible reactions are commonly asymmetric with respect to the time scale and nature of the stimuli which drive the forward and backward processes.In applications for which switching behavior is required,it is desirable that the reversible reaction goes as close to symmetric as possible;however,such systems are uncommon.Herein,we report an example of ultraviolet(UV)-visible light-regulated asymmetric reversible structural switching involving a diene-based coor...     

糖尿病综合症新药Epalrestat的光敏异构化研究

Epalrestat是一种治疗糖尿病晚期综合症的新药。它可以缓解糖尿病型视网膜病变,运动神经传导阻滞等症状。绕丹宁乙酸与α-甲基肉桂醛在乙酸中缩合得到了Epalrestat,并利用了高压液相色谱,X衍射,高分辨率核磁共振,对它的立体异构进行了研究,还研究了它的保存条件。发现Epalrestat的四个立体异构体中(Z,E)构型占96.5%。见光后易发生异构化,产物中(Z,Z)构型的含量可达到37.7%。而避光保存一年后(Z,E)仍能保持93.6%的含量。     

Method for performing a single act of the reversible separation of ideal solution components

Russian Journal of Physical Chemistry A - A method for performing a single act of separation of the components contained in a liquid solution of optical isomers in a reversible process is proposed....     

Modelling the hydrolysis of succinimide: formation of aspartate and reversible isomerization of aspartic acid via succinimide

In the present study, we have modelled the nucleophilic attack of water and a hydroxyl anion on the carbonyl carbon of a succinimide derivative leading to aspartate and aspartic acid. Calculations have been carried out at the B3LYP/6-31 +G* level in a vacuum. The IEF-PCM methodology has been used to carry out single point calculations in solution. In neutral medium, hydrolysis is facilitated by the presence of a polar continuum, whereas in basic medium the polar environment hinders the hydrolysis of succinimide. The deltaH degrees and deltaS degrees values for the cyclization reactions of aspartic acid yielding succinimide are 29.2 kJ mol(-1) and 133.5 kJ mol(-1) K(-1) respectively in accordance with the experimental results on the isomerization of the Ac-Asp-Gly-NHMe dipeptide unit. In a neutral medium, the isoaspartate: aspartate is found to be 2.2:1 in a vacuum and 3.4:1 in solution, in line with the experimental findings based on the hydrolysis of a tetrapeptide (Ac-Gly-Asn-Gly-Gly-NHMe) and a hexapeptide (Val-Tyr-Pro-Asn-Gly-Ala) where this ratio was found to be 3.1:1.     

On the scattering of a light pulse on a single atom perturbed by collisions with inert gas atoms

The excitation of the strontium-like systemS ₀ —P ₁ by the light pulse of duration comparable or larger than relaxation times is considered. The influence of the different pulse envelopes on the time evolution of the density matrix components and on energy spectrum is analyzed. In the case of large detuning and small Rabi frequency the secular approximation is adopted.     

On the scattering of a light pulse on a single atom perturbed by collisions with inert gas atoms

Scattering of a laser pulse on a single atom perturbed by collisions with inert gas atoms is described in terms of suitably defined cross-sections. The relations of the energy balance are explored to show the connection between attenuation and total cross-section for scattering. The different scattering channels, corresponding to the polarisation, spectral decomposition and coherence properties of the light are analysed in terms of the cross-sections. As an example we consider the scattering of a light pulse on an alkali metal atom with a frequency close to the atomic transition frequency from the ground stateS _1/2 to the first excited stateP _1/2.     

Redox-induced coordination isomerization of a phosphoniobenzophospholide

1-Triphenylphosphoniobenzo[c]phospholide 1 reacts with [M(CO)(5)Br] (M = Mn, Re) and [Mn(CO)(3)(naphthalene)][BF(4)] to give complexes cis-[M(CO)(4)(1)Br] (5 a,b) and [Mn(CO)(3)(1)][BF(4)] (6 a[BF(4)]), respectively, featuring eta(1)(P)- and eta(5)(pi)-coordination of the phosphole ring. The corresponding reactions with [M(2)(CO)(10)] proceed with conservation of the metal-metal bond and yield, depending on the reaction temperature, dinuclear complexes [M(2)(CO)(8)(1)] (M=Mn, 7 a) or [M(2)(CO)(6)(1)(2)] (M=Mn, Re, 8 a,b) with mu(2)-bridging eta(1)(P):eta(2)(Pdbond;C) coordination of the phosphole moiety. All complexes formed were characterized by spectroscopic data; 5 b, 6 a[BF(4)], and 8 a,b were characterized by X-ray diffraction studies as well. The structural and (31)P NMR data of the dinuclear manganese complex 8 a suggest that the interaction between the metal atoms and the eta(2)-bound Pdbond;C double bond moieties is dominated by the L-->M charge-transfer contribution; this hints at a very low back-donation ability of the central M(2)(CO)(6) fragment. Investigation of the reactions of the Mn complexes 6 a and 8 a with Mg or ferrocenium hexafluorophosphate ([Fc][PF(6)]), respectively, revealed that the chemically reversible mutual interconversion between both species was feasible. Likewise, oxidation of the rhenium complex 8 b with [Fc][PF(6)] gave spectroscopic evidence for the formation of a Re analogue of 6 a. Electrochemical studies suggested that the oxidation 8 a-->2 6 a involves two consecutive single-electron-transfer steps, the first of which is electrochemically reversible and produces a metastable radical cation that is detectable by ESR spectroscopy. The mutual interconversion between 6 a and 8 a represents the first case of a reversible coordination isomerization of a phosphaarene that is triggered by a redox process and might stimulate further studies directed at the use of dinuclear phosphaarene complexes in redox-catalysis.     

Kinetics of the iodine atom catalyzed gas phase geometrical isomerization of diiodoethylene. Rotation about a single bond

The spectrophotometric determination of the rate of iodine atom catalyzed geometrical isomerization of diiodoethylene in the gas phase from 502.8 to 609.1°K leads to a rate constant for the bimolecular reaction between I and trans-diiodoethylene of log k_t?c(M^?1 sec^?1) = 8.85 ± 0.12 ? (11.01 ± 0.30)/θ. Estimates of the entropy and enthalpy change for the addition of I atoms to trans-diiodoethylene (process a.b) lead to log K_a.b(M^?1) = ?2.99 ? 4.0/θ, and thus to log k_c (sec^?1) = log k_t?c – log K_ab = 11.8 ?7.0/θ for the rate constant for rotation about the single bond in the adduct radical. The theory for calculation of the rotation rate constant is presented and it is shown that while the exact value depends on the barrier height, a value of 6.8 kcal/mole for this quantity leads to log k (sec^?1) = 11.8 ?6.7/θ. The activation energy points to a better value of the group contribution to heat of formation of the group C -(I)₂(H)(C) than one based on bond additivity.