A highly efficient precatalyst for amination of aryl chlorides: synthesis, structure and application of a robust acenaphthoimidazolylidene palladium complex

A robust palladium NHC complex was synthesized and exhibits exceptional activity and selectivity as a precatalyst in the amination of aryl chlorides and tolerates a wide range of substrates at low catalyst loadings.     

Blue organic light-emitting supramolecular microfibers: the self-assembly of a 1,2,4-triazolo[1,5-a]pyrimidine derivative

The design and synthesis of 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine-2-thioaceto-(2-fluorobenzyl) hydrazone (TPTH), which self-assembled into supramolecular microfibers with blue organic light-emitting properties, is reported. This is the first occurrence of the molecular self-assembly of 1,2,4-triazolo[1,5-a]pyrimidine derivatives.     

Dynamic effects on reaction rates in a Michael addition catalyzed by chalcone isomerase. Beyond the frozen environment approach

We present a detailed microscopic study of the dynamics of the Michael addition reaction leading from 6'-deoxychalcone to the corresponding flavanone. The reaction dynamics are analyzed for both the uncatalyzed reaction in aqueous solution and the reaction catalyzed by Chalcone Isomerase. By means of rare event simulations of trajectories started at the transition state, we have computed the transmission coefficients, obtaining 0.76 +/- 0.04 and 0.87 +/- 0.03, in water and in the enzyme, respectively. According to these simulations, the Michael addition can be seen as a formation of a new intramolecular carbon-oxygen bond accompanied by a charge transfer essentially taking place from the nucleophilic oxygen to the carbon atom adjacent to the carbonyl group (C (alpha)). As for intermolecular interactions, we find a very significant difference in the evolving solvation pattern of the nucleophilic oxygen in water and in the enzyme. While in the former medium this atom suffers an important desolvation, the enzyme provides, through variations in the distances with some residues and water molecules, an essentially constant electric field on this atom along the reaction progress. Grote-Hynes (GH) theory provides a useful framework to systematically analyze all the couplings between the reaction coordinate and the remaining degrees of freedom. This theory provides transmission coefficients in excellent agreement with the Molecular Dynamics estimations. In contrast, neither the frozen environment approach nor Kramers theory gives results of similar quality, especially in the latter case, where the transmission coefficients are severely underestimated. The (unusual) failure of the frozen environment approach signals the importance of some dynamical motions. Within the context of GH theory, analysis of the friction spectrum obtained in the enzymatic environment, together with normal-mode analysis, is used to identify those motions, of both the substrate and the environment, strongly coupled to the reaction coordinate and to classify them as dynamically active or inactive.     

Synthesis of nanocrystals via microreaction with temperature gradient: towards separation of nucleation and growth

By utilizing the symmetrical temperature distribution in a tube furnace chamber, a capillary microreactor was designed with the microchannel passing two well-controlled, stable temperatures in steep temperature gradients. The two-temperature microreator, first developed and implemented by this research team, provides an opportunity to separate the nucleation and growth of semiconductor nanocrystals, leading to better control of nucleation and growth kinetics. For the synthesis of CdSe nanocrystals as a model system, we demonstrated the improved size uniformity achieved by the two-temperature approach, confirming the success of the use of high temperature to burst nucleation and low temperature to promote growth.     

Theoretical study of catalytic efficiency of a Diels-Alderase catalytic antibody: an indirect effect produced during the maturation process

The Diels-Alder reaction is one of the most important and versatile transformations available to organic chemists for the construction of complex natural products, therapeutics agents, and synthetic materials. Given the lack of efficient enzymes capable of catalyzing this kind of reaction, it is of interest to ask whether a biological catalyst could be designed from an antibody-combining site. In the present work, a theoretical study of the different behavior of a germline catalytic antibody (CA) and its matured form, 39 A-11, that catalyze a Diels-Alder reaction has been carried out. A free-energy perturbation technique based on a hybrid quantum-mechanics/molecular-mechanics scheme, together with internal energy minimizations, has allowed free-energy profiles to be obtained for both CAs. The profiles show a smaller barrier for the matured form, which is in agreement with the experimental observation. Free-energy profiles were obtained with this methodology, thereby avoiding the much more demanding two-dimensional calculations of the energy surfaces that are normally required to study this kind of reaction. Structural analysis and energy evaluations of substrate-protein interactions have been performed from averaged structures, which allows understanding of how the single mutations carried out during the maturation process can be responsible for the observed fourfold enhancement of the catalytic rate constant. The conclusion is that the mutation effect in this studied germline CA produces a complex indirect effect through coupled movements of the backbone of the protein and the substrate.     

Molecular dynamics simulations of polycarbonate doped with Lemke chromophores

In the search for optimal electro-optical modulating materials we report in this work molecular dynamics simulations of polycarbonate doped with Lemke chromophores which is a promising candidate system for materials with such functionality. The simulations cover the electric field poling effects on the chromophore order at a temperature above the glass transition temperature (Tg) of the material, the cooling procedure from liquid state to the glass state in the presence of the poling field, and the back relaxation of the system after removal of the field. Our study shows that electric field poling results in a higher chromophore order and that the order is also maintained during the cooling procedure with the poling field applied. In the liquid state, the applied poling field has little effect on the structure of the material. However, after the cooling procedure, the structure changes significantly because the polymer matrix tends to become closely packed. Our study thus indicates that for the bulk material, the structure of the host matrix is very important in determining the performance of the material.     

Intramolecular electron transfer initiated cation and radical formation through carbon-carbon bond activation

Radical cations can be formed in a spatially and temporally controlled manner by appending a sacrificial photooxidant to an easily oxidized substrate, leading to intramolecular electron transfer upon irradiation. The anthraquinone carboxyl group is an effective photooxidant that can promote single electron oxidation from an appended arene. The resulting intermediates undergo a cleavage reaction through carbon-carbon bond activation to provide either cations or radicals that react to form a range of products.     

Stabilization of continuum generation from normally dispersive nonlinear optical fibers for a tunable broad bandwidth source for optical coherence tomography

Continuum generation from normally dispersive ultrahigh-numerical-aperture fibers deteriorates in relatively short times, limiting its application as a practical optical source for high-resolution optical coherence tomography. We find that reversible light-induced structural modification of fiber optic materials, rather than permanent optical damage, is responsible for this deterioration. By examining how the optical properties of corresponding light-induced waveguides depend on pumping wavelength, we isolate a waveguide that is beneficial for stable continuum generation. The performance deterioration due to the formation of other waveguides can be reversed by overwriting them with this particular waveguide.     

A new synthesis method for benzo[f]quinolin‐3‐carbonyl urea and thiourea derivatives in aqueous media catalyzed by TEBAC

A clean and simple synthesis procedure for benzo[f]quinolin‐3‐carbonyl urea and thiourea derivatives was developed based on the reaction between N‐arylidenenaphthalen‐2‐amine and barbituric acid or thiobarbituric acid in aqueous media catalyzed by triethylbenzylammonium chloride (TEBAC). It was interesting that the structures of products in solvent of DMSO‐d₆ solution were different from those of the crystal states, which keep the enol form. The products were characterized by ¹H NMR, and ¹³C NMR, and the crystal state was confirmed by X‐ray diffraction study of 3e . In addition, water was chosen as green solvent.     

Study on Spectrophotometric Method for Determination of Bismuth after Flotation Separation Using Microcrystalline Adsorption System

The paper presents a novel method for the flotation separation of Bi³⁺ using microcrystalline adsorption system prior to the determination by spectrophotometry. The effects of different parameters, such as the dosages of KI and dodecyl trimethyl ammonium bromide (DTMAB), various salts and acidity etc. on the flotation yield of Bi³⁺ have been investigated to select the optimum experimental conditions. The possible flotation separation mechanism of Bi³⁺ was discussed. The results showed that under the optimum conditions, dodecyl trimethyl ammonium bromide cation (DTMAB⁺ ) reacted with I^? to produce themicrocrystalline matter (Ms‐M) of (DTMAB⁺·I^?), the water‐insoluble ternary association complex of (DTMAB)₃[BiI₆] which produced by Bi³⁺ and I^?, DTMAB⁺ was quantificationally adsorbed on the surface of Ms‐M of (DTMAB⁺·I^?) and was floated above water phase, the liquid‐solid phases were formed with clear interface. In this condition, K⁺, Na⁺, Ca²⁺, Mg²⁺, Co²⁺, Ni²⁺, Mn²⁺, Zn²⁺, Fe²⁺ and Al³⁺ could not be floated. Therefore, Bi³⁺ was separated completely from the above metal ions. A new method for flotation separation and determination of bismuth using microcrystalline adsorption system was established. The proposed method has been successfully applied to the determination of Bi³⁺ in bismuthiferous drug samples, and the results agreed well with those obtained by pharmacopoeia method. The recoveries were 94.1%～106.8%, and the RSD was 1.5%～2.3%.