On the perturbation of the H-bonding interaction in ethylene glycol clusters upon hydration

Ab initio and density functional methods have been employed to study the structure, stability, and spectral properties of various ethylene glycol (EG(m)) and ethylene glycol-water (EG(m)W(n)) (m = 1-3, n = 1-4) clusters. The effective fragment potential (EFP) approach was used to explore various possible EG(m)W(n) clusters. Calculated interaction energies of EG(m)W(n) clusters confirm that the hydrogen-bonding interaction between EG molecules is perturbed by the presence of water molecules and vice versa. Further, energy decomposition analysis shows that both electrostatic and polarization interactions predominantly contribute to the stability of these clusters. It was found from the same analysis that ethylene glycol-water interaction is predominant over the ethylene glycol-ethylene glycol and water-water interactions. Overall, the results clearly illustrate that the presence of water disrupts the ethylene glycol-ethylene glycol hydrogen bonds.     

Generation of phosphorescent triplet states via photoinduced electron transfer: energy and electron transfer dynamics in Pt porphyrin-Rhodamine B dyads

Control over generation and dynamics of excited electronic states is fundamental to their utilization in all areas of technology. We present the first example of multichromophoric systems in which emissive triplet states are generated via a pathway involving photoinduced electron transfer (ET), as opposed to local intrachromophoric processes. In model dyads, PtP-Ph(n)-pRhB(+) (1-3, n = 1-3), comprising platinum(II) meso-tetraarylporphyrin (PtP) and Rhodamine B piperazine derivative (pRhB(+)), linked by oligo-p-phenylene bridges (Ph(n)), upon selective excitation of pRhB(+) at a frequency below that of the lowest allowed transition of PtP, room-temperature T(1)→S(0) phosphorescence of PtP was observed. The pathway leading to the emissive PtP triplet state includes excitation of pRhB(+), ET with formation of the singlet radical pair, intersystem crossing within that pair, and subsequent radical recombination. Because of the close proximity of the triplet energy levels of PtP and pRhB(+), reversible triplet-triplet (TT) energy transfer between these states was observed in dyads 1 and 2. As a result, the phosphorescence of PtP was extended in time by the long decay of the pRhB(+) triplet. Observation of ET and TT in the same series of molecules enabled direct comparison of the distance attenuation factors β between these two closely related processes.     

Synthetic study on the relationship between structure and sweet taste properties of steviol glycosides

The structure activity relationship between the C??-C?? methylene double bond on the aglycone of steviol glycosides and the corresponding impact on their sweet taste has been reported here for the first time. It has been observed that converting stevioside and rebaudioside A to their corresponding ketones by switching the doubly bonded methylene on C-17 for a ketone group actually removes the sweet taste properties of these molecules completely. Regenerating the original molecules tends to restore the sweet taste of both the steviol glycosides. Thus this C??-C?? methylene double bond in rebaudioside A and stevioside can be regarded as a pharmacophore essential for the sweetness property of these molecules.     

Self-supported chiral titanium cluster (SCTC) as a robust catalyst for the asymmetric cyanation of imines under batch and continuous flow at room temperature

A robust heterogeneous self-supported chiral titanium cluster (SCTC) catalyst and its application in the enantioselective imine-cyanation/Strecker reaction is described under batch and continuous processes. One of the major hurdles in the asymmetric Strecker reaction is the lack of availability of efficient and reusable heterogeneous catalysts that work at room temperature. We exploited the readily hydrolyzable nature of titanium alkoxide to synthesize a self-supported chiral titanium cluster (SCTC) catalyst by the controlled hydrolysis of a preformed chiral titanium-alkoxide complex. The isolated SCTC catalysts were remarkably stable and showed up to 98 % enantioselectivity (ee) with complete conversion of the imine within 2 h for a wide variety of imines at room temperature. The heterogeneous catalysts were recyclable more than 10 times without any loss in activity or selectivity. The robustness, high performance, and recyclability of the catalyst enabled it to be used in a packed-bed reactor to carry out the cyanation under continuous flow. Up to 97 % ee and quantitative conversion with a throughput of 45 mg h(-1) were achieved under optimized flow conditions at room temperature in the case of benzhydryl imine. Furthermore, a three-component Strecker reaction was performed under continuous flow by using the corresponding aldehydes and amines instead of the preformed imines. A good product distribution was obtained for the formation of amino nitriles with ee values of up to 98 %. Synthetically useful ee values were also obtained for challenging α-branched aliphatic aldehyde by using the three-component continuous Strecker reaction.     

Photosensitive Surfactants with Various Hydrophobic Tail Lengths for the Photocontrol of Genomic DNA Conformation with Improved Efficiency

We report the synthesis and characterisation of photosensitive cationic surfactants with various hydrophobic tail lengths. These molecules, called AzoCx, are used as photosensitive nucleic acid binders (pNABs) and are applied to the photocontrol of DNA conformation. All these molecules induce DNA compaction in a photodependent way, originating in the photodependent polarity of their hydrophobic tails. We show that increasing hydrophobicity strongly enhances the compaction efficiencies of these molecules, but reduces the possibility of reversible photocontrol of a DNA conformation. Optimal performance was achieved with AzoC5, which allowed reversible control of DNA conformation with light at a concentration seven times smaller than previously reported.     

Multiple parents crossover operators: A new approach removes the overlapping solutions for sequencing problems

Maintaining population diversity throughout generations of Genetic Algorithms (GAs) is key to avoid premature convergence. Redundant solutions is one cause for the decreasing population diversity. To prevent the negative effect of redundant solutions, we propose a framework that is based on the multi-parents crossover (MPX) operator embedded in GAs. Because MPX generates diversified chromosomes with good solution quality, when a pair of redundant solutions is found, we would generate a new offspring by using the MPX to replace the redundant chromosome. Three schemes of MPX will be examined and will be compared against some algorithms in literature when we solve the permutation flowshop scheduling problems, which is a strong NP-Hard sequencing problem. The results indicate that our approach significantly improves the solution quality. This study is useful for researchers who are trying to avoid premature convergence of evolutionary algorithms by solving the sequencing problems.     

Integration of barotropic vorticity equation over spherical geodesic grid using multilevel adaptive wavelet collocation method

In this paper, we present the multilevel adaptive wavelet collocation method for solving non-divergent barotropic vorticity equation over spherical geodesic grid. This method is based on multi-dimensional second generation wavelet over a spherical geodesic grid. The method is more useful in capturing, identifying, and analyzing local structure [1] than any other traditional methods (i.e. finite difference, spectral method), because those methods are either full or partial miss important phenomena such as trends, breakdown points, discontinuities in higher derivatives of the solution. Wavelet decomposition is used for interpolation and adaptive grid refinement on different levels.     

Regioselective reductive openings of acetals; mechanistic details and synthesis of fluorescently labeled compounds

Regioselective reductive openings of mixed phenolic-benzylic acetals, using BH3.NMe3-AlCl3, was investigated, and a mechanism where the outcome is directed by the electrostatic potential of the two oxygen atoms is presented. The regioselective acetal opening was used in the synthesis of a fluorescently labeled analogue to antiproliferative xylosides. The fluorescently labeled xyloside was tested for uptake, antiproliferative activity, and glycosaminoglycan priming in different cell lines. The xyloside was taken up by all cell lines but did not initiate glycosaminoglycan biosynthesis.     

Stereoselective synthesis of Z-alpha-aryl-alpha,beta-unsaturated esters

An efficient method for the stereoselective synthesis of (Z)-alpha-arylacrylates is described. Treatment of alpha-hydroxyesters with triflic anhydride and pyridine at 0 degrees C followed by warming to room temperature afforded the corresponding (Z)-alpha-aryl-alpha,beta-unsaturated esters in very good yields and excellent stereoselectivity.     

Error estimation and adaptation for functional outputs in time-dependent flow problems

The paper presents an adjoint-based approach for determining global error in the time domain that is relevant to functional outputs from unsteady flow simulations. The algorithm is derived for the unsteady Euler equations that are discretized for second-order accuracy in both space and time and takes into account the effect of dynamic meshes. In addition to error due to temporal resolution, the formulation also takes into account algebraic error arising from partial convergence of the governing equations at each implicit time-step. The resulting error distributions are then used to drive adaptation of the temporal resolution and the convergence tolerances for the governing equations at each time-step. The method is demonstrated in the context of both time-integrated and instantaneous functionals and the results are compared against traditional adaptation methods.