Synthesis of new binol based [1+1] macrocyclic chiral manganese(III) Schiff bases as catalysts for asymmetric epoxidation

A series of new chiral binol based [1+1] macrocyclic Schiff bases have been synthesized in high yields in short reaction times via cyclo-condensation of dialdehydes with long tethers and chiral diamines. Macrocyclic Mn(salen) complexes containing N₂O₂ salen units incorporated with spacers of increased tether lengths were synthesized and characterized. The newly synthesized catalyst system was successfully employed for the enantioselective epoxidation of unfunctionalized olefins with high yields and good enantioselectivity.     

Design of bicontinuous donor/acceptor morphologies for use as organic solar cell active layers

In recent works, we demonstrated the achievement of bicontinuous donor/acceptor morphologies by the addition of conjugated block copolymers to a blend of conjugated homopolymer donors and fullerene acceptors. However, the domain sizes resulting in experiments were much larger than those of interest for high‐performance organic solar cells. Moreover, a significant concentration of fullerene acceptors was present in the donor domains. Here, we utilize simulations to study the bicontinuous donor/acceptor morphologies that result for different parametric conditions. Using such results, we provide guidelines for how to blend polymer materials to give rise to bicontinuous phases with the smaller and more compositionally pure domains that are desirable for organic photovoltaic applications. Our results can be generalized to treat a large range of donor and acceptor monomers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 884–895     

Synthesis,Characterization, DNA Binding,Light Switch “On and Off”, Docking Studies and Cytotoxicity,of Ruthenium(II) and Cobalt(III) Polypyridyl Complexes

The novel ligand (dmbip) 2-(4-N, N-dimethylbenzenamine)1H-imidazo[4, 5-f][1, 10]phenanthroline and its complexes [Ru(phen)₂dmbip]²⁺ (1), [Ru(bpy)₂dmbip]²⁺ (2), [Co(phen)₂dmbip]³⁺ (3) and [Co(bpy)₂dmbip]³⁺ (4) [where phen?=?1, 10-phenanthroline, bpy?=?2, 2^′-bipyridine], have been synthesized and characterized by elemental analysis, IR, UV-Vis, ¹H NMR, ¹³C NMR and Mass spectra. The DNA binding properties of the complexes were investigated by absorption, emission, quenching studies, light switch “on and off”, salt dependent, sensor (cation and anion) studies, viscosity measurements, cyclic voltammetry, molecular modeling and docking studies. The four complexes were screened for Photo cleavage of pBR322 DNA, antimicrobial activity and cytotoxicity. The experimental results indicate that the four complexes can intercalate into DNA base pairs. The DNA-binding affinities of these complexes follow the order [Ru(phen)₂dmbip]²⁺ > [Co(phen)₂dmbip]³⁺ > [Ru(bpy)₂dmbip]²⁺ > [Co(bpy)₂dmbip]³⁺.     

Novel Asymmetric Synthesis of (S)-Esmolol Using Hydrolytic Kinetic Resolution

An efficient asymmetric synthesis of (S)-methyl 3-[4-[2-hydroxy-3-(isopropyl amino) propoxy] phenyl] propanoate is described. The key intermediate (S)-methyl 3-[4-(oxiran-2-ylmethoxy) phenyl] propanoate was obtained by hydrolytic kinetic resolution method using Jacobsen catalyst.

Sampling free energy surfaces as slices by combining umbrella sampling and metadynamics

Metadynamics (MTD) is a very powerful technique to sample high‐dimensional free energy landscapes, and due to its self‐guiding property, the method has been successful in studying complex reactions and conformational changes. MTD sampling is based on filling the free energy basins by biasing potentials and thus for cases with flat, broad, and unbound free energy wells, the computational time to sample them becomes very large. To alleviate this problem, we combine the standard Umbrella Sampling (US) technique with MTD to sample orthogonal collective variables (CVs) in a simultaneous way. Within this scheme, we construct the equilibrium distribution of CVs from biased distributions obtained from independent MTD simulations with umbrella potentials. Reweighting is carried out by a procedure that combines US reweighting and Tiwary–Parrinello MTD reweighting within the Weighted Histogram Analysis Method (WHAM). The approach is ideal for a controlled sampling of a CV in a MTD simulation, making it computationally efficient in sampling flat, broad, and unbound free energy surfaces. This technique also allows for a distributed sampling of a high‐dimensional free energy surface, further increasing the computational efficiency in sampling. We demonstrate the application of this technique in sampling high‐dimensional surface for various chemical reactions using ab initio and QM/MM hybrid molecular dynamics simulations. Further, to carry out MTD bias reweighting for computing forward reaction barriers in ab initio or QM/MM simulations, we propose a computationally affordable approach that does not require recrossing trajectories. © 2016 Wiley Periodicals, Inc.     

Monte Carlo simulation of electrodeposition of copper: a multistep free energy calculation

Electrodeposition of copper (Cu) involves length scales of a micrometer or even less. Several theoretical techniques such as continuum Monte Carlo, kinetic Monte Carlo (KMC), and molecular dynamics have been used for simulating this problem. However the multiphenomena characteristics of the problem pose a challenge for an efficient simulation algorithm. Traditional KMC methods are slow, especially when modeling surface diffusion with large number of particles and frequent particle jumps. Parameter estimation involving thousands of KMC runs is very time-consuming. Thus a less time-consuming and novel multistep continuum Monte Carlo simulation is carried out to evaluate the step wise free energy change in the process of electrochemical copper deposition. The procedure involves separate Monte Carlo codes employing different random number criterion (using hydrated radii, bare radii, hydration number of the species, redox potentials, etc.) to obtain the number of species (CuCl(2) or CuSO(4) or Cu as the case may be) and in turn the free energy. The effect of concentration of electrolyte, influence of electric field and presence of chloride ions on the free energy change for the processes is studied. The rate determining step for the process of electrodeposition of copper from CuCl(2) and CuSO(4) is also determined.     

Influence of molecular weight and degree of segregation on local segmental dynamics of ordered block copolymers

Experiments in the context of block copolymer electrolyte materials have observed intriguing dependence of the ionic conductivities upon the polymer molecular weight and the degree of segregation between the blocks. Such results have been partly rationalized by invoking the spatial extent of dynamical inhomogeneities that manifest in ordered phases of block copolymers comprised of a rubbery and a glassy block. Motivated by such observations, we use molecular dynamics simulations to study the extent of spatial inhomogeneities in segmental dynamics of lamellar diblock copolymer systems where the blocks possess different mobilities. We probed the local average relaxation times and the dynamical heterogeneities as a function of distance from the interface. Our results suggest that the relaxation times of rubbery segments are strongly influenced by both the spatial proximity to the interface and the relative mobility of the glassy segments. Scaling of our results indicate that the interfacial width of the ordered phases serves as the length scale underlying the spatial inhomogeneities in segmental dynamics of the fast monomers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 859–864     

Versatile Fluorescent Carbon Dots from Citric Acid and Cysteine with Antimicrobial,Anti-biofilm,Antioxidant, and AChE Enzyme Inhibition Capabilities

Nanostructured fluorescent particles derived from natural molecules were prepared by a green synthesis technique employing a microwave method. The precursors citric acid (CA) and cysteine (Cys) were used in the preparation of S- and N-doped Cys carbon dots (Cys CDs). Synthesis was completed in 3 min. The graphitic structure revealed by XRD analysis of Cys CDs dots had good water dispersity, with diameters in the range of 2–20 nm determined by TEM analysis. The isoelectric point of the S, N-doped CDs was pH value for 5.2. The prepared Cys CDs displayed excellent fluorescence intensity with a high quantum yield of 75.6?±?2.1%. Strong antimicrobial capability of Cys CDs was observed with 12.5 mg/mL minimum bactericidal concentration (MBC) against gram-positive and gram-negative bacteria with the highest antimicrobial activity obtained against Staphylococcus aureus. Furthermore, Cys CDs provided total biofilm eradication and inhibition abilities against Pseudomonas aeruginosa at 25 mg/mL concentration. Cys CDs are promising antioxidant materials with 1.3?±?0.1 μmol Trolox equivalent/g antioxidant capacity. Finally, Cys CDs were also shown to inhibit the acetylcholinesterase (AChE) enzyme, which is used in the treatment of Alzheimer’s disease, even at the low concentration of 100 μg/mL.

     

Computational Modeling of Boundary Layer Flashback in a Swirling Stratified Flame Using a LES-Based Non-Adiabatic Tabulated Chemistry Approach

When operating under lean fuel–air conditions, flame flashback is an operational safety issue in stationary gas turbines. In particular, with the increased use of hydrogen, the propagation of the flame through the boundary layers into the mixing section becomes feasible. Typically, these mixing regions are not designed to hold a high-temperature flame and can lead to catastrophic failure of the gas turbine. Flame flashback along the boundary layers is a competition between chemical reactions in a turbulent flow, where fuel and air are incompletely mixed, and heat loss to the wall that promotes flame quenching. The focus of this work is to develop a comprehensive simulation approach to model boundary layer flashback, accounting for fuel–air stratification and wall heat loss. A large eddy simulation (LES) based framework is used, along with a tabulation-based combustion model. Different approaches to tabulation and the effect of wall heat loss are studied. An experimental flashback configuration is used to understand the predictive accuracy of the models. It is shown that diffusion-flame-based tabulation methods are better suited due to the flashback occurring in relatively low-strain and lean fuel–air mixtures. Further, the flashback is promoted by the formation of features such as flame tongues, which induce negative velocity separated boundary layer flow that promotes upstream flame motion. The wall heat loss alters the strength of these separated flows, which in turn affects the flashback propensity. Comparisons with experimental data for both non-reacting cases that quantify fuel–air mixing and reacting flashback cases are used to demonstrate predictive accuracy.