Preparation,characterization and electroluminescence studies of copper doped zinc sulfide nanocrystals

Copper doped zinc sulfide nanoparticles were prepared by chemical precipitation method. The size of the particles was varied by changing the concentration of capping agent. The XRD studies indicate that most of the samples are cubic in nature. The broadening of peaks tends to increase with increasing capping agent concentration showing decrease in particle size. The crystalline size computed using Scherrer formula is found to be in range of 3–10 nm. Absorption spectra show absorption edge in UV region. The edge was found to shift towards shorter wavelength as the capping agent concentration is increased. This indicates increased effective band gap and hence reduced particle size. The nanoparticle size has been estimated in the range 5–10 nm using effective mass approximation model. For electroluminescence (EL) study of ZnS:Cu nanocrystals, the EL cells were prepared by placing ZnS:Cu nanoparticles between SnO₂ coated conducting glass plate and aluminum foil. Alternating voltage of various frequencies was applied and EL brightness (B) at different voltages (V) was measured and reported in this paper.     

First example of an ice-like water hexamer boat tape structure in a supramolecular organic host

A T6(2) tape of hydrogen bonded water molecules in boat cyclohexane conformation resides in the channel structure of a dibromophloroglucinol (DBPG) host; water escapes at 40-90 degrees C but is readily re-absorbed by the sponge-like apohost.     

Deriving crisp and consistent priorities for fuzzy AHP-based multicriteria systems using non-linear constrained optimization

Fuzzy optimization models are used to derive crisp weights (priority vectors) for the fuzzy analytic hierarchy process (AHP) based multicriteria decision making systems. These optimization models deal with the imprecise judgements of decision makers by formulating the optimization problem as the system of constrained non linear equations. Firstly, a Genetic Algorithm based heuristic solution for this optimization problem is implemented in this paper. It has been found that the crisp weights derived from this solution for fuzzy-AHP system, sometimes lead to less consistent or inconsistent solutions. To deal with this problem, we have proposed a consistency based constraint for the optimization models. A decision maker can set the consistency threshold value and if the solution exists for that threshold value then crisp weights can be derived, otherwise it can be concluded that the fuzzy comparison matrix for AHP is not consistent for the given threshold. Three examples are considered to demonstrate the effectiveness of the proposed method. Results with the proposed constraint based fuzzy optimization model are more consistent than the existing optimization models.     

Unravelling the Role of Water in Ultrafast Excited-State Relaxation Dynamics within Nano-Architectures of Chlorophyll a

Water plays a pivotal role in structural stability of supramolecular pigment assemblies designed for natural light harvesting (for example, chlorosome antenna complex) as well as their artificial analogs. However, the dynamic role of water in the context of excite-state relaxation has not been explored till date, which we report here. Using femtosecond transient absorption spectroscopy, we investigate the excited-state dynamics of two types of nano-scale assemblies of chlorophyll a with different structural motifs, rod-shaped and micellar assemblies, that depend on the water content. We show how water participates in excess energy dissipation by vibrational cooling of the non-thermally populated Q_y band at different rates in different types of clusters but exhibits no polar solvation dynamics. For the micelles, we observe a bifurcation of stimulated emission line shape, whereas a positive-to-negative switching of differential absorption is observed for the rods; both these observations are correlated with their specific structural aspects. Density functional theory calculations reveal two possible stable ground state geometries of dimers, accounting for the bifurcation of line shape in micelles. Thus, our study elucidates water-mediated structure–function relationship within these pigment assemblies.     

Design and Synthesis of Imidazole and Triazole Pyrazoles as Mycobacterium Tuberculosis CYP121A1 Inhibitors

The emergence of untreatable drug-resistant strains of Mycobacterium tuberculosis is a major public health problem worldwide, and the identification of new efficient treatments is urgently needed. Mycobacterium tuberculosis cytochrome P450 CYP121A1 is a promising drug target for the treatment of tuberculosis owing to its essential role in mycobacterial growth. Using a rational approach, which includes molecular modelling studies, three series of azole pyrazole derivatives were designed through two synthetic pathways. The synthesized compounds were biologically evaluated for their inhibitory activity towards M. tuberculosis and their protein binding affinity (K_D). Series 3 biarylpyrazole imidazole derivatives were the most effective with the isobutyl ( 10 f ) and tert-butyl ( 10 g ) compounds displaying optimal activity (MIC 1.562 μg/mL, K_D 0.22 μM ( 10 f ) and 4.81 μM ( 10 g )). The spectroscopic data showed that all the synthesised compounds produced a type II red shift of the heme Soret band indicating either direct binding to heme iron or (where less extensive Soret shifts are observed) putative indirect binding via an interstitial water molecule. Evaluation of biological and physicochemical properties identified the following as requirements for activity: LogP >4, H-bond acceptors/H-bond donors 4/0, number of rotatable bonds 5–6, molecular volume >340 ų, topological polar surface area <40 Ų.     

Experimental study of transient heat transfer characteristics of single-phase natural convection in multidimensional porous bed with volumetric heat generation

Natural convection in an internally heated porous bed of height and diameter of 450 mm and 500 mm, respectively, and superposed with the fluid layer has been experimentally investigated. The onset of natural convection in the bed is indicated by change in the rate of temperature rise within the bed. An empirical model based on local Nusselt number and local Rayleigh number has been developed. A comparison of the present model with the models in literature is made to draw out the differences between the local heat transfer of large multidimensional beds and the average heat transfer of small beds.     

Lewis acid-catalyzed one-pot, three-component route to chiral 3,3'-bipyrroles

3,3'-Bipyrroles 3 could be synthesized using a double Michael addition reaction involving diaroyl acetylene 1 and the appropriate 1,3-dicarbonyls 2 using ammonium acetate as a nitrogen source. The axial chirality of bipyrrole was anticipated from the X-ray crystal structure and DFT calculations and confirmed by separating the racemates on a chiral column and subsequent CD spectra of the enantiomers. The absolute configuration of the enantiomers was achieved by theoretical CD spectra calculation using the ZINDO method.     

Tri­phenyl(3,4,5‐tri­iodo­phenyl)­methane

The crystal structure of the title compound, alternatively called 1,2,3‐triiodo‐5‐(triphenylmethyl)benzene, C₂₅H₁₇I₃, is analysed in terms of I⋯I and I⋯π interactions and the herring‐bone T motif between phenyl groups. There are two mol­ecules in the asymmetric unit, denoted A and B. Inversion‐related A mol­ecules are connected via an I⋯π interaction (3.641 Å, to a C—C bond mid‐point) to form an I⋯π dimer, and these dimers are connected through symmetry‐independent B mol­ecules via I⋯I [3.5571 (15) Å] and I⋯π (3.561 Å, to a C—C bond mid‐point) interactions.     

Directed transverse flow and its disappearance for asymmetric reactions

We study the directed transverse flow for mass asymmetry reactions. This is done by keeping the target fixed and varying the projectile mass from ⁴He to ¹³¹Xe. We find that directed transverse flow is sensitive to the mass of the projectile. We also study the disappearance of flow at a particular impact parameter called Geometry of Vanishing Flow (GVF) for such mass asymmetry reactions. Our results indicate that GVF is sensitive to the beam energy as well as to the mass of the projectile.