Enhancement of titanium dioxide photocatalysis by water-soluble fullerenes

Fullerenes are known for their unique electronic properties including high electron affinity. Although use of fullerenes for scavenging photo-generated electrons from titanium dioxide particles has been demonstrated, no attempts have been made to utilize the unique properties of fullerenes to increase the efficacy of photocatalysis. The present study has demonstrated that a mixture of water-soluble polyhydroxy fullerenes (PHF) and titanium dioxide (anatase polymorph) enhances photocatalytic degradation of organic dye. The PHF molecules adsorbed to the surface of titanium dioxide due to electrostatic forces, with adsorption density being higher at lower pH values. The surface coverage of titanium dioxide nanoparticles by PHF molecules determined the extent of enhancement, with an optimum dosed weight ratio of PHF to titanium dioxide at 0.001. Hydroxylation and concomitant solubilization of fullerenes allow their unique electronic properties to be harnessed for photocatalysis.     

Adsorption of Ni(II) on clays

The present work investigates the adsorptive interactions of Ni(II) ions with kaolinite, montmorillonite, and their poly(oxo zirconium) and tetrabutylammonium derivatives in aqueous medium. Batch adsorption studies were carried out with various Ni(II) concentrations, amount of clay adsorbents, pH, agitation time and temperature. The adsorption is strongly dependent on pH of the medium with enhanced adsorption as the pH turns from acidic to alkaline side till precipitation sets in. The process was very fast initially and maximum adsorption was observed within 180 min of agitation. The kinetics of the interactions, tested with pseudo first order Lagergren equation, second order kinetics, Elovich equation, liquid film diffusion model and intra-particle diffusion mechanism, showed better agreement with second order kinetics (k2 = 1.3 x 10(-2) to 5.3 x 10(-2) g/(mg min)). The adsorption data gave good fits with Langmuir and Freundlich isotherms and yielded Langmuir monolayer capacity of 2.75 to 21.14 mg/g and Freundlich adsorption capacity of 0.70 to 3.40 mg(1-1/n) l(1/n)/g for the clay adsorbents. The adsorption process was exothermic with Delta H in the range of -24.0 to -45.1 kJ/mol accompanied by decrease in entropy (DeltaS: -118.2 to -160.5 J/(mol K)) and Gibbs energy (Delta G: -34.6 to -49.5 kJ/mol). The results have shown that montmorillonite has the largest adsorption capacity followed by ZrO-montmorillonite, TBA-montmorillonite, kaolinite, ZrO-kaolinite and TBA-kaolinite. Introduction of ZrO- and TBA- groups into the clays reduced their adsorption capacity by blocking the available adsorption sites.     

Solid state structural evidence of chloroform-benzene-chloroform adduct trapped in hexaanthryl octaaminocryptand channels

Structural aspects governing the formation and stabilization of adducts in the organic channels were examined. An unprecedented structural evidence of an inverted sandwich-type benzene/chloroform (1:2) adduct was isolated within the channel formed by close packing of an aromatic substituted aminocryptand 1 host. Interestingly, this adduct was stabilized through several short contacts with the channel wall. Crystallographic study further showed that a channel formed by self-assembly of 1 can also encapsulate chloroform as a guest. Thermal analysis confirms that the chloroform-benzene-chloroform adduct as a guest has better thermal stability than that of the chloroform guest within the channel.     

Synthesis of [6,n] cis-fused ring compounds via Cr-mediated dearomatisation-ring-closing metathesis

cis-Fused [6,8], [6,7], [6,6] and [6,5] ring systems containing a cyclohexadiene ring unit, a cycloenone ring and a quaternary carbon at the ring junction were obtained in only two steps from [Cr(CO)3(eta6-p-methoxyphenyl oxazoline)]. The sequence proceeds via diastereoselective addition of three C-substituents across an arene double bond, followed by allylation and ring closing metathesis (RCM). RAMP-hydrazone and (R)-isopropyloxazoline were used as chiral auxiliaries to provide, after removal of the auxiliaries, the enantiomerically highly enriched [6,7] cis-fused system.     

Time-resolved measurements of hydroxyl in stable and extinguishing partially premixed turbulent opposed-jet flames

Quantitative hydroxyl time-series measurements from a set of stable and extinguishing turbulent opposed-flow partially premixed CH₄/air flames are used to investigate the effect of Reynolds number and fuel-side equivalence ratio on the structure of turbulent partially premixed flames. The hydroxyl (OH) integral time scale, computed from the autocorrelation function, is used to characterize OH fluctuations and is found to reach a minimum at the axial location of peak OH. Analyses of the duration of and period between bursts in the OH time series are used to examine the dynamics of flame-front motion. In general, with increasing Reynolds number (Re), the distribution in OH burst times shifts towards smaller time scales. A hydroxyl intermittency parameter is also defined from the bursts to quantify the presence or absence of OH. For flames with the same fuel-side equivalence ratio, the hydroxyl intermittency at peak OH remains almost constant when going from stable to extinguishing flames. However, histograms portray an increase in burst separation times for flames displaying occasional extinction events. Hydroxyl time series for a partially premixed flame at a fuel-side equivalence ratio of 2.0 and Re = 6650 are synthesized by using mixture-fraction simulations based on calculated state relationships for OH versus mixture fraction (f). The laminar-flamelet model is employed to explore relations between OH and f so as to predict trends in mixture-fraction time scales.“Time-Series Measurements in Turbulent Opposed-Jet Flames" is submitted for consideration as a full length article to Flow Turbulence and Combustion.     

Testing bridge-mediated differences in dinuclear valence tautomeric behavior

Two structurally characterized dinuclear valence tautomers are described. Cobalt ions are bridged by p- and m-phenylene units connected to 2,2'-bipyridines. X-ray crystal structures show that the molecules are in the [(Co(III))(Co(III))] forms at ca. 125 K, while spectroscopic studies show that both molecules can achieve the [(Co(II))(Co(II))] form above 400 K and confirm the [(Co(III))(Co(III))] form below 10 K. Magnetic susceptibility studies are also included. Our results highlight the necessity of studying both crystalline and amorphous samples to distinguish the effects of intrinsic electronic structure and intermolecular forces on valence tautomeric behavior.     

MASPIT: three-hybrid trap for quantitative proteome fingerprinting of small molecule-protein interactions in mammalian cells

Organic small molecules generally act by perturbing the function of one or more cellular target proteins, the identification of which is essential to an understanding of the molecular basis of drug action. Here we describe the application of methotrexate-linked small molecule ligands to a mammalian three-hybrid interaction trap for proteome-wide identification of small molecule targets, quantification of the targeting potency of unmodified small molecules for such targets in intact cells, and screening for inhibitors of small molecule-protein interactions. During the course of this study we also identified the pyrido[2,3-d]pyrimidine PD173955, a known SRC kinase inhibitor, as a potent inhibitor of several ephrin receptor tyrosine kinases. This finding could perhaps be exploited in the design of inhibitors for this kinase subfamily, members of which have been implicated in the pathogenesis of various diseases, including cancer.     

Structure of the boronic acid dimer and the relative stabilities of its conformers

Despite the widespread use of boronic acids in materials science and as pharmaceutical agents, many aspects of their structure and reactivity are not well understood. In this research the boronic acid dimer, [HB(OH)(2)](2), was studied by second-order M?ller-Plesset (MP2) perturbation theory and coupled cluster methodology with single and double excitations (CCSD). Pople split-valence 6-31+G*, 6-311G**, and 6-311++G** and Dunning-Woon correlation-consistent cc-pVDZ, aug-cc-pVDZ, cc-pVTZ, and aug-cc-pVTZ basis sets were employed for the calculations. A doubly hydrogen-bonded conformer (1) of the dimer was consistently found to be lowest in energy; the structure of 1 was planar (C(2h)) at most computational levels employed but was significantly nonplanar (C(2)) at the MP2/6-311++G** and CCSD/6-311++G** levels, the result of an intrinsic problem with Pople-type sp-diffuse basis functions on heavy atoms. The dimerization energy, enthalpy, and free energy for the formation of (1) from the exo-endo conformer of the monomer were -10.8, -9.2, and +1.2 kcal/mol, respectively, at the MP2/aug-cc-pVTZ level. Several other hydrogen-bonded conformers of the dimer were local minima on the potential energy surface (PES) and ranged from 2 to 5 kcal/mol higher in energy than 1. Nine doubly OH-bridged conformers, in which the boron atoms were tetracoordinated, were also local minima on the PES, but they were all greater than 13 kcal/mol higher in energy than 1; doubly H-bridged structures proved to be transition states. MP2 and CCSD results were compared to those from the BLYP, B3LYP, OLYP, O3LYP, PBE1PBE, and TPSS functionals with the 6-311++G** and aug-cc-pVTZ basis sets; the PBE1PBE functional performed best relative to the MP2 and CCSD results. Self-consistent reaction field (SCRF) calculations predict that boronic acid dimerization is less favorable in solution than in vacuo.     

Suppression of charge ordering phenomenon in nanocrystalline Nd0.67Ca0.33MnO3 manganite

A systematic investigation of electrical, magnetic and elastic properties was undertaken in nano and microcrystalline Nd_0.67Ca_0.33MnO₃ manganite, mainly to understand the charge ordering phenomenon. There is a clear and distinct behaviour in the electrical and magnetic properties of nano and microcrystalline samples and the observed behaviour is explained.