Synthesis, structure, and magnetic properties of a novel pillared layered iron(III) arsenate, [4,4'-bpyH2]3[Fe9(H2O)6F3(HAsO4)12(AsO4)2].2H2O

A three-dimensional iron arsenate [4,4'-bpyH2]3[Fe9(H2O)6F3(HAsO4)12(AsO4)2].2H2O, 1, has been synthesized using 4,4'-bipyridine as the templating agent under hydrothermal conditions. The structure is formed by FeO6, FeO3F3 octahedral units connected with HAsO4 and AsO4 units, forming one- and two-dimensional units in which the one-dimensional units act as a pillar. The presence of face-shared Fe-dimer units in the one-dimensional unit is noteworthy. Detailed magnetic studies indicate two possible magnetic interactions: antiferromagnetic interactions within the layer and a weak ferromagnetic polarization between the layers at very low temperatures through the Fe-dimer units.     

Atomic force microscopy imaging and electrical recording of lipid bilayers supported over microfabricated silicon chip nanopores: lab-on-a-chip system for lipid membranes and ion channels

We describe a silicon chip-based supported bilayer system to detect the presence of ion channels and their electrical conductance in lipid bilayers. Nanopores were produced in microfabricated silicon membranes by electron beam lithography as well as by using a finely focused ion beam. Thermal oxide was used to shrink pore sizes, if necessary, and to create an insulating surface. The chips with well-defined pores were easily mounted on a double-chamber plastic cell recording system, allowing for controlling the buffer conditions both above and below the window. The double-chamber system allowed using an atomic force microscopy (AFM) tip as one electrode and inserting a platinum wire as the second electrode under the membrane window, to measure electrical current across lipid bilayers that are suspended over the pores. Atomic force imaging, stiffness measurement, and electrical capacitance measurement show the feasibility of supporting lipid bilayers over defined nanopores: a key requirement to use any such technique for structure-function study of ion channels. Online addition of gramicidin, an ion-channel-forming peptide, resulted in electrical current flow across the bilayer, and the I-V curve that was measured using the conducting AFM tip indicates the presence of many conducting gramicidin ion channels.     

Reflected shock tube and theoretical studies of high-temperature rate constants for OH+CF3H<-->CF3+H2O and CF3+OH-->products

The reflected shock tube technique with multipass absorption spectrometric detection of OH radicals at 308 nm, using either 36 or 60 optical passes corresponding to total path lengths of 3.25 or 5.25 m, respectively, has been used to study the bimolecular reactions, OH+CF3H-->CF3+H2O (1) and CF3+H2O-->OH+CF3H (-1), between 995 and 1663 K. During the course of the study, estimates of rate constants for CF3+OH-->products (2) could also be determined. Experiments on reaction -1 were transformed through equilibrium constants to k1, giving the Arrhenius expression k1=(9.7+/-2.1)x10(-12) exp(-4398+/-275K/T) cm3 molecule(-1) s(-1). Over the temperature range, 1318-1663 K, the results for reaction 2 were constant at k2=(1.5+/-0.4)x10(-11) cm3 molecule(-1) s(-1). Reactions 1 and -1 were also studied with variational transition state theory (VTST) employing QCISD(T) properties for the transition state. These a priori VTST predictions were in good agreement with the present experimental results but were too low at the lower temperatures of earlier experiments, suggesting that either the barrier height was overestimated by about 1.3 kcal/mol or that the effect of tunneling was greatly underestimated. The present experimental results have been combined with the most accurate earlier studies to derive an evaluation over the extended temperature range of 252-1663 K. The three parameter expression k1=2.08x10(-17) T1.5513 exp(-1848 K/T) cm3 molecule(-1) s(-1) describes the rate behavior over this temperature range. Alternatively, the expression k1,th=1.78x10(-23) T3.406 exp(-837 K/T) cm3 molecule(-1) s(-1) obtained from empirically adjusted VTST calculations over the 250-2250 K range agrees with the experimental evaluation to within a factor of 1.6. Reaction 2 was also studied with direct CASPT2 variable reaction coordinate transition state theory. The resulting predictions for the capture rate are found to be in good agreement with the mean of the experimental results and can be represented by the expression k2,th=2.42x10(-11) T-0.0650 exp(134 K/T) cm3 molecule(-1) s(-1) over the 200-2500 K temperature range. The products of this reaction are predicted to be CF2O+HF.     

Cointegration analysis of brand and category sales: Stationarity and long‐run equilibrium in market shares

The present study uses modern time series methodology to understand long‐run equilibrium in markets and provides additional evidence of the frequent existence of stationary market shares for frequently purchased consumer products. Dekimpe and Hanssens, Marketing Science 1995; 14(2):G109–121 using a database of over 400 prior studies, found that 78 per cent of the market share series they studied were stationary, but that 68 per cent of the sales series were evolving. Our findings reconcile these results. A major contribution of this paper is its demonstration that the prior empirical evidence that a majority of sales series is in evolution is consistent with stationary market shares, if brand sales and category sales are cointegrated. To the extent that competitive activities have an effect on market share, an implication of our findings is that these activities may, in general, only have a temporary effect on market share. Finally, we distinguish, from a strategic perspective, between sales and share response at the primary‐demand level (category sales), selective‐demand level (brand sales) and relative‐position level (market share) and identify strategic scenarios depending upon their stable/evolving nature. Copyright © 2000 John Wiley & Sons, Ltd.     

A Novel Method to Enhance Metastable Zone Width for Crystal Growth from Solution

A novel method has been found to enhance the metastable zone width of solutions in their supersaturated region in order to grow large size crystals. In which, the incorporation of a small quantity of Ethylenediamine tetra acetic acid (EDTA), a well‐known chelating agent, enhances the zone width significantly due to its chelating action. Also this incorporation reduces the nucleation rate and enhances the growth rate of the crystal. X‐ray rocking curve experiment for the grown crystals reveals that EDTA addition does not affect the crystalline quality. This concept was first realized with Potassium acid phthalate (KAP) solutions and then confirmed with Potassium dihydrogen phosphate (KDP) and Triglycine Sulphate (TGS).     

The photo-Arbuzov rearrangement of dimethyl 9-anthrylmethyl phosphite and the photodimerization of the corresponding phosphonate

Upon irradiation, 9-anthrylmethyl phosphite ( 2 ) undergoes the photo-Arbuzov rearrangement to give the corresponding phosphonate 3 . Prolonged irradiation led to the clean formation of the centrosymmetric, head to tail, [4 + 4] photocycloaddition product 4 as indicated by X-ray crystallographic analysis. The same photodimer results on irradiation of phosphonate 3 itself in solution or in the solid phase. Phosphite 2 does not undergo photodimerization to 6 . © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:155–160, 1998     

Chain transfer to polymer in emulsion copolymerizations

Chain transfer to polymer in emulsion copolymerizations of (i) vinyl acetate (VAc) with n‐butyl acrylate (BA) and (ii) BA/acrylic acid with (a) methyl methacrylate (MMA) and (b) styrene (S) has been studied using ¹³C NMR spectroscopy to quantify the level of branching in the copolymers produced. The results reveal synergistic effects in which the inclusion of a small amount of comonomer leads to disproportionate changes in the level of branching. The data from the VAc/BA copolymerizations show that radicals with VAc end units abstract hydrogen atoms from BA repeat units more frequently than from VAc repeat units and that radicals with VAc end units are more effective in abstracting hydrogen atoms from BA repeat units than are radicals with BA end units. These effects lead to higher levels of branching in VAc/BA copolymers than results from the corresponding homopolymerizations and are a consequence of the efficacy of hydrogen abstraction at BA backbone tertiary C‐H bonds by the highly‐reactive VAc‐ended chain radicals. In contrast, the effect of introducing MMA or S to an acrylate polymerization is to disproportionately reduce the level of branching, with S being more effective than MMA in moderating chain transfer to polymer. These effects arise because propagating radicals with MMA or S end‐groups have longer lifetimes compared to those with acrylate end groups and have a very much lower tendency to abstract hydrogen atoms from acrylate repeat units.