Relative stability of planar versus double-ring tubular isomers of neutral and anionic boron cluster B20 and B20-

High-level ab initio molecular-orbital methods have been employed to determine the relative stability among four neutral and anionic B20 isomers, particularly the double-ring tubular isomer versus three low-lying planar isomers. Calculations with the fourth-order Moller-Plessset perturbation theory [MP4(SDQ)] and Dunning's correlation consistent polarized valence triple zeta basis set as well as with the coupled-cluster method including single, double, and noniteratively perturbative triple excitations and the 6-311G(d) basis set show that the double-ring tubular isomer is appreciably lower in energy than the three planar isomers and is thus likely the global minimum of neutral B20 cluster. In contrast, calculations with the MP4(SDQ) level of theory and 6-311+G(d) basis set show that the double-ring anion isomer is appreciably higher in energy than two of the three planar isomers. In addition, the temperature effects on the relative stability of both 10B20- and 11B20- anion isomers are examined using the density-functional theory. It is found that the three planar anion isomers become increasingly more stable than the double-ring isomer with increasing the temperature. These results are consistent with the previous conclusion based on a joint experimental/simulated anion photoelectron spectroscopy study [B. Kiran et al., Proc. Natl. Acad. Sci. U.S.A. 102, 961 (2005)], that is, the double-ring anion isomer is notably absent from the experimental spectra. The high stability of the double-ring neutral isomer of B20 can be attributed in part to the strong aromaticity as characterized by its large negative nucleus-independent chemical shift. The high-level ab initio calculations suggest that the planar-to-tubular structural transition starts at B20 for neutral clusters but should occur beyond the size of B20- for the anion clusters.     

On the Uniform Distribution of Certain Sequences

We investigate the uniform distribution of the sequence n as n ranges over the natural numbers and is a fixed positive real number which is not an integer. We then apply this in conjunction with the Linnik-Vaughan method to study the uniform distribution of the sequence p as p ranges over the prime numbers.     

Two new macrocyclic diaryl ether heptanoids from Boswellia ovalifoliolata

The stems of Boswellia ovalifoliolata BAL. & HENRY (Burseraceae) afforded two new macrocyclic diaryl ether heptanoids, ovalifoliolatin A (1) and B (2) together with three known compounds; acerogenin C (3), 3 alpha-hydroxyurs-12-ene (4), and sitost-4-en-3-one (5). The structures were established by means of spectroscopic analysis and compounds 1, 3-5 were evaluated for their antibacterial activity.     

Electroinitiated cationic polymerization of styrene in the presence of ferric chloride

The electroinitiated polymerization of styrene has been studied in acetone with ferric chloride as the electrolyte. At a fixed monomer concentration, the polymer yield depends on the current strength as well as the concentration of ferric chloride. The molecular weight of the polymer lies in the range of 1000–3000. Addition of zinc chloride to the system or replacement of the solvent by DMF (partly or fully) or methanol retards the polymerization. The current exponent of polymerization is unity with a reaction rate constant of 4.416 × 10^?2 reaction percent per hour. The locus of polymerization is the anode compartment. A cationic mechanism has been proposed for the polymerization, the initiating step consisting of an electron transfer from an adsorbed charge transfer complex of styrene and ferric chloride.     

Approximate Queueing Formulae Based on Consideration of the Busy Period

An approximation formula to one in M/M/1 queueing theory for hours in a queue is examined. Then it is extended to models M/D/1 and M/E _k /1 whereby wasted time or queue length is found to lie between two extremes. An empirical approximation to traffic intensity called utilization rate is used.     

Kinetics of oxidation of Indigo Carmine by potassium peroxydisulfate

The reaction is first order in potassium peroxydisulfate and zero order in Indigo Carmine. Hydrogen ions have no effect on the rate in the acidity range of 0.0–0.2 M. Allyl acetate inhibits the reaction. A radical chain mechanism is proposed.

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. 0 0,2 M . . .

     

Novel analogues of ascomycin with modifications in the amino acid unit through photochemistry: the synthesis of 5,6-dehydroascomycin, SDZ ASQ 871

Irradiation of ascomycin 1a and its derivatives in MeOH, EtOH and propanol resulted in alkoxylation of the pipecolic acid moiety in the ε-position with concomitant reduction in the tricarbonyl region leading to 6-alkoxy-9-hydroxy derivatives in high stereoselectivities and good yields. The products, after reoxidation of the C(9)-OH, afforded the 6-alkoxy analogues of the parent compounds. Elimination of MeOH from the photoproducts, followed by oxidation gave the corresponding 5,6-dehydro amino acid analogues. Similarly, starting from the proline analogue 7 modifications in the pyrrolidine moiety could be achieved.     

Surfactant immobilized interlayer species bonded to montmorillonite as recyclable adsorbent for lead ions

Removal of lead ( Pb2+ ) ions from aqueous solution by adsorption onto surfactant-immobilized interlayer species bonded to montmorillonite clay (SIIS-clay) was investigated. Surfactant-immobilized interlayer chromate bound to clay (SIICr-clay) was prepared by treatment of montmorillonite clay with hexadecyltrimethylammonium (HDTMA) bromide followed by chromate adsorption at the intergallery framework of the clay. Experiments were carried out as a function of solution pH, solute concentration, and temperature (5-45 degrees C). The Dubinin-Kaganer-Radushkevich (DKR) model was adopted to describe the single-solute adsorption isotherms. Adsorption energy for lead ions on SIICr-clay computed from the DKR equation shows that a precipitation mechanism was operative. The thermodynamic parameters ( Delta G 0, Delta H 0, and Delta S 0) for lead ion adsorption on SIICr-clay were also determined from the temperature dependence. The kinetics of metal ion adsorption was examined and the first-order rate constant was finally evaluated. Adsorbed lead ions could be recovered completely on leaching with the disodium salt of ethylenediamine tetraacetic acid (EDTA) solution and the adsorbent was found to readsorb lead ions repeatedly after leaching. Thus, surfactant-modified smectite clays offer an effective method for designing a recyclable adsorbent for lead ions.