Arthur J. Ashe

Carboxyl-ebselen-based layer-by-layer films as potential antithrombotic and antimicrobial coatings

A carboxyl-ebselen-based layer-by-layer (LbL) film was fabricated by alternatively assembling carboxyl-ebselen immobilized polyethylenimine (e-PEI) and alginate (Alg) onto substrates followed by salt annealing and cross-linking. The annealed films exhibiting significantly improved stability are capable of generating nitric oxide (NO) from endogeneous S-nitrosothiols (RSNOs) in the presence of a reducing agent. The NO generation behaviors of different organoselenium species in solution phase are compared and the annealing mechanism to create stable LbL films is studied in detail. An LbL film coated polyurethane catheter is capable of generating physiological levels of NO from RSNOs even after blood soaking for 24 h, indicating potential antithrombotic applications of the coating. Further, the LbL film is also demonstrated to be capable of reducing living bacterial surface attachment and killing a broad spectrum of bacteria, likely through generation of superoxide (O(2)(·-)) from oxygen. This type of film is expected to have potential application as an antithrombotic and antimicrobial coating for different biomedical device surfaces.

BORATABENZENES : FROM CHEMICAL CURIOSITIES TO PROMISING CATALYSTS

Abstract Boratabenzenes ( 4 ) are six π-electron aromatic anions which can serve as versatile ligands towards Zr(IV) and Zr(II). The reaction of 4 with ZrCl 4 affords bis(boratabenzene)zirconium(IV) dichlorides ( 11 ), which on treatment with BuLi and excess PMe 3 give bis(boratabenzene)bis(trimethylphosphine)zirconium(II) ( 27 ). On activation by excess methylaluminoxane 11 are the catalysts for the polymerization or oligomerization of ethylene. Bridged boratabenzene zirconium dichlorides 19 , 20 , and 21 , which closely resemble the corresponding ansa-zirconocenes, can be similarly activated for polymerization of ethylene. Compound 27 reacts with 1,3-diynes to afford zirconacycles 31 and with acetylene by ring annulation to afford 32 .

The microwave spectrum, dipole moment and low frequency vibrational states for phosphabenzene

Abstract The microwave spectrum of the ground vibrational state and seven lowfrequency vibrational states for phosphabenzene (C5H5P) have been assigned. The small positive inertial defect and the alternation of intensities due to nuclear spin statistics for the ground state confirm a plannar structure with C2v symmetry. A PC bond distance of 1.70–1.73 A and 〈CPC of 101°–104° were estimated based on plausible assumptions for the other ring parameters. Four low-frequency fundamental modes of vibration were identified and vibrational assignments discussed. The nuclear spin statistics indicate that three of these modes were antisymmetric to the C2 axis while one mode was symmetric. The dipole moment has been determined as 1.54±0.02 D.

The exchange reaction of tetramethyldipnictogens with dimethyldichalcogenides

Tetramethyldipnictogens Me4E2 (E = P, As, Sb, Bi) undergo exchange reactions with dimethyldichalcogenides Me2A2 (A = S, Se, Te) to produce the corresponding (dimethylpnicto)methylchalcogenides Me2EAMe. These compounds have been characterized by NMR, Raman and mass spectroscopy.

AROMATIC ANTIMONY COMPOUNDS. TRANSITION METAL COMPLEXES OF 2,5-DIMETHYLSTIBACYCLOPENTADIENYL

Abstract Hydrostannation of 2,4-hexadiyne with dibutyltin dihydride gave 1,1-dibutyl-2,5-dimethylstannole, which was converted to 2,5-dimethylstibacymantrene and to bis(2,5-dimethylstibacyclopentadienyl)iron.

Thermochromic Distibines and Dibismuthines

Publisher Summary This chapter discusses thermochromic distibines and dibismuthines. Distibines and dibismuthines show a propensity to stack in the solid state. The first well-characterized distibine, tetraphenyldistibine was reported in 1931. Paneth also obtained tetramethyldibismuthine in trace quantities from methyl radicals and a heated bismuth mirror. The dibismuthine is conveniently purified by recrystallization from pentane at –20°C. Most distibines appear yellow, while dibismuthines are red, either in their liquid phases or in solution in organic solvents. On crystallization, nonthermochromic distibines and dibismuthines show little visual change. The thermochromic effect of distibines has been treated in three papers by Hoffmann and colleagues using a tight bonding model based on extended Huckel calculations. Raman spectroscopy is extremely useful for the characterization of distibines and dibismuthines, because the metal–metal stretching vibrations give rise to intense, easily identifiable peaks. No diarsines or diphosphines show thermochromic behavior similar to that of the distibines and dibismuthines. A recent theoretical study by Canadell and Shaik, however, has suggested that the incorporation of antimony into conjugated organic networks, such as phenalenyl, will lead to distibinelike stacked molecules with an open-band structure.

Molecular structure of arsabenzene by gas-phase electron diffraction

Abstract Vapor-phase molecules of C 5 H 5 As were found, assuming C 2v symmetry, to have the following structure parameters and uncertainties (2.5σ): r g (C-As)= 1.850 ± 0.003 A, r g (C 2 –C 3 ) = 1.390 ± 0.032 /rA, r g (C 3 –C 4 ) = 1.401 ± 0.032 /rA, r g (C-C ave ) = 1.395 4 ± 0.002 A, ∠CAsC = 97.3 ± 1.7°, ∠AsCC = 125.1 ± 2.8°, and ∠C 3 C 3 C 4 = 124.2 ± 2.9°. Amplitudes of vibration were also determined. Auxiliary information is more restrictive than pure electron diffraction intensities as evidence that the molecule is rigorously planar. Structural characteristics of arsabenzene reinforce prior indications that the heterocyclic molecule is genuinely aromatic.

The exchange reaction of tetramethyl-diphosphine, -diarsine, -distibine and -dibismuthine

Abstract Tetramethyldiphosphine and tetramethyldiarsine undergo an exchange reaction to give (dimethylarsino)dimethylphosphine. The equilibrium constant at 25°C in benzene is found to be 0.26. Similarly, mixtures of tetramethyldistibine with tetramethyldiarsine or tetramethyldibismuthine are partially converted to (dimethylarsino)dimethylstibine or (dimethylbismuthino)dimethylstibine, respectively. The thermochromic arsinostibine, 1-(2,5-dimethylarsolo)-2,5-dimethylstibole, has been prepared by a similar reaction.

Electronic structure of arsabenzene: Microwave spectrum, dipole moment, and nuclear quadrupole coupling constants

Abstract The microwave spectrum of arsabenzene was analyzed; a dipole transitions were observed. The following rotational constants were obtained; A = 4871.03 ± 0.18 MHz, B = 2295.87 ± 0.01 MHz, C = 1560.10 ± 0.01 MHz. The dipole moment was 1.10 ± 0.04 D. The nuclear quadrupole coupling constants due to the 75As nucleus were χaa = −186.4 ± 0.1 MHz, χbb = 43.5 ± 0.2 MHz, χcc = 142.9 ± 0.2 MHz, and the asymmetry parameter, η = 0.533 ± 0.002. Analysis of the quadrupole coupling constants indicated that the population of the 4p orbitals on arsenic decrease in the order na > nb > nc.

The molecular and crystal structure of pentacarbonyl(phosphabenzene)molybdenum(0)

Abstract Pentacarbonyl(phosphabenzene)molybdenum(0) crystallizes in the Pbam space group with Z = 8, a 15.880(4), b 20.162(4) and c 7.971(3) A. The crystal structure was determined and refined from 1404 independent reflections to R 1 = 0.034. The pentacarbonylmolybdenum moiety is symmetrically coordinated to the phosphorus atom of the phosphabenzene ring, which closely resembles the free ligand in geometry.