Synthesis and Some Reactions of 2,4,6-Cycloheptatrienethione

The synthesis of 2,4,6-cycloheptatrienethione ( 1 ) was accomplished by reaction of tropone and phosphorus pentasulfide. Although 1 proved to be extremely unstable in concentrated solution, its UV. spectrum was measured, the ε-values being determined indirectly by hydrolysis to tropone. The proof of structure rests on analytical data, conversion to tropone oxime on reaction with hydroxylamine and reaction with the sodium salt of malonitrile to give 2-amino-3-cyano-3aH-cyclohepta[b]thiophene ( 4 ) which rearranged on chromatography to give what is probably the corresponding 8H-compound ( 5 ). On dissolving 1 in 95% sulfuric acid, a large hypsochromic shift in the UV. spectrum was observed, which may be due to the mercaptotropylium ion.     

Spectroscopy and reactivity of a photogenerated tryptophan radical in a structurally defined protein environment

Near-UV irradiation of structurally characterized [Re(I)(CO)3(1,10-phenanthroline)(Q107H)](W48F/Y72F/H83Q/Y108W)AzM(II) [Az = Pseudomonas aeruginosa azurin, M = Cu, Zn]/[Co(NH3)5Cl]Cl2 produces a tryptophan radical (W108*) with unprecedented kinetic stability. After rapid formation (k = 2.8 x 106 s-1), the radical persists for more than 5 h at room temperature in the folded ReAzM(II) structure. The absorption spectrum of ReAz(W108*)M(II) exhibits maxima at 512 and 536 nm. Oxidation of K4[Mo(CN)8] by ReAz(W108*)Zn(II) places the W108*/W108 reduction potential in the protein above 0.8 V vs NHE.     

Dry etching of InGaP and AlInP in CH4/H2/Ar

Electron cyclotron resonance (ECR) plasma etching with additional rf-biasing produces etch rates 2,500 A/min for InGaP and AlInP in CH₄/H₂/Ar. These rates are an order of magnitude or much higher than for reactive ion etching conditions (RIE) carried out in the same reactor. N₂ addition to CH₄/H₂/Ar can enhance the InGaP etch rates at low flow rates, while at higher concentrations it provides an etch-stop reaction. The InGaP and AlInP etched under ECR conditions have somewhat rougher morphologies and different stoichiometries up to 200 Å from the sur face relative to the RIE samples.     

Photochemistry of 5-phenyl-1-pentene in the gas phase

The photochemistry of the title compound has been studied in the gas phase using 254-nm irradiation. In addition to meta cycloadducts analogous to those observed in solution, population of S1(vib) in the gas phase gives several products, the relative amounts of which depend on quencher gas pressure but not on excitation wavelength. For example, in the absence of butane, the major photoproduct is compound 5. This product is formed by a [1,5] hydrogen shift in the primary photoproduct, compound 4. Compound 4 is an intramolecular meta cycloadduct that is generated in the gas phase with sufficient excess vibrational energy to undergo rearrangement unless quencher gas is present. Likewise, there is evidence that two other meta cycloadducts (2 and 3) are also formed with appreciable vibrational energy in the absence of a quencher gas. A unique intramolecular ortho cycloadduct is also formed from 1 but only within a narrow range of quencher gas pressures. This is a two-photon product, with the initial cycloadduct (11) ring opening to a cyclooctatriene (12) that photochemically closes to 6. The pressure dependence of this ortho cycloaddition may be due to a requirement for vibrational deactivation of 11 (Scheme 5) or a precursor species (Scheme 6). The overall chemistry is outlined in Scheme 7.     

On the electron affinity of Cu atom

The electron affinity (EA) of the Cu atom is computed using large STO and GTO basis sets at several levels of correlation. The best computed value is 1     

Comparison of Methionine α,γ‐Lyase and Homocysteine α,γ‐Lyase for Electrochemical Determination of Homocysteine

Recently, a novel enzymatic method was developed for determination of homocysteine. This method utilizes the electrochemical hydrogen sulfide sensor along with methionine α,γ‐lyase to accomplish the fast, accurate, sensitive and selective measurements. As a continuation of this work, another enzyme, homocysteine α,γ‐lyase, was used and the parallel experiments of using both enzymes were carried out against the effect of pH, sensitivity, linearity, and interferences, in an intended comparison between these two enzymes. The excellent linearity of amperometric currents against homocysteine concentrations, high sensitivities and low detection limits for both enzymes reconfirmed that the electrochemical method is superior over other analytical means. The high enzymatic activity of methionine α,γ‐lyase surpassing homocysteine α,γ‐lyase endowed the former higher sensitivity, lower detection limit and faster response than the latter, suggesting methionine α,γ‐lyase a better candidate for homocysteine measurement by electrochemical method. The differences between these two enzymes on the trends of response time and sensitivity at different pH environments, reactivity toward several forms of homocysteine as well as on the interference from several agents were also addressed and discussed.     

Perturbational approach to the electron correlation cusp applied to helium‐like atoms

A recently proposed perturbational approach to the electron correlation cusp problem 1 is tested in the context of three spherically symmetrical two‐electron systems: helium atom, hydride anion, and a solvable model system. The interelectronic interaction is partitioned into long‐ and short‐range components. The long‐range interaction, lacking the singularities responsible for the electron correlation cusp, is included in the reference Hamiltonian. Accelerated convergence of orbital‐based methods for this smooth reference Hamiltonian is shown by a detailed partial wave analysis. Contracted orbital basis sets constructed from atomic natural orbitals are shown to be significantly better for the new Hamiltonian than standard basis sets of the same size. The short‐range component becomes the perturbation. The low‐order perturbation equations are solved variationally using basis sets of correlated Gaussian geminals. Variational energies and low‐order perturbation wave functions for the model system are shown to be in excellent agreement with highly accurate numerical solutions for that system. Approximations of the reference wave functions, described by fewer basis functions, are tested for use in the perturbation equations and shown to provide significant computational advantages with tolerable loss of accuracy. Lower bounds for the radius of convergence of the resulting perturbation expansions are estimated. The proposed method is capable of achieving sub‐μHartree accuracy for all systems considered here. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

5‐Butyl‐4‐(4,4,5,5‐tetra­methyl‐1,3,2‐dioxaborolan‐2‐yl)‐3‐(2,4,6‐tri­methyl­phenyl)­isoxazole

A novel [3+2]‐cyclo­addition reaction of alkynyl­boronates and nitrile oxides gave the title compound, C₂₂H₃₂BNO₃, as a single regioisomer. The X‐ray crystal structure analysis of this compound shows two independent mol­ecules in the asymmetric unit, each with approximately coplanar isoxazole and boronate rings.