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Biomedical subjects

Shiwei Zhang

Publications and source records attributed to Shiwei Zhang.

At least 19 recordsLinked to original sources
PubMed2026

The first complete genome sequence of Ammi majus latent virus from the new natural host culantro.

A potyvirus (isolate AMLV-CQ) infecting culantro (Eryngium foetidum L.) imported from Vietnam was identified by RT-PCR. The complete genome sequence of AMLV-CQ was determined to be 9,549 nucleotides in length. It contains a large open reading frame encoding a 3,082-amino-acid putative polyprotein, flanked by 5´ and 3´ untranslated regions (UTRs) of 77 and 226 nt, respectively. AMLV-CQ is closely related to five other completely sequenced potyviruses, sharing 68-69% nucleotide and 69-70% amino acid sequence identity. However, the coat protein (CP) gene shares 89% nucleotide and 93% amino acid sequence identity with that of a partially sequenced potyvirus, Ammi majus latent virus (isolate AMLV-WF17). These results suggest that AMLV-CQ and AMLV-WF17 are isolates of the same species. To our knowledge, this is the first report of a complete genome sequence of an AMLV isolate, and culantro was identified as a new natural host for this virus. In addition, a one-step RT-PCR assay was developed that provides a rapid, robust, and highly sensitive approach for the detection of AMLV.

Eryngium↗
PubMed2007

Amination of [60]fullerene by ammonia and by primary and secondary aliphatic amines--preparation of amino[60]fullerene peroxides.

Ammonia and aliphatic amines react readily in the oxygen-rich regions of the Cs symmetric fullerene peroxides C60(O)(OOtBu)4 (1) and C60(OH)(Br)(OOtBu)4 (2 c). Michael addition-type hydroamination of the 1,4-diene moiety on the central skew-pentagon was observed when 1 was treated with ammonia or with nonbulky primary amines, while sterically demanding primary amines opened the epoxy moiety to form vicinal aminohydroxy fullerene compounds with the amino group on the central pentagon. In 2 c the bromo group was replaced under similar conditions by ammonia and primary amines. Cyclic secondary amines showed different reaction patterns, forming hydrogenation products or aminoketal-fullerenes when treated with 1 and 2 c, respectively. Single-electron transfer (SET) is the key step in all the proposed mechanisms. The compounds were characterized by their spectroscopic data, and in addition, three single-crystal X-ray structures were obtained.

Journal Article↗
PubMed2006

Nitrene equivalent mediated metal-free ring expansions of alkylidenecyclopropanes and an alkylidenecyclobutane.

The ring expansion of small-ring compounds provides a powerful method for the construction of various cyclic compounds. Herein, nitrene equivalent mediated metal-free ring expansions of alkylidenecyclopropanes (ACPs) and an alkylidenecyclobutane (ACB) were described. In this synthesis, a series of aryl-substituted cyclobutylidene and cyclopentylidene hydrazine derivatives were obtained under mild conditions in moderate to good yields. [reaction: see text]

Journal Article↗
PubMed2006

Auxiliary-field quantum Monte Carlo study of first- and second-row post-d elements.

A series of calculations for the first- and second-row post-d elements (Ga-Br and In-I) are presented using the phaseless auxiliary-field quantum Monte Carlo (AF QMC) method. This method is formulated in a Hilbert space defined by any chosen one-particle basis and maps the many-body problem into a linear combination of independent-particle solutions with external auxiliary fields. The phase/sign problem is handled approximately by the phaseless formalism using a trial wave function, which in our calculations was chosen to be the Hartree-Fock solution. We used the consistent correlated basis sets of Peterson et al. [J. Chem. Phys. 119, 11099 (2003); 119, 11113 (2003)], which employ a small-core relativistic pseudopotential. The AF QMC results are compared with experiment and with those from density functional (generalized gradient approximation and B3LYP) and CCSD(T) calculations. The AF QMC total energies agree with CCSD(T) to within a few millihartrees across the systems and over several basis sets. The calculated atomic electron affinities, ionization energies, and spectroscopic properties of dimers are, at large basis sets, in excellent agreement with experiment.

Journal Article↗
PubMed2006

Auxiliary-field quantum Monte Carlo calculations of molecular systems with a Gaussian basis.

We extend the recently introduced phaseless auxiliary-field quantum Monte Carlo (QMC) approach to any single-particle basis and apply it to molecular systems with Gaussian basis sets. QMC methods in general scale favorably with the system size as a low power. A QMC approach with auxiliary fields, in principle, allows an exact solution of the Schrodinger equation in the chosen basis. However, the well-known sign/phase problem causes the statistical noise to increase exponentially. The phaseless method controls this problem by constraining the paths in the auxiliary-field path integrals with an approximate phase condition that depends on a trial wave function. In the present calculations, the trial wave function is a single Slater determinant from a Hartree-Fock calculation. The calculated all-electron total energies show typical systematic errors of no more than a few millihartrees compared to exact results. At equilibrium geometries in the molecules we studied, this accuracy is roughly comparable to that of coupled cluster with single and double excitations and with noniterative triples [CCSD(T)]. For stretched bonds in H(2)O, our method exhibits a better overall accuracy and a more uniform behavior than CCSD(T).

Journal Article↗
PubMed2006

Lewis acid promoted preparation of isomerically pure fullerenols from fullerene peroxides C60(OOt-Bu)6 and C60(O)(OOt-Bu)6.

Fullerene mixed peroxides C60(t-BuOO)6 and C60(O)(t-BuOO)6 react with Lewis acids to form various fullerenols through the partial fragmentation of t-BuOO groups. Two monohydroxyl fullerenols with the general formula C60(OH)(t-BuOO)5 and six monohydroxyl fullerenols with the general formula C60(O)(OH)(t-BuOO)5 were prepared, which are essentially the same except the location of the OH group. An additional reaction of the monohydroxyl fullerenols gave bis- and trishydroxyl fullerenols. Single-crystal X-ray structures have been obtained for the two monohydroxyl fullerenols. Other compounds are characterized by chemical correlation and their spectroscopic data. Cuprous bromide could protect the most reactive t-BuOO group from being attacked by stronger Lewis acids. The proposed mechanism mainly involves Lewis acid induced heterolysis of the peroxo O-O bond.

Crystallography, X-Ray↗
PubMed2006

Metal-mediated efficient synthesis, structural characterization, and skeletal rearrangement of octasubstituted semibullvalenes.

The first metal-mediated efficient synthesis of octasubstituted semibullvalenes, including octaalkyl and mixed tetraalkyl and tetraphenyl derivatives, was developed. The structures of these semibullvalenes were determined by single-crystal X-ray structural analysis. Their intramolecular skeletal rearrangement and reaction chemistry were investigated.

Crystallography, X-Ray↗
PubMed2006

A versatile method for the synthesis of 3-alkoxycarbonyl beta-lactam derivatives.

[reaction: see text] Ketene-imine cycloaddition reactions (the Staudinger reaction) of ethoxycarbonyl(phenylthio)ketene with various imines and subsequent desulfurization reactions were employed to synthesize 3-ethoxycarbonyl beta-lactam derivatives. The results indicate that the current approach provides a convenient, mild, and versatile method for synthesizing a variety of 3-alkoxycarbonyl trans-beta-lactam derivatives with good to excellent yields and diastereoselectivities.

Alkylation↗
PubMed2006

Preparation of fullerendione through oxidation of vicinal fullerendiol and intramolecular coupling of the dione to form hemiketal/ketal moieties.

[reaction: see text] Vicinal fullerendiol is oxidized to fullerendione in good yield by (diacetoxy)iodobenzene. The resulting cage-opened fullerendione reacts with oxygen nucleophiles in the presence of BF(3).Et(2)O to form fullerene hemiketal/ketal derivatives through coupling of the two carbonyl groups. Fullerene-mixed peroxide derivatives are involved in all these reactions. The compounds are characterized by spectroscopic data and single-crystal X-ray analysis.

Journal Article↗
PubMed2005

Interactions between metal ions and carbohydrates. The coordination behavior of neutral erythritol to lanthanum and erbium ions.

Lanthanide ions and erythritol form metal-alditol complexes with various structures. Lanthanum nitrate and erbium chloride coordinate to erythritol to give new coordination structures. The lanthanum nitrate-erythritol complex (LaEN), 2La(NO3)3.C4H10O(4).8H2O, La3+ exhibits the coordination number of 11 (namely 11 polar atoms bound to one lanthanum) and is 11-coordinated to two hydroxyl groups from one erythritol molecule, six oxygen atoms from three nitrate ions and three water molecules. One erythritol molecule is coordinated to two La3+ ions and links the two metal ions together. The ratio of M:L is 2:1. The erbium chloride-erythritol complex (ErE), ErCl2.C4H9O(4).2C2H5OH was obtained from ErCl3 and erythritol in aqueous ethanol solution and the structure shows that deprotonation reaction occurs in the reaction process. The Er3+ cation is 8-coordinated with three hydroxyl groups of one erythritol molecule, two hydroxyl groups from another erythritol molecule, two ethanol molecules, and one chloride ion. Erythritol provides its three hydroxyl groups to one erbium cation and two hydroxyl groups to another erbium cation, that is, one hydroxyl group is coordinated to two metal ions and therefore loses its hydrogen atom and becomes a oxygen bridge. Another chloride ion is hydrogen bonded in the structure. The results indicate the complexity of metal-sugar coordination.

Crystallization↗
PubMed2005

Preparation of [5,6]- and [6,6]-oxahomofullerene derivatives and their interconversion by Lewis acid assisted reactions of fullerene mixed peroxides.

[60]Fullerene mixed peroxides C60(O)(OOtBu)4 exhibit chemo- and regioselective reactions under mild conditions. The epoxy moiety is opened by ferric chloride to form vicinal hydroxy chloride C60Cl(OH)(OOtBu)4. BF3 is also effective in opening the epoxy moiety. The O-O bond of the fullerene mixed peroxide is cleaved by aluminum chloride to form both [5,6]- and [6,6]-fullerene hemiketals (oxohomo[60]fullerenes). A Hock-type rearrangement is proposed for the formation of the hemiketals, in which a fullerene C-C bond is cleaved. Lewis acids and/or visible light can initiate isomerization of the hemiketal isomers. Single-crystal X-ray analysis and theoretical calculations confirmed the results.

Journal Article↗
PubMed2005

Accurate, efficient, and simple forces computed with quantum Monte Carlo methods.

Computation of ionic forces using quantum Monte Carlo methods has long been a challenge. We introduce a simple procedure, based on known properties of physical electronic densities, to make the variance of the Hellmann-Feynman estimator finite. We obtain very accurate geometries for the molecules H(2), LiH, CH(4), NH(3), H(2)O, and HF, with a Slater-Jastrow trial wave function. Harmonic frequencies for diatomics are also in good agreement with experiment. An antithetical sampling method is also discussed for additional reduction of the variance.

Journal Article↗
PubMed2005

Microwave- and photoirradiation-induced staudinger reactions of cyclic imines and ketenes generated from alpha-diazoketones. A further investigation into the stereochemical process.

Reactions of ketenes generated from alpha-diazoketones with a series of acyclic and cyclic imines were investigated under both microwave and photoirradiation conditions. The results indicate that the zwitterionic azabutadiene-type intermediates yielded from imines and ketenes undergo a conrotatory ring closure exclusively to produce beta-lactams. It is notable that no Woodward-Hoffmann product was found under the ultraviolet irradiation. The photoirradiation-induced Staudinger reaction shows a different stereoselectivity from the electrocyclic reaction of substituted 1,3-butadiene.

Azo Compounds↗
PubMed2005

Interactions between metal ions and carbohydrates. The coordination behavior of neutral erythritol to neodymium ion.

A single crystal of a coordinated complex of neutral erythritol (C4H10O4,E) with a neodymium ion, NdE(II), was synthesized and studied using FT-IR and X-ray diffraction analysis. In NdE(II) (NdCl3.2.5C4H10O4.C2H5OH) the Nd3+ coordinates with one chloride ion and eight OH groups from three erythritol molecules. There are two neodymium centers linked by one erythritol molecule with same coordination structure in the molecule. Two erythritol molecules provide 1,3,4-hydroxyl groups to coordinate with a neodymium ion; another erythritol molecule coordinates to two Nd ions via its 1,2-hydroxyl groups and 3,4-hydroxyl groups, respectively. The OH groups of erythritol act as ligand to coordinate to neodymium ions, and OH groups of erythritol form hydrogen bond networks that link chain and layer together to build three-dimensional structures. The ratio of metal to ligand is 1:2.5. The structure of NdE(II) is more complicated than the previously reported NdE(I), which is NdCl3.C4H10O4.6H2O; in NdE(I), Nd3+ is coordinated to four hydroxyl groups from two erythritol molecules, four water molecules and one chloride ion. The results indicate the complexity of metal-sugar interaction.

Journal Article↗
PubMed2004

Quantum Monte Carlo method for the ground state of many-boson systems.

We formulate a quantum Monte Carlo (QMC) method for calculating the ground state of many-boson systems. The method is based on a field-theoretical approach, and is closely related to existing fermion auxiliary-field QMC methods which are applied in several fields of physics. The ground-state projection is implemented as a branching random walk in the space of permanents consisting of identical single-particle orbitals. Any single-particle basis can be used, and the method is in principle exact. We illustrate this method with a trapped atomic boson gas, where the atoms interact via an attractive or repulsive contact two-body potential. We choose as the single-particle basis a real-space grid. We compare with exact results in small systems and arbitrarily sized systems of untrapped bosons with attractive interactions in one dimension, where analytical solutions exist. We also compare with the corresponding Gross-Pitaevskii (GP) mean-field calculations for trapped atoms, and discuss the close formal relation between our method and the GP approach. Our method provides a way to systematically improve upon GP while using the same framework, capturing interaction and correlation effects with a stochastic, coherent ensemble of noninteracting solutions. We discuss various algorithmic issues, including importance sampling and the back-propagation technique for computing observables, and illustrate them with numerical studies. We show results for systems with up to N approximately 400 bosons.

Journal Article↗