Search PubMed⌕ Search

Biomedical subjects

Shiwei Zhang

Publications and source records attributed to Shiwei Zhang.

25 records · Page 2Linked to original sources
PubMed2004

Complexation of trivalent lanthanide cations by erythritol in the solid state. The crystal structure and FT-IR study of 2EuCl3.2C4H10O4.7H2O.

Erythritol was chosen to study the interactions between metal ions and carbohydrates. FTIR spectroscopy results indicate that a EuCl3-erythritol complex different from a previously reported one was obtained. The crystal structure of EuCl3-erythritol complex, 2EuCl3.2C4H10O4.7H2O, Mr=443.49, a=13.846(3) A , b=7.4983(15) A, c=14.140(3) A, beta=116.39(3) degrees, V=1315.1(5) A(3), Z=4, mu=5.394 mm(-1) and R=0.0395 for 2965 observed reflections and 143 parameters, was determined. Characteristic of this complex is the presence of binuclear europium ions with different coordination structures. One Eu3+ ion is nine-coordinated, with five Eu-O bonds from water molecules, and four from hydroxyl groups of two erythritol molecules and another Eu3+ is eight-coordinated with two water molecules, two chloride ions, and four hydroxyl groups from two erythritol molecules. Erythritol provides two hydroxyl groups to one lanthanide ion and the other two to another rare earth ion. The OH, CO stretching and other vibrations are shifted in the IR spectra of the complexes and the results are consistent with the crystal structure.

Cations↗
PubMed2004

Zirconocene-mediated intermolecular coupling of one molecule of Si-tethered diyne with three molecules of organonitriles: one-pot formation of pyrrolo[3,2-c]pyridine derivatives via cleavage of CN triple bonds of organonitriles.

One Si-tethered diyne is coupled in one pot with three molecules of organonitriles promoted by a low-valent zirconocene species. Cleavage of one of the three CN triple bonds and cleavage of the two Si-C bonds take place to afford pyrrolo[3,2-c]pyridine derivatives after hydrolysis.

Journal Article↗
PubMed2004

Selective preparation of oxygen-rich [60]fullerene derivatives by stepwise addition of tert-butylperoxy radical and further functionalization of the fullerene mixed peroxides.

tert-Butylperoxy radicals add to C(60) selectively to form multi-adducts C(60)(O)(m)(OO(t)Bu)(n) (m = 0, n = 2, 4, 6; m = 1, n = 0, 2, 4, 6) in moderate yields under various conditions. Visible light irradiation favors epoxide formation. High concentration of tert-butylperoxy radicals mainly produces the hexa-homoadduct C(60)(OO(t)Bu)(6) 6; low concentration and long reaction time favor the epoxy-containing C(60)(O)(OO(t)Bu)(4) 7. The reaction can be stopped at the bis-adducts with limited TBHP. A stepwise addition mechanism is discussed involving mono-, allyl-, and cyclopentadienyl C(60) radical intermediates. m-CPBA reacts with the 1,4-bis-adduct to form C(60)(O)(OO(t)Bu)(2) and C(60)(O)(3)(OO(t)Bu)(2). The C-O bond of the epoxy ring in 7 can be cleaved with HNO(3) and CF(3)COOH. Nucleophilic addition of NaOMe to 7 follows the S(N)1 and extended S(N)2' mechanism, from which four products are isolated with the general formula C(60)(O)(a)(OH)(b)(OMe)(c)(OO(t)Bu)(d). Visible light irradiation of the hexa-adduct 6 results in partial cleavage of both the C-O and O-O bonds of peroxide moieties and formation of the cage-opened compound C(60)(O)(O)(2)(OO(t)Bu)(4). All the fullerene derivatives are characterized by spectroscopic data. A single-crystal structure has been obtained for an isomer of C(60)(O)(OH)(2)(OMe)(4)(OO(t)Bu)(2).

Journal Article↗
PubMed2004

Interactions between metal ions and carbohydrates: the coordination behavior of neutral erythritol to zinc and europium nitrate.

The single crystals of coordinated complexes of neutral erythritol (C4H10O4) with zinc nitrate and europium nitrate were synthesized and studied using FT-IR and single crystal X-ray diffraction analysis. In the structure of Zn(NO3)2.C4H10O4, ZnEN (E denotes erythritol, N represents nitrate), Zn2+ is coordinated to four hydroxyl groups from two erythritol molecules and two oxygen atoms from two nitrates. Two Zn2+ are connected by one erythritol molecule to form Zn(C4H10O4)(NO3)2 chain, and layers formed by above chain pile to produce 3D structures. In the structure of Eu(NO3)3.C4H10O4.C2H5OH, EuEN, Eu3+ is 10-coordinated by six oxygen atoms from three nitrate ions, three hydroxyl groups from one erythritol molecule and one hydroxyl group from ethanol. In the above erythritol complexes, two hydroxyl groups of erythritol coordinate to one metal ion and the other two to another metal ion or erythritol acts as three-hydroxyl groups donor. The OH groups of erythritol act as ligand to coordinate to metal ions on one hand, one the other hand, OH groups form hydrogen bonds network to build three-dimensional structures.

Journal Article↗
PubMed2003

Interactions between metal ions and carbohydrates. Coordination behavior of neutral erythritol to Ca(II) and lanthanide ions.

The study of the sugar-metal ion interactions remains one of the main objectives of carbohydrate coordination chemistry because the interactions between metal ions and carbohydrates are involved in many biochemical processes. This paper presents a comparison of coordination structures of erythritol with alkaline-earth-metal and lanthanide chloride and nitrate in the solid state using FT-IR and X-ray diffraction. Neutral, nondeprotonated erythritol (E) reacts with CaCl(2) to give three CaCl(2)(-)erythritol (CaE(I), CaE(II), CaE(III)) complexes, showing that three of the five general features of calcium-carbohydrate complexes deduced in the reference encounter contrary examples. Different coordination structures have been observed for calcium and lanthanide chloride and nitrates. The coordination of carbohydrates to metal ions is complicated, and erythritol, chloride ions, nitrates, water molecules, and ethanol (crystallization medium and reaction solvents) have the chance to coordinate to metal ions. IR spectral results show that different lanthanide ions, from LaCl(3) to TbCl(3), have similar coordination structures with erythritol. The results show that erythritol can act as two bidentate neutral ligands (CaE(I), CaE(II), CaE(III), CaEN, PrE, NdE) or as a three-hydroxyl donor (NdEN). The IR results are consistent with the crystal structures.

Calcium↗
PubMed2003

Quantum Monte Carlo method using phase-free random walks with slater determinants.

We develop a quantum Monte Carlo method for many fermions using random walks in the space of Slater determinants. An approximate approach is formulated with a trial wave function |Psi(T)> to control the phase problem. Using a plane-wave basis and nonlocal pseudopotentials, we apply the method to Be, Si, and P atoms and dimers, and to bulk Si supercells. Single-determinant wave functions from density functional theory calculations were used as |Psi(T)> with no additional optimization. The calculated binding energies of dimers and cohesive energy of bulk Si are in excellent agreement with experiments and are comparable to the best existing theoretical results.

Journal Article↗