Biomedical subjects

Xiaoping Wang

Publications and source records attributed to Xiaoping Wang.

At least 37 records · Page 2Linked to original sources

PubMed2005

Strong electronic couplings between ferrocenyl centers mediated by bis-ethynyl/butadiynyl diruthenium bridges.

A series of trans-(FcC(2n))Ru(2)(Y-DMBA)(4)(C(2m)Fc) with n, m = 1 and 2 and Y-DMBA as N,N'-dimethylbenzamidinate or N,N'-dimethyl-(3-methoxy)benzamidinate have been synthesized and characterized. The intramolecular Fc...Fc distances, established through single-crystal X-ray diffraction studies, range from 11.6 to 16.6 A. Results from both voltammetric and spectroelectrochemical studies indicate that the (-C(2n))Ru(2)(Y-DMBA)(4)(C(2m-) fragments are among the most efficient mediators of intramolecular hole transfer. Density-functional calculations offer both the insight on the ground-state electronic properties and unambiguous assignment for the observed electronic absorptions.

Crystallography, X-Ray↗

PubMed2005

Proof of large positive zero-field splitting in a Ru2 5+ paddlewheel.

We present the synthesis, as well as the structural and magnetic characterization, of [Ru2(D(3,5-Cl2Ph)F)4Cl(0.5H2O)].C6H14 (D(3,5-Cl2Ph)F = N,N'-di(3,5-dichlorophenyl)formamidinate), a Ru2(5+) compound having a 4B(2u) ground state derived from a sigma2pi4delta2pi2delta electron configuration. The persistence of this configuration from 27 to 300 K is shown by the invariance of the Ru-Ru distance. Orientation-dependent magnetic susceptibility (chiT) and magnetization (M(H)) data are in accord with a spin quartet ground state with large magnetocrystalline anisotropy associated with a large axial zero-field splitting (D) parameter. Theoretical fits to chiT and M(H) plots yielded D/kB = +114 K, implying an S = +/-1/2 Kramers doublet ground state at low temperature. Single-crystal and powder EPR data are consistent with this result, as the only observed transition is between the M(s) = +/1/2 Zeeman levels. The g values are g(perpendicular) = 2.182, g(parallel) = 1.970, and D = 79.8 cm(-1). The totality of the results demands D >> 0.

Crystallography, X-Ray↗

PubMed2005

Searching for precursors to metal-metal bonded dipalladium species: a study of Pd2(4+) complexes.

Reactions of Pd3(OAc)6 with lithium salts of mononegative bidentate N,N-ligands, L, of various types, such as formamidinates, benzamidinates, triazinates, and guanidinates, were investigated in a search for ways to obtain Pd2(4+) compounds that could serve as precursors to paddlewheel complexes with a metal-metal bond and a Pd2(5+) core. It was found that the reactions are complex and that either square planar mononuclear or dinuclear species may be formed depending on the reaction conditions or the method of isolation. For Pd2L4 compounds, alpha and beta isomers were sometimes obtainable. In the alpha isomer, all N,N-ligands serve as bridges, whereas in the beta isomer, two ligands bridge the Pd2(4+) unit and each of the other two chelate to a metal atom. Electrochemistry shows that the paddlewheel compounds Pd2(TolNC(H)NTol)4, Pd2(PhNC(Ph)NPh)4, and Pd2(PhNC(Ph)NPh)3(OAc) and the orthometalated complex cis-Pd2[eta2-C6H4NC(Ph)N(H)Ph]2(mu-OAc)2 have reversible oxidation waves between 0.70 and 0.92 V vs Ag/AgCl, which makes them good candidates for chemical oxidation.

Journal Article↗

PubMed2005

Induction of immunological tolerance in chickens inoculated with xenogeneic antigens at an early stage of embryonic development.

To induce immunotolerance, laboratory chicken embryos were inoculated with casein via embryonic blood vessel microinjection or with bovine serum albumin (BSA) by either embryonic blood vessel or yolk sac injection. All hatched chickens were challenged with the same protein four times at 10-day intervals beginning at 3 weeks old. Serum anti-casein and anti-BSA antibodies were analyzed by enzyme-linked immunosorbent assay (ELISA). Significantly reduced serum specific antibody, demonstrating immunotolerance, was observed in 53.8% of chickens exposed to casein in embryo by microinjection at 65-70 h of incubation; and in 62.5% (inoculating at 65-67 h of incubation) and 33.33% (inoculating at 67-70 h of incubation) of chickens exposed to BSA. Tolerant chickens presented in those groups inoculated with BSA at 5-7 days of embryogenesis by in ovo injection. The results showed tolerance could be induced by injecting xenogeneic protein into early developing embryo by both inoculation methods.

Animals↗

PubMed2005

The hybrid enzymes from alpha-aspartyl dipeptidase and L-aspartase.

With combinative functionalities as well as the improved activity and stability, the novel hybrid enzymes (HEs) from the heterogeneous enzymes of alpha-aspartyl dipeptidase (PepE, monomer) and l-aspartase (l-AspA, tetramer) were constructed successfully by gene random deletion strategy. The wild-type hybrid enzyme (WHE) and the evolved hybrid enzyme (EHE) were selected, respectively, upon the phenotype and the enzyme activity. The relative activity of the WHE tested was about 110% of the wild-type PepE and 26% of the wild-type l-AspA, whilst the activity of EHE was about 340% of the PepE and 87% of the l-AspA. In comparison to its individual wild-type enzymes, the EHE exhibited an improved thermostability, when examined at the enzyme concentration of 10(-7)mol/L, but the WHE showed a reduced thermostability. The activity of the EHE was about 3-fold compared to that of the WHE. The current results give a good example that the hybridization of enzymes could be attained between the monomer and multimer enzymes. In addition, they also indicate that construction hybrid enzyme from evolved enzymes is feasible.

Aspartate Ammonia-Lyase↗

PubMed2005

Structural and magnetic evidence concerning spin crossover in formamidinate compounds with ru2 5+ cores.

The magnetic and structural properties of two Ru2(DArF)4Cl compounds, where DArF is the anion of a diaryl formamidine, are presented here. The compounds with Ar = p-anisyl and m-anisyl both show temperature dependence of chiT (chi = molar magnetic susceptibility), but for different reasons. For the para compound, there is a Boltzmann distribution between a pi*3 ground state and a delta*pi*2 upper state, and this is confirmed by a temperature dependence of the Ru-Ru bond length: 2.4471(5) A at 23 K and 2.3968(5) A at 300 K. For the meta compound, a delta*pi*2 configuration persists over the range of 23-300 K as shown by an invariant Ru-Ru bond length, but the chiT drops with decreasing temperature owing to zero-field splitting of a 4B2u ground state.

Journal Article↗

PubMed2005

Synthesis of core/shell nanoparticles of Au/CdSe via Au-Cd bialloy precursor.

We present a novel method for the preparation of ultrasmall Au/CdSe core/shell particles. Au-Cd bialloy particles of 4.7 nm diameter were prepared as the precursor. The Cd component in the precursor reacted with the Se source at a temperature of 205 degrees C and was heated to 250 degrees C, leading to formation of a Au/CdSe core/shell structure. The sizes of Au/CdSe nanoparticles have a narrow distribution with an average size of 6.0 nm and Au core of 2.2 nm diameter. The X-ray diffraction pattern and the images of the high-resolution electron transmission microscopy show that the Au cores and the CdSe shells of Au/CdSe core/shell nanoparticles are both well crystallized, and the CdSe shells are in a cubic phase. The absorption spectrum of the Au/CdSe nanoparticles combines the absorption behaviors of the Au cores and the CdSe shells.

Journal Article↗

PubMed2005

Modeling spin interactions in a cyclic trimer and a cuboidal Co4O4 core with Co(II) in tetrahedral and octahedral environments.

The X-ray crystallographic structures, the magnetic susceptibilities from 2 to 300 K, and a theoretical analysis of the magnetism for a triangular and a tetranuclear molecule consisting of linked high-spin cobalt(II) centers are described. The interpretation of the magnetic data for the triangular compound [Co(depa)Cl](3) (depa is the anion of 2,2'-(bis-4-ethylpyridyl)amine), which has tetrahedrally coordinated Co(2+) ions, entails isotropic antiferromagnetic exchange interaction and antisymmetric exchange acting within the two low-lying spin doublets. Two strong isotropic ferromagnetic interactions have been modeled in the cuboidal compound Co(4)(DPM)(4)(CH(3)O)(4)(CH(3)OH)(4) (DPM represents the anion of dipivaloylmethane), which has octahedral coordination, and the system can be approximately considered as two weakly coupled S = 3 species.

Journal Article↗

PubMed2005

Somatostatin, somatostatin receptors, and pancreatic cancer.

Somatostatin may play an important role in the regulation of cancer growth including pancreatic cancer by interaction with somatostatin receptors (SSTRs) on the cell surface. Five SSTRs were cloned, and the function of these SSTRs is addressed in this review. SSTR-2, SSTR-5, and SSTR-1 are thought to play major roles in inhibiting pancreatic cancer growth both in vitro and in vivo. SSTR-3 may be involved in mediating apoptosis, but the role of SSTR-4 is not clear. In most pancreatic cancers, functional SSTRs are absent. Reintroduction of SSTR genes has been shown to inhibit pancreatic cancer growth in cell cultures and animal models.

Animals↗

PubMed2004

Paramagnetism at ambient temperature, diamagnetism at low temperature in a Ru2(6+) core: structural evidence for zero-field splitting.

Variable temperature magnetic studies of the Ru(2)(6+) guanidinate compounds Ru(2)(hpp)(4)Cl(2) (1) and Ru(2)(hpp)(4)(CF(3)SO(3))(2) (2) show that they are paramagnetic with two unpaired electrons at room temperature and that they appear essentially diamagnetic at 2 K. In neither compound do the Ru-Ru distances vary by more than 0.008(1) A from 27 to 296 K. This argues strongly that the ground state electronic configuration remains constant over this temperature range and that the decrease in magnetism as the temperature is lowered must be attributable to zero-field splitting of the (3)A(2g) ground state arising from the electronic configuration sigma(2)pi(4)delta(2)pi(2). The Ru-Ru distance in 1 is about 0.04-0.05 A longer than that in 2 which indicates that the Ru(2)(hpp)(4)(2+) core is quite sensitive to the nature of the axial ligands. The electronic spectra show three absorption bands for each compound.

Journal Article↗

PubMed2004

Paramagnetic precursors for supramolecular assemblies: selective syntheses, crystal structures, and electrochemical and magnetic properties of Ru2(O2CMe)4-n(formamidinate)nCl complexes, n = 1-4.

Reactions of Ru(2)(O(2)CMe)(4)Cl with two formamidines, HDXyl(2,6)F = N,N'-di(2,6-xylyl)formamidine and HDAniF = N,N'-di(p-anisyl)formamidine, have been investigated with the idea of synthesizing compounds with a mixed set of ligands having different labilities to be used as precursors of paramagnetic, higher-order assemblies. Depending on the formamidine and the reaction conditions, several Ru(2)(5+) compounds of the type Ru(2)(O(2)CMe)(4)(-)(n)(DArF)(n)Cl (DArF = anion of an N,N'-diarylformamidine) have been isolated. With the bulky formamidine HXyl(2,6)F, the compounds Ru(2)(O(2)CMe)(3)(DXyl(2,6)F)Cl (1) and trans-Ru(2)(O(2)CMe)(2)(DXyl(2,6)F)(2)Cl (2) were obtained. From reactions with appropriate amounts of HDAniF in THF and in the presence of NEt(3) and LiCl, complexes of the general type Ru(2)(O(2)CMe)(4)(-)(n)(DArF)(n)Cl (n = 1-4) were selectively obtained. For n = 2, only the cis isomer was obtained. The choice of solvent in reactions of Ru(2)(O(2)CMe)(4)Cl and HDAniF is of great importance. Toluene favored the formation of the fully substituted Ru(2)(5+) complex Ru(2)(DAniF)(4)Cl (3), whereas MeOH resulted in a disproportionation reaction that gave the edge-sharing bioctahedral Ru(3+)Ru(3+) complex [trans-Ru(2)(mu-OMe)(2)(mu-O(2)CMe)(2)(HDAniF)(4)]Cl(2) (6) and the Ru(2)(4+) complex Ru(2)(DAniF)(4) (7). Complexes 6 and 7 with an Ru(2)(6+) and Ru(2)(4+) core, respectively, are diamagnetic, whereas all Ru(2)(5+) complexes are paramagnetic with sigma(2)pi(4)delta(2)(pi*delta*)(3) ground-state electronic configurations and large zero-field splitting contributions. All compounds show rich and complex electrochemical behavior.

Journal Article↗

PubMed2004

Chiral organometallic triangles with Rh-Rh bonds. 1. Compounds prepared from racemic cis-Rh2(C6H4PPh2)2(OAc)2.

Reaction of racemic cis-Rh(2)(C(6)H(4)PPh(2))(2)(OAc)(2)(HOAc)(2) with excess Me(3)OBF(4) in CH(3)CN results in the formation of racemic cis-[Rh(2)(C(6)H(4)PPh(2))(2)(CH(3)CN)(6)](BF(4))(2).0.5H(2)O (1.0.5H(2)O), an ionic dirhodium complex which has two cisoid nonlabile orthometalated phosphine bridging anions and six labile CH(3)CN ligands in equatorial and axial positions. Reactions of 1 with tetraethylammonium salts of the linear dicarboxylates, oxalate, terephthalate, and 4,4'-biphenyl-dicarboxylate, in organic solvents, produced racemic crystals of the triangular compounds [Rh(2)(C(6)H(4)PPh(2))(2)](3)(C(2)O(4))(3)(py)(6).6MeOH.H(2)O (2.6MeOH.H(2)O), [Rh(2)(C(6)H(4)PPh(2))(2)](3)(O(2)CC(6)H(4)CO(2))(3)(DMF)(6).6.5DMF.0.5H(2)O (3.6.5DMF.0.5H(2)O), and [Rh(2)(C(6)H(4)PPh(2))(2)](3)(O(2)CC(6)H(4)C(6)H(4)CO(2))(3)(py)(6).4.5CH(3)OH.0.75H(2)O (4.4.5CH(3)OH.0.75H(2)O), respectively. All compounds are electrochemically active. The relative chiralities of the dirhodium units in each triangle have been established using a combination of data from X-ray crystallography and (31)P NMR spectroscopy.

Journal Article↗

PubMed2004

Strong electronic coupling between dimolybdenum units linked by the N,N'-dimethyloxamidate anion in a molecule having a heteronaphthalene-like structure.

Very strong electronic communication, manifested in a K(C) value of ca. 10(9), has been found in a system of three compounds separated by one electron oxidation where each compound contains two metal-metal bonded Mo(2)(n+) units linked by a dimethyloxamidate anion, CH(3)N(O)C-C(O)NCH(3)(2)(-). The Mo-Mo distances increase as the oxidation state increases and the bond order decreases, while the diamagnetic, doubly oxidized species becomes essentially planar and resembles a naphthalene molecule. Calculations at the DFT level indicate that a strong transition in the near-IR region, shown by the singly oxidized and paramagnetic species, is best described as a HOMO-1 --> SOMO transition.

Journal Article↗

PubMed2004

Pancreatic carcinoma cells express neuropilins and vascular endothelial growth factor, but not vascular endothelial growth factor receptors.

BACKGROUND: Neuropilins (NRPs) are characterized as coreceptors of vascular endothelial growth factor (VEGF). In the current study, the authors assessed the expression of NRPs, VEGF, and vascular endothelial growth factor receptors (VEGFRs), as well as VEGF-induced cell proliferation, in pancreatic carcinoma cell lines and tissue specimens. METHODS: Human pancreatic carcinoma cell lines (Panc-1 and MIA PaCa-2), normal human pancreatic ductal epithelial cells (HPDE), and human umbilical vein endothelial cells (HUVECs) were cultured. Human pancreatic adenocarcinoma tissue specimens were also studied. Expression levels of NRPs, VEGFRs, and VEGF were determined by real-time polymerase chain reaction analysis and immunostaining. Cell proliferation was examined using a [3H]thymidine incorporation assay. RESULTS: Both NRP-1 and NRP-2 were expressed in Panc-1 cells, HPDE cells, and HUVECs but were expressed minimally in MIA PaCa-2 cells. Panc-1 expressed 30 times more NRP-1 mRNA than NRP-2 mRNA. NRP-1 levels in Panc-1 cells were 5.3 times higher than in HPDE cells but were similar to NRP-1 levels in HUVECs. NRP-2 levels in Panc-1 cells were similar to NRP-2 levels in HPDE cells but lower than NRP-2 levels in HUVECs. Expression of all three VEGFRs was observed only in HUVECs. However, VEGF mRNA was detected in all cell types except for HUVECs. NRP-1 immunoreactivity levels were much higher than NRP-2 immunoreactivity levels in Panc-1 and human pancreatic adenocarcinoma tissue specimens, whereas VEGFRs were not detected in either of these two settings. In response to VEGF165, [3H]thymidine incorporation in Panc-1 cells increased significantly (by 61%; P < 0.01). A monoclonal antibody against human NRP-1 significantly blocked VEGF-induced cell proliferation in Panc-1 cells. CONCLUSIONS: The pancreatic carcinoma cell line Panc-1 and adenocarcinoma tissue specimens expressed high levels of NRP-1 and VEGF, but not VEGFRs, and exogenous VEGF significantly increased NRP-1-mediated, but not VEGFR-mediated, Panc-1 cell proliferation. These data suggested that NRP-1 may be involved in the pathogenesis of pancreatic carcinoma.

Adenocarcinoma↗

PubMed2004

Fate of carbon tetrachloride during phytoremediation with poplar under controlled field conditions.

The fate of carbon tetrachloride (CT) during phytoremediation with poplar was assessed by examining the transpiration of CT from leaves, diffusion from soil, tree trunks, and surface roots, and accumulation of chloride ion in soil and plant tissues. Feedwater containing 12-15 mg/L CT was added to the field test beds planted with poplar, and over 99% of the CT was removed. No significant amount of CT was transpired or diffused into the air, and no significant amount of CT-chlorine accumulated in the tree tissues. Chloride ion accumulated in the soil accounted for all of the CT-chlorine removed. When soils from the root zones were compared to unvegetated soils, microbial mineralization of CT was not enhanced in soils from the root zones as compared to unvegetated soils. Thus, we conclude that uptake and dechlorination of CT by plant tissues is likely the primary mechanism for phytoremediation by poplar.

Carbon Tetrachloride↗

PubMed2004

Extended metal atom chains (EMACs) of five chromium or cobalt atoms: symmetrical or unsymmetrical?

Structural studies of pentachromium and pentacobalt extended metal atom chain (EMAC) systems are presented in which the metal chains are helically wrapped by either the pentadentate dianion tripyridyldiamide (tpda) or its diethyl-substituted analogue bis(4-ethyl-2-pyridylamido)pyridine (etpda). The compound Cr(5)(tpda)(4)(NCS)(2), has alternating long and short Cr-Cr distances, contrary to recent reports that describe it as symmetrical with essentially equally spaced chromium atoms. The linear Cr(5)(10+) chain is composed of two Cr(2)(4+) quadruply bonded units and an isolated high spin Cr(II) unit. The new compounds Cr(5)(etpda)(4)Cl(2), [Cr(5)(etpda)(4)FCl]PF(6), and Co(5)(etpda)(4)(NCS)(2)() employ the etpda ligand as "insulation" around a central pentametal-atom "wire." Compound, like all other oxidized pentachromium compounds, has very disparate alternating short-long-short-long Cr-Cr distances, 2.032(3) A, 2.560(6) A, 1.873(5) A, and 2.509(4) A. Compound shows a nearly uniform spacing of the Co atoms, although the outer Co-Co distances (2.279[4] A) are slightly longer than the inner ones (2.239[4] A).

Journal Article↗

PubMed2004

Molecular and electronic structures by design: tuning symmetrical and unsymmetrical linear trichromium chains.

The preparation, properties, and crystal structures of 12 trichromium extended metal atom chain (EMAC) compounds of the type Cr(3)(L)(4)X(2) (L = equatorial ligands dipyridylamide (dpa) or di-4,4'-ethyl-2,2'-pyridylamide (depa), and X = axial ligands, e.g., halide or pseudohalide ions) with large variations in metal-metal distances are reported here. These complexes, which belong to a broad class of fundamentally interesting trinuclear molecules over which the electrons may or may not be delocalized, pose significant theoretical and experimental challenges which are dealt with in this report. Complexes with strongly donating axial or equatorial ligands tend to favor a symmetrical (D(4)) molecular structure, while more weakly donating ligands give rise to unsymmetrical (C(4)) structures; the physical properties of these two classes of compounds are discussed fully, and important comparisons with a reported DFT model of the electronic structures of the compounds are made.

Journal Article↗

PubMed2004

Dielectric properties and frequency response of self-assembled monolayers of alkanethiols.

This paper presents dielectric properties of alkanethiol self-assembled monolayers (SAMs) under an ac electric field. Using a Hg-SAM/SAM-Hg junction, we measured the ac impedance of alkanethiol SAMs using a sinusoidal perturbation of 30 mV (peak-to-peak) with frequency ranging from 1 Hz to 1 MHz at zero bias. Semicircles at higher frequencies and at middle frequencies along with Warburg lines at lower frequencies were observed in complex plane impedance plots, that is, Nyquist plots. The frequency response of SAMs was analyzed by modeling the junction using an equivalent circuit and fitting the Nyquist plots. The semicircles at higher frequencies are attributed to the effect of the SAM/SAM interfaces, and the ones at middle frequencies are attributed to the effect of alkanethiol SAMs. The comparison in the plots of the imaginary part of the impedance Z against frequency for the bare Hg electrodes (in pure ethanal) and the SAM-covered Hg electrodes (in alkanethiol solution) supports the analysis. The Warburg lines are attributed to a certain ionic impurity. The dielectric loss spectra are further analyzed. Chain-length-dependent peaks, which correspond to different relaxation mechanisms, at higher frequencies and middle frequencies were observed in the spectra of the dissipation factor (tan delta vs frequency). The peaks move to small frequency with the increase of chain length of alkanethiols. Using a correlation of peak position with the chain length, we then derived active energies of 39-99 meV for alkanethiol SAMs of C7-C18 under an ac electric field.

Journal Article↗