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Biomedical subjects

Xi Zhang

Publications and source records attributed to Xi Zhang.

At least 37 records · Page 2Linked to original sources
PubMed2006

[Effect of particles on the photodegradation of PAHs in natural waters of the Yellow River].

Photodegradation of chrysene, benzo(a)pyrene and benzo(ghi)perylene in natural water of the Yellow River was studied using simulation sunlight. The effects of particulates on the photodegradation were explored. Several results arose from this study: (1) The photodegradation of PAHs can be fitted with first-order kinetics when no particulates exist in water system, and the first-order constant increase with the decrease of initial concentration of PAHs. The photodegradation rates of the three PAHs are related to their molecule absorption spectrum. (2) The presence of loess exerts two kinds of effects on the photodegradation of PAHs, which include the inner filter effects and the photosensitizing effects of humic substance in Loess. These two opposite effects lead to the difference of net effects among different contents of loess. When the loess contents are 0.1 g/L and 5.0 g/L, the presence of loess stimulates the photodegradation of chrysene, benzo(a)pyrene. When the loess content is 5.0 g/L, the presence of loess stimulates the photodegradation of benzo(ghi)perylene. In addition, the photodegradation of PAHs can be fitted with the second-order kinetics when there is loess in the water system. (3) The dissolvable humic substances in loess can accelerate the photodegradation of PAHs while the indissoluble part cannot. (4) Since the dissolvable humic substances in the suspended solids of the river have been dissolved in water, the addition of suspended solids to the water system can only cause the decrease of photodegradation rate of PAHs due to its inner filter effects, and the photodegradation rate decreases with the suspended solid content as a power exponent function.

Benzo(a)pyrene↗
PubMed2006

[Expression of transforming growth factor-beta 1, vascular cell adhesion molecule-1 and endothelium-selectin in placenta of patients with pre-eclampsia].

OBJECTIVE: To study the change and significance of the expression of transforming growth factor-beta 1 (TGF-beta1), vascular cell adhesion molecule-1 (VCAM-1) and endothelium-selectin (E-selectin) in placenta of patients with pre-eclampsia. METHODS: Twenty normal pregnant women (control group) and 40 women with pre-eclampsia (pre-eclampsia group, including 16 women with mild pre-eclampsia and 24 women with severe pre-eclampsia) were selected. The cellular distribution of TGF-beta1, VCAM-1 and E-selectin in placenta in both groups was determined by immunohistochemistry, and the mean density was measured by computer image analysis system. RESULTS: (1) The level of TGF-beta1 in placental villous syncytiotrophoblast of pre-eclampsia group (70.7 +/- 0.5) was significantly higher than that of control group (70.3 +/- 0.6), while the level of VCAM-1 and E-selectin in pre-eclampsia group (VCAM-1: 82.5 +/- 0.5, E-selectin: 53.5 +/- 0.5) was significantly lower than that of control group (VCAM-1: 82.8 +/- 0.3, E-selectin: 53.8 +/- 0.4) (P < 0.05). However, there were no significant differences in women with mild pre-eclampsia (TGF-beta1: 70.6 +/- 0.6, VCAM-1: 82.4 +/- 0.6, E-selectin: 53.4 +/- 0.5) and severe ones (TGF-beta1: 70.8 +/- 0.4, VCAM-1: 82.6 +/- 0.5, E-selectin: 53.6 +/- 0.5) (P > 0.05); (2) The level of E-selectin in placental villous capillary endothelial cells of pre-eclampsia group (63.0 +/- 0.5) was significantly higher than that of control group (62.6 +/- 0.4) (P < 0.05), while there was no significant difference in women with mild pre-eclampsia (63.2 +/- 0.4) and severe pre-eclampsia (62.9 +/- 0.5) (P > 0.05). CONCLUSION: TGF-beta1, VCAM-1 and E-selectin are not only related to placenta shallow bed of pre-eclampsia, but also participate in pathogenic process of vascular endothelial damage of pre-eclampsia.

Adult↗
PubMed2005

Self-assembled morphologies of monotethered polyhedral oligomeric silsesquioxane nanocubes from computer simulation.

Self-assembly of functionalized nanoscale building blocks is a promising strategy for "bottom-up" materials design. Recent experiments have demonstrated that the self-assembly of polyhedral oligomeric silsesquioxane (POSS) "nanocubes" functionalized with organic tethers can be utilized to synthesize novel materials with highly ordered, complex nanostructures. We have performed molecular simulations for a simplified model of monotethered POSS nanocubes to investigate systematically how the parameters that control the assembly process and the resulting equilibrium structures, including concentration, temperature, tether lengths, and solvent conditions, can be manipulated to achieve useful structures via self-assembly. We report conventional lamellar and cylindrical structures that are typically found in block copolymer and surfactant systems, including a thermotropic order-order transition, but with interesting stabilization of the lamellar phase caused by the bulkiness and cubic geometry of the POSS nanocubes.

Journal Article↗
PubMed2005

Single-chain mechanical property of poly(N-vinyl-2-pyrrolidone) and interaction with small molecules.

The single-chain nanomechanical properties of poly(N-vinyl-2-pyrrolidone) (PVPr) and povidone-iodine (PVPr-I2) under different solution conditions have been investigated by using an atomic force microscopy based technique-single-molecule force spectroscopy. The force-extension curve (force curve) of PVPr in water is markedly deviated from that obtained in ethanol or tetrahydrofuran, suggesting a different interaction between PVPr and the solvents. Moreover, we have comparatively studied the force signals of PVPr-I2 and PVPr in an aqueous solution of KI or KI3 and found that only KI3 influences the elastic property of PVPr dramatically. These experimental results indicate that there exists a specific interaction between PVPr and KI3, which is also supported by Fourier transform infrared data. By the integration of the deviated area between the force curve and the modified freely jointed chain fitting curve, we estimate that the energy needed to destroy the interaction between PVPr and water is 5.3 kT and between PVPr and KI3 is 3.6 kT per repeating unit, respectively.

Journal Article↗
PubMed2005

STM study on quinacridone derivative assemblies: modulation of the two-dimensional structure by coadsorption with dicarboxylic acids.

We describe the two-dimensional (2D) assemblies of N,N'-dialkyl-substituted quinacridone derivatives on highly orientated pyrolytic graphite observed by scanning tunneling microscopy, and focus our discussion on whether the supramolecular organization can be modulated by the coadsorption of dicarboxylic acids. Our experiments have demonstrated that the quinacridone derivatives can form different 2D nanostructures when coadsorbed with dicarboxylic acids of different length at the liquid/graphite interface. Interestingly, N,N'-dihexadecyl-substituted quinacridone derivative alternately takes two different conformations in two columns for its coadsorption with pentadecanedioic acid and form a gridlike structure. It is shown that a cooperative effect of different interactions can be modulated by introducing guest molecule, leading to formation of different self-assembled nanostructures.

Journal Article↗
PubMed2005

Surgical intervention for advanced valvular heart disease in 227 cases.

BACKGROUND: Although the results of surgical treatment in cardiac valve disease continue to improve, the postoperative mortality rate and the rate of complications in patients with advanced valvular heart disease (AVHD) are still very high. We did this retrospective study to summarize the surgical experience of heart valve replacement for patients with AVHD and discuss effective ways to improve the surgical outcome. METHODS: From January 1994 to October 2003, surgical procedures of heart valve replacement were performed on 227 (136 men and 91 women) patients with AVHD in our Department of Cardiothoracic Surgery. The clinical data of all patients were collected and analysed. Patients' age ranged from 10 years to 77 years. In preoperative cardiac function grading, 157 cases were NYHA III and 70 cases NYHA IV. Fifty-one patients had had cardiac operations. The ultrasonic cardiac graphs showed that 145 patients suffered from moderate or severe pulmonary hypertension and 73 had combined giant left ventricle. Mitral valve replacement was performed in 32 cases, aortic valve replacement in 90, tricuspid valve replacement in 1, combined mitral and aortic replacement in 103 and combined mitral and tricuspid replacement in 1. Nineteen patients also received surgical corrections for other minor abnormalities during the operations. A logistic model was established to evaluate the influence of perioperative factors on the mortality rate. RESULTS: The operative mortality rate was 13.2% (30/227). The main causes of death included multiple organ dysfunction syndrome (MODS), low cardiac output syndrome and ventricular fibrillation. From the results of the binary noncounterpart multivariate logistic regression, the following statistically significant factors were found to influence the operative mortality rate: redo operation, age >/= 55 years, preoperative NYHA cardiac function grading, extracorporeal circulation time >/= 120 minutes and postoperative usage of GIK (glucose, insulin and potassium) solution. All factors were risk ones except postoperative application of GIK. The Hosmer-Lemeshow goodness of fit coefficient of this model was 0.976. CONCLUSIONS: The risk factors associated with postoperative mortality rate in the patients with AVHD were redo operation, age >/= 55 years, preoperative NYHA cardiac function grading and extracorporeal circulation time >/= 120 minutes. Postoperative usage of GIK acted as a kind of metabolic therapy and will improve the recovery for patients with AVHD. Active perioperative management and care will play a very important role in reducing the operative risk and improving the short term outcome of surgical treatment for the patients with AVHD.

Adolescent↗
PubMed2005

Anisotropic aggregation and phase transition in Langmuir monolayers of methyl/ethyl esters of 2,3-dihydroxy fatty acids.

We studied interfacial properties of a series of methyl and ethyl esters of enantioenriched syn-2,3-dihydroxy fatty acids with different chain lengths at the air-water interface, using a Langmuir type film balance and a Brewster angle microscope (BAM). After analyzing their surface pressure (Pi)-area (A) isotherms, we inferred that these molecules existed as an E conformation in the liquid-expanded (LE) phase of monolayers, and the E conformation of molecules changed into a Z conformation during the LE-LC transition in a monolayer. BAM images evidenced the formation of elongated LC aggregates. This is possibly induced by the intermolecular hydrogen bonds, leading to the anisotropic growth of LC domains, on the basis of the FT-IR spectroscopy data. The enthalpy change of the LE-LC phase transition is considered to result from the three types of intermolecular interactions at the air-water interface during compression of these amphiphiles. These findings are discussed in terms of various physical factors that influenced intermolecular interactions and macroscopic aggregations of these amphiphiles.

Journal Article↗
PubMed2005

Combining layer-by-layer assembly with electrodeposition of silver aggregates for fabricating superhydrophobic surfaces.

Taking advantage of the stability and penetrability of layer-by-layer (LbL) films, we develop a novel method to fabricate a branchlike structure of Ag aggregates on the matrix of a LbL polyelectrolyte multilayer by an electrodeposition technique. The morphology of Ag aggregates can be adjusted by electrodeposition time and potential. Moreover, after further chemisorption of a self-assembled monolayer of n-dodecanethiol, the as-prepared surface becomes superhydrophobic with a contact angle as high as 154 degrees and a tilt angle lower than 3 degrees.

Journal Article↗
PubMed2005

Distinctive conflict processes associated with different stimulus presentation patterns: an event-related potential study.

Twelve subjects were asked to perform visual stimulus presentation tasks. Two figures were presented either simultaneously or sequentially. They were either in congruity (same shapes) or in conflict (different shapes) with each other. Conflicting stimulus pairs presented sequentially evoked a negative event-related component with a fronto-central and bilateral posterior scalp distribution, referred to as N270. In contrast, stimuli displayed simultaneously elicited a N220 with fronto-central prominence, irrespective of whether they were in conflict or in congruity. The results suggest that the N270 may be associated with the processing of a conflict with working memory information whereas the N220 might reflect the detection and evaluation of attention to visual information in the human brain.

Adult↗
PubMed2005

Self-assembled monolayers of dendron thiols for electrodeposition of gold nanostructures: toward fabrication of superhydrophobic/superhydrophilic surfaces and pH-responsive surfaces.

This paper describes the fabrication of surfaces with different wettability, superhydrophobic/superhydrophilic, and pH-responsive properties. We used a self-assembled monolayer (SAM) of a dendron thiol as the underlying surface for electrodeposition of gold nanostructures. After this modification with a SAM of n-dodecanethiol or 11-mercaptoundecanol, the surface shows remarkable superhydrophobic properties with a contact angle of about 155 degrees and a tilt angle of less than 2 degrees or superhydrophilic properties with a contact angle of about 0 degrees , respectively. Moreover, a large-scale pH-responsive surface was obtained by modification with 2-(11-mercaptoundecanamido)benzoic acid (7) (MUABA). The pH-responsive behavior was amplified by using rough surfaces.

Journal Article↗
PubMed2005

Patterned polyelectrolyte multilayer: surface modification for enhancing selective adsorption.

This paper describes the use of surface chemical modification to enhance the difference of the surface charge on a patterned polyelectrolyte multilayer, which can be used for selectively adsorbing functional materials. We fabricated a patterned multilayer by combining the layer-by-layer self-assembly technique and photolithography and taking advantage of the different solubility of polyelectrolyte multilayers of diazo resins (DAR)/poly(acrylic acid) before and after UV irradiation. This patterned surface can be used as a matrix for selective adsorption of small molecular dyes, such as Methylene Blue. However the difference in surface charge on the patterned surface was not enough when we used it to selectively adsorb polystyrene (PS) nanoparticles using electrostatic force as the driving force. Therefore, we modified the patterned surface by interfacial chemistry. After modification, the patterned polyelectrolyte multilayer can be used as a good matrix for selective adsorption of PS nanoparticles with both positive and negative charges.

Journal Article↗
PubMed2005

Structural and spectroscopic characterization of (mu-hydroxo or mu-oxo)(mu-peroxo)diiron(III) complexes: models for peroxo intermediates of non-heme diiron proteins.

(mu-Hydroxo or oxo)(mu-1,2-peroxo)diiron(III) complexes having a tetradentate tripodal ligand (L) containing a carboxylate sidearm [Fe2(mu-OH or mu-O)(mu-O2)(L)2]n+ were synthesized as models for peroxo-intermediates of non-heme diiron proteins and characterized by various physicochemical measurements including X-ray analysis, which provide fundamental structural and spectroscopic insights into the peroxodiiron(III) complexes.

Biomimetic Materials↗
PubMed2005

Directed evolution for engineering pH profile of endoglucanase III from Trichoderma reesei.

The potential of cellulase has been revealed not only in biomass conversion but also in various industrial processes, including food, textiles, laundry, pulp, and paper. Due to the need for alkali-tolerant cellulase with high specific activity at alkaline pH, for example, for application in detergent industry an error-prone PCR approach was employed for enhancing the alkali-tolerant ability of endoglucanase III (EG III) from Trichoderma reesei by error-prone PCR. One mutant (N321T) which exhibited an optimal activity at pH 5.4, corresponded to a basic shift of 0.6 pH unit compared to the wild-type enzyme, was selected and characterized. In addition, two site-directed mutations, N321D and N321H, were designed to study the role of residue at position 321. As expected, the N321D mutation changed enzyme's optimal activity to pH 4.0, resulting in a large decrease in the specific activity. However, the N321H mutated enzyme was active over a broader pH range compared to the wild type, with no much change in the specific activity. These properties suggest that the residue at position 321 is important amino acid residue in determining the pH activity profile of the EG III from T. reesei.

Amino Acid Sequence↗
PubMed2005

Preparation of fullerene-shell dendrimer-core nanoconjugates.

Generation 4 amine-terminated polyamidoamine dendrimer (PAMAM G4) was allowed to react with an excess of buckminsterfullerene (C60) to form a nanoconjugate containing a PAMAM core and C60 shell. The PAMAM-C60 conjugate was characterized by MALDI-TOF, TGA, UV-vis, and IR spectroscopy. Approximately thirty shell fullerenes surround each dendrimer core. The conjugates catalyze photooxidation of thioanisole by generation of singlet oxygen (1O2). The oxidation reactions occur in both organic and aqueous solvents, but the reactivity is enhanced in aqueous solution, possibly due to a nanoreactor effect resulting from diffusion of hydrophobic reactant molecules into dendrimer cavities.

Catalysis↗
PubMed2005

PVD following plasmin but not hyaluronidase: implications for combination pharmacologic vitreolysis therapy.

PURPOSE: To study whether intravitreal injection of plasmin + hyaluronidase safely induces posterior vitreous detachment (PVD). METHODS: Rabbits were randomized into three groups: (A) 20 rabbits, intravitreal injection of plasmin 1 U + hyaluronidase 20 U in balanced salt solution (BSS) 0.1 mL into one eye; (B) 12 rabbits, plasmin alone; (C) 12 rabbits, hyaluronidase alone. The fellow eye of each rabbit was injected BSS 0.1 mL. In Group A, scanning electron microscopy (SEM) was done in four rabbits at 0.5 hour and in four rabbits at 1 hour. After 7 days, all the remaining 36 rabbits received electroretinography, SEM was examined in eight of each group, and immunohistochemistry was done in four of each group. RESULTS: SEM disclosed the eyes of Group A had complete PVD (8/8), Group B partial PVD (7/8), and Group C (8/8) and all the control eyes (24/24) no PVD after 7 days. Partial PVD was found in 4/4 at 0.5 hour and complete PVD was seen in 3/4 at 1 hour in Group A. Immunohistochemistry showed that the amounts of laminin and fibronectin in the vitreoretinal interface were decreased in Group A and B versus the control eyes (P <0.001), but not in Group C versus the control eyes (P >0.05). Electroretinography showed no changes in any group (P >0.05). CONCLUSION: Vitreous injection of plasmin + hyaluronidase induced complete PVD with no obvious toxicity. Plasmin induced partial PVD, but hyaluronidase had no effects.

Animals↗