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Xinhua Wan

Publications and source records attributed to Xinhua Wan.

7 recordsLinked to original sources
PubMed2006

Molecular reorganization of rod-coil diblock copolymers at the air-water interface.

Amphiphilic rod-coil diblock copolymers consisting of flexible poly(ethylene oxide) (PEO) and rodlike poly{(+)-2,5-bis[4'-((S)-2-methylbutoxy)phenyl]styrene} (PMBPS) with predominant hydrophobic contents formed ordered monolayers at the air-water interface. The structures of monolayers transferred to a mica substrate at different surface pressures by the Langmuir-Blodgett method were investigated by atom force microscopy (AFM). For PEO(104)-b-PMBPS(17) copolymer (the subscripts denote the number-averaged polymerization degree of each block), a complete spectrum of molecular reorganization at variable surface pressures was observed. Spherical surface aggregates of LB monolayers were spontaneously formed during the solvent evaporation after the deposition of polymer solution. Continuous compression led to the pancake-to-brush conformation transition of the copolymer that PEO chains desorbed from the air-water interface and went into the water subphase. The effective content of the rod block changed continuously from 61% at zero pressure to 93% at the start of the monolayer collapse, igniting the molecular reorganization. As a result, coalescence of individual spherical aggregates into long cylindrical aggregates with an increase of the surface pressure was observed. For a series of block copolymers PEO(104)-b-PMBPS(m)() (m = 17, 30, 45, 53), as the rod contents increased from 61% to 83%, the morphological transition from spherical aggregates to long cylindrical aggregates in orientational order developed at zero pressure, which showed a similar dependence on the effective contents of the rod block to PEO(104)-b-PMBPS(17) at different pressures. In comparison to coil-coil block copolymers PEO-b-PS, the rod-coil block copolymers PEO-b-PMBPS exhibited distinct structure reorganization behavior, in which the orientation of rod block might play an important role.

Journal Article↗
PubMed2005

Perforated layer structures in liquid crystalline rod-coil block copolymers.

We report a novel observation of the tetragonal perforated layer structures in a series of rod-coil liquid crystalline block copolymers (BCPs), poly(styrene-block-(2,5-bis[4-methoxyphenyl]oxycarbonyl)styrene) (PS-b-PMPCS). PMPCS forms rigid rods while PS forms the coil block. Differential scanning calorimetry (DSC), polarized light microscopy (PLM), small-angle X-ray scattering (SAXS), wide-angle X-ray diffraction (WAXD), and transmission electron microscopy (TEM) techniques were used to investigate these rod-coil molecules, and a perforated layer structure was observed at f(PMPCS) approximately 0.37 in relatively low molecular weight (M(w)) samples and approximately 0.5 in high M(w) PS-b-PMPCS. This substantial phase boundary shift was attributed to the rod-coil nature of the BCP. The perforation obeys a tetragonal instead of hexagonal symmetry. The "onset" of perforation was also observed in real space in sample PS(272)-b-PMPCS(93) (f(PMPCS) approximately 0.52), in which few PS chains punctuate PMPCS layers. A slight increase in f(PS), by blending with PS homopolymer, led to a dramatic change in the BCP morphology, and uniform tetragonal perforations were observed at f(PMPCS) approximately 0.48.

Journal Article↗
PubMed2005

Direct proteins electrochemistry based on ionic liquid mediated carbon nanotube modified glassy carbon electrode.

A novel glassy carbon electrode modified by a gel containing multi-walled carbon nanotubes (MWNTs) and ionic liquid of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF6) is reported. The gel is formed by grinding of MWNTs and BMIPF6. Such gel is then coated on the surface of a glassy carbon electrode. We have employed scanning electron microscopy, Fourier transform infrared spectrometry (FTIR) and cyclic voltammetry to characterize the modified electrode. The direct electron transfers of hemoglobin and catalase on the modified electrode have been observed and studied in detail electrochemically. Hemoglobin is verified to be adsorbed on the modified electrode with the retention of conformation, which has been proved by microscopic FTIR. The electrochemical response of the adsorbed hemoglobin on the modified electrode is very stable, and shows repeated changes in the different pH solutions. It also has shown electrocatalysis to the reduction of oxygen and trichloroacetic acid. Catalase adsorbed on the gel modified electrode still keep activity to hydrogen peroxide. This work provides a simple and easy approach to construct biosensors based on the carbon nanotubes and ionic liquids.

Carbon↗
PubMed2005

Age-dependent dopaminergic dysfunction in Nurr1 knockout mice.

The Nurr1 gene, which codes for a transcriptional factor in the nuclear receptor superfamily, plays an important role in the development of the mesencephalic dopaminergic (DAergic) system. To study the age-dependent effects of Nurr1 expression in maintaining mature nigrostriatal DAergic neuronal function, we examined motor behaviors, determined nigrostriatal dopamine (DA) levels and the number of nigral DAergic neurons, and measured the expression of several DAergic neuron-associated genes in heterozygous Nurr1-deficient (Nurr1+/-) and wild-type mice of different ages. In contrast to the same-aged, wild-type mice, old Nurr1+/- mice (>15 months) had a significant decrease in both rotarod performance and locomotor activities, suggesting a motor impairment that is analogous to parkinsonian deficit. Furthermore, the abnormal motor behaviors in old Nurr1+/- mice were associated with decreased DA levels in the striatum, decreased number of DAergic neurons in the nigra, and reduced expression of Nurr1 and DA transporter in the nigra. Our data indicate that Nurr1 plays an important role in the functional maintenance and survival of nigral DAergic neurons and suggest that the Nurr1+/- mouse is a useful animal model to study the pathogenesis of Parkinson disease (PD) and to explore disease-modifying strategies.

Aging↗
PubMed2003

Matrix-assisted laser desorption/ionization study of cationization of PEO-PPP rod-coil diblock polymers.

Five PEO-PPP rod-coil diblock polymers were synthesized and characterized using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). By using a series of alkali chlorides as cation salts, relative cation affinities were studied. Different cation affinities and shifts in molecular weight distributions were found as a result of changing the cation type and size. Also, a study of lithium cationization resulted in determination of a recommended quantity of lithium to be used.

Journal Article↗
PubMedDate not supplied

Dopaminergic properties and experimental anti-parkinsonian effects of IPX750 in rodent models of Parkinson disease.

With a view toward improving the neural bioavailability of administered dopaminergic compounds, including dopamine, synthetic efforts have been directed toward enhancing the brain bioavailability of these compounds by accessing cellular sugar transport systems with stereoselective dopaminergic drugs. While synthesis and chemistry of the resultant class of compounds has recently been described in US Patent No. 6,548,484, the associated biologic properties have not previously been reported. One member of this new class, IPX-750, is a pro-drug dopamine-gluconamine designed to retain stereospecificity of binding at: glucose transporters (GLUT 1/GLUT 3 and intestinal Na/glucose co-transporters SGLT1), dopamine transporter (DAT); and, dopaminergic receptors of the D1/D2 families. Designed to be cleavable by tissue amidases, results reported here show that intact IPX-750 pro-drug retains dopaminergic agonist binding and biologic activities both in vitro and in vivo. IPX-750, like dopamine, exhibited predominant D5/D1 binding specificity with lower binding activity at D2. As expected, binding was highly stereo-specific, ie, IPX-760, a benzamide differing in just a hydrogen atom and keto oxygen from IPX-750, bound with 6-fold lower activity at D5. In cell culture, activation resulted from binding of IPX-750 at D1 or D5 in transfected cells was measured by increased intracellular cAMP. Interestingly, considering prior reported in vitro toxicity of dopamine oxidized and metabolic product dopamine, no evidence of in vitro toxicity was observed at up to 72 hrs in cell cultures at the EC50 of IPX-750 for increasing intracellular cAMP. IPX-750 was evaluated in the Parkinson's disease animal models, including MPTP mouse model, the 6-hydroxydopamine (6-OHDA) rat model and the Nurr1(+/-) knockout mouse model. In MPTP-lesioned and Nurr1+/- knockout mice, IPX-750 significantly increased Rota-rod time. In 6-OHDA-lesioned rats, IPX-750 significantly decreased apomorphine (APO)-induced rotation. Worthy of note, after cessation of IPX-750 treatments the anti-parkinsonian activity in MPTP-lesioned and Nurr1+/- mice required about 2 weeks to washout, suggesting a possible biologic reservoir of drug. In addition, after eight weeks of twice daily administration of 20 mg/kg IPX-750, mice did not show statistical difference in the total number of TH-positive neurons in substantia nigra (SN). These combined results suggest (i) that stereo-specific glycoconjugation may be an effective method to improve penetrability of drugs through the blood brain barrier; (ii) treatment with bioavailable IPX-750 in vitro did not show evidence for neurotoxicity; and, (iii) IPX-750 possesses dopaminergic properties and exerts anti-parkinsonian effects in three different PD rodent models, suggesting therapeutic potential for this new class of drugs in treating dopamine deficiency diseases.

Animals↗