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Lijia An

Publications and source records attributed to Lijia An.

At least 19 recordsLinked to original sources

Investigation of sol-gel transition in pluronic F127/D2O solutions using a combination of small-angle neutron scattering and monte carlo simulation.

Physical gelation in the concentrated Pluronic F127/D2O solution has been studied by a combination of small-angle neutron scattering (SANS) and Monte Carlo simulation. A 15% F127/D2O solution exhibits a sol-gel transition at low temperature and a gel-sol transition at the higher temperature, as evidenced by SANS and Monte Carlo simulation studies. Our SANS and simulation results also suggest that the sol-gel transition is dominated by the formation of a percolated polymer network, while the gel-sol transition is determined by the loss of bound solvent. Furthermore, different diffusion behaviors of different bound solvents and free solvent are observed. We expect that this approach can be further extended to study phase behaviors of other systems with similar sol-gel phase diagrams.

Journal Article↗

Effects of chain flexibility on polymer conformation in dilute solution studied by lattice monte carlo simulation.

Effects of chain flexibility on the conformation of homopolymers in good solvents have been investigated by Monte Carlo simulation. Bond angle constraint coupled with persistence length of polymer chains has been introduced in the modified eight-site bond fluctuation simulation model. The study about the effects of chain flexibility on polymer sizes reveals that the orientation of polymer chains under confinement is driven by the loss of conformation entropy. The conformation of polymer chains undergoing a gradual change from spherical iso-diametric ellipsoid to rodlike iso-diametric ellipsoid with the decrease of polymer chain flexibility in a wide region has been clearly illustrated from several aspects. Furthermore, a comparison of the freely jointed chain (FJC) model and the wormlike chain (WLC) model has also been made to describe the polymer sizes in terms of chain flexibility and quasi-quantitative boundary toward the suitability of the models.

Adsorption↗

A self-consistent field theory study on the morphologies of linear ABCBA and H-shaped (AB)(2)C(BA)(2) block copolymers.

By using a combinatorial screening method based on the self-consistent field theory, we investigate the equilibrium morphologies of linear ABCBA and H-shaped (AB)(2)C(BA)(2) block copolymers in two dimensions. The triangle phase diagrams of both block copolymers are constructed by systematically varying the volume fractions of blocks A, B, and C. In this study, the interaction energies between species A, B, and C are set to be equal. Four different equilibrium morphologies are identified, i.e., the lamellar phase (LAM), the hexagonal lattice phase (HEX), the core-shell hexagonal lattice phase (CSH), and the two interpenetrating tetragonal lattice phase (TET2). For the linear ABCBA block copolymer, the reflection symmetry is observed in the phase diagram except for some special grid points, and most of grid points are occupied by LAM morphology. However, for the H-shaped (AB)(2)C(BA)(2) block copolymer, most of the grid points in the triangle phase diagram are occupied by CSH morphology, which is ascribed to the different chain architectures of the two block copolymers. These results may help in the design of block copolymers with different microstructures.

Journal Article↗

How does solvent molecular size affect the microscopic structure in polymer solutions?

Monte Carlo simulation has been used to investigate the effects of linear solvent molecular size on polymer chain conformation in solutions. Increasing the solvent molecular size leads to shrinkage of the polymer chains and increase of the critical overlap concentrations. The root-mean-square radius of gyration of polymer chains (R(g)) is less sensitive to the variation of polymer concentration in solutions of larger solvent molecules. In addition, the dependency of R(g) on polymer concentration under normal solvent conditions and solvent molecular size is in good agreement with scaling laws. When the solvent molecular size approaches the ideal end-to-end distance of the polymer chain, an extra aggregation of polymer chains occurs, and the solvent becomes the so-called medium-sized solvent. When the size of solvent molecules is smaller than the medium size, the polymer chains are swollen or partially swollen. However, when the size of solvent molecules is larger than the medium size, the polymer coils shrink and segregate, enwrapped by the large solvent molecules.

Journal Article↗

Comparing the morphology and phase diagram of H-shaped ABC block copolymers and linear ABC block copolymers.

By using a combinatorial screening method based on the self-consistent field theory (SCFT) for polymers, we have investigated the morphology of H-shaped ABC block copolymers (A2BC2) and compared them with those of the linear ABC block copolymers. By changing the ratios of the volume fractions of two A arms and two C arms, one can obtain block copolymers with different architectures ranging from linear block copolymer to H-shaped block copolymer. By systematically varying the volume fractions of block A, B, and C, the triangle phase diagrams of the H-shaped ABC block copolymer with equal interactions among the three species are constructed. In this study, we find four different morphologies (lamellar phase (LAM), hexagonal lattice phase (HEX), core-shell hexagonal lattice phase (CSH), and two interpenetrating tetragonal lattice (TET2)). Furthermore, the order-order transitions driven by architectural change are discussed.

Models, Molecular↗

Genotyping of Sporothrix schenckii by analysis of ribosomal DNA regions.

An attempt was made to identify the genotypes of 31 Sporothrix schenckii strains and the relationship between the genotypes, the geographic distributions and clinical manifestations using restriction fragment length polymorphic analysis. The total DNA was extracted by cetyltrimethyl ammonium bromide. The polymorphisms were detected by hybridisation of ApaI-digested Sporothrix genomic DNA with a probe amplified from the small subunit ribosomal DNA and adjacent internal transcribed spacer regions. The band patterns manifested by Southern blotting were explored to investigate the genotypes of the 31 strains of S. schenckii collected from five different areas in China. Of the data from the 31 strains of S. schenckii studied, 15 individual patterns (DNA type A-O) were recognised. Type A-C accounted for 51.61% of all the strains. The DNA typing of S. schenckii by Southern blotting was highly sensitive and highly distinguishable. We also found a significant correlation between DNA patterns and different geographic areas and clinical manifestations.

Blotting, Southern↗

[Alzheimer's disease and oxidative stress].

Alzheimer's disease (AD) has abstracted many scientists' interests with the aging of people in the world, but its mechanisms are still remaining unclear. This review will focus on some of the mediators of oxidative stress occurring in AD pathology and their possible role in the AD pathogenesis. Meanwhile, antioxidant approaches for the prevention and treatment of AD are discussed.

Alzheimer Disease↗

A new two-phase route to high-quality CdS nanocrystals.

A new two-phase route has been developed to synthesize high-quality CdS nanocrystals with a narrow size distribution and a high photoluminescence (PL) quantum yield (QY). In the two-phase system, toluene and water were used as separate solvents for cadmium myristate (CdM2) and thiourea, which served as cadmium source and sulfur source, respectively, and oleic acid (OA) was used as a ligand for stabilizing the nanocrystals. The reactions were completed in the heated autoclaves. The initial Cd/S molar ratio of the precursors and the reaction temperature were found to be factors that affected the growth of nanocrystals. Furthermore, a seeding-growth technique was developed to synthesize CdS nanocrystals of different sizes, which exhibit PL peaks with quite similar full width at half-maximum (FWHM) values compared to those of the initial nanocrystal seeds in all cases.

Cadmium↗

Isoflavonoids from Astragalus mongholicus protect PC12 cells from toxicity induced by L-glutamate.

lsoflavonoids, formononetin, 9,10-dimethoxypterocarpan 3-O-beta-D-glucoside, ononin, calycosin 7-O-glc and calycosin, were isolated from the roots of Astragalus mongholicus Bunge (Leguminosae). The neuroprotective roles and direct antioxidant effects of these isoflavonoids were investigated by using PC12 cell model and DPPH (1,1-diphenyl-2-picrylhydrazyl) assay. Formononetin, ononin and calycosin were found inhibiting glutamate-induced cell injury, with an estimated 50% effective concentration (EC50) of 0.027 microg/ml, 0.047 microg/ml and 0.031 microg/ml, respectively. Pretreatment with them increased the activities of antioxidant enzymes, including superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px), and prevented the release of lactate dehydrogenase (LDH) in glutamate-injured PC12 cells. On the other hand, calycosin 7-O-glc and calycosin showed more scavenging activity to DPPH radicals than formononetin in the cell-free system. The inconsistency between the neuroprotective capabilities of isoflavonoids and their directly scavenging activity to DPPH radicals indicated that formononetin, ononin and calycosin probably depended on increasing endogenous antioxidant and stabilizing the cells' membrane structures to inhibit the cell damage induced by glutamate.

Animals↗

Nanoscopic surface patterns of diblock copolymer thin films.

The surface topography of thin diblock copolymer films is studied by atomic force microscopy (AFM). With AFM an island-to-ribbon transition is observed for symmetric polystyrene-b-poly (4-vinylpyridine) (PS-b-P4VP) on mica with increasing solution concentration. Our study also demonstrates how the formation of the pattern strongly depends on the copolymer composition based on the volume fraction. The substrate and solvent used both have great effects on the morphology of the thin films. Only by using highly polar substrate (mica), can we gain regular pattern. The reason why the regular islands cannot be obtained with symmetric PS-b-P4VP on graphite is also explained. On mica using nonselective and selective solvents, a rather regular pattern can be obtained. The difference is only in the solution concentration for forming regular patterns.

Coated Materials, Biocompatible↗

Purification, characterization and gene cloning of a novel phospholipase A2 from the venom of Agkistrodon blomhoffii ussurensis.

A new phospholipase A2 with Gln at the site 49, abbreviated as Gln49-PLA2, has been purified from the venom of Agkistrodon blomhoffii ussurensis by using ion-exchange chromatography, gel filtration chromatography and reversed-phase HPLC, and behaves as a single-band on SDS-PAGE. Its molecular weight is 13881.85+/-0.33 Da given by mass spectrometry and pI is about 8.56 given by isoelectric focusing. Gln49-PLA2 does not show phospholipase A2 and hemorrhagic activity, whereas shows weak toxic and apparent anticoagulant activity. Based on the N-terminal sequencing and peptide mass fingerprint analysis, Gln49-PLA2 cDNA has been cloned by means of RT-PCR. Gln49-PLA2 consists of 122 amino acid residues and has the structural features of class II of snake venom phospholipase A2.

Agkistrodon↗

PfADA2, a Plasmodium falciparum homologue of the transcriptional coactivator ADA2 and its in vivo association with the histone acetyltransferase PfGCN5.

The transcriptional coactivator ADA2 is an evolutionarily conserved component of histone acetyltransferase (HAT) complexes involved in chromatin remodeling and transcriptional regulation in eukaryotes. The Plasmodium falciparum homologue, PfADA2, has a 7737 bp open reading frame, encoding a protein of 2578 amino acids with an ADA2-like domain located near the C-terminus. The annotated PfADA2 in the parasite genome is Pf10_143, located on chromosome 10. Sequence analysis demonstrated the presence of an ADA2 homologue in each Plasmodium species selected for genome sequencing. Mapping of the 5' transcriptional initiation sites suggested that PfADA2 transcription was initiated from multiple sites. Northern analysis detected a major transcript of approximately 8.5 kb in erythrocytic stage parasites. An antiserum raised against the internal ADA2-like domain detected multiple proteins from mixed blood stages, suggesting that PfADA2 may be proteolytically processed. In comparison, affinity-purified anti-GCN5 antibodies reacted with a major protein of approximately 200 kDa and immunoprecipitated proteins from the parasite lysate with HAT activity similar to that of the recombinant GCN5. Moreover, this GCN5-like HAT activity could also be precipitated with anti-PfADA2 antibodies, indicating that PfADA2 is associated with PfGCN5 in vivo. To illustrate whether PfADA2 could functionally replace the yADA2, complementation experiments were performed. However, the ADA2-like domain of PfADA2 failed to rescue the yeast ada2(-) mutant, probably due to significant divergence between the two genes. Taken together, these results indicate the presence of PfADA2-PfGCN5 complex(es) in the malaria parasite, which may have conserved functions in chromatin remodeling and gene regulation.

Acetyltransferases↗

Conformation studies on sol-gel transition in triblock copolymer solutions.

The gelation of physically associating triblock copolymers in a good solvent was investigated by means of the Monte Carlo simulation and a gelation process based on the conformation transition of the copolymer that was described in detail. In our simulative system, it has been found that the gelation is closely related with chain conformations, and there exist four types of chains defined as free, dangling, loop, and bridge conformations. The copolymer chains with different conformations contribute to the formation of gel in different ways. We proposed a conformational transition model, by which we evaluated the role of these four types of chains in sol-gel transition. It was concluded that the free chains keeping the conformation transition equilibrium and the dangling conformation being the hinge of conformation transition, while the chain with loop conformation enlarges the size of the congeries and the chain with bridge conformations binds the congeries consisted of the copolymer chains. In addition, the effects of temperature and concentration on the physical gelation, the association of the copolymer congeries, and the copolymer chain conformations' distribution were discussed. Furthermore, we employed the structure factor analysis to study the association of copolymer conformations and long-range order of the simulation system and found our results are in agreement with the previous experimental conclusions.

Journal Article↗

Plasmodium falciparum histone acetyltransferase, a yeast GCN5 homologue involved in chromatin remodeling.

The yeast transcriptional coactivator GCN5 (yGCN5), a histone acetyltransferase (HAT), is part of large multimeric complexes that are required for chromatin remodeling and transcriptional activation. Like other eukaryotes, the malaria parasite DNA is organized into nucleosomes and the genome encodes components of chromatin-remodeling complexes. Here we show that GCN5 is conserved in Plasmodium species and that the most homologous regions are within the HAT domain and the bromodomain. The Plasmodium falciparum GCN5 homologue (PfGCN5) is spliced with three introns, encoding a protein of 1,464 residues. Mapping of the ends of the PfGCN5 transcript suggests that the mRNA is 5.2 to 5.4 kb, consistent with the result from Northern analysis. Using free core histones, we determined that recombinant PfGCN5 proteins have conserved HAT activity with a substrate preference for histone H3. Using substrate-specific antibodies, we determined that both Lys-8 and -14 of H3 were acetylated by the recombinant PfGCN5. In eukaryotes, GCN5 homologues interact with yeast ADA2 homologues and form large multiprotein HAT complexes. We have identified an ADA2 homologue in P. falciparum, PfADA2. Yeast two-hybrid and in vitro binding assays verified the interactions between PfGCN5 and PfADA2, suggesting that they may be associated with each other in vivo. The conserved function of the HAT domain in PfGCN5 was further illustrated with yeast complementation experiments, which showed that the PfGCN5 region corresponding to the full-length yGCN5 could partially complement the yGCN5 deletion mutation. Furthermore, a chimera comprising the PfGCN5 HAT domain fused to the remainder of yeast GCN5 (yGCN5) fully rescued the yGCN5 deletion mutant. These data demonstrate that PfGCN5 is an authentic GCN5 family member and may exist in chromatin-remodeling complexes to regulate gene expression in P. falciparum.

Acetyltransferases↗

Influence of shear on polypropylene crystallization kinetics.

Isothermal crystallization kinetics under shear in the melt of iPP was investigated by optical microscopy. It appears that shearing from 200 to the crystallization temperatures enhanced the kinetics, but the shear effect was not obvious if the melt of iPP was sheared only at 200. The experiment results show that relaxation plays an important role during crystallization, and that spherulite growth rates increased with shear rates and were governed by relaxation. The effect of flow on the crystallization kinetics can be understood by considering that the increase of the degree of order due to flow results is an effective change of the melt free energy. The Laurizen-Hoffman theory and the DE-IAA model were used to describe the shear-induced crystallization kinetics of iPP excellently.

Journal Article↗

Investigation of the neuronal death mode induced by glutamate treatment in serum-, antioxidant-free primary cultured cortical neurons.

Glutamate, the principal excitatory amino acid neurotransmitter in the central nervous system, is also a potential toxin leading to excitotoxicity when it is over-accumulated in extracellular space. Glutamate excitotoxicity has been implicated in many neurological disorders. To date, the death mode of neurons induced by glutamate remains ambiguous and is widely debated. To further clarify the neuronal death mode after glutamate treatment, we investigated this issue in mouse embryonic cortical neurons that were cultured in a serum-, antioxidant-free condition. Our study shows that exposure to low concentration of glutamate (30 microM) in a delayed time course induces neuronal death in a prevailing form of apoptosis which is accompanied by caspases activation and oligonucleosomal DNA fragmentation. Transient exposure to high concentration of glutamate (300 microM) induces the concurrence of necrosis and apoptosis in individual neurons characterized by necrotic cytoplasm-membrane features and apoptotic nuclear morphology which is not accompanied by caspases activation and oligonucleosomal DNA fragmentation.

Animals↗