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Yongfang Li

Publications and source records attributed to Yongfang Li.

17 recordsLinked to original sources
PubMed2006

Effect of branched conjugation structure on the optical, electrochemical, hole mobility, and photovoltaic properties of polythiophenes.

Four branched polythiophenes (PTs) with different ratios of conjugated terthiophene-vinylene side chains, PT-TThV10 to PT-TThV40, were synthesized by Stille coupling reaction. The polymers exhibited reversible p-doping/dedoping (oxidation/re-reduction) and n-doping/dedoping (reduction/reoxidation) processes. The absorption spectra, hole mobility, and photovoltaic properties of the polymers were much improved in comparison with the PT derivative without the terthiophene-vinylene side chain and were influenced by the content of the conjugated side chains. With the increase of the content of the conjugated side chains, the absorption peak of the branched PTs enhanced and blue-shifted. The maximum hole mobility reached 6.35 x 10(-4) cm2/V.s (SCLC method) and the maximum power conversion efficiency of the polymer solar cell reached 1.91% under the illumination of AM 1.5, 100 mW/cm2, for the polymer with 20% terthiophene-vinylene side chains. The results indicate that the branched PTs with suitable content of the terthiophene-vinylene side chains could be promising photovoltaic materials.

Journal Article↗
PubMed2006

The cardioprotective effect of isosteviol on rats with heart ischemia-reperfusion injury.

This study was designed to assess the cardioprotective effect of isosteviol on rats with heart ischemia-reperfusion (IR) injury and to explore the mechanism of action of the compound. Sprague Dawley rats were divided into 8 groups (n=10-12): a sham-operated control and 7 ischemia-reperfusion groups (IR control, 3 isosteviol pre-treated (0.5, 1.0 and 2.0 mg kg(-1)), ligustrazine pre-treated, 5-hydroxydecanoate (5-HD) pre-treated and 5-HD+ isosteviol pre-treated groups). IR was produced by occluding the left coronary artery for 30 min followed by re-opening the artery for 90 min. The compounds under investigation were administered intravenously 10 min prior to occluding the artery. Hemodynamic parameters (+/-dp/dt(max), LVSP, LVDevP, MAP), heart rate, ventricular tachycardia (VT) and ventricular fibrillation (VF) were determined during the IR period. The myocardial infarct size, activities of serum lactate dehydrogenase and creatine kinase were determined at the end of the experiment. In the isosteviol pre-treated groups, the hemodynamic parameters were improved and the myocardial infarct size, the activities of serum enzymes, and the incidences of VT and VF were all decreased when compared to the control group. These effects of isosteviol were similar to that of a traditional cardioprotective agent, ligustrazine. The 5-HD+ isosteviol group displayed parameters that were between those in the equivalent isosteviol pre-treated group and the IR control group. In conclusion, damage due to a standard rat heart IR injury was reduced by pretreatment with intravenous isosteviol, and this effect was partly attenuated by a mitochondrial ATP-sensitive potassium channel blocker, 5-HD.

Animals↗
PubMed2006

Progressive segregation of the Escherichia coli chromosome.

We have followed the fate of 14 different loci around the Escherichia coli chromosome in living cells at slow growth rate using a highly efficient labelling system and automated measurements. Loci are segregated as they are replicated, but with a marked delay. Most markers segregate in a smooth temporal progression from origin to terminus. Thus, the overall pattern is one of continuous segregation during replication and is not consistent with recently published models invoking extensive sister chromosome cohesion followed by simultaneous segregation of the bulk of the chromosome. The terminus, and a region immediately clockwise from the origin, are exceptions to the overall pattern and are subjected to a more extensive delay prior to segregation. The origin region and nearby loci are replicated and segregated from the cell centre, later markers from the various positions where they lie in the nucleoid, and the terminus region from the cell centre. Segregation appears to leave one copy of each locus in place, and rapidly transport the other to the other side of the cell centre.

Cell Cycle↗
PubMed2006

Synthesis and photovoltaic properties of two-dimensional conjugated polythiophenes with bi(thienylenevinylene) side chains.

Three two-dimensional (2-D) conjugated polythiophenes with bi(thienylenevinylene) side chains (biTV-PTs), P1, P2, and P3, were designed and synthesized for application in polymer solar cells. The absorption spectral, electrochemical, and photovoltaic properties of the biTV-PTs were investigated and compared with those of poly(3-hexylthiophene) (P3HT). The biTV-PTs show a broad absorption band from 350 to 650 nm; especially, the absorption spectrum of P3 displays a broad plateau and much stronger absorbance than that of P3HT in the wavelength range from 350 to 480 nm. Cyclic voltammograms reveal that the onset oxidation and reduction potentials of the biTV-PTs positively shifted by ca. 0.2 V in comparison with those of P3HT, indicating that the HOMO energy level of the biTV-PTs is ca. 0.2 eV lower than that of P3HT. Polymer solar cells (PSCs) were fabricated based on the blend of the polymers and 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-C-61 (PCBM) with a weight ratio of 1:1. The open circuit voltage of the PSCs based on the biTV-PTs is ca. 0.1 V higher than that of P3HT, which is benefited from the lower HOMO levels of the biTV-PTs. The maximum power conversion efficiency (PCE) of the PSCs based on P3 reached 3.18% under AM 1.5, 100 mW/cm2, which is 38% increased in comparison with that (2.41%) of the devices based on P3HT under the same experimental conditions. The results indicate that the 2-D conjugated biTV-PTs are promising polymer photovoltaic materials.

Journal Article↗
PubMed2006

Electron transport through a self-assembled monolayer of thiol-end-functionalized tetraphenylporphines and metal tetraphenylporphines.

The monolayers of several thiol-end-functionalized tetraphenylphophines (SH-TPP) and metal tetraphenylporphines (SH-MTPP) were self-assembled on gold surfaces and identified by cyclic voltammetry (CV), electrochemical impedance spectroscopy, scanning electrochemical microscopy, and the contact angle. The CV peaks of the [Fe(CN)6]3-/ [Fe(CN)6]4- couple were used to identify the efficiency of electrons transferring through the self-assembled monolayer (SAM). The results suggested that SH-TPP and SH-MTPP could form high-quality SAMs on gold surfaces. The SAMs blocked electron transport from the gold electrode to solution. When the length of the thiol-end-link spacer (alkyl group) increased, the electron transport ability of the SAM decreased because of the increased insulator properties of the alkyl chain. With the insertion of metallic ions, the electron transport ability of the SAM of SH-MTPP increased compared to that of the SAM of SH-TPP, which was probably due to the fact that (i) the insertion of metallic ions changed the molecular structure and the molecular structure of SH-MTPP played an important role in electron transport through the SAM and (ii) the insertion of metallic ions increased the electron tunneling probability through the monolayer.

Journal Article↗
PubMed2005

Actuator based on MWNT/PVA hydrogels.

The first actuator based on multiwalled carbon nanotube (MWNT) hydrogels was developed through simple hydrogelation with poly(vinyl alcohol) (PVA). This actuator exhibited excellent actuating properties compared with the corresponding actuator based on poly(acrylic acid)/PVA hydrogels.

Letter↗
PubMed2005

Novel electroactive and photoactive molecular materials based on conjugated donor-acceptor structures for optoelectronic device applications.

Four donor-acceptor functionalized molecular materials with symmetrical structures have been synthesized and investigated for their use in optoelectronic applications. These pi-conjugated molecules consist of one electron-donating moiety, for instance, carbazole, triphenylamine, or phenothiazine at the center, and two acceptors at each side. Introduction of different donor moieties decreases the band gaps allowing a fine-tuning of the optical and electrical properties. These materials exhibit multifunctional properties, such as a red light-emitting behavior and a large photovoltaic effect. Red organic light-emitting diodes were fabricated in a facile nondoping configuration based on these materials. Saturated red-emission is observed with a CIE of x = 0.64 and y = 0.33, and an external quantum efficiency of 0.19%. In addition, our first observation of photovoltaic response in the pi-conjugated molecule with donor-acceptor-donor structure is reported. The organic single-component photovoltaic cells were fabricated and characterized. Their open-circuit voltage and short-circuit current density are 1.1 V and 0.07 mA cm(-2), respectively. The photovoltaic effect corresponds to the absorption characteristics of the compound and depends on the nature of the electron-donating group.

Journal Article↗
PubMed2004

Liposome induced self-assembly of gold nanoparticles into hollow spheres.

Gold nanoparticles were prepared by the reduction of [(C7H15)4N]+ [AuCl4]- with 3,4-ethylenedioxythiophene (EDOT) as reductant in toluene solution. The employed stabilizers include 3,3'-thiodipropionic acid (TDPA), 1-dodecanethiol (DDT), (+/-)-10-camphorsulfonic acid (CSA), and 11-mercaptoundecanoic acid (MUA). The reaction processes were tracked by UV-vis and FT-IR spectroscopy, and the as-prepared gold nanoparticles were characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy, and X-ray photoelectron spectroscopy measurements. When TDPA and MUA, which possess both -S- and -COOH groups, were used as the stabilizer in the preparation, the as-prepared nanoparticles could self-assemble into hollow spheres. While when DDT with a -SH group or CSA with a -SO3H group was used as the protecting agents, only discrete gold nanoparticles were observed. The results show that the groups of both -S- and -COOH in the stabilizer play an important role in forming the hollow nanospheres. It is proposed that the formation mechanism of the hollow spheres is a liposome that formed between -COO- and [(C7H15)4 N]+ could act as a template to induce the self-assembly of the gold nanoparticles into the hollow spheres.

Gold↗
PubMed2004

The role of Par proteins in the active segregation of the P1 plasmid.

The parS centromere-like site promotes active P1 plasmid segregation in the presence of P1 ParA and ParB proteins. At the modest growth rate used here, time-lapse and still photomicroscopy shows that the plasmid copies are clustered as a focus at the Escherichia coli cell centre. Just before cell division, the focus is actively divided and ejects bidirectionally into opposite halves of the dividing cell. In the absence of the wild-type parS binding protein ParB, a focus was formed, but generally did not go to the cell centre. The randomly placed focus did not divide and was inherited by one daughter cell only. In the absence of ParA, foci formed and frequently fixed to the cell centre. However, they failed to divide or eject and were left at the new cell pole of one cell at division. Thus, ParB appears to be required for recognition of the plasmid and its attachment to the cell centre, and ParA is required for focus division and energetic ejection from the cell centre. The ATPase active site mutation, parAK122E, blocked ejection. Mutant parAM314I ejected weakly, and the daughter foci took two generations to reach a new cell centre. This explains the novel alternation of segregation and missegregation in successive generations seen in time-lapse images of this mutant.

Bacterial Proteins↗
PubMed2003

Preparation of silver nanocrystals in the presence of aniline.

The preparation and characterization of silver nanocrystals by chemical reduction of silver ions in the presence of aniline using hydrazine monohydrate (N(2)H(4).H(2)O) or sodium citrate as the reducing agent are described. A high yield of aniline-derivatized hexagonal silver nanoparticles is obtained by the reduction of Ag(2)SO(4) with N(2)H(4).H(2)O. An alternative strategy is the reduction of Ag(+) by citrate in the presence of aniline, by which the size and morphology of the Ag nanocrystals can be controlled to a certain degree by changing the concentration ratio of aniline to Ag(+). It is believed that the amount of aniline added in the starting solutions for the preparation influences the morphology of the Ag nanoparticles. In addition, the long Ag nanorods with a high mean aspect ratio are prepared in the presence of aniline at a low concentration or o-anisidine.

Journal Article↗
PubMed2003

Segregation of the Escherichia coli chromosome terminus.

We studied the segregation of the replication terminus of the Escherichia coli chromosome by time-lapse and still photomicroscopy. The replicated termini lie together at the cell centre. They rapidly segregate away from each other immediately before cell division. At fast growth rate, the copies move progressively and quickly toward the centres of the new-born cells. At slow growth rate, the termini usually remain near the inner cell pole and migrate to the cell centre in the middle of the cell cycle. A terminus domain of about 160kb, roughly centred on the dif recombination site, segregated as a unit at cell division. Sequences outside this domain segregated before division, giving two separate foci in predivision cells. Resolution of chromosome dimers via the terminus dif site requires the XerC recombinase and an activity of the FtsK protein that is thought to align the dif sequences at the cell centre. We found that anchoring of the termini at the cell centre and proper segregation at cell division occurred normally in the absence of recombination via the XerC recombinase. Anchoring and proper segregation were, however, frequently disrupted when the C-terminal domain of FtsK was truncated.

Base Sequence↗
PubMed2003

Synthesis, characterization, and antibacterial activities of some rare Earth metal complexes of pipemidic acid.

Eight new solid complexes of pipemidic acid (PPA) with trichlorizated rare earth metals LaCl(3), CeCl(3), PrCl(3), NdCl(3), SmCl(3), TbCl(3), DyCl(3), and YCl(3) have been synthesized. The complexes were characterized by elemental analyses, IR, NMR, and molar conductance measurements. The general formulas of the complexes are [M(PPA)(4)]Cl(3) (M=Ce(III), Pr(III), Nd(III), Sm(III), Tb(III), Dy(III), Y(III)), and [La(PPA)(4)Cl]Cl(2). At the same time, the antibacterial activities of PPA and four of its complexes were tested. The results show that PPA and its complexes all have inhibitory action against bacteria of Escherichia coli, Bacillus subtilis, Streptococcus pneumoniae, and Pseudomonas aeruginosa but not Staphylococcus aureus. We compared their antibacterial activities and found that the antibacterial activity of [La(PPA)(4)Cl]Cl(2) against S. pneumoniae is much stronger than that of PPA and the other complexes.

Anti-Infective Agents↗
PubMed2002

The P1 plasmid in action: time-lapse photomicroscopy reveals some unexpected aspects of plasmid partition.

The prophage of bacteriophage P1 is a low copy number plasmid in Escherichia coli and is segregated to daughter cells by an active partition system. The dynamics of the partition process have now been successfully followed by time-lapse photomicroscopy. The process appears to be fundamentally different from that previously inferred from statistical analysis of fixed cells. A focus containing several plasmid copies is captured at the cell center. Immediately before cell division, the copies eject bi-directionally along the long axis of the cell. Cell division traps one or more plasmid copies in each daughter cell. These copies are free to move, associate, and disassociate. Later, they are captured to the new cell center to re-start the cycle. Studies with mutants suggest that the ability to segregate accurately at a very late stage in the cell cycle is dependent on a novel ability of the plasmid to control cell division. Should segregation be delayed, cell division is also delayed until segregation is successfully completed.

Bacteriophage P1↗
PubMed2002

The P1 plasmid is segregated to daughter cells by a 'capture and ejection' mechanism coordinated with Escherichia coli cell division.

The fate of the P1 plasmid of Escherichia coli was followed by time-lapse photomicroscopy. A GFP-ParB fusion marked the plasmid during partition (segregation) to daughter cells at slow growth rate. The process differs from that previously inferred from statistical analysis of fixed cells. A focus of plasmid copies is captured at the cell centre. Immediately before cell division, the copies eject bidirectionally along the long axis of the cell. Cell division traps one or more plasmid copies in each daughter. They are not directed to a prescribed position but are free to move, associate and disassociate. Later, they are captured to the new cell centre to restart the cycle. A null P1 par mutant associates to form a focus, but it is neither captured nor ejected. A dominant negative ParB protein forms a plasmid focus that attaches to the cell centre but never ejects. It remains captive at the centre and blocks host cell division. The cells elongate. Eventually the intact focus is pushed to one side and the cells divide simultaneously in several places at the same time. This suggests that the wild-type plasmid imposes a regulatory node on the host cell cycle, preventing cell division until its own segregation is completed.

Bacterial Proteins↗
PubMed2002

The segregation of the Escherichia coli origin and terminus of replication.

Escherichia coli chromosome replication forks are tethered to the cell centre. Two opposing models describe how the chromosomes segregate. In the extrusion-capture model, newly replicated DNA is fed bi-directionally from the forks toward the cell poles, forming new chromosomes in each cell half. Starting with the origins, chromosomal regions segregate away from their sisters progressively as they are replicated. The termini segregate last. In the sister chromosome cohesion model, replication produces sister chromosomes that are paired along much of their length. The origins and most other chromosomal regions remain paired until late in the replication cycle, and all segregate together. We use a combination of microscopy and flow cytometry to determine the relationship of origin and terminus segregation to the cell cycle. Origin segregation frequently follows closely after initiation, in strong support of the extrusion-capture model. The spatial disposition of the origin and terminus sequences also fits this model. Terminus segregation occurs extremely late in the cell cycle as the daughter cells separate. As the septum begins to invaginate, the termini of the completed sister chromosomes are transiently held apart at the cell centre, on opposite sides of the cell. This may facilitate the resolution of topological linkages between the chromosomes.

Base Sequence↗
PubMed2002

Transcriptional interference by a complex formed at the centromere-like partition site of plasmid P1.

The partition site, parS, promotes accurate segregation of the replicated P1 plasmid to daughter cells when the P1-encoded ParA and ParB proteins are supplied. The parS site was inserted into the Escherichia coli chromosome between the promoter and the structural gene for beta-galactosidase, lacZ. There was little interference with lacZ expression when ParA and ParB were supplied in trans. However, when a mutant ParA protein, ParAM314I, was supplied along with ParB, expression of lacZ was shut down. ParAM314I, ParB, and parS appear to form a nucleoprotein complex that blocks transcription. Mutations in parA and parB that relieved the parAM314I-dependent block were found. In addition, new mutations which impose the block were selected. Five of the latter mapped to parA and one to parB; all had a propagation-defective phenotype (Par(PD)) similar to that of parAM314I. Thus, whereas a null par mutant P1 plasmid segregates its DNA randomly, these mutants prevent even random distribution of the plasmid. We propose that ParA protein normally interacts transiently with the ParB-parS complex for partition to proceed but that the mutations block ParA dissociation. This "permanent" ParA-ParB-parS complex acts as a transcription block. Consistent with this hypothesis, we found that three of the seven blocking mutations lie within regions of ParA and ParB that are known to interact with each other. When the transcription block is imposed, regional silencing of nearby genes occurs. However, the requirement for ParA and a mutant parA or parB allele distinguishes the transcription block from the regional ParB-dependent gene silencing previously described.

Bacterial Proteins↗