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Biomedical subjects

X Z Yan

Publications and source records attributed to X Z Yan.

9 recordsLinked to original sources
PubMed2006

High dielectric hyperbranched polyaniline materials.

New organic materials for the purpose of high speed capacitor applications are discussed. The effect of the microcrystalline size dependence of different polyaniline polymeric systems on the dielectric constant is investigated. Two different methods are described for the preparation of the polyaniline dielectric materials. By sonication polymerization, the prepared polyaniline with a suggested hyperbranched structure showed much larger microcrystalline domains in comparison to the conventional linear polyaniline. Investigations of the dielectric constant and capacitance at a relatively high frequency (>100 kHz) suggested that the system with the larger microcrystalline domains (hyperbranched) gives rise to a larger dielectric constant. The mechanism of the increased dielectric response at higher frequencies is investigated by EPR spectroscopy, and these results suggest that delocalized polarons may provide a way to enhance the dielectric response at high frequency.

Journal Article↗
PubMed2005

Polaron delocalization in ladder macromolecular systems.

Organic macromolecules with conjugated building blocks have been the focus of extensive research that is motivated, in part, by the potential to create optical and electronic devices. We have shown that palladium-catalyzed amination can assemble triarylamine ladder materials with extended structures. Two ladder macromolecules have been prepared in high yields by a series of twelve or sixteen C-N coupling reactions. Studies of the electronic and optical properties of neutral and oxidized forms of the ladder structures were conducted. The optical and electronic properties of the ladder systems are compared to those of the linear tetra-phenyl-p-phenylenediamine as well as the tetra-p-anisyl-p-tetraazacyclophane. The electrochemistry of the ladder systems consists of a multiwave voltammogram with a relatively low first oxidation potential. Electron paramagnetic resonance spectroscopy of the ladder systems suggests the presence of a large density of delocalized polarons. Linear absorption measurements of the chemically oxidized ladders revealed both polaron and intervalence absorption bands. Steady-state and time-resolved fluorescence measurements were also carried out to characterize the dynamics in these novel systems.

Amines↗
PubMed1999

Beta-amyloid peptide fragment 31-35 induces apoptosis in cultured cortical neurons.

A synthetic fragment 31-35 of beta-amyloid peptide was used in cultured cortical neurons to examine whether this smaller sequence could trigger apoptotic degeneration in vitro by using morphological, biochemical and flow-cytometric examinations. The results showed that: (i) neurons treated with fragment 31-35 of beta-amyloid peptide exhibited membrane blebbing, compaction of nuclear chromatin, nuclear shrinkage and nuclear fragmentation; (ii) a typical DNA ladder was revealed by agarose gel electrophoresis following fragment 31-35 of beta-amyloid peptide exposure; (iii) the internucleosome DNA fragmentation was also detected by flow-cytometric examination following fragment 31-35 of beta-amyloid peptide exposure; and (iv) the DNA fragmentation induced by fragment 31-35 of beta-amyloid peptide in the above two examinations could be blocked by co-treatment with aurintricarboxylic acid or actinomycin D. It is suggested that fragment 31-35 of the beta-amyloid peptide may be a shorter sequence of beta-amyloid peptide responsible for triggering an apoptotic process in cultured neurons.

Amyloid beta-Peptides↗
PubMed1989

[Experimental study of qi deficiency syndrome and Codonopsis pillosulae and Astragalus injection on the immune response in mice].

According to TCM theory "hunger impairs one's Qi", the authors had made mouse model of Qi deficiency syndrome (QDS) through controlling amount of food fed. Compared with mice of normal group, the body weight, thymus index and spleen index obviously decreased in mice of QDS group. The similar effects on humoral immunity and cell-mediated immunity were also obtained. It was found that the Codonopsis pilosulae and Astragalus Injection (CPAI) possessed the promoting action of thymus index, spleen index, humoral immunity and cell mediated immunity on QDS mice and normal mice except spleen index. However, QDS mice were more sensitive to CPAI than the normal mice. 4 x 10(9) SRBC/mouse was administered to normal donor mice by i.p., the super-optimal immunization could obviously induce generation of Ts cells. The CPAI could also reduce generation of Ts cells. This paper had proved that the inherent relation between Qi and immune response of organism, and that the CPAI could promote immune response by means of reducing Ts cells.

Adjuvants, Immunologic↗