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Biomedical subjects

J W Wu

Publications and source records attributed to J W Wu.

At least 19 recordsLinked to original sources
PubMed2006

Photoinduced circular anisotropy in a photochromic W-shaped-molecule-doped polymeric liquid crystal film.

Photoinduced circular anisotropy has been demonstrated in thin films of a main-chain polymeric liquid crystal (PLC) system doped with photochromic W-shaped molecules containing two azobenzene groups by irradiating with circularly polarized light (CPL). Reversible photoinduced circular dichroism (CD) was observed with sign relevant to the handedness of the CPL. The experimentally observed CD spectra were analyzed using the DeVoe polarizability model associated with the coupled oscillator method. We also propose a mechanism for the photoinduced circular anisotropy in our system; nucleating the W-shaped molecules with preferential twisted conformation by CPL irradiation, and triggering the local formation of a chiral structure in the W-shaped-molecule-doped main-chain PLC medium.

Journal Article↗
PubMed2006

Picosecond pump-probe measurement of bandgap changes in SiO2/TiO2 one-dimensional photonic bandgap structures.

A picosecond pump-probe nonlinear optical measurement is performed in SiO2/TiO2 one-dimensional photonic bandgap structures fabricated by a solgel method. Both high and low band edges were examined by varying the probe wavelengths and angle tuning was also employed to further clarify the mechanism of a nonlinear optical response. The third-order nonlinear optical response in one-dimensional photonic bandgap structures that comprise TiO2 films is responsible for the nonlinear optical transmissions at both bandgap edges, with an 8% decrease at the low-energy edge and a 4.5% increase at the high-energy edge for a 355 nm pump intensity of 430 MW/cm2.

Journal Article↗
PubMed2005

Analysis of surface second-harmonic generation by orientational distribution function in a chiral polymer film.

By adopting classical models of molecular chirality, contributions of the coupled-oscillator and helix natures to the chiral surface second-order susceptibilities are identified through introduction of a molecular orientational distribution. Experimentally, surface orientational distribution functions at interfaces of an isotropic chiral chitosan polymer film are determined from second harmonic generation measurement. The largest chiral component of surface nonlinear optical susceptibility is from the electric-magnetic coupling with dominant contribution from the helix nature of chitosan.

Journal Article↗
PubMed2005

Electro-tunable optical diode based on photonic bandgap liquid-crystal heterojunctions.

Manipulation of light is in strong demand in information technologies. Among the wide range of linear and nonlinear optical devices that have been used, growing attention has been paid to photonic crystals that possess a periodic modulation of dielectric function. Among many photonic bandgap (PBG) structures, liquid crystals with periodic structures are very attractive as self-assembled photonic crystals, leading to optical devices such as dye lasers. Here we report a new hetero-PBG structure consisting of an anisotropic nematic layer sandwiched between two cholesteric liquid-crystal layers with different helical pitches. We optically visualized the dispersion relation of this structure, displaying the optical diode performance: that is, the non-reciprocal transmission of circular polarized light at the photonic-bandgap regions. Transmittance spectra with circularly polarized light also reveal the diode performance, which is well simulated in calculations that include an electro-tunable diode effect. Lasing action was also confirmed to show the diode effect with a particular directionality.

Journal Article↗
PubMed2005

Determination of optical Kerr nonlinearity of a photonic bandgap structure by Z-scan measurement.

Through analysis of the dispersion relation in a photonic bandgap structure, the effective optical Kerr nonlinearity that determines a Z-scan profile particularly near the stop-band edges, is derived. Near and inside the stop band, the nonlinear optical phase change that originates from an off-resonant response is converted into a change in nonlinear optical intensity through Bragg reflection. The Z-scan measurement of a cholesteric liquid-crystal photonic bandgap structure confirmed that off-resonant Kerr nonlinearity is responsible for the characteristic open-aperture Z-scan profiles near the stop-band edges.

Journal Article↗
PubMed2005

Twist-grain-boundary structure in the B4 phase of a bent-core molecular system identified by second harmonic generation circular dichroism measurement.

Second harmonic generation circular dichroism (SHG CD) measurements are performed on the B4 phase of a bent-core molecular system. Numerical analysis of SHG CD incorporating magnetic-dipole as well as electric-dipole interaction shows that the B4 phase is in a twist-grain-boundary structure with the helical axis along the bent direction of the molecules. The result is extremely important in the sense that achiral molecules are spontaneously optically resolved, i.e., deracemization, the chiral domains of which give rise to huge chiral nonlinear optical effect.

Journal Article↗
PubMed2005

Microstructure of a poled surface-relief grating and its electro-optic response.

The microstructure of a poled surface-relief grating of an azobenzene side-chain polymer film is investigated. From the in situ monitoring of diffraction efficiency and second-harmonic generation, as well as dynamic-contact electrostatic force microscopy images, the point group symmetry of C2nu is identified. The polarization-dependent electro-optic measurement of the reflected diffraction order further confirms the optically biaxial structure of the poled surface-relief grating.

Journal Article↗
PubMed2004

Enhanced optical nonlinearity near the photonic bandgap edges of a cholesteric liquid crystal.

The third-order Kerr nonlinear optical effect of a one-dimensional photonic bandgap structure of a cholesteric liquid crystal is investigated. In a femtosecond nonlinear transmission measurement, nonlinear optical changes in the bandgap edges are observed. From analysis of the dispersion relation, Kerr nonlinear coefficients of nematics, forming the cholesteric liquid crystal, are found to be enhanced by 1-2 orders of magnitude through the photonic bandgap structure.

Journal Article↗
PubMed2004

Optimal degradation rate for collagen chambers used for regeneration of peripheral nerves over long gaps.

The experimental study of peripheral nerve regeneration has depended heavily on the use of a nerve chamber in which the stumps of the transected nerve are inserted. A large variety of chamber fillings and chamber types have been used in an effort to induce a higher quality of regeneration across the gap initially separating the two stumps. In this study we studied the morphology of nerves regenerated across a 15 mm gap following implantation of a series of five chambers. The chambers were fabricated from type I collagen and possessed identical pore volume fractions as well as average pore diameters, but differed in cross-link density continuously along the series. The residual mass of the implanted chambers at 9 weeks was observed to increase continuously with increasing cross-link density along the series, indicating a continuous decrease in degradation rate. The quality of regenerated nerves, determined by the number of large diameter fibers (A-fibers) per nerve, the average diameter of all axons and the ratio of area occupied by axons (N-Ratio), was superior at an intermediate level of chamber degradation rate. The maximal quality of peripheral nerve regeneration corresponded to an optimal degradation rate with an estimated chamber half-life of approximately 2-3 weeks following implantation. A speculative mechanistic explanation of the observed optimum focuses on the hypothetical role of cell and cytokine traffic that may take place through holes in the chamber generated by the degradation process. The data show the presence of a hitherto unreported optimal chamber degradation rate that leads to regenerated nerves of maximum quality.

Absorbable Implants↗
PubMed2001

Formation of a stable heterodimer between Smad2 and Smad4.

Smad proteins mediate transforming growth factor beta signaling from the cell membrane to the nucleus. Upon phosphorylation by the activated receptor kinases, the receptor-regulated Smad, such as Smad2, forms a heterocomplex with the co-mediator Smad, Smad4. This heterocomplex is then translocated into the nucleus, where it associates with other transcription factors and regulates expression of ligand-responsive genes. The stoichiometry between receptor-regulated Smad and co-mediator Smad is important for understanding the molecular mechanisms of the signaling process. Using purified recombinant proteins, we demonstrate that Smad2 and Smad4 form a stable heterodimer and that the Smad4 activation domain is important for the formation of this complex. Many tumor-derived missense mutations disrupt the formation of this heterocomplex in in vitro interaction assays. Mapping these mutations onto the structures of Smad4 and Smad2 identifies a symmetric interface between these two Smad proteins. Importantly, two previous models on the formation of a heterocomplex are incompatible with our observations and other reported evidence.

Chromatography, Gel↗
PubMed2001

Generalized mean-field potential description for ferroelectric ordering in nematic liquid crystals.

Ferroelectric ordering in a nematic liquid crystal system is described using a generalized mean-field potential including effective potentials for both axial and polar interactions. From a self-consistent numerical analysis, a complete phase diagram is obtained as a function of the axial and polar interaction potential strengths. The obtained phase diagram exhibits not only the usual isotropic-nematic phase transition but also nematic-ferroelectric nematic and direct isotropic-ferroelectric nematic phase transitions with a tricritical point among the phases. The phase transition behaviors and the angular orientational distribution function of the molecules were investigated by studying the dependence of the polar and the axial order parameters on the reduced temperature. Moreover, the other polar order parameters responsible for second-harmonic generation (SHG) were also investigated in the generalized mean-field potential description. As a concrete example, we performed a quantitative analysis of the SHG signal reported previously in a lyotropic poly L-glutamate system, detailing the relationship between the angular distribution function and the order parameters based on our potential model. This clarifies the nature of the ferroelectric phase responsible for SHG in nematics.

Journal Article↗
PubMed2001

Structural analysis of a functional DIAP1 fragment bound to grim and hid peptides.

The inhibitor of apoptosis protein DIAP1 suppresses apoptosis in Drosophila, with the second BIR domain (BIR2) playing an important role. Three proteins, Hid, Grim, and Reaper, promote apoptosis, in part by binding to DIAP1 through their conserved N-terminal sequences. The crystal structures of DIAP1-BIR2 by itself and in complex with the N-terminal peptides from Hid and Grim reveal that these peptides bind a surface groove on DIAP1, with the first four amino acids mimicking the binding of the Smac tetrapeptide to XIAP. The next 3 residues also contribute to binding through hydrophobic interactions. Interestingly, peptide binding induces the formation of an additional alpha helix in DIAP1. Our study reveals the structural conservation and diversity necessary for the binding of IAPs by the Drosophila Hid/Grim/Reaper and the mammalian Smac proteins.

Amino Acid Sequence↗
PubMed2001

Crystal structure of a phosphorylated Smad2. Recognition of phosphoserine by the MH2 domain and insights on Smad function in TGF-beta signaling.

Ligand-induced phosphorylation of the receptor-regulated Smads (R-Smads) is essential in the receptor Ser/Thr kinase-mediated TGF-beta signaling. The crystal structure of a phosphorylated Smad2, at 1.8 A resolution, reveals the formation of a homotrimer mediated by the C-terminal phosphoserine (pSer) residues. The pSer binding surface on the MH2 domain, frequently targeted for inactivation in cancers, is highly conserved among the Co- and R-Smads. This finding, together with mutagenesis data, pinpoints a functional interface between Smad2 and Smad4. In addition, the pSer binding surface on the MH2 domain coincides with the surface on R-Smads that is required for docking interactions with the serine-phosphorylated receptor kinases. These observations define a bifunctional role for the MH2 domain as a pSer-X-pSer binding module in receptor Ser/Thr kinase signaling pathways.

Amino Acid Motifs↗
PubMed2001

Kinetic analysis of a simplified scheme of autocatalytic zymogen activation.

Proteolytic enzymes are usually biosynthesized as somewhat larger inactive precursors known as zymogens. These zymogens must undergo an activation process, usually a limited proteolysis, to attain their catalytic activity. When the activating enzyme and the activated enzyme coincide, the process is an autocatalytic zymogen activation. In the present study, a kinetic analysis of the entire progress curve for the autocatalytic zymogen activation reactions is presented. On the basis of the kinetic equations, a novel procedure is developed to evaluate the kinetic parameters of the reactions. This procedure is particularly useful for the fast zymogen autoactivation reactions. As two examples, the novel procedure is used to analyse the autocatalytic activation of bovine trypsinogen and human blood coagulation factor XII (Hageman factor).

Animals↗
PubMed2001

[A study on pathological changes of closed diffuse brain injury in rats with H.E., esterification-silver stain and albumin immunohistochemical stain].

OBJECTIVE: To observed the pathological changes of closed diffuse brain injury in the rats died immediately and 15 min to 5 days after the injury. METHODS: H.E. staind and esterification-silver stain were applied to investigate the closed diffuse brain injury. RESULTS: In rats died immediately after the concussive injury, a number of shrunken neurons(type I change), distended neurons(type II change) and wave-like nerve fibers were identified in the brain tissue, especially in brain-stem. At 2 h and 8 h after injury, brain edema and axonal swelling appeared clearly in the cortex and white matter, especially in brain-stem. At post-traumatic 8 h and 24 h, the axonal retraction balls began to appear. The amount of neurons undergoing type I and II changes and constraction balls increased along with the survivor time. After 4 days and 5 days, brain edema alleviated, but the retraction balls and axonal swelling still existed. With Esterifica-tion silver stain, the above changes of neurons and nerve fibers were more obvious. With ABC stain, the distribution of albumin(Al) was extended from the perio-vascular area to diffuse distribution. Al positive staining were more obvious in injuried neurons and nerve fibers. CONCLUSION: The distribution of the concussive damage in the brain are coup, contra-coup and centripental.

Albumins↗
PubMed2000

Structural and biochemical basis of apoptotic activation by Smac/DIABLO.

Apoptosis (programmed cell death), an essential process in the development and homeostasis of metazoans, is carried out by caspases. The mitochondrial protein Smac/DIABLO performs a critical function in apoptosis by eliminating the inhibitory effect of IAPs (inhibitor of apoptosis proteins) on caspases. Here we show that Smac/DIABLO promotes not only the proteolytic activation of procaspase-3 but also the enzymatic activity of mature caspase-3, both of which depend upon its ability to interact physically with IAPs. The crystal structure of Smac/DIABLO at 2.2 A resolution reveals that it homodimerizes through an extensive hydrophobic interface. Missense mutations inactivating this dimeric interface significantly compromise the function of Smac/DIABLO. As in the Drosophila proteins Reaper, Grim and Hid, the amino-terminal amino acids of Smac/DIABLO are indispensable for its function, and a seven-residue peptide derived from the amino terminus promotes procaspase-3 activation in vitro. These results establish an evolutionarily conserved structural and biochemical basis for the activation of apoptosis by Smac/DIABLO.

Amino Acid Sequence↗