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Chun-Hsien Chen

Publications and source records attributed to Chun-Hsien Chen.

8 recordsLinked to original sources
PubMed2006

Promotion of the electrochemical activity of a bimetallic platinum-ruthenium catalyst by oxidation-induced segregation.

An alloy catalyst of 15 wt % Pt(50)Ru(50)/C was prepared by the method of incipient wetness impregnation and activated by hydrogen reduction at 620 K. Physical characterization of the freshly reduced catalyst indicated that bimetallic crystallites, Pt rich in the shell and Ru rich in the core, were finely dispersed in a diameter of dPtRu approximately 2 nm on carbon support. The reduced catalyst was subsequently modified by oxidization in air. On increasing the temperature of oxidation (T(o)), atoms of Ru in the core were found segregated to the surface of bimetallic crystallites and oxidized to amorphous RuO(2). Crystalline RuO(2) (RucO(2)) was formed on extensive segregation at To > 520 K. Catalytic activity of the alloy catalyst for electro-oxidation of methanol was examined by cyclic voltammetry. Electrochemical activity of the Pt-Ru/C catalyst was found to be significantly enhanced by oxidation treatments. The enhancement was, therefore, attributed to the segregation of Ru and the formation of RucO(2). Extensive oxidation treatment at elevated temperatures of To > 600 K, however, caused the deactivation of the electroactivity. The deactivation should be the result of excessive oxidation of the carbon support.

Journal Article↗
PubMed2005

On the rigidity of polynorbornenes with dipolar pendant groups.

A range of polynorbornenes (PNBs) with fused dipolar pendant groups at C-5,6 positions was synthesized by ring-opening metathesis polymerization catalyzed by a ruthenium carbene complex (Grubbs I). Photophysical studies, EFISH measurements, and atomic force microscopy images have been used to investigate the structures and morphology of these polymers. These results suggest that the polymers may adopt rigid rod-like structures. The presence of the double bonds in PNBs appeared to be indispensable for the rigidity of the polymers. Interaction between unsaturated pendant groups may result in coherent alignment leading to a rod-like structure.

Journal Article↗
PubMed2005

Monolayers of diphenyldiacetylene derivatives: Tuning molecular tilt angles and photopolymerization efficiency via electrodeposited Ag interlayer on Au.

An electrodeposited Ag adlayer (upd, underpotential deposition) is utilized to improve monolayer photopolymerization of diphenyldiacetylene derivatives (DPDAs) that would otherwise exhibit no polymerization in solid state. Topochemical reaction of diacetylene derivatives via solid-state 1,4-addition yields polydiacetylenes which are of great importance due to properties associated with their ene-yne conjugated backbones. The polymerization efficiency heavily depends on the molecular arrangement in the crystals. For example, crystals of most DPDA derivatives show no activity for topochemical reaction because the bulky phenyl end groups space out the triple bonds and thus DPDAs require relatively large translation and rotation angles for polymerization. In principle, topochemical reaction is viable if molecules are in optimal arrangement. The upd interlayer can be applied to tune the adsorbate-substrate interactions, intermolecular spacing, and the molecular tilt angle by controlling the coverage of the Ag adlayer. It is thus possible to manipulate the molecular arrangement of DPDAs for the subsequent polymerization. Successful photopolymerization of DPDA monolayers is realized from the decrease in nu(C[triple bond]C) intensity by infrared reflectance absorbance spectroscopy, growth of ene-yne pi-pi* transition by UV-vis measurements, and enhanced electrochemical stability by the cathodic desorption protocol. The optimal efficiency of polymerization takes place on upd-modified substrates that can generate approximately 45 degrees tilt angle for DPDA derivatives.

Journal Article↗
PubMed2005

Areca (betel) nut extract activates mitogen-activated protein kinases and NF-kappaB in oral keratinocytes.

Areca (betel) was recently proved a carcinogenic substance by the International Agency for Research on Cancer. However, the signaling impact of areca in oral keratinocyte is still obscure. Mitogen-activated protein kinase superfamilies, including extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinases (JNK) and p38, together with transcription factor NF-kappaB, are important signaling elements. We examined the activation of these signaling pathways in OECM-1 and SAS oral keratinocytes, treated with ripe areca nut extract (ANE). In both cells, a rapid increase in JNK1 activity at 0.5 hr was noted following treatment of ANE. ERK was profoundly activated during 0.5-2 hr in OECM-1 cells. Contrasting p38 activity was noted in these 2 cells. In both cells, ANE also activated NF-kappaB pathway in a biphasic manner, particularly for SAS cells. NF-kappaB was activated by approximately 2- to 4-fold at 0.5-1 hr and a plateau or slight decrease of activity existed between 1 and 6 hr. Later, another higher episode of NF-kappaB activity was raised. This was accompanied with the rapid degradation in cytosolic IkappaBalpha as well as an increase of nuclear NF-kappaB in both cells. ANE treatment did not activate epidermal growth factor receptor signaling system, but blockage of NF-kappaB activation rendered the suppression of ANE-modulated COX-2 upregulation in OECM-1. This study identified that ANE affected interactive signaling systems in oral keratonocytes that could be the pathogenetic basis for areca.

Areca↗
PubMed2005

Monolayer structures of highly photoluminescent furan oligoaryls: an approach to improve packing crystallinity of dithiolated aromatics.

We demonstrated that mono- and dithiolated furan-containing oligoaryls (II-IV, see Chart 2) can be successfully synthesized via a one-pot strategy starting from propargylic dithioacetals. IRAS (infrared reflection-absorption spectroscopy) and STM (scanning tunneling microscopy) experiments revealed that single-component monolayers of II, III, and IV are essentially disordered, an important property that prevents excited photoluminescent molecules from self-quenching in the organic layers of an OLED device. Surprisingly, localized lattice packing of crystalline dithiolated furan oligoaryls on Au(111) can be assembled by immersing preadsorbed n-dodecanethiol SAMs in the corresponding deposition solutions. The discrepancy in the formation of disordered or localized crystalline structures is discussed. For single-component monolayers, the facile formation of S-Au bonds generates chaotically distributed monolayers in which the arched molecules hinge each other and block the desorptive pathways. The absence of crystalline packing is mainly attributed to the difficulty for the dithiols to simultaneously break two S-Au bonds, to desorb, and then to readsorb, the key step to improve the intermolecular attractions for crystalline SAMs. By preassembling n-dodecanethiol SAMs, the space for dithiolated compounds III and IV to adsorb is limited to domain boundaries or packing defects where crystalline packing of III and IV can grow.

Journal Article↗
PubMed2003

Interfaces to connect thin-layer chromatography with electrospray ionization mass spectrometry.

This study has developed two interfaces to connect small-size thin-layer chromatography (TLC) with electrospray ionization mass spectrometry (ES-MS) for the continuous analysis of organic mixtures. The interfaces are (1) two bound optical fibers inserted into the C18-bonded particles at the exit of a small TLC channel and (2) a small commercial TLC strip with a sharpened tip. A reservoir continuously supplied a makeup solution to the tip of the TLC channel. The high voltage required for electrospray ionization was introduced into the makeup solution or mobile phase through a Pt wire, and electrospray was generated at the tip of the bonded optical fibers and at the sharp end of the TLC strip. Since small-size TLC channels were used, the elution time was short and less than 0.2 microL of the sample solution and 200 microL of the eluting solvent were required. Organic mixtures were separated successfully and detected on-line using the TLC/ES-MS techniques.

Chromatography, Thin Layer↗