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Biomedical subjects

JS Kim

Publications and source records attributed to JS Kim.

At least 19 recordsLinked to original sources
PubMed2000

Relationships between activities of xylanases and xylan structures.

Structures of five water-soluble xylans have been determined. Four purified xylanase enzymes have been studied for the hydrolysis of the xylans. Different xylanases have different activities against various xylan structures. The key factors that influence the rate of xylan hydrolysis are chain length and degree of substitution. Two family 11 xylanases, Orpinomyces pc2 xylanase and Trichoderma longibrachiatum xylanase, can rapidly hydrolyze xylans that have a chain length greater than 8 xylose residues, and their hydrolytic rates are not sensitive to substituents on the xylan backbone. A family 11 xylanase from Aureobasidium pullulans is most effective on xylans that have a long chain (greater than 19 xylose residues), and also is effective against substituent groups. Although Thermatoga maritima xylanase is also more active on a long xylan chain (greater than 19 xylose residues), its hydrolytic rate is greatly reduced by substituents on xylan backbones.

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PubMed2000

Antioxidant responses of cucumber (Cucumis sativus) to photoinhibition and oxidative stress induced by norflurazon under high and low PPFDs.

Photooxidative damage is exacerbated by norflurazon (NF), which blocks carotenoid biosynthesis. This study examined the influence of photosynthetic photon flux density (PPFD) on the overall responses of both non-enzymatic and enzymatic antioxidants to NF-caused oxidative damage in leaves of cucumber (Cucumis sativus). Seven-day-old cucumber plants were exposed to NF under either low PPFD (30 µmol m(-2) s(-1)) or high PPFD (300 µmol m(-2) s(-1)) for 3 days. The NF plants exposed at high PPFD had lower levels of F(v)/F(m) ratio, quantum yield of electron transport, and 33-kDa protein of photosystem II as compared with the NF plants at low PPFD. In the NF plants, there was a reduction in total chlorophylls and carotenoids except newly formed zeaxanthin in either PPFD. The NF plants at high PPFD resulted in less level of photochemical quenching, q(P), and Stern-Volmer quenching, NPQ, than those of the plants at low PPFD, whereas both plants had similar level of non-photochemical quenching coefficient, q(N). However, the level of PPFD did not significantly affect the NF-caused induction of antioxidant enzymes including peroxidase, superoxide dismutase, glutathione reductase, and ascorbate peroxidase.

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PubMed2000

Synthesis and metal ion complexation studies of proton-ionizable calix

A series of novel N-chromogenic calix[4]arene azacrown ethers were synthesized as selective extractants of potassium ion. 1,3-Alternate calix[4]arene azacrown ethers were prepared by reacting 25,27-dipropyloxy-26,28-bis(5-chloro-3-oxapentyloxy) calix[4]arenes with p-toluenesulfonamide in the presence of potassium carbonate. The coupling reaction of calix[4]arene azacrown ether with 2-hydroxy-5-nitrobenzyl bromide in the presence of triethylamine in THF gave the chromogenic calix[4]arene azacrown ether in moderate yield. These compounds show high potassium selectivity over other metal ions as shown by two-phase extraction, bulk liquid membrane, and 1H NMR studies on a ligand-metal complex. It is assumed that the OH of the chromogenic group attached on nitrogen can assist the complexation by encapsulation of the metal.

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PubMed2000

Molecular-scale interface engineering for polymer light-emitting diodes

Achieving balanced electron-hole injection and perfect recombination of the charge carriers is central to the design of efficient polymer light-emitting diodes (LEDs). A number of approaches have focused on modification of the injection contacts, for example by incorporating an additional conducting-polymer layer at the indium-tin oxide (ITO) anode. Recently, the layer-by-layer polyelectrolyte deposition route has been developed for the fabrication of ultrathin polymer layers. Using this route, we previously incorporated ultrathin (<100 A) charge-injection interfacial layers in polymer LEDs. Here we show how molecular-scale engineering of these interlayers to form stepped and graded electronic profiles can lead to remarkably efficient single-layer polymer LEDs. These devices exhibit nearly balanced injection, near-perfect recombination, and greatly reduced pre-turn-on leakage currents. A green-emitting LED comprising a poly(p-phenylene vinylene) derivative sandwiched between a calcium cathode and the modified ITO anode yields an external forward efficiency of 6.0 per cent (estimated internal efficiency, 15-20 per cent) at a luminance of 1,600 candelas per m2 at 5 V.

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PubMed2000

Prediction of sound transmission loss through multilayered panels by using Gaussian distribution of directional incident energy

In this study, a new prediction method is suggested for sound transmission loss (STL) of multilayered panels of infinite extent. Conventional methods such as random or field incidence approach often given significant discrepancies in predicting STL of multilayered panels when compared with the experiments. In this paper, appropriate directional distributions of incident energy to predict the STL of multilayered panels are proposed. In order to find a weighting function to represent the directional distribution of incident energy on the wall in a reverberation chamber, numerical simulations by using a ray-tracing technique are carried out. Simulation results reveal that the directional distribution can be approximately expressed by the Gaussian distribution function in terms of the angle of incidence. The Gaussian function is applied to predict the STL of various multilayered panel configurations as well as single panels. The compared results between the measurement and the prediction show good agreements, which validate the proposed Gaussian function approach.

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PubMed1999

Isolation of a new cerebroside from the root bark of aralia elata

A new cerebroside, named Aralia cerebroside (1), was isolated from the root bark of Aralia elata. The structure of 1 was determined to be 1-O-beta-D-glucopyranosyl-(2S,3S,4R, 8E)-2-[(2'R)-2'-hydroxypalmitoylamino]-8-octadecene-1,3,4-triol on the basis of physicochemical and spectroscopic studies.

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