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HJ Lee

Publications and source records attributed to HJ Lee.

At least 19 recordsLinked to original sources
PubMed2000

Remarkable Anionic Axial Ligand Effects of Iron(III) Porphyrin Complexes on the Catalytic Oxygenations of Hydrocarbons by H(2)O(2) and the Formation of Oxoiron(IV) Porphyrin Intermediates by m-Chloroperoxybenzoic Acid This work was supported by Center for Cell Signaling Research (1999-2-122-002-4), the Korean Research Foundation (KRF-99-042-D00068), and the MOST through the Women's University Research Fund (99-N6-01-01-A-07).

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PubMed2000

Platelet and bacterial repellence on sulfonated poly(ethylene glycol)-acrylate copolymer surfaces.

Novel poly(ethylene glycol) (PEG) and sulfonated PEG (PEG-SO(3)) acrylate copolymers have been prepared and characterized to apply as coating and blending materials for biomedical applications. The modified surfaces using acrylate copolymers demonstrated increased hydrophilicity, possibly due to the hypothesized reorientation of PEG/PEG-SO(3) chains into water phase. All copolymer surfaces demonstrated less platelet adhesion than control. In addition, platelet adhesion on copolymer surfaces decreased as the chain length of PEG and sulfonated PEG in copolymers increases. All copolymer surfaces reduced bacterial adhesion significantly and the adhesion level differs depending on surfaces as well as media. The obtained results attest to the usefulness of these copolymers as a coating or additive material to improve the blood compatibility of blood contacting devices.

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PubMed2000

Potentiometric evaluation of solvent polymeric carbonate-selective membranes based on molecular tweezer-type neutral carriers

Potentiometric properties of the ion-selective electrodes) based on highly plasticized PVC membranes doped with the carbonate-selective cholic acid (CA) derivatives have been measured. The carbonate-selective neutral carriers have been prepared by coupling one to three trifluoroacetobenzoyl (TFAB) groups to a cholic acid derivative which has three hydroxyl linkers lining on the C3, C7, and C12 positions of its rigid steroidal ring structure. The membranes based on cholic acid derivatives with two TFABs [3,7-bis(TFAB)CA, 3,12-bis(TFAB)CA, and 7,12-bis(T-FAB)CA] exhibited remarkably improved carbonate selectivity, indicating that the bis(FAB)CAs behave like molecular tweezers for the carbonate ion. For example, 3,12-bis(TFAB)CA resulted in 10-300-fold-enhanced carbonate selectivity over other anions (e.g., salicylate, ClO4-, SCN-, (HPO4)2-, NO3-, NO2-, Br-, and Cl-) compared to that of the neutral carriers with a single TFAB group. The distances between the carbonate binding centers of bis(TFAB)CAs, i.e., the carbonyl carbons of the two TFAB groups, are in the 7.3-7.9-A range at the AM1 level semiempirical calculation, which is too far for the carbonate ion to form direct covalent bonding. The fast atom bombardment mass spectra of bis(TFAB)CAs show that significant fractions of the compounds are either mono- or dihydrated before complexing the carbonate ion. These findings seem to suggest that bis(TFAB)CAs recognize the incoming carbonate ion by forming both covalent and hydrogen bonding between the hydrated and unhydrated TFAB groups. The analytical utility of the carbonate-selective electrode based on 3,12-bis(TFAB)-CA has been demonstrated by measuring the total carbon dioxide in human serum in the presence of lipophilic anion interferents, e.g., salicylate.

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PubMed2000

Electronic resonance and symmetry in single-molecule inelastic electron tunneling

Inelastic electron tunneling spectroscopy and microscopy with a scanning tunneling microscope revealed two vibrational modes showing a decrease in conductance at +/-82.0 and +/-38.3 mV sample bias for single oxygen molecules chemisorbed on the fourfold hollow sites of Ag(110) surface at 13 K. The spatial distribution of the vibrational intensities exhibited pi(g)-orbital (perpendicular to surface) symmetry of O2 with the molecular axis along the [001] direction. These results are attributed to resonant inelastic electron tunneling.

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PubMed2000

NBS-Promoted reactions of symmetrically hindered methylphenols via p-benzoquinone methide

Symmetrically hindered methylphenols 1 react smoothly with NBS to form transient intermediates, p-benzoquinone methides (BM), which can be further processed to give hydroxybenzaldehydes in the presence of DMSO. This reaction is initiated by the formation of the phenoxy radical, followed by disproportionation to afford BM. None of the side-chain-brominated product is observed. The existence of BM is supported by the following observations: the formation of BM in solution can be monitored by GC and GC-MS; the electrophilic methine part participates in electrophilic aromatic substitution with anisoles to give hydroxybenzylated products 15; and the double bond character of the exocyclic methine plays a role in [4 + 2] cycloaddition with diene to afford Diels-Alder adducts. In contrast, unsymmetrically hindered or simple methylphenol (p-cresol) with NBS gives the nuclear brominated products, as usual. The energies of symmetrically hindered BMs, unsymmetrically hindered BM, and simple BM were calculated using density functional theories. Relative stabilization energies calculated at the B3LYP/6-31G//B3LYP/6-31G level by an isodesmic equation are enhanced 3-6 kcal/mol for symmetrically hindered BMs.

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PubMed2000

Nonrelativistic electromagnetic surface waves: dispersion properties in a magnetized dusty electron-positron plasma

Nonrelativistic electromagnetic surface waves propagating on the plane interface between dusty electron-positron plasma and vacuum are investigated by specular reflection procedure. In the presence of an applied magnetic field (B(0)=B(0)yinsertion mark) directed perpendicular to both the interface normal and the wave vector, transverse electromagnetic modes are studied in terms of the dispersion relation. The analytic modes are derived and discussed with the aid of some numerical analysis. The cold electromagnetic surface wave dispersion relation considering the effect of dust particle shows that possible modes appear only when the normalized frequency (omega;) and the wave vector (&Kmacr;) satisfy the condition Omega; Omega;, where delta(=n(0-)/n(0+)) is the parameter of charge imbalance in the plasma and Omega; is the normalized cyclotron frequency.

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PubMed1999

Single-bond formation and characterization with a scanning tunneling microscope

A scanning tunneling microscope (STM) was used to manipulate the bonding of a carbon monoxide (CO) molecule and to analyze the structure and vibrational properties of individual products. Individual iron (Fe) atoms were evaporated and coadsorbed with CO molecules on a silver (110) surface at 13 kelvin. A CO molecule was transferred from the surface to the STM tip and bonded with an Fe atom to form Fe(CO). A second CO molecule was similarly transferred and bonded with Fe(CO) to form Fe(CO)(2). Controlled bond formation and characterization at the single-bond level probe chemistry at the spatial limit.

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PubMed1998

Surfactant Effect on the Stability and Electrorheological Properties of Polyaniline Particle Suspension.

In this paper, the colloidal stability and electrorheological responses of semi-conductive polyaniline particles dispersed in a mineral oil were investigated experimentally. The polyaniline was synthesized by polymerization of aniline monomer. The surfactants used for the colloidal stability were commercially available nonionic Span20, Span80, and Span85, which are distinctly different in their molecular structures. Dynamic yield stress of polyaniline suspension, which possessed the quadratic dependence on electric field strength at low electric field, exhibited the linear dependence at high electric field. In addition, the conductivity of polyaniline particles influenced the electrorheological response and there existed the optimal conductivity for the maximum yield stress. In the presence of nonionic surfactants used here, the yield stress of polyaniline exhibited a local maximum at a certain surfactant concentration. The existence of optimal surfactant concentration was confirmed by the surfactant adsorption isotherm. We hypothesized that below the optimal threshold concentration, the electrorheological activity was enhanced by the increased interfacial polarization induced by the adsorbed surfactant molecules. Above the threshold concentration, however, the electrorheological activity was degraded by the conduction through the field-induced surfactant-rich bridge between adjacent particles. This optimal concentration coincided with the saturation concentration in the adsorption isotherm. The surfactants used in this study showed the improved colloidal stability due mainly to the induced steric hindrance effect. For the colloidal stability, Span80 was the most effective. However, considering that ER activity comes mainly from relatively large particles of O(µm), which are mostly present in our system, Span85 was the best choice for a stabilizing additive in the present ER suspension. In addition, our results showed that the presence of the nonionic surfactants considered here did not cause any sensible degradation at high temperatures. Copyright 1998 Academic Press.

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PubMed1998

Correlation of Lipid Peroxidation in Botrytis cinerea Caused by Dicarboximide Fungicides with Their Fungicidal Activity.

Dicarboximide fungicides iprodione, vinclozolin, and procymidone were examined for their capacity to inhibit mycelial growth, to cause cellular leakage, and to cause lipid peroxidation on Botrytis cinerea isolate BC2. All three fungicides effectively inhibited the mycelial growth of the fungi. The IC(50) values were found to be about 2 µM for all three fungicides, indicating that the fungicidal activity of the individual fungicides was almost the same. The fungicides caused significant cellular leakage and lipid peroxidation on the fungi in a concentration-dependent manner. Fungicidal activity of the three individual fungicides on inhibiting mycelial growth of the fungi correlated positively well with both cellular leakage and lipid peroxidation that were caused by the respective fungicides. Positive correlations were also found between the degree of cellular leakage and lipid peroxidation following treatment with the fungicides. Our results support the view that dicarboximide fungicides exert their fungicidal activity mainly through membrane lipid peroxidation and subsequent cellular leakage from the treated fungi.

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PubMed1996

Lipid Peroxidation and Membrane Disruption by Vinclozolin in Dicarboximide-Susceptible and -Resistant Isolates of Botrytis cinerea

A dicarboximide-susceptible (DS) isolate and a dicarboximide-resistant (DR) isolate of Botrytis cinerea were compared with regard to spore germination, mycelial growth, cellular leakage, and lipid peroxidation upon treatment with the dicarboximide fungicide vinclozolin. The fungicide inhibited spore germination and mycelial growth of the DS isolate, but not those of the DR isolate. The inhibitory effect of the fungicide was greater on mycelial growth than on spore germination of the DS isolate. Significant cellular leakage from the fungicide-treated DS or DR isolate began to increase after 24 hr incubation, depending on the concentration of the fungicide and the duration of incubation time. However, the magnitude of cellular leakage was much greater from the DS isolate than from the DR isolate. Vinclozolin caused considerable lipid peroxidation in the DS isolate, whereas little or no lipid peroxidation occurred in the DR isolate treated with the fungicide. Lipid peroxidation preceded cellular leakage from the DS isolate following fungicide treatment. The effects of the fungicide on mycelial growth, cellular leakage, and lipid peroxidation of the DS isolate were all reversed by the addition of alpha-tocopherol to the incubation medium. These results demonstrate that vinclozolin causes significant lipid peroxidation and subsequent cellular leakage from a DS isolate, but not from a DR isolate. Furthermore, they suggest that the mechanism of action of dicarboximide fungicides is associated with membrane lipid peroxidation.

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