Biomedical subjects

KH Lee

Publications and source records attributed to KH Lee.

At least 19 recordsLinked to original sources

PubMed2000

Thermal isomerizations of ketenimines to nitriles: evaluations of sigma-Dot (sigma(*)) constants for spin-delocalizations

Rate constants (k(Y)) of the isomerizations of 11 diphenyl N-(substituted benzyl) ketenimines were measured at 40, 50, 60, and 70 degrees C. Activation parameters DeltaH()(Y) and DeltaS()(Y) were obtained using the Eyring equation. The relative rates (k(Y)/k(H)) were fitted into Hammett single correlations (log k(Y)/k(H) = rhosigma and log k(Y)/k(H) = rho(*)sigma(*)). The single correlations have been compared with Hammett dual correlations (log k(Y)/k(H) = rhosigma + rho(*)sigma(*) ). Separate treatments of para and meta substituents yielded even better correlations. Para substituents control the rates through spin-delocalizations and inductive effects. The former outweighs the latter when the latter exerts a modest but distinct influence on the rates. On the other hand, inductive effects are the "major" or the sole interactions triggered by meta substituents.

Journal Article↗

PubMed2000

Dimer to monomer phase transition in alkali-metal fullerides: magnetic susceptibility changes

Ab initio calculations have been employed to investigate the peculiar change in magnetic property (from diamagnetic to paramagnetic) of the dianionic C60-dimer phase in a rapidly cooled AC60 samples ( A: alkali metal). We first note that the triplet state of (C60)-22 which was never considered previously is nearly degenerate with the singlet state, and the transition barrier between the two states is reasonably small. This explains the susceptibility increase with an increase in temperature and the magnetic phase transition in the process of the dimer to monomer phase transition.

Journal Article↗

PubMed2000

Relative binding affinities of alkali metal cations to

The binding affinity and selectivity of a new ionophore, [1(8)]starand (1), toward alkali metal cations in methanol were examined through NMR titration experiments and free energy perturbation (FEP) and molecular dynamics simulations. The preference was determined to be K(+) > Rb(+) > Cs(+) > Na(+) >> Li(+) in both FEP simulations and NMR experiments. The FEP simulation results were able to predict the relative binding free energies with errors less than 0.13 kcal/mol, except for the case between Li(+) and Na(+). The cation selectivity was rationalized by analyzing the radial distribution functions of the M-O and M-C distances of free metal cations in methanol and those of metal-ionophore complexes in methanol.

Journal Article↗

PubMed1998

Effects of Ascorbic Acid on the Light-Induced Riboflavin Degradation and Color Changes in Milks.

Effects of ascorbic acid (0.025, 0.05, and 0.1%, w/v) on the light-induced riboflavin degradation and color changes in whole and skim milks were studied during 10 h fluorescent light illumination at 7 +/- 2 degrees C. As the time of light illumination increased, the riboflavin content in milks greatly decreased, resulting in 30.1 and 59.1% reduction of riboflavin in whole milk and skim milk after 10 h exposure to fluorescent light, respectively. The ascorbic acid treatment effectively protected the photodegradation of riboflavin in both whole milk and skim milk, and its effectiveness is concentration dependent. The 0.1% ascorbic acid treatments resulted in 50.0 and 25.5% inhibition of riboflavin reduction in whole milk and skim milk after 10 h fluorescent light illumination, respectively. The color parameters of lightness (L), greenness (-a), and yellowness (b) in both whole milk and skim milk decreased after light illumination. Ascorbic acid treatment also protected effectively the changes in greenness and yellowness in both milks during the light illumination.

Journal Article↗

PubMed1996