• Bulletin of the Korean Chemical Society
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• v.2 no.4
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• pp.132-138
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• 1981

Ab initio molecular orbital calculations have been performed in an effort to determine which types of chemical interactions play essential roles for the system, , $H_2O+CH_2SH^+$, and $H_2O+ CH_2S$. The most important contribution to the interaction energy in controlling reaction path is the exchange repulsion energy, EX, which is largely responsible for the shape of the total interaction energy curve. In the ion-molecule reaction, prior protonation of thioformaldehyde or prior deprotonation of water leads to formation of the corresponding ionic adducts ($H_2O+CH_2SH$ and $HOCH_2S^-$), with no barrier to reaction, simulating specific acid and base catalysis, respectively, as in the case of formaldehyde. Otherwise, approach of water to thioformaldehyde gives rise to a completely repulsive interaction.

• Bulletin of the Korean Chemical Society
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• v.6 no.1
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• pp.3-7
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• 1985

The general formulas for SCF atomic orbitals |5s > and |6p > have been derived separately by expressing the spherical harmonics part in terms of the coordinate($r_1,\;$r_2$) of the reference point, and by translating the exponential part, $r^4\;exp\;(-{\beta}r)$), in terms of $r_1,\;and\;r_2$ and the modified Bessel functions. Master formulas for overlap and dipole moment matrix elements are derived. The computed values of overlap and dipole moment matrix elements for hypothetical NO molecule are exactly in agreement with those for the previous methods.

• Bulletin of the Korean Chemical Society
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• v.4 no.2
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• pp.68-72
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• 1983

The $pK_{a}$ of $-NH_{3}^{+}$ group of chitosan in water was 6.2, while that of D-glucosamine-HCl, monomer of chitosan, was found to be 7.8. The difference of $pK_{a}$ values between chitosan and D-glucosamine was attributed to the strong electrostatic interaction between $-NH_{3}^{+}$ groups in chitosan. The apparent binding constant of $Cu^{2+}$ to D-glucosamine was estimated to be $1{\times}10^{4}$. For chitosan, no significant binding of $Cu^{2+}$ to the polymer was observed when pH < 5, but strong cooperative binding was observed near pH 5.1. The mechanism of such cooperativity was proposcd. Chitosan in solution exhibited typical polyelectrolytic behaviors: viscosity increases with increased amount of charged group, and decreases with addition of salt. The concentration dependence of viscosity was measured, and the Huggins parameters and intrinsic viscosity were calculated at various ionic strength. The results were interpreted in terms of molecular properties of the chitosan molecule.

• Bulletin of the Korean Chemical Society
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• v.19 no.1
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• pp.86-93
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• 1998

Trans-4-(9-anthrylethenyl)-4'-methyl-2,2'-bipyridine(t-aemb) and its bipyridyl Ru complex $[Ru(bpy)_2(t-aemb)](PF_6)_2$ (bpy=2,2'-bipyridine) 1 have been prepared and their excited state properties have been studied. t-Aemb exhibits solvent-dependent fluorescence and efficient trans→cis photoisomerization. 1 shows very weak fluorescence and its photochemically reactive. Fluorescence is wavelength-dependent. While the excitation into the MLCT band makes the complex fluorescent, direct absorption by the t-aemb ligand leads to the photoreaction of t-aemb ligand and no fluorescence is observed. 1 is considered to behave in part as bichromophoric molecule in which $[Ru(bpy)_3](PF_6)_2$ and anthryl group are covalently linked by ethenyl linkage. Because anthryl moiety is not effectively conjugated with bipyridylethenyl moiety due to steric hindrance, weak fluorescence can be explained due to the efficient energy or electron transfer.

• Bulletin of the Korean Chemical Society
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• v.20 no.6
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• pp.712-714
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• 1999

The rate constants for the nucleophilic addition of potassium cyanide to α,N-diphenylnitrone and its derivatives (p-OCH3, p-CH3, p-Cl, and p-NO2) were determined by ultraviolet spectrophotometer at 25℃, and the rate equations which can be applied over a wide pH range were obtained. On the basis of pH-rate profile, adduct analysis, general base catalysis and substituent effect, a plausible mechanism of this addition reaction was proposed: At high pH, the cyanide ion to carbon-nitrogen double bond was rate controlling, however, in acidic media, the reaction proceeded by the addition of hydrogen cyanide molecule to carbon-nitrogen double bond after protonation at oxygen of a,N-diphenylnitrone. In the range of neutral pH, these two reactions occured competitively.

• Bulletin of the Korean Chemical Society
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• v.20 no.9
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• pp.999-1004
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• 1999

Two compact sized globular proteins, β-lactoglobulin and α-lactalbumin were kinetically characterized at the aqueous solution surface with the measurement of surface pressure (π) and surface concentration (Γ) via a radiotracer method. The adsorption kinetics was of diffusion control at early times, the rates of increase of πand Γ being lower at longer times due to growing energy barrier. At low concentrations, an apparent time lag was observed in the evolution of π for β-lactoglobulin but not for α-lactalbumin which was shown to be due to the non-linear nature of the p- G relationship for the former. The area per molecule of an adsorbed β-lactoglobulin during adsorption was smaller than that for spread monolayer since β-lactoglobulin was not fully unfolded during the adsorption. For α-lactalbumin, however, no such difference in the molecular areas for adsorbed and spread monolayer was observed indicating thereby that α-lactalbumin unfolded much more rapidly (has looser tertiary structure) than β-lactoglobulin. Surface excess concentrations of α-lactalbumin was found to evolve in two steps possibly due to the change in the orientation of the adsorbed protein from a side-on to an end-on orientation.

• Bulletin of the Korean Chemical Society
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• v.22 no.9
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• pp.1009-1014
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• 2001

In aqueous mixtures of cationic OTAC (octadecyl trimethyl ammonium chloride) and anionic ADS (ammonium dodecyl sulfate) surfactants, mixed micelles were formed at low (< 0.2 wt %) total surfactant concentrations. For these mixtures mixed micelliza tion and interaction of surfactant molecules were examined. Mixed critical micelle concentration (CMC), thermodynamic potentials of micellization, and minimum area per surfactant molecule at the interface were obtained from surface tensiometry and electrical conductometry. The mixed micellar compositions and the estimation of interacting forces were determined on the basis of a regular solution model. The CMCs were reduced, although not substantial, and synergistic behavior of the ADS and OTAC in the mixed micelles was observed. The CMC reductions in this anionic/cationic system were comparable to those in nonionic/anionic surfactant systems. The interaction parameter $\beta$ of the regular solution model was estimated to be -5 and this negative value of $\beta$ indicated an overall attractive force in the mixed state.

• Bulletin of the Korean Chemical Society
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• v.18 no.4
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• pp.374-379
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• 1997

The rate constants for the nucleophilic addition of thiophenol derivatives (p-OCH3, H, p-CH3, m-CH3, p-Br and p-NO2) to 4'-[N-(9-acridinyl)]-1'-(N-methanesulfonyl)-3'-methoxyquinonediimide (AMQD) were determined by ultraviolet spectrophotometer in water at 5 ℃, and rate equations which can be applied over a wide pH range were obtained. On the basis of pH-rate profile, Bronsted plot, adduct analysis, general base catalysis and substituent effect, a plausible mechanism of this addition reaction was proposed: Below pH 2.5, the reaction proceeded by the addition of thiophenol molecule to 6'-position of quinonoid after protonation at the acridinyl nitrogen. Above pH 6.2, the addition of sulfide anion to 6'-position of quinonoid was rate controlling. However, in the range of pH 3.0-6.0, these two reactions occured competively.

• Bulletin of the Korean Chemical Society
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• v.8 no.6
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• pp.444-449
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• 1987

Solvent effects on gas phase reactions of methoxide ion with substituted ethylenes, $CH_2$ = CHR where R = CN, CHO and $NO_2$, are investigated theoretically using the AM1 method. Results show that the methoxide approaches in-plane in all reactions, but subsequently rotate out-of-plane to form tetrahedral complexes in additon reactions. All reactions of a bare methoxide are found to be exothermic, the exothermicity being the greatest in the ${\beta}$-addition, in which the excess energy is forced to be contained within the ${\beta}$-adduct rendering extreme instability. However a part of the excess energy can be removed by a solvate molecule giving a stable complex prior to the product formation. The hydride transfer processes were found to be unfavorable due to the high activation barriers. The ${\alpha}-H^+$ abstraction process from acrylonitrile becomes endothermic as a result of monosolvation of the methoxide, in agreement with experimental results.

• Bulletin of the Korean Chemical Society
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• v.22 no.5
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• pp.455-462
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• 2001

The time-dependent tracking inversion method is studied to extract the potential energy surface of the electronic excited state in the photodissociation of triatomic molecules. Based on the relay of the regularized inversion procedure and time-dependent wave packet propagation, the algorithm extracts the underlying potential energy surface piece by piece by tracking the time-dependent data, which can be synthesized from Raman excitation profiles. We have demonstrated the algorithm to extract the potential energy surface of electronic excited state for NO2 molecule where the wave packet split on a saddle-shaped surface. Finally, we describe the merits of the time-dependent tracking inversion method compared with the time-independent inversion method and discussed several extensions of the algorithm.