• Bulletin of the Korean Chemical Society
• /
• v.26 no.10
• /
• pp.1505-1511
• /
• 2005

The excitation energy transfer process occurring in energy donor-acceptor linked porphyrin array system is theoretically simulated using the on-the-fly filtered propagator path integral method. The compound consists of an energy donating meso-meso linked Zn(II) porphyrin array and an energy accepting 5,15-bisphenylethynylated Zn(II) porphyrin, in which the donor array and the acceptor are linked via a 1,4-phenylene spacer. Real-time path integral simulations provide time-evolution of the site population and the excitation energy transfer rate constants are determined. Simulations and experiments show an excellent agreement indicating that the path integration is a useful tool to investigate the energy transfer dynamics in molecular assemblies.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.10 no.1
• /
• pp.103-118
• /
• 2018

When collision accident between ships or between ship and offshore platform occurs, a common phenomenon that occurs in structures is the plastic deformation accompanied by a large strain such as fracture. In this study, for the rational design against accidental limit state, the plastic material constants of steel plate which is heated by line heating and steel plate formed by cold bending procedure have been defined through the numerical simulation for the high speed tension test. The usefulness of the material constants included in Cowper-Symonds model and Johnson-Cook model and the assumption that strain rate can be neglected when strain rate is less than the intermediate speed are verified through free drop test as well as comparing with numerical results in several references. This paper ends with describing the future study.

• Bulletin of the Korean Chemical Society
• /
• v.14 no.1
• /
• pp.47-52
• /
• 1993

The vibrational relaxation rate constants of NO(v = 1-7) by $O_2\;and\;N_2$ have been calculated in the temperature range of 300-1000 K using the solution of the time-dependent Schrodinger equation. The calculated relaxation rate constants by $O_2$ increase monotonically with the vibrational energy level v, which is compatible with the experimental data, while those by $N_2$ are nearly independent of v in the range of $3.40 {\pm}1.60{\times}10_{-16} cm^3$/molecule-sec at 300 K. Those for NO(v) + $N_2$ are about 2-3 orders of magnitude smaller than those for NO(v) + $O_2$, because the latter is an exothermic processes while the former an endothermic. Relaxation processes can be interpreted by single-quantum V-V transition. The contributions of V-T/R transition and double-quantum V-V transition to the relaxation are negligible over the entire temperature range.

• Bulletin of the Korean Chemical Society
• /
• v.11 no.2
• /
• pp.99-105
• /
• 1990

The Gutmann acceptor number(AN), solvatochromic parameters $({\alpha},{\beta}\;and\;{\pi}^{\ast})$ and hydrogen bonding equilibrium constants (KHB) were determined for three binary systems of methanol with 1,2-dimethoxyethane(DME), 1,2-dichloroethane(DCE) and pyridine (PYD). The solvolysis rate constants of t-butyl chloride, bromide and iodide were also determined in the three binary systems. Solvent properties and solvolysis rates have been discussed in the light of various solvent parameters. Solvolysis of t-butyl halides are most conveniently explained by the two-stage mechanism involving ion-pair intermediate with the ion-pair formation for chloride and ion pair dissociation for iodide as rate limiting.

• Bulletin of the Korean Chemical Society
• /
• v.20 no.7
• /
• pp.805-808
• /
• 1999

Second-order-rate constants (kN) have been measured spectrophotometrically for the reactions of 4-nitrophenyl 2-furoate (1) with a series of secondary alicyclic amines in H2O containing 20 mole % DMSO at 25.0℃. 1 is about 5-8 times more reactive than 4-nitrophenyl benzoate (2), although 1 is expected to be less reactive than 2 based on MO calculations and 13 C NMR study. The Brфnsted-type plots for the aminolysis reactions of 1 and 2 are linear with βnuc values of 0.78 and 0.85, respectively. The replacement of the CH=CH group by an O atom in the acyl moiety (2->1) does not cause any mechanism change. The reaction of piperidine with a series of substituted phenyl 2-furoates gives a linear Hammett plot with a large ρ- value (ρ- = 2.88) when σ- constants are used. The linear Brфnsted and Hammett plots with a large ρ- value suggest that the aminolysis reaction of 1 proceeds via rate-determining break-down of the addition intermediate to the porducts.

• Bulletin of the Korean Chemical Society
• /
• v.10 no.5
• /
• pp.448-452
• /
• 1989

NADH analogs, 1-benzyl-3-substituted (X)-1,4-dihydropyridines 1-4 (1: X = $CONH_2$; 2: X = $CSNH_2$; 3: X = $COOCH_3$; 4: X = $COCH_3$) were synthesized. The second order rate constants for hydration reaction and oxidation reactions by $Cu^{2+}$, $Fe(CN)_6^{3-}$ or methylacridinium iodide (MAI) of the compounds were determined. For all reactions investigated, the rate constants increased with decreasing electronegative character of the 3-substituents of 1,4-dihydropyridines : the decreasing order of the reaction rates was 2>1>3>4. However, the sensitivity of the reaction rates on the 3-substituents differed among the reactions. This was explained in view of mechanisms of the reactions.

• Bulletin of the Korean Chemical Society
• /
• v.13 no.6
• /
• pp.599-605
• /
• 1992

Rate constants of methanolyses of para-Z-substituted benzenesulfonyl chlorides have been determined in various isodielectric solvent mixtures. A third-order kinetic behavior has been observed in the methanolysis of p-nitrobenzenesulfonyl chloride in methanol-nitromethane mixture from the correlation figure of logarithms of rate constants were plotted against Y-values based on solvolyses of 1-adamantyl tosylate. $S_N1$-$S_N2$ mixing mechanisms are favored by neutral or weak electron-donating and weak electron-withdrawing substituents of p-Z-substituted benzenesulfonyl chlorides in methanol-nitrobenzene mixture. While the methanolyses of para-Z-substituted benzenesulfonyl chlorides in methanol-ethylene glycol solvent mixture are appropriate for $S_N2$ mechanism from the mechanistic criterion by means of m-values.

• Bulletin of the Korean Chemical Society
• /
• v.31 no.7
• /
• pp.1920-1926
• /
• 2010

Yoon et $al.^1$ presented an approximate mathmatical model to describe ammonia removal from an experimental batch reactor system with gaseous headspace. The development of the model was initially based on assuming instantaneous equilibrium between ammonia in the aqueous and gas phases. In the model, a "saturation factor, $\beta$" was defined as a constant and used to check whether the equilibrium assumption was appropriate. The authors used the trends established by the estimated $\beta$ values to conclude that the equilibrium assumption was not valid. The authors presented valuable experimental results obtained using a carefully designed system and the model used to analyze the results accounted for the following effects: speciation of ammonia between $NH_3$ and $NH^+_4$ as a function of pH; temperature dependence of the reactions constants; and air flow rate. In this article, an alternative model based on the exact solution of the governing mass-balance differential equations was developed and used to describe ammonia removal without relying on the use of the saturation factor. The modified model was also extended to mathematically describe the pH dependence of the ammonia removal rate, in addition to accounting for the speciation of ammonia, temperature dependence of reactions constants, and air flow rate. The modified model was used to extend the analysis of the original experimental data presented by Yoon et $al.^1$ and the results matched the theory in an excellent manner.

• Journal of the Korean Chemical Society
• /
• v.26 no.6
• /
• pp.407-413
• /
• 1982

The rate constants of the nucleophilic addition of cysteine to 3,4-methylenedioxyphenylmethylene malononitrile were determined by UV Spectrophotometry and a rate equation which can be applied over wide pH range was obtained. On the basis of rate equation, it may be concluded that the rate constants were dependent upon only the concentration of hydroxide ion above pH 9.0, however, below pH 6.0, the reaction were initiated by the addition of neutral cysteine molecule to carbon-carbon double bond and at pH 7.0~9.0, the addition of a neutral cysteine molecule and it's anion occurred competitively.

• Bulletin of the Korean Chemical Society
• /
• v.29 no.3
• /
• pp.585-589
• /
• 2008

Second-order rate constants (kN) have been measured for reactions of Y-substituted phenyl 2-thiophenecarboxylates (6a-h) with morpholine and piperidine in 80 mol % H2O/20 mol % DMSO at 25.0 0.1 oC. The Brnsted-type plot for the reactions of 6a-h with morpholine is linear with b lg = 1.29, indicating that the reactions proceed through a tetrahedral zwitterionic intermediate (T?). On the other hand, the Brnsted-type plot for the reactions of 6a-h with piperidine exhibits a downward curvature, implying that a change in the rate-determining step occurs on changing the substituent Y in the leaving group. Dissection of kN into microscopic rate constants (i.e., k1 and k2/k1 ratio) has revealed that k1 is smaller for the reactions of 6a-h than for those of Y-substituted phenyl 2-furoates (5a-h), while the k2/k1 ratio is almost the same for the reactions of 5a-h and 6a-h. It is also reported that modification of the nonleaving group from the furoyl (5a-h) to the thiophenecarbonyl (6a-h) does not influence pKao (defined as the pKa at the center of the Brnsted curvature) as well as the k2/k1 ratio.