• Bulletin of the Korean Chemical Society
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• v.19 no.10
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• pp.1047-1054
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• 1998

We present the results of molecular dynamics simulations for three different systems of bilayers of long-chain alkyl thiol [S(CH2)15CH3] molecules on an solid-solid interface using the extended collapsed atom model for the chain-molecule. It is found that there exist two possible transitions: a continuous transition characterized by a change in molecular interaction between sites of different chain molecules with increasing area per molecule and a sudden transition from an ordered lattice-like state to a liquid-like state due to the lack of interactions between sites of chain molecules on different surfaces with increasing distance between two solid surfaces. The third system displays a smooth change in probability distribution characterized by the increment of gauche structure in the near-tail part of the chain with increasing area per molecule. The analyses of energetic results and chain conformation results demonstrate the characteristic change of chain structure of each system.

• Bulletin of the Korean Chemical Society
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• v.12 no.2
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• pp.143-148
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• 1991

In the unhydrated and hydrated states, conformational free energies of L-ascorbic acid anion (AAA) were computed with an empirical potential function and the hydration shell model (a program CONBIO). The conformational energy was minimized from possible starting conformations expressed with five torsion angles of the molecule. The conformational entropy of each low energy conformation in both states was computed using a harmonic approximation. As found in L-ascorbic acid (AA), intramolecular hydrogen bonds (HBs) are proved to be of significant importance in stabilizing the overall conformations of AAA in both states, and give the folded conformations, which are quite different from those in crystal. There are competitions between HBs and hydration around O3 atom of the lactone ring and hydroxyls of the acyclic side chain. Especially, the whole conformation of AAA is strongly dependent on the water-accessibility of O3 atom. Though there is a significant effect of the hydration on conformational surface, the lowest energy conformation of the unhydrated AAA is conserved. The different patterns of HBs and hydration result in the conformations of AAA in both states being different from those of AA. It can be drawn by several feasible conformations obtained in the hydrated state that there exists an ensemble of several conformations in aqueous solution.

• Membrane Journal
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• v.12 no.4
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• pp.207-215
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• 2002

The hindered diffusion in confined spaces is an important phenomenon to understand in a micro-scale the filtration mechanism determined by the particle motion in membrane pores. Compared to the case of spherical colloids, both the theoretical investigations and the experiments on the hindered diffusion of polyelectrolytes is actually more difficult, due to lots of relevant parameters resulting from the complicated conformational properties of the polyelectrolyte chain. We have successfully performed the Brownian dynamics simulations upon a single polyeiectrolyte confined in a slit-like pore, where a coarse-grained bead-spring model incorporated with Debye-Huckel interaction is properly adopted. For the given sizes of both the polyelectrolyte and the pore width, the hindered diffusion coefficient decreases as the solution ionic concentration decreases. It is evident that a charge effect of the pore wall enhances the hindered diffusion of polyelectrolyte. Simulation results allow us to make sense of the diffusive transport through the micro-pore, which is restricted by the influences of the steric hindrance of polyelectrolytes as well as the electrostatic repulsion between the polyelectrolytes and pore wall.

• Bulletin of the Korean Chemical Society
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• v.18 no.5
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• pp.528-534
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• 1997

The conformation and stabilization effects of acridine derivatives 9-aminoacridine, an acridine with an aminoalkyl side chain, bis acridine (two acridines linked by an aminoalkyl side chain), and proflavin in the triplex helical poly(dA)·[poly(dT)]2 were investigated by optical spectroscopies. Based on the negative LD and weak positive CD in the acridine absorption wavelength region, we concluded that the acridine moiety of all derivatives are intercalated. We also examined the melting temperatures. Of all the compounds examined, the acridine with an amino alkyl side chain had the strongest effect on the stabilization of the third strand of a poly (dA)·[poly(dT)]2 triplex. The role of the side chain, based on this observation, is discussed.

• Journal of the Korean Chemical Society
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• v.49 no.2
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• pp.129-137
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• 2005

• Proceedings of the Korean Fiber Society Conference
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• 1986.06a
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• pp.38-38
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• 1986

• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.19-20
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• 2006

We report the design of electroluminescent conjugated polymers for high efficiency, turn-on voltage, color Tuning, and easy processing. Three approaches for the design are reported, being: (1) single chain consideration, (2) supramolecular structure consideration, and (3) conformation manipulation. Two polymer systems are to be reported, being fluorene-based and carbazole-based conjugated polymers.

• Bulletin of the Korean Chemical Society
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• v.12 no.1
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• pp.61-67
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• 1991

Conformational free energy calculations using an empirical potential function and the hydration shell model (a program CONBIO) were carried out on the neutral L-ascorbic acid (AA) in the unhydrated and hydrated states. The conformational energy was minimized from starting conformations which included possible conformations of six torsion angles in the molecule. The conformational entropy of each low energy conformation in both states was computed using a harmonic approximation. From the analysis of conformational free energies for AA in both states, intramolecular hydrogen bonds (HBs) are proved to be an essential factor in stabilizing the overall conformations, and cause the conformations in both states to be quite different from those in crystal. In the case of hydrated AA, there is a competition between HBs and hydration, and the hydration around the two hydroxyl groups attached to the acyclic side chain forces the molecule to form less stable HBs. The hydration affects strongly the conformational energy surfaces of AA. Several feasible conformations obtained in this work indicate that there exists an ensemble of several conformations in aqueous solution. The calculated probable conformations for the rotation about the C5-C6 bond of the acyclic side chain are trans and gauche +, which are in good agreement with results of NMR experiment.

• Journal of the Korea Safety Management & Science
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• v.3 no.1
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• pp.45-56
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• 2001

In the supply chain, The ATP function doesn't only give customers to confirmation of delivery. It can be used by the core function with ATP rule that can reconcile supplies and demands on the supply chain. Therefore We can acquire the conformation about accuracy on the due date of supplier by using the ATP function of management about real and concurrent access on the supply chain, also can decide the affect about product availability due to forecasting or customer's orders through the ATP. This study analyze the data concerned with ATP and define the necessity on a SCM solution. Under the these environments, after defining the ATP rule that can improve the customer value and data flow related the CRM, we propose the advanced ATP model that proposes the method and classification system that can flexibly aggregate the ATP data with ATP rule on the supply chain.

• Korea-Australia Rheology Journal
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• v.12 no.1
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• pp.39-53
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• 2000

Using a variety of examples from the recent literature on extensional flow of polymer solutions, this paper shows that simple constitutive equations are unable to capture the diversity of chain conformations in such flows. Such diversity is a feature of extensional flows and arises because deformation leads to significant chain extension. Substantial local extension appears even at low strains and the behaviour of these stretched out portions influences the dynamics of the chain and makes a dominant contribution to the stress. Both the distribution function and the chain conformation appear to follow different paths during stretching and relaxation. As a result the second moment of the distribution function does not contain enough information to correctly predict the dynamics. Resolution of this deficiency in simple constitutive models is one of the challenges for rheology.