• Bulletin of the Korean Chemical Society
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• v.34 no.10
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• pp.2973-2977
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• 2013

In this study, we developed a liquid crystal (LC)-based optical sensor for monitoring enzymatic activity through orientational changes in liquid crystals (LCs) coupled to the properties of a poly-${\small{L}}$-lysine (PLL)-based polymeric membrane. We prepared a PLL-based polymeric membrane at the planar interface between the thermotropic liquid crystal and aqueous phases. The PLL-based polymeric membrane was obtained by contacting the PLL solution with water immiscible LCs, 4-cyano-4'-pentyl-biphenyl (5CB) doped with adipoyl chloride. We then investigated the membrane properties by examining the permeability of the membrane to phospholipids, 1,2-didodecanoyl-rac-glycero-3-phosphocholine (DLPC). The permeability of the membrane to transport phospholipids was monitored through the orientational transition of 5CB in contact with the dispersions of DLPC. Since trypsin can enzymatically catalyze the hydrolysis of PLL, we incubated an aqueous trypsin solution with the membrane for 2 h at room temperature to cause an increase in the permeability of the polymeric membrane to DLPC. As a result, a bright to dark optical shift of LCs was observed, which implied that an enzymatic reaction between trypsin and PLL-based membrane occurred. Two control experiments using chymotrypsin and bovine serum albumin (BSA) revealed no sign of improved permeability based on the orientational transition of LCs.

• Bulletin of the Korean Chemical Society
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• v.21 no.4
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• pp.434-440
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• 2000

We present the results of computer simulation for the steady shear flows of rodlike molecules using nonequi-librium molecular dynamics simulation (NEMD) method. The model particle is a rigid rod composed of lin-early connected 6-sites and the Lennard-Jones 12-6 potential governs interactions between sites in different molecules. The system of rodlike molecules exhibits the change of orientational structure, that is, isotropic-nematic transition at high shear rates. We elucidate the nature of the ordered system developed from an isotro-pic phase by steady shear through an analysis of various quantities: orientational order parameters, orientational pair correlation functions, orientational distribution function, and snapshots of configurations. The effects of temperature and density on the shear rate dependence of orientational structure are described.

• Bulletin of the Korean Chemical Society
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• v.12 no.2
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• pp.199-206
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• 1991

A statistical thermodynamic theory of thermotropic main-chain polymeric liquid crystalline melts is developed within the framework of the lattice model by a generalization of the well-known procedure of Flory and DiMarzio. According to the results of Vasilenko et al., the theory of orientational ordering in melts of polymers containing rigid and flexible segments in the main chain is taken into account. When the ordering of flexible segments in the nematic melt is correlated with that of rigid mesogenic groups, the former is assumed to be given as a function of the ordering of rigid mesogenic cores. A free energy density that includes short-range packing contributions is formulated. The properties of the liquid-crystalline transiton are investigated for various cases of the system. The results calculated in this paper show not only the order-parameter values but also the first-order phase transition phenomena that are similar to those observed experimentally for the thermotropic liquid-crystalline polymers and show the transitional entropy terms which actually increase upon orientational ordering. In the orientational ordering values, it is shown that mesogenic groups, flexible segments, and gauche energy (temperature) may be quite substantial. Finally, by using the flexibility term, we predict the highly anisotropic mesophase which was shown by Vasilenko et al.

• Bulletin of the Korean Chemical Society
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• v.33 no.10
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• pp.3269-3273
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• 2012

In this study, we report a new method for the high contrast imaging of biomolecular interactions at roller printed protein surfaces using thermotropic liquid crystals (LCs). Avidin was roller printed and covalently immobilized onto the obliquely deposited gold surface that was decorated with carboxylic acid-terminated self-assembled monolayers (SAMs). The optical response of LCs on the roller printed film of avidin contrasted sharply with that on the obliquely deposited gold surface. The binding of biotin-peroxidase to the roller printed avidin was then investigated on the obliquely deposited gold substrate. LCs exhibited a non-uniform and random orientation on the roller printed area decorated with the complex of avidin and biotin-peroxidase, while LCs displayed a uniform and planar orientation on the area without roller printed proteins. The orientational transition of LCs from uniform to non-uniform state was triggered by the erasion of nanometer-scale topographies on the roller printed surface after the binding of biotin-peroxidase to the surface-immobilized avidin. The specific binding events of protein-receptor interactions were also confirmed by atomic force microscopy and ellipsometry. These results demonstrate that the roller printing of proteins on obliquely deposited gold substrates could provide a high contrast signal for imaging biomolecular interactions using LC-based sensors.

• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1217-1219
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• 1995

The organization of phospholipid monolayers on a water surface was investigated by means of Maxwell-Displacement-Current(MDC)-Measuring technique. The phase transition from the gaseous phase to the gaseous-fluid phase which accompanies the polar ordering of lipid molecules was detected by the technique in the range of immeasurable low surface pressure and the molcular-area which gives the onset of the transition was determined for lipid monolayers. The vertical component of dipole moment of lipid membranes was determined from the charge flowing the rough the circuit, and we measured differential themal analysis of sample.

• Journal of the Korean Graphic Arts Communication Society
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• v.13 no.1
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• pp.1-12
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• 1995

Polymeric mesogens having a regularly alternating rigid-flexible repeating structure in the main-chain polymer exhibit distinct even-odd oscillation in their thermodynamic quantities with respect to the number of methylene units in the spacer. The even-odd oscillation depends on the number of methylene groups in the spacer the entropy change at the NI(nematic-isotropic) phase transition becomes less distinct when the linking group is replaced by the carbonate. In our previous work, we have suggested that the characteristics arise from the geometrical arrangement of the linkage. In this work, we have prepared a series of carbonate-type monomer and dimer liquid crystals. The thermodynamic behaviors at the NI phase transition have been compared with those previous reported for the ether- or ester-type liquid crystals. For the dimer series, the orientational order parameter of the mesogenic core was determined by using H-NMR technique. The origin of the difference observed among linking groups was found to the geometrical characteristics of chemical structure.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.05a
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• pp.6.1-10
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• 1996

Starting from the Debye theory of rotational Brownian motion equation, we derive an expression for explaining the generation of Maxwell displacement current (MDC) across single monolayers on a material surface. The orientational order parameter and the dielectric relaxation the of monolayers are derived. Based on fille analyses developed here, we examine the MDC across phospholipid monolayers with thermal stimulation due to the change in the spontaneous polarization, and the generation of MDC from 4-cyano-4\`-5-alkayl-biphenyl(5CB) Langmuir-film at the onset of transition by monolayer compression

• Bulletin of the Korean Chemical Society
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• v.24 no.8
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• pp.1091-1096
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• 2003

The effects of different polarization conditions on vibrational echo signals are systematically explored for the rigid cyclic dipeptide 2,5-diazabicyclo[2,2,2]octane-3,6-dione. An anharmonic vibrational Hamiltonian is constructed by computing energy derivatives to fourth order using density functional theory. Molecular frame transition dipole orientations are then used to calculate polarization dependent orientational factors corresponding to various Liouville space pathways. Enhancement and elimination of specific peaks in twodimensional correlation plots is accomplished by identifying appropriate pulse configurations.

• Journal of Industrial and Engineering Chemistry
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• v.67
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• pp.478-485
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• 2018

The effect of reduced graphene oxide (RGO) addition on the dielectric and piezoelectric behavior of the polyvinylidene fluoride (PVDF) films was studied. Dielectric constant increased by four times and piezoelectric coefficient also increased twice by the addition of RGO in the PVDF films. Based on capacitance-voltage and ellipsometry measurements and the Kramers-Kronig transformation, it is concluded that the enhanced dielectric and piezoelectric properties of the PVDF/RGO films resulted from the increased orientational polarization due to a phase transition from nonpolar crystalline ${\alpha}$ phase to polar crystalline ${\beta}$ phase in the PVDF structure.

• Analytical Science and Technology
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• v.8 no.2
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• pp.107-116
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• 1995

The critical micelle concentration(CMC) of CTAB was determined with changes in absorbance at 202nm band of 4-biphenyl acetate($BPA^-$). With $BPA^-$ as a probe, the effect of temperature on CMC of CTAB has been observed between $30^{\circ}C{\sim}70^{\circ}C$. In this range of temperature the values of CMC are $1.18{\times}10^{-4}{\sim}2.02{\times}10^{-4}M$. The free energy(${\Delta}G^{\circ}m$) and enthalpy(${\Delta}H^{\circ}m$)for the micellization of CTAB was negative and the entropy(${\Delta}S^{\circ}m$) was a large positive value. The micellization of CTAB is considered as a spontaneous process and to involve a phase transition. The orientational binding of 4-biphenyl acetate anion to the CTAB micelle interface has been studied with $300MHz\;H^1-NMR$ data. The change in chemical shift of proton in CTAB as well as those of the protons in $BPA^-$ have been investigated by increasing the mole fraction of the anion in the mixed solutions. The changes in chemical shift with increasing mole fraction of anion($BPA^-$) indicate the formation of mixed micelle between CTAB and $BPA^-$. The changes in chemical shifts of methylene protons in CTAB, demonstrate the penetration of $BPA^-$ into the palisade layer of the CTAB micelle.