• Journal of the Korean Chemical Society
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• v.35 no.5
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• pp.493-499
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• 1991

The circular dichroism (CD) spectrum of trans-[Co(R,R-chxn)$_2Cl_2]^+$ complex with different counter-ions have been measured in several organic solvents, where R,R-chxn is (1R,2R)-1,2-diaminocyclohexane. The observed variations in the CD spectrum of the complex exhibited remarkable solvent dependences. And it has been observed that the degree of the change of CD spectrum in the first absorption band region $(^1A_{2g})$ depends on the donor number (DN) of the solvents. From $^1H$ NMR spectrum, it is interpreted that these variations in the CD spectrum of trans-[Co(R,R-chxn)$_2Cl_2]^+$ complex are due to the favorable interaction between solvent molecules and the equatorial N-H protons of R,R-chxn ligands.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.81-81
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• 2012

XMCD (X-ray Magnetic Circular Dichroism)는 원형 편광 X-선의 helicity 방향이 시료의 자화 방향과 평행, 또는 반평행할 때 시료의 색이 바뀌는 현상, 즉 흡수율이 달라지는 현상이다. XMCD측정이 가지는 장점은 첫째, 이 실험이 특정 원소의 흡수선에서 이루어지기 때문에 시료 전체에서 특정 원소에 의한 자기적 성질을 분리해서 측정할 수 있을 뿐만 아니라, 같은 원소라 하더라도 다른 화학적 환경에 있는 원자들의 자기적 성질의 분리가 가능하다는 점이다. 이러한 성질로 인해 XMCD는 다른 원소들로 이루어진 다층 박막(GMR, TMR 등의 자기저항박막 구조물)의 층별 자기적 성질 연구 및 신자성물질의 자기적 성질의 고유성 연구에 많이 이용되었다. XMCD가 가지는 두 번째 장점은 sum rule을 통하여 자기 모멘트의 두 가지 성분인 궤도 모멘트(orbital moment)와 스핀 모멘트(spin moment)의 구별이 가능하다는 점이다. 이러한 장점은 수직자기 메모리 연구 및 스핀과 격자 간의 상호작용이 중요한 역할을 하는 다강체 등의 연구에 많이 이용되어 왔다. XMCD 측정이 또 다른 장점이 될 수 있는 것은 표면에 대단히 민감하다는 점이다. VSM, SQUID 등의 측정방법으로는 시료의 체적이 대단히 작은 수 ${\AA}$ 정도의 초박막에 대해서는 충분한 민감도를 가질 수 없다. 그러나, XMCD의 측정 깊이는 수십 ${\AA}$ 정도로 표면에 민감하기 때문에 이러한 초박막에 대해서도 충분한 민감도를 가질 수 있어서 SMOKE(Surface Magneto-Optical Kerr Effect)와 표면 자성연구에 있어서 독보적인 장치로 이용되어 왔다. 이러한 장점으로 인해 XMCD는 1990년대 이후 분광학적으로 활발히 이용되어 왔을 뿐만 아니라, 대단히 빠르고 신호가 큰 현상이기 때문에 최근 들어서는 자구(magnetic domain) 관찰 등을 목적으로 한 자기 현미경 및 자기현상의 동역학 연구에도 많이 응용되고 있다. 이 강연에서는 이러한 X-선 자기 원형 이색성 현상의 원리 및 실험 방법 등을 설명하겠다. 또한 몇 가지 X-선 자기 원형 이색성을 이용한 최근 몇 가지 연구도 소개하려 한다.

• Polymer(Korea)
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• v.31 no.5
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• pp.393-398
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• 2007

We studied the mechanism of liquid crystal alignment on polyvinylfluorocinnamate (PVCN-F) films which were irradiated by UV using polarized fourier transform infrared (FT-IR) spectroscopy and ultraviolet/visible (UV/Vis) spectroscopy. UV irradiation of PVCN-F films caused decrease of vinylene -C=C- stretching peak area at $1638cm^{-1}$ and shift of conjugated C:0 stretching vibration at $1712cm^{-1}\;to\;1734cm^{-1}$ which is caused by nonconjugated C=O stretching nitration. To study the orientation direction of 5CB liquid crystal (LC) molecules in the liquid crystal cell with PUV irradiation, rubbing treatment or without any treatment on the PVCN-F alignment layer, we used polarized FT-IR dichroism technique. We successfully measured 5CB LC alignment directions, which are perpendicular to the irradiated PUV polarization direction and parallel to the rubbing direction in the liquid crystal cell without using dichroic dyes.

• Molecules and Cells
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• v.26 no.1
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• pp.61-66
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• 2008

Cyclic AMP receptor protein (CRP) is allosterically activated by cAMP and functions as a global transcription regulator in enteric bacteria. Structural information on CRP in the absence of cAMP (apo-CRP) is essential to fully understand its allosteric behavior. In this study we demonstrated interdomain interactions in apo-CRP, using a comparative thermodynamic approach to the intact protein and its isolated domains, which were prepared either by limited proteolysis or using recombinant DNA. Thermal denaturation of the intact apo-CRP, monitored by differential scanning calorimetry, revealed an apparently single cooperative transition with a slight asymmetry. Combined with circular dichroism and fluorescence analysis, the thermal denaturation of apo-CRP could be interpreted as a coupled process involving two individual transitions, each attributable to a structural domain. When isolated individually, both of the domains exhibited significantly altered thermal behavior, thus pointing to the existence of non-covalent interdomain interactions in the intact apo-CRP. These observations suggest that the allosteric conformational change of CRP upon binding to cAMP is achieved by perturbing or modifying pre-existing interdomain interactions. They also underline the effectiveness of a comparative approach using calorimetric and structural probes for studying the thermodynamics of a protein.

• Bulletin of the Korean Chemical Society
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• v.28 no.6
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• pp.965-969
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• 2007

The spectral properties, namely the circular dichroism, electric absorption and luminescence properties, of Λ- and Δ-[Ru(II)(1,10-phenanthroline)2benzodipyrido[b:3,2-h:2',3'-j]phenazine]2+ ([Ru(phen)2BDPPZ]2+) in the presence and absence of single stranded poly(dA) and poly(dT) were compared in this work. In the presence of single stranded DNAs, hypochromism in the absorption spectrum and significant changes in the circular dichroism spectrum in the ligand absorption band were apparent, indicating the strong interaction of the [Ru(phen)2BDPPZ]2+ complex with the single stranded DNAs. The luminescence intensity of the Ru(II) complex decreased stoichiometrically with increasing concentrations of the single stranded DNAs. All of these spectral changes were independent of the configuration of the Ru(II) complex and the nature of the DNA bases. Therefore, it is conceivable that both enantiomers of the [Ru(phen)2BDPPZ]2+ complex interact electrostatically with the negatively charged phosphate groups of DNA. However, the spectral properties of [Ru(II)(1,10-phenanthroline)3]2+ were not altered even in the presence of single stranded DNAs. Therefore, the size of the ligand involved in the interaction of the metal complex with the phosphate group of DNA may play an important role, even when the nature of the interaction is electrostatic.

• Korean Journal of Food Science and Technology
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• v.31 no.6
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• pp.1488-1494
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• 1999

Effect of ${\gamma}-irradiation$ on the SDS-PAGE pattern, secondary structure content, the solubility of commercial soy protein isolate (SPI) and whey protein concentrate (WPC) was investigated. The change in the subunit molecular weight of SPI and WPC irradiated in aqueous solution or dried state was studied using SDS-PAGE. The SDS-PAGE pattern of SPI irradiated in aqueous solution revealed the fragmentation and aggregation of the subunit protein. For WPC irradiated in aqueous solution. fragmentation of the subunit protein up to 10 kGy was observed. In contrast, ${\gamma}-irradiation$ of SPI and WPC in dried state did not cause any significant changes in the SDS-PAGE pattern. The change In the secondary structure of irradiated SPI and WPC solution was studied using circular dichroism. The aperiodic structure content of SPI and WPC solution increased at higher irradiation doses, which suggests that ${\gamma}-irradiation$ caused the disruption of the ordered structure of SPI and WPC solution. Gamma-irradiation also caused the change in solubility of SPI and WPC in dried state.

• Korean Journal of Food Science and Technology
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• v.21 no.5
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• pp.714-720
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• 1989

Effects of acetylation on conformational changes of glycinin was studied using solvent perturbation, second derivative spectroscopy, near uv circular dichroism spectra and viscosity. Glycinin with purity of more than 93% was used for the experiment. Modification was carried out with acetic anhydride and glycinin with lysine residue modification of 0%, 28%, 65%, 85%, and 95% were used for the experiment. The result of solvent perturbation using some selected perturbants, such as glycerol, ethylene glycol, and dimethyl sulfoxide revealed that acetylation has caused increase In solvent accessibility of tyrosine residues from less than 40% in native protein to more than 70% for 95% acetylated glycinin. This was confirmed by second derivative spectroscopy. Near ultraviolet circular dichroism revealed that the spectra of native and acetylated glycinin were almost identical differing only in intensity and no other useful information could be derived from it. However, in the case of 95% acetylated glycinin the influence of tryptophan on the spectrum was more pronounced Specific viscosity of glycinin also increased by modification, the extent of which depended upon the degree of acetylation. These results supported that acetylation had caused globular conformation of glycinin to be expanded and denatured.

• Korean Journal of Materials Research
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• v.8 no.8
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• pp.733-736
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• 1998

The change of electronic absorption spectra of the fullerene $C_{60}$ in the visibJe- near UV range was examined when the molecules aggregated into different clusters such as clusters in solution and clusters in thin films. Absorption peaks were observed at 2.73 eV. These peaks did probably not come from the feature of the isolated molecules but from the direct interaction of the molecules. Absorption peaks were also observed at 3.35 eV from grained fullerene films. We think these peaks came from the interaction of the molecules at interfaces of grains. Dichroism of this absorption was also found from samples with anisotropic macrostructures.

• Journal of the Korean Magnetic Resonance Society
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• v.20 no.3
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• pp.95-101
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• 2016

Apolipoprotein B-100 (Apo-B100) is a major component of low density lipoprotein (LDL). Apo B-100 protein has 4,536 amino acid sequence and these amino acids are classified into peptide groups A to G with subsequent 20 amino acids (P1-P302). The peptide groups were act as immunoglobulin (Ig) antigens which oxidized via malondialdehyde (MDA). The mimetic peptide P1 (EEEMLENVSLVCPKDAT RFK) out of D-group peptides carrying the highest value of IgG antigens were selected for structural studies that may provide antigen specificity. Circular Dichroism (CD) spectra were measured for peptide secondary structure in the range of 190-250 nm. Experimental results show that P1 exhibit partial of ${\beta}-sheet$ and random coil structure. Homonuclear (COSY, TOCSY, NOESY) 2D-NMR experiments were carried out for NMR signal assignments and structure determination for P1. On the basis of these completely assigned NMR spectra and distance data, distance geometry (DG) and Molecular dynamics (MD) were carried out to determine the structures of P1. The proposed structure was selected by comparisons between experimental NOE spectra and back calculated 2D NOE results from determined structure showing acceptable agreement. The total Root-Mean-Square-Deviation (RMSD) value of P1 obtained upon superposition of all atoms was in the range $0.33{\AA}$. The solution state P1 has mixed structure of ${\beta}-sheet$ (Glu[1] to Cys[12]) and random coil (Pro[13] to Lys[20]). These NMR results are well consistent with secondary structure from experimental results of circular dichroism. Structural studies based on NMR may contribute to the studies of atherosclerosis and observed conformational characteristics of apo B-100 in LDL using monoclonal antibodies.

• Journal of the Korean Magnetic Resonance Society
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• v.24 no.4
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• pp.136-142
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• 2020

Apolipoprotein B-100 (apo B-100), the main protein component that makes up LDL (Low density lipoprotein), consists of 4,536 amino acids and serves to combine with the LDL receptor. The oxidized LDL peptides by malondialdehyde (MDA) or acetylation in vivo were act as immunoglobulin (Ig) antigens and peptide groups were classified into 7 peptide groups with subsequent 20 amino acids (P1-P302). The biomimetic peptide P99 (KGTYG LSCQR DPNTG RLNGE) out of B-group peptides carrying the highest value of IgM antigens were selected for structural studies that may provide antigen specificity. Circular Dichroism (CD) spectra were measured for peptide secondary structure in the range of 190-260 nm. Experimental results show that P99 has pseudo α-helice and random coil structure. Homonuclear (COSY, TOCSY, NOESY) 2D-NMR experiments were carried out for NMR signal assignments and structure determination for P99. On the basis of these completely assigned NMR spectra and proton distance information, distance geometry (DG) and molecular dynamic (MD) were carried out to determine the structures of P99. The proposed structure was selected by comparisons between experimental NOE spectra and back-calculated 2D NOE results from determined structure showing acceptable agreement. The total Root-Mean-Square-Deviation (RMSD) value of P99 obtained upon superposition of all atoms were in the set range. The solution state P99 has mixed structure of pseudo α-helix and β-turn(Gln[9] to Thr[13]). These NMR results are well consistent with secondary structure from experimental results of circular dichroism. Structural studies based on NMR may contribute to the prevent oxidation studies of atherosclerosis and observed conformational characteristics of apo B-100 in LDL using monoclonal antibodies.