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안상두,박태정,최종인 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.5
Molecular structures of the various conformational stereoisomers of 2,8,14,20-cyanophenyl pyrogallol[4]arenes 1 were optimized using the mPW1PW91 (hybrid Hartree-Fock density functional) calculation method. The total electronic and Gibbs free energies and the normal vibrational frequencies of the different structures from three major conformations (CHAIR, TABLE, and 1,2-Alternate) of the four stereoisomers [1(rccc), 1(rcct), 1(rctt), and 1(rtct)] were analyzed. The mPW1PW91/6-31G(d,p) calculations suggested that 1(rcct)1,2-A, 1(rctt)CHAIR, and 1(rtct)CHAIR were the more stable conformations of the respective stereoisomers. Hydrogen bonding is the primary factor for the relative stabilities of the various conformational isomers, and maximizing the π-π interaction between the cyanophenyl rings is the secondary factor. The calculated IR spectra of the more stable conformers [1(rctt)CHAIR, 1(rcct)1,2-A, 1(rtct)CHAIR] were compared with the experimental IR spectrum of 1(rctt)CHAIR.
DFT Calculated Structures and IR Spectra of the Conformers of para-Bromocalix[4]aryl Derivatives
안상두,이동국,최종인 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.12
Molecular structures of the various conformers of para-bromocalix[4]aryl derivatives 1–4 were optimized using the DFT B3LYP calculation method. The total electronic and Gibbs free energies and normal vibrational frequencies of the different structures (CONE, partial cone (PACO), 1,2-Alternate(1,2-A) and 1,3- Alternate(1,3-A)) were calculated from the four kinds of para-bromocalix[4]aryl derivatives. The B3LYP/6- 31G(d,p) calculations suggested the following: 1(PACO) is the most stable among four conformers of 1; 2(CONE) is the most stable among five conformers of 2; 3(PACO) is the most stable among four conformers of 3; 4(1,3-A) is the most stable among four conformers of 4. All the most stable structures optimized by the B3LYP calculation method were in accordance with the experimental crystal structures of 1–4. The calculated IR spectra of the various conformers (CONE, PACO, 1,2-A and 1,3-A) of 1–4 were compared.
안상두,이상혁 한국자기공명학회 1999 Journal of the Korean Magnetic Resonance Society Vol.3 No.2
The dynamics of the dipolar demagnetizing field is investigated by numerical simulation. The effects of radiation damping, molecular diffusion, and relaxation processes on the dipolar demagnetizing field are examined in terms of the modulation pattern of the z-magnetization and the signal intensity variation. Simulations for multi-components suggest applications for sensitivity enhancement in favorable conditions.
A Systematic Study on MR Contrast Agents for Constructing Specific Relaxation Times
안상두,조재현,이철현,조장근 한국자기공명학회 2010 Journal of the Korean Magnetic Resonance Society Vol.14 No.1
The water proton relaxation rates increase linearly with concentrations of contrast agents, and could be expressed as a function of the concentrations. In this paper, we have investigated MR properties of two different contrast agents, GdCl3 and CoCl2. Relaxivity coefficients were calculated from individual contrast agent solutions, and used for predicting relaxation rates at mixtures of two contrast agents. From the experimental results, we have discussed the feasibility of constructing water solutions with the desired relaxation times using specific mixtures of contrast agents.
안상두,Sudeuk Kim,Yun Jung Lee,Hyun Hye Joo 한국자기공명학회 2008 Journal of the Korean Magnetic Resonance Society Vol.12 No.1
Convection effect in liquids has been one of the main targets to be overcome in pulsed-field-gradient NMR measurements of self-diffusion coefficients since the temperature gradient along the sample tube generated by the heating and/or cooling process causes the effect, resulting in additional diffusion. It is known that the capillary is the most appropriate tube type for diffusion experiments at variable temperatures since the narrower tube suppresses convection effectively. For evaluating the properties of hydrogen bonding, diffusion coefficients of the K+-complexed and free valinomycin in a micro tube have been determined at various temperatures. From the analysis of the obtained diffusion coefficient values, we could conclude that the intramolecular hydrogen bonding in both of the K+-complexed and free valinomycin in a non-polar solvent is preserved over the observed temperature range, and the temperature dependence of hydrogen bonding is more pronounced in free valinomycin. It is also thought that there is no big change in the radius of the K+-complexed as temperature is varied, and the ratio of overall radius, rcomplex/rfree is slightly decreased as temperature rises.
Magnetic Resonance Imaging with Intermolecular Double Quantum Coherences
안상두 한국자기공명학회 2004 Journal of the Korean Magnetic Resonance Society Vol.8 No.2
Recently a new method for magnetic resonance imaging based on the detection of relatively strong signal from intermolecular multiple quantum coherences (iMQCs) is reported. Such a signal would not be observable in the conventional framework of magnetic resonance; it originates in long-range dipolar couplings that are traditionally ignored. In this paper, we present the results of experimental studies to assess the feasibility of intermolecular double quantum coherences (iDQCs) imaging in humans. We show that the iDQC images are readily observable at 4T and that they do indeed provide different contrast than appears in conventional images 영어논문
정기주,안상두 한국자기공명학회 2006 Journal of the Korean Magnetic Resonance Society Vol.10 No.1
With a simple pulse sequence (/2 – {gradient, duration T} – acquisition) in solution NMR, detected signal has slowly grown up to percents of the equilibrium magnetization. The source of this unusual resurrection of dephased magnetization after a crushed gradient is cross-correlated effects of radiation damping and the distant dipolar field, which has been demonstrated by a numerical simulation and theoretical analysis. 영어논문