• Journal of the Korean Chemical Society
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• v.28 no.1
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• pp.34-40
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• 1984

The reorientational motion of $C_6F_6$ in neat liquid is investigated in the temperature range 293∼333K by analyzing ${\nu}_2$ and ${\nu}_16$ bands of its Raman spectrum. Diffusion constants for the tumbling ($D_{\bo}$) and spinning ($D_{\parallel}$) motions are determined. The reorientation of the molecule seems to be distinctly anisotropic. Based on the hydrodynamic model, the tumbling motion of the figure axis of $C_6F_6$ is largely diffusional. On the other hand, the spinning motion of the same axis looks mostly inertial.

• Korea-Australia Rheology Journal
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• v.19 no.3
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• pp.147-156
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• 2007

The orientation and deformation of polymer chains in a confined channel flow has been investigated. The polymer chain was modeled as a Finitely Extensible Nonlinear Elastic (FENE) dumbbell. The Brownian configuration field method was extended to take the interaction between the flow and local chain dynamics into account. Drag and Brownian forces were treated as anisotropic in order to reflect the influence of the wall in the confined flow. Both Poiseuille flow and 4 : 1 contraction flow were considered. Of particular interest was molecular tumbling of polymer chains near the wall. It was strongly influenced by anisotropic drag and high shear close to the wall. We discussed the mechanism of this particular behavior in terms of the governing forces. The dumbbell configuration was determined not only by the wall interaction but also by the flow type of the geometric origin. The effect of extensional flow on dumbbell configuration was also discussed by comparing with the Poiseuille flow.

• Bulletin of the Korean Chemical Society
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• v.4 no.1
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• pp.10-14
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• 1983

Anisotropic rotation of C$_{6}$F$_{6}$ in neat liquid is investigated by the analysis of the ν$_{1}$ and ν$_{15}$ (both C-F stretching) bands of Raman spectrum and diffusion constants for the spinning (D$_{II}$) and tumbling (D$_{⊥}$) motions are obtained by the rotational dffusion theory. The same analysis is also carried out for the ν$_{2}$ and ν$_{16}$ (both C-C stretching) bands and both results are compared with the results obtained for benzene in neat liquid. The results show that the reorientation of C$_{6}$F$_{6}$ is highly anisotropic and the anisotropy is greater for C$_{6}$F$_{6}$ than benzene. This is due to the fact that the spinning rate is about the same but the tumbling rate is sharply reduced for C$_{6}$F$_{6}$.

• Journal of the Korean Magnetic Resonance Society
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• v.18 no.2
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• pp.47-51
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• 2014

Larger proteins (above molecular weight 50 kDa) usually show slow motional tumbling in solution, which facilitates the decay of NMR signal, resulting in poor signal-to-noise. In the past twenty years, researchers have tried to overcome this problem with higher molecular weight by improvement of hardware (higher magnetic field and cryoprobe), optimization of pulse sequences for lager molecules, and development of isotope-labeling techniques. Actually, GroEL/ES complex (${\approx}$ 900 kDa) was successfully studied using combination of above techniques. Among the techniques used in large molecular studies, the impact of isotope-labeling for large molecules study is summarized and discussed here.

• Journal of the Korean Chemical Society
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• v.26 no.4
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• pp.205-209
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• 1982

Anisotropic rotation of $CDCl_3$ in neat liquid is investigated by the analysis of ${\nu}_1$ band of Raman spectrum and the diffusion constant($D_{\perp}$) for the tumbling motion is obtained. The diffusion constant ($D_{II}$) for the spinning motion is obtained from the above $D_{\perp}$ value and the chlorine-35 nuclear quadrupole relaxation time. The diffusion constants thus obtained seem to agree very well with the ones obtained from $^2H$ and $^35C$l in NQR results within experimental errors. The data suggest fairly anisotropic character of reorientational motions in neat $CDCl_3$.

• Korean Journal of Digital Imaging in Medicine
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• v.15 no.2
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• pp.63-68
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• 2013

Purpose : The relaxation times of tissue in MRI depend on strength of magnetic field, morphology of nuclear, viscosity, size of molecules and temperature. This study intended to analyze quantitatively that materials' temperatures have effects on T1 and T2 relaxation times without changing of other conditions. Materials and Methods : The equipment was used MAGNETOM SKYRA of 3.0T(SIEMENS, Erlagen, Germany), 32 channel spine coil and Gd-DTPA water concentration phantom. To find out T1 relaxation time, Inversion Recovery Spin Echo sequences were used at 50, 400, 1100, 2500 ms of TI. To find out T2 relaxation time, Multi Echo Spin Echo sequences were used at 30, 60, 90, 120, 150, 180, 210, 240, 270 ms of TE. This experiment was scanned with 5 steps from 25 to $45^{\circ}C$. next, using MRmap(Messroghli, BMC Medical Imaging, 2012) T1 and T2 relaxation times were mapped. on the Piview STAR v5.0(Infinitt, Seoul, Korea) 5 steps were measured as the same ROI, and then mean values were calculated. Correlation between the temperatures and relaxation times were analyzed by SPSS(version 17.0, Chicago, IL, USA). Results : According to increase of temperatures, T1 relaxation times were $214.39{\pm}0.25$, $236.02{\pm}0.87$, $267.47{\pm}0.48$, $299.44{\pm}0.64$, $330.19{\pm}1.72$ ms. T2 relaxation times were $180.17{\pm}0.27$, $197.17{\pm}0.44$, $217.92{\pm}0.39$, $239.89{\pm}0.53$, $257.40{\pm}1.77$ ms. With the correlation analysis, the correlation coefficients of T1 and T2 relaxation times were statistically significant at 0.998 and 0.999 (p< 0.05). Conclusion : T1 and T2 relaxation times are increased as temperature of tissue goes up. In conclusion, we suggest to recognize errors of relaxation time caused local temperature's differences, and consider external factors as well in the quantitative analysis of relaxation time or clinical tests.

• Investigative Magnetic Resonance Imaging
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• v.3 no.2
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• pp.159-166
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• 1999

Purpose : To evaluate the effect of rotational correlation time (${\tau}_R$) and the possible related changes of other parameters, ${\tau}_M,{\;}{\tau}_S,{\;}and{\;}(\tau}_V$ of gadolinium (Gd) chelate on T1 relaxation enhancement in two pool model. Materials and Methods : The NMRD (Nuclear Magnetic Relaxation Dispersion) profiles were simulated from 0.02 MHz to 800 MHz proton Larmor frequency for different values of rotational correlation times based on Solomon-Bloembergen equation for inner-sphere relaxation enhancement. To include both unbound pool (pool A) and bound pool (pool B), the relaxivity was divided by contribution from unbound pool and bound pool. The rotational correlation time for pool A was fixed at the value of 0.1 ns, which is a typical value for low molecular weight complexes such as Gd-DTPA in solution and ${\tau}_R$ for pool B was changed from 0.1 ns to 20 ns to allow the slower rotation by binding to macromolecule. The fractional factor of was also adjusted from 0 to 1.0 to simulate different binding ratios to macromolecule. Since the binding of Gd-chelate to macromolecule cab alter the electronic environment of Gd ion and also the degree of bulk water access to hydration site of Gd-chelate, the effects of these parameters were also included. Results : The result shows that low field profiles, ranged from 0.02 to 40 MHz, and dominated by contribution from bound pool, which is bound to macromolecule regardless of binding ratios. In addition, as more Gd-chelate bound to macromolecule, sharp increase of relaxivity at higher field occurs. The NMRD profiles for different values of ${\tau}_S$ show the enormous increase of low field profile whereas relaxivity at high field is not affected by ${\tau}_S$. On the other hand, the change in ${\tau}$V does not affect low field profile but strongly in fluences on both inflection fie이 and the maximum relaxivity value. The results shows a fluences on both inflection field and the maximum relaxivity value. The results shows a parabolic dependence of relaxivity on ${\tau}_M$. Conclusion : Binding of Gd-chelate to a macromolecule causes slower rotational tumbling of Gd-chelate and would result in relaxation enhancement, especially in clinical imaging field. However, binding to macromolecule can change water enchange rate (${\tau}_M$) and electronic relaxation ($T_le$) vis structural deformation of electron environment and the access of bulk water to hydration site of metal-chelate. The clinical utilities of Gd-chelate bound to macromolecule are the less dose requirement, the tissue specificity, and the better perfusion and intravascular agents.