Browsing by Author "Lin, Chen"

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    Macromolecular dynamics studied by magnetic resonance and neutron scattering
    (1992) Lin, Chen; Rorschach, Harold E., Jr.
    Macromolecular dynamics is important for both understanding biological processes and practical applications such as MR imaging data interpretation. We have used the QNS method to study the dynamics of trypsin chain segments. Trypsin powder and trypsin in D$\sb2$O were studied for temperatures from 100K to 300K. Energy spectra of the scattered neutrons were measured for various neutron momentum transfer. Diffusive type motion of chain segments are observed for trypsin solutions at temperatures above the freezing point, while powder and frozen samples display minimum chain motion. The motion of trypsin chain segments can be fitted by a general "jump-diffusion" model which describes the conformational changes of a macromolecule as transitions between its substates. The diffusion coefficient of the trypsin chain segment is 2.4 $\times$ 10$\sp{-6}$ cm$\sp2$/sec and the average residence time of trypsin in its substates is 1.3 $\times$ 10$\sp{-11}$ second when trypsin is in D$\sb2$O at 300K. We measured the average mean square thermal vibration amplitude of trypsin (0.65 A$\sp2$) which is slightly larger than the results from computer simulations and X-ray diffraction studies. We also have tested macromolecular dynamics theory on poly-acrylic acid. We measured the frequency dependence of proton T$\sb1$ relaxation rates of poly-acrylic acid in D$\sb2$O solutions with different pDs and salt concentrations. Frequency dispersion data analyzed using both a flexible chain model and a stiff chain model give a maximum correlation time of 1.5-2.3 $\times$ 10$\sp{-7}$ second depends on the model. No significant change due pD and salt concentration difference was found.
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    The development and applications of Fourier transformed relaxation measurements in nuclear magnetic resonance (NMR)
    (1988) Lin, Chen; Rorschach, Harold E., Jr.
    A method has been developed to measure the spin-lattice and spin-spin relaxation times of the various components of a multi-component spectrum. By Fourier transforming the free induction decay after the inversion recovery or spin echo pulse sequences, the different frequency components can be resolved and their individual relaxation times can be measured. This method has great advantages over the conventional method of analysis for multiple component decays which are very common in chemical and biological system. Based on this method, many interesting studies can now be done with NMR. The details of this method are presented with a comparison between our method and the conventional method and results and discussion of some applications.