Font Size: a A A

Studies On Kinetic Properties Involved In Chemical Exchange By Dynamic Nuclear Magnetic Resonance

Posted on:2003-01-11Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y H ZhangFull Text:PDF
GTID:1101360185477871Subject:Radio Physics
Abstract/Summary:PDF Full Text Request
This dissertation is focused on some problems of chemical exchange in NMR. By demonstrating a few typical exchange systems, the dissertation undertakes theoretical and experimental study on several kinetic problems concerning chemical exchange in liquid solutions using DNMR (Dynamic Nuclear Magnetic Resonance) methods. Four aspects are covered: (a) the relaxation law of inversion-recovery involved in two-site exchange, (b) diffusion-independent proton exchange kinetics based on the mechanism of chemical-bond/hydrogen-bond exchange, (c) diffusion-controlled halogen exchange kinetics, (d) deuterium discrimination in P-H/P-D exchange of phosphorous acid.Relaxation time is a useful NMR parameter, which is normally measured by IR (Inversion Recovery) method with mono-exponential fitting. But for a two-site exchange system, AB (R1A1B is assumed; R1 represents relaxation rate), the recovery of invertedmagnetization follows a bi-exponential law, C+e-λ+t + C-e-λ-t with λ+>λ-. The theoreticalsimulation in the dissertation shows one of the four coefficients in the AB system must be positive, while the other three must be negative. The bi-exponential function can be approximated to a mono-exponential law only when the system satisfies one of the four conditions, i.e. slow exchange limit, fast exchange limit, small relaxation-different limit or large population-different limit (only to the most populated spin). Then a precise relaxation time can be obtained from IR measurement.Hydrogen exchange belongs to an important type of exchange reactions in biochemistry, and plays a crucial role in structure biology. As far as its mechanism is concerned, it is commonly accepted that hydrogen exchange in solutions is diffusion-controlled. However, the quantitative relationship between exchange and diffusion has not yet experimentally established. In the dissertation, the relationship is studied experimentally in two solution systems of hydrogen exchange under thermal equilibrium, one of which is the DMSO-d6 solution of quercetin, and the other is the...
Keywords/Search Tags:DNMR, chemical exchange, molecular self-diffusion, NMR relaxation, inversion recovery, data fitting, bi-exponential, restraints, approximation to mono-exponential, quercetin, DMSO-d6, residual water, ammonium aqueous solution, hydrogen exchange
PDF Full Text Request
Related items