Rates of Paramagnetic Pulse Reactions by Nuclear Magnetic Resonance

Abstract

Certain fast chemical reactions involving both paramagnetic and diamagnetic molecular species are termed "paramagnetic pulse" reactions when each reaction event results in a change in a large hypedine magnetic field acting at one or more of the molecular nuclei. The frequency distribution of the magnetic pulses is directly related to the reaction rate. The hyperfine intensity and frequency distribution of the paramagnetic pulses affects the nuclear magnetic resonance (NMR) line shapes. The Bloch equations are used to establish a quantitative relation between nuclear resonance line shape, nuclear, and electron relaxation times, and the reaction rate. The theory is discussed in terms of the Cu 63 NMR work of McConnell and Weaver on electron exchange between Cu++ and Cu+ ions in hydrochloric acid solutions, and the HI NMR work of Bruce, Norberg, and Weissman on the electron exchange between neutral and positive ion molecules of N,N'-tetramethyI-p-phenylenediamine.

Nuclear magnetic resonance studies of the coordination of vanadyl complexes in solution and the rate of elimination of coordinated water molecules

“…The transverse relaxation of the coordinated nuclei arising from scalar coupling is expected to be given by (7)4,9…”

“…scalar coupling between the unpaired electron and the nuclear spin 17. Assuming that the shift of the 0 resonance in the bulk water(10) is entirely due to fast water exchange from the axial position, Reuben and Fiat 3 fow1d A/h = 2.06 x 10 6 cps for 0 17 of the axial water.The enhanced nuclear relaxation could arise from dipolar coupling(8) and quadrupolar coupling(9) as well as scalar coupling(7).To distinguish between the three possible relaxation mechanisms we have studied the data on the proton nuclear relaxation in solutions of V0 2 + -UCRL-17526, ions, which have been reported by Hausser and Laukien,~l and by Mazitov and Rivkind. 5 Hausser and Laukien's data are given in Fig.…”

Toward understanding transverse relaxation in human brain through its field dependence

“…As our measurements were performed with rather long echo times (≥26 ms) and a single exponential function was fitted to the obtained data, only the relaxation rate of the slow‐relaxing site ( R 2s ) was considered as expressed by where R 2s0 and R 2f0 are the intrinsic R 2 values due to dipolar interactions at the two relaxing sites (25), and k f and k s are the exchange rates from the fast‐relaxing site to the slow‐relaxing site and vice versa, respectively. k f and k s obey the McConnel relationship P f k f = P s k s , where P f and P s are populations of fast and slow sites, respectively (26). The size of the fast‐relaxing (i.e., slow tumbling with long rotational correlation time τ c ) proton pool was set to the literature value of f M .…”

A variable temperature study of the transport properties of aqueous solutions of VOSO4 and NH4VO3 in 2 M H2SO4

“…The first involves relaxation through a change in the precessional frequency that results from the nuclei exchange between the bulk of the solution and the coordination sites of the metal ion [21]. The second, called the 'T 2m mechanism', involves the fast relaxation of the coordinated nuclei.…”