Dynamic nuclear polarization application

Among NMR methods providing insight into radical ions, chemically induced dynamic nuclear polarization (CIDNP) has proved especially useful it results in enhanced transient signals, in absorption or emission CIDNP effects were first reported in 1967 their application was soon extended to radical ions. The method lends itself to modest time resolution. 

H. R. Ward, "Chemically Induced Dynamic Nuclear Polarization (CIDNP). I. The Phenomenon, Examples, and Applications, Accfs. Chem. Res. 5, 18 (1972). 

The second approach is the use of the dynamic nuclear polarization (DNP) detection principle. Dorn and co-workers have pioneered the application of this technique [9,10], Whereas the NOE enhancement of 13C nuclei in the conventional 13C H recording is dependent upon the 7h/7c ratio (NOE = Th/ Tc = 2 1), the DNP enhancement relates to the ye/yuc ratio (2640 1). In an electron-nucleus spinsystem, the electron-electron transitions are saturated by microwave irradiation and magnetization transfer from electron to nucleus (Overhauser effect) occurs via a scalar and/or dipolar mechanism. The DNP enhancement, A, is described by the following equation ... 

Nuclear magnetic resonance has proved to be an invaluable technique for many applications and it has been used prominently in the characterization of organic radical ions. We mention three areas of application in this context selective chemical shift differences differential line broadening and chemically induced dynamic nuclear polarization. Each of these methods has provided insights into the structures and reactivities of numerous radical ions. 

Whereas NMR spectroscopy is generally applied to the diamagnetic allyl, pentadienyl, or cyclopentadienyl cations or anions, this technique is generally not applicable to the analogous radical species, although CIDNP (chemically induced dynamic nuclear polarization) has been observed for allyl140 and pentadienyl radical species139. More useful for the radicals, naturally, is EPR spectroscopy. 

The first discovery of chemically induced dynamic electron polarization (CIDEP) was made by Fessenden and Schuler in 1963 (58). These authors observed the abnormal spectra of the H atoms produced during the irradiation of liquid methane. The low-field line in the esr spectrum was inverted compared to the corresponding high-field line. The related chemically induced dynamic nuclear polarization effect (CIDNP) was reported independently four years later by Bargon et al. (22) and by Ward and Lawler (134). Because of the wider application of nmr in chemistry, the CIDNP effect immediately attracted considerable theoretical and experimental attention, and an elegant theory based on a radical-pair model (RPM) was advanced to explain the effect. The remarkable development of the radical-pair theory has obviously brought cross-fertilization to the then-lesser-known CIDEP phenomenon. 

Porter N A, Marnett L J, Lochmuller C H, Closs G L and Shobtaki M 1972 Application of chemically induced dynamic nuclear polarization to a study of the decomposition of unsymmetric azo compounds J. 

Pavlova A, McCamey ER, Peterson DW, Dahlquist EW, Lew J, Han S (2009) Site-specific dynamic nuclear polarization of hydration water as a generally applicable approach to monitor protein aggregation. Phys Chem Chem Phys ll(31) 6833-6839... 

Chemically Induced Dynamic Nuclear Polarization (CIDNP) This term has been used to describe the enhancement of nuclear spin polarization observed In the NMR spectra of compounds undergoing radical reactions. Some exciting applications are described In Chapter X. 

Enhanced NMR spectroscopy by dynamic nuclear polarization (DNP) will become a very promising technique for a broad range of applications in heterogeneous catalysis. In [60] it is shown that surface NMR spectra can be greatly enhanced using... 

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