Chemically Induced Dynamic Nuclear Polarization During Irradiation of Phenol in the Presence of Amides

1975 ◽  
Vol 53 (16) ◽  
pp. 2459-2464
Author(s):  
Shiv P. Vaish ◽  
Holger E. Chen ◽  
Micha Tomkiewicz ◽  
Robert D. McAlpine ◽  
Michael Cocivera
Keyword(s):  
Carbonyl Group ◽  
Spin Polarization ◽  
Dynamic Nuclear Polarization ◽  
Nuclear Spin ◽  
Nuclear Polarization ◽  
Radical Pair ◽  
Hydroxybenzoic Acid ◽  
Nuclear Spin Polarization ◽  
Ph Values ◽  
Chemically Induced

Irradiation of D2O solutions containing various phenols with aliphatic amides at pH values between 9 and 12 results in nuclear spin polarization which is observed as n.m.r. emission signals during irradiation. No polarization is observed for the phenols which include tyrosine, cresol, p-hydroxybenzoic acid, phenol, and others. For the amides which include acetamide, propionamide, N-methylacetamide, and N,N-dimethylacetamide, polarization was observed for only the protons on the carbon bonded to the carbonyl group. Because excited phenolate ions are known to eject electrons, it is proposed that the radical RĊ(O−)NR2 is formed by reaction of the amide with the hydrated electron. The polarization observed for the amides can be explained by reaction of RĊ(O−)NR2 with a benzosemiquinone radical via a radical pair.

Dynamical Nuclear Polarization

2018 ◽  
Author(s):  
M. M. Glazov
Keyword(s):  
Spin Polarization ◽  
Nuclear Spin ◽  
Nuclear Polarization ◽  
Magnetic Moments ◽  
Nonlinear Effects ◽  
Many Body ◽  
Nuclear Spin Polarization ◽  
Optical Resonances ◽  
Dynamical Nuclear Polarization ◽  
Temperature Concept

The transfer of nonequilibrium spin polarization between the electron and nuclear subsystems is studied in detail. Usually, a thermal orientation of nuclei in magnetic field is negligible due to their small magnetic moments, but if electron spins are optically oriented, efficient nuclear spin polarization can occur. The microscopic approach to the dynamical nuclear polarization effect based on the kinetic equation method, along with a phenomenological but very powerful description of dynamical nuclear polarization in terms of the nuclear spin temperature concept is given. In this way, one can account for the interaction between neighbouring nuclei without solving a complex many-body problem. The hyperfine interaction also induces the feedback of polarized nuclei on the electron spin system giving rise to a number of nonlinear effects: bistability of nuclear spin polarization and anomalous Hanle effect, dragging and locking of optical resonances in quantum dots. Theory is illustrated by experimental data on dynamical nuclear polarization.

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