Dynamic nuclear polarization

Y nuclei such as Si, and by cross-polarization (a process called indirect DNP). DNP-NMR has first been successfully applied to biologically relevant molecules and more recently in materials science to an increasingly large range of nuclei [8-13]. Efforts have been targeted to the introduction of new radicals [14,15], especially biradicals, to reach higher DNP enhancement factors in terms of sensitivity. Commercial equipment is now available. Examples illustrating the potentialities of DNP experiments to characterize sol-gel materials are presented in Section 20.4. 

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Lawler R G 1967 Chemically Induced dynamic nuclear polarization J. Am. Chem. Soc. 89 5519-21... 

Kaptein R and Oosterhoff J L 1969 Chemically Induced dynamic nuclear polarization III (anomalous multiplets of radical coupling and disproportionation products) Chem. Phys. Lett. 4 214-16... 

Goez M 1995 An introduction to chemically induced dynamic nuclear polarization Concepts Magn. Reson. 7 69-86... 

Kaptein R 1971 Simple rules for chemically induced dynamic nuclear polarization J. Chem. See. Chem. Commun. 732-3... 

Morozova O B, Tsentalovich Y P, Yurkovskaya A V and Sagdeev R Z 1998 Consecutive biradicals during the photolysis of 2,12-dihydroxy-2,12-dimethylcyclododecanone low- and high-field chemically induced dynamic nuclear polarizations (CIDNP) study J. Rhys. Chem. A 102 3492-7... 

Carboxamides, formation from ArNj 243 2-Carboxybenzenediazonium zwitterion, see 2-Diazoniobenzenecarboxylate Carboxy-de-diazoniation 241 f. Carcinogenicity 319 Chemically induced dynamic nuclear polarization, see CIDNP Chloro-de-diazoniation 194, 230ff., 247, 270, 277... 

CIDNP chemically induced dynamic nuclear polarization... 

Methods of disturbing the Boltzmann distribution of nuclear spin states were known long before the phenomenon of CIDNP was recognized. All of these involve multiple resonance techniques (e.g. INDOR, the Nuclear Overhauser Effect) and all depend on spin-lattice relaxation processes for the development of polarization. The effect is referred to as dynamic nuclear polarization (DNP) (for a review, see Hausser and Stehlik, 1968). The observed changes in the intensity of lines in the n.m.r. spectrum are small, however, reflecting the small changes induced in the Boltzmann distribution. 

Kaptein, R. (1971b). Chemically Induced Dynamic Nuclear Polarization , Thesis, Leiden. 

Stevenson, S. and Dorn, H. C., 13C dynamic nuclear polarization a detector for continuous-flow, on-line chromatography, Anal. Chem., 66, 2993, 1994. 

Chemically Induced Dynamic Nuclear Polarization Complete Neglect of Differential Overlap cyclopentadienyl diethyl azodicarboxylate... 

Observation of spin-polarized products resulting from these radical pairs by the method of chemically induced dynamic nuclear polarization (CIDNP)<67) was accomplished by photolysis in the probe of an NMR spectrometer using perfluoromethylcyclohexane as solvent. The results obtained were consistent with nuclear spin polarization steps involving radical pairs formed from dissociated radicals and also directly from excited states, although the former could not be detected in carbon tetrachloride, probably due to radical scavenging by the solvent. It was not possible to determine the fraction of the reaction proceeding by singlet and triplet radical pairs.<68)... 

Using the OPENCORE spectrometer, a research group led by M. Kitagawa in Osaka have developed an experimental setup for dynamic nuclear polarization (DNP) using electron spins in the photo-excited triplet state. This nuclear hyperpolarization technique, called hereafter triplet DNP,... 

K. Takeda, Triplet State Dynamic Nuclear Polarization. VDM Verlag, 2009. 

Griffin RG, Prisner TF (2010) High field dynamic nuclear polarization-the renaissance. Phys Chem Chem Phys 12 5737-5740... 

The chemically induced dynamic nuclear polarization (DNP) opened perspective to study products formed from free radicals [102], The basis of this study is the difference in NMR spectra of normal molecules and those formed from free radicals and radical pairs. The molecules formed from radicals have an abnormal NMR spectrum with lines of emission and abnormal absorption [102]. DNP spectra help to obtain the following mechanistic information ... 

On the other hand, in accord with the free radical mechanism peroxynitrite is dissociated into free radicals, which are supposed to be genuine reactive species. Although free radical mechanism was proposed as early as in 1970 [111], for some time it was not considered to be a reliable one because a great confusion ensued during the next two decades because of misinterpretations of inconclusive experiments, sometimes stimulated by improper thermodynamic estimations [85]. The latest experimental data supported its reliability [107-109]. Among them, the formation of dityrosine in the reaction with tyrosine and 15N chemically induced dynamic nuclear polarization (CIDNP) in the NMR spectra of the products of peroxynitrite reactions are probably the most convincing evidences (see below). 

Finally, Podoplelov and coworkers41 have prepared trimethyltin hydride and benzyltrimethyltin labelled with tin-117 from a tin sample enriched to 92% in 117Sn. The photochemical reaction between dibenzyl ketone and trimethyltin-117 hydride was used to investigate the chemically induced dynamic nuclear polarization of tin-containing radicals. 

For more complex spin systems, a computer program PHIP+ has been developed [13, 45] which allows the expected PHIP spectra to be calculated from the chemical shifts and coupling constants of the products. Depending upon which proton pair in the product molecule stems from p-H2, different - but characteristic - polarization patterns result [14]. The patterns also depend on the sign of the coupling constants. Simple sign rules governing the relative sequence of the emission and absorption lines in the PHIP spectra (i.e., their phase ) can be formulated in similar manner to the Kaptein Rules of chemically induced dynamic nuclear polarization (CIDNP) [15]. 

Further evidence for the formation of alkene radical cations derives from the work of Giese, Rist, and coworkers who observed a chemically induced dynamic nuclear polarization (CIDNP) effect on the dihydrofuran 6 arising from fragmentation of radical 5 and electron transfer from the benzoyl radical within the solvent cage (Scheme 6) [67]. 

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