Dynamic nuclear polarization chemical systems

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]. 

Lehnig M (2001) N-15 Chemically induced dynamic nuclear polarization during reaction of N-acetyl-L-tyrosine with the nitrating systems nitrite/hydrogen peroxide/horseradish peroxidase and nitrite/hypochloric acid. Arch Biochem Biophys 393 245-254... 

NMR imaging was used to study the spatial distribution of molecules with chemically induced dynamic nuclear polarization. It is shown that heating of a system during the photolysis can cause a highly nonuniform distribution of reaction products due to a convective effect. 

Key Words Chemically induced dynamic nuclear polarization, Photochemistry, Paramagnetic NMR, NMR in reacting systems. 

The photochemistry of this series of benzyl/allyl systems 34 was studied by chemically induced dynamic nuclear polarization (CIDNP) experiments [31]. Contrary to the assertion made here, the authors concluded that the formation of the (unisolated) sulfme 35 was an electrocyclic process, under either direct or sensitized irradiation, because no CIDNP signals were observed. On the other hand, CIDNP results for the acyclic 38 suggest that homolytic cleavage occurs on either side of the sulfoxide. Products were not identified. 

When discussing the general aspects of FTNMR, we have to remember that all principal statements about Fourier methods have been introduced for a strictly linear system (mechanical oscillator) in Chapter 1. In Chapter 2, on the other hand, we have seen that the nuclear spin system is not strictly linear (with Kramer-Kronig-relations between absorption mode and dispersion mode signal >). Moreover, the spin system has to be treated quantummechanically, e.g. by a density matrix formalism. Thus, the question arises what are the conditions under which the Fourier transform of the FID is actually equivalent to the result of a low-field slow-passage experiment Generally, these conditions are obeyed for systems which are at thermal equilibrium just before the initial pulse but are mostly violated for systems in a non-equilibrium state (Oberhauser effect, chemically induced dynamic nuclear polarization, double resonance experiments etc.). 

There are many experimental techniques for the determination of the Spin-Hamiltonian parameters g, Ux, J. D, E. Often applied are Electron Paramagnetic or Spin Resonance (EPR, ESR), Electron Nuclear Double Resonance (ENDOR) or Triple Resonance, Electron-Electron Double Resonance (ELDOR), Nuclear Magnetic Resonance (NMR), occasionally utilizing effects of Chemically Induced Dynamic Nuclear Polarization (CIDNP), Optical Detections of Magnetic Resonance (ODMR) or Microwave Optical Double Resonance (MODR), Laser Magnetic Resonance (LMR), Atomic Beam Spectroscopy, and Muon Spin Rotation (/iSR). The extraction of data from the spectra varies with the methods, the system studied and the physical state of the sample (gas, liquid, unordered or ordered solid). For these procedures the reader is referred to the monographs (D). Further, effective magnetic moments of free radicals are often obtained from static... 

In another class of experiments, hyperpolarized states are generated by spin-sensitive chemical reactions. These include para-hydrogen-induced polarization (PHIP) [3-5] and chemically induced dynamic nuclear polarization (CIDNP) [6-8]. The latter involves non-equilibrium nuclear spin state populations that are produced in chemical reactions that proceed through radical pair intermediates. CIDNP s applicability has been focused towards the study of chemical reactions and the detection of surface exposed residues in proteins [9], but has so far remained limited to specialized chemical systems. 

The existence of the biradicals and the multipHcity of the surfaces on which these are formed have not been demonstrated directly however, experimental results (stereochemistry of the reaction, CIDNP [chemically induced dynamic nuclear polarization], radical trapping experiments, and quantum yield measurements) support their existence. Recently, the mechanism of 1,3-migration and oxa-di-Jt-methane reactions in terms of potential energy surface and decay funnels has been described this also supports the aforementioned mechanistic impHcations. The detailed mechanism, however, depends, in a very subtle way, on the structure of the chromophoric system and the presence of the functional groups. 

Chain processes, free radical, in aliphatic systems involving an electron transfer reaction, 23,271 Charge density-NMR chemical shift correlation in organic ions, 11,125 Chemically induced dynamic nuclear spin polarization and its applications, 10, 53 Chemiluminescence of organic compounds, 18,187... 

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