Dynamic nuclear polarisation

In aniline derivatives (458) the mechanism of this reaction is still not fully settled (459-461). However, the latest results seem to favor a pathway that, applied to 2-nitraminothiazole, would give Scheme 138, where the key step is the formation of a radical ion (223). Reexamination of the original reports on this reaction (16, 374, 378. 462) with EPR and Chemically Induced Dynamic Nuclear Polarisation techniques could be fruitful. 

Dynamic nuclear polarisation (DNP) enhanced 15N CP MAS NMR has been exploited by Mark-Jurkauskas et al.79 in the studies of intermediates of the bacteriorhodopsin photocycle. The data for L intermediate were similar to those found for 13-ds,15-anti retylidene chloride, while those for K intermediate were similar to those of acid blue bacteriorhodopsin in which the Schiff base counterion was neutralised (Table 3). The 15N chemical shifts observed have shown that for bacteriorhodopsin, the Schiff base in K intermediate state loses contact with its counterion and establishes a new one in L intermediate state. The proton energy stored at the beginning in the electrostatic modes has been transformed to torsional modes. The transfer of energy is facilitated by the reduction of bond order alternation in the polyene chain when the counterion interaction is initially broken and is driven by the attraction of the Schiff base to a new counterion. 3D CP MAS experiments of NCOCX, NCACX, CONCA and CAN(CO)CA types have been used in studies of proteorhodopsin.71... 

Since the heroic early mechanistic investigations, there have been two developments of major significance in radical chemistry. The first was the advent of electron spin resonance (ESR) spectroscopy (and the associated technique of chemically induced dynamic nuclear polarisation, CIDNP) [24], which provided structural as well as kinetic information the second is the more recent development of a wide range of synthetically useful radical reactions [20]. Another recent development, the combination of the pulse radiolysis and laser-flash photolysis techniques, is enormously powerful for the study of radicals but beyond the scope of this book. 

Dynamic nuclear polarisation (DNP) To increase sensitivity Magnetisation transferred from unpaired electrons to 13C spins via 1H spins if required. Sensitivity improvement of about 100-fold... 

Cellular Metabolites. - A review of methods for the measurement of ml has been produced with 95 references. It examines the quantitative measurement of ml by mass spectrometry and in vivo NMR. The NMR chemical shifts and /-coupling values of 35 metabolites which can be detected by in vivo or in vitro investigations of the mammalian brain have been published. The principles and recent applications of dynamic nuclear polarisation, which combines the sensitivity to oxygen of EPR and the tractability of NMR imaging, have been reviewed with 244 references. A review of studies of intermediary metabolism, including the use of NMR in the analysis of substrate selection under in vivo conditions, has been produced. A review has been produced, with 74 references, on the study of metabolic flux and subcellular transport of metabolites using NMR. " ... 

Among the nuclear spins, those of the protons are most easily polarised. Nevertheless, the proton spin polarisation reaches only P(H) = 0.25 % in a field of 2.5 Tesla at T = 1 K in about one hour. The time to reach more favourable equilibria at lower temperatures increases dramatically to days and weeks. Proton spins are most easily aligned by dynamic nuclear polarisation (DNP), which is achieved by irradiating the sample with 4 mm microwaves at helium bath temperatures at 0.3 K in a magnetic field of 2.5 T in the presence of an organic radical (e. g. 

Abragam A, Goldman M (1978) Principles of dynamic nuclear polarisation. Rep Prog Phys 41 395... 

An alternative method, termed DNP (Dynamic Nuclear Polarisation), relies on the transfer of polarisation from unpaired electrons onto nuclear spins in the solid state but has been further developed to significantly enhance the sensitivity of solution-state NMR, as described briefly below. The technique has been applied to boost the polarisation levels for low-7 heteronuclear spins in particular and shows most promise to date for and N observation the initial report on the technique described a gain in signal-to-noise in excess of 10,000-fold for both these elements when compared to data collected at thermal equilibrium [115]. The hyperpolarisation of P and Si has also been demonstrated. 

CIDNP chemically induced dynamic nuclear polarisation... 

Dynamic nuclear polarisation study of (CH3)3CN(0-)C(CH3)3 CHCl3 complex. 

The fundamental processes involved in the physical formation of a radiation track and in its subsequent evolution by diffusion and reaction are stochastic in nature. Every track is unique and even identical tracks may evolve differently. Thus most recent simulation methods [5-8] are stochastic in these senses (i.e. for the underlying track and for the diffusion and reaction of the reactive particles that can take place). Unfortunately, these methods ignore the spin-dynamics because of the complexity it introduces. As most radicals in radiation chemistry are paramagnetic species, there is a possibility of spin-controlled reactions and other spin effects such as quantum beats [9], chemically induced dynamic nuclear polarisation (CIDNP) [10-13] and chemically induced dynamic electron polarisation (CIDEP) [11, 12], which would... 

Radical pair theory states that the rate of 5 - To mixing is directly related to the nuclear spin configuration through the hyperflne interaction, which in turn determines the recombination yield. The nuclear spin polarisation generated in both the recombined and escaped products is known as chemically induced dynamic nuclear polarisation [6, 31-33]. 

Lelli, M. D. Gajan, A. Lesage, M. A. Caporini, V. Vitzthum, P. Mieville, F. Heroguel, F. Rascon, A. Roussey, C. Thieuleux, M. Boualleg, L. Veyre, G. Bodenhausen, C. Coperet and L. Emsley. 2011. Fast characterisation of functionalised silica materials by silicon-29 surface-enhanced NMR spectroscopy using dynamic nuclear polarisation./. Awj. Chem. Soc. 133, 2104-2107. 

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