Resonance broadening paramagnetic

The selective reduction of a solvent water resonance can also be achieved in a similar way if the transverse relaxation time of the water protons can be reduced (i.e. the resonance broadened) such that this becomes very much shorter than that of the solutes under investigation. This can be achieved by the addition of suitable paramagnetic relaxation agents (about which the water molecules form a hydration sphere) or by reagents that promote chemical exchange. Ammonium chloride and hydroxylamine have been used to great effect in this way [4,5], as illustrated for the proton spectrum of the reduced arginine... 

The (C Me ) Sm(THF) metal vapor product provided the first opportunity ta see if Smdl) complexes (y =3.5—3.8 Ufi) could be characterized by H NMR spectroscopy (24). Fortunately, the paramagnetism doesn t cause large shifting and broadening of the resonances and hence samarium provides the only Ln(III)/Ln(II) couple in which both partners are NMR accessible. Once the existence and identity of (C Mej- SmdHF) was known, a solution synthesis was developed from KC Me and Sml THF) (44). This system is the preferred preparative route and also provides another soluble organosamarium(II) complex, [(C Me )Sm(THF)2(u-I)]2, under appropriate conditions. This is another xample of how solution studies subsequently catch up to the research targets often identified first in metal vapor reactions. 

This chapter considers the distribution of spin Hamiltonian parameters and their relation to conformational distribution of biomolecular structure. Distribution of a g-value or g-strain leads to an inhomogeneous broadening of the resonance line. Just like the g-value, also the linewidth, W, in general, turns out to be anisotropic, and this has important consequences for powder patterns, that is, for the shape of EPR spectra from randomly oriented molecules. A statistical theory of g-strain is developed, and it is subsequently found that a special case of this theory (the case of full correlation between strain parameters) turns out to properly describe broadening in bioEPR. The possible cause and nature of strain in paramagnetic proteins is discussed. 

Hagen, W.R. 1981. Dislocation strain broadening as a source of anisotropic linewidth and asymmetrical lineshape in the electron paramagnetic resonance spectrum of metal-loproteins and related systems. Journal of Magnetic Resonance 44 447-469. 

Characterization of the modified plastocyanins was by Inductively Coupled Plasma Emission Spectroscopy to analyze for Ru and Cu (1 1 ratio), and by HNMR spectroscopy. In the HNMR characterization the C2H resonance of His59 at 8.2 ppm is seen to be lost due to paramagnetic line broadening effect of the attached Ru(III), Fig. 13 [50]. In a further test it is known that the His59 s of both native plastocyanins react with diethyl pyrocarbonate (DEPC) to give an JV-ethoxyhistidine derivative, (12), which absorbs strongly at 238 nm (e 2750M- cm-i), Fig. 14 [133]. 

The linewidth of the diamagnetic MnOT resonance, fV°, is broadened on the addition of the paramagnetic MnO ", but there is no shift in the signal position, which is proof that we are in the slow-exchange region. The broadened line width is a linear function of added MnOj"... 

Paramagnetic broadening, due to unpaired electrons, is usually much greater than quadrupolar broadening, and the nuclear resonance... 

The broadening of the heme proton-resonances is mainly due to the increase in the rotational correlation time of the heme inside micelle. The increase in linewidth, Aoobs of a paramagnetic complex inside micelles compared to that in simple aqueous or non-aqueous solution is given as [20-22] ... 

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