Resonance condition aqueous solutions

An illustrative example is the work of Clark et al, on the conformation of poly(vinyl pyrrolidone) (PVP) adsorbed on silica 0). These authors determined bound fractions from magnetic resonance experiments. In one instance they added acetone to an aqueous solution of PVP in order to achieve theta conditions for this polymer. They expected to observe an increase in the bound fraction on the basis of solvency effects as predicted by all modern polymer adsorption theory (2-6), but found exactly the opposite effect. Their explanation was plausible, namely that acetone, with ability to adsorb strongly on silica due to its carbonyl group, would be able to partially displace the polymer by competing for the available surface sites. 

Measurements of the chemical composition of an aqueous solution phase are interpreted commonly to provide experimental evidence for either adsorption or surface precipitation mechanisms in sorption processes. The conceptual aspects of these measurements vis-a-vis their usefulness in distinguishing adsorption from precipitation phenomena are reviewed critically. It is concluded that the inherently macroscopic, indirect nature of the data produced by such measurements limit their applicability to determine sorption mechanisms in a fundamental way. Surface spectroscopy (optical or magnetic resonance), although not a fully developed experimental technique for aqueous colloidal systems, appears to offer the best hope for a truly molecular-level probe of the interfacial region that can discriminate among the structures that arise there from diverse chemical conditions. 

Fig. 12. Experimental and calculated NMRD profiles for GdEDTA in aqueous solution in the presence (upper curve) and absence (lower curve) of bovine serum albumin. Reprinted from J. Magn. Reson. vol. 162, Kruk, D. Kowalewski, J., Nuclear Spin Relaxation in Paramagnetic Systems (S > 1) under Fast Rotation Conditions , pp. 229-240, Copyright 2003, with permission from Elsevier.

Nishimoto S, Hatta H, Ueshima H, Kagiya T (1992) 1-(5 -Fluoro-6 -hydroxy-5, 6 -dihydrouracil-5 -yl)-5-fluorouracil,a novel N(1)-C(5) linked dimer that releases 5-fluorouracil by radiation activation under hypoxic conditions. J Med Chem 35 2711-2712 Norman ROC, Storey PM, West PR (1970) Electron spin resonance studies, part XXV. Reactions of the sulphate radical anion with organic compounds. J Chem Soc (B) 1087-1095 Novais HM, Steenken S (1986) ESR studies of electron and hydrogen adducts of thymine and uracil and their derivatives and of 4,6-dihydroxypyrimidines in aqueous solution. Comparison with data from solid state. The protonation at carbon of the electron adducts. J Am Chem Soc 108 1-6... 

Raman scattering spectrometry has some advantages over an infrared (IR) spectrometry in the sensitivity, the space resolution, and the applicability to aqueous solution. It can attain high sensitivity, when it is performed under the resonance Raman condition, or under the surface enhanced condition, where silver or gold nanoparticle is used as a source of plasmon. These techniques have been applied successfully for the measurement of extremely small amount of molecules adsorbed at the liquid-liquid interfacial region. 

Electron Paramagnetic Resonance Spectra. Only two of these complexes exhibit well-resolved EPR spectra. A narrow, isotropic signal observed at g = 2.005 for the trinuclear complex 12 at low temperatures is consistent with an S = 1/2 ground state169), but a detailed description of the electronic properties of the complex remains to be developed. The [Fe(MoS4)2]3 ion shows a rhombic S = 3/2 EPR spectrum that is very solvent dependent and, under certain conditions, is somewhat similar in apperance to that of FeMo-com). For example, in frozen aqueous solution, the apparent g values are 5.3,2.6, and 1.7181). If complex 14 also proves to have an S = 3/2 ground state, a somewhat similar EPR spectrum at low temperature would be expected as well. 

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