Aqueous solutions Magnetic properties

The development of magnetic resonance techniques coupled with computer time averaging has made the study of enzyme structure and function by these techniques more fruitful. H NMR, 13C NMR and 19F NMR have been used successfully to determine the structure of B 12-compounds in solution. We are rapidly approaching the point where the structure and function of the B 12-coenzymes will be completely understood, and the need for the synthesis and study of simple Bi2-model compounds such as the cobaloximes (3) will be no longer necessary. However, even though studies on the chemistry of B 12-coenzymes is a necessary prerequisite to our understanding of their biochemical role, it is a wrong assumption to expect that the chemical properties of free coenzymes in aqueous solution should be duplicated in the enzymes. 

The three different mechanisms which traditionally describe the ability of a CA to catalyze the water proton nuclear magnetic relaxation present themselves in different degrees of relative importance in determining the overall relaxivity. This latter attribute primarily depends on the structural properties of the CA, the temperature and the pH of the aqueous solution, and on the observation frequency. The CAs that are currently used in clinical practice are low molecular weight hydrophilic monoaqua Gd(III) complexes (Chart 2) that, at 25° C and 20 MHz, possess a relaxivity of about... 

The electronic301 and magnetic properties of mononuclear chromium(III) complexes are quite well understood however there is a distinct tendency for octahedral symmetry to be invoked in cases where the true symmetry is much lower. Chromium(III) is a hard Lewis acid and many stable complexes are formed with oxygen donors. In particular hydroxide complexes are readily formed in aqueous solution, and this may be a problem in synthesis. Substitution at chromium(III) centres is slow302,303 and may well have some associative character in many cases. The kinetic inertness of chromium(III) has led to the resolution of many optically active complexes this work has been extensively reviewed.304... 

Since the first synthesis of mesoporous materials MCM-41 at Mobile Coporation,1 most work carried out in this area has focused on the preparation, characterization and applications of silica-based compounds. Recently, the synthesis of metal oxide-based mesostructured materials has attracted research attention due to their catalytic, electric, magnetic and optical properties.2 5 Although metal sulfides have found widespread applications as semiconductors, electro-optical materials and catalysts, to just name a few, only a few attempts have been reported on the synthesis of metal sulfide-based mesostructured materials. Thus far, mesostructured tin sulfides have proven to be most synthetically accessible in aqueous solution at ambient temperatures.6-7 Physical property studies showed that such materials may have potential to be used as semiconducting liquid crystals in electro-optical displays and chemical sensing applications. In addition, mesostructured thiogermanates8-10 and zinc sulfide with textured mesoporosity after surfactant removal11 have been prepared under hydrothermal conditions. 

The physical properties of the aqueous solutions were studied by Bucknall and coworkers 14 Ray and Bharls studied the magnetic susceptibility of the hexachloro complex. Potassium pentachloroaquomolybdate(III) exists as rhombic crystals and is isomorphous with potassium pentachloroaquoferrate(III).16 Potassium hexachloromo-lybdate(III) has been used for the preparation of potassium hexathiocyanatomolybdate(III), potassium heptacyano-aquomolybdate(III),17and potassium octacyanomolybdate-(IV).18... 

Rega N, Cossi M, Barone V (1997) Intrinsic and environmental effects in the structure and magnetic properties of glycine radical in aqueous solution. J Am Chem Soc 119 12962—12967... 

---