Mn2+ complexes

A representative structure is shown in Figure 3. In all cases, Mn...Mn separations are long (ca 3.3A), similar to values found for the mono-oxlde-brldged Mn2 complexes described above. Even in the trapped-valence complex Mn30(02CPh)s(py)2(H20) (18) shown in Figure 3, where the Mn3 unit is isosceles rather than equilateral, the Mn...Mn separations are not distinctly different, and no separation is found in the ca 2.7k range. It could thus be concluded that an MnsO-type unit cannot represent the complete... 

Mechanochemically introduced V3+ and Mn2+ complexes of PET also exhibit enhanced thermal stability of the base polymer - an observation in line with the usual expectation [93]. 

Such studies on creatine kinase (Eq. 12-31) utilized both a bound Mn2+ ion and a nitroxide spin label to estimate distances of various protons from the nitroxide.683 Together with EPR measurements (Box 8-C), which gave the Mn2+-nitroxide distance, a model of the ATP Mn2 complex in the active site was constructed. Additional EPR experiments on Mn2+ complexes with ATP and ADP containing 170 in the a, (3, or y phospho groups showed that in the enzyme ATP creatine complex the metal ion is bound to all three phospho groups of ATP. It remained coordinated with the two phospho groups of ADP and also that of the phospho-creatine product in the enzyme ADP creatine-P complex as well as in the transition state, which is pictured occurring via a metaphosphate ion.684... 

For the second method, samples obtained from reactions run under different conditions (milling duration, ratio of reactants and inorganic salt, etc.) were used (see Figures 18 through 22). The results show that the fraction of thermostable polymer from both Fe3+ and Mn2+ complexes increased with an increase in chemically linked nitrogen quantity which, in turn, was determined by the established parameters. 

McBride, M. B. (1982a). Electron spin resonance investigation of Mn2+ complexation in natural and synthetic organics. Soil Sci. Soc. Am. J. 46,1137-1143. 

On the other hand, when rotational motion is slow, or when the symmetry of the complex is less than cubic, as in Mn2+ complexes with macromolecules, Au)Xr is often greater than one, the anisotropic interactions are incompletely averaged and EPR spectra similar to those for randomly oriented solid samples are observed. In these cases the spectra depend upon the angular relationships between the magnetic field vector and the crystal field axis of the ion. Moreover, when the symmetry of the manganese ion complexes deviate greatly from cubic, the EPR spectra depend upon the sharing of spectral intensity between the normal and forbidden (AMS = + 1, Amp = + 1) transitions. 

The impact of solvent molecules and the resulting transient distortions of the Mn2+ complex determine the electron spin relaxation time of the system (26). Thus efficient solvent collisions at the bound Mn2+ will yield broad EPR lines, while narrow lines should result when Mn + is inaccessible to this rapid, fluctuating motion. 

Figure 2. Electron paramagnetic resonance spectra of Mr bound to the single catalytic site on (Na + K )-ATPase. The X-hand spectrum (9.5 GHz) is shown in A, while the K-band spectrum (35 GHz) of the same complex is shown in B. The enzyme-Mn2 complex was centrifuged out of 20mM Tes-TMA, pH 7.5, and then combined with buffer so that the final concentrations were 0.15mM (Ha 4-K )-A TPase, 0.1 mM MnCl, 20mM Tes-TMA, pH 7.5. T = 23°C.

Figure 6. K-hand EPR spectra for Mn2 complexes of (Na + K )-A TPase and / , y-hidentate CrATP. Conditions were the same as in Figures 2 and 3, except pH = 7.0, with the concentrations of CrATP shown.

Somewhat different conclusions were reached for mandelate racemase [38], Dissociation constants for the enzyme substrate complexes in the absence (k5) and presence (/c3) of Mn2+ were obtained (from proton relaxation rate titration of E-Mn2+ complex and other means). Evidence was obtained that in this case k3 was approximately equal to k4. Thus the authors concluded that the enzyme-catalyzed racemization steps should be approximately equal for both the D- and L-enantiomers , and termed this a rather startling prediction . Clearly, more detailed studies of the behavior of this, and other racemase enzymes would be desirable. 

Fig. 20-17 shows the spectra of octahedrally coordinated Mn2 +, in [Mn(H20)6]2+, and tetrahedrally coordinated Mn2 +, in the [MnBr4]2- ion. Let us look first at the [Mn(H20)6]2+ spectrum. The spectra of other octahedrally coordinated Mn2+ complexes are quite similar.9 The most striking features are (a) the weakness of the bands, (b) the large number of bands and (c) the great variation in the widths of the bands, with one extremely narrow... 

Different XANES spectra can be compared to each other only when properly normalized(we adopt an integral-equalizing method). Fig.1(c) shows the normalized-absorption difference spectrum for S2"S] (solid curve A) to be compared with the halves of those for Mn(lV)-Mn(HI) (dashed curve B) and Mn(IK)-Mn(II) (dotted curve C) in each ligand-conserved Mn2 complex. 

Huang P, Magnuson A, Lomoth R, Abrahamsson M, Tamm M, Sun L, Van Rotterdam B, Park J, Hammarstrdm L, Akermark B, Styring S (2002) Photo-induced oxidation of a dinuclear Mn2° ° complex to the Mn2 state by inter- and intramolecular electron transfer to Ru trw-bipyridine. J Inorg Biochem 91 159-172... 

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