Imidazole complexes

The reaction of the (necessarily) cis-oxalato complex with HCI in the last example, ensures the c/s-configuration for the chloro complex on recrystallization, the thermodynamically more stable fra s-isomer forms. fra s-Rupy4Cl2 has Ru-N 2.079 A and Ru—Cl 2.405 A. An imidazole complex (imH) tra s-[RuCl4(im)2] shows promise as a tumour inhibitor and is currently undergoing preclinical trials [135]. 

Gajda et al. have produced a number of zinc imidazole complexes with substituted imida-... 

Diamine chelate complexes are more stable than the monodentate amine heterocycles and, therefore, can be studied under physiological conditions. The imidazole complexes are unstable in aqueous solution and decompose rapidly to technetium oxide hydrate. Six-membered ring chelates are significantly less stable than five-membered ones. Lesser flexibility of the ligand, such as 1.2-diamino-cyclohexane, parallels somewhat lower stability of the complex [53] ... 

As a further approach for novel electrolytes appropriate for selective cation transport, we have prepared poly(organoboron halide)-imidazole complexes.35 Even though boron-amine complexes are widely known materials reported by the early works of H. C. Brown et al.,52-54 they had not been investigated as solvents or electrolytes to the best of our knowledge. 

It is known that organoboron halide-imidazole complexes dissociate diming equilibrium 56 however, charges disappear upon dissociation. In such a matrix, mobile ions should not originate from the matrix. Therefore, the polymer electrolytes composed of boron halide-imidazole complexes were considered to be appropriate for selective ion transport. 

Figure 5 Temperature dependence of ionic conductivity for poly(organoboron halide)-imidazole complexes in the presence of various lithium salts.

Figure 6 VFT plots for poly(organoboron halide)-imidazole complexes. 

Table 2 VFT Parameters for Poly(organoboron halide)-imidazole Complexes...

The imidazole complex raras-[Ir(imid)2Cl4]- is stable for days in neutral aqueous solution, and for hours in the presence of added thiocyanate. Addition of silver nitrate precipitates the silver salt of the complex, with no indication of Ag+-catalyzed removal of coordinated chloride. Thus this iridium(III) complex is substitutionally much more inert than its much-studied (because (potentially) anti-tumor) ruthenium(III) analogue (96). 

The crystal structure of the sodium salt of 30 (NAMI) is shown in Fig. 9, where Na(I) bridges two molecules of 30 via oxygens of S-bound DMSO and water. This complex may be readily reduced in vivo (E1/2, -0.001 V) (166), whereas the bis-imidazole complex 28 has a lower redox potential and is more difficult to reduce. The reduction potential of 28 is strongly pH dependent (AE = —118 mV/pH unit near pH 7), reduction being more favorable at acidic pH values (167). This complex hydrolyses at a similar rate to cisplatin (ty ca. 3 h at 310 K) and, like cis-platin, aquation appears to be necessary for DNA binding (168). 

Fig. 3 Relative dipole-bound anion formation rates in RET collisions between Rydberg Xe(nf) atoms with (a) adenine (circles) or imidazole (squares) molecules and (b) adenine-imidazole complex produced in a supersonic beam. Experimental data are fitted to curvecrossing model calculations which lead to the experimental determination of EAdS values, equal to 11 meV for adenine, 23 meV for imidazole and 54 meV for adenine-imidazole complex (reproduced by permission of the American Chemical Society).

The imidazole complexes are unstable in aqueous solution and decompose rapidly to TCO2. At lower pH the complexes undergo acid-catalyzed decomposition. None of the complexes exhibited oxidation or reduction processes by cyclic voltammetry. However, it was chemically possible to reduce the imidazole complex with Zn in IM HCl. A defined complex formed that did not contain the Tc=0 group probably reduction to Tc complexes occurred. " ... 

Table 4 was unity, which indicated the five-coordinate structure as in the PVMI-heme complex. PBLGIm forms an a-helix, and the helix content and intrinsic viscosity were unchanged in the PBLGTm ferriheme complex. The formation constant of the ferriheme complex with PBLGTm was not so different from that of the imidazole complex (Table 4). The strong coordination was thought to be due to an additional hydrogen bond between a propionic residue of ferriheme and a carbonyl residue in the side chain of PBLGTm, as shown in Fig. 4(d)w ...

From the increase in pH and rate constant [with consequent increase in free (Im)] in going from experiment 1 to 4 in Table II, it is seen that the stability of the imidazole complexes is in the order Ni+2 > Cd+2 Ca+2. This is in agreement with the order of formation constants of these complexes (I), and with the finding (II) that there is no appreciable interaction between calcium ion and imidazole. Moreover, in a solution with an initial composition of 0.238M imidazole and 0.158M HC1, k was found to be 0.0977 min.-1 (Table I), so that the increase in k for this solution in the presence of 0.020M Ca(N03)2 (experiment 4 in Table II) amounts to only 3.6%. 

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