S. Balt

Binding of metal ions to polysaccharides. V.: Potentiometric, spectroscopic, and viscosimetric studies of the binding of cations to chondroitin sulfate and chondroitin in neutral and acidic aqueous media

Binding of cations to chondroitin sulfate A and C, chondroitin, and D-glucuronate was investigated in neutral and acidic aqueous media using H+, Cu2+, and Na+ ion-specific electrodes, viscometry, electron spin resonance (esr), and ligand-field spectroscopy. Site binding to the carboxylate group and only electrostatic interaction with the sulfate group could describe the results well. The nitrogen atom of the N-acetyl group appeared not to be involved in bonding of cations to chondroitin(sulfate) systems. The interaction of the divalent metal ions follows the Irving-Williams series. The value of the electrostatic potential at the carboxylate group of chondroitin(sulfate), as experienced by a cation, was determined in dependence of cation bonding. It proved to be difficult to establish the composition of a complex of a metal ion with a polyion by means of a molar ratio curve.

Intramolecularly alkylated Costa complexes: New models for coenzyme B12 with a cobalt-to-ligand carbon bridge

Abstract The synthesis of Costa-type B 12 models 1 with a carbon bridge between the equatorial ligand and cobalt has been accomplished by condensation of butanedione monoxime and 2-(ω-functionalized)alkyl-1,3-diaminopropanes 8 followed by complexation with Co(II), introduction of a leaving group and intramolecular alkylation via Co(I) intermediates. The solution structure of intramolecularly alkylated Costa complexes with a bridge of two ( 1a ) or of three ( 1b ) methylene groups was investigated by NMR spectroscopy and compared with that of propyl(iodo) Costa complex 13 .

Effects of solvent and ionic medium on the kinetics of axial ligand substitution in vitamin B12. Part III. Reactions of aquocobalamin and aquamethylcobaloxime with sulfur-coordinating ligands

Abstract Rate constants for the reactions of aquocobalamin and aquamethylcobaloxime with a series of uncharged sulfur-coordinating ligands were measured in the solvents water and 50 vol% dioxane-water. For both complexes in both solvent systems a linear free energy relationship was found with unit slope, indicating a dissociative mode of activation. With the help of solubility measurements a complete quantitative analysis of solvent effects on the reaction profile could be made. For both cobalt complexes the solvent effects on the reaction profiles are comparable, but in the case of aquocobalamin the kinetic parameters are more influenced by steric factors and hydrogen bonding. From the quantitative analysis of the reactivity of aquocobalamin and aquamethylcobaloxime it is concluded, that for biological reactions where steric effects and/or hydrogen bonding play an important role, aquamethylcobaloxime is not a good model compound for vitamin B12.

Intramolecularly alkylated Cosalen complexes: thermolysis and photolysis of coenzyme B12 models with a cobalt-to-ligand carbon bridge.

Abstract Product and kinetic studies on the anaerobic thermolysis and photolysis of the cobalt-carbon bond in intramolecularly bridged organoCosalen compounds are presented. NMR, UV-Vis and electron spin resonance spectroscopic investigations reveal the formation of paramagnetic Co(II) complexes upon thermolysis or photolysis in solution. Solid state thermolysis (studied by differential thermal analysis, thermogravimetry, mass spectrometry and magnetochemistry) also leads to cobalt (II) products. The fate of the carbon radical produced by homolytic cleavage of the Co C bond in solution depends on the reaction conditions used. In the presence of a radical trap (tempo, pbn), carbon radical spin trapping is the major pathway. On the other hand, a Co(II) salen complex carrying an ω-alkenyl side chain was shown to be the major product when Cosalen(CH 2 ) 4 ( 2 ) was subjected to prolonged photolysis in the absence of a radical trap. While the chemistries of intramolecularly bridged organoCosalen and open chain alkylCosalen complexes are qualitatively quite similar, kinetic studies using the radical trap method reveal large quantitative differences. The bridged complex Cosalen(CH 2 ) 3 ( 1 ) is quite unreactive towards thermolysis and photolysis, even at high trap concentration. Quantum yields (Φ) of Cosalen(CH 2 ) 4 ( 2 ) and butylCosalen ( 4 ) were determined in toluene as a function of the concentration of tempo. For 2 , Φ max is reached at 0.5 M of tempo, while for 4 Φ is already maximal at a very small excess of tempo (≈0.0005 M); in both cases the complex concentration is ca. 10 4 M. These results are discussed in terms of the solvent-caged radical pair concept.

Mode of action of copper complexes of some 2,2'-bipyridyl analogs on Paracoccus denitrificans.

Copper complexes of 2,2-bipyridyl and related compounds and CuSO4 inhibited the growth of paracoccus denitrificans. The copper(I) complex of 2,9-dimethyl-1,10-phenanthroline [Cu(DMP)2NO3] showed the highest activity, whereas the copper(II) complex of 1,10-phenanthroline and CuSO4 inhibited the growth to a lesser extent. The uncomplexed ligands (1,10-phenanthroline and 2,9-dimethyl-1,10-phenanthroline) showed little activity, but in the presence of noninhibitory amounts of CuSO4 this activity increased markedly. Copper ions therefore proved to be essential for the growth-inhibitor effect. The extent of inhibition appeared to be strongly dependent on the initial cell density and on the growth medium. No selective inhibition of deoxyribonucleic acid, ribonucleic acid, or protein synthesis was observed with Cu(DMP)2NO3. Respiratory electron transport of P. denitrificans appeared to be strongly inhibited by Cu(DMP)2NO3 and to a somewhat lesser extent by CuSO4. Both aerobic and anaerobic respirations were inhibited to the same extent, and from the cytochrome redox kinetics it is concluded that the site of this inhibition in the respiratory electron transport chain must be located before cytochrome b. Cu(DMP)2NO3 did not significantly influence the H+/O ratio with whole cells of P. denitrificans, suggesting that the efficiency of oxidative phosphorylation is not affected by CU(DMP)2NO3. Growing cultures of P. denitrificans showed a decrease in intracellular potassium ion content in the presence of increasing amounts of Cu(DMP)2NO3. It is concluded that interference with the cytoplasmic membrane, resulting in inhibition of respiratory electron transport, probably constitutes the main mode of action of copper complexes of 2,2-bipyridyl analogs on P. denitrificans.

The electrical conductance of hexaamminemetal nitrates in liquid ammonia

The electrical conductance behavior of hexaamminemetal nitrates of Cr(III), Co(II–III), Ni(II), and Cu(II) in liquid ammonia has been measured at temperatures varying from −40 to −75°C. Both univalent and divalent dissociations have been considered. The two outer-sphere association constantsK1 andK2, which control the properties in the concentration range employed, have been determined together with Λ0 in a way described earlier by Fuoss. The thermodynamic quantities ΔHo and ΔSo of the univalent dissociation, evaluated from the temperature dependence of the association constants, are remarkably independent of the nature and charge of the metal ion. Walden products of the cations are presented and discussed.

Proton magnetic resonance spectra and stereochemistry of ammine nitrocobalt(III) complexes

Abstract Proton magnetic resonance (PMR) spectra in hexa-deuterodimethylsulfoxide are reported for a number of ammine nitrocobalt(III) complexes, containing one to four coordinated nitro groups. It is shown that PMR provides a reliable method to determine the stereochemistry of these complexes, contrary to results obtained by other workers. The influence of complex concentration on the spectra has also been investigated.

Acid dissociation of hexaamminemetal nitrates in liquid ammonia

The proton dissociation of hexaamminemetal nitrates of Cr(III), Co(II), Co(III), Ni(II), and Cu(II) in liquid ammonia has been investigated at a temperature of −39°C. This could be realized by using a specially constructed thin-walled glass electrode combined with a Ag/Ag(I) (in liquid ammonia) reference electrode. The potential of the couple used has been found to obey the Nernst equation in liquid ammonia. The pKa values of the hexaamminemetal nitrates in liquid ammonia are 7.27 [Cr(III)], 6.99 [Co(II)], 7.78 [Co(III)], 8.95 [Ni(II)], and 8.24 [Cu(II)]. The temperature dependence of the pKavalues falls within the experimental error.

Nitrito–nitro linkage isomerisation of the penta-amminecobalt(III) complex in liquid ammonia

The nitrito–nitro linkage Isomerisation reaction of the penta-amminecobalt(III) complex in liquid ammonia proceeds entirely via an intramolecular conjugate-base mechanism. The reaction is fully retentive and the penta-ammine(nitro)cobalt(III) complex is the only species that could be detected by 1H n.m.r. after the reaction was completed. The advantage of liquid ammonia as solvent is demonstrated by the separate determination of the pre-equilibrium constant Kc.b(ΔH= 27 kJ mol–1; ΔS=–14 J K–1 mole–1) and the rate constant of the rate-determining step k2(ΔH‡= 78 kJ mol–1; ΔS‡= 29 J K–1 mol–1). Comparison of the activation parameters of the latter rate constant with the activation parameters reported earlier for the ammoniation reactions of a number of cobalt(III) and rhodium(III) amine complexes in liquid ammonia shows the expected deviation from a limiting dissociative activation.

Electrochemistry of solutions in liquid ammonia. Part VII. The use of glass electrodes for ammonium and sodium cations as ion-selective sensors at −40 °C

The behavior of Li/La glass electrodes as specific ion sensors for NH4+ and Na+ cations in liquid ammonia solutions at −40°C has been assessed using concentration cells with transference. The measurement of emfs of cells with very high resistances due to glass at −40°C has been overcome partly by the use of thinly blown Li/La glass and mainly through the design and use of a ‘floating shield’ emf measuring system. For solutions of NH4NO3, NH4I, NH4BF4, and NH4Cl almost linear pNH4 vs. emf responses were observed between pNH4 0 and 5; for NH4NO3 solutions the slope (40±1 mV/pNH4) was invariant for substantial increases in Na+ concentrations. Solutions of NaNO3, NaCN, NaClO4, NaNCS, NaN3, and NaNO2 gave almost linear pNa vs. emf responses but the slopes were markedly dependent upon the NH4+ concentration. Estimates of the mean molal ion activity coefficients for nitrate solutions were obtained from earlier transference data: γ±(NaNO3)=0.14±0.02 and γ±(NH4NO3)=0.30±0.03 at 10− molal concentration in fair agreement with earlier data.