Coordination complexes dissociation constant

Maximal speed (Vmax) and supposed Michaelis constant (K ) of pectin hydrolysis reaction (catalyzed by the studied pectinesterase) were determined in Zinewedwer — Berk coordinated, They were determined in the range of substrate concentration values that was below optimum one V = 14.7 10 M min K = 5.56 10 M. The value of dissociated constant (KJ of the triple enzyme—substrate complex was determined from the experimental data at high substrate concentration. It was the following Kj= 0.22 M. Bunting and Murphy method was used for determination. 

Under these conditions, the formation rate constant, k, can be estimated from the product of the outer sphere stability constant, Kos, and the water loss rate constant, h2o, (equation (28) Table 2). The outer sphere stability constant can be estimated from the free energy of electrostatic interaction between M(H20)q+ and L and the ionic strength of the medium [5,164,172,173]. Consequently, Kos does not depend on the chemical nature of the ligand. A similar mechanism will also apply to a coordination complex with polydentate ligands, if the rate-limiting step is the formation of the first metal-ligand bond [5]. Values for the dissociation rate constants, k, are usually estimated from the thermodynamic equilibrium constant, using calculated values of kf ... 

The interchange character of the water-exchange mechanism of the studied seven-coordinate complexes can be a reason why there is no clear correlation between their rates for the exchange process and the energies required for the dissociation of the coordinated water molecule. AE is also not possible to correlate with the catalytic rate constants published in the literature. 

Diphosphinedihalonickel(II) complexes planar-tetrahedral spin equilibrium, 32 29-30 reaction coordinate profile, 32 31 Diphosphoric acid, dissociation constants for, 4 25... 

Tetrakis(triethylphosphine)platinum(0) is extremely air sensitive and readily soluble in saturated aliphatic hydrocarbons. The complex can be stored under dry nitrogen in a freezer (-35°) for several months. The complex readily loses one of the coordinated phosphine molecules to give Pt(PEt3)36 (dissociation constant (K ) in heptane is 3.0 X 10" ). The H NMR spectrum measured in benzene-d6 shows two multiplets at 5 1.56 (CH2) and 1.07 ppm (CH3). Tetrakis-(triethylphosphine)platinum(O) is a strong nucleophile and reacts readily with chlorobenzene and benzonitrile to give a-phenyl complexes PtX(Ph)(PEt3)2 (X = Cl, CN).7 Oxidative addition of EtOH affords [PtH(PEt3)3] +. 

We can now make sensible guesses as to the order of rate constant for water replacement from coordination complexes of the metals tabulated. (With the formation of fused rings these relationships may no longer apply. Consider, for example, the slow reactions of metal ions with porphyrine derivatives (20) or with tetrasulfonated phthalocyanine, where the rate determining step in the incorporation of metal ion is the dissociation of the pyrrole N-H bond (164).) The reason for many earlier (mostly qualitative) observations on the behavior of complex ions can now be understood. The relative reaction rates of cations with the anion of thenoyltrifluoroacetone (113) and metal-aqua water exchange data from NMR studies (69) are much as expected. The rapid exchange of CN " with Hg(CN)4 2 or Zn(CN)4-2 or the very slow Hg(CN)+, Hg+2 isotopic exchange can be understood, when the dissociative rate constants are estimated. Reactions of the type M+a + L b = ML+(a "b) can be justifiably assumed rapid in the proposed mechanisms for the redox reactions of iron(III) with iodide (47) or thiosulfate (93) ions or when copper(II) reacts with cyanide ions (9). Finally relations between kinetic and thermodynamic parameters are shown by a variety of complex ions since the dissociation rate constant dominates the thermodynamic stability constant of the complex (127). A recently observed linear relation between the rate constant for dissociation of nickel complexes with a variety of pyridine bases and the acidity constant of the base arises from the constancy of the formation rate constant for these complexes (87). 

Consider a metal complex CM, where C is a multidentate ligand that leaves an empty coordination position on the metal, in the presence of a monodentate ligand L. CM could also be a metalloenzyme interacting with a substrate or an inhibitor L. The paramagnetic effects observed on a nucleus of L can then be used to obtain information on its dissociation constant ... 

There are three NMR-based approaches suitable to propose the bioactive conformation of ligands in the absence of the coordinates of the whole complex 1. conformation analysis of free ligand in solution has a high chance to find with some population the bound conformation, although it may be solvent dependent (refer to Sect. 2.2.2) 2. determination of bound ligand conformation by means of transferred NMR methods if the dissociation constant is not smaller than approximately 50 pM (refer to Sects. 2.1 and 2.3) 3. solid-state NMR of the complex if the ligand can be obtained with 13C labels (Sect. 2.2.3). 

Poly(acrylhydroxamic acid)-Cu(II) complex has a high catalytic activity in the decomposition reaction of hydrogen peroxide. From the comparison of complex formation constants (stabilization constants) both in the polymer and the low molecular weight molecule, it was considered that the high activity is owed to a partly dissociated or a solvent coordinated moiety (104,105). Poly(methacryloylacetone)-Cu(II) complex is also investigated (108). 

Ligand size determines coordination numbers as well as reactivity. Thus phosphine complexes of Pd°, frequently used as precursors in palladium catalyzed reactions, may be 4-, 3-, or 2-coordinate, as in Pd(PMe3)4, Pd(PPr )3, and Pd(PPhBu 2)2, respectively. For nickel phosphine and phosphite complexes, the dissociation constant Kd for the equilibrium... 

---