Constants, association dissociation

NEIGHBORING GROUP MECHANISM ASSOCIATION ASSOCIATION CONSTANT DISSOCIATION CONSTANT STABILITY CONSTANT Association/dissociation rate constants, determination,... 

Maintaining quasi-steady-state conditions for in vitro systems, we may assume constant association-dissociation rates so that probability of interaction/reaction is written as the rate of cmisumption of the ligand [see Eq. (73)], to saturation ... 

Heat capacity, latent heat, ionic conductivity, enthalpy, entropy Viscosity, thermal conductivity, diffusion coefficients Equilibrium constants, association/dissociation constants, enthalpy of formation, enthalpy of combustion, heat of reaction, Gibbs free energy of formation, reaction rates Surface tension... 

This association/dissociation is assumed to be a rapid equilibrium, and is the enzyme substrate dissociation constant. At equilibrium,... 

The dynamics of a supramolecular system are defined by the association and dissociation rate constants of the various components of the system. The time-scale for the dynamic events is influenced by the size (length-scale) and by the complexity of the system. The fastest time for an event to occur in solution is limited by the diffusion of the various components to form encounter complexes. This diffusion limit provides an estimate for the shortest time scale required for kinetic measurements. The diffusion of a small molecule in water over a distance of 1 nm, which is the length-scale for the size of small host systems such as CDs or calixarenes, is 3 ns at room temperature. In general terms, one can define that mobility within host systems can occur on time scales shorter than nanoseconds, while the association/dissociation processes are expected to occur in nanoseconds or on longer time scales. The complexity of a system also influences its dynamics, since various kinetic events can occur over different time scales. An increase in complexity can be related to an increase in the number of building blocks within the system, or complexity can be related to the presence of more than one binding site. 

The equilibrium constant and dissociation rate constant were determined simultaneously by non-linear least-squares fitting, unless the absorption signal was too low157 or no dependence of relaxation frequency on concentration was observed.159,161,162 The association rate constant was then calculated from the definition of the equilibrium constant. The equilibrium constants determined from the dynamics in this manner agree fairly well with equilibrium constants determined independently. 

Stop-flow experiments have been performed in order to study the kinetics of micellization, as illustrated by the work of Tuzar and coworkers on PS-PB diblocks and the parent PS-PB-PS triblocks [63]. In these experiments, the block copolymers are initially dissolved as unimers in a nonselective mixed solvent. The composition of the mixed solvent is then changed in order to trigger micellization, and the scattered light intensity is recorded as a function of time. The experiment is repeated in the reverse order, i.e., starting from the block copolymer micelles that are then disassembled by a change in the mixed solvent composition. The analysis of the experimental results revealed two distinct processes assigned as unimer-micelle equilibration at constant micelle concentration (fast process) and association-dissociation equilibration, accompanied by changes in micellar concentration (slow process). 

Since this is the equilibrium constant associated with a weak acid dissociation, this particular Kc is the weak add dissociation constant, Ka. The IQ expression is ... 

The stability of the complex ML is characterized by the equilibrium constant, for which various terms are used stability constant, binding constant, association constant, affinity constant (Ks or, 6) or dissociation constant (ka, reciprocal of ks). From... 

BF3, lna ln[P(10BF3)/P(nBF3)] = — 0.0075, is sufficiently large to permit useful separation by distillation. Compare this effect, however, with association-dissociation constants for reactions of the type... 

Kinetic modeling of the transient absorption spectra is necessary in order to obtain estimates of the lifetimes and rate constants associated with the evolution of the intermediates observed during the dissociation. A detailed description of the modeling may be found in our work on the picosecond photodissociation of the natural car-boxy- and oxy- heme complexes (3,4). The model is designed to treat the dissociation as a series of first or second order steps indicated in pathways I and II, ones that are consistent with the transient absorption data and with arguments based on bottlenecks... 

In connection with the subject of the relation between association state and kinetic order, it is germane to mention observations of Roovers and Bywater (45). They measured the dissociation constant for the tetramer , dimer case for polyiso-prenyllithium in benzene. The technique involved a study of the electronic spectra at 272 and 320 nm. If the process they measured can be directly related to the association-dissociation equilibrium, their results can be used to calculate the dissociation constant for the correct dimer monomer system. This value is ca. 2xl0-5 at 30.5°C. If this value is accepted, then the situation is encountered where the degree of dissociation of the polyisoprenyllithium chain ends varies from about 0.10 to... 

One of our aims in using ultrasonics was to study the kinetics of the association-dissociation process. Kinetic effects would produce a maximum of absorption when the pH is changed at constant frequency. No information about the kinetics has been obtained so far. However, the difference of absorption in capsides and in the dissociated system turned out to be of interest, because of the unexpected increase of absorption by capsides. 

Thus, if the macromolecule forms only one loop around the particle, then the quantity of the bonds of the particle with the macromolecule is proportional to the length of the particle s circumference, and the correspondent constant of equilibrium of the association-dissociation depends on the radius of particles in accordance with... 

The reactions of poly(styryl)lithium in benzene with an excess of diphenyl-ethylene 272) and bis[4-(l-phenylethenyl)phenyl]ether158) also were found to proceed by a first order process. However, the reactions of poly(styryl)lithium with the double diphenylethylenes l,4-bis(l-phenylethenyl)benzene and 4,4 bis(l-phenyl-ethenyl)l,l biphenyl gave l58) non-linear first order plots with the gradients decreasing with time. This curvature was attributed to departure from a geometric mean relationship between the three dimerization equilibrium constants (Ka, Kb and Kab). The respective concentrations of the various unassociated, self-associated and cross-associated aggregates involved in the systems described by Equations (49) to (51) are dependent upon the relative concentrations of the two active centers and the respective rate constants which govern the association-dissociation events. 

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