Dissociation constant ratio

The difference in anomerie equilibrium between protonated and neutral glucosylimidazoles can thus be measured as an acid dissociation constant ratio i.e. pATa difference). 

Since the position of an acid-base equilibrium depends on the pH, the distribution ratio must also be pH-dependent. To derive an equation for D showing this dependency, we begin with the acid dissociation constant for HA. 

A sample contains a weak acid analyte, HA, and a weak acid interferent, HB. The acid dissociation constants and partition coefficients for the weak acids are as follows Ra.HA = 1.0 X 10 Ra HB = 1.0 X f0 , RpjHA D,HB 500. (a) Calculate the extraction efficiency for HA and HB when 50.0 mF of sampk buffered to a pH of 7.0, is extracted with 50.0 mF of the organic solvent, (b) Which phase is enriched in the analyte (c) What are the recoveries for the analyte and interferent in this phase (d) What is the separation factor (e) A quantitative analysis is conducted on the contents of the phase enriched in analyte. What is the expected relative erroi if the selectivity coefficient, Rha.hb> is 0.500 and the initial ratio ofHB/HA was lO.O ... 

This equation states that the ratio of oxygenated, heme groups (F) to 02-free heme (1 F) is equal to the nth power of the PO2 divided by the apparent dissociation constant, K. 

Thus, the enzymatic rate acceleration is approximately equal to the ratio of the dissociation constants of the enzyme-substrate and enzyme-transition-state complexes, at least when E is saturated with S. 

This means that, with increasing length of chain, the equilibrium constants K1 and K2 (the first and second dissociation constants at infinite dilution of the acid) should not tend to equality rather their ratio K1/K2 should tend toward the value 4, as recognized by Adams.1... 

Using these acid dissociation constants for glycine, calculate the ratios [Z]/[C+] and [Z]/[A-] at pH... 

In the presence of a competitive antagonist, the EC50 of the agonist dose-response curve will be shifted to the right by a factor equal to the dose ratio. This is given by the Schild equation as [B]/Kb-I-1, where the concentration of the antagonist is [B] and KB is the equilibrium dissociation constant of the antagonist-receptor complex ... 

Dissociation constant, the ratio of the rate of offset of ligand away from a receptor divided by the rate of onset of the ligand approaching the receptor. It has the units of concentration and specifically is the concentration of ligand that occupies 50% of the total number of sites available for ligand binding at equilibrium (see Affinity). 

Equilibrium (dissociation) constant, reciprocal of the association constant and affinity characterizes the binding of a molecule to a receptor. Specifically, it is the ratio of the rate of offset of the molecule away from the receptor divided by the rate of onset toward the receptor. It also is a molar concentration that binds to 50% of the receptor population. 

The preparation of a buffer solution of a definite pH is a simple process once the acid (or base) of appropriate dissociation constant is found smhll variations in pH are obtained by variations in the ratios of the acid to the salt concentration. One example is given in Table 2.2. 

Receptor occupancy refers to the ratio of receptors occupied by a ligand at equilibrium and the total number of receptors available, usually expressed as a percentage of the total number of receptors. Since it is often not possible to quantify the total number of receptors or the number of receptors occupied by a ligand, another parameter called binding potential is often used to measure receptor occupancy. Binding potential (BP) refers to the ratio of the maximum number of receptors and the equilibrium dissociation constant of the drug, so that % receptor occupancy equals to... 

Referring to each amine shown in Table 11.5, as the temperature increases so the dissociation constant Kb decreases (although ratios between amines may change). Conversely, as temperature decreases, so Kb increases. Generally, because we are concerned with relatively high temperatures, the Kb value is likely to be lower than shown in some published tables, and so more product will be required than possibly anticipated. 

Figure 15. Data from single channel experiments, plotted to show the relationship between kinetic and equilibrium parameters for several of the saxitoxins, tetrodotoxin, and Conus geographus toxin GIIIA. Compound numbering corresponds to that in Figure 1. The vertical axis is and the horizontal axis is dwell time, the reciprocal of k j. The dissociation constant, the ratio of k jj/k, therefore corresponds to distance along the diagonal. Data primarily from Ref. 95.

It is worth mentioning that an attempt was made by Tsao and Willmarth to determine the acid dissociation constant of HO2. The reaction between hydrogen peroxide and peroxydisulphate was used for the generation of the HO2 radical. However, these experiments, like others where the HO2 radical is studied under steady-state conditions, could yield only a value of acidity constant multiplied by a coefficient consisting of a ratio of kinetic parameters. Unfortunately, in this case there are no independent data for the kinetic coefficient, and the value of cannot be evaluated. Considering the kinetic analogue of the titration curve it can be stated only that ionization of HO2 becomes important in the pH range from 4.5-6.5. The value of acidity constant of HO2 obtained by Czapski and Dorfman is (3.5 + 2.0)x 10 mole.l. . ... 

The binary complex ES is commonly referred to as the ES complex, the initial encounter complex, or the Michaelis complex. As described above, formation of the ES complex represents a thermodynamic equilibrium, and is hence quantifiable in terms of an equilibrium dissociation constant, Kd, or in the specific case of an enzyme-substrate complex, Ks, which is defined as the ratio of reactant and product concentrations, and also by the ratio of the rate constants kM and km (see Appendix 2) ... 

Miller and Wolfenden, 2002). This latter ratio is the inverse of the rate enhancement achieved by the enzyme. In other words, the enzyme active site will have greater affinity for the transition state structure than for the ground state substrate structure, by an amount equivalent to the fold rate enhancement of the enzyme (rearranging, we can calculate KJX = Ksik Jk, )). Table 2.2 provides some examples of enzymatic rate enhancements and the calculated values of the dissociation constant for the /A binary complex (Wolfenden, 1999). 

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