Ionization constant intrinsic

It can be seen from Table 2 that the intrinsic values of the pK s are close to the model compound value that we use for Cys(8.3), and that interactions with surrounding titratable residues are responsible for the final apparent values of the ionization constants. It can also be seen that the best agreement with the experimental value is obtained for the YPT structure suplemented with the 27 N-terminal amino acids, although both the original YPT structure and the one with the crystal water molecule give values close to the experimentally determined one. Minimization, however, makes the agreement worse, probably because it w s done without the presence of any solvent molecules, which are important for the residues on the surface of the protein. For the YTS structure, which refers to the protein crystallized with an SO4 ion, the results with and without the ion included in the calculations, arc far from the experimental value. This may indicate that con-... 

The ionization eonstant should be a function of the intrinsic heterolytic ability (e.g., intrinsic acidity if the solute is an acid HX) and the ionizing power of the solvents, whereas the dissoeiation constant should be primarily determined by the dissociating power of the solvent. Therefore, Ad is expeeted to be under the eontrol of e, the dieleetrie eonstant. As a consequenee, ion pairs are not deteetable in high-e solvents like water, which is why the terms ionization constant and dissociation constant are often used interchangeably. In low-e solvents, however, dissociation constants are very small and ion pairs (and higher aggregates) become important species. For example, in ethylene chloride (e = 10.23), the dissociation constants of substituted phenyltrimethylammonium perchlorate salts are of the order 10 . Overall dissociation constants, expressed as pArx = — log Arx, for some substanees in aeetie acid (e = 6.19) are perchloric acid, 4.87 sulfuric acid, 7.24 sodium acetate, 6.68 sodium perchlorate, 5.48. Aeid-base equilibria in aeetie acid have been earefully studied beeause of the analytical importance of this solvent in titrimetry. 

The above surface complexation models enable adsorption to be related to such parameters as the number of reactive sites available on the oxide surface, the intrinsic, ionization constants for each type of surface site (see Chap. 10), the capacitance and the binding constants for the adsorbed species. They, therefore, produce adsorption isotherms with a sounder physical basis than do empirical equations such as the Freundlich equation. However, owing to differences in the choice of adjustable... 

Photon correlation spectroscopy, carried out under very dilute conditions, has unambiguously demonstrated the expansion of carboxylic emulsion polymers at high pH, but it may not always be useful in predicting properties of practical interest. Of special concern is the apparent decrease in the intrinsic ionization constant of surface carboxyls at very low concentration. Since most uses of emulsion polymer occur at high concentrations, the measurement of particle-particle interactions is of great practical importance (21J. It has been found that the sedimentation and viscometric techniques closely reflect viscosity changes in latexes at much higher solids. Extension of the PCS approach to more concentrated systems is underway but not without problems (22). 

This equation is essentially an equilibrium constant relationship between the electron and hole concentrations in the semiconductor. It is much like the ionization constant expression for the dissociation of water, which can be related to the concentrations of H+(aq) and OH (aq) through the relationship [H+][OH ] = /fw = 1 x 10 " M. The only difference between these two expressions is that the temperature dependence of the water dissociation equilibrium constant is contained implicitly in the value of K, but is explicit in the relationship expressed by equations (5) and (6). The most important point to remember is that increases in the sample temperature will produce exponential increases in the electron and hole concentrations for an intrinsic semiconductor. Thus, the conductivity of intrinsic semiconductors increases exponentially with temperature. In contrast, the conductivity of metals decreases with increasing temperature. ... 

Here e is the electron charge, e is the dielectric constant of the medium, a is the distance of the maximum approach of a small ion and a spherical particle, often taken equal to (b-H 2.5A), X is the Debye-Hiickel parameter, 3.57 is the constant coefficient for aqueous systems at 25°C on condition that distances are measured in angstroms), pkjnt is the intrinsic ionization constant, Z = —on is the average value of the total charge of a particle (it is equal numerically to the number of protons having formed on dissociation), n is the number of dissociating groups in a particle. 

It follows from Eq. (9) that when a macromolecule is in the shape of a globe, the intrinsic ionization constant for a definite type of ion-exchangeable sites is changed in the presence of a charge so that ... 

However, it is found experimentally that not only a stretching of a titration curve occurs but also an increase in the intrinsic ionization constant of silanol groups (a decrease in pkint) is observed with increasing the ionic strength (a shift of a titration curve into the... 

This behaviour may be explained if equilibrium (5) and isotherms (6) and (8) are taken into account. Then an intrinsic ionization constant ki t is equal to Ka(l + /3[Mj) and the... 

Hou, W.G. et al.. Studies on zero point of charge and intrinsic ionization constant of Zn-Mg-Al hydrotalcite-like compounds. Colloid Polym. Sci., 281, 738, 2003. 

The simplest representation is the empirical chemical formula, while a molecular electrostatic potential (MEP) representation on the Van der Waals surface includes both steric and electronic information. Molecular properties can be divided into various categories (see Fig. 22.4). There are experimental and calculated properties. Intrinsic properties are directly related to the stracture without considering any interaction, such as molecular weight. Some properties are related to a substituent or fragment. When a compound interacts with a chemical or biological environment, we may define physicochemical properties, e.g. lipophilicity or ionization constants, biochemical properties, such as binding constants, and biological properties, such as activity or toxicity. 

The (solubility-pH) data were analyzed by regression analysis with a zero intercept second order polynomial that was based on eqn. (5) and employed an intrinsic solubility of 3 n,g/mL. The resulting polynomial had a correlation coefficient of 0.997 and provided ionization constants standard error of pJCai = 1.68 0.14 and pK = 4.93 0.096. 

The solubility of an acid in an alkaline solution depends on two properties the ionization constant, and the intrinsic solubility of the neutral molecule. Thus heptanoic acid readily dissolves in a buffer solution of pH 7 whereas its higher homologue stearic acid is practically insoluble, although both acids have the same pKg. The low intrinsic solubility of stearic acid provides the explanation. 

In addition, we may write the intrinsic ionization constant from Eq. (7) ... 

The holes and electrons will interact as determined by the intrinsic ionization constant K,. Because intrinsic ionization is small at low temperatures (<400°C), holes will remove electrons by the vertical reaction shown, thus driving Eq. (103) to the right and correspondingly increasing the solubility of lithium. It was found that for boron concentrations in excess of the normal lithium solubility in silicon, the solubility of lithium increased with the concentration of boron. An analytical expression for the concentration of Li " as a function [B ] can be obtained by simultaneously solving the following two... 

The formation of associates will affect the solubility of impurities in the same manner that the hole-electron equilibrium does, as was illustrated for the case of Li and B in Si. For example, Ga in Ge will increase the solubility of Li far more than expected from the known value of the intrinsic ionization constant K. This can be explained by the formation of a (Lij Gac ) associate as shown ... 

From these equations it is possible to predict the effective lipophilicity (log D) of an acidic or basic compound at any pH value. The data required in order to use the relationship in this way are the intrinsic lipophilicity (log P), the dissociation constant (pKa) and the pH of the aqueous phase. The overaU effect of these relahonships is the effechve hpophilicity of a compound, at physiological pH, is approximately the log P value minus one unit of hpophilicity, for every unit of pH the pKa value is below (for acids) and above (for bases) pH 7.4. Obviously for compounds with mul-hfunchonal ionizable groups the relahonship between log P and log D, as weU as log D as a function of pH become more complex [65, 68, 70]. For diprotic molecules there are already 12 different possible shapes of log D-pH plots. 

The behavior of hydrogen ions in the gel is very similar to that in polyelectrolyte solutions and the same theoretical treatment may be applied. The pH of a polyelectrolyte solution is dependent on the intrinsic dissociation constant (p °) of the functional group—which is normally that of a monomer—on the degree of ionization (a), and on the potential... 

Whenever electrons and holes are generated in a solid through ionization, another equilibrium is set up 0 = c +h. The corresponding intrinsic equilibrium constant is... 

As we saw in Chapter 1, the importance of numbers in chemistry derives from the fact that experimental measurement of a particular chemical or physical property will always yield a numerical value to which we attach some significance. This might involve direct measurement of an intrinsic property of an atom or molecule, such as ionization energy or conductivity, but, more frequently, we find it necessary to use theory to relate the measured property to other properties of the system. For example, the rotational constant, B, for the diatomic molecule CO can be obtained directly from a measurement of the separation of adjacent rotational lines in the infrared spectrum. Theory provides the link between the measured rotational constant and the moment of inertia, I, of the molecule by the formula ... 

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