Ionizable sites

The first line contains the number of ionizable sites, M. Subsequent lines are organized in blocks whose first line contains information about the group... 

In some processes, development additives such as benzyl alcohol are added to the developer to increase the hydrophilic nature of the organic phase. More frequentiy, higher pX couplers are designed to have additional ionizable sites, such as carboxyl, sulfo, or phenoHc groups, to accomplish the same end (57). 

In PB based methods, the pKa for a protein ionizable site i is given by [6],... 

Smejtek, P., Barstad, A. W. and Hsu, K. (1987). Dielectric properties of adsorp-tion/ionization site of pentachlorophenol in lipid membranes, Biochim. Biophys. Acta, 902, 109-127. 

This strategy consists in the initial modification of the silica surface with organosilanes having suitable anchoring groups, which are either reactive themselves or can be additionally activated for the final attachment of the chiral selector. The choice of the proper silane will depend on the presence of suitable functional groups on the chiral entity to be fixed to the matrix. As macrocyclic antibiotics contain hydroxyl, amine, and carboxylic acid functionalities, they can be linked to the silica surface in a variety of different ways [7, 55]. The obvious drawback of the stepwise assemblage of chiral selectors on the silica surface is the eventual formation of additional polar or ionizable sites on the matrix, which may cause unselective retention of chiral analytes. 

Generally, they have multiple ionizable sites that are spread throughout the molecule. 

The authors of the present paper (7, 10, 21) used the planar soap monolayers as a simple model for the complex surface of a porous ion exchanging resin. Thus, a study of the effect of the separation between the ionized sites of a model exchanger on its selectivity between two competing counterions can be attempted. 

From the equilibrium values we calculated the coefficient of selectivity (9) and the corresponding free energy and determind their variation as a function of the separation between the ionized sites. 

The identicalness of the ionization sites in a linear polyelectrolyte (Tanford, 1961) stimulated the interest of Walter and Jacon (1994) in a possible relationship between Kz and M of ionic polysaccharides displaying the characteristic titration curve of a weak, monobasic acid. Without any theoretical assumption, Eq. (S.4) was derived from simple algebra by combining elementary principles of the dissociation theory of weak acids with polymer segment theory ... 

In this paper, a two-dimensional model is proposed, in which the polyelectrolyte chains are treated as rigid cylinders normally grafted to each of the plates. On the surface of the cylinders, ionizable sites are uniformly distributed and the surface charge of the cylinder is generated through their dissociation. Using this two-dimensional model, the repulsive force between two plates is calculated as a function of electrolyte concentration, surface density of polyelectrolyte chains on the plate, thickness of the polyelectrolyte brushes, and bulk pH (denoted in what follows as pHo). 

The dissociation of the two kinds of ionizable sites provides the chain surface with positive and negative charges through the dissociation equilibria [19]... 

Tables 2-8 contain pA-values for a range of aromatic compounds. The compounds are mostly classified according to their ring systems, but carbonyl compounds are grouped together for convenience. It has proved impossible to include some material in tabular form and a few molecules with more than one ionizable site have not been included (see e.g. Hercules and Rogers, 1959 Ellis and Rogers, 1964 Mayer and Himel, 1972). Where such polyfunctional molecules are included, the tables may be ambiguous as to the position of protonation or dissociation to which the quoted pA-values refer. For example, the excited state dissociation of protonated hydroxy-...

The procedure is based on the proton competition with metal ions and may therefore easily be detected by pH titration. The limitations are, however, that in itself it gives no information as to where the exact ionizing site is located on the molecule. 

The ions obtained from large molecules carry a greater number of charges if several ionizable sites are present. Typically, a protein will carry one charge per thousand daltons... 

Large molecules with several ionizable sites produce by ESI multiply charged ions, as shown for lysozyme positive ions in Figure 1.23. 

Kb initio MO and DFT calculations at several levels of theory revealed a marked effect of the medium on the ionization sites of pyrrole- and indolecarboxylic acids, showing that (1) pyrrole- and indole-3-carboxylic acids behave as NH acids in the gas phase, (2) in the gas phase, pyrrole- and indole-2-carboxylic acids are deprotonated at the COOH group, although competing ionizations may take place, and (3) all these acids behave in aqueous solution as OH acids <1998JA13224>. 

Since there are many charge transfer and spin transfer processes that occur after an initial ionization, the specific location of the chemical damage and, consequently, the ultimate biological damage from DNA irradiation may be removed from the initial ionization site. ° The pertinent charge and spin transfer processes have recently been reviewed. ... 

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