Charge and Acidity

The presence of salts in NOM often disturbs charge titration. Tipping et al. (1988) determined a lower charge of NOM compared to purified species due to strongly bound metal ions. 

The charge of natural organics determines their interaction with membranes, cations, colloids and their solubility. Charge is therefore a very relevant characteristic for water treatment and the distinction between the charges of functional groups is of particular interest in the interpretation of pH effects on membrane rejection and fouling. 

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A given substituent affects the basicity of an amine and the acidity of a carboxylic acid in opposite ways (compare Sec. 18.14). This is to be expected, since basicity depends upon ability to accommodate a positive charge, and acidity depends upon ability to accommodate a negative charge. 

Hamieh, T. and Siffert, B., Determination of point of zero charge and acid-base superficial coal groups in water. Colloids Surf., 61. 83, 1991. 

There are a number of experimental methods to measure particle charge, but most, if not all of them, fall into one of two categories those based on electrophoresis, which measure the net particle charge, and acid-base titrations, which determine proton charge. 

Water-soluble globular proteins usually have an interior composed almost entirely of non polar, hydrophobic amino acids such as phenylalanine, tryptophan, valine and leucine witl polar and charged amino acids such as lysine and arginine located on the surface of thi molecule. This packing of hydrophobic residues is a consequence of the hydrophobic effeci which is the most important factor that contributes to protein stability. The molecula basis for the hydrophobic effect continues to be the subject of some debate but is general considered to be entropic in origin. Moreover, it is the entropy change of the solvent that i... 

When hydrochloric acid is cautiously added to an aqueous solution containing both sodium nitrite and the sodium salt of sulphanilic acid, NaOsSCgH NH, the amino group of the latter undergoes normal diazotisation, giving the diazonium chloride (A). The latter, however, ionises in solution, giving sodium and chloride ions and the internal salt (B), which possesses two opposite charges and is therefore neutral this internal salt is stable under... 

The Hard-Soft-Add-Base (HSAB) theory was developed by Pearson in 1963. According to this theory, Lewis acids and Lewis bases are divided into two groups on one hand hard acids and bases, which are usually small, weakly polarizable species with highly localised charges, and on the other hand soft acids and bases which are large, polarizable species with delocalised charges. A selection of Lewis acids, ordered according to their hardness in aqueous solution is presented in Table 1.3. 

The Pullman method is a combination of the Del Re method for computing the a component of the charge and a semiempirical Hrickel calculation for the 7t portion. It has been fairly successful in describing dipole moments and atomic charges for nucleic acids and proteins. 

FIGURE 1 8 Electrostatic potential maps of ethanol and 2 2 2 tnfluoroethanol As indi cated by the more blue less green color in the region near the OH proton in 2 2 2 trifluoro ethanol this proton bears a greater degree of positive charge and is more acidic than the OH proton in ethanol... 

Wnte an equation for the Brpnsted acid-base reaction that occurs when each of the fol lowing acids reacts with water Show all unshared electron pairs and formal charges and use curved arrows to track electron movement... 

Short chains of amino acid residues are known as di-, tri-, tetrapeptide, and so on, but as the number of residues increases the general names oligopeptide and polypeptide are used. When the number of chains grow to hundreds, the name protein is used. There is no definite point at which the name polypeptide is dropped for protein. Twenty common amino acids appear regularly in peptides and proteins of all species. Each has a distinctive side chain (R in Figure 45.3) varying in size, charge, and chemical reactivity. 

The process of reabsorption depends on the HpophiHc—hydrophiHc balance of the molecule. Charged and ioni2ed molecules are reabsorbed slowly or not at all. Reabsorption of acidic and basic metaboHtes is pH-dependent, an important property in detoxification processes in dmg poisoning. Both passive and active carrier-mediated mechanisms contribute to tubular dmg reabsorption. The process of active tubular secretion handles a number of organic anions and cations, including uric acid, histamine, and choline. Dmg metaboHtes such as glucuronides and organic acids such as penicillin are handled by this process. 

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