Titration curves of wool with 18 strong acids at 0°, 25°, or 50° C have been added to the data for 19 others presented earlier. Several have been investigated at more than one t emperature. The reversibility of the equilibria m easured has been demonstrated quantitatively. N ew anion-wool dissociation constants, based on modifications of equations previously used to calculate anion-wool affinities, are tabulated for 33 anions, and h eats of dissociation of a few anionwool complexes are also given. The previously reported t endency of affinity to rise with molecular-weight is confirmed ; fairly consist ent relationships between the affinity and the molecular weights of strong organic acids appear.

The fastness of wool dyes to washing varies widely not only among different classes of dyes but even among members of a given class. These variations are manifestations of the differences in affinities of the dyestuffs for the fibers. A possible basis for understanding such differences in affinities was described in two earlier papers in which it was shown that wool immersed in hydro chloric acid solutions combines not only with hydrogen ions but with chloride ions as well. As a consequence of this, it appeared that the affinities for wool of the anions of different acids might vary considerably and that therefore the positions of the titration curves with respect to the pH axis might vary by correspondingly large amounts, according to the acid used. The determination of the titration curve of wool with a gvien acid could then be used to measure the affinity of the anion of the acid for the fiber. Measurements have therefore been made by Research Associates of the Textile Foundation at the National Bureau of Standards of the combination of wool with nineteen different acids, including, in addition to some of the common mineral acids, several of the simpler aromatic sulfonic, carboxylic, and phenolic acids and a soluble mono-azo acid dye. Wide differences were found between the positions of the resulting nineteen titration curves. A gen eralized form of the equations previously developed to account for the effect of the concentration of chloride ion on the amounts of hydrochloric acid combined was utilized to calculate the affinity for wool of each of seventeen anions involved. Predictions, based on the equations, as to the effects of variations of anion concentrations and of temperature were tested and confirmed. Measurements of the combination of a number of the same acids with a soluble protein, crystalline egg albumin, were also made. Since qualitatively similar differences in the corresponding titration curves were found with both proteins, it is concluded that the property of combining with anions is not restricted to insoluble proteins, such as wool, but is an inherent property of proteins in general. The affinity of the anions appears to increase with their dimensions, and is higher in aromatic than in aliphatic ions of the same size. These relationships are used as the basis of a consid eration of the nature of the forces involved in the binding by pro teins of anions, including the anions of acid dyes.

The rates of hydrolysis by dilute acids of both a dissolved protein (egg albumin) and an insoluble protein (wool) are shown to depend not only on the temperature and acidity but also on t he acid used. When hydrolyzed at 65° C by certain strong monobasic acids of high molecular weight, the amide and the peptide bonds are broken over 100 times as fast as when they are hydrolyzed with hydrochloric acid. Even among the common mineral acids, large differences appear. These differences in hydrolytic effectiveness parallel differences in the affinities of the anions of the acids for protein. A further reason for attributing t his effect to the anions is the attainment, with anions of high affinity, of a maximum rate of amide hydrolysis at r elatively low concentrations, stoichiometrically equivalent to the sum of the amino plus the amide groups. A similar limiting anion concentration or maximum rate of hydrolysis of t he much more numerous peptide groups is not observed. On the basis of details of t he dependence of the rate of hydrolysis on concentration of effective anions and hydrogen ions, a m echanism which involves combination of the groups hydrolyzed with hydrogen ions, is proposed.At low concentrations of effective anions, amide hydrolysis is catalyzed more strongly than peptide hydrolysis. By keeping the concentration slightly below stoichiometric equivalence to the sum of the amino plus amide groups the amide groups may be rapidly hydrolyzed without extensive hydrolysis of the peptide bonds in the protein. Practical applications are suggested.

No abstract

Evidence presented in previous papers supported the view that wool immersed in solutions containing hydrochloric lWit! combines stoichiometrically not only with the hydrogen ions of the acid but with chloride ions as well. As a consequence it appeared that the specific affinities for wool of the anions of different acids might vary considerably, and that therefore the positions of the titration curves of this protein with respect to the pH axis might vary by correspondingly large amounts according to the acid used.The present paper describes measurements of the combination of wool with 19 different acids, ranging in complexity from some of the mineral acids most commonly used through the simpler aromatic sulfonic, carboxylic, and phenolic acids to a soluble monoazo acid dye. It is shown that wide differences exist between the positions with respect to the pH axis of the titration curves of wool obtained with different strong acids, and that these differences may be ascribed to wide variations in the anion dissociation constants characterizing the corresponding protein-anion combinations. Equations previously derived to account for effects caused by variations in chloride concentration have been generalized for use in calculating these dissociation constants. A scale of relative affinities of anions for wool, based on these constants, and applicable to acid dyes, is proposed. Predic· tions as to the effects of variations of anion concentration and of temperature, based on the same generalized equations, have been tested and confirmed.Measurements of the combination of a number of the same acids with a soluble protein, crystalline egg albumin, have also been made. Since qualitatively similar differences in the positions, with respect to the pH axis , of the titration curves obtained with different acids are found with both proteins, it is concluded that the property of combining with anions is not restricted to insoluble proteins. The affinity of anions for proteins of both classes appears to increase with the dimensions of the anion, and is higher in aromatic than in aliphatic ions of the same size. The bearing of these relationships on the well known specific effects of ions on proteins and on the nature of the forces involved in the binding of anions by proteins is considered.