The swelling of collagen in alkaline solutions. 1. Swelling in solutions of sodium hydroxide

Abstract

The swelling of collagen and other fibrous proteins in acid and alkaline solutions is governed by the osmotic pressure differences arising between the protein phase and the external solution as a result of the formation of protein salts-Donnan membrane effect- (Procter, 1914;Bolam, 1932;Donnan, 1933), and by the cohesion of the protein (Procter, 1914; Jordan Lloyd, 1920, 1938, i.e. the forces opposing swelling, such as interweaving ofthe fibres and intermolecular forces. In order to interpret the effect of pH changes on swelling it is, therefore, necessary to consider the influence ofthe acid or alkali both on the Donnan equilibria and on the cohesion ofthe protein.The swelling of collagen and gelatin in alkaline solutions has received much less attention than that in acid solutions. A number of swelling curves of gelatin in alkaline solutions have been reported (Jordan Lloyd, 1920, 1930Jordan Lloyd & Pleass, 1927, 1928 Loeb, 1921a, b, c, d; Kunitz, 1923-4;Pleass, 1930), but in general these do not extend above pH 12-0 and make no allowance for solution of the gelatin. A few aLkaline swelling curves of collagen have also been reported (Kaye & Jordan Lloyd, 1924a, b;Jordan Lloyd, Marriott & Pleass, 1933;Highberger, 1936), but in all these there are insufficient points to determine the exact shape of the curves above pH 11-0. They show, however, no definite decrease in swelling at high pH values corresponding to that occurring in acid solutions below pH 2-0. With keratin (Jordan Lloyd & Marriott, 1934) and silk Coleman & Howitt, 1947) there is also an increase rather than a decrease in swelling at high pH values. With silk this increased swelling is accompanied by splitting up of the fibres, and is attributed to a weakening of the cohesive forces of the fibre.The swelling of gelatin in alkaline solutions up to pH 10 is reduced by the addition of sodium chloride or other appropriate salts, in the same manner as swelling in acid solutions, but at higher pH values the curves have an upward trend, and the suppression of swelling is less marked (Jordan Lloyd & Pleass, 1927, 1928. There is also some evidence that the nature of the anion has some influence on swelling; e.g. sodium nitrate depresses swelling to a lesser extent than sodium chloride at the same molar concentration (Jordan Lloyd & Pleass, 1927, 1928

On the Significance of the Extractable Collagens

“…To obtain solution the swelling pressure must exceed the cohesive forces. Thus a good proportion of collagen fibers from a young growing animal (about 20 per cent) can be extracted readily with organic acids around pH 3, which is close to the point of maximum swelling (5). In the rest of the fiber the remaining collagen can only be rendered soluble by applying even more disruptive forces by gelatinization.…”

Studies on the Formation of Collagen

“…Solubilization of bovine hide collagen at 20°C. begins at pH 13 after many days of incubation, mounting to about 5 per cent after 14 days (21). That which occurs between pH 2.5 and 5 represents a dissolution of the fibrils to their component molecules and aggregates.…”

The interplay between surface micro-topography and -mechanics of type I collagen fibrils in air and aqueous media: An atomic force microscopy study

“…Furthermore, the collagen fibrils were found to deform considerably upon increase in the contact force, as evidenced in Figure 5. These results can be attributed to the hydration of collagen fibrils in aqueous media [30], which serves to restructure the contracted fibrils into the intact form with higher elasticity. The non-linear dependence seen in the force-separation profile in the contact regime (Fig.…”