EQUILIBRIUM MECHANOCHEMISTRY OF COLLAGEN FIBERS

The isothermal shrinkage of a fiber under constant tensile force by varying the concentration of a component of the surrounding medium has been demonstrated previously. The thermodynamic corollary of this process states that the extent of chemical interaction between the fiber and such a component should be altered by applying force to the fiber. The interaction between collagen fibers and the denaturant LiBr, its variation with tensile force or relative length of the fiber, and the analysis of the mechanochemical properties of this system in terms of a two-state model are the subjects of this report. The experimental procedure included (1) preliminary exposure of the fibers to extremes of denaturant concentration and force to enhance reversibility of measured effects, (2) mercurimetric titration of LiBr, (3) use of a mechano chemically inert tracer [14C]glycerol in evaluating excess LiBr in the fiber phase relative to the external solution (enrichment), and (4) correlation of length and enrichment measurements for individual fibers. The variations of fiber length with tensile force and denaturant activity were semiquantitatively consistent with computations according to the two-state model of Hill. In solutions of constant denaturant activity, the measured enrichment decreased linearly with fiber length; in 5 m LiBr the molar ratio of excess LiBnamino acid residue varied from 1:4 in relaxed fibers to 1:7 in fully stretched fibers. The relationship between the sigmoidal force dependence of the enrichment and the sigmoidal dependence of fiber length upon denaturant activity fulfilled the thermodynamic predictions. © 1969, American Chemical Society. All rights reserved.