Aqueous dispersions (or colloidal solutions) of collagen may include pH buffers, salt(s) added to adjust ionic strength, salts with plurivalent cations which may possibly act as flocculants, and peptizing agents. Obviously, the conformation of the solvated collagen protein molecules, and the stability of the colloidal solution, is highly pH dependent. Gellation and/or coagulation is not only determined by temperature and the protein concentration, but also by applied shear stress (on stirring) and by thermal history, being thermal hysteresis commonly observed. Besides type of collagen, it is also important to consider its original raw source, and prior treatments, particularly those that may possibly have induced more or less extensive chemical irreversible changes, such as either acid or alkaline hydrolysis, or thermally induced denaturation. Particular attention should be given to drying methodology. All this possibly influencing factors should be carefully considered and experimentally controlled. It is not clear, from the question enunciate, the kind of buffer-exchange that seemingly may have been pursuit by applying dialysis to the protein colloidal solution. About the effect of pH, you may want to check the following related discussion: https://www.researchgate.net/post/Can_anyone_suggest_me_the_buffer_conditions_or_methods_for_solubilising_collagen_powder_other_than_acidic_condition

Thanks for the comments, Carlos.  We have a stock solution of collagen in acidic pH (3.2).  In the experiments described, we dialyse it into pH 9.3 or else into pH 3.2 (control) and run both samples on a gel.  The control sample (acidic pH) shows many bands shorter than full-length alpha chains, while the sample in basic pH shows nothing shorter than alpha chains.  It is extremely puzzling to me why shorter chains should be apparent when collagen is in acidic pH and not basic.  Both samples are heated in loading buffer containing DTT prior to loading into the gel.  Gels are silver stained for detection.

Dear Nancy:

Upon heating, owing to added 1,4-dithiothreitol (DTT), disulfide bridges may possibly have been broken to some extent, accordingly: DTT + R–S–S–R' + 2H3O+ + 2e− → DTT-oxidized + R–SH + R'–SH + 2H2O; DTT + 2H2O → DTT-oxidized + 2H3O+ + 2e−. Addition of sodium dodecyl sulfate (SDS) for polyacrylamide gel electrophoresis (SDS-PAGE) can be expected to reinforce such (seemingly possible) DTT-induced denaturation. Thermal denaturation of collagen can generally be expected to be particularly noticeably above approx. 50―60 ºC. Extensive crosslink breaking can, in principle, occur for higher temperatures, hence compromising supramolecular structure.