The effect of polyethylene glycol (PEG) with different molecular weights and concentrations on the structure of collagen in crowded environment has been investigated by microcalorimetry (VP-DSC) and fluorescence spectroscopy. The results show that PEG does not destroy the triple helix structure of collagen, while it can influence the conformation of collagen, which is closely related to the molecular weight and the concentration of PEG. The larger the molecular weight or the higher the concentration of PEG, the greater it contributes to the increase in the thermal stability of collagen, due to the volume exclusion effect of PEG. Moreover, such impact is more evident for the pre-transition than the major transition during the thermal denaturation of collagen. Fluorescence spectroscopy analysis indicates that the volume exclusion effect exerted by the crowers, i.e. PEG, increases the fluorescence intensity of collagen. The reason can also be owing to the more compact conformational structure of collagen in the PEG-crowded solutions. It was also found that the fluorescent emission peaks of collagen slightly red-shift in the presence of PEG 6000 or higher molecular weights PEG.
