Changes in the X-ray diffraction pattern from lens during a solid-to-liquid phase transition

Purpose: The purpose of this study is to compare the structural integrity of bovine lenses using small-angle X-ray diffraction techniques, before and after freezing, using both liquid nitrogen and a −20°C freezer to understand the molecular changes that occur and to see if any permanent structural changes result from the freezing and thawing process. Materials and Methods: We used small-angle X-ray scattering to investigate the effects of freezing whole bovine eye lenses (i) in liquid nitrogen and (ii) at −20°C, to better understand the structural basis of the phase transitions. Results: Lenses frozen in liquid nitrogen thawed more rapidly than those placed at −20°C. With both freezing methods, X-ray patterns taken during the thawing process indicated less protein order than before or after freezing. After both freezing methods, the X-ray reflection returned to its original spacing and close to its original intensity values before freezing. Conclusions: We explain these phenomena in terms of a simple model based on the melting of ice crystals. We also suggest that the liquid nitrogen method of freezing is probably the better method of cryo-preservation for maintaining lens crystallin order