W0244

Comparison of Glycerol Concentration Required to Vitrify Samples Using Helium or Nitrogen as the Cryogen. U. Chinte^*, B. Shah^*, B.L. Hanson⁺, Y.-S. Chen, K. Kirschbaum, A. Pinkerton^*, K. DeWitt^*, C. Schall^*, ^*University of Toledo, ⁺University of Tennessee.

Hampton Screen I crystallization solutions were flash cooled with varying glycerol concentrations to ascertain the minimum glycerol concentration needed for vitrification of solutions using a liquid helium cryostat developed at the University of Toledo. Temperature and flow rate of the helium cryogen were varied. Protocols were similar to those reported by Garman¹ and Snell² for flash cooling these same solutions using a nitrogen cryostat and results were compared. At set temperatures of 8, 50 and 100 K, significantly less glycerol was required for vitrification when compared to results of Garman and Snell. As set temperature of the helium cryostat was increased, the concentration of glycerol required to vitrify some samples also increased. For selected samples, helium cryogen flow rate was varied at a set temperature of 50K. The glycerol concentration needed for vitrification was found to be lower at higher helium flow rates, providing insight into the role of convective cooling on vitrification. The results obtained from our 100 K experiment were compared with those obtained by Garman et al. using an Oxford 600 Series nitrogen cryostat. The glycerol concentrations needed for vitrification were found to be lower in many solutions using helium at 100 K than that using the Oxford cryostat at the same set temperature. The Oxford system delivers a lower velocity stream than the helium cryostat used for our experiments. The effects of temperature, velocity and cryogen properties on vitrification will be discussed.

¹Garman, E. F.; Mitchell, E. P. J. Appl. Crystallogr. 1996, 29, 584-587.

²McFerrin, M. B.; Snell, E. H. J. Appl. Crystallogr. 2002, 35, 538-545.