【摘要】 在0.40-4.35g(water)/g(DNA)范围内用差示扫描量热法(DSC)研究了DNA内水的热力学状态与水合度R的关系.实验中观察到突出的冻结/熔融滞后.在R≤0.70g/g时无冻结放热峰可见,然而在218K下恒温15min于0.49g/g时即测到吸热峰.在R≥0.95和0.60-0.95g/g范围,积分熔融热Q_f-R分别呈线性和接近线性关系,表观微分熔融热分别为72.29和47.73cal/g.R≤0.60g/g时Q_f-R呈非线性关系.在0.49g/g时,Q_f随恒温时间t_k指数增加.实验表明,水的状态参数是依赖于t_k等动力学因素而随R连续变化的热力学量.由此我们提出了有关大分子内不冻水的两个概念.更多还原

【Abstract】 The thermodyamic states of the water in DNA and their relations to hydration were investigated in the water content R range from 0.40 to 4.35gwater/g DNA by means of differential scanning calorimetry. The extremely pronounced hysteresis in freezing/melting was always observed. At R≤about 0.70g/g no exotherms were observed during cooling down to 218K, however,the endotherms were observed at as low hydration as 0.49g/g after keeping samples at 218K for 15min. At R≥0.95g/g and in the range from 0.60 to 0.95g/g,the hydration dependences of the integral heat of fusion of water Qf are linear and closely linear, and the apparent differential heats of fusion 72.29 and 41.73 caI/g water, respectively. At R≤0.60g/g the relationship between Qf and R is nonlinear, At 0.49g/g the measured Qf increase exponentially with the increase of keeping time tk. Both the thermodynamic and kinetic results suggest that the meassured thermodynamic state parameters at subzero temperature are apparent thermodnamic quantities which depend closely upon kinetic factors and alter continuously with hydration. On the basis of the results obtained we have proposed two concepts on the non-freezing fraction. One is the limit hydration at which no freezable water can be detec ted by various techniques. Another is what degree the water in the metastable system can freeze to at various hydrations under the condition studied.Both of them, howeevr, require close specification of the experiment conditions.更多还原