溶液热历史对蛋白质晶体生长影响的内在原因研究

从溶液中聚集体的角度研究了溶液的热历史改变生长出的蛋白质晶体的数目和尺寸的内在原因.将在281和309 K下保存1 d的两组溶菌酶溶液按不同比例混合,加入沉淀剂生长晶体.随着高温溶液的比例增加,生长出的晶体数目减少,同时溶液中生长基元的尺寸增大.在5周内,采用动态光散射对281,293和309K三种温度下保存的溶菌酶溶液中聚集体的变化情况进行监测,发现溶液中均存在大小不同的两部分聚集体,称之为小聚集体与多聚体.前者的尺寸基本不随保存时间而变化,而后者尺寸随保存时间增加而减小,减小的速度与保存温度有关.多聚体的尺寸经过5周后和小聚集体基本相同.研究结果表明,处于无序聚集阶段的溶液的均一化程度和成核阶段生长基元的尺寸受到了溶液热历史的影响,并最终对晶体的数目产生影响.

<br /> La₆₄Al₁₄(Cu,Ni)₂₂, La_63.1Al1_5.2(Cu,Ni)_21.7, La_57.6Al_17.5(Cu,Ni)_24.9, and La₅₅Al₂₅Cu₁₀Ni₅Co₅ bulk metallic glasses (BMGs) with low glass transition temperature (<i>T_g</i>) were prepared by copper-mould casting method. The homologous temperature (the ratio of room temperature to <i>T_g</i>) of the four BMGs ranges from 0.64 to 0.73. Plastic deformation behavior of the BMGs at various loading rates was studied by nanoindentation. The results showed that the loading rate dependency of serrated flow, which is related to the nucleation and propagation of shear bands, depends strongly on the homologous temperature. The alloys with relatively high homologous temperature exhibit an increase in flow serration with increasing loading rate, whereas, the alloys with low homologous temperature exhibit prominent serrations at low rates. No distinct shear band is observed around the indents for all alloys after nanoindentation at all the studied loading rates. Alternately, shear band pattern are characterized through macro-indentation, which shows that shear band spacing decreases with the increase of the homologous temperature.