Dilatometric and refractometric studies of the helix—coil transition of poly‐L‐glutamic acid in aqueous solution
Dilatometric and refractometric studies of the helix—coil transition of poly‐L‐glutamic acid in aqueous solution
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聚-L-谷氨酸在水溶液中螺旋-螺旋转变的膨胀和折射研究
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发表时间：
1963
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影响因子：
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通讯作者：
Jen
中科院分区：
文献类型：
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作者：
H. Noguchi;Jen
聚-L-谷氨酸（PGA）在水溶液中的螺旋-卷曲转变之后是体积变化ΔV和差示折射率Δn。将PGA钠盐与稀HCl混合后，ΔV的增加或Δn的减少在pH 7和4之间产生三条直线，这两条断裂对应于通过其他物理方法观察到的过渡区。对于反应：HCOO − + H+ → HCOO − OH，每摩尔H+结合的ΔV为11.4和11.1 ml。分别在0.01和0.2M NaCl溶液中。约0.5-1 ml的额外构象变化。在考虑静电相互作用后，观察到每个氨基酸残基的反应：卷曲→螺旋。这可能是由于当多肽螺旋转化为α-螺旋时，酰胺键处的水合水释放，或者甚至是由于原子的不完美堆积而导致多肽链中出现空隙，尽管这种体积变化的起源目前仍不完全清楚。通过假设聚合物的极化率恒定，由Δn计算的体积变化被发现对于缔合反应比上述那些更高。另一方面，计算的转变ΔV与直接测量的ΔV相当一致。
The helix—coil transition of poly‐L‐glutamic acid (PGA) in aqueous solutions was followed by volume changes, ΔV, and also differential refractive indices, Δn. The increase in ΔV or decrease in Δn upon mixing the sodium salt of PGA with dilute HCl gave three straight lines between pH 7 and 4, the two breaks corresponding to the transition zone observed by other physical methods. For the reaction: COO− + H+ → CO‐OH, ΔV per mole of H+ bound was 11.4 and 11.1 ml. in 0.01 and 0.2M NaCl solutions, respectively. An additional conformational change of about 0.5–1 ml. per amino acid residue was observed for the reaction: coil → helix, after taking electrostatic interaction into consideration. This was probably due to the release of the water of hydration at the amide linkages when the polypeptide coil is converted into the α‐helix, or even the occurrence of voids in the polypeptide chain as a result of imperfect packing of the atoms, although the origin of this volume change is still not fully understood at the present time. The volume changes as calculated from Δn by assuming a constant polarizability of the polymer was found to be higher for the association reaction than those mentioned above. On the other hand, the calculated ΔV for the transition was in fair agreement with those by direct measurements.