Universal charge quenching and stability of proteins in 1-methyl-3-alkyl (hexyl/octyl) imidazolium chloride ionic liquid solutions.
Universal charge quenching and stability of proteins in 1-methyl-3-alkyl (hexyl/octyl) imidazolium chloride ionic liquid solutions.
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DOI：
10.1021/jp3049108
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发表时间：
2012-08
期刊：
影响因子：
--
通讯作者：
Kamla Rawat;H. Bohidar
中科院分区：
文献类型：
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作者：
Kamla Rawat;H. Bohidar
本文报道了五种常见蛋白质--牛血清白蛋白、人血清白蛋白、免疫球蛋白、β-乳球蛋白和明胶-B等电点的蛋白质分散体在1-甲基-3-烷基(己基/辛基)咪唑氯化物(浓度为0-0.2%w/v)的室温离子液体溶液中的等电点≈5的稳定性。这些分子的疏水性指数(H指数=疏水性/亲水性)介于0.43-0.87之间。电泳特征、表面张力数据和流体力学尺寸信息表明，IL溶液由于特定的蛋白质-IL结合而提供分散稳定性，尽管其表面电荷被相当程度地屏蔽，但并未改变其等电点。在pH~3(最大质子化状态)和pH~8(最大去质子化状态)下观察到的最大(ζ(Max))和最小(ζ(Min))zeta电位值的变化可以普遍地描述为IL浓度的函数，c为Δζ(X)=[1-EXP(-Ac)]，其中Δζ(X)是|(ζ(Max)-ζ(W))|/ζ(W)或|(ζ(Min)-ζ(W))|/ζ(W)，ζ(W)是水中相应的值。张力计量学数据显示蛋白质-IL相互作用的两个主要阶段：(1)对于c-CMC，开始形成游离的IL-聚集体。同样，我们可以将Δγ(X)定义为：在pH为3时的|(γ(Max)-γ(W))|/γ(W)或在pH为8时的|(γ(Min)-γ(W))|/γ(W)。Δζ(X)和Δγ(X)都与c呈线性关系，Δγ(min，max)(或Δζ(min，max))=(1-K(γ)(或K(ζ))H指数)，其中斜率K(ζ)和K(γ)定义了分子间相互作用。流体动力学半径数据显示蛋白质稳定，圆二色谱表明二级结构保持不变，拉曼光谱证实水结构略有增加。结果表明，IL分子以双层形式选择性地结合到蛋白质表面，从而屏蔽蛋白质表面电荷，从而有助于其分散稳定性。
This study reports pH dependent stability of protein dispersions of five common proteins, bovine serum albumin (BSA), human serum albumin (HSA), immunoglobulin (IgG), β-lactoglobulin (β-Lg), and gelatin-B (Gel-B), all having isoelectric pH, pI ≈ 5, in room temperature ionic liquid solutions of 1-methyl-3-alkyl (hexyl/octyl) imidazolium chloride (concentration 0-0.2% w/v). Molecular hydrophobicity index, (H-index = hydrophobicity/hydrophilicity) of these molecules spanned the range 0.43-0.87. Electrophoretic characteristics, surface tension data and hydrodynamic size information revealed that IL solutions provide dispersion stability owing to specific protein-IL binding which did not alter their pI values though their surface charge was considerably screened. Change in maximum (ζ(max)) and minimum (ζ(min)) zeta potential values observed at pH ~3 (maximum protonated state) and pH ~8 (maximum deprotonated state) could be described universally as function of IL concentration, c as Δζ(x) = [1 - exp(-ac)] where Δζ(x) is either |(ζ(max) - ζ(w))|/ζ(w) or |(ζ(min) - ζ(w))|/ζ(w), and ζ(w) is the corresponding value in water. Tensiometry data showed two major stages of protein-IL interactions: (i) for c cmc free IL-aggregates begin to form. Similarly, we can define Δγ(x) as either |(γ(max) - γ(w))|/γ(w) at pH 3 or |(γ(min) - γ(w))|/γ(w) at pH 8. Both Δζ(x) and Δγ(x) showed linear dependence with c, Δγ(min, max) (or Δζ(min, max)) = (1 - K(γ) (or K(ζ)) H-index), where the slopes K(ζ) and K(γ) defined intermolecular interactions. Hydrodynamic radii data revealed protein stabilization, circular dichroism spectra implied retention of secondary structures, and Raman spectra confirmed a marginal increase in water structure. Results concluded that selective binding of IL molecules to protein surface in the form of bilayer screen protein surface charge, thereby, contributing to its dispersion stability.