Instituto de Química, Universidade de São Paulo, São Paulo, Brazil.
Langmuir. 2010 Sep 7;26(17):14032-8. doi: 10.1021/la102254g.
Ellipsometry was used to investigate the influence of ionic strength (I) and pH on the adsorption of bovine serum albumin (BSA) or beta-lactoglobulin (BLG) onto preabsorbed layers of two polycations: poly(diallyldimethylammonium chloride) (PDADMAC) or poly(4-vinylpyridine bromide) quaternized with linear aliphatic chains of two (QPVP-C2) or five (QPVP-C5) carbons. Comparisons among results for the three polycations reveal hydrophobic interactions, while comparisons between BSA and BLG-proteins of very similar isoelectric points (pI)-indicate the importance of protein charge anisotropy. At pH close to pI, the ionic strength dependence of the adsorbed amount of protein (Gamma) displayed maxima in the range 10 < I < 25 mM corresponding to Debye lengths close to the protein radii. Visualization of protein charge by Delphi suggested that these ionic strength conditions corresponded to suppression of long-range repulsion between polycations and protein positive domains, without diminution of short-range attraction between polycation segments and locally negative protein domains, in a manner similar to the behavior of PE-protein complexes in solution. (1-4) This description was consistent with the disappearance of the maxima at pH either above or below pI. In the former case, Gamma values decrease exponentially with I(1/2), due to screening of attractions, while in the latter case adsorption of both proteins decreased at low I due to strong repulsion. Close to or below pI both proteins adsorbed more strongly onto QPVP-C5 than onto QPVP-C2 or PDADMAC due to hydrophobic interactions with the longer alkyl group. Above pI, the adsorption was more pronounced with PDADMAC because these chains may assume more loosely bound layers due to lower linear charge density.
利用椭圆光度法研究了离子强度 (I) 和 pH 值对牛血清白蛋白 (BSA) 或β-乳球蛋白 (BLG) 在两种聚阳离子：聚二烯丙基二甲基氯化铵 (PDADMAC) 或带线性脂肪链的 4-乙烯基吡啶溴化物季铵化产物 (QPVP-C2 或 QPVP-C5) 预吸附层上吸附的影响。三种聚阳离子的结果比较表明存在疏水相互作用，而 BSA 和 BLG-等电点 (pI) 非常相似的蛋白质之间的比较表明蛋白质电荷各向异性的重要性。在接近 pI 的 pH 值下，蛋白质吸附量 (Gamma) 随离子强度的变化显示出在 10 < I < 25 mM 范围内的最大值，对应于接近蛋白质半径的德拜长度。Delphi 对蛋白质电荷的可视化表明，在这些离子强度条件下，聚阳离子和蛋白质正域之间的长程排斥得到抑制，而聚阳离子段和局部负的蛋白质域之间的短程吸引没有减弱，类似于 PE-蛋白质复合物在溶液中的行为。(1-4) 这种描述与在 pH 值高于或低于 pI 时最大值的消失是一致的。在前一种情况下，Gamma 值随 I(1/2) 呈指数下降，这是由于吸引力的屏蔽，而在后一种情况下，由于强烈的排斥作用，两种蛋白质在低 I 时的吸附都减少了。在接近或低于 pI 时，由于与较长的烷基发生疏水相互作用，两种蛋白质在 QPVP-C5 上的吸附都比在 QPVP-C2 或 PDADMAC 上更强。在 pI 以上，由于较低的线性电荷密度，PDADMAC 上的吸附更为明显，因为这些链可能形成更松散结合的层。
