Hindered diffusion in agarose gels: Test of effective medium model
Hindered diffusion in agarose gels: Test of effective medium model
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DOI：
10.1016/s0006-3495(96)79645-5
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发表时间：
1996-02-01
影响因子：
3.4
通讯作者：
Deen, WM
中科院分区：
文献类型：
--
作者：
Johnson, EM;Berk, DA;Deen, WM
不带电荷的大分子在凝胶(D)中的扩散系数(D)通常低于在自由溶液(D)中的扩散系数(D-无穷大)，这是由于流体动力和空间因素的共同作用。为了检验这些因素，我们测量了几种荧光素标记的大分子的稀溶液的D和D，使用基于图像的荧光漂白后恢复技术。在琼脂糖体积分数(Phi)为0.038-0.073的琼脂糖凝胶中，研究了斯托克斯-爱因斯坦半径(r(S))为2.16.2 nm的大分子，包括三种球状蛋白(牛血清白蛋白、卵白蛋白、乳清蛋白)和四种Ficoll的窄组分。凝胶的表征是通过测量支撑琼脂糖膜的水力渗透性，从而计算每个凝胶样品的达西渗透率(K)。结果发现，随着phi的增加，凝胶的固有水力传导性的量度K下降了一个数量级。扩散比D/D-无穷大的变化范围为0.2~0.63，随r(S)或Phi的增大而减小。因此，正如预期的那样，对于大分子和/或相对浓缩的凝胶来说，扩散障碍是最严重的。根据最近提出的纤维介质中的受阻扩散理论，扩散系数比是流体动力因子(F)和空间因子(S)的乘积。其泛函形式为D/D-无穷=F(r/(S)/K-1/2)S(F)，其中f=[(r(S)+r(F))/r(F)](2)phi，r(F)为纤维半径。用这种有效介质理论计算的D/D无穷大值，在不使用可调参数的情况下，与实测值的一致性比基于其他方法的预测值要好得多。讨论了有效介质理论用于预测凝胶中扩散系数的优点和局限性。
The diffusivities of uncharged macromolecules in gels (D) are typically lower than in free solution (D-infinity, because of a combination of hydrodynamic and steric factors. To examine these factors, we measured D and D, for dilute solutions of several fluorescein-labeled macromolecules, using an image-based fluorescence recovery after photobleaching technique. Test macromolecules with Stokes-Einstein radii (r(s)) of 2.1-6.2 nm, including three globular proteins (bovine serum albumin, ovalbumin, lactalbumin) and four narrow fractions of Ficoll, were studied in agarose gels with agarose volume fractions (phi) of 0.038-0.073. The gels were characterized by measuring the hydraulic permeability of supported agarose membranes, allowing calculation of the Darcy permeability (K) for each gel sample. It was found that K, which is a measure of the intrinsic hydraulic conductance of the gel, decreased by an order of magnitude as phi was increased over the range indicated. The diffusivity ratio D/D-infinity, which varied from 0.20 to 0.63, decreased with increases in r(s) or phi. Thus as expected, diffusional hindrances were the most severe for large macromolecules and/or relatively concentrated gels. According to a recently proposed theory for hindered diffusion through fibrous media, the diffusivity ratio is given by the product of a hydrodynamic factor (F) and a steric factor (S). The functional form is D/D-infinity = F(r/(s)/K-1/2) S(f), where f = [(r(s) + r(f))/r(f)](2) phi and r(f) is the fiber radius. Values of D/D-infinity calculated from this effective medium theory, without use of adjustable parameters, were in much better agreement with the measured values than were predictions based on other approaches. The strengths and limitations of the effective medium theory for predicting diffusivities in gels are discussed.