Department of Chemical and Biological Engineering, University of Sheffield , Sheffield S1 3JD, U.K.
Biological Physics Group, University of Manchester , Schuster Building, Manchester M13 9PL, U.K.
Langmuir. 2016 Aug 16;32(32):8202-11. doi: 10.1021/acs.langmuir.6b02068. Epub 2016 Aug 5.
Regenerated silk fibroin (RSF) is a Food and Drug Administration-approved material and has been widely used in many biomedical and cosmetic applications. Because of the amphiphilic nature of the primary repeat amino acid sequence (e.g., AGAGAS), RSF peptides can significantly reduce the water surface tension and therefore have the potential to be used as a surface active component for many applications, particularly in the biomedical, cosmetic, pharmaceutical, and food industries. In this paper, the adsorption of RSF peptides separated into molecular fractions of 5-30, 30-300, and >300 kDa has been studied at the solid-water interface by neutron reflection and spectroscopic ellipsometry to assess its surface active behavior. A stable layer of RSF was found to be irreversibly adsorbed at the hydrophilic SiO2-water interface. Changes in solution concentration, pH, and ionic strength all had an impact on the final adsorbed amount found at the interface. There were no significant differences between the final adsorbed amounts or layer structure among the three RSF molecular fractions studied; however, >300 kDa RSF was more stable to changes in solution ionic strength. Adsorption of conventional anionic and cationic surfactants, sodium dodecyl sulfate (SDS) and dodecyl trimethylammonium bromide (C12TAB), to the preadsorbed 5-30 kDa RSF revealed penetration of the surfactant into the RSF layer, at concentrations below the critical micellar concentration (CMC). SDS was found in the preadsorbed RSF layer and gradually removed RSF from the surface with an increase in SDS concentration. At concentrations above the CMC, there is near complete removal of RSF by SDS at the interface. C12TAB adsorbed into the preadsorbed RSF layer with considerably less removal of RSF from the interface compared to SDS. At concentrations above the CMC, both C12Tab and RSF were found to coexist at the interface, forming a less thick layer but with a considerable amount of RSF still present.
再生丝素蛋白（RSF）是一种获得美国食品和药物管理局批准的材料，已广泛应用于许多生物医学和化妆品应用中。由于初级重复氨基酸序列的两亲性质（例如，AGAGAS），RSF 肽可以显著降低水的表面张力，因此有可能作为许多应用的表面活性剂成分，特别是在生物医学、化妆品、制药和食品工业中。在本文中，通过中子反射和光谱椭圆术研究了分离成 5-30、30-300 和>300 kDa 分子分数的 RSF 肽在固-水界面的吸附，以评估其表面活性行为。发现 RSF 稳定层不可逆地吸附在亲水 SiO2-水界面上。溶液浓度、pH 值和离子强度的变化都对界面上最终吸附量有影响。在所研究的三种 RSF 分子分数中，最终吸附量或层结构没有明显差异；然而，>300 kDa 的 RSF 对溶液离子强度的变化更稳定。在预吸附的 5-30 kDa RSF 上吸附常规阴离子和阳离子表面活性剂十二烷基硫酸钠（SDS）和十二烷基三甲基溴化铵（C12TAB），发现表面活性剂在胶束浓度（CMC）以下时渗透到 RSF 层中。在预吸附的 RSF 层中发现 SDS，并随着 SDS 浓度的增加逐渐从表面去除 RSF。在 CMC 以上浓度时，SDS 在界面处几乎完全去除 RSF。与 SDS 相比，C12TAB 吸附到预吸附的 RSF 层中，从界面去除的 RSF 要少得多。在 CMC 以上浓度时，发现 C12Tab 和 RSF 都存在于界面上，形成一个较薄的层，但仍有相当多的 RSF 存在。
