Nagase Kenichi, Kobayashi Jun, Kikuchi Akihiko, Akiyama Yoshikatsu, Kanazawa Hideko, Okano Teruo
Institute of Advanced Biomedical Engineering and Science, Tokyo Women's Medical University, 8-1 Kawadacho, Shinjuku, Tokyo 162-8666, Japan.
Langmuir. 2008 Jan 15;24(2):511-7. doi: 10.1021/la701839s. Epub 2007 Dec 18.
We have prepared various poly(N-isopropylacrylamide) (PIPAAm)-grafted silica bead surfaces through surface-initiated atom transfer radical polymerization (ATRP) by changing graft densities and brush chain lengths. The prepared surfaces were characterized by chromatographic analysis using the modified silica beads as chromatographic stationary phases. ATRP initiator (2-(m,p-chloromethylphenyl)ethyltrichlorosilane) density on silica bead surfaces was modulated by changing the feed composition of the self-assembled monolayers (SAMs) of mixed silane coupling agents consisting of ATRP initiator and phenethyltrichlorosilane on the surfaces. IPAAm was then polymerized on SAM-modified silica bead surfaces by ATRP in 2-propanol at 25 degrees C. The chain length of the grafted PIPAAm was controlled by simply changing the ATRP reaction time at constant catalyst concentration. The thermoresponsive surface properties of the PIPAAm-grafted silica beads were investigated by temperature-dependent elution behavior of hydrophobic steroids from the surfaces using Milli-Q water as a mobile phase. On the surfaces grafted with shorter PIPAAm chains, longer retention times for steroids were observed on sparsely grafted PIPAAm surfaces compared to dense PIPAAm brushes at low temperature, because of hydrophobic interactions between the exposed phenethyl groups of SAMs on silica surfaces and steroid molecules. Retention times for steroids on dilute PIPAAm chain columns decreased with temperature similarly to conventional reverse-phase chromatographic modes on octadecyl columns. This effect was due to limited interaction of solutes with the PIPAAm-grafted surfaces. Retention times for steroids on dilute PIPAAm brush surfaces with longer PIPAAm chains became greater above the PIPAAm transition temperature. At low-temperature regions, hydrated and expanded PIPAAm at low temperatures prevented hydrophobic interactions between the phenethyl group of SAMs on the silica bead surfaces and steroid molecules. Retention times for steroids on a dense PIPAAm brush column increased with temperature since solvated polymer segments within the dense brush layer undergo dehydration over a broad range of temperatures. In conclusion, PIPAAm graft density has a crucial influence on the elution behavior of steroids because of the interaction of analytes with silica bead interfaces, and because of the characteristic dehydration of PIPAAm in dense-pack brush surfaces.
我们通过改变接枝密度和刷链长度，利用表面引发原子转移自由基聚合（ATRP）制备了各种聚（N-异丙基丙烯酰胺）（PIPAAm）接枝的二氧化硅珠表面。以改性后的二氧化硅珠作为色谱固定相，通过色谱分析对制备的表面进行了表征。通过改变由ATRP引发剂和苯乙基三氯硅烷组成的混合硅烷偶联剂在表面自组装单分子层（SAMs）的进料组成，调节二氧化硅珠表面上的ATRP引发剂（2-（间、对-氯甲基苯基）乙基三氯硅烷）密度。然后，在25℃下于2-丙醇中通过ATRP使IPAAm在SAM修饰的二氧化硅珠表面上聚合。通过在恒定催化剂浓度下简单地改变ATRP反应时间来控制接枝的PIPAAm的链长。以超纯水为流动相，通过温度依赖性的疏水性甾体从表面的洗脱行为，研究了PIPAAm接枝的二氧化硅珠的热响应表面性质。在接枝有较短PIPAAm链的表面上，与低温下的密集PIPAAm刷相比，在稀疏接枝的PIPAAm表面上观察到甾体的保留时间更长，这是由于二氧化硅表面上SAMs的暴露苯乙基与甾体分子之间的疏水相互作用。甾体在稀PIPAAm链柱上的保留时间随温度降低，这与十八烷基柱上的传统反相色谱模式类似。这种效应是由于溶质与PIPAAm接枝表面的相互作用有限。在具有较长PIPAAm链的稀PIPAAm刷表面上，甾体的保留时间在PIPAAm转变温度以上变得更长。在低温区域，低温下水合和膨胀的PIPAAm阻止了二氧化硅珠表面上SAMs的苯乙基与甾体分子之间的疏水相互作用。甾体在密集PIPAAm刷柱上的保留时间随温度增加，因为密集刷层内的溶剂化聚合物链段在很宽的温度范围内发生脱水。总之，由于分析物与二氧化硅珠界面的相互作用，以及由于密集堆积刷表面中PIPAAm的特征性脱水，PIPAAm接枝密度对甾体的洗脱行为有至关重要的影响。
