Molecular recognition process in the ultrathin-film surface observed by surface plasmon spectroscopy (SPR)

聚乙二醇（PEG）与α-环糊精（α-CD）的分子识别作用使其与α-CD形成聚轮烷。本研究采用自组装技术制备了一种由混合硫醇MeAzoPEGn（n= 6，10，16）和稀释剂硫醇（11-十一烷醇硫醇：HSC 11 OH或十二烷硫醇：HSC 12），并利用表面等离子体共振光谱（SPR）研究了聚轮烷-α-环糊精（α-CD）成膜过程及其光可控性，合成了新化合物MeAzoPEGn，由4-甲基偶氮苯部分、PEG（单元数：6，10，16）和巯基组成。加入α-CD溶液后，在MeAzoPEG 6的SAM处观察到膜厚度增加2.0±0.2 nm。发现α-CD环与MeAzoPEG 6链选择性地形成聚轮烷膜，而与稀释剂硫醇的种类无关。4-在MeAzoPEG 6末端取代的甲基偶氮苯部分被认为是捕获α-CD环的触发分子，然后CD环可以穿透PEG链。结果，PEG链被延长并且观察到新的轮烷层。在MeAzoPEG 10和MeAzoPEG 16的SAM的情况下，通过添加α-CD而增加的膜厚度较大。这可能是由于PEG链越长，CD分子越多，聚轮烷膜越厚。紫外光照射引起偶氮苯部分的异构化，加入α-CD后膜厚的增加被抑制了1.4nm。完全控制是不可能的，但部分控制是可能的，用于通过UV光照射形成聚轮烷膜。

It has been known that poly (ethylene glycol)(PEG) can form a polyrotaxane with α-cyclodextrin(α-CD) due to the molecular recognition. In this study, a self-assembled-monolayer(SAM) composed of mixture thiols, MeAzoPEGn (n=6,10,16) and diluent thiol (11-undecanol thiol : HSC11OH or dodecane thiol : HSC12), was prepared, and the formation process of polyrotaxane-ultrathin film with α-CD and its photo-controllability were investigated by the surface plasmon resonance spectroscopy(SPR).The novel compounds, MeAzoPEGn, synthesized by ourselves consist of 4-methyl azobenzene moiety, PEG (unit number:6,10,16), and mercapt group. The increase in the film thickness of 2.0±0.2 nm was observed at the SAM of MeAzoPEG6 after addition of α-CD solution. α-CD rings were found to form polyrotaxane-film selectively with MeAzoPEG6 chain regardless of the kind of the diluent thiols. 4-methyl azobenzene moiety substituted at the end of MeAzoPEG6 is considered to be a trigger molecule to capture α-CD rings and then, CD rings can penetrate through a PEG chain. As the result, a PEG chain was extended and a new rotaxane layer was observed. In the case of the SAM of MeAzoPEG10 and MeAzoPEG16,the increase in the film thickness by adding α-CD was larger. It is considered to be due to that more CD molecules are possible to form a thicker polyrotaxane-film for the longer PEG chain.Furthermore, the formation of polyrotaxane-film was investigated under UV irradiation. UV irradiation induces the isomerization of azobenzene moiety and the increase in the film thickness after adding α-CD was suppressed by 1.4 nm. The complete control was impossible but the partial control was possible for the formation of the polyrotaxane-film by UV light irradiation.