Cationic self-assembled monolayers composed of gemini-structured sulfur compounds on gold : A new approach to control ionic functions on surfaces and chiral detection.

合成了由季铵(QA)硫衍生物组成的阳离子自组装单分子膜(SAM)，以控制金表面带电头基之间的距离。本研究选用了两个具有相似分子结构的分子--双子结构的二硫醇(HS-gQA-SH)和二硫代十二烷基二硫醇(QA-SS-QA)或十二烷基硫醇(QA-SH)，用表面等离子体共振谱(SPR)、X射线光电子能谱(XPS)、傅里叶变换红外反射吸收光谱(FTIR-RAS)和开尔文探针法对自组装膜的形成和结构进行了表征。在HS-gQA-SH SAM中，QA基团之间的取向和距离是由与乙烯间隔基的共价键决定的，而QA-SS-QA SAM和QA-SH中的取向和距离是由带电头基之间的电斥力决定的，即QA-SS-QA SAM和QA-SH中的QA基团分布更随机，距离比HS-gQA-SH SAM中的更远。KP的接触电势差数据表明，与QA-SH SAM相比，HS-gQA-SH SAM上存在更大的偶极，这是由于官能团密度较高所致。我们发现具有两个羧基的探针分子L-酒石酸(TA)在HS-gQA-SH SAM上表现出很强的亲和力。相反，QA-SS-QA SAM和QA-SH SAM上几乎没有观察到特异性结合。我们证明了L-TA在固定了QA-SH自组装膜的TA对映体(L或D-TA)上的晶体生长，并发现在相同的手性表面(L-TA在L-TA上)选择性地生长了晶体。在本研究中，我们还尝试了以QA-SS-QA SAM为封端的金纳米粒子的一步合成。

Cationic self-assembled monolayers (SAMs) composed of quaternary ammonium (QA) sulfur derivatives have been synthesized to control the distance between charged head groups on gold substrates. Two molecules bearing resembling molecular structures, "gemini"-structured didodecyl dithiol (HS-gQA-SH) and didodecyl disulfide (QA-SS-QA) or dodecyl thiol (QA-SH), were utilized in this study, and the formation and structure of the SAMs were characterized by surface plasmon resonance spectroscopy (SPR), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared-reflection adsorption spectroscopy (FTIR-RAS) and Kelvin Probe method. In the HS-gQA-SH SAM, the orientation and distance between QA groups are specified by the covalent bonding with ethylene spacer, while those of the QA-SS-QA SAM and QA-SH are determined by the electric repulsion between charged head groups, that is, QA groups in the QA-SS-QA SAM and QA-SH are more randomly located, being more distant than with those in the HS-gQA-SH SAM. Contact potential difference data obtained by KP suggested the existence of much larger dipoles on HS-gQA-SH SAM compared with on QA-SH SAM as a result of higher density of the functional group.We found that L-tartaric acid (TA), a probe molecule with two carboxyl groups having the distance of an ethylene unit, exhibits a strong affinity on the HS-gQA-SH SAM. In contrast, a specific binding was little observed on the QA-SS-QA SAM and QA-SH SAM. We demonstrate the crystal growth of L-TA on TA enantiomers (L or D-TA) immobilized QA-SH SAM, and found selective crystal growth on the same chiral surfaces (L-TA on L-TA). We have also tried one-step synthesis of gold nanoparticles capped by the QA-SS-QA SAM in this study.