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

本文合成了由季铵硫衍生物组成的阳离子自组装单层（SAMs），以控制金衬底上带电头基之间的距离。本研究采用了两种具有类似分子结构的分子，“双子座”结构的二十二烷基二硫醇（HS-gQA-SH）和二十二烷基二硫醇（QA-SS-QA）或十二烷基硫醇（QA-SH），并采用表面等离子体共振光谱（SPR）、x射线光电子能谱（XPS）、傅里叶变换红外反射吸附光谱（FTIR-RAS）和开尔文探针方法对其形成和结构进行了表征。在HS-gQA-SH SAM中，QA基团的取向和距离是由与乙烯间隔键的共价键决定的，而QA- ss -QA SAM和QA- sh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基团位置更随机，与HS-gQA-SH SAM中的QA基团距离更远。KP得到的接触电位差数据表明，由于官能团密度更高，HS-gQA-SH SAM上的偶极子比QA-SH SAM上的偶极子大得多。我们发现l -酒石酸（TA）是一种探针分子，其两个羧基的距离为一个乙烯单元，对HS-gQA-SH SAM具有很强的亲和力。相比之下，在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TA对映体（L或D-TA）固定化QA-SH SAM上的晶体生长，并发现了相同手性表面（L-TA在L-TA上）的选择性晶体生长。在本研究中，我们还尝试了一步合成由QA-SS-QA SAM覆盖的金纳米颗粒。

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.