Malmos Kristoffer, Dong Mingdong, Pillai Saju, Kingshott Peter, Besenbacher Flemming, Pedersen Steen U, Daasbjerg Kim
Department of Chemistry, University of Aarhus, Langelandsgade 140, DK-8000 Aarhus C, Denmark.
J Am Chem Soc. 2009 Apr 8;131(13):4928-36. doi: 10.1021/ja809816x.
A methodology is described for introducing a thin layer of covalently attached benzaldehyde on glassy carbon surfaces using aryl diazonium chemistry. Usually the electroreduction of aryl diazonium salts leads to the formation of an ill-defined multilayer because of the involvement of highly reactive aryl radicals that can add to already-grafted aryl groups. However, in this study we used a two-step "formation-degradation" procedure to solve this problem with the first step consisting of an electrografting of an aryl diazonium salt of a long-chain and bulky alkyl hydrazone onto a glassy carbon surface. The design of the hydrazone group serves to minimize multilayer formation by greatly diminishing the grafting rate after the first-layer formation and at the same time preventing radical additions from taking place at the inner aryl ring. Another valuable property of the hydrazone group is that it easily can be deprotected to the corresponding aldehyde by acid hydrolysis (i.e., the degradation step). In this manner, a thin and well-defined film of covalently attached benzaldehyde with an estimated coverage of 4 x 10(-10) mol cm(-2) was formed. The electrochemical responses of benzaldehyde were highly reproducible and largely independent of grafting medium (water or DMSO) and along with that also the thickness of the initially grafted film. AFM and contact angle measurements support the findings. The "formation-degradation" approach thus lays the foundation for carrying out further functionalization reactions in a controlled manner.
本文描述了一种利用芳基重氮化学在玻碳表面引入共价连接的苯甲醛薄层的方法。通常，芳基重氮盐的电还原会导致形成不确定的多层结构，这是因为高活性的芳基自由基会参与反应，这些自由基会加成到已经接枝的芳基上。然而，在本研究中，我们使用了两步“形成-降解”程序来解决这个问题，第一步是将长链和庞大烷基腙的芳基重氮盐电接枝到玻碳表面。腙基团的设计旨在通过在第一层形成后极大地降低接枝速率，同时防止自由基在内部芳基环上加成，从而使多层结构的形成最小化。腙基团的另一个有价值的特性是它可以通过酸水解（即降解步骤）轻松地脱保护为相应的醛。通过这种方式，形成了共价连接的苯甲醛的薄且明确的膜，估计覆盖度为4×10(-10) mol cm(-2)。苯甲醛的电化学响应具有高度可重复性，并且在很大程度上与接枝介质（水或二甲基亚砜）无关，同时也与初始接枝膜的厚度无关。原子力显微镜和接触角测量结果支持了这些发现。因此，“形成-降解”方法为以可控方式进行进一步的功能化反应奠定了基础。
