Ohira Shin-Ichi, Wanigasekara Eranda, Rudkevich Dmitry M, Dasgupta Purnendu K
Department of Chemistry and Biochemistry, The University of Texas at Arlington, Arlington, TX 76019-0065, USA.
Talanta. 2009 Mar 15;77(5):1814-20. doi: 10.1016/j.talanta.2008.10.024. Epub 2008 Oct 25.
Calixarenes are interesting building blocks in supramolecular receptor design. They can be easily functionalized to give the desired guest binding and sequestration properties. We demonstrate here the use of simple alkylated calixarenes as novel NO(2) sensors. Upon reacting with gaseous NO(2), alkylated calixarenes form stable calixarene-NO(+) (nitrosonium) complexes that have a deep purple color. This specific and selective formation of the colored complex was used to develop a fiber optic based colorimetric NO(2) sensor. Several alkylated calixarenes are used and tested as sensing materials. The calixarene compound was immobilized on a fine mesh silica-gel coated thin layer chromatography plate. The sensing plate was coupled with a fiber optic based photodetector. Gas samples were sampled in a manner where they impinged on the surface of sensing plate. The light transmission through the plate was continuously monitored. For a 5 min sample, the limit of detection was 0.54 ppmv with 1,3-alternate O-hexyl calix[4]arene (1a). There were no significant response differences between different conformations of calixarenes such as 1,3-alternate or cone. This chemistry can form the basis of a colorimetric sensor that relies on extant filter tape technology. With calixarenes however, such a reaction is potentially reversible - color formed upon reaction with NO(2) can be reversed by flushing the sensing plate by purified air. While we found that the removal of the developed color can be accelerated by simultaneous heating and suction, permitting the reuse of the same sensing area multiple times, we also observed that the sensitivity gradually decreased. The nitrosonium calixarene derivative tends to transform to the nitrated form; this process is catalyzed by light. Several methylated calixarenes were synthesized and tested but a fully satisfactory solution has proven elusive.
杯芳烃是超分子受体设计中有趣的结构单元。它们可以很容易地进行功能化修饰，以赋予所需的客体结合和螯合性能。我们在此展示了使用简单的烷基化杯芳烃作为新型NO₂传感器。与气态NO₂反应时，烷基化杯芳烃会形成稳定的杯芳烃 - NO⁺（亚硝基鎓）络合物，该络合物呈深紫色。这种有色络合物的特异性和选择性形成被用于开发一种基于光纤的比色法NO₂传感器。几种烷基化杯芳烃被用作传感材料并进行了测试。杯芳烃化合物被固定在涂有细网硅胶的薄层色谱板上。传感板与基于光纤的光电探测器相连。气体样品以撞击传感板表面的方式进行采样。通过该板的光传输被持续监测。对于5分钟的样品，使用1,3 - 交替O - 己基杯[4]芳烃（1a）时检测限为0.54 ppmv。杯芳烃的不同构象（如1,3 - 交替或锥形）之间没有明显的响应差异。这种化学方法可以构成一种基于现有滤带技术的比色传感器的基础。然而，对于杯芳烃来说，这样的反应可能是可逆的——与NO₂反应形成的颜色可以通过用净化空气冲洗传感板来逆转。虽然我们发现同时加热和抽吸可以加速已显色的去除，从而允许同一传感区域多次重复使用，但我们也观察到灵敏度逐渐降低。亚硝基鎓杯芳烃衍生物倾向于转化为硝化形式；这个过程由光催化。几种甲基化杯芳烃被合成并进行了测试，但尚未找到完全令人满意的解决方案。
