Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
J Am Chem Soc. 2012 Oct 24;134(42):17620-7. doi: 10.1021/ja307085h. Epub 2012 Oct 15.
Phenyl boronic acids (PBA) are important binding ligands to pendant diols useful for saccharide recognition. The aromatic ring can also function to anchor an otherwise hydrophilic polymer backbone to the surface of hydrophobic graphene or carbon nanotube. In this work, we demonstrate both functions using a homologous series of seven phenyl boronic acids conjugated to a polyethylene glycol, eight-membered, branched polymer (PPEG8) that allows aqueous dispersion of single-walled carbon nanotubes (SWNT) and quenching of the near-infrared fluorescence in response to saccharide binding. We compare the 2-carboxyphenylboronic acid (2CPBA); 3-carboxy- (3CPBA) and 4-carboxy- (4CPBA) phenylboronic acids; N-(4-phenylboronic)succinamic acid (4SCPBA); 5-bromo-3-carboxy- (5B3CPBA), 3-carboxy-5-fluoro- (5F3CPBA), and 3-carboxy-5-nitro- (5N3CPBA) phenylboronic acids, demonstrating a clear link between SWNT photoluminescence quantum yield and boronic acid structure. Surprisingly, quantum yield decreases systematically with both the location of the BA functionality and the inclusion of electron-withdrawing or -donating substituents on the phenyl ring. For three structural isomers (2CPBA, 3CPBA, and 4CPBA), the highest quantum yields were measured for para-substituted PBA (4CPBA), much higher than ortho- (2CPBA) and meta- (3CPBA) substituted PBA, indicating the first such dependence on molecular structure. Electron-withdrawing substituents such as nitro groups on the phenyl ring cause higher quantum yield, while electron-donating groups such as amides and alkyl groups cause a decrease. The solvatochromic shift of up to 10.3 meV was used for each case to estimate polymer surface coverage on an areal basis using a linear dielectric model. Saccharide recognition using the nIR photoluminescence of SWNT is demonstrated, including selectivity toward pentoses such as arabinose, ribose, and xylose to the exclusion of the expected fructose, which has a high selectivity on PBA due to the formation of a tridentate complex between fructose and PBA. This study is the first to conclusively link molecular structure of an adsorbed phase to SWNT optical properties and modulation in a systematic manner.
苯硼酸（PBA）是一种重要的结合配体，可与悬垂二醇结合，用于识别糖。芳环还可以将原本亲水的聚合物主链锚定到疏水性石墨烯或碳纳米管的表面。在这项工作中，我们使用一系列七个苯硼酸与聚乙二醇、八元支化聚合物（PPEG8）偶联来证明这两种功能，这使得单壁碳纳米管（SWNT）在水中分散，并在糖结合时响应近红外荧光猝灭。我们比较了 2-羧基苯硼酸（2CPBA）；3-羧基（3CPBA）和 4-羧基（4CPBA）苯硼酸；N-（4-苯硼酸）琥珀酸酰胺（4SCPBA）；5-溴-3-羧基（5B3CPBA）、3-羧基-5-氟（5F3CPBA）和 3-羧基-5-硝基（5N3CPBA）苯硼酸，清楚地表明 SWNT 光致发光量子产率与硼酸结构之间存在明显联系。令人惊讶的是，量子产率随着 BA 官能团的位置以及苯环上吸电子或供电子取代基的存在而系统地降低。对于三个结构异构体（2CPBA、3CPBA 和 4CPBA），对位取代的 PBA（4CPBA）的量子产率最高，远高于邻位（2CPBA）和间位（3CPBA）取代的 PBA，这表明首次依赖于分子结构。苯环上的吸电子取代基如硝基会导致更高的量子产率，而供电子基团如酰胺和烷基会导致量子产率降低。对于每种情况，我们都使用溶剂化位移高达 10.3 meV 来估计聚合物在面积基础上的表面覆盖率，使用线性介电模型。我们使用 SWNT 的近红外光致发光来证明糖的识别，包括对戊糖（如阿拉伯糖、核糖和木糖）的选择性，而排除了预期的果糖，由于果糖与 PBA 之间形成了一个三齿配合物，果糖对 PBA 具有很高的选择性。这项研究首次以系统的方式将吸附相的分子结构与 SWNT 的光学性质和调制联系起来。
