Graduate School of Science and Engineering, Saitama University , 255 Shimo-Okubo, Sakura-ku, Saitama 338-8570, Japan.
Anal Chem. 2015 Feb 3;87(3):1933-40. doi: 10.1021/ac504201b. Epub 2015 Jan 14.
We designed a new series of boronic acid-functionalized squarylium cyanine dyes (SQ-BA) with different lengths of alkyl chain residues, suitable for multiple discriminant analysis (MDA) of sialic acid (Neu5Ac) in biological samples. The SQ-BA dyes form aggregates based on hydrophobic interactions, which result in quenched fluorescence in aqueous solutions. When the boronic acid binds with saccharides, the fluorescence intensity increases as a result of dissociation to the emissive monomeric complex. We inferred that different dye aggregate structures (H-aggregates and J-aggregates) were induced depending on the alkyl chain length, so that monosaccharides would be recognized in different ways (especially, multipoint interaction with J-aggregates). A distinctive emission enhancement of SQ-BA dyes with shorter-alkyl-chains in the presence of Neu5Ac was observed (2.4-fold fluorescence enhancement; with formation constant 10(1.7) M(-1)), with no such enhancement for SQ-BA dyes with longer-alkyl-chain. In addition, various enhancement factors for other monosaccharides were observed depending on the alkyl chain length. Detailed thermodynamic and NMR studies of the SQ-BA complexes revealed the unique recognition mechanism: the dye aggregate with a shorter-alkyl-chain causes the slipped parallel structure and forms a stable 2:1 complex with Neu5Ac, as distinct from longer-alkyl-chain dyes, which form a 1:1 monomeric complex. MDA using the four SQ-BA dyes was performed for human urine samples, resulting in the successful discrimination between normal and abnormal Neu5Ac levels characteristic of disease. Thus, we successfully controlled various responses to similar monosaccharides with a novel approach that chemically modified not the boronic acid moiety itself but the length of the alkyl chain residue attached to the dye in order to generate specificity.
我们设计了一系列带有不同长度烷基链残基的硼酸功能化 Squarylium 氰染料（SQ-BA），适用于生物样品中唾液酸（Neu5Ac）的多元判别分析（MDA）。SQ-BA 染料基于疏水相互作用形成聚集体，导致在水溶液中荧光猝灭。当硼酸与糖结合时，由于解离为发射单体复合物，荧光强度增加。我们推断，不同的染料聚集体结构（H-聚集体和 J-聚集体）是由烷基链长度引起的，因此单糖将以不同的方式被识别（特别是，与 J-聚集体的多点相互作用）。在 Neu5Ac 存在下，短烷基链 SQ-BA 染料的发射增强明显（荧光增强 2.4 倍；形成常数为 10(1.7) M(-1)），而长烷基链 SQ-BA 染料则没有这种增强。此外，还观察到其他单糖的各种增强因子取决于烷基链长度。对 SQ-BA 配合物的详细热力学和 NMR 研究揭示了独特的识别机制：短烷基链的染料聚集体导致滑动平行结构，并与 Neu5Ac 形成稳定的 2:1 配合物，与长烷基链染料不同，后者形成 1:1 单体配合物。使用四种 SQ-BA 染料对人尿样进行 MDA，成功区分了正常和异常 Neu5Ac 水平，这是疾病的特征。因此，我们成功地控制了对类似单糖的各种反应，这种方法不是对硼酸部分本身进行化学修饰，而是对连接到染料上的烷基链残基的长度进行化学修饰，以产生特异性。
