Centre of Chemistry-Vila Real (CQ-VR), Department of Chemistry, University of Trás-os-Montes and Alto Douro, Quinta de Prados, 5001-801 Vila Real, Portugal; Centre of Chemistry (CQ-UM), Department of Chemistry, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal.
Health Sciences Research Centre (CICS-UBI), University of Beira Interior, Av. Infante D. Henrique, 6201-506 Covilhã, Portugal.
Bioorg Chem. 2021 Oct;115:105221. doi: 10.1016/j.bioorg.2021.105221. Epub 2021 Jul 28.
Three barbiturate squaraine dyes derived from indolenine or benzothiazole, with different barbituric acid derivatives were prepared, characterized and photophysically evaluated by standard spectroscopic methods. As expectable for squaraines, these dyes showed narrow and intense absorption and emission bands in the Vis/NIR region. The interaction of synthesized dyes with bovine and human serum albumins (BSA and HSA) was also evaluated in phosphate buffer (PB). The results revealed that upon the addition of BSA or HSA the complex dye-protein emit more fluorescence, and the emission intensity is directly proportional to the concentration of protein used (0-3.5 µM). The titration tests allowed to calculate the binding constants, in an order of magnitude of 10-10 M, as well as the limits of detection and quantification in the nanomolar tens range. All dyes showed a good response to the interaction with both proteins, but the most pronounced envisioning their use as protein labeling was observed for the squaraine dye derived from the indolenine with a 1,3-dimethylbarbituric acid moiety. The molecular docking studies revealed the existence of a binding between the compounds and four sites on the HSA molecule, where one of these four locations is a new binding site with which this series of dye interacts.
三种源自吲哚啉或苯并噻唑的、带有不同巴比妥酸衍生物的方酸 squaraine 染料被制备、表征，并通过标准光谱方法进行了光物理评估。正如方酸所预期的那样，这些染料在可见/近红外区域显示出狭窄而强烈的吸收和发射带。还在磷酸盐缓冲液 (PB) 中评估了合成染料与牛血清白蛋白 (BSA) 和人血清白蛋白 (HSA) 的相互作用。结果表明，加入 BSA 或 HSA 后，复合染料-蛋白质的荧光发射增强，发射强度与所用蛋白质的浓度（0-3.5 µM）成正比。滴定测试允许计算结合常数，数量级为 10-10 M，以及纳摩尔范围内的检测限和定量限。所有染料都对与两种蛋白质的相互作用表现出良好的响应，但对于衍生自吲哚啉和 1,3-二甲基巴比妥酸部分的 squaraine 染料，其与蛋白质相互作用的可视化效果最为显著，表明其可用于蛋白质标记。分子对接研究表明，化合物与 HSA 分子上的四个位点之间存在结合，其中四个位置之一是与该系列染料相互作用的新结合位点。
