Meso-Substituent-Directed Aggregation Behavior and Water Solubility: Direct Functionalization of Methine Chain in Thiazole Orange and Biological Applications in Aqueous Buffer

Abstract

A new strategy is presented to preclude aggregation and enhance water solubility of cyanine dyes. Namely, a heteroatom-containing substituent, for distorting molecular plane and increasing interaction with water molecules, is introduced to the methine chain of 2-thiazole orange (1, a monocyanine) via one-step, and 2-thiazole orange derivatives 2a–g are prepared accordingly. The X-ray crystal structures show that the molecular plane of 2a–g is drastically twisted, which reduces intermolecular π–π stacking. The derivatives 2a–g exhibit good to excellent water solubility and can be dissolved in aqueous phosphate-buffered saline (PBS) at concentrations suitable for biomedical applications. No aggregation in aqueous PBS, relatively high molar extinction coefficients, and low solvatochromism of 2a–g are reflected by the UV–vis spectra. Compound 2b shows fast response and high selectivity for biothiols (Cys, Hcy, and GSH) in aqueous PBS and is further employed to detect endogenous biothiols with decent biocompatibility as demonstrated by live cell fluorescence imaging.

Sustainable Approach to Methine-Substituted Heptamethine Cyanines from Bioderived Furfural and Their Phototherapy Potential

“…The development of new synthetic methodologies that reduce our dependence on fossil resources is of great significance in the current synthetic chemistry. − The bioderived starting materials can replace fossil raw materials to generate high value-added chemicals, thereby helping to reduce CO 2 emissions and causing less damage to the environment. − Furfural is a platform molecule of biorefinery highly valuable and can be produced by acid hydrolysis and dehydration of biomass in million-ton quantities annually. ,, Under certain conditions, its furan ring can be opened to form versatile biobased C5 platform molecules. In this context, based on our previous work, − we report a general synthetic method to economically and easily access methine-substituted Cy7 (γ-acyloxy-Cy7) from cheap, readily available bioderived furfural (Scheme c), which is the first report on the synthesis of methine-substituted Cy7 from renewable biomass resources.…”