New pH-sensitive, Hydrophilic Norsquaraine Dyes for Protein Labeling

author.DisplayName 2 author.DisplayName 2 author.DisplayName 2,3 author.DisplayName 1 author.DisplayName 2 author.DisplayName 2 author.DisplayName 2 author.DisplayName 4 author.DisplayName 1
1Department of Chemical Sciences, Faculty of Natural Sciences, Ariel University, Ariel, Israel
2Department of Chemistry, SSI "Institute for Single Crystals" of the National Academy of Sciences of Ukraine, Kharkiv, Ukraine
3Chemical Department, V. N. Karazin Kharkiv National University, Kharkiv, Ukraine
4-, SETA BioMedicals, Urbana, IL, USA

Fluorescent pH-sensitive dyes whose spectral properties are sensitive to the acidity of the medium are used in biomedical research, molecular and cell biology, analytical and bioanalytical chemistry, clinical diagnostics, intracellular and extracellular studies. In particular, these dyes are applicable to determine the intracellular pH, which plays an important role in many cellular processes such as growth, nutrition, motion and the regulation of calcium balance. Principle of functioning of the pH-sensitive dyes is to change their spectral and photophysical properties (position and/or intensity of the absorption and emission bands, fluorescence quantum yield, and fluorescence lifetime) in the train of protonation—deprotonation.

A series of novel, pH-sensitive, long-wavelength fluorescent norsquaraine dyes (Nor-SqO) and their barbituric (Nor-SqB) and dicyanomethylene (Nor-SqB) derivatives was synthesized and investigated. Some of these dyes contain a carboxy-functionality, which was converted into an NHS ester to facilitate bio-conjugation. The molecular structure of these dyes was investigated using NMR spectroscopy, X-ray analysis and ab initio simulations. The absorption and emission spectra, fluorescence quantum yields, lifetimes, polarizations, and photostabilities were measured free in solution and after binding to bovine serum albumin (BSA) and compared to those for conventional squaraines and norcyanine CypHer5. In contrast to squaraines, norsquaraines are pH-sensitive but almost insensitive to a non-covalent interaction with protein. These new dyes can be potentially used as advanced fluorescent labels for biomedical applications in particular for protein labeling, polarization based assays, cell-based and pH-sensing measurements.

Fig. 1. Protonation-deprotonation of norsquaraine dyes

Fig. 2. Absorption and fluorescence spectra
of norsquaraine dyes
Fig. 3. Titration cureves for norsquaraine dyes









Powered by Eventact EMS