Two boron-dipyrrin (BODIPY) based dyes with dimethylaminophenyl and carboxyphenyl substituents in 8-position of dipyrrin ligand have been synthesized and characterized. Photophysical and spectral properties of the obtained compounds have been investigated in water-ethanol mixture and water-cyclohexane system with variation of pH values. The equilibria constants of the compounds were identified by classical methods of acid-base titration. BODIPY bearing dimethylaminophenyl and carboxyphenyl subunits show deprotonation/protonation dependent fluorescence off/on-switching. The change of the emission could be mechanistically explained by a PET (photoinduced electron transfer) from the 8-substituent to the fluorophore. The present study demonstrates that BODIPY-based fluorescent sensors can be used to measure the pH in the range of 2-13 extending the scope of BODIPY dyes available as pH-indicators. Investigated compounds demonstrate weak dye-dye interaction allowing their cooperative usage as indicators.
A boron-dipyrromethene (BODIPY) derivative reactive towards amino groups of proteins (NHS-Ph-BODIPY) was synthesized. Spectroscopic and photophysical properties of amine-reactive NHS-Ph-BODIPY and its non-reactive precursor (COOH-Ph-BODIPY) in a number of organic solvents were investigated. Both fluorescent dyes were characterized by green absorption (521–532 nm) and fluorescence (538–552 nm) and medium molar absorption coefficients (46,500–118,500 M−1·cm−1) and fluorescence quantum yields (0.32 – 0.73). Solvent polarizability and dipolarity were found to play a crucial role in solvent effects on COOH-Ph-BODIPY and NHS-Ph-BODIPY absorption and emission bands maxima. Quantum-chemical calculations were used to show why solvent polarizability and dipolarity are important as well as to understand how the nature of the substituent affects spectroscopic properties of the fluorescent dyes. NHS-Ph-BODIPY was used for fluorescent labeling of a number of proteins. Conjugation of NHS-Ph-BODIPY with bovine serum albumin (BSA) resulted in bathochromic shifts of absorption and emission bands and noticeable fluorescence quenching (about 1.5 times). It was demonstrated that the sensitivity of BSA detection with NHS-Ph-BODIPY was up to eight times higher than with Coomassie brilliant blue while the sensitivity of PII-like protein PotN (PotN) detection with NHS-Ph-BODIPY and Coomassie brilliant blue was almost the same. On the basis of the molecular docking results, the most probable binding sites of NHS-Ph-BODIPY in BSA and PotN and the corresponding binding free energies were estimated.
The present work describes direct one-pot synthesis of the two novel amino acids – boron-dipyrromethene (BODIPY) conjugates with histidine and tyrosine residues bound to fluorophore via amino group. The synthesized compounds were fully characterized by means of 1H and 11B nuclear magnetic resonance spectroscopy, infrared spectroscopy, time-of-flight mass spectrometry with matrix-activated laser desorption / ionization. All the data are in accordance with the proposed structures. The amino acids – BODIPY conjugates under study were investigated by means of absorbance and fluorescence spectroscopy. Absorption and emission spectra of the compounds in dimethyl sulfoxide (DMSO) – buffer solution (BS) mixture (1:1) were obtained. Moreover, a number of photophysical characteristics of the conjugates, namely: relative fluorescence quantum yield, molar extinction coefficient, relative fluorescence lifetime, radiative and non-radiative rate constants were calulated. 3D fluorescence spectra of the compounds in DMSO – BS mixture (1:1) were obtained. Absorption and emission titration of the compounds was carried out. The results of the titration allowed us to confirm additionally a stoichiometric composition of the conjugates. Quantum chemical analysis of structural and spectral properties of the compounds in a ground state was carried out. The results of quantum chemical calculations gave an insight to a nature of the BODIPY – amino acid interactions in the conjugates. Besides, the synthesized amino acids – BODIPY conjugates are found to be highly soluble in polar solvents. Thus, a range of unique properties of the objects of the present research enables us to use them for visualization of bioactive macromolecules as well as biochemical processes in living cells.
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