Abstract
A fluorescently labeled peptide that exhibited fast excited state intramolecular proton transfer (ESIPT) was synthesized, and the nature of its electronic properties was comprehensively investigated, including linear photophysical and photochemical characterization, specific relaxation processes in the excited state, and its stimulated emission ability. The steady-state absorption, fluorescence, and excitation anisotropy spectra, along with fluorescence lifetimes and emission quantum yields, were obtained in liquid media and analyzed based on density functional theory quantum-chemical calculations. The nature of ESIPT processes of the peptide’s chromophore moiety was explored using a femtosecond transient absorption pump-probe technique, revealing relatively fast ESIPT velocity (∼10 ps) in protic MeOH at room temperature. Efficient superluminescence properties of the peptide were realized upon femtosecond excitation in the main long-wavelength absorption band with a corresponding threshold of the pump pulse energy of ∼1.5 μJ. Quantum-chemical analysis of the electronic structure of the peptide was performed using the density functional theory/time-dependent density functional theory level of theory, affording good agreement with experimental data.
Highlights
We present the synthesis and comprehensive investigation of linear steady-state and time-resolved photophysical properties, along with femtosecond transient absorption pump-probe spectroscopy of a new fluorescently labeled peptide 1, which exhibited the excited state intramolecular proton transfer (ESIPT) phenomenon in liquid media at room temperature and efficient superluminescence under femtosecond pumping into the main absorption band
The main linear spectral and photochemical parameters of peptide 1 are presented in Figures 2−5 and Figure 1), which can exhibit ESIPT processes under photoexcitation.[9,14,16,51]
Linear photophysical and photochemical properties, fast relaxation processes, and stimulated emission of new fluorescent peptide 1 were comprehensively investigated in liquid media at room temperature
Summary
The synthesis and characterization of new environmentally sensitive fluorescently labeled peptides are of great interest for a broad range of fundamental and applied research fields, including protein−protein and peptide−oligonucleotide interactions,[1,2] dynamics of peptide binding,[3,4] ion sensing,[5,6] pH monitoring,[7,8] and fluorescence cellular bioimaging.[9,10] The fluorescence characteristics of a peptide’s emission are primarily determined by the properties of the chromophore moiety incorporated into the peptide structure[11,12] and can serve as a starting point in the development of corresponding applications mentioned above. We present the synthesis and comprehensive investigation of linear steady-state and time-resolved photophysical properties, along with femtosecond transient absorption pump-probe spectroscopy of a new fluorescently labeled peptide 1, which exhibited the ESIPT phenomenon in liquid media at room temperature and efficient superluminescence under femtosecond pumping into the main absorption band. Known antimicrobial peptidic antibiotic gramicidin S (cyclo[VOLfP]2 (O, ornithine; f, D-phenylalanine) This peptide was discovered more than 75 years ago,[41] its mechanism of action is still under study and is relevant to its therapeutic applications.[42] Incorporation of a fluorescent label into the gramicidin S molecule would provide a valuable tool for its study, in particular, in living cells and tissues. Density functional theory/time-dependent density functional theory (DFT/TD-DFT) quantum-chemical calculations of the electronic parameters of the normal and tautomeric forms of the chromophore moiety in the peptide were performed, and good agreement with experimental parameters was obtained
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