Modulation and Salt-Induced Reverse Modulation of the Excited-State Proton-Transfer Process of Lysozymized Pyranine: The Contrasting Scenario of the Ground-State Acid–Base Equilibrium of the Photoacid

2016 ◽  
Vol 120 (29) ◽  
pp. 7076-7087 ◽  
Author(s):  
Ishita Das ◽  
Sudipta Panja ◽  
Mintu Halder
Keyword(s):  
Excited State ◽  
Proton Transfer ◽  
Transfer Process ◽  
Ground State ◽  
Acid Base ◽  
Base Equilibrium ◽  
Acid Base Equilibrium ◽  
Excited State Proton Transfer ◽  
Proton Transfer Process

Excited state acid–base equilibrium of tyrosine

1978 ◽  
Vol 56 (9) ◽  
pp. 1238-1245 ◽  
Author(s):  
David Michael Rayner ◽  
Donald Theodore Krajcarski ◽  
Arthur Gustav Szabo
Keyword(s):  
Excited State ◽  
Proton Transfer ◽  
Quantum Yields ◽  
Acid Base ◽  
Large Shift ◽  
Fluorescence Quantum Yields ◽  
Base Equilibrium ◽  
Tyrosine Fluorescence ◽  
Acid Base Equilibrium ◽  
Buffer Base

Fluorescence attributable to the tyrosinate form of the amino acid tyrosine, previously only observed at pH > pK(S0) = 10.3 where tyrosinate exists in the ground state, has been observed at neutral pH in the presence of high buffer base concentrations. This observation is consistent with the large shift in pK(Sl) predicted from absorption measurements and confirms that proton transfer is indeed a mechanism by which carboxylate ions quench tyrosine fluorescence. The dependence of the fluorescence quantum yields of tyrosine and tyrosinate on pH does not fit a simple excited state acid–base equilibrium model but a more complicated system where carboxylate is also capable of simultaneously quenching tyrosine fluorescence by a mechanism not involving proton transfer. Kinetic analysis of the system allows calculation of pK(S1) = 4.2 for tyrosine. The quantum yield of tyrosinate fluorescence can be appreciably higher than that normally measured at alkaline pH where a separate quenching mechanism must operate. These results have significance in the interpretation of the fluorescence properties of proteins.

A theoretical investigation on excited-state single or double proton transfer process for aloesaponarin I

2018 ◽  
Vol 96 (1) ◽  
pp. 83-88 ◽  
Author(s):  
Qiang Wei ◽  
Jiyu Wang ◽  
Meiyu Zhao ◽  
Meixia Zhang ◽  
Yuzhi Song ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Excited State ◽  
Potential Energy ◽  
Proton Transfer ◽  
Transfer Process ◽  
Ground State ◽  
Excitation Energies ◽  
Single Proton ◽  
Intramolecular Hydrogen ◽  
Proton Transfer Process

The excited-state proton transfer (ESPT) dynamical behavior of aloesaponarin I (ASI) was studied using density functional theory (DFT) and time-dependent DFT (TDDFT) methods. Our calculated vertical excitation energies based on TDDFT reproduced the experimental absorption and fluorescence spectra well [Nagaoka et al. J. Phys. Chem. B, 117, 4347 (2013)]. Two intramolecular hydrogen bonds were confirmed to be strengthened in the S1 state, which makes ESPT possible. Herein, the ESPT process is more likely to happen, along with one hydrogen bond (O1–H2⋯O3). Qualitative analyses about charge distribution further demonstrate that the ESPT process could occur because of the intramolecular charge transfer. Our constructed potential energy surfaces of both S0 and S1 states show that a single proton transfer reactive is more reasonable along with the intramolecular hydrogen bond (O1–H2⋯O3) rather than O4–H5⋯O6 in the S1 stated potential energy surface. Then, ASI-SPT* decays to the ground state with a 640 nm fluorescence; subsequently, the ASI-SPT form shows that reverse ground state single-proton transfer back to the ASI structure occurs. Particularly, dependent on relatively accurate potential energy barriers among these excited-state stable structures, we confirmed the excited-state single proton transfer process rather than using the controversial nodal plane model.

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