Formation of Quinone Methides by Ultrafast Photodeamination: A Spectroscopic and Computational Study

Abstract

Formation of quinone methides (QMs) by photoelimination of an ammonium salt from cresol derivatives was investigated by femtosecond transient absorption spectroscopy (fs-TA) and computationally by timedependent density functional theory using the PCM(water)/(TD-)B3LYP/6-311++G(d,p) level of theory. The photoelimination takes place in an adiabatic ultrafast reaction on the S 1 potential energy surface delivering the corresponding QMs(S 1 ), which were detected by fs-TA. Computations predicted a high-energy cation intermediate in the pathway between the Franck−Condon state of a monoammonium salt and the corresponding QM(S 1 ) that was not detected by fs-TA. On the other hand, elimination from a disalt in H 2 O takes place in one step, giving directly the QM(S 1 ). The combined experimental and theoretical investigation fully disclosed the formation of QMs by the deamination reaction mechanism, which is important in the application of cresols or similar molecules in biological systems.

Labeling of Proteins by BODIPY-Quinone Methides Utilizing Anti-Kasha Photochemistry

“…In particular, upon population of higher excited states S8 and S9 (Figures S23 and S24 and Tables S3-S6 in the SI), which correspond to λ < 355 nm, the excitation is localized on the phenolic moiety, leading to a change in electron density on the phenolic oxygen and methylamino nitrogen, which is a requirement to initiate the deamination process. Since the deamination is an ultrafast reaction taking place in one ps, 36 it can compete with fast IC from higher excited states. Therefore, excitation of 2-4 to Sn leads to the observed anti-Kasha photochemical reaction of deamination.…”

Photogeneration of quinone methide from adamantylphenol in an ultrafast non-adiabatic dehydration reaction

“…The viability of the used TD-DFT method was supported by the benchmarking performed in our previous work where computational results were further verified by comparison with experimental data. 19,29 Conical intersection optimization scan for QM 4(S 0 ) formation was performed on the same level of theory using ORCA 4.2.0. 37,38…”

“…16 The mechanism of photodeamination has therefore been investigated by a variety of approaches, including nanosecond laser flash photolysis (LFP), 17 computations, 18 and femtosecond transient absorption (fs-TA) spectroscopy. 19 The major discovery was that photodeamination takes place in an adiabatic ultrafast photochemical reaction on the S 1 potential energy surface, delivering QMs in the excited state and without any detectable intermediate en route. 19 However, one serious drawback of photodeamination reactions is the fact that QMs react efficiently with water molecules, 20,21 resulting in hydration products and loss of the starting material.…”

“…19 The major discovery was that photodeamination takes place in an adiabatic ultrafast photochemical reaction on the S 1 potential energy surface, delivering QMs in the excited state and without any detectable intermediate en route. 19 However, one serious drawback of photodeamination reactions is the fact that QMs react efficiently with water molecules, 20,21 resulting in hydration products and loss of the starting material.…”

Non-Covalent Binding of Tripeptides-Containing Tryptophan to Polynucleotides and Photochemical Deamination of Modified Tyrosine to Quinone Methide Leading to Covalent Attachment

“…These findings prompted us to investigate the non-covalent binding to polynucleotides for a series of tripeptides 1×HCl – 3×HCl ( Figure 1 ) containing bis-tryptophan units, wherein the C-terminus contained Phe, Tyr, or modified Tyr, which is photochemically reactive [ 52 ]. Upon excitation by light, the modified tyrosine undergoes photodeamination delivering QM [ 53 , 54 ], and if such peptide is non-covalently bound to DNA or RNA, that would allow QM to react with DNA/RNA and induce permanent covalent damage. Herein we demonstrate that tripeptides 1 – 3 bind to DNA by non-covalent interactions.…”