<i>p</i>-Hydroxyphenacyl Phototriggers: The Reactive Excited State of Phosphate Photorelease

Conrad, Peter G.; Givens, Richard S.; Hellrung, Bruno; Rajesh, C.; Ramseier, Markus; Wirz, Jakob

doi:10.1021/ja001134f

Cited by 79 publications

(175 citation statements)

References 6 publications

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“…One could expect that deprotonation of the 3 HA 0 species may be quicker in basic solution than in a near neutral solution, and thus the new triplet species is tentatively attributed to the triplet anion of HA formed from the 3 HA 0 deprotonation (or ionization) reaction. This attribution is consistent with previous nanosecond laser flash photolysis (LFP) results reported by Givens et al, who found that the TA spectra of HA triplet and HA triplet anion are very similar to one another [20]. It appears that the direct UB3LYP/6-311G(d, p) density functional theory (DFT) calculations were performed to determine the optimized geometry, vibrational frequencies and predicted Raman spectrum for free HA triplet anion (designated as 3 HA À hereafter) and anion triplet complexes ( 3 HA 0 À ) with the water molecule(s) H-bonded to the oxygen lone pairs of the carbonyl and deprotonated hydroxy groups [26].…”

Section: Hydrogen-bonding Effects On the Excited States Of Selected Psupporting

confidence: 93%

“…The 341.5 nm probe TR 3 experimental results are consistent with results from a previous transient absorption investigation by Givens et al [20], which indicated that ultraviolet photolysis of HA in neutral water solution formed an intermediate with l max ¼ 325 nm absorption band, which is close to the 341.5 nm probe wavelength for the TR 3 spectra shown in Figure 13.6. This species yield and lifetime are not influenced by oxygen, and the absorption spectrum is essentially identical to that of the HA ground-state anion in aqueous base, which indicates that the new intermediate seen in the 341.5 nm TR 3 spectra is the anion ground-state species [26].…”

Section: Hydrogen-bonding Effects On the Excited States Of Selected Psupporting

confidence: 89%

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Hydrogen‐Bonding Effects on Excited States of Para ‐Hydroxyphenacyl Compounds

Phillips

2010

Hydrogen Bonding and Transfer in the Excited State

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Section: Hydrogen-bonding Effects On the Excited States Of Selected Psupporting

confidence: 93%

Section: Hydrogen-bonding Effects On the Excited States Of Selected Psupporting

confidence: 89%

Hydrogen‐Bonding Effects on Excited States of Para ‐Hydroxyphenacyl Compounds

Phillips

2010

Hydrogen Bonding and Transfer in the Excited State

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“…Rapid proton loss might have been anticipated since it is known that triplet state of this chromophore has a significantly lower pk a . 11 Intersystem crossing, however, is too rapid (10 11 s~− 1 ) for deprotonation to be competitive.…”

Section: Discussionmentioning

confidence: 99%

Fluorinated photoremovable protecting groups: the influence of fluoro substituents on the photo-Favorskii rearrangement

Stensrud

Heger

Šebej

et al. 2008

Photochem Photobiol Sci

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To further explore the nature of the photo-Favorskii rearrangement and its commitment to substrate photorelease from p-hydroxyphenacyl (pHP), an array of ten new fluorinated pHP γ-aminobutyric acid (GABA) derivatives was synthesized and photolyzed. The effects of fluorine substitution on the chromophore and the photophysical and photochemical properties of these new chromophores were shown to be derived primarily from the changes in the ground state pK a of the phenolic groups. The quantum yields and rate constants for release are clustered around Φ dis = 0.20 ± 0.05 and k r = 8 ± 7 × 10 7 s −1 (H 2 O), respectively. The triplet lifetimes of the pHP GABA derivatives were concentrated in the range of 0.4-6.0 ns (H 2 O). The corresponding deprotonated conjugate bases displayed reduced efficiencies by 50% or more (one exception) and exhibited a weak fluorescence in pH 8.2 buffer. Pump-probe spectroscopy studies have further defined the rates of intersystem crossing and the lifetimes of the reactive triplet state of the fluoro pHP chromophore.

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“…The compounds studied in the present paper were optimized by the Gaussian 98 program [31] both at the ab initio HF/3-21G and the hybrid-density-functional B3LYP/6-31G** method [32]. The latter method was extensively used in recent calculations of enols of carboxylic acid derivatives and was shown to give pK Enol values reliable to within 2 units [2a] [28] [33]. All optimized structures, including higher-energy conformers, were verified by means of their Hessian matrices to be local minima on the potential-energy surfaces at both levels of theories, except for the ditipyl derivatives, for which frequency calculations at the higher level are too demanding.…”

Section: Experimental Partmentioning

confidence: 99%

Observable Enols of Anhydrides: Claimed Literature Systems, Calculations, and Predictions

Rappoport¹,

Lei²,

Yamataka³

2001

HCA

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Dedicated to Prof. Edgar Heilbronner on the occasion of his 80th birthdayThe literature describing the observation of enols of carboxylic anhydrides and mixed carboxylic-sulfuric anhydrides was examined. In the phenylbutyric anhydride system, the alleged enol was shown to be ethylphenylketene, and the monoenol EtC(Ph)C(OH)OC(O)CH(Ph)Et (5) and the dienol (6) should not be observed according to calculations. Calculations also show that the claimed enols H 2 CC(OH)OSO 2 Y, Y SO À 3 , Ac (15) and the enol of 2H-pyran-2,6(3H)-dione (7) are too unstable to be observed. The bulky enols of b,b-ditipylacetic formic (35a) or trifluoroacetic (35b) anhydride were calculated to be unstable with pK Enol 7.7 (6.2). The suggestion that compounds with the 3-acyl or 3-aroyl-2H-pyran-2,6(3H)-dione skeleton are enolic was examined. In the solid state, all the known structures show that enolization takes place on C(5)O. However, B3LYP/6-31G** calculations show that, for 3-acetyl-4-methyl-2H-pyran-2,6(3H)-dione (10, R 1 Me, R 2 H), which is completely enolic, the enol on the acetyl group (cf. 12) is only 0.9 kcal/mol more stable than the enol on the anhydride (cf. 11). Calculations also revealed that 3-(trifluoroacetyl)-2H-pyran-2,6(3H)-dione (28) should exist in nearly equal amounts of the enol of anhydride (cf. 30) and the enol of the acyl group (cf. 29), whereas the enol of anhydride (cf. 32) is the only stable species for 3-(methoxycarbonyl)-2H-pyran-2,6(3H)-dione (31). Furan-2,5-diol (27) and 5-hydroxyfuran-2-one (26) are calculated not to give observable isomers of succinic anhydride (25) (pK Enol 30 and 18, resp.) in spite of the expected aromatic stabilization of 27. Surprisingly, the calculations reveal that the enol (NC) 2 CC(OH)OCHO (38) is less stable than its tautomeric anhydride (37) (pK Enol 1.6). Comparison of calculated pK Enol values for (NC) 2 CHC(O)X (41) and MeC(O)X indicates that the assumption that substitution by two b-CN groups affects similarly all the systems regardless of X is incorrect. A pK Enol ((NC) 2 CHC(O)X) vs. pK Enol (MeC(O)X) plot is linear for most substituents with severe and mild negative deviations, respectively, for X NH 2 and MeO. Appropriate isodesmic reactions have shown that the b,b-(CN) 2 substitution increases the stabilization of the enol of amide (X NH 2 ) by 14.6 kcal/mol over that for the anhydride (X OCHO), whereas the amide form is 7.1 kcal/mol less destabilized than for the anhydride. The pK Enol value for (MeOCO) 2 CHCOOCHO (43) is 3.6, i.e., stabilization by these b-electron-withdrawing groups is insufficient to make the enols observable.1. Introduction. ± Enols of carboxylic acid derivatives are rare species [1]. The calculated energy differences between the favored tautomer, i.e., the parent (b,b-di-H) carboxylic acid or its derivatives (2) and its enols (1) are 24 ± 33 kcal/mol, depending on the derivative and the method of calculation [2]. Nevertheless, enols of carboxylic acids, esters, and amides were observed in recent years, based on three approaches. Their generation ...

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p-Hydroxyphenacyl Phototriggers: The Reactive Excited State of Phosphate Photorelease

Cited by 79 publications

References 6 publications

Hydrogen‐Bonding Effects on Excited States of Para ‐Hydroxyphenacyl Compounds

Hydrogen‐Bonding Effects on Excited States of Para ‐Hydroxyphenacyl Compounds

Fluorinated photoremovable protecting groups: the influence of fluoro substituents on the photo-Favorskii rearrangement

Observable Enols of Anhydrides: Claimed Literature Systems, Calculations, and Predictions

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