Excited-State Processes in Polycyclic Quinones:  The Light-Induced Antiviral Agent, Hypocrellin, and a Comparison with Hypericin

Das, Kaustuv; English, Douglas S.; Fehr, Michael J.; Smirnov, Alexandre V.; Petrich, Jacob W.

doi:10.1021/jp961156h

Cited by 60 publications

(70 citation statements)

References 37 publications

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“…For hypocrellin A, as observed in the fluorescence upconversion data and in the transient absorption data, 12,15 8 For hypocrellin A, the time constant of the longer-lived H atom transfer is very strongly dependent on viscosity. 14,17 (2) No deuterium isotope effect is observed for hypericin 7 or for the ∼10 ps component of hypocrellin A (Figure 5).…”

Section: Resultsmentioning

confidence: 81%

“…These have been the subject of several reviews [1][2][3][4][5] and have been referred to in detail in our previous work. One of the most interesting photophysical processes that these molecules execute is excited-state proton or H atom transfer, both intramolecular [6][7][8][9][10][11][12][13][14][15][16][17][18][19] and intermolecular. [20][21][22] We have suggested that the intermolecular proton transfer plays a role in certain aspects of the biological activity of hypericin and hypocrellin.…”

Section: Introductionmentioning

confidence: 99%

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Excited-State Intramolecular H Atom Transfer of Hypericin and Hypocrellin A Investigated by Fluorescence Upconversion

et al. 1999

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The excited-state intramolecular H atom transfer reaction occurring in hypericin and hypocrellin A is investigated by means of the fluorescence upconversion technique in a variety of solvents. Rising components of ∼10 ps, attributable to intramolecular H atom transfer, are clearly observed in the fluorescence upconversion traces of both hypericin and hypocrellin A. The amplitude of the rising component is emission wavelength dependent and occurs on the blue edge of the emission spectra. Neither in hypericin nor in hypocrellin A does this fluorescent component exhibit a deuterium isotope effect. This result identifies it with the ∼10 ps component, also lacking a deuterium isotope effect, observed in hypericin in transient absorption measurements monitoring stimulated emission. The clear and complementary observation in fluorescence of the ∼10 ps component in both hypericin and hypocrellin A is a crucial link in refining a unified model of the hypericin and hypocrellin photophysics that we first proposed in J. Phys The excited-state intramolecular H atom transfer reaction occurring in hypericin and hypocrellin A is investigated by means of the fluorescence upconversion technique in a variety of solvents. Rising components of ∼10 ps, attributable to intramolecular H atom transfer, are clearly observed in the fluorescence upconversion traces of both hypericin and hypocrellin A. The amplitude of the rising component is emission wavelength dependent and occurs on the blue edge of the emission spectra. Neither in hypericin nor in hypocrellin A does this fluorescent component exhibit a deuterium isotope effect. This result identifies it with the ∼10 ps component, also lacking a deuterium isotope effect, observed in hypericin in transient absorption measurements monitoring stimulated emission. The clear and complementary observation in fluorescence of the ∼10 ps component in both hypericin and hypocrellin A is a crucial link in refining a unified model of the hypericin and hypocrellin photophysics that we first proposed in

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Section: Resultsmentioning

confidence: 81%

Section: Introductionmentioning

confidence: 99%

Excited-State Intramolecular H Atom Transfer of Hypericin and Hypocrellin A Investigated by Fluorescence Upconversion

et al. 1999

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“…8,[25][26][27][28][29][30][31][32][33][34][35][36][37] By means of H/D substitution, investigation of methoxy analogues, and complementary studies using both transient absorption and fluorescence upconversion spectroscopies, we have argued that the major primary photophysical process in hypericin in organic solvents is excited-state intramolecular hydrogen-atom transfer.…”

Section: Introductionmentioning

confidence: 99%

Interaction of Glutathione S-Transferase with Hypericin: A Photophysical Study

et al. 2005

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The photophysics of hypericin have been studied in its complex with two different isoforms, A1-1 and P1-1, of the protein glutathione S-transferase (GST). One molecule of hypericin binds to each of the two GST subunits. Comparisons are made with our previous results for the hypericin/human serum albumin complex (Photochem. Photobiol. 1999, 69, 633−645). Hypericin binds with high affinity to the GSTs: 0.65 μM for the A1-1 isoform and 0.51 μM for the P1-1 isoform (Biochemistry 2004, 43, 12761−12769). The photophysics and activity of hypericin are strongly modulated by the binding protein. Intramolecular hydrogen-atom transfer is suppressed in both cases. Most importantly, while there is significant singlet oxygen generation from hypericin bound to GST A1-1, binding to GST P1-1 suppresses singlet oxygen generation to almost negligible levels. The data are rationalized in terms of a simple model in which the hypericin photophysics depends entirely upon the decay of the triplet state by two competing processes, quenching by oxygen to yield singlet oxygen and ionization, the latter of these two are proposed to be modulated by A1-1 and P1-1. The photophysics of hypericin have been studied in its complex with two different isoforms, A1-1 and P1-1, of the protein glutathione S-transferase (GST). One molecule of hypericin binds to each of the two GST subunits. Comparisons are made with our previous results for the hypericin/human serum albumin complex (Photochem. Photobiol. 1999, 69, 633-645). Hypericin binds with high affinity to the GSTs: 0.65 µM for the A1-1 isoform and 0.51 µM for the P1-1 isoform (Biochemistry 2004, 43, 12761-12769). The photophysics and activity of hypericin are strongly modulated by the binding protein. Intramolecular hydrogen-atom transfer is suppressed in both cases. Most importantly, while there is significant singlet oxygen generation from hypericin bound to GST A1-1, binding to GST P1-1 suppresses singlet oxygen generation to almost negligible levels. The data are rationalized in terms of a simple model in which the hypericin photophysics depends entirely upon the decay of the triplet state by two competing processes, quenching by oxygen to yield singlet oxygen and ionization, the latter of these two are proposed to be modulated by A1-1 and P1-1.

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“…[1][2][3][4][5] We have argued that they also present a fascinating system with which to study excited-state intramolecular H-atom transfer. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Hypericin executes an intramolecular excited-state H-atom transfer in ∼10 ps. 20 This reaction is independent of solvent.…”

Section: Introductionmentioning

confidence: 99%

Coupling of Large-Amplitude Side Chain Motions to the Excited-State H-Atom Transfer of Perylene Quinones: Application of Theory and Experiment to Calphostin C

et al. 2001

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The excited-state intramolecular H-atom transfer reactions of hypocrellins B and A are compared with those of calphostin C. On the basis of the results of transient absorption measurements and ab initio quantum mechanical calculations, it is concluded that large-amplitude conformational changes are coupled to the Hatom transfer in calphostin C, just as they are in hypocrellins A and B. The calculations on this very large molecule with a very complex ground electronic state potential energy surface were made possible by the use of highly scalable electronic structure theory codes on large parallel computers. Disciplines Chemistry CommentsReprinted (adapted) The excited-state intramolecular H-atom transfer reactions of hypocrellins B and A are compared with those of calphostin C. On the basis of the results of transient absorption measurements and ab initio quantum mechanical calculations, it is concluded that large-amplitude conformational changes are coupled to the H-atom transfer in calphostin C, just as they are in hypocrellins A and B. The calculations on this very large molecule with a very complex ground electronic state potential energy surface were made possible by the use of highly scalable electronic structure theory codes on large parallel computers.

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Excited-State Processes in Polycyclic Quinones: The Light-Induced Antiviral Agent, Hypocrellin, and a Comparison with Hypericin

Cited by 60 publications

References 37 publications

Excited-State Intramolecular H Atom Transfer of Hypericin and Hypocrellin A Investigated by Fluorescence Upconversion

Excited-State Intramolecular H Atom Transfer of Hypericin and Hypocrellin A Investigated by Fluorescence Upconversion

Interaction of Glutathione S-Transferase with Hypericin: A Photophysical Study

Coupling of Large-Amplitude Side Chain Motions to the Excited-State H-Atom Transfer of Perylene Quinones: Application of Theory and Experiment to Calphostin C

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