Oxidation of tryptophan and N-methylindole by N3.cntdot., Br2.-, and (SCN)2.- radicals in light- and heavy-water solutions: a pulse radiolysis study

Solar, Sonja; Getoff, N.; Surdhar, Parminder S.; Armstrong, David A.; Singh, Ajit

doi:10.1021/j100162a038

Cited by 161 publications

(220 citation statements)

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“…Our findings with azidyl radicals are compatible with the data reported by Solar et al, 21 who showed that azidyl radicals generated by pulse radiolysis can oxidize L-Trp to give the radical cation TrpH •+ , which deprotonates to give the neutral Trp • radical, a process which is energetically favored at pH 7. 19−22 Solar et al 21 found that one-electron oxidation of L-Trp is the primary reaction of azidyl radicals in solution, so we focused our attention on the detection of free azide as a photoproduct at pH 7.…”

supporting

confidence: 93%

“…19−22 Solar et al 21 found that one-electron oxidation of L-Trp is the primary reaction of azidyl radicals in solution, so we focused our attention on the detection of free azide as a photoproduct at pH 7. The formation of free azide was confirmed by the 14 N NMR spectrum of a phosphate-buffered D 2 O solution (pH* 7.4) containing 1 (9 mM), DMPO (18 mM), and 2 molar equiv of L-Trp after irradiation with blue light (463 nm, 64 mW cm −2 ) for 30 min (Figure S5A), which contained peaks at 228.6 and 77.3 ppm assignable to the terminal nitrogen atom (overlapped with Nβ of the coordinated azide) and the central nitrogen atom, respectively, of N 3 − .…”

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confidence: 99%

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Tryptophan Switch for a Photoactivated Platinum Anticancer Complex

Butler¹,

Woods

Farrer³

et al. 2012

J. Am. Chem. Soc.

110

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Copies of full items can be used for personal research or study, educational, or not-forprofit purposes without prior permission or charge. Provided that the authors, title and full bibliographic details are credited, a hyperlink and/or URL is given for the original metadata page and the content is not changed in any way. (1) is potently cytotoxic to cancer cells when irradiated with visible (blue) light. We show that the acute photocytotoxicity can be switched off by low doses (500 μM) of the amino acid L-tryptophan. EPR and NMR spectroscopic experiments using spin traps show that L-Trp quenches the formation of azidyl radicals, probably by acting as an electron donor. L-Trp is wellknown as a mediator of electron transfer between distant electron acceptor/donor centers in proteins, and such properties may make the free amino acid clinically useful for controlling the activity of photochemotherapeutic azido Pt IV drugs. Since previous work has demonstrated the ability of photoactivated 1 to platinate DNA, this suggests that the high potency of such photoactive platinum complexes is related to their dual attack on cancer cells by radicals and Pt II photoproducts.

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supporting

confidence: 93%

mentioning

confidence: 99%

Tryptophan Switch for a Photoactivated Platinum Anticancer Complex

Butler¹,

Woods

Farrer³

et al. 2012

J. Am. Chem. Soc.

110

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“…The transient signals obtained for assemblies containing both the GMG and GGG sites, Ru-GGG-GMG and Ru-GMG-GGG, are consistent with decay profiles for assemblies containing either GMG or GGG. For these assemblies the signal heights are smaller, as expected from the smaller extinction coefficient for the neutral guanine radical, than for the methylindole cation radical (44)(45)(46). Moreover, the signals do not decay appreciably over the 50-s time window, consistent with our earlier measurements of guanine radical decay in flash͞ quench experiments.…”

supporting

confidence: 88%

“…The finding of oxidative damage at the guanine bases flanking M in the biochemical experiments supports this formation of guanine radical in Ru-GMG and in Ru-GGG-GMG and Ru-GMG-GGG. The neutral guanine radical does absorb at 600 nm but with an extinction coefficient 3.5-fold lower than that for the methylindole cation radical (44)(45)(46).…”

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confidence: 90%

Charge equilibration between two distinct sites in double helical DNA

Delaney

Yoo

Stemp

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

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DNA assemblies containing a pendant dipyridophenazine complex of Ru(II) along with two oxidative traps, a site containing the nucleoside analog methylindole (5-GMG-3) and a 5-GGG-3 site, have been constructed to explore long-range charge transport through the base pair stack. With these chemically well defined assemblies, in combination with the flash͞quench technique, formation of the methylindole cation radical and the neutral guanine radical is monitored directly by using transient absorption spectroscopy, and yields of oxidative damage are quantitated biochemically by gel electrophoresis. In these assemblies the base radicals form with a rate of >10 7 s ؊1 . The rate of base radical formation does not change upon the addition of a second radical trap, the 5-GGG-3 site; however, the yield of methylindole oxidation is significantly lower. This observation indicates that the 5-GGG-3 site is effective in competing for the migrating charge and provides a second trapping site. Switching the orientation of the two trapping sites does not affect the yield of oxidized products at either site. Therefore, in DNA both forward and reverse charge transport occur so as to provide equilibration across the duplex on a timescale that is fast compared with trapping at a particular site. Further evidence of charge equilibration results from incorporating an intervening base-stacking perturbation and monitoring the fate of the injected charge. These experiments underscore the dynamic nature of DNA charge transport and reveal the importance of considering radical propagation in both directions along the DNA duplex. N umerous spectroscopic and biochemical experiments have shown that the base stack of DNA can mediate charge transport (CT) reactions (1-4). Chemically well defined assemblies, consisting of DNA duplexes with covalently bound oxidants, have been particularly useful in exploring the effects of base-stacking perturbations (5-8), intervening DNA sequence (9, 10), and donor-acceptor distance (11-13) on CT. Long-range oxidative DNA damage has been demonstrated over a distance of 200 Å (14, 15). Indeed, DNA either packaged in nucleosome core particles (16) or inside the cell nucleus (17) has been found to be susceptible to long-range oxidative damage.Based on spectroscopic and biochemical experiments using Ru and Rh intercalating oxidants along with temperaturedependent base-base CT chemistry, we have proposed a model for CT involving conformationally gated charge hopping among DNA domains (18)(19)(20). Domains over which charge may be delocalized are defined by sequence and dynamics; a domain size of Ϸ4 bp has been characterized in assemblies containing repetitive tracts of adenines. Earlier, using measurements only of oxidative DNA damage yield as a function of intervening sequence, Giese, Jortner, and coworkers proposed a model involving a mixture of base hopping and tunneling (21-23). Also based on oxidative yield determinations, Schuster and coworkers (24) proposed phonon-assisted polaron hopping between guanine bases. ...

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“…Only the cation radical would exhibit low reactivity towards oxygen; therefore its spectrum (l max at 345 and 500-650 nm) [11] was obtained under aerated conditions ( Figure 1f). It is known that skatolyl radicals are formed from 3-methylindole upon photosensitization by BT.…”

Section: Resultsmentioning

confidence: 99%

Intramolecular Electron Transfer between Tyrosine and Tryptophan Photosensitized by a Chiral π,π* Aromatic Ketone

Galian

Pastor‐Pérez

Miranda

et al. 2005

Chemistry A European J

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The photochemical reaction of Trp and Tyr and related peptides with Suprofen (SUP) as sensitizer in H2O/CH3CN (28:1 v/v) solutions has been studied by time-resolved spectroscopy. The results show that SUP induces oxidation of both Trp and Tyr, as well as intramolecular-ET reactions in the related peptides. The influence of photosensitizer configuration on the involved processes has been studied by using the enantiomerically pure compounds. A significant chiral recognition is observed in which the concentration of the radicals formed after triplet quenching depends on the configuration of the chiral center; the quenching process is higher when using the (R)-SUP enantiomer.

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Oxidation of tryptophan and N-methylindole by N3.cntdot., Br2.-, and (SCN)2.- radicals in light- and heavy-water solutions: a pulse radiolysis study

Cited by 161 publications

References 0 publications

Tryptophan Switch for a Photoactivated Platinum Anticancer Complex

Tryptophan Switch for a Photoactivated Platinum Anticancer Complex

Charge equilibration between two distinct sites in double helical DNA

Intramolecular Electron Transfer between Tyrosine and Tryptophan Photosensitized by a Chiral π,π* Aromatic Ketone

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