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Author = Keane, Páraic M.;
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Displaying Results 1 - 12 of 12 on page 1 of 1
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A comparative picosecond transient infrared study of 1-methylcytosine and 5'-dCMP that sheds further light on the excited states of cytosine derivatives
(2013)
Keane, Páraic M.; Wojdyla, Michal; Doorley, Gerard W.; Watson, Graeme W.; Clark, Ian P....
A comparative picosecond transient infrared study of 1-methylcytosine and 5'-dCMP that sheds further light on the excited states of cytosine derivatives
(2013)
Keane, Páraic M.; Wojdyla, Michal; Doorley, Gerard W.; Watson, Graeme W.; Clark, Ian P.; Greetham, Gregory M.; Parker, Anthony W.; Towrie, Michael; Kelly, John M.; Quinn, Susan J.
Abstract:
The role of N1-substitution in controlling the deactivation processes in photoexcited cytosine derivatives has been explored using picosecond time-resolved IR spectroscopy. The simplest N1-substituted derivative, 1-methylcytosine, exhibits relaxation dynamics similar to the cytosine nucleobase and distinct from the biologically relevant nucleotide and nucleoside analogues, which have longer-lived excited-state intermediates. It is suggested that this is the case because the sugar group either facilitates access to the long-lived (1)n(O)Ï * state or retards its crossover to the ground state.
AMS
http://hdl.handle.net/10197/4323
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Direct observation by time-resolved infrared spectroscopy of the bright and the dark excited states of the [Ru(phen)2(dppz)]2+ light-switch compound in solution and when bound to DNA
(2020)
Poynton, Fergus E.; Hall, James P.; Keane, Páraic M.; Quinn, Susan J.; et al.
Direct observation by time-resolved infrared spectroscopy of the bright and the dark excited states of the [Ru(phen)2(dppz)]2+ light-switch compound in solution and when bound to DNA
(2020)
Poynton, Fergus E.; Hall, James P.; Keane, Páraic M.; Quinn, Susan J.; et al.
Abstract:
The [Ru(phen)2(dppz)]2+ complex (1) is non-emissive in water but is highly luminescent in organic solvents or when bound to DNA, making it a useful probe for DNA binding. To date, a complete mechanistic explanation for this “light-switch” effect is still lacking. With this in mind we have undertaken an ultrafast time resolved infrared (TRIR) study of 1 and directly observe marker bands between 1280–1450 cm−1, which characterise both the emissive “bright” and the non-emissive “dark” excited states of the complex, in CD3CN and D2O respectively. These characteristic spectral features are present in the [Ru(dppz)3]2+ solvent light-switch complex but absent in [Ru(phen)3]2+, which is luminescent in both solvents. DFT calculations show that the vibrational modes responsible for these characteristic bands are predominantly localised on the dppz ligand. Moreover, they reveal that certain vibrational modes of the “dark” excited state couple with vibrational modes of two coordinating water mo...
http://hdl.handle.net/10197/11596
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Enantiomeric conformation controls rate and yield of photoinduced electron transfer in DNA sensitized by Ru(II) dipyridophenazine complexes
(2020)
Keane, Páraic M.; Poynton, Fergus E.; Hall, James P.; Quinn, Susan J.; et al.
Enantiomeric conformation controls rate and yield of photoinduced electron transfer in DNA sensitized by Ru(II) dipyridophenazine complexes
(2020)
Keane, Páraic M.; Poynton, Fergus E.; Hall, James P.; Quinn, Susan J.; et al.
Abstract:
Photosensitized oxidation of guanine is an important route to DNA damage. Ruthenium polypyridyls are very useful photosensitizers, as their reactivity and DNA-binding properties are readily tunable. Here we show a strong difference in the reactivity of the two enantiomers of [Ru(TAP)2(dppz)]2+, by using time-resolved visible and IR spectroscopy. This reveals that the photosensitized one-electron oxidation of guanine in three oligonucleotide sequences proceeds with similar rates and yields for bound Δ-[Ru(TAP)2(dppz)]2+, whereas those for the λ enantiomer are very sensitive to base sequence. It is proposed that these differences are due to preferences of each enantiomer for different binding sites in the duplex.
Irish Research Council
Science Foundation Ireland
University College Dublin
Royal Irish Academy/Royal Society exchange program
UK Biotechnology and Biological Sciences Research Council
http://hdl.handle.net/10197/11607
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Inosine Can Increase DNA′s Susceptibility to Photo‐oxidation by a RuII Complex due to Structural Change in the Minor Groove
(2020)
Keane, Páraic M.; Hall, James P.; Poynton, Fergus E.; Quinn, Susan J.; et al.
Inosine Can Increase DNA′s Susceptibility to Photo‐oxidation by a RuII Complex due to Structural Change in the Minor Groove
(2020)
Keane, Páraic M.; Hall, James P.; Poynton, Fergus E.; Quinn, Susan J.; et al.
Abstract:
Weinheim Key to the development of DNA-targeting phototherapeutic drugs is determining the interplay between the photoactivity of the drug and its binding preference for a target sequence. For the photo-oxidising lambda-[Ru(TAP)2(dppz)]2+ (Λ-1) (dppz=dipyridophenazine) complex bound to either d{T1C2G3G4C5G6C7C8G9A10}2 (G9) or d{TCGGCGCCIA}2 (I9), the X-ray crystal structures show the dppz intercalated at the terminal T1C2;G9A10 step or T1C2;I9A10 step. Thus substitution of the G9 nucleobase by inosine does not affect intercalation in the solid state although with I9 the dppz is more deeply inserted. In solution it is found that the extent of guanine photo-oxidation, and the rate of back electron-transfer, as determined by pico- and nanosecond time-resolved infrared and transient visible absorption spectroscopy, is enhanced in I9, despite it containing the less oxidisable inosine. This is attributed to the nature of the binding in the minor groove due to the absence of an NH2 group. ...
http://hdl.handle.net/10197/11614
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Long-lived excited states in i-motif DNA studied by picosecond time-resolved IR spectroscopy
(2020)
Keane, Páraic M.; Wojdyla, Michal; Doorley, Gerard W.; Magno, Luís M.; Quinn, Susan J.;...
Long-lived excited states in i-motif DNA studied by picosecond time-resolved IR spectroscopy
(2020)
Keane, Páraic M.; Wojdyla, Michal; Doorley, Gerard W.; Magno, Luís M.; Quinn, Susan J.; et al.
Abstract:
The transient IR absorption spectrum for UV-excited i-motif DNA is reported for the first time and found to possess complex dynamics pointing to multiple decay processes, including possible charge transfer between packed hemi-protonated C bases.
European Commission - Seventh Framework Programme (FP7)
Science Foundation Ireland
http://hdl.handle.net/10197/11611
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Long-Lived Excited-State Dynamics of i-Motif Structures Probed by Time-Resolved Infrared Spectroscopy
(2020)
Keane, Páraic M.; Baptista, Frederico R.; Gurung, Sarah P.; Devereux, Stephen J.; Quinn...
Long-Lived Excited-State Dynamics of i-Motif Structures Probed by Time-Resolved Infrared Spectroscopy
(2020)
Keane, Páraic M.; Baptista, Frederico R.; Gurung, Sarah P.; Devereux, Stephen J.; Quinn, Susan J.; et al.
Abstract:
UV-generated excited states of cytosine (C) nucleobases are precursors to mutagenic photoproduct formation. The i-motif formed from C-rich sequences is known to exhibit high yields of long-lived excited states following UV absorption. Here the excited states of several i-motif structures have been characterized following 267 nm laser excitation using time-resolved infrared spectroscopy (TRIR). All structures possess a long-lived excited state of ∼300 ps and notably in some cases decays greater than 1 ns are observed. These unusually long-lived lifetimes are attributed to the interdigitated DNA structure which prevents direct base stacking overlap.
University College Dublin
Biotechnology and Biological Sciences Research Council
Royal Irish Academy/Royal Society
http://hdl.handle.net/10197/11613
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Monitoring guanine photo-oxidation by enantiomerically resolved Ru(II) dipyridophenazine complexes using inosine-substituted oligonucleotides
(2020)
Keane, Páraic M.; Poynton, Fergus E.; Hall, James P.; Quinn, Susan J.; et al.
Monitoring guanine photo-oxidation by enantiomerically resolved Ru(II) dipyridophenazine complexes using inosine-substituted oligonucleotides
(2020)
Keane, Páraic M.; Poynton, Fergus E.; Hall, James P.; Quinn, Susan J.; et al.
Abstract:
The intercalating [Ru(TAP)2(dppz)]2+ complex can photo-oxidise guanine in DNA, although in mixed-sequence DNA it can be difficult to understand the precise mechanism due to uncertainties in where and how the complex is bound. Replacement of guanine with the less oxidisable inosine (I) base can be used to understand the mechanism of electron transfer (ET). Here the ET has been compared for both Λ- and Δ-enantiomers of [Ru(TAP)2(dppz)]2+ in a set of sequences where guanines in the readily oxidisable GG step in {TCGGCGCCGA}2 have been replaced with I. The ET has been monitored using picosecond and nanosecond transient absorption and picosecond time-resolved IR spectroscopy. In both cases inosine replacement leads to a diminished yield, but the trends are strikingly different for Λ- and Δ-complexes.
Irish Research Council
Science Foundation Ireland
Royal Irish Academy/Royal Society exchange programme
UK Biotechnology and Biological Sciences Research Council
UK Scienc...
http://hdl.handle.net/10197/11606
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Monitoring one-electron photo-oxidation of guanine in DNA crystals using ultrafast infrared spectroscopy
(2020)
Hall, James P.; Poynton, Fergus E.; Keane, Páraic M.; Quinn, Susan J.; et al.
Monitoring one-electron photo-oxidation of guanine in DNA crystals using ultrafast infrared spectroscopy
(2020)
Hall, James P.; Poynton, Fergus E.; Keane, Páraic M.; Quinn, Susan J.; et al.
Abstract:
To understand the molecular origins of diseases caused by ultraviolet and visible light, and also to develop photodynamic therapy, it is important to resolve the mechanism of photoinduced DNA damage. Damage to DNA bound to a photosensitizer molecule frequently proceeds by one-electron photo-oxidation of guanine, but the precise dynamics of this process are sensitive to the location and the orientation of the photosensitizer, which are very difficult to define in solution. To overcome this, ultrafast time-resolved infrared (TRIR) spectroscopy was performed on photoexcited ruthenium polypyridyl-DNA crystals, the atomic structure of which was determined by X-ray crystallography. By combining the X-ray and TRIR data we are able to define both the geometry of the reaction site and the rates of individual steps in a reversible photoinduced electron-transfer process. This allows us to propose an individual guanine as the reaction site and, intriguingly, reveals that the dynamics in the cry...
http://hdl.handle.net/10197/11601
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Photophysical studies of CdTe quantum dots in the presence of a zinc cationic porphyrin
(2013)
Keane, Páraic M.; Gallagher, Shane A.; Magno, Luís M.; Leising, Miriam J.; Clark, Ian P...
Photophysical studies of CdTe quantum dots in the presence of a zinc cationic porphyrin
(2013)
Keane, Páraic M.; Gallagher, Shane A.; Magno, Luís M.; Leising, Miriam J.; Clark, Ian P.; Greetham, Gregory M.; Towrie, Michael; Gun'ko, Yurii; Kelly, John M.; Quinn, Susan J.
Abstract:
The photophysical properties of 2.3 nm thioglycolic acid (TGA) coated CdTe quantum dots (QDs) prepared by a reflux method have been studied in the presence of cationic meso-tetrakis(4-N-methylpyridyl) zinc porphyrin (ZnTMPyP4). Addition of the CdTe QDs to the porphyrin in H2O results in a marked red-shift and hypochromism in the porphyrin absorption spectrum, indicative of a non-covalent binding interaction with the QD surface. Only low equivalents of the quantum dot were required for complete quenching of the porphyrin fluorescence revealing that one quantum dot may quench more than one porphyrin. Similarly addition of porphyrin to the quantum dot provided evidence for very efficient quenching of the CdTe photoluminescence, suggesting the formation of CdTe'porphyrin aggregates. Definitive evidence for such aggregates was gathered using small angle X-ray spectroscopy (SAXS). Ultrafast transient absorption data are consistent with very rapid photoinduced electron trans...
http://hdl.handle.net/10197/4319
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Reversal of a Single Base-Pair Step Controls Guanine Photo-Oxidation by an Intercalating Ruthenium(II) Dipyridophenazine Complex
(2020)
Keane, Páraic M.; Poynton, Fergus E.; Hall, James P.; Quinn, Susan J.
Reversal of a Single Base-Pair Step Controls Guanine Photo-Oxidation by an Intercalating Ruthenium(II) Dipyridophenazine Complex
(2020)
Keane, Páraic M.; Poynton, Fergus E.; Hall, James P.; Quinn, Susan J.
Abstract:
Small changes in DNA sequence can often have major biological effects. Here the rates and yields of guanine photo-oxidation by Λ-[Ru(TAP)2(dppz)]2+ have been compared in 5′-{CCGGATCCGG}2 and 5′-{CCGGTACCGG}2 using pico/nanosecond transient visible and time-resolved IR (TRIR) spectroscopy. The inefficiency of electron transfer in the TA sequence is consistent with the 5′-TA-3′ versus 5′-AT-3′ binding preference predicted by X-ray crystallography. The TRIR spectra also reveal the differences in binding sites in the two oligonucleotides.
Irish Research Council
Science Foundation Ireland
Royal Irish Academy/Royal Society International Exchange Scheme
UK Biotechnology and Biological Sciences Research Council
College of Science, UCD
UK Science and Technology Facilities Council
http://hdl.handle.net/10197/11605
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Spectro-electrochemical Studies on [Ru(TAP)2 (dppz)]2+ - Insights into the Mechanism of its Photosensitized Oxidation of Oligonucleotides
(2020)
Keane, Páraic M.; Tory, Joanne; Towrie, Michael; Quinn, Susan J.
Spectro-electrochemical Studies on [Ru(TAP)2 (dppz)]2+ - Insights into the Mechanism of its Photosensitized Oxidation of Oligonucleotides
(2020)
Keane, Páraic M.; Tory, Joanne; Towrie, Michael; Quinn, Susan J.
Abstract:
[Ru(TAP) 2 (dppz)] 2+ (TAP = 1,4,5,8-tetraazaphenanthrene; dppz = dipyrido[3,2-a:2′,3′-c]phenazine) is known to photo-oxidize guanine in DNA. Whether this oxidation proceeds by direct photoelectron transfer or by proton-coupled electron transfer is still unknown. To help distinguish between these mechanisms, spectro-electrochemical experiments have been carried out with [Ru(TAP) 2 (dppz)] 2+ in acetonitrile. The UV-vis and mid-IR spectra obtained for the one-electron reduced product were compared to those obtained by picosecond transient absorption and time-resolved infrared experiments of [Ru(TAP) 2 (dppz)] 2+ bound to guanine-containing DNA. An interesting feature of the singly reduced species is an electronic transition in the near-IR region (with λ max at 1970 and 2820 nm). Density functional and time-dependent density functional theory simulations of the vibrational and electronic spectra of [Ru(TAP) 2 (dppz)] 2+ , the reduced complex [Ru(TAP) 2 (dppz)] + , and four isomers of ...
http://hdl.handle.net/10197/11604
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Ultrafast IR spectroscopy of polymeric cytosine nucleic acids reveal the long-lived species is due to a localised state
(2013)
Keane, Páraic M.; Wojdyla, Michal; Doorley, Gerard W.; Kelly, John M.; Clark, Ian P.; P...
Ultrafast IR spectroscopy of polymeric cytosine nucleic acids reveal the long-lived species is due to a localised state
(2013)
Keane, Páraic M.; Wojdyla, Michal; Doorley, Gerard W.; Kelly, John M.; Clark, Ian P.; Parker, Anthony W.; Greetham, Gregory M.; Towrie, Michael; Magno, Luís M.; Quinn, Susan J.
Abstract:
The decay pathways of UV-excited cytosine polymers are investigated using picosecond time-resolved infrared spectroscopy. Similar yields of a non-emissive (1)nÏ * state are found in the single-stranded dC(30) polymer as in the dCMP monomer, but with a longer lifetime in the polymer (80 ps vs. 39 ps). A longer lifetime is also found in the d(CpC) dinucleotide. No evidence of excimer states is observed, suggesting that localised (1)nÏ * excited states are the most significant intermediates present on the picosecond timescale.
AS
http://hdl.handle.net/10197/4322
Displaying Results 1 - 12 of 12 on page 1 of 1
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