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Ultrafast IR spectroscopy of polymeric cytosine nucleic acids reveal the long-lived species is due to a localised state

2012-02-22, 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.

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.

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Long-lived excited states in i-motif DNA studied by picosecond time-resolved IR spectroscopy

2014-03-21, Keane, Páraic M., Wojdyla, Michal, Doorley, Gerard W., Magno, Luís M., Quinn, Susan J., et al.

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.

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Tracking DNA excited states by picosecond-time-resolved infrared spectroscopy: Signature band for a charge-transfer excited state in stacked adenine-thymine systems

2013-07-29, Doorley, Gerard W., Wojdyla, Michal, Watson, Graeme W., Quinn, Susan J., et al.

UV photoexcitation of an adenine-thymine heterodimer (ApT) in D 2O yields a complex transient infrared signature in the 1500-1600 cm-1 spectral region. The spectral dynamics fit well to a biexponential decay assignable to two transient species. The first, a short-lived species with a lifetime of ca. 5 ps, originates from the vibrationally hot electronic ground state of the unstacked form of the dinucleotide. The second species is longer-lived (ca. 75 ps), and its yield correlates to the amount of stacked dinucleotide present in solution. We assign the longer-lived component to a charge-transfer (A•+pT •-) state by comparison with calculated spectra for the adenine radical cation and thymine radical anion. Significantly, the CT feature is also identified in UV-excited [poly(dA-dT)]2. This experimental observation gives a powerful insight into how base-base interactions lead to extended-lifetime electronic excited states of the nucleic acid bases and how a dimeric structure controls the relaxation pathway. © 2013 American Chemical Society.

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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

2011-03, 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.

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.