A study of the pH dependence of electronically excited guanosine compounds by picosecond time-resolved infrared spectroscopy

McGovern, David A.; Doorley, Gerard W.; Whelan, Áine M.; Parker, Anthony W.; Towrie, Michael; Kelly, John M.; Quinn, Susan J.

doi:10.1039/b817756b

Cited by 10 publications

(19 citation statements)

References 33 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…4b) is well fitted by a single exponential function with a lifetime of 200 AE 10 ps in excellent agreement with a previous UV-pump/visible-probe experiment (191 AE 4 ps), 1 and an earlier UV-pump/broadband-mid-IR-probe study (214 AE 20 ps). 22,50 Strong positive D A signals are observed at 1441, 1518 and 1632 cm À1 . Although the latter two bands appear on the low frequency side of the strong bleach bands at 1575 and 1683 cm À1 , they do not cause the frequency of the bleach bands to shift with time as seen for GMP (compare Fig.…”

Section: (A) Experimental Resultsmentioning

confidence: 98%

Mode-specific vibrational relaxation of photoexcited guanosine 5′-monophosphate and its acid form: a femtosecond broadband mid-IR transient absorption and theoretical study

Zhang

Improta

Kohler

2014

Phys. Chem. Chem. Phys.

View full text Add to dashboard Cite

UV-pump/broadband-mid-IR-probe transient absorption (TA) experiments and ab initio quantum mechanical (QM) calculations were used to investigate the photophysics in heavy water of the neutral and acid forms of guanosine 5'-monophosphate (GMP and GMPD(+), respectively). Excited GMP undergoes ultrafast internal conversion (IC) and returns to the electronic ground state in less than one picosecond with a large amount of excess vibrational energy. The spectroscopic signals are dominated by vibrational cooling - a process in which the solute dissipates vibrational energy to the solvent. For neutral GMP, cooling proceeds with a time constant of 3 ps. Following IC, at least some medium-frequency modes such as the carbonyl stretch and an in-plane ring vibration are excited, suggesting that the vibrational energy distribution is non-statistical. This is consistent with predicted structural changes upon passage through the S1/S0 conical intersection. GMPD(+) differs from GMP by a single deuteron at the N7 position, but has a dramatically longer lifetime of 200 ps. Vibrational cooling of the S1 state of GMPD(+) was monitored via several medium-frequency modes that were assigned using QM calculations. These medium-frequency modes are also vibrationally excited in a non-statistical fashion. Excitation of these modes is in line with the change in geometry at the S1 minimum of GMPD(+) predicted by QM calculations. Furthermore, these modes relax at different rates, fully consistent with QM calculations, which predict that excited vibrational states of the carbonyl stretch couple strongly to the D2O solvent and thus deactivate via intermolecular energy transfer (IET). In contrast, the ring stretch couples strongly to other ring modes of the guanine chromophore and appears to decay via intramolecular vibrational energy redistribution (IVR).

show abstract

Section: (A) Experimental Resultsmentioning

confidence: 98%

Mode-specific vibrational relaxation of photoexcited guanosine 5′-monophosphate and its acid form: a femtosecond broadband mid-IR transient absorption and theoretical study

Zhang

Improta

Kohler

2014

Phys. Chem. Chem. Phys.

View full text Add to dashboard Cite

show abstract

“…The subsequent decoupling of the C═O stretch from the solvent through weaker hydrogen bonding leads to a high frequency shift of this mode. 37 An alternative assignment for the sharp band in cationic FA is suggested by the IR spectrum of adenosine as shown in the Supporting Information (Figures S1 and S2). Neutral adenosine shows a broad band at 1625 cm −1 , while its acidic form exhibits a sharp and strong band at 1668 cm −1 due to protonation (p K a = 3.5) of the heterocyclic ring.…”

Section: Resultsmentioning

confidence: 99%

Photoinduced Electron Transfer in Folic Acid Investigated by Ultrafast Infrared Spectroscopy

Magana

Dyer

2012

J. Phys. Chem. B

View full text Add to dashboard Cite

Conformational control of excited-state intramolecular electron transfer (ET) in folic acid (FA) has been investigated using femtosecond time-resolved infrared (TRIR) spectroscopy. Ultrafast excited-state ET between the pterin and the 4-aminobenzoyl subunits of FA is observed for the anionic form (at pH 10.0). An ET lifetime of 2.5 ps is estimated from Marcus theory for FA in the “U” conformation, in close agreement with the observed lifetime of 2.0 ps. Return to the ground state through the reverse ET reaction happens almost as rapidly, within 5 ps, resulting in rapid quenching of the singlet excited state. In mixed water:dimethyl sulfoxide solvent, ET becomes more unfavorable as FA adopts a more open conformation, thereby increasing the effective donor–acceptor distance and reducing the coupling energy. In contrast, no ET is observed for the cationic form of FA at low pH (6.0). In this case, the initial singlet excited state is localized on the pterin moiety of FA, and the excited-state charge distribution evolves with time. The charge redistribution in the pterin that occurs with intersystem crossing to the triplet state is characterized by changes in the transient IR spectrum. The excited-state lifetime is much longer in the absence of an ET quenching pathway. These results provide new insight into the mechanism of photodegradation and toxicity of FA. Ultrafast intramolecular ET in closed conformations of FA rapidly quenches the excited state and prevents efficient triplet state formation. Thus, conformations of FA that allow ultrafast intra-ET and rapid quenching of the singlet excited state play a key role in inhibiting pathological pathways following photoexcitation of FA.

show abstract

“…(b) ps-TRIR spectra of a mixture of species in unbuffered solution D 2 O at 2 and 30 ps after excitation at 267 nm. 19 The spectrum at 2 ps is characteristic of GMP, while the spectrum at 20 ps is characteristic of the excited state of GMPD + . state shows similarities to the spectrum of the exciplex spectrum of the dinucleotides dApT and TpdA, although the lifetime is significantly longer for the polynucleotide.…”

Section: Oligo-and Poly-nucleotide Systemsmentioning

confidence: 99%

“…This example also nicely illustrates the power of ps-TRIR in unravelling the behaviour of complex systems, such as those which might be found in natural DNA samples. 19…”

Section: Protonated Gmpmentioning

confidence: 99%

ps-TRIR covers all the bases – recent advances in the use of transient IR for the detection of short-lived species in nucleic acids

Towrie

Doorley

George

et al. 2009

Analyst

Self Cite

View full text Add to dashboard Cite

show abstract

A study of the pH dependence of electronically excited guanosine compounds by picosecond time-resolved infrared spectroscopy

Cited by 10 publications

References 33 publications

Mode-specific vibrational relaxation of photoexcited guanosine 5′-monophosphate and its acid form: a femtosecond broadband mid-IR transient absorption and theoretical study

Mode-specific vibrational relaxation of photoexcited guanosine 5′-monophosphate and its acid form: a femtosecond broadband mid-IR transient absorption and theoretical study

Photoinduced Electron Transfer in Folic Acid Investigated by Ultrafast Infrared Spectroscopy

ps-TRIR covers all the bases – recent advances in the use of transient IR for the detection of short-lived species in nucleic acids

Contact Info

Product

Resources

About