Ultrafast Electronic Deactivation Dynamics of Xanthosine Monophosphate

Abstract

Ultrafast energy dissipation is a crucial factor for the photostability of DNA and RNA, but even some of the key electronic deactivation pathways in monomeric nucleic acid building stones are still controversial. Here, we report on the excited-state dynamics of the rare nucleotide xanthosine monophosphate as a function of deprotonation state (XMP vs. XMP−) and excitation wavelength (λpump= 278–243 nm) by femtosecond time-resolved fluorescence and absorption spectroscopy. We show that the predominating relaxation channel leads to a return of the photo-excited molecules to the electronic ground state in τ∼1 ps. The mechanism likely involves an out-of-plane deformation of the five-membered ring, different from the main electronic deactivation pathways in the canonical purine bases adenine and guanine. The results are discussed in terms of the structural and electronic differences of XMP compared to the canonical nucleotides.

The tautomer‐specific excited state dynamics of 2,6‐diaminopurine using resonance‐enhanced multiphoton ionization and quantum chemical calculations

“…The relative energy levels of the ππ* state versus the nearest nπ* states affect the excited state dynamics, as shown with 2AP 18,71 . With a few exceptions (guanine, 13 isoguanine, 14 and hypoxanthine 20 ), it appears most purines (adenine, 26–31 2AP, 18 2‐oxopurine, 19 xanthine, 15,16 purine 11 ) and pyrimidines (cytosine, 74 thymine, 75,76 and uracil 77 ) relax from their initially excited ππ* to an nπ* to the ground state. Instead, 2,6‐dAP follows the 1 ππ*/S 0 CI path exclusively for 9H and both 1 ππ*/S 0 internal conversion and 1 ππ*/ 3 ππ* ISC for 7H.…”

“…Although the picture is far from complete, there are some indications that heterosubstituted purines (e.g. guanine 13 and isoguanine 14 ) may be more photostable than the homosubstituted purines (2,6‐diaminopurine and xanthine 15,16 ), while purines with a single ligand (adenine, 17 2AP, 18 2‐oxopurine, 19 and hypoxanthine 20 ) appear to be more photostable than most purines with two ligands 13 . Martinez‐Fernandez et al 19 .…”

“…Although the picture is far from complete, there are some indications that heterosubstituted purines (e.g. guanine 13 and isoguanine 14 ) may be more photostable than the homosubstituted purines (2,6-diaminopurine and xanthine 15,16 ), while purines with a single ligand (adenine, 17 2AP, 18 2-oxopurine, 19 and hypoxanthine 20 ) appear to be more photostable than most purines with two ligands. 13 Martinez-Fernandez et al 19 in a thorough computational study on the photostability effects of position and oxo/amino substitution for purines with a single ligand, found that amino or oxo substitution at C 2 has little effect on the photodynamics, while C 6 functionalization leads to photostability.…”

The tautomer-specific excited state dynamics of 2,6-diaminopurine using REMPI and quantum chemical calculations

“…Although the picture is far from complete, there are some indications that heterosubstituted purines (e.g. guanine (13) and isoguanine (14)) may be more photostable than the homosubstituted purines (2,6-diaminopurine and xanthine (15,16)), while purines with a single ligand (adenine, (17) 2AP,(18) 2-oxopurine, (19) and hypoxanthine (20)) appear to be more photostable than most purines with two ligands. (13) Martinez-Fernandez et al in a thorough computational study on the photostability effects of position and oxo/amino substitution for purines with a single ligand, (19) found that amino or oxo substitution at C 2 has little effect on the photodynamics, while C 6 functionalization leads to photostability.…”

Photorelaxation and Photorepair Processes in Nucleic and Amino Acid Derivatives

“…Four contributions in this Special Issue investigate the electronic relaxation mechanisms in nucleic and amino acid derivatives. Röttger, Temps, and co-workers [ 24 ] examine the excited-state dynamics of the nucleotide xanthosine monophosphate in its neutral and deprotonated forms in aqueous solutions by using a combination of fluorescence up-conversion and transient absorption spectroscopy techniques with femtosecond time resolution. Gustavsson, Markovitsi, and co-workers [ 25 ] report on the time-resolved fluorescence decay and fluorescence anisotropy measurements of seven mono-, di-, and tri-methylated xanthine derivatives in water and in methanol.…”