Excited state behaviour of substituted dipyridophenazine Cr(iii) complexes in the presence of nucleic acids

Abstract

The photophysics and photochemistry of [Cr(phen) 2 (dppz)] 3+ and its 11,12-substituted derivatives [Cr(phen) 2 (X 2 dppz)] 3+ {X = Me or F} have been studied in the presence of purine nucleotides or DNA using steady state and time-resolved absorption and luminescence spectroscopy. 5′-Adenosine monophosphate (5′-AMP) shows only a weak interaction with the excited states of each complex. By contrast they are efficiently quenched by 5′-guanosine monophosphate (5′-GMP), consistent with photo-induced electron transfer. Laser flash photolysis spectroscopy in the presence of 5′-GMP suggests that both forward and back electron-transfers are rapid. All complexes also display a strong affinity for DNA and evidence for both static and dynamic quenching mechanisms is provided.Graphical Abstract:

Study of picosecond processes of an intercalated dipyridophenazine Cr(iii) complex bound to defined sequence DNAs using transient absorption and time-resolved infrared methods

“…4 The binding modes are likely to be similar to those revealed by recent crystal structures of [Ru( phen) 2 (dppz)] 2+ or [Ru(TAP) 2 (dppz)] 2+ bound to short defined-sequence DNA. 8 In both cases, while the quenching is fully consistent with electron transfer to the excited state of the metal complex from the guanine, no evidence of this could be found in our nanosecond laser flash photolysis experiments. 6 In solution the excited state, which is a doublet metal-centred ( 2 MC) species, has a lifetime of (>50 µs) and is readily monitored both by its phosphorescence and by transient absorption.…”

“…5 Chromium polypyridyls are also known to have a strongly oxidising long-lived excited state making them potentially powerful photooxidative agents. 8 This suggests that the back reaction must also be rapid. As with other Cr(III) polypyridyls, 7 the excited state of 1 is quenched by 5′-GMP via a dynamic process.…”

Adenine Radical Cation Formation by a Ligand-Centered Excited State of an Intercalated Chromium Polypyridyl Complex Leads to Enhanced DNA Photo-oxidation

“… 32 − 37 It was also found that the luminescence of [Cr(phen) 2 (dppz)] 3+ is dynamically quenched by 5′-guanosine monophosphate (GMP) with a rate constant close to that of diffusion control, while 5′-adenosine monophosphate (AMP) was almost 3 orders of magnitude less effective. 34 Though the behavior with GMP is entirely consistent with quenching via electron transfer, no evidence of the reduced complex could be found using nanosecond flash photolysis, 33 , 34 suggesting that the back reaction with the oxidized GMP must also be very fast.…”

Theoretical Study of the Molecular Geometries, Electronic and Thermodynamic Properties of Chlorinated Dipyrido-(3,2-a:,-c)-Phenazine

“…While the thermodynamic properties of polychlorinated phenazine (pcpz) by density functional theory calculations have been reported [1], theoretical studies on the geometries, electronic and thermodynamic properties of dppz, especially by semiempirical methods are sparse. Dppz is a polypyridine compound, and polypyridines have been severally reported [4][5][6] to have excellent ability to bind metal ions in solutions, and various derivatives of the ligands have been studied in order to explore their binding abilities, biological and electrochemical behavior, as well as excited state behaviour. In these reports, their metal complexes are known to bind DNA and their spectroscopic and electrochemical properties can be tuned.…”

“…e DNA-binding of dppz complexes of other transition metals, such as platinum, iridium, rhodium, rhenium, and chromium have also been investigated, and the chromium (III) complexes of dppz have also been studied because of their special photophysical properties [4]. Reports focusing on substituted dppzs, especially its Cr 3+ complexes, exploring its binding interactions with DNA, its photophysical and photochemical properties and the excited state behavior of these complexes are also available in the literature [4,5].…”