Charge Photoinjection in Intercalated and Covalently Bound [Re(CO)₃(dppz)(py)]⁺–DNA Constructs Monitored by Time-Resolved Visible and Infrared Spectroscopy

Abstract

The complex [Re(CO)3(dppz)(py′-OR)]+ (dppz = dipyrido[3,2-a:2′,3′-c]phenazine; py′-OR = 4-functionalized pyridine) offers IR sensitivity and can oxidize DNA directly from the excited state, making it a promising probe for the study of DNA-mediated charge transport (CT). The behavior of several covalent and noncovalent Re-DNA constructs was monitored by time-resolved IR (TRIR) and UV/visible spectroscopies, as well as biochemical methods, confirming the long-range oxidation of DNA by the excited complex. Optical excitation of the complex leads to population of MLCT and at least two distinct intraligand states. Experimental observations that are consistent with charge injection from these excited states include similarity between long-time TRIR spectra and the reduced state spectrum observed by spectroelectrochemistry, the appearance of a guanine radical signal in TRIR spectra, and the eventual formation of permanent guanine oxidation products. The majority of reactivity occurs on the ultrafast timescale, although processes dependent on slower conformational motions of DNA, such as the accumulation of oxidative damage at guanine, are also observed. The ability to measure events on such disparate timescales, its superior selectivity in comparison to other spectroscopic techniques, and the ability to simultaneously monitor carbonyl ligand and DNA IR absorption bands makes TRIR a valuable tool for the study of CT in DNA.

Probing the excited state nature of coordination complexes with blended organic and inorganic chromophores using vibrational spectroscopy

“…[47] While the photo-oxidation of DNA by ruthenium dppz complexes often proceeds via reactive oxygen intermediates, [160] complexes of rhenium have been shown to be able to directly photo-oxidize guanine while bound to DNA. [45,46] TRIR has been used to monitor this, using [Re(CO)3(dppz)(py-R)] + (R is propanoic acid or propanoate ester). [46] As well as MLCT(phen) states, two  * excited states were observed, assigned as phenbased and phz-based.…”

“…[45,46] TRIR has been used to monitor this, using [Re(CO)3(dppz)(py-R)] + (R is propanoic acid or propanoate ester). [46] As well as MLCT(phen) states, two  * excited states were observed, assigned as phenbased and phz-based. By monitoring both the (CO) and (DNA) regions of the IR spectrum it was established that hole-transfer, from the excited complex to guanine can occur directly from the MLCT(phen) or  *(phen) state, while the  *(phz) state appeared to be inactive.…”

Absorption Spectroscopy and Photophysics of a ReI‐dppz Probe for DNA‐Mediated Charge Transport

“…However, a growing interest has been recently dedicated to other metals such as iridium(III) complexes and rhenium‐dppz carbonyl compounds. The latter in particular possess an additional coordination site and can easily bind DNA with a great potential for in vivo applications . such as light‐assisted chemotherapy …”

Long Chain Effects on DNA‐Binding and Cytotoxicity to Cancer Cells in Metallo‐Supramolecular Oligomers

“…Planar metal complexes serve as an anticancer agent because the planar structure accelerates the molecular intercalation between base pairs of DNA. It interferes the transcription and replication of DNA leading to cell death . On the other hand, the groove binding is based on weak interactions including ionic interactions, hydrogen bonds, and van der Waals interactions ,.…”