Design of New Anticancer Compounds based on the Photoreactivity of Polyazaaromatic RutheniumII Complexes

In this section, we present the development of new potential anti-cancer agents, which is based upon some special properties that have been determined for some Ru11 complexes. More specifically, the photoreactivity of these ruthenium complexes has guided this investigation. The use of light to cure certain diseases is called phototherapy.45 Usually, in phototherapy, the primary process is the absorption of light by a photosensitizer which, in a second step, reacts with a targeted endogenous molecule (O2 or DNA) via energy or electron transfer.

Photosensitizer* + Target—>photosensitizer + Target* (energy transfer)

Photosensitizer* + Target—^photosensitizer* + Target*+ (electron transfer)

Metal compounds such as polyazaaromatic ruthenium(II) complexes are particularly good candidates as photosensitizers.46 Indeed, their properties can be modulated by varying the ligands chelated to the metal center as shown by their different photophysical and photochemical behaviors in the absence and in the presence of DNA.47 51 The interaction of ruthenium(II) complexes with DNA enables their reaction with the nucleic acids. Three interaction geometries are possible: the complex can be externally associated in the electrostatic environment of the DNA double helix, adsorbed in the DNA grooves or intercalated between two DNA base pairs via one of its ligands. Finally, their reaction in the electronic excited state is favored (i) by their strong absorption in the visible part of the spectrum, which increases the probability of population of this excited state and (ii) by a rather long lifetime of this excited state (i.e. longer than 100 ns).

The photophysics of most Run polypyridyl complexes can be described on the basis of the photophysical scheme established for the reference complex [RuII(bpy)3]2+ (Figure 19.5).47,48 The photon absorption populates a singlet metal to ligand charge transfer excited state (1MLCT), which deactivates rapidly by intersystem crossing (ISC) to the triplet MLCT state (3MLCT) with a quantum yield of 1.52 This triplet can deactivate to the ground state by radiative deactivation, radiationless deactivation or thermal activation to a 3MC (metal centered) state. This latter is a bit higher in energy than the 3MLCT

MLCT

MLCT

Ground state

Figure 19.5 Photophysical scheme for [RuII(bpy)3]'

Ground state

Figure 19.5 Photophysical scheme for [RuII(bpy)3]'

state and deactivates without emission to the ground state. In the presence of DNA, the 3MLCT excited state of the complex generally gives rise to electron or energy transfer processes.48,49

Was this article helpful?

0 0
10 Ways To Fight Off Cancer

10 Ways To Fight Off Cancer

Learning About 10 Ways Fight Off Cancer Can Have Amazing Benefits For Your Life The Best Tips On How To Keep This Killer At Bay Discovering that you or a loved one has cancer can be utterly terrifying. All the same, once you comprehend the causes of cancer and learn how to reverse those causes, you or your loved one may have more than a fighting chance of beating out cancer.

Get My Free Ebook


Post a comment