Computational Design of Rhenium(I) Carbonyl Complexes for Anticancer Photodynamic Therapy

Abstract

New Re(I) carbonyl complexes are proposed as candidates for photodynamic therapy after investigating the effects of the pyridocarbazole-type ligand conjugation, addition of substituents to this ligand, and replacement of one CO by phosphines in [Re(pyridocarbazole)(CO) 3 (pyridine)] complexes by means of the density functional theory (DFT) and time-dependent DFT. We have found, first, that increasing the conjugation in the bidentate ligand reduces the highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) energy gap of the complex, so its absorption wavelength red-shifts. When the enlargement of this ligand is carried out by merging the electron-withdrawing 1 H -pyrrole-2,5-dione heterocycle, it enhances even more the stabilization of the LUMO due to its electron-acceptor character. Second, the analysis of the shape and composition of the orbitals involved in the band of interest indicates which substituents of the bidentate ligand and which positions are optimal for reducing the HOMO–LUMO energy gap. The introduction of electron-withdrawing substituents into the pyridine ring of the pyridocarbazole ligand mainly stabilizes the LUMO, whereas the HOMO energy increases primarily when electron-donating substituents are introduced into its indole moiety. Each type of substituents results in a bathochromic shift of the lowest-lying absorption band, which is even larger if they are combined in the same complex. Finally, the removal of the π-backbonding interaction between Re and the CO trans to the monodentate pyridine when it is replaced by phosphines PMe 3 , 1,4-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane (DAPTA), and 1,4,7-triaza-9-phosphatricyclo[5.3.2.1]tridecane (CAP) causes another extra bathochromic shift due to the destabilization of the HOMO, which is low with DAPTA, moderate with PMe 3 , but especially large with CAP. Through the combination of the PMe 3 or CAP ligands with adequate electron-withdrawing and/or electron-donating substituents at the pyridocarbazole ligand, we have found several complexes with significant absorption at the therapeutic window. In addition, according to our results on the singlet–triplet energy gap, all of them should be able to produce cytotoxic singlet oxygen.

Intramolecular Hydrogen Bond in Pyridine Schiff Bases as Ancillary Ligands of Re(I) Complexes Is a Switcher between Visible and NIR Emissions: A Relativistic Quantum Chemistry Study

“…For relativistic calculations performed on organometallic Re­(I) tricarbonyl complexes, ZORA expands the Dirac equation in E /(2 mc 2 – V ), contains corrections in 1/c 2 to all orders, and can be written as the sum of a scalar relativistic (SR) and SOC parts. , For excited triplet states (T 1 ), geometry optimizations were performed using regular unrestricted KS ground-state calculations with a spin polarization of 2. To perform geometry optimization of T 1 and S 0 states, we used the generalized gradient approximation (GGA) potentials with non-local exchange and correlation corrections with the PBE functional without symmetry restrictions. − The GGA PBE functional is the most used strategy to reproduce the possible symmetry breaking in the excited triplet state. − In addition, frequency calculations were performed to identify the stationary points as minima, where we did not find imaginary frequencies.…”

A neutral mononuclear rhenium(i) complex with a rare in situ-generated triazolyl ligand for the luminescence “turn-on” detection of histidine

“…The chemistry of rhenium-based coordination complexes and supramolecules with nitrogen-containing heterocyclic ligands has attracted substantial research interest in the past two decades due to their novel redox, photophysical, catalytic, and electrochemical properties. 1–5 The inherent characteristics of the Re center in combination with multifunctional heterocyclic ligands may involve the coupling of C–N and N–N bonds thus resulting in a variety of applications. 6 In 2007, Chen and co-workers reported on the generation of an intriguing 3,5-bis(2-pyridyl)-4 H -1,2,4-triazole (Hbpt) ligand during the one-pot synthesis of dinuclear metal complexes.…”