Fluorescence probes for prokaryotic and eukaryotic cells using Re(CO)₃⁺complexes with an electron withdrawing ancillary ligand

Abstract

Research in fluorescence microscopy presents new challenges, especially with respect to the development of new metal-based fluorophores. In this work, the news fac-[Re(CO) 3 (bpy)L]PF 6 (C3) and fac-[Re(CO) 3 (dmb)L]PF 6 (C4) complexes, where L is an ancillary ligand E-2-((3-amino-pyridin-4-ylimino)-methyl)-4,6-diterbutylphenol, both exhibiting an intramolecular hydrogen bond, have been synthesized for its use as preliminary probes for fluorescence microscopy. The complexes were characterized using chemical techniques such as UV-Vis, 1 H-NMR, TOCSY, FT-IR, cyclic voltammetry, mass spectra (EI-MS 752.22 M + for C3 and 780.26 M + for C4) and DFT calculations including spin-orbit effects. The electron withdrawing nature of the ancillary ligand L in C3 and C4 explains their electrochemical behavior, which shows the oxidation of Re I at 1.84 V for C3 and at 1.88 V for C4. The UV-vis absorption and emission properties have been studied at room temperature in acetonitrile solution. The complexes show luminescent emission with a large Stokes shift (λ ex = 366 nm; λ em = 610 nm for C3 and λ ex = 361 nm; λ em = 560 nm for C4). The TDDFT calculations suggest that an experimental mixed absorption band at 360 nm could be assigned to MLCT (d(Re) →π*(dmb))and LLCT (π(L)→π*(dmb)) transitions. We also assessed the cytotoxicity of C3 and C4 in an epithelial cell line (T84). We found that 12.5 µg/ml of C3 or C4 is the minimum concentration needed to kill the 80% of cell population, as determined by neutral red uptake. Finally, the potential of C3 and C4 as biological dyes for use in fluorescent microscopy was assessed in bacteria (Salmonella enterica) and yeasts (Candida albicans and Cryptococcus spp.), and in an ovarian cancer cell line (SKOV-3). We found that, in all cases, both C3 and C4 are suitable compounds to be used as fluorescent dyes for biological purposes. In addition, we present evidence suggesting that these rhenium (I) tricarbonyl complexes may be also useful as differential fluorescent dyes in yeasts (Candida albicans and Cryptococcus spp.), without the need of antibodies.

A PRELIMINARY STUDY ON ELECTROCATALYTIC REDUCTION OF CO2 USING FAC-ReI(CO)3(4,4′-DI-METHYL-2,2′-BIPYRIDYL)((E)-2-((3-AMINO-PYRIDIN-4-YLIMINO)-METHYL)-4,6-DI-TERT-BUTYLPHENOL))+ COMPLEX

“…As previously described by Carreño et al 17 , under the experimental conditions employed both for C1 and C2 complexes in acetonitrile, may undergo two single-electron reduction processes and two single-electron oxidations. The reductions, C1 and C2, behave similarly for both compounds, all reversible and with diffusional control during the first reduction and not diffusional at the second; their electrochemical reaction mechanism corresponds to an electrochemical-electrochemical-chemical pathway (EEC) described elsewhere 36 with slight potential differences between complexes.…”

“…[44][45] These potential values match with the usual voltammetric profiles informed for a family of neutral fac-Re(CO) 3 (2,2'-bipyridyl)Cl substituted complexes but in acetonitrile (MeCN) 29 and they are negatively shifted regarding the potentials found for the same compound in MeCN (E 1/2 = -1.25 V and E pc = -1.68 V). 17 An extra reduction process at E pc = -0.90 V (irreversible) is preceding the two described peaks and is the first wave found by scanning on the cathodic direction which is attributed to the reduction of the azomethine group (-CH=N-), the fragment of the Schiff Base on the ancillary ligand (L). 46 On the other hand, is very well known that azomethine electroreduction is favored by the presence of H + .…”

“…When a polished Vitreous Carbon plate as working electrode is modified by cycling anodic region of C2 complex in CH 2 Cl 2 which involve the typic oxidative redox profile for amino (-NH 2 ) and phenolic (-OH) groups presenting in the L (cation radical method). 15,17,34 The voltammogram profile evolve by growing a polymeric deposit on the plate surface (see Figure 5, A). This plate with the immobilized layer of C2 complex is then transferred to a CO 2 saturated solution buffer, pH=7.0 (allowing it evolve to solution buffer, pH=5.5) and the voltammogram profile registered (see Figure 5, B).…”

“…Theoretical evidence, using DFT level of theory that included spin-orbit effect confirm the former effect. [17][18][19][20] On the other hand, complexes of type neutral fac-Re(CO) 3 (X)Cl (with X=2,2′-bipyridyl or similar), have demonstrated activity for the selectively reduction of CO 2 to CO and the mechanistic pathways have been studied. [21][22][23][24][25] Based on these findings, our group have also been exploring a new kind of rhenium(I) tricarbonyl complexes of type fac-Re(CO) 3 (4,4'-di-methyl-2,2'bipyridyl)L + (C2, See Scheme 1), and its potential properties to the reduction of CO 2 .…”

Confocal Microscopy Studies of Living Fungal Hyphae and Conidia Using Rhenium (I) Tricarbonyl Complexes as Fluorescent Dyes.

“…The fac-[Re(I)(CO) 3 (2,2'-bpy)L]PF 6 (C3) and fac-[Re(I)(CO) 3 (4,4'dimethyl-2,2'-bpy)L]PF 6 (C4) complexes (See Scheme 1) have been recently reported [12,13]. The luminescent properties of these complexes were tuned by the withdrawing electronic nature of the ancillary ligand L (E-2-((3-aminopyridin-4-ylimino)-methyl)-4,6-di-tert-butylphenol), a pyridine Schiff base presenting an intramolecular hydrogen bond (IHB) [14].…”