The impact of biomolecule interactions on the cytotoxic effects of rhenium(I) tricarbonyl complexes.

Rhenium complexes show great promise as anticancer drug candidates. Specifically, compounds with a Re(CO)3(NN)(py)+ core in their architecture have shown cytotoxicity equal to or greater than that of well-established anticancer drugs based on platinum or organic molecules. This study aimed to evaluate how the strength of the interaction between rhenium(I) tricarbonyl complexes fac-[Re(CO)3(NN)(py)]+, NN = 1,10-phenanthroline (phen), dipyrido[3,2-f:2',3'-h]quinoxaline (dpq) or dipyrido[3,2-a:2'3'-c]phenazine (dppz) and biomolecules (protein, lipid and DNA) impacted the corresponding cytotoxic effect in cells. Results showed that fac-[Re(CO)3(dppz)(py)]+ has higher Log Po/w and binding constant (Kb) with biomolecules (protein, lipid and DNA) compared to complexes of fac-[Re(CO)3(phen)(py)]+ and fac-[Re(CO)3(dpq)(py)]+. As consequence, fac-[Re(CO)3(dppz)(py)]+ exhibited the highest cytotoxicity (IC50 = 8.5 µM for HeLa cells) for fac-[Re(CO)3(dppz)(py)]+ among the studied compounds (IC50 > 15 µM). This highest cytotoxicity of fac-[Re(CO)3(dppz)(py)]+ are probably related to its lipophilicity, higher permeation of the lipid bilayers of cells, and a more potent interaction of the dppz ligand with biomolecules (protein and DNA). Our findings open novel avenues for rational drug design and highlight the importance of considering the chemical structures of rhenium complexes that strongly interact with biomolecules (proteins, lipids, and DNA).

DNA structural changes (photo)induced by tricarbonyl (pterin)rhenium(I) complex.

We report on interactions of different types of DNA molecules including double-stranded and plasmid DNA as well as polynucleotides (poly[dGdC]2 and poly[dAdT]2) with fac-[ReI(CO)3(pterin)(H2O)] (or Reptr) complex. The interaction was characterized spectroscopically and changes in the plasmid structure were verified by both electrophoresis and AFM microscopy. For comparative reasons, two others related tricarbonyl rhenium(I) complexes, fac-[(4,4'-bpy)ReI(CO)3(dppz)]+ (or Redppz) and fac-[(CF3SO3)ReI(CO)3(2,2'-bpy)] (or Rebpy) were also studied to further explore the influence of the different co-ligands on the interaction and DNA (photo)damage. Data reported herein suggests that DNA molecules can be structurally modified either by direct interaction with Re(I) complexes in their ground states inducing DNA relaxation, and/or through photoinduced cross-linking processes. The chemical nature of the co-ligands modulates the extent of the damage observed.

Selective Oxidation of Inner Pnictogenide Ligands in Mixed-Ligand Rhenium Cubane-Type Cluster Complexes.

Reactivity of new tetrahedral rhenium cluster complexes with pnictogenide inner ligands µ3-As3-, µ3-Sb3-, and µ3-Bi3- has been investigated in reactions with aqueous H2O2. It has been found that the oxidation of clusters [{Re4As3Q}(CN)12]7- (Q = S or Se) led to the formation of stable clusters with µ3-(AsO)3- ligands. Under the same conditions, the oxidation of [{Re4As2S2}(CN)12]6- cluster led to substitution of µ3-As3- ligands to µ3-O2-. The resulting cluster [{Re4O2S2}(CN)12]4- easily undergoes further oxidation, and even at room temperature, a unique {Re4} to {Re3} rearrangement occurs with the formation of the new triangular cluster [{Re3(µ3-S)(µ-O)2(µ-SO2)}(CN)9]5-. Upon heating, this process proceeds faster and the triangular cluster can be isolated as individual compounds. Cluster anions [{Re4SbSe3}(CN)12]5- and [{Re4BiS3}(CN)12]5- reacted with H2O2, yielding clusters containing µ3-O2- ligands, namely, [{Re4OSe3}(CN)12]4- and [{Re4OS3}(CN)12]4-. This indicates that oxidized forms of µ3-Sb3- and µ3-Bi3- ligands can be easily substituted.

Application of microwave plasma atomic emission spectrometry in bioanalytical chemistry of bioactive rhenium compounds.

Five newly synthetized fac-Re(I) tricarbonyl compounds were explored as prospective antitrypanosomal agents. The biological activity of the whole series was evaluated preliminarily against the epimastigote form of Trypanosoma cruzi. All compounds showed activity against epimastigotes with IC50 values in the low micromolar range. The most active compound [fac-Re(I)(CO)3(tmp)(CTZ)](PF6), with CTZ = clotrimazole and tmp = 3,4,7,8-tetramethyl-1,10-phenantroline, showed good selectivity towards the parasites and thus was selected to carry out further metallomic studies. For this task, a newly bioanalytical method based on microwave plasma atomic emission spectrometry (MP-AES) was developed and validated. The accuracy of the method was ensured by testing a certified reference material. Results of rhenium elemental analysis by MP-AES agreed with the proposed formula of the studied compounds, contributing to the overall validation of the method, which was then applied to evaluate the percentage of rhenium uptaken by the parasites and the association of the compounds with parasite biomacromolecules. Metallomics results showed low total rhenium percentage uptaken by parasites (∼1.2%) and preferential accumulation in the soluble proteins fraction (∼82.8%). Thus, the method based on MP-AES turned out to be an economical and green alternative for metallomics studies involving potential rhenium metallodrugs. Moreover, a comparison against rhenium determination by electrothermal atomic absorption spectrometry (ET-AAS) was included.

Understanding the photophysical properties of rhenium(I) compounds coordinated to 4,7-diamine-1,10-phenanthroline: synthetic, luminescence and biological studies.

In the present study, the photophysical properties and preliminary time-dependent density functional theory (TD-DFT) data of new rhenium(i) polypyridyl compounds, fac-[Re(L)(Am2phen)(CO)3]0/+, where Am2phen = 4,7-diamine-1,10-phenanthroline and L = Cl and ethyl isonicotinate (et-isonic), provided new insights into excited-state deactivation through an unusual inversion between two metal-to-ligand charge-transfer excited states. In addition, their cellular uptake using breast cancer (MCF-7) and melanoma (SkMel-147 and SkMel-29) cell lines and bioactivity were investigated and their cell-killing mechanism and protein expression were also studied. Preliminary TD-DFT results showed that both compounds exhibited a strong and broad absorption band around 300-400 nm which corresponds to a combination of ILAm2phen and MLCTRe→Am2phen transitions, and a strong contribution of charge transfer transition MLCTRe→et-isonic for fac-[Re(et-isonic)(Am2phen)(CO)3]+ is also observed. In contrast to typical Re(i) polypyridyl complexes, the substitution of Cl with the et-isonic ligand showed a bathochromic shift of the emission maxima, relatively low emission quantum yield and fast lifetime. Photophysical investigation of the fac-[ReCl(et-isonic)2(CO)3] compound provided meaningful information on the excited state manifold of the fac-[Re(L)(Am2phen)(CO)3]0/+ complexes. As shown in the absorption profile, a remarkable inversion of the lowest-lying excited state takes place from the usually observed MLCTRe→Am2phen to the unusual MLCTRe→et-isonic. The lipophilicity of the positive-complex was higher than that of the non-charge compound and the same trend for the activity against cells was observed, in the absence of light. In addition, flow cytometry and Western Blot analyses showed an overexpression of pro-caspase-9, suggesting a caspase proteolytic cascade through an intrinsic-pathway apoptosis mechanism. The photophysical properties of these compounds reported herein provide new fundamental insights into the understanding of substituent groups on polypyridyl ligands which are relevant to practical development.

Electrochemical Hydrogen Evolution over Hydrothermally Synthesized Re-Doped MoS2 Flower-Like Microspheres.

In this research, we report a simple hydrothermal synthesis to prepare rhenium (Re)- doped MoS2 flower-like microspheres and the tuning of their structural, electronic, and electrocatalytic properties by modulating the insertion of Re. The obtained compounds were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Structural, morphological, and chemical analyses confirmed the synthesis of poorly crystalline Re-doped MoS2 flower-like microspheres composed of few stacked layers. They exhibit enhanced hydrogen evolution reaction (HER) performance with low overpotential of 210 mV at current density of 10 mA/cm2, with a small Tafel slope of 78 mV/dec. The enhanced catalytic HER performance can be ascribed to activation of MoS2 basal planes and by reduction in charge transfer resistance during HER upon doping.

[Radionuclide synoviorthesis in hemophilia: experience in 107 patients]. / Sinoviortesis con radioisótopos en hemofilia: Experiencia de un centro en Chile.

BACKGROUND: In patients with hemophilia, radionuclide synoviorthesis, or the intra-articular injection of a radionuclide to decrease the synovial hypertrophy tissue, aims to decrease or avoid hemarthrosis. AIM: To evaluate the effectiveness of radionuclide synoviorthesis in hemophilia. MATERIAL AND METHODS: Observational retrospective study of the evolution of 107 male patients aged 3 to 54 years who were subjected to radionuclide synoviorthesis between 2007 and 2015. RESULTS: Of 164 treated joints, in 65% treatment was successful, (defined as zero to two hemarthroses and absence of synovitis during the follow up period), in 17% it was partially successful (defined as two or less hemarthroses, but persistence of the synovitis) and failed in 18% of the procedures. No important complications were recorded. CONCLUSIONS: Radionuclide synoviorthesis has an overall 82% success rate, is minimally invasive, can be used at any age and is inexpensive We recommend its implementation in Chilean hemophilia treatment centers.

Sinoviortesis con radioisótopos en hemofilia: Experiencia de un centro en Chile / Radionuclide synoviorthesis in hemophilia: experience in 107 patients

Background: In patients with hemophilia, radionuclide synoviorthesis, or the intra-articular injection of a radionuclide to decrease the synovial hypertrophy tissue, aims to decrease or avoid hemarthrosis. Aim: To evaluate the effectiveness of radionuclide synoviorthesis in hemophilia. Material and Methods: Observational retrospective study of the evolution of 107 male patients aged 3 to 54 years who were subjected to radionuclide synoviorthesis between 2007 and 2015. Results: Of 164 treated joints, in 65% treatment was successful, (defined as zero to two hemarthroses and absence of synovitis during the follow up period), in 17% it was partially successful (defined as two or less hemarthroses, but persistence of the synovitis) and failed in 18% of the procedures. No important complications were recorded. Conclusions: Radionuclide synoviorthesis has an overall 82% success rate, is minimally invasive, can be used at any age and is inexpensive We recommend its implementation in Chilean hemophilia treatment centers.

Evaluation of chromosomal aberrations induced by 188Re-dendrimer nanosystem on B16f1 melanoma cells.

PURPOSE: To study the rhenium-188 labeling of polyamidoamine (PAMAM) generation 4 (G4) dendrimer and its evaluation on biodistribution and chromosomal aberrations in melanoma cells induced by ionizing radiation as potential treatment agent. MATERIALS AND METHODS: Dendrimers were first conjugated with Suc-HYNIC (succinimidyl 6-hydrazinopyridine-3-carboxylic acid hydrochloride). Dendrimer-HYNIC was then incubated with 188ReO4-. Biodistribution was performed administrating 188Re-dendrimer to normal (NM) or melanoma-bearing mice (MBM). Chromosome aberration test was conducted in order to measure treatment capacity of 188Re-dendrimer in melanoma cells. RESULTS: Radiolabeling yield of dendrimer was approx. 70%. Biodistribution studies in NM showed blood clearance with hepatic and renal depuration. MBM showed a similar pattern of biodistribution with tumor uptake of 6% of injected dose. Aberrant metaphases quantified in control cells were 7%, increasing to 29.5% in cells treated with 15µCi (0.555 MBq) of 188Re-dendrimer for 24 h. CONCLUSIONS: 188Re-dendrimer can produce double-stranded breaks in DNA induced by ionizing radiation in melanoma cells in vitro.

DNA Oxidation Photoinduced by Norharmane Rhenium(I) Polypyridyl Complexes: Effect of the Bidentate N,N'-Ligands on the Damage Profile.

ReI -polypyridyl complexes have interesting and distinctive photochemical and photosensitizing properties. This work describes the capability to induce (or photoinduce) DNA damage of three ReI -complexes with a naturally occurring alkaloid called norharmane (nHo) as ligand: [Re(CO)3 (nHo)(L)]CF3 SO3 where L=2,2'-bipyridine (ReBpy), phenanthroline (RePhen) or dipyrido[3,2-a:2',3'-c]phenazine (ReDppz). The interaction of the complexes with DNA was investigated by steady-state and time-resolved spectroscopy. Data show that the mode and strength of interaction depend on the chemical structure of the bidentate ligand. The complexes show a major static contribution to the overall interaction, giving rise to the formation of noncovalent adducts with DNA, and the particular trend observed was RePhen>ReDppz>ReBpy. Photo-oxidation at the purine bases represents the major DNA damaging mechanism. RePhen also induces single-strand breaks in a yield similar to that of base damage, suggesting an additional photosensitizing pathway. We also performed the Ames test to evaluate the cytotoxic and mutagenic properties of both non-irradiated and photoexcited complexes. RePhen, but not the other complexes, turned out to be both toxic and phototoxic for the bacteria.

The cluster [Re6Se8I6]3- penetrates biological membranes: drug-like properties for CNS tumor treatment and diagnosis.

Tumorigenic cell lines are more susceptible to [Re6Se8I6]3- cluster-induced death than normal cells, becoming a novel candidate for cancer treatment. Still, the feasibility of using this type of molecules in human patients remains unclear and further pharmacokinetics analysis is needed. Using coupled plasma optical emission spectroscopy, we determined the Re-cluster tissue content in injected mice, as a biodistribution measurement. Our results show that the Re-cluster successfully reaches different tissues, accumulating mainly in heart and liver. In order to dissect the mechanism underlying cluster biodistribution, we used three different experimental approaches. First, we evaluate the degree of lipophilicity by determining the octanol/water partition coefficient. The cluster mostly remained in the octanol fraction, with a coefficient of 1.86 ± 0.02, which indicates it could potentially cross cell membranes. Then, we measured the biological membrane penetration through a parallel artificial membrane permeability assays (PAMPA) assay. The Re-cluster crosses the artificial membrane, with a coefficient of 122 nm/s that is considered highly permeable. To evaluate a potential application of the Re-cluster in central nervous system (CNS) tumors, we analyzed the cluster's brain penetration by exposing cultured blood-brain-barrier (BBB) cells to increasing concentrations of the cluster. The Re-cluster effectively penetrates the BBB, reaching nearly 30% of the brain side after 24 h. Thus, our results indicate that the Re-cluster penetrates biological membranes reaching different target organs-most probably due to its lipophilic properties-becoming a promising anti-cancer drug with high potential for CNS cancer's diagnosis and treatment.

Rhenium(I) tricarbonyl compounds of bioactive thiosemicarbazones: Synthesis, characterization and activity against Trypanosoma cruzi.

American Trypanosomiasis is a chronic infection discovered and described in 1909 by the Brazilian scientist Carlos Chagas. It is caused by the protozoan parasite Trypanosoma cruzi. Although it affects about 10million people in Latin America, the current chemotherapy is still inadequate. The discovery of new drugs is urgently needed. Our group is focused on the development of prospective metal-based drugs mainly based on bioactive ligands and pharmacologically interesting metal ions. In this work three new rhenium(I) tricarbonyl compounds fac-[ReI(CO)3Br(HL)] where HL=5-nitrofuryl containing thiosemicarbazones were synthesized and fully characterized in solution and in the solid state. The in vitro evaluation of the compounds on T. cruzi trypomastigotes (Dm28c strain) showed that the Re(I) compounds are 8 to 15 times more active than the reference drug Nifurtimox and show a 4 to 17 fold increase in activity in respect to the free (HL) ligands. Obtained compounds also show good selectivity indexes (IC50 endothelial cells Ea.hy926/IC50 T. cruzi (Dm28c tripomastigotes)). 1H NMR and MS studies, performed with time, showed that the fac-[Re(CO)3Br(HL)] species convert into the dimers [Re2(CO)6(L)2] in solution. Crystal structure of [ReI2(CO)6(L2)2], the product of complexes' dimerization, was solved. Related to the mechanism of action, the studied compounds do not generate radical oxygen species in the parasite (as 5-nitrofuryl derived thiosemicarbazones do) probably due to the unfavorable nitro reduction potential of the generated dimeric species. On the contrary, the compounds produce a decrease of the oxygen consumption rate of the parasites, maybe inhibiting their mitochondrial respiration.

Association studies to transporting proteins of fac-ReI(CO)3(pterin)(H2O) complex.

A new synthetic route to acquire the water soluble complex fac-ReI(CO)3(pterin)(H2O) was carried out in aqueous solution. The complex has been obtained with success via the fac-[ReI(CO)3(H2O)3]Cl precursor complex. ReI(CO)3(pterin)(H2O) has been found to bind strongly with bovine and human serum albumins (BSA and HSA) with intrinsic-binding constants, Kb, of 6.5 × 105 M-1 and 5.6 × 105 M-1 at 310 K, respectively. The interactions of serum albumins with ReI(CO)3(pterin)(H2O) were evaluated employing UV-vis fluorescence and absorption spectroscopy and circular dichroism. The results suggest that the serum albumins-ReI(CO)3(pterin)(H2O) interactions occurred in the domain IIA-binding pocket without loss of helical stability of the proteins. The comparison of the fluorescence quenching of BSA and HSA due to the binding to the Re(I) complex suggested that local interaction around the Trp 214 residue had taken place. The analysis of the thermodynamic parameters ΔG0, ΔH0, and ΔS0 indicated that the hydrophobic interactions played a major role in both HSA-Re(I) and BSA-Re(I) association processes. All these experimental results suggest that these proteins can be considered as good carriers for transportation of ReI(CO)3(pterin)(H2O) complex. This is of significant importance in relation to the use of this Re(I) complex in several biomedical fields, such as photodynamic therapy and radiopharmacy.

The characterization of anti-T. cruzi activity relationships between ferrocenyl, cyrhetrenyl complexes and ROS release.

Trypanosoma cruzi (T. cruzi) is the parasite that causes Chagas disease. Nifurtimox is the most used drug against the T. cruzi, this drug increases intermediaries nitro group, being mainly responsible for the high toxicity component, for this reason it is important to study new organic compounds and thus improve therapeutic strategies against Chagas disease. The electronic effects of ferrocenyl and cyrhetrenyl fragments were investigated by DFT calculation. A close correlation was found between HOMO-LUMO gap of nitro radical NO 2 (-) with the experimental reduction potential found for nitro group and IC50 of two forms the T. cruzi (epimastigote and trypomastigote). The IC50 on human hepatoma cells is higher for both compounds compared to IC50 demonstrated in the two forms the T. cruzi, and additionally show reactive oxygen species release. The information obtained in this paper could generate two new drugs with anti-T. cruzi activity, but additional studies are needed.

Norharmane rhenium(I) polypyridyl complexes: synthesis, structural and spectroscopic characterization.

Two novel Re(i) complexes with the general formula fac-[Re(CO)3(L)(nHo)]CF3SO3, where L = 2,2'-bipyridine (bpy) or 1,10 phenanthroline (phen) and nHo (9H-pyrido[3,4-b]indole; norharmane) have been synthesized. The Re(i)-nHo complexes were characterized by structural X-ray diffraction, (1)H and (13)C NMR, UV-vis absorption and FT-IR spectroscopy, and by a combination of two mass spectrometry techniques, namely ESI-MS and UV-MALDI-MS. All characterizations showed that nHo is coordinated to the metal atom by the pyridine nitrogen of the molecule. X-ray structural analysis revealed that the crystal lattices for both complexes are further stabilized by a strong >N-HO bond between the pyrrole NH group of the pyridoindole ligand and one oxygen atom of the trifluoromethanesulfonate counter-ion. Ground state geometry optimization by DFT calculations showed that in fluid solution the nHo ligand may rotate freely. The nature of the electronic transitions of Re(CO)3(bpy)(nHo)(+) were established by TD-DFT calculations. The set of the most important electronic transitions present in this complex are comprised of π→π* electronic transitions centered on bpy and nHo moieties, LLCTnHo→COs, MLLCTRe(CO)3→bpy and LLCTnHo→bpy transitions. Additionally, TD-DFT calculations predict the existence of another two intense MLLCTRe(CO)3→nHo electronic transitions. Calculated UV-vis absorption spectra are in good agreement with the corresponding experimental data for the bpy-containing complex.

The cluster [Re6Se8I6]3- induces low hemolysis of human erythrocytes in vitro: protective effect of albumin.

The cluster Re6Se8I63- has been shown to induce preferential cell death of a hepatic carcinoma cell line, thus becoming a promising anti-cancer drug. Whether this cluster induces acute hemolysis or if it interacts with albumin remains unclear. The effect of acute exposure of human red blood cells to different concentrations of the cluster with and without albumin is described. Red blood cells from healthy donors were isolated, diluted at 1% hematocrit and exposed to the cluster (25-150 µM) at 37 °C, under agitation. Hemolysis and morphology were analyzed at 1 and 24 h. The potential protection of 0.1% albumin was also evaluated. Exposition to therapeutic doses of the cluster did not induce acute hemolysis. Similar results were observed following 24 h of exposition, and albumin slightly reduced hemolysis levels. Furthermore, the cluster induced alteration in the morphology of red blood cells, and this was prevented by albumin. Together, these results indicate that the cluster Re6Se8I63- is not a hemolytic component and induces moderate morphological alterations of red blood cells at high doses, which are prevented by co-incubation with albumin. In conclusion, the cluster Re6Se8I63- could be intravenously administered in animals at therapeutic doses for in vivo studies.

Solvent dependent switching of 3MLLCT and 1IL luminescent states in [ClRe(CO)3(bathocuproinedisulfonate)]2-: spectroscopic and computational study.

Steady state and time-resolved luminescence experiments and calorimetric studies, as well as time-dependent density functional theory calculations performed on [ClRe(CO)(3)(Bathocuproinedisulfonate)](2-), show that the photophysical properties of the Re(I) anionic complex are determined by the balance between intraligand ((1)IL) and metal-ligand-to-ligand charge transfer ((3)MLLCT) excited states. In organic solvents, (3)MLLCT states prevail and the usual expected behavior is observed: bathochromic shift of the emission maximum, a reduced luminescence quantum yield and the shortening of the excited-state lifetime upon increasing the polarity of the solvent. In addition, singlet oxygen ((1)O2) is generated with high quantum yields (Φ(Δ) ≈ 0.5 in CH(3)CN) due to the quenching of the (3)MLLCT luminescence by (3)O2. The total quenching rate constant of triplet state by oxygen, k(q), reach values between 2.2 and 2.4 × 10(9) M(-1) s(-1) for the organic solvents studied. In CH(3)CN, the fraction of triplet states quenched by O2 which yield (1)O2, f(O2)T, is nearly unity. In aqueous solution, where no singlet oxygen is generated, the luminescence of the Re(I) complex is of (1)IL character with a emission quantum yield (Φ(em)) strongly pH dependent: Φ(em,(pH=2))/Φ(em,(pH=10)) ≈ 5.6. The variation of the pH of the solution tunes the photophysical properties of the Re(I) complex by changing the relative amount of the different species existing in aqueous solutions: [ClRe(CO)3(BCS)](2-), [(OH)Re(CO)3(BCS)](2-) and [(H2O)Re(CO)3(BCS)](−). TD-DFT calculations show that the percentage of charge transfer character of the electronic transitions is substantially higher in the organic solvents than in aqueous solutions, in agreement with the increase of (1)IL character of HOMO in [(H2O)Re(CO)3(BCS)](−) relative to [ClRe(CO)3(BCS)](2-).

The photophysics of fac-[Re(CO)3(NN)(bpa)](+) complexes: a theoretical/experimental study.

The influence of the polypyridyl ligand on the photophysics of fac-[Re(CO)3(NN)(bpa)](+), bpa = 1,2-bis-(4-pyridyl)ethane and NN = 1,10-phenanthroline (phen), pyrazino[2,3-f][1,10]-phenanthroline (dpq), and dipyrido[3,2-a:2'3'-c]phenazine (dppz) has been investigated by steady state and time-resolved emission spectroscopy combined with theoretical calculations using time-dependent density functional theory (TD-DFT). The fac-[Re(CO)3(phen)(bpa)](+) is a typical MLCT emitter in acetonitrile with ϕ = 0.11 and τ = 970 ns. The emission lifetime and quantum yield decrease significantly in fac-[Re(CO)3(dpq)(bpa)](+) (ϕ = 0.05; τ = 375 ns) due to the presence of a close lying dark charge transfer state located at the pyrazine ring of dpq, as indicated by TD-DFT data. The luminescence of these complexes is quenched by hydroquinone with kq = (2.9 ± 0.1) × 10(9) and (2.6 ± 0.1) × 10(9) L mol(-1) s(-1), respectively, for NN = phen or dpq. These values are increased respectively to (4.6 ± 0.1) × 10(9) and (4.2 ± 0.1) × 10(9) L mol(-1) s(-1) in the 1 : 1 H2O-CH3CN mixture. In this medium Stern-Volmer constants determined by steady-state and time-resolved measurements differ from each other, which is indicative of static quenching, i.e. the pre-association of hydroquinone and the complexes through hydrogen bonding between the remote N-atom in the bpa ligand (KA ≅ 1-2 × 10(1) L mol(-1)), followed by a concerted proton-electron transfer. In contrast to other investigated complexes, fac-[Re(CO)3(dppz)(bpa)](+) is weakly emissive in acetonitrile at room temperature (ϕ ≅ 10(-4)) and does not exhibit a rigidochromic effect. This photophysical behaviour as well as TD-DFT data indicate that the lowest lying triplet excited state can be described as (3)ILdppz. The results provide additional insight into the influence of the polypyridyl ligand on the photophysical properties of Re(I) complexes.

Photosensitized generation of singlet oxygen from Re(I) complexes: a photophysical study using LIOAS and luminescence techniques.

Quantum yields and efficiencies of (1)O2 ((1)Δg) production along with photophysical properties for a number of Re(I) complexes in acetonitrile solutions are reported. Two different classes of Re(I) complexes, L(S)-CO2-Re(CO)3(bpy) (L(S) = 2-pyrazine, 2-naphthalene, 9-anthracene, 1-pyrene, 2-anthraquinone) and XRe(CO)3L (X = CF3SO3, py; L = bpy, phen), were probed as photosensitizers for (1)O2 ((1)Δg) production in air-saturated acetonitrile solutions. Depending on the nature of the Re(I) complex, the excited state responsible for the generation of (1)O2 ((1)Δg) is either a metal-to-ligand charge transfer ((3)MLCT) or a ligand centered ((3)LC) state. With L(S)-CO2-Re(CO)3(bpy) complexes, (1)O2 ((1)Δg) is produced by oxygen quenching of (3)LC states of anthracene and pyrene with high quantum yields (ΦΔ between 0.8 and 1.0), while the complexes bearing the ligands L(S) = 2-anthraquinone, 2-pyrazine, and 2-naphthalene did not yield (1)O2. XRe(CO)3L complexes generate (1)O2 ((1)Δg) mainly by oxygen quenching of their (3)MLCT luminescence with an efficiency of (1)O2 ((1)Δg) formation close to unity. Bimolecular rate constants for the quenching of the XRe(CO)3L complexes' emission by molecular oxygen range between 1 × 10(9) and 2 × 10(9) M(-1) s(-1), and they are all ≤ (1/9)kd, in good agreement with the predominance of the singlet channel in the mechanism of (1)O2 ((1)Δg) generation using these Re(I) complexes as photosensitizers. All the experimental singlet oxygen efficiencies are consistent with calorimetric and luminescence data for the studied complexes. With L(S)-CO2-Re(CO)3(bpy) complexes, calorimetric experiments were utilized in the calculation of the quantum yields of triplet formation; namely φT = 0.76 and 0.83 for the triplet states of anthracene and pyrene, respectively.

Solid state molecular device based on a rhenium(I) polypyridyl complex immobilized on TiO2 films.

The photochemical and photophysical behaviors of fac-[Re(CO)3(phen)(trans-stpyCOOH)](+) (phen = 1,10-phenanthroline, trans-stpyCOOH = 4-[trans-(pyridin-4-yl-vinyl)]benzoic acid) in acetonitrile solution and adsorbed on a TiO2 film have been investigated. The trans-to-cis photoisomerization at 404 nm irradiation of coordinated stpyCOOH occurs efficiently in fluid solution as shown by quantum yield determined spectrophotometrically (Φ(UV-vis) = 0.37 ± 0.04) and, more accurately, by (1)H NMR (Φ(NMR) = 0.48 ± 0.04), following the photoproduct signals in the distinct region of the reactant. For the first time, the trans-to-cis isomerization is also reported for the complex adsorbed on the TiO2 surface (Φ(UV-vis) = 0.23 ± 0.03). The photoproduct, fac-[Re(CO)3(phen)(cis-stpyCOOH)](+), is emissive in acetonitrile (ϕ = 0.032), but its radiative decay is highly quenched on the oxide surface by electron photoinjection into the semiconductor, leading to an increasing photocurrent as the trans-to-cis isomerization takes place. Therefore, the photoinduced trans-to-cis isomerization of coordinated ligand immobilized on TiO2 films acts as a trigger for the electron injection process. This system exemplifies the use of photoinduced molecular motion to yield electrical current, which can be used as a "proof of concept" for molecular machines/devices.