Interaction of polypyridyl Cr(III) complexes with bovine serum albumin.

We report a detailed investigation of the interaction of Cr(NN)33+ with bovine serum albumin (BSA), an important protein for the transport of drugs in blood plasma which allows us to understand further the role of Cr(NN)33+ as a sensitizer in photodynamic therapy (PDT). Chromium(III) complexes, Cr(5Cl-phen)33+, Cr(5Me-phen)33+ and Cr(5Ph-phen)33+ (where Cl = chlorine, Me = methyl and Ph = phenyl are substituents in position 5 of the phen = 1,10-phenanthroline bidentate ligand), were used for the present study. The interactions of BSA with Cr(NN)33+ were assessed employing fluorescence spectroscopy and UV-Vis absorption spectroscopy; in addition electrochemical experiments carried out at a liquid/liquid interface gave insight into the relative hydrophobicities of the complexes. We found that chromium complexes bind strongly with bovine serum albumins (BSA) with intrinsic binding constants, Kb, of (3.33 ± 0.08) × 105 M-1, (5.92 ± 0.08) × 105 M-1 and (1.64 ± 0.05) × 105 M-1 at 300.3 K. Analysis of the thermodynamic parameters ΔG, ΔH, and ΔS indicated that hydrophobic interactions played a major role in all the BSA-Cr(NN)33+ association processes. The binding distances and transfer efficiencies for BSA binding reactions were calculated according to the Förster theory of non-radiation energy transfer giving distance (r) of 2.63 nm, 2.94 nm and 3.00 nm for 5Clphen, 5Mephen and 5Ph phenanthroline complexes, respectively. All these experimental results indicate that Cr(NN)33+ binds to serum albumins, by which these proteins could act as carriers of this complex for further applications in PDT.

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.

Binding of [Cr(phen)3](3+) to transferrin at extracellular and endosomal pHs: potential application in photodynamic therapy.

BACKGROUND: Transferrin is an iron-binding blood plasma glycoprotein that controls the level of free iron in biological fluids. This protein has been deeply studied in the past few years because of its potential use as a strategy of drug targeting to tumor tissues. Chromium complex, [Cr(phen)3](3+) (phen=1,10-phenanthroline), has been proposed as photosensitizers for photodynamic therapy (PDT). Thus, we analyzed the binding of chromium complex, [Cr(phen)3](3+), to transferrin for a potential delivery of this diimine complex to tumor cells for PDT. METHODS: The interaction between [Cr(phen)3](3+) and holotransferrin (holoTf) was studied by fluorescence quenching technique, circular dichroism (CD) and ultraviolet (UV)-visible spectroscopy. RESULTS: [Cr(phen)3](3+) binds strongly to holoTf with a binding constant around 10(5)M(-1), that depends on the pH. The thermodynamic parameters indicated that hydrophobic interactions played a major role in the binding processes. The CD studies showed that there are no conformational changes in the secondary and tertiary structures of the protein. CONCLUSIONS: These results suggest that the binding process would occur in a site different from the specific iron binding sites of the protein and would be the same in both protein states. As secondary and tertiary structures of transferrin do not show remarkable changes, we propose that the TfR could recognize the holoTf despite having a chromium complex associated. GENERAL SIGNIFICANCE: Understanding the interaction between [Cr(phen)3](3+) with transferrin is relevant because this protein could be a delivery agent of Cr(III) complex to tumor cells. This can allow us to understand further the role of Cr(III) complex as sensitizer in PDT.

Aspartame-stabilized gold-silver bimetallic biocompatible nanostructures with plasmonic photothermal properties, antibacterial activity, and long-term stability.

Gold-silver core-shell nanoparticles stabilized with a common sweetener, aspartame (AuNP@Ag@Asm), combine the antimicrobial properties of silver with the photoinduced plasmon-mediated photothermal effects of gold. The particles were tested with several bacterial strains, while biocompatibility was verified with human dermal fibroblasts.

Interaction of UO2 2+ with sodium dodecyl sulfate micelles: association of phenols to micelles through fluorescence quenching data.

Time-resolved laser-induced fluorescence (TRLIF) has been used to study the interaction of uranyl ion with sodium dodecyl sulfate (SDS) micelles in H(3)PO(4) 1 M. The titration curve consists of two curved regions with different slopes, one of them more pronounced at low concentration of SDS and the other, with a less pronounced positive slope at larger [SDS] until a plateau is reached. The fluorescence quenching of uranyl ion by para-substituted phenol compounds was studied by TRLIF and steady-state emission intensity measurements. The results were interpreted in terms of binding of phenolic compounds to the micelle. The binding constant (K(Q)) as well as the entrance and exit rate constants were determined for all the quenchers used.

Interaction of α-diimine-chromium(III) complexes with non-ionic surfactant Triton X-100.

Using either luminescence intensity or lifetime measurements, we have studied the binding interactions of Cr(NN)(3)(3+) (NN=α-diimine ligands) with non-ionic solutions of surfactant p-(1,1,3,3-tetramethylbutyl)phenoxypoly(ethylene glycol), Triton X-100 (TX-100). The titration curves consisted of two curved regions with different slopes. This biphasic behavior of lifetime-TX-100 concentration data revealed the presence of premicellar aggregates at low TX-100 concentration and the formation of normal micelles at high surfactant concentration. The results were analyzed with a model that includes binding of Cr(NN)(3)(3+) (probe) to small premicellar aggregates and to micelles. There is a good correlation between the hydrophobicity of the ligands of Cr(III) complex and the strength of the binding of the complexes to the micelles. A comparison with the binding of Cr(NN)(3)(3+) to sodium dodecylsulfate (SDS) is discussed.

Oxidative stress and antimicrobial activity of chromium(III) and ruthenium(II) complexes on Staphylococcus aureus and Escherichia coli.

The prevalence of antibiotic resistance has resulted in the need for new approaches to be developed to combat previously easily treatable infections. The main aim of this work was to establish the potential of the synthetic α-diimine chromium(III) and ruthenium(II) complexes (where the α-diimine ligands are bpy = 2,2-bipyridine, phen = 1,10-phenanthroline, and dppz = dipyrido[3,2-a:2',3'-c]-phenazine) like [Cr(phen)3](3+), [Cr(phen)2(dppz)](3+), [Ru(phen)3](2+), and [Ru(bpy)3](2+) as antibacterial agents by generating oxidative stress. The [Cr(phen)3](3+) and [Cr(phen)2(dppz)](3+) complexes showed activity against Gram positive and Gram negative bacteria with minimum inhibitory concentrations (MICs) ranging from 0.125 µg/mL to 1 µg/mL, while [Ru(phen)3](2+) and [Ru(bpy)3](2+) do not exhibit antimicrobial activity against the two bacterial genera studied at the concentration range used. When ciprofloxacin was combined with [Cr(phen)3](3+) for the inhibition of Staphylococcus aureus and Escherichia coli, an important synergistic effect was observed, FIC 0.066 for S. aureus and FIC 0.064 for E. coli. The work described here shows that chromium(III) complexes are bactericidal for S. aureus and E. coli. Our results indicate that α -diimine chromium(III) complexes may be interesting to open new paths for metallodrug chemotherapy against different bacterial genera since some of these complexes have been found to exhibit remarkable antibacterial activities.

New advances in the study on the interaction of [Cr(phen)2(dppz)]3+ complex with biological models; association to transporting proteins.

The present study reports a detailed investigation with the interaction of [Cr(phen)(2)(dppz)](3+) with serum albumins, the key protein for the transport of drugs in the blood plasma, which allows us to understand further the role of [Cr(phen)(2)(dppz)](3+) as sensitizer in Photodynamic Therapy (PDT). Chromium(III) complex [Cr(phen)(2)(dppz)](3+), (dppz = dipyridophenazine and phen=1,10-phenanthroline), where dppz is a planar bidentate ligand with an extended π system, has been found to bind strongly with bovine and human serum albumins (BSA and HSA) with an intrinsic binding constants, K(b), of (1.7±0.3)×10(5) M(-1) and (2.2±0.3)×10(5) M(-1) at 295K, respectively. The interactions of serum albumins with [Cr(phen)(2)(dppz)](3+) were assessed employing fluorescence spectroscopy, circular dichroism and UV-vis absorption spectroscopy. The serum albumins-[Cr(phen)(2)(dppz)](3+) interactions caused conformational changes with the loss of helical stability of the protein and local perturbation in the domain IIA binding pocket. The relative fluorescence intensity of the albumin (BSA or HSA) bound to the Cr(III) complex decreased, suggesting that perturbation around the Trp 214 residue took place. The analysis of the thermodynamic parameters ΔG, ΔH, ΔS indicated that the hydrophobic interactions played a major role in both BSA-Cr(III) and HSA-Cr(III) association processes. The binding distances and transfer efficiencies for BSA-Cr(III) and HSA-Cr(III) binding reactions were calculated according to the Föster theory of non-radiation energy transfer. All these experimental results suggests that [Cr(phen)(2)(dppz)](3+) binds to serum albumins, by which these proteins could act as carriers of this complex for further applications in PDT.

Advances on the interaction of polypyridyl Cr(III) complexes with transporting proteins and its potential relevance in photodynamic therapy.

The present study reports a detailed investigation into the interaction of [Cr(phen)(2)(dppz)](3+) and [Cr(phen)(3)](3+) with transferrin, the key protein for the transport of Fe(3+) in blood plasma; its cycle holds promise as an attractive system for strategies of drug targeting to tumor tissues. This can allow us to understand further the role of both complexes as sensitizers in photodynamic therapy (PDT). Chromium(III) complexes, [Cr(phen)(2)(dppz)](3+) and [Cr(phen)(3)](3+), (phen=1,10-phenanthroline and dppz=dipyridophenazine), where dppz is a planar bidentate ligand with an extended π system, have been found to bind strongly with apotransferrin (apoTf) with an intrinsic binding constant, K(b), of (1.8±0.3)×10(5)M(-1) and (1.1±0.1)×10(5)M(-1) at 299K, for apoTf-[Cr(phen)(2)(dppz)](3+) and apoTf-[Cr(phen)(3)](3+), respectively. The interactions of apoTf with the different Cr(III) complexes were assessed employing UV-visible absorption, fluorescence and circular dichroism spectroscopy. The relative fluorescence intensity of the protein decreased when the increasing concentration of Cr(III) complex was added, suggesting that perturbation around the Trp and Tyr residues took place. The analysis of the thermodynamic parameters ΔG, ΔH, ΔS indicated that the presence of the Cr(III) complex stabilizes the protein with a strong entropic contribution. The binding distances and transfer efficiencies for apoTf-[Cr(phen)(2)(dppz)](3+) and apoTf-[Cr(phen)(3)](3+) binding reactions were calculated according to Föster theory of non-radiation energy transfer. All these experimental results suggest that [Cr(phen)(2)(dppz)](3+) and [Cr(phen)(3)](3+) bind strongly to apoTf indicating that this protein could act as a carrier of these complexes for further applications in PDT.

Separation, purification, and characterization of analogues components of a commercial sample of new Fuchsin.

New Fuchsin (NF), also known as Magenta III, has potential applications in photodynamic therapy. The commercial product labeled NF contains two other dye components in different proportions, Magenta II and Magenta I (Rosaniline). The proportions of NF, Magenta II, and Magenta I determined by reversed-phase high-performance liquid chromatography (RP-HPLC) in the commercial sample used were 71.6 +/- 0.4%, 25.2 +/- 0.2%, and 2.8 +/- 0.1% (n = 7), respectively. The isolation, purification, and characterization of commercial NF dye components were carried out applying different techniques, such as preparative column liquid chromatography (PCLC), thin layer chromatography (TLC), RP-HPLC, absorption spectrophotometry, nuclear magnetic resonance spectroscopy (NMR), electrospray ionization mass spectrometry (ESI-MS), and tandem electrospray ionization mass spectrometry (ESI-MS-MS). After separation and isolation, the degree of purity obtained for NF compound was higher than 95% and 92% for Magenta II and Magenta I compounds, respectively. Therefore, it is essential to ensure a high degree of purity of these dyes as raw material to obtain new drugs intended for therapeutic treatments.

New insights in the DNA-[Cr(phen)2(dppz)]3+ binding and photocleavage properties by the complex with an intercalating ligand.

Due to the key role of DNA in cell life and pathological processes, the design of specific chemical nucleases, DNA probes and alkylating agents is an important research area for the development of new therapeutic agents and tools in Biochemistry. Hence, the interaction of small molecules with DNA has attracted in particular a great deal of attention. The aim of this study was to investigate the ability of [Cr(phen)(2)(dppz)](3+) to associate with DNA and to characterize it as photocleavage reagent for Photodynamic Therapy (PDT). Chromium(III) complex [Cr(phen)(2)(dppz)](3+), (dppz = dipyridophenazine, phen = 1,10-phenanthroline), where dppz is a planar bidentate ligand with an extended pi system, has been found to bind strongly to double strand oligonucleotides (ds-oligo) and plasmid DNA with intrinsic DNA binding constants, K(b,) of (3.9+/-0.3)x10(5) M(-1) and (1.1+/-0.1)x10(5) M(-1), respectively. The binding properties to DNA were investigated by UV-visible (UV-Vis) absorption spectroscopy and electrophoretic studies. UV-Vis absorption data provide clearly that the chromium(III) complex interacts with DNA intercalatively. Competitive binding experiments show that the enhancement in the emission intensity of ethidium bromide (EthBr) in the presence of DNA was quenched by [Cr(phen)(2)(dppz)](3+), indicating that the Cr(III) complex displaces EthBr from its binding site in plasmid DNA. Moreover, [Cr(phen)(2)(dppz)](3+), non-covalently bound to DNA, promotes the photocleavage of plasmid DNA under 457 nm irradiation. We also found that the irradiated Cr(III)-plasmid DNA association is able to impair the transforming capacity of bacteria. These results provide evidence confirming the responsible and essential role of the excited state of [Cr(phen)(2)(dppz)](3+) for damaging the DNA structure. The combination of DNA, [Cr(phen)(2)(dppz)](3+) and light, is necessary to induce damage. In addition, assays of the photosensitization of transformed bacterial suspensions suggest that Escherichia coli may be photoinactivated by irradiation in the presence of [Cr(phen)(2)(dppz)](3+). In sum, our results allow us to postulate the [Cr(phen)(2)(dppz)](3+) complex as a very attractive candidate for DNA photocleavage with potential applications in Photodynamic Therapy (PDT).