Ru(EDTA) mediated partial reduction of O2 by H2S

An effective procedure for selective reduction of O2 to H2O2 exploring the use of hydrogen sulfide, an obnoxious industrial pollutant as reductant is reported herein. The reduction of [RuIII(EDTA)pz]− (EDTA4− = ethylenediaminetetraacetate; pz = pyrazine) by hydrogen sulfide resulting in the formation of a red [RuII(EDTA)pz]2− complex (λmax = 462 nm) has been studied spectrophotometrically and kinetically using both rapid scan and stopped-flow techniques. The time course of the reaction was followed as a function of [HS−]i, pH (5.5–8.5), and temperature. Alkali metal ions were found to have a positive influence (K+ > Na+ > Li+) on the reaction rate. Kinetic data and activation parameters are interpreted in terms of a mechanism (admittedly speculative) involving outer-sphere electron transfer between the reaction partners. Reaction of the red [RuII(EDTA)pz]2− complex with molecular oxygen regenerates the [RuIII(EDTA)pz]− species in the reacting system along with the formation of H2O2, a partially reduced product of dioxygen (O2) reduction. A detailed reaction mechanism in agreement with the spectral and kinetic data is presented

Electrochemical Conversion of Bicarbonate to Formate Mediated by the Complex RuIII(edta) (edta4– = ethylenediaminetetraacetate)

In this paper, we present the first example of a ruthenium(III) complex, [RuIII(edta)] (edta = ethylenediaminetetraacetate), that catalyzes the electrochemical conversion of hydrogen carbonate to formate selectively. The formation of an [RuIII(edta)(HCO3)]2– species through the reaction of the [RuIII(edta)(H2O)]– catalyst and hydrogen carbonate (HCO3–) was studied kinetically by using the stopped-flow technique. The value of the second-order rate constant for the formation of the [RuIII(edta)(HCO3)]2– complex was 82 ± 7 M–1 s–1 at 25 °C and pH = 6.4. Electrochemical reduction of hydrogen carbonate (HCO3–) was achieved by carrying out constant-potential bulk electrolysis at –0.4 V (vs. SCE) with a mercury-pool cathode at pH = 6.4. The formation of formate as the only reduction product was evidenced by a 13C NMR analysis of the reaction mixture obtained after electrolysis

Nitrite reduction mediated by the complex RuIII(EDTA)

Reported is the first example of a ruthenium(III)-complex, RuIII(EDTA) (EDTA4− = ethylenediaminetetraacetate), that mediates O-atom transfer from nitrite to the biological thiols cysteine and glutathione, leading to the formation of [RuIII(EDTA)(NO+)]0. However, at pH below 5.0, the coordinated nitrite ion in the [RuIII(EDTA)(NO2)]2− complex undergoes proton-assisted decomposition, resulting in the formation of a [RuIII(EDTA)(NO+)]0 species

Mechanism of the oxidation of thiosulfate with hydrogen peroxide catalyzed by aqua-ethylenediaminetetraacetatoruthenium(III)

Catalytic ability of [RuIII(edta)(H2O)]− (edta4− = ethylenediaminetetraacetate) complex toward oxidation of thiosulfate (S2O32−) in presence of H2O2 has been explored in the present work. The kinetics of the catalytic oxidation of thiosulfate (S2O32−) has been studied spectrophotometrically as a function of [RuIII(edta)], [H2O2], [S2O32−] and pH. Spectral analyses and kinetic data indicate a catalytic pathway involving activation of both substrate (S2O32−) and oxidant (H2O2). Substrate activation pathway involves the formation of a red [RuIII(edta)(S2O3)]3− species through the reaction of the [RuIII(edta)(H2O)]− catalyst complex and the substrate (S2O32−). Hydrogen peroxide reacts directly with thiosulfate coordinated to the RuIII(edta) complex to yield sulfite as immediate oxidation product. Peroxide activation pathway is governed by the formation of [RuV(edta)(O)]− catalytic intermediate which oxidize thiosulfate, however, at slower rate (View the MathML source at 25 °C) as compared to the rate of oxidation of the coordinated thiosulfate (View the MathML source at 25 °C). Sulfite and sulfate were found to be the oxidation products of the above described catalytic oxidation process. A detailed mechanism in agreement with the spectral and kinetic data is presented

Direct evidence for the catalase activity of [RuV(edta)(O)]−[Ru^V(edta)(O)]^-

Reported is the first example of a ruthenium(III) complex, RuIII(edta) (edta4− = ethylenediaminetetraacetate), that catalyzes the disproportion of H2O2 to O2 and water in resemblance to catalase activity, and shedding light on the possible mechanism of action of the [RuV(edta)(O)]− formed in the reacting system

Direct evidence for catalase activity of [RuV(edta)(O)]−

Reported is the first example of a ruthenium(III) complex, RuIII(edta) (edta4− = ethylenediaminetetraacetate), that catalyzes the disproportion of H2O2 to O2 and water in resemblance to catalase activity, and shedding light on the possible mechanism of action of the [RuV(edta)(O)]− formed in the reacting system

Development of 6-Thioguanine conjugated PLGA nanoparticles through thioester bond formation: Benefits of electrospray mediated drug encapsulation and sustained release in cancer therapeutic applications

Polymeric nanoparticle-based successful delivery of hydrophobic drugs is highly desirable for its controlled and sustained release at the disease site, which is a challenge with the current synthesis methods. In the present study, an electrospray mediated facile one-step synthesis approach is explored in which a solution mixture of a hydrophobic drug, 6-thioguanine (Tg) and a biocompatible FDA approved polymer, Poly (d, l-lactide-co-glycolide) (PLGA) is injected in an applied electric field of suitable intensity to prepare drug encapsulated PLGA nanoparticles, PLGA-Tg with high yield. In order to explore the effect of external electric field on Tg loading and delivery applications, the nanoparticles are characterized using EDX, AFM, FESEM, TEM, FTIR, Raman, fluorescence, and mass spectroscopy techniques. The characterization studies indicate that the electric field mediated synthesis exhibits spherical nanoparticles with a homogenous core size distribution of ~60 nm, high encapsulation (~97.22%) and stable conjugation of Tg (via thioester linkages) with PLGA molecules in the presence of the applied electric field. The kinetic study demonstrates the ‘anomalous diffusion’ (non-Fickian diffusion) release mechanism in which Tg escapes from PLGA matrix with a slow, but steady diffusion rate and the sustained drug release profile continues for 60 days. To check the biological activity of the encapsulated Tg, in-vitro cell studies of the PLGA-Tg are performed on HeLa cells. The MTT assay shows significant cell death after 48 h of treatment, and the cellular internalization of the drug-loaded nanoparticles occurs through pinocytosis mediated uptake, which is established by the AFM analysis. The Raman and mass spectroscopy studies suggest that the PLGA-Tg nanoparticles are rapidly hydrolyzed inside cell cytoplasm to release Tg which initiates apoptosis-mediated cell death confirmed by as DNA fragmentation and membrane blebbing studies. The results clearly emphasize the benefits of electrospray based synthesis of polymeric nanodrug formulation through the formation of chemical bonds between polymer and drug molecules that could be easily implemented in the design and development of an effective nanotherapeutic platform with no typical ‘burst effect,’ prolonged release profile, and significant toxicity to the cancer cells

Ethylenediamine assisted functionalization of self-organized poly (D, L-lactide-co-glycolide) patterned surface to enhance cancer cell isolation

Abstract Protein functionalized micro-scale patterned structures are developed using a biocompatible polymer PLGA (poly (D, L-lactide-co-glycolide)) via thin film dewetting and by step-wise chemical conjugations with EDA (ethylenediamine) and anti-EpCAM (Epithelial Cell Adhesion olecule) antibodies to target the epithelial cell adhesion molecules of cancer cells. The effectiveness of such protein functionalized patterned surface is checked through cell isolation process using blood samples spiked with different cancer cells such as MCF-7, A549, MDA-MB-231. An efficient capture yield of 92% is obtained with MCF-7 cells over a two hour incubation time. The study demonstrates the effects of cell concentration and incubation time on the binding of cancer cells to the modified patterned surfaces. For the first time, a simple and inexpensive method is reported to fabricate functionalized PLGA patterned surface for an efficient isolation of cancer cells from diluted blood samples. The method shows the potential to be used as an effective platform for the development of an improved circulating tumor cell (CTC) isolation device from the clinical blood sample

Interaction of RuIII(EDTA) with cellular thiols and O2: biological implications thereof

Reaction of [RuIII(EDTA)(CyS)]2− (edta4− = ethylenediaminetetraacetate; CySH = cysteine) with molecular oxygen (O2) has been studied as a function of pH (4.0–8.0) and cysteine concentration (0.2–2.0 mM) at room temperature (25 °C). Biological activities of the [Ru(EDTA)]/CySH/O2 system pertaining to cleavage of supercoiled plasmid DNA to its nicked open circular form has been explored in this work. Results are discussed in regard to the reaction of the ruthenium(III)-complex with molecular oxygen) and a working mechanism is proposed for the biological activities of the ruthenium(III)-complex in the presence of O2