Aqueous Phosphate Buffer Solution Research Articles

Moment analysis method for determination of rate constants of solute permeation across interface of spherical molecular aggregates by means of high-performance liquid chromatography

A moment analysis method was developed for the study of solute permeation at the interface of spherical molecular aggregates. At first, new moment equations were developed for determining the partition equilibrium constant (Kp) and permeation rate constants (kin and kout) of solutes from the first absolute (μ1A) and second central (μ2C) moments of elution peaks measured by using high-performance liquid chromatography (HPLC). Then, the method was applied to the analysis of mass transfer phenomena of three solutes, i.e., hydroquinone, resorcinol, and catechol, at the interface of sodium dodecylsulfate (SDS) micelles. HPLC data were measured by using an ODS column and an aqueous phosphate buffer solution (pH = 7.0) as the mobile phase solvent. Pulse response experiments were conducted while changing SDS concentration (5 - 20 mmol dm−3) in the mobile phase under the conditions that the surface of ODS stationary phase was dynamically coated by SDS monomers. In order to demonstrate the effectiveness of the moment analysis method using HPLC, the values of Kp, kin, and kout were determined for the three solutes as 35 - 69, 2.4 × 10−8 - 1.4 × 10−6 m s−1, and 7.0 × 10−10 - 2.1 × 10−8 m s−1, respectively. Their values increase with an increase in the hydrophobicity of the solutes. The method has some advantages for the study of interfacial solute permeation of molecular aggregates. For example, neither immobilization nor chemical modification of both solute molecules and molecular aggregates is required when elution peaks are measured by using HPLC. Interfacial solute permeation takes place in the mobile phase without any chemical reaction or physical action on molecular aggregates. The values of Kp, kin, and kout were analytically determined from those of μ1A and μ2C by using the moment equations. The results of this study must contribute to the dissemination of an opportunity for studying the interfacial solute permeation of molecular aggregates to many researchers because of extremely high versatility of HPLC.

Exploring the effect of a pendent amine group poised over the secondary coordination sphere of a cobalt complex on the electrocatalytic hydrogen evolution reaction.

A CoIII complex (2) of a bispyridine-dioxime ligand (H2LNMe2) containing a tertiary amine group in the proximity of the Co center is synthesized and characterized. One of the oxime protons of the ligand is deprotonated, and the amine group remains protonated in the solid-state structure of the CoII complex (2a). The acid-base properties of 2 showed pKa values of 5.9, 8.4, and 9.6, which are assigned to the dissociation of two consecutive oxime protons and amine protons, respectively. The electrocatalytic proton reduction of 2 was investigated in an aqueous phosphate buffer solution (PBS), revealing a catalytic hydrogen evolution reaction (HER) at an Ecat/2 of -1.01 V vs. the SHE, with an overpotential of 673 mV and a kobs value of 2.6 × 103 s-1 at pH 7. For comparison, the HER of the Co complex (1) lacking the tert-amine group at the secondary sphere was investigated in PBS, which showed a kobs of 1.3 × 103 s-1 and an overpotential of 577 mV. At pH 4, however, 2 revealed a ∼3 times higher kobs value than 1, which suggests that the protonated amine group likely works as a proton relay site. Notably, no significant change in the reaction rate was observed at different pH values for 1, implying that oxime protons may not be involved in the intramolecular proton-coupled electron transfer reaction in the HER. The kobs values for Co complexes at pH 7.0 are significantly higher than those of the [Co(dmgH)2(pyridine)(Cl)] complex, implying that the primary coordination sphere around 1 or 2 enhances the HER and offers better catalyst stability in acidic buffer solutions.

A Theoretical and Experimental Square-Wave Voltammetric Study of Ascorbic Acid in Light of Multi-Step Electron Transfer Mechanism

A detailed theoretical and experimental study of the complex redox mechanism of ascorbic acid in aqueous phosphate buffer solution (pH = 7.3) by square-wave voltammetry is presented. Experimental square-wave voltammograms at edge plane pyrolytic graphite electrode consist of a typical irreversible peak for a direct two-step electrode oxidation of the ascorbic acid. The complex mechanism of oxidation of the ascorbic acid was represented by a theoretical model for E1C’E2C mechanism. Morphology of theoretical square-wave voltammograms greatly depended on different specific parameters of the model. This feature was used to make the best fit between experimental and theoretical voltammograms for 2 different step potentials, which resulted in revelation of all specific parameters (standard electrochemical rate constant, diffusion coefficient, electron transfer coefficient and rate constants for both chemical reactions) of the model. Therefore, we showed that using only square-wave voltammetry, both experimentally and theoretically, it is possible to make a detailed study of the complex oxidation of ascorbic acid and further enlighten its redox mechanism.

Electrochemistry and Stability of 1,1'-Ferrocene-Bisphosphonates.

Here, we investigate the electrochemical properties and stability of 1,1'-ferrocene-bisphosphonates in aqueous solutions. 31P NMR spectroscopy enables to track decomposition at extreme pH conditions revealing partial disintegration of the ferrocene core in air and under an argon atmosphere. ESI-MS indicates the decomposition pathways to be different in aqueous H3PO4, phosphate buffer, or NaOH solutions. Cyclovoltammetry exhibits completely reversible redox chemistry of the evaluated bisphosphonates, sodium 1,1'-ferrocene-bis(phosphonate) (3) and sodium 1,1'-ferrocene-bis(methylphosphonate) (8), from pH 1.2 to pH 13. Both the compounds feature freely diffusing species as determined using the Randles-Sevcik analysis. The activation barriers determined by rotating disk electrode measurements revealed asymmetry for oxidation and reduction. The compounds are tested in a hybrid flow battery using anthraquinone-2-sulfonate as the counterside, yielding only moderate performance.

Hydrolysis kinetics of the prodrug myristyl nicotinate

Myristyl nicotinate is a prodrug of nicotinic acid. In this research, the kinetics of hydrolysis for myristyl nicotinate was studied in an aqueous phosphate buffer solution within a 5–10 pH range and constant ionic strength at a high temperature which was 80 °C to perform accelerated hydrolysis experiments. The effect of temperature, ionic strength, buffer concentrations, and buffer type was studied. The degradation was monitored using a validated HPLC method. The kinetics of hydrolysis of myristyl nicotinate was also studied in skin and liver homogenates. The hydrolysis was found to follow pseudo-first-order kinetics. The rate constant was calculated from the slope of a linear plot of Ln transformation (Ln) of the remaining parent prodrug concentration versus time. The hydrolysis was found pH- dependent, and a pH rate profile was constructed. Moreover, the hydrolysis rate of the prodrug was found to be buffer species dependent. Carbonate buffer has the most catalytic effect over borate and phosphate buffers. The effect of temperature on the kinetics of hydrolysis of myristyl nicotinate in phosphate buffer at pH 9 at 343, 348, 353, and 358°K was studied. The hydrolysis was found to follow the Arrhenius equation. From the Arrhenius plot, the half-life at 25 °C, and the activation energy were calculated and were found to be 466.5 days and 24.57 kcal mol−1, respectively. The hydrolysis of the prodrug was faster in liver and skin homogenates than those in aqueous buffer solutions. The pseudo-first-order rate constants were found to be 0.012, 0.028 min−1 for myristyl nicotinate in the liver, and skin homogenates, respectively.

(Digital Presentation) Electrochemical Single Impact Method for Electroactive Bacterial Detection Onto Carbon Ultramicroelectrode

This work aims to design a high sensitivity and selectivity biosensor based on the electrochemistry of single impacts onto ultramicroelectrode (UME) to detect and identify various bacterial strains. The main objective is to establish a unique electrochemical signature for each bacterial cell through the individual impact event signal on the surface of the UME [1, 2]. First, we focus on the detection of well-known electroactive Gram-negative bacteria such as Shewanella oneidensis in order to be able to selectively detect these different single cells. In this case, the strategy currently used is to record a chronoamperometric curve in an aqueous potassium phosphate buffer (pH = 7.4) solution containing a redox probe at an UME polarized at the oxidation or reduction potential of the electrochemical active aqueous species and to observe a “current step” when one bacterium impacts the UME, corresponding to a “blocking effect” [3] (Figure A). The response signal expected from single bacterium collision may also be a “current spike” corresponding to either the own electrochemical activity of the bacterium toward the redox probe and the UME applied potential or a “bouncing effect” of the bacterium which does not stick onto UME surface (Figure B).In order to be able to identify the type of bacterial cell striking the UME surface, an adapted functionalization (covalent grafting via reduction of diazonium aryl salts) with appropriate affinity (bio)chemical species such as antibodies or aptamers could be performed. This strategy could confer to the UME surface a selectivity of the signal generated during single impacts. For example, the electro-grafting of diazo-pyridinium cations for microbial fuel cell electrodes showed to promote and improve the development of bacterial electroactive films [4].[1] E. Lebègue, N. L. Costa, R. O. Louro, F. Barrière, J. Electrochem. Soc. 16 (2020) 105501[2] A. T. Ronspees, S. N.Thorgaard, Electrochimica Acta. 278 (2018) 412-420[3] G. Guanyue, W. Dengchao, B. Ricardo, Z. Jinfang, M. Michael V. Anal. Chem. 90 (2018) 12123−12130[4] H. Smida, E. Lebègue, J-F. Bergamini, F. Barrière, C. Lagrost, Bioelectrochemistry. 120 (2018) 157-165 Figure 1

Photochemical degradation of the antidepressant sertraline in aqueous solutions by UVC, UVC/H2O2, and UVC/S2O82−

Antidepressants are released into the aquatic environment because of their incomplete removal from wastewater treatment plants. In the present work, we investigated the photochemical degradation of a commonly prescribed antidepressant, namely sertraline, in aqueous matrices. The molar absorption coefficient of sertraline at 254 nm and at various pH values in the range from 4.0 to 9.0 was 444±65 L•mol–1•cm–1, while the quantum yield of its direct photolysis under UVC radiation (λ = 254 nm) was (1.7±0.1) × 10−2 mol∙einstein−1 (i.e., both values were relatively low). Next, we investigated the photochemical degradation of sertraline under UVC radiation in the presence of hydrogen peroxide, H2O2 (i.e., UVC/H2O2) or persulfate ions, S2O82− (i.e., UVC/PS). Several parameters were studied, such as the initial concentrations of the oxidants, solution pH, and the composition of the aqueous matrix (experiments were carried out in aqueous phosphate buffers, in synthetic wastewater, as well as in synthetic fresh and hydrolyzed human urine). It was found that, in all aqueous matrices, the photochemical degradation of sertraline followed pseudo first-order kinetics. The values of the observed pseudo first-order rate constants in the UVC/H2O2 and UVC/PS processes were from one to three orders of magnitude higher than the corresponding value in the UVC process. The UVC/PS process was more efficient than the UVC/H2O2 process, either in aqueous phosphate buffer solutions or in synthetic wastewaters, despite the comparable reactivity of sertraline towards hydroxyl and sulfate radicals. However, both processes resulted in partial mineralization of the compound after prolonged irradiation. In the UVC/H2O2 process, there was an optimum H2O2 concentration which depended on the aqueous matrix, while in the UVC/PS process, there was an almost linear increase in treatment efficiency as a function of PS concentration, at least in the range of concentrations studied in the present work. Solution pH in the range from 6.0 to 9.0 had a relatively negligible effect on treatment performance for both processes. In synthetic urine matrices, despite the reduction in reaction rate (the observed pseudo first-order rate constants were reduced by approximately one to two orders of magnitude), the photochemical degradation of sertraline proceeded to a relatively satisfactory degree. Finally, the calculations of the electrical energy per order and the associated cost showed that the UVC/H2O2 and UVC/PS processes are cost-efficient and suitable for full-scale applications.

THE ROLE AND SIGNIFICANCE OF MORPHOLOGICAL CHANGES IN INTRAORGAN VESSELS IN ANIMALS DURING PATHOGENESIS OF BABESIOSIS

The aim of this study is to investigate morphological changes in intraorgan vessels and their role in susceptible animals in the pathogenesis of babesiosis. The material of the study included the intraorgan vessels of domestic dogs with clinically and laboratory confirmed babesiosis and wild mouse-like rodents from latent foci of babesiosis in Volyn, Zhitomir, Kiev, Poltava, Sumy, Kharkov, Chernigov regions. For histological study, we used standard fixation in a 12% aqueous formalin solution in phosphate buffer (pH = 7.0-7.2). After the post-fixation and dehydration, the samples were placed into paraffin blocks; then a series of histological slices (5 μm) were prepared. The preparations were stained with hematoxylin and eosin, according to Van Gieson technique. All test animals, regardless of the species taxonomy, were divided into two groups. The control group included clinically healthy animals (∑ = 36). The group under clinical study consisted of animals with clinically and laboratory confirmed babesiosis (∑ = 91). Histological changes in intraorgan vessels in the control group corresponded to the anatomical and functional parameters in the health. The preparations taken from the group with basesiosis demonstrate that microvessels are branched, different in size, spasmodic; their walls have signs of delamination and through lesions. Delamination developed gradually, started with the detachment of a small horizontal fragment of the outer layer. Defects in the integrity of microvessels resulted in penetrations; there was an active diapedesis of erythrocytes into the periovascular space. The accumulation of erythrocytes directed to the areas of connective tissue, branching of blood vessels, and fatty fragments. Hemorrhages were local in nature, concentrated in the form of small blurred foci of irregular shape. In the pathogenesis of babesiosis, the defects in the walls of blood vessels with their further penetration and dissection, hemorrhages, microvesiculation of the endothelium, and its desquamation play a critical role. Other manifestations included the development of intravascular blood coagulation, thrombosis, stasis, microcirculation disorders followed by ischemia, destructive and degenerative changes in the walls of blood vessels.

In vitro cytotoxic activities, DNA- and BSA-binding studies of dinuclear palladium(II) complexes with different pyridine-based bridging ligands

Three new dinuclear palladium(II) complexes with general formula [{Pd(en)Cl}2(μ-L)]2+ (L is pyridine-based bridging ligand 4,4′-bipyridine (4,4′-bipy, 1), 1,2-bis(4-pyridyl)ethane (bpa, 2), 1,2-bis(4-pyridyl)ethylene (bpe, 3) and en is bidentate coordinated ethylenediamine) were synthesized and characterized by elemental microanalyses, NMR (1H and 13C), IR and UV–Vis spectroscopy. In vitro cytotoxic activity of these complexes against human A549 and murine LLC1 lung cancer cells, as well as two human HCT116 and SW480 and one murine CT26 colon cancer cells was investigated using MTT assay (MTT is 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide). The potential of complexes 1–3 to induce apoptosis was tested by flow cytometric analysis of Annexin V and propidium iodide stained treated cells, while their antiproliferative activity was analyzed by detection of Ki67 expression in treated cancer cells. The DNA binding affinity of complexes 1–3 was evaluated by UV–Vis, fluorescence emission spectroscopy and by viscosity measurements in aqueous phosphate buffer solution at pH 7.40. Furthermore, interaction of these complexes with bovine serum albumin was investigated by fluorescence spectrometry. The present study showed that the nature of pyridine-based bridging ligand (L) in dinuclear [{Pd(en)Cl}2(μ-L)]2+ complex has an influence on the complex preference for the cytotoxic activity and CT-DNA/BSA (CT-DNA is calf thymus DNA and BSA is bovine serum albumin) binding affinity.

Photocatalytic H2O2 production from O2 under visible light irradiation over phosphate ion-coated Pd nanoparticles-supported BiVO4

H2O2 production from O2 over Pd nanoparticle (NP) co-catalysts-supported BiVO4 was studied. Several deposition methods and conditions (active metal, co-catalyst loading, solution pH) were investigated for catalyst preparation, and the photo-assisted deposition (PAD) of Pd from an aqueous phosphate buffer solution (pH = 7) was found to be optimal, resulting in small and uniform phosphate ion (PO43−)-coated Pd NPs being selectively deposited on the reductive surfaces of the BiVO4. This catalyst exhibited better H2O2 production from O2 in the presence of methanol (CH3OH) as a hole scavenger under visible light irradiation than that by the catalysts prepared by the other methods and under other PAD conditions. It is surmised that PO43− partially coats smaller Pd NPs with a narrow size distribution on the reductive surfaces of the BiVO4, and that these NPs promote H2O2 generation synergistically by catalyzing the two-electron reduction of O2 while simultaneously inhibiting the four-electron reduction of O2 and the two-electron reduction of H2O2 to H2O.

Communication—Electrochemical Single Nano-Impacts of Electroactive Shewanella Oneidensis Bacteria onto Carbon Ultramicroelectrode

Electrochemical single nano-impacts of electroactive Shewanella oneidensis bacteria at a 7 μm diameter carbon fibre ultramicroelectrode in an aqueous potassium phosphate buffer (pH = 7.2) solution containing a redox active probe (potassium ferro- or ferricyanide) is reported. We present chronoamperometric measurements recorded at the ultramicroelectrode polarized at the potential of the steady-state current of the redox probe in solution (oxidation for K4Fe(CN)6 or reduction for K3Fe(CN)6) in the presence of bacteria. The shape of current transients associated to single bacteria nano-impacts is compared and discussed as a function of the redox probe in solution and of the ultramicroelectrode applied potential.

Dinuclear ruthenium(II) polypyridyl complexes: Mechanistic study with biomolecules, DNA/BSA interactions and cytotoxic activity

The substitution reactions of dinuclear Ru(II) polypyridyl complexes, i.e. [{RuCl(bpy)2}2(μ-pzn)][PF6]2 (1) and [{RuCl(phen)2}2(μ-pzn)][PF6]2 (2) (bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, μ-pzn = pyrazine), with mononucleotide guanosine-5′-monophosphate (5′-GMP) and sulfur-containing nucleophiles, such as l-methionine (l-Met) and glutathione (GSH) were studied by UV–Vis spectroscopy. The structures of dinuclear Ru(II) complexes 1 and 2 were preserved during the substitution processes and the calculated enthalpies and entropies of activation (ΔH≠ > 0, ΔS≠ < 0) supported an associative mechanism of substitution. The DNA binding affinity of complexes 1 and 2 was evaluated by UV–Vis, fluorescence emission spectroscopy and by viscosity measurements in aqueous phosphate buffer solution (PBS) at pH 7.40. Additionally, competitive binding reactions with an intercalative agent ethidium bromide (EB) and the known minor groove binder Hoechst 33258 were studied as well. The obtained results indicate that complexes 1 and 2 can interact with DNA through the intercalation and/or minor groove binding, where the latest was preferred. This observation is in a good agreement with the results obtained by molecular docking. Furthermore, both complexes strongly quenched the fluorescence of tryptophan residues in serum albumin (BSA) through both static and dynamic quenching (Ksv = 104–105 M−1). In addition, complexes 1 and 2 showed moderate cytotoxic activity against human breast cancer cells (MDA-MB-231), while both were inactive against human colorectal cancer cells (HCT-116).

Capturing the Role of Phosphate in the Ni‐PY5 Catalyzed Water Oxidation

AbstractThe mononuclear Nickel complex Ni‐PY5 [PY5=2, 6‐bis(1,1‐bis(2‐pyridyl)ethyl)pyridine] has been disclosed to catalyze water oxidation electrochemically with an applied potential of 1.5 V at pH 10.8 in aqueous phosphate buffer solution. Density functional calculations were used to elucidate the reaction mechanism of water oxidation catalyzed by this nickel complex and to capture the role of the phosphate. The calculations demonstrated that the oxidations of the starting [OH2−NiII‐PY5]2+ complex by two sequential proton‐coupled electron‐transfer processes lead to the formation of a key intermediate [O=NiIV‐PY5]2+. O−O bond formation then takes place through a water nucleophilic attack on the high‐valent NiIV=O moiety of the catalyst, facilitated by a hydrogen phosphate anion, with a total barrier of 11.5 kcal mol−1. The calculated barrier agrees very well with the experimental turnover frequency of about 2000 s−1, which corresponds to a barrier of 12.9 kcal mol−1. The calculated deuterium kinetic isotope effect of 1.99 is also in excellent agreement with the experimental value of 2.06. Finally, we also predicted the catalytic activity of other PY5‐based first‐row transition metal complexes, namely, involving Mn, Fe, Co and Cu. The calculations showed that the Mn, Fe, Co complexes have higher barrier for water oxidation, while the Cu complex has lower barrier and higher water oxidation activity compared with the Ni complex.

New dinuclear palladium(II) complexes with benzodiazines as bridging ligands: interactions with CT-DNA and BSA, and cytotoxic activity

Three new dinuclear Pd(II) complexes with general formula [{Pd(en)Cl}2(μ-L)](NO3)2 [L is bridging ligand quinoxaline (Pd1), quinazoline (Pd2) and phthalazine (Pd3)] were synthesized and characterized by elemental microanalyses, UV-Vis, IR and NMR (1H and 13C) spectroscopy. The interaction of dinuclear Pd1-Pd3 complexes with calf thymus DNA (CT-DNA) has been monitored by viscosity measurements, UV-Vis and fluorescence emission spectroscopy in aqueous phosphate buffer solution (PBS) at pH 7.40 and 37°C. In addition, these experimental conditions have been applied to investigate the binding affinities of Pd1-Pd3 complexes to the bovine serum albumin (BSA) by fluorescence emission spectroscopy. In vitro antiproliferative and apoptotic activities of the dinuclear Pd(II) complexes have been tested on colorectal and lung cancer cell lines. All tested Pd(II) complexes had lower cytotoxic effect than cisplatin against colorectal cancer cells, but also had similar or even higher cytotoxicity than cisplatin against lung cancer cells. All complexes induced apoptosis of colorectal and lung cancer cells, while the highest antiproliferative effect exerted Pd2 complex.

Oxidative Cleavage of Cellobiose by Lytic Polysaccharide Monooxygenase (LPMO)-Inspired Copper Complexes.

The potentially tridentate ligand bis[(1-methyl-2-benzimidazolyl)ethyl]amine (2BB) was employed to prepare copper complexes [(2BB)CuI]OTf and [(2BB)CuII(H2O)2](OTf)2 as bioinspired models of lytic polysaccharide copper-dependent monooxygenase (LPMO) enzymes. Solid-state characterization of [(2BB)CuI]OTf revealed a Cu(I) center with a T-shaped coordination environment and metric parameters in the range of those observed in reduced LPMOs. Solution characterization of [(2BB)CuII(H2O)2](OTf)2 indicates that [(2BB)CuII(H2O)2]2+ is the main species from pH 4 to 7.5; above pH 7.5, the hydroxo-bridged species [{(2BB)CuII(H2O)x}2(μ-OH)2]2+ is also present, on the basis of cyclic voltammetry and mass spectrometry. These observations imply that deprotonation of the central amine of Cu(II)-coordinated 2BB is precluded, and by extension, amine deprotonation in the histidine brace of LPMOs appears unlikely at neutral pH. The complexes [(2BB)CuI]OTf and [(2BB)CuII(H2O)2](OTf)2 act as precursors for the oxidative degradation of cellobiose as a cellulose model substrate. Spectroscopic and reactivity studies indicate that a dicopper(II) side-on peroxide complex generated from [(2BB)CuI]OTf/O2 or [(2BB)CuII(H2O)2](OTf)2/H2O2/NEt3 oxidizes cellobiose both in acetonitrile and aqueous phosphate buffer solutions, as evidenced from product analysis by high-performance liquid chromatography-mass spectrometry. The mixture of [(2BB)CuII(H2O)2](OTf)2/H2O2/NEt3 results in more extensive cellobiose degradation. Likewise, the use of both [(2BB)CuI]OTf and [(2BB)CuII(H2O)2](OTf)2 with KO2 afforded cellobiose oxidation products. In all cases, a common Cu(II) complex formulated as [(2BB)CuII(OH)(H2O)]+ was detected by mass spectrometry as the final form of the complex.

Interactions Study of Co-enzyme-Q0 with Aniline and Pyrrole Using Square Wave Voltammetric Technique

The interactions of Co-enzyme Q0 with Aniline and Pyrrole were studied in aqueous phosphate buffer solution at (pH=7.0) as supporting electrolyte using square wave voltammetry, Co-enzyme Q0 gives a well-defined square wave voltammetric peak at (-0.0415) volt against the reference electrode (Ag/AgCl/3M KCl). The binding constants (K) were calculated at different temperatures. Vant's hoff equation is applied to calculate the thermodynamic parametrs (ΔH enthalpy changes, ΔS entropy changes and ΔG free energy changes), and then the type of interaction was estimated. The results indicated that the interaction between Co-enzyme –Q0 and Aniline (ΔH and ΔS negative values) was probably due to Vander Waals forces or hydrogen bonding interaction, and the second interaction between Co-enzyme-Q0 with Pyrrole (ΔH and ΔS positive values) might be due to the hydrophobic interaction .

Unusual Behavior of Fluorescein under Conditions of Electrochemical Oxidation in an Aqueous Phosphate Buffer Solution

Unusual Behavior of Fluorescein under Conditions of Electrochemical Oxidation in an Aqueous Phosphate Buffer Solution

Low-cost and green dispersive solid phase extraction of hydrophilic compounds using titanium dioxide nanoparticles

Selective extraction of hydrophilic compounds is a challenging task for analytical laboratories. In an attempt to address this issue, application of titanium dioxide nanoparticles as a dispersive solid phase extraction sorbent was investigated. In the study, three model analytes were used for method optimization: flavin mononucleotide, thiamine monophosphate and thiamine pyrophosphate. The influence of various parameters on sorption and desorption process was evaluated. Under optimized conditions, the sorption was performed in a presence of 1 M formic acid (pH 1.9) for 10 min under vortex stirring providing efficiency up to 94%. The influence of salt content in sample matrix was found to be negligible while the organic solvent presence slightly improved the sorption efficiency. Elution of analytes from TiO2 sorbent was obtained with both aqueous ammonia and phosphate buffer (pH 11.8) solutions. Under optimized conditions dispersive solid phase extraction method was shown to provide high selectivity with extraction recoveries >89.0% for studied compounds. The susceptibility of the method on various matrices was assayed for extraction of model analytes from enriched tap water, milk, apple juice and human urine samples. Moreover, the methodology was applied for phospholipids removal from pharmaceutical formulation (lecithin microemulsion) of propofol. Due to the utilization of titanium dioxide nanoparticles, the cost of sample preparation step was estimated to be about 0.1 Euro per sample, providing >100-fold reduction of the price for typical analysis using titanium dioxide microspheres.

A coumarin-based fluorescent probe for ratiometric detection of hydrazine and its application in living cells.

A new ratiometric fluorescent probe (1) was developed for the detection of hydrazine. The probe was obtained by incorporating the recognition moiety of acetyl group onto a coumarin fluorophore. Probe 1 displayed a distinct cyan emission in a 100% aqueous phosphate buffer solution. In the presence of hydrazine, probe 1 undergoes a hydrazinolysis process to release the coumarin fluorophore, which exhibited significant hypsochromic shifts in both absorption and emission spectra, and thus achieving a ratiometric response. This ratiometric probe is highly selective and sensitive towards hydrazine detection. The limit of detection (LOD) was calculated to be 34 nM. Moreover, cellular toxicity and imaging experiments suggested that probe 1 is can be used to monitor hydrazine in live cells.

Synthesis of a water-soluble 2,2'-biphen[4]arene and its efficient complexation and sensitive fluorescence enhancement towards palmatine and berberine.

A water-soluble 2,2′-biphen[4]arene (2,2’-CBP4) containing eight carboxylato moieties was synthesized and characterized. Its complexation behavior towards two alkaloids, palmatine (P) and berberine (B), was investigated by means of fluorescence and 1H NMR spectroscopy in aqueous phosphate buffer solution (pH 7.4). In the presence of 2,2’-CBP4, 1H NMR signals of P and B displayed very large upfield shifts, indicating the formation of inclusion complexes with strong binding affinities. Fluorescence titration experiments showed that P and B exhibited dramatic fluorescence enhancement of more than 600 times upon complexation with 2,2’-CBP4. Particularly, the fluorescence intensity is strong enough to be readily distinguished by the naked eye. Although the two guests have similar structures, the association constant of B with 2,2’-CBP4 (Ka = (2.29 ± 0.27) × 106 M−1) is 3.9 times larger than that of P (Ka = (5.87 ± 0.24) × 105 M−1).