Showing papers on "Buffer solution published in 2016"

Label-Free Carbon-Dots-Based Ratiometric Fluorescence pH Nanoprobes for Intracellular pH Sensing

Abstract: Measuring pH in living cells is of great importance for better understanding cellular functions as well as providing pivotal assistance for early diagnosis of diseases. In this work, we report the first use of a novel kind of label-free carbon dots for intracellular ratiometric fluorescence pH sensing. By simple one-pot hydrothermal treatment of citric acid and basic fuchsin, the carbon dots showing dual emission bands at 475 and 545 nm under single-wavelength excitation were synthesized. It is demonstrated that the fluorescence intensities of the as-synthesized carbon dots at the two emissions are pH-sensitive simultaneously. The intensity ratio (I475 nm/I545 nm) is linear against pH values from 5.2 to 8.8 in buffer solution, affording the capability as ratiometric probes for intracellular pH sensing. It also displays that the carbon dots show excellent reversibility and photostability in pH measurements. With this nanoprobe, quantitative fluorescence imaging using the ratio of two emissions (I475 nm/I54...

Detoxification of Chemical Warfare Agents Using a Zr6-Based Metal–Organic Framework/Polymer Mixture

Abstract: Owing to their high surface area, periodic distribution of metal sites, and water stability, zirconium-based metal-organic frameworks (Zr6 -MOFs) have shown promising activity for the hydrolysis of nerve agents GD and VX, as well as the simulant, dimethyl 4-nitrophenylphosphate (DMNP), in buffered solutions. A hurdle to using MOFs for this application is the current need for a buffer solution. Here the destruction of the simulant DMNP, as well as the chemical warfare agents (GD and VX) through hydrolysis using a MOF catalyst mixed with a non-volatile, water-insoluble, heterogeneous buffer is reported. The hydrolysis of the simulant and nerve agents in the presence of the heterogeneous buffer was fast and effective.

Electro-Oxidation of Ni42 Steel: A Highly Active Bifunctional Electrocatalyst

Abstract: Janus type water-splitting catalysts have attracted highest attention as a tool of choice for solar to fuel conversion. AISI Ni42 steel is upon harsh anodization converted into a bifunctional electrocatalyst. Oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are highly efficiently and steadfast catalyzed at pH 7, 13, 14, 14.6 (OER) and at pH 0, 1, 13, 14, 14.6 (HER), respectively. The current density taken from long-term OER measurements in pH 7 buffer solution upon the electro-activated steel at 491 mV overpotential (η) is around four times higher (4 mA cm−2) in comparison with recently developed OER electrocatalysts. The very strong voltage–current behavior of the catalyst shown in OER polarization experiments at both pH 7 and at pH 13 are even superior to those known for IrO2-RuO2. No degradation of the catalyst is detected even when conditions close to standard industrial operations are applied to the catalyst. A stable Ni-, Fe-oxide based passivating layer sufficiently protects the bare metal for further oxidation. Quantitative charge to oxygen (OER) and charge to hydrogen (HER) conversion are confirmed. High-resolution XPS spectra show that most likely γ−NiO(OH) and FeO(OH) are the catalytic active OER and NiO is the catalytic active HER species.

Ferric reducing anti-oxidant power assay in plant extract

Abstract: The ferric reducing anti-oxidant power (FRAP) assay involved the following steps: a) preparation of samples, b) reactions and c) finally measuring absorbance of sample and standard at 700 nm using spectrophotometer. The samples were methanolic extract, different fractions ( n -hexane, chloroform) and standard ascorbic acid. The solutions prepared were buffer solution (pH 6.6), 1% potassium ferricyanide solution, 10% trichloroacetic acid and 0.1% ferric chloride. Video Clip of Methodology: Ferric reducing anti-oxidant power assay: 21 min 18 sec Full Screen Alternate

Not only pH. Specific buffer effects in biological systems

Abstract: The aim of this work is to overview the specific effect of pH buffers in biological systems. The pH of a buffer solution changes only slightly when a small amount of a strong acid or bases is added to it. This is widely accepted and applied both in chemical and in biological (i.e. enzyme catalysis) systems. Here we show some examples – spanning from pH measurements, enzyme activities, electrophoretic mobilities, antibody aggregation, protein thermal stability – that demonstrate additional roles of buffers. They not only set pH, but also address specific ion effects, in terms of Hofmeister series, when strong electrolytes are also added. From the experimental data referred to some charged biological moieties it emerges that different buffers, at the same nominal pH, can specifically adsorb at the charged surface. Buffer specific adsorption modifies several molecular and macroscopic properties amongst which electrophoretic mobilities, and hence effective surface charges, are particularly significant. More importantly, buffers' weak electrolytes, even at low concentration, are found to compete for the adsorption at the charged surfaces with strong electrolytes, thus modulating Hofmeister effects.

Catalytic H2O2 Disproportionation and Electrocatalytic O2 Reduction by a Functional Mimic of Heme Catalase: Direct Observation of Compound 0 and Compound I in Situ

Abstract: A phenolate-bound Fe-porphyrin complex assembled in situ, atop self-assembled monolayer (SAM) covered Au surfaces, can disproportionate hydrogen peroxide chemically with a turnover frequency (TOF) of 25 s–1 and turnover number (TON) >105 in a pH 7 buffer solution at room temperature. The same catalase mimic is found to selectively reduce oxygen to water when the cathodic potential is applied to the same surface: i.e., electrochemically. In situ resonance Raman (rR) experiments reveal the accumulation of compound I during chemical H2O2 disproportionation and compound 0 during electrochemical O2 reduction, allowing spectroscopic detection of two key intermediates proposed to be involved in the mechanism of heme catalases that have, so far, remained elusive. The Fe═O vibration of a phenolate-bound compound I species is identified at 803 cm–1, which shifts to 796 cm–1 on hydrogen bonding. The Fe–O and O–O vibrations of the compound 0 species are identified at 587 and 830 cm–1, respectively. The observation of...

A highly selective and sensitive fluorescent turn-on Al3+ chemosensor in aqueous media and living cells: experimental and theoretical studies

Abstract: A highly selective and sensitive fluorescent chemosensor (1) based on a 2-aminobenzoic acid Schiff base has been synthesized in one step. The binding properties of 1 with metal ions were investigated by fluorescence, UV-vis, 1H NMR and electrospray ionization mass spectra. This sensor exhibited enhanced fluorescence in the presence of Al3+ in aqueous solution and also in living cells. The sensing mechanism of 1 toward Al3+ was explained by DFT/TDDFT calculations. The binding constant was determined to be 3.1 × 108 M−1 which is one of the highest binding affinities among such simple Schiff bases for Al3+ in buffer solution. The calibration curve for the analytical performance of Al3+ was found to be linear over a concentration range with a very low detection limit of 290 nM (3σ).

Electrochemical sensing of dopamine at the surface of a dopamine grafted graphene oxide/poly(methylene blue) composite modified electrode

Abstract: The simultaneous electrochemical reduction of graphene oxide (GO) and oxidative polymerization of methylene blue yielding a polymer composite on a glassy carbon electrode surface is demonstrated. The stability of the reduced graphene oxide (ERG)/poly(methylene blue) (PMB) composite in buffer solution is also studied in detail. Interestingly, methylene blue initially forms a radical cation, which donates an electron to GO, then GO undergoes reduction and during the subsequent cycles, it forms the polymer composite through covalent interactions between simultaneously reduced GO and oxidized methylene blue. The formation of the polymer composite is characterized using electrochemical impedance spectroscopy, laser Raman spectroscopy, SEM and UV-Visible absorption studies. Dopamine is a neurotransmitter with primary amine and phenolic functional groups. The electrografting of dopamine onto an ERG/PMB composite modified electrode is carried out and is evaluated by FT-IR and XPS studies and the electrochemical stability of the grafted dopamine is demonstrated using CV studies. Differential pulse voltammetry studies reveal that the modified electrode shows a high selectivity and sensitivity towards the detection of dopamine in the presence of ascorbic acid (AA) and uric acid (UA) with a detection limit of 1.03 × 10−6 mol L−1 from a calibration curve with a linear range of 0.96 × 10−6 mol L−1 to 7.68 × 10−6 mol L−1. Hence, this dopamine grafted on polymer composite modified electrode provides an attractive platform for the selective sensing of dopamine in the presence of interferents.

Two-Component Fluorescent-Semiconducting Hydrogel from Naphthalene Diimide-Appended Peptide with Long-Chain Amines: Variation in Thermal and Mechanical Strengths of Gels.

Abstract: Two-component fluorescent hydrogels have been discovered, containing the mixtures of naphthalene diimide (NDI)-conjugated peptide-functionalized bola-amphiphile and primary amines with long alkyl chains at physiological pH 7.46. The aggregation-induced enhanced emission associated with an NDI-appended peptide in aqueous medium is rare, as water is known to be a good quencher of fluorescence. In this study, an NDI-containing gelator peptide forms a highly fluorescent aggregate in aqueous medium. Absorption and emission spectroscopic techniques reveal the formation of J-aggregates among the chromophoric moieties in their aggregated state in aqueous medium. However, this NDI-containing peptide does not form any gel in aqueous medium. In the presence of the primary amines with long alkyl chains in the buffer solution, it forms two-component fluorescent hydrogels exhibiting bright yellow fluorescence under a UV lamp (365 nm). Probably, the acid–amine interaction between the amines and the bola-amphiphile trigg...

A colorimetric and fluorometric investigation of Cu(II) ion in aqueous medium with a fluorescein-based chemosensor

Abstract: As a selective colorimetric and fluorometric chemosensor, a novel fluorescein-based Schiff base (FNSB), 1,4-bis(1-fluorescein)-2,3-diaza-1,3-butadiene (L, 3) exhibits efficient binding for Cu2+ ion in water and allows naked-eye detection as a result of the formation of a 1 : 1 copper–ligand complex. The complexations of Cu2+ ion due to molecular interaction with 3 resulted in a rapid change in color from colorless to deep yellow with a characteristic change in the UV-vis absorption to a longer wavelength by 130 nm in acetonitrile and significant quenching of the fluorescence intensity (∼2.5 fold for Cu2+ ion) with maxima at 519 nm in 1% DMSO–Tris buffer solution at physiological pH (7.4). The detection limit of Cu2+ ion in acetonitrile is found to be 20 μM by UV spectroscopy, whereas in aqueous solution, the limit is reduced to 1.25 μM by fluorescence spectroscopy.

Selective Conversion of 5-Hydroxymethylfuraldehyde Using Cp*Ir Catalysts in Aqueous Formate Buffer Solution

Abstract: The highly selective hydrogenation/hydrolytic ring-opening reaction of 5-hydroxymethylfuraldehyde (5-HMF) was catalyzed by homogeneous Cp*IrIII half-sandwich complexes to produce 1-hydroxy-2,5-hexanedione (HHD). Adjustment of pH was found to regulate the distribution of products and reaction selectivity, and full conversion of 5-HMF to HHD with 99 % selectivity was achieved at pH 2.5. A mechanistic study revealed that the hydrolysis/ring-opening reaction of 2,5-bis-(hydroxymethyl)furan is the important intermediate reaction step. In addition, an isolated yield of 85 % for HHD was obtained in a 10 g-scale experiment, and the reaction with fructose as the starting material also led to a 98 % GC yield (71.9 % to fructose) of HHD owing to the excellent tolerance of the catalyst under acidic conditions.

A Cu-Based Nanoparticulate Film as Super-Active and Robust Catalyst Surpasses Pt for Electrochemical H2 Production from Neutral and Weak Acidic Aqueous Solutions

Abstract: Electrocatalysts that are stable and highly active at low overpotential (η) under mild conditions as well as cost-effective and scalable are eagerly desired for potential use in photo- and electro-driven hydrogen evolution devices. Here the fabrication and characterization of a super-active and robust Cu-CuxO-Pt nanoparticulate electrocatalyst is reported, which displays a small Tafel slope (44 mV dec-1) and a large exchange current density (1.601 mA cm-2) in neutral buffer solution. The catalytic current density of this catalyst film reaches 500 mA cm-2 at η = -390 ± 12 mV and 20 mA cm-2 at η = -45 ± 3 mV, which are significantly higher than the values displayed by Pt foil and Pt/C electrodes in neutral buffer solution and even comparable with the activity of Pt electrode in 0.5 m H2SO4 solution.

A selective fluorescent probe for the detection of Cd2+ in different buffer solutions and water

Abstract: A simple fluorescent probe NHQ based on quinoline was successfully prepared via one-step synthesis. The probe NHQ exhibited “turn-on” fluorescence and excellent selectivity toward Cd2+ in different buffer solutions such as Tris-HCl buffer solution, HEPES buffer solution, and PBS buffer solution, and even in water. Moreover, the binding model of NHQ with Cd2+ was definitely confirmed by the single crystal X-ray diffraction studies of the complex.

Semicarbazide-based naphthalimide as a highly selective and sensitive colorimetric and “turn-on” fluorescent chemodosimeter for Cu2+

Abstract: A semicarbazide-based naphthalimide was designed and synthesized as a colorimetric fluorescent probe. Upon reaction with Cu2+ in a buffer solution of pH 7.4 (buffer water/acetonitrile = 80:20, v/v), the probe exhibits color changes from colorless to jade-green accompanying remarkable enhancement in its fluorescence, which could be mechanistically ascribed to the Cu2+-promoted hydrolysis of the semicarbazide moiety leading to the release of the green fluorescent 4-amino-1,8-naphthalimide fluorophore. The probe also displayed excellent performance in high sensitivity as well as good selectivity for Cu2+ over other metallic cations.

Highly stable and ultrasensitive chlorogenic acid sensor based on metal-organic frameworks/titanium dioxide nanocomposites

Abstract: Metal–organic frameworks/titanium dioxide (UiO-66-NH2/TiO2) nanocomposites have been prepared by a simple hydrothermal reaction and they exhibit excellent electrocatalytic activity for chlorogenic acid oxidation due to the synergic effect of UiO-66-NH2 and TiO2. Under the optimal conditions, the sensor can be employed in the quantification of chlorogenic acid in the ranges of 0.01–1.0 μmol L−1 and 1.0–15 μmol L−1 with an ultralow detection limit of 7 nmol L−1 (S/N = 3). Moreover, UiO-66-NH2/TiO2 nanocomposites demonstrate significant stability in acidic buffer solution and maintain their electrocatalytic activities at least up to 90 cycles. The potential utility was validated by the analysis of coffee and tea samples and good recoveries were obtained from different spiked values. The UiO-66-NH2/TiO2 based sensor with highly sensitive, selective and stable consecutive monitoring of chlorogenic acid is a promising candidate for the construction of highly active electrocatalyst in electrochemical biosensors.

Electrochemical determination of mesalazine by using graphene oxide coated with a molecularly imprinted sol–gel

Abstract: Graphene oxide coated with a molecularly imprinted sol–gel was prepared by one-pot synthesis from phenyltriethoxysilane and tetramethoxysilane. The composite modified electrode was used for electrochemical determination of mesalazine (ASA) by differential pulse voltammetry (DPV) in Britton–Robinson buffer solution (pH = 2.0). The peak current was linear with the concentration in the range from 2 to 20 μmol L−1 (r2 = 0.9955) and 20 to 150 μmol L−1 (r2 = 0.9987) with a detection limit of 0.97 μmol L−1 (S/N = 3). Interferents with similar structures such as salicylic acid, 4-aminophenol, 2-aminobenzoic acid and 4-acetamidophenol were examined. The utilizability and reliability of this method were confirmed by the determination of mesalazine in a drug tablet.

Ciprofloxacin Hippurate Salt: Crystallization Tactics, Structural Aspects, and Biopharmaceutical Performance

Abstract: Ciprofloxacin is a widely prescribed fluoroquinolone antibacterial for the treatment of several types of bacterial infections; however, it suffers from unfavorable biopharmaceutical characteristics such as solubility as well as bioavailability. To improve dissolution and bioavailability characteristics, a salt of the drug has been prepared by treating hippuric acid with ciprofloxacin using the solvent assisted grinding technique. Furthermore, single crystals of the salt were obtained by the vapor diffusion technique. The new phase was analyzed using Fourier transform infrared spectroscopy, differential scanning calorimetry, and powder X-ray diffraction, and structural parameters were determined using single crystal X-ray diffraction. The solubility and intrinsic dissolution rate of the salt were measured in pharmaceutically relevant buffer solution with pH 1.2 and water (pH 6.3). In the aqueous solution, the salt demonstrated solubility improvement (22-fold) and a faster dissolution rate than the parent f...