Showing papers on "Buffer solution published in 2015"

Synthesis of copper ion incorporated horseradish peroxidase-based hybrid nanoflowers for enhanced catalytic activity and stability

Abstract: In this study, we report the preparation, catalytic activity and stability of a hybrid nanoflower (hNF) formed from horseradish peroxidase (HRP) enzyme and copper ions (Cu2+). We studied the morphology of hNFs as a function of the concentrations of copper (Cu2+) ions, chloride ions (Cl−) and HRP enzyme, the pH of the buffer solution (phosphate buffered saline), and the temperature of the reaction. The effects of morphology on the catalytic activity and stability of hNFs were evaluated by oxidation of guaiacol (2-methoxyphenol) to colored 3,3-dimethoxy-4,4-diphenoquinone in the presence of hydrogen peroxide (H2O2). The enhanced activity of hNFs synthesized (from 0.02 mg mL−1 HRP in 10 mM PBS (pH 7.4) at +4 °C) was 17595 U mg−1, which was ∼300% higher than free HRP in PBS, where it achieved an activity of 5952 U mg−1. In terms of stability, these hNFs stored in PBS buffer at +4 °C and room temperature (RT = 20 °C) lost 4% and 20%, respectively, of their initial catalytic activities within 30 days. Finally, we demonstrated that these hNFs can be utilized as sensors for the detection of dopamine.

A voltammetric sensor based on the glassy carbon electrode modified with multi-walled carbon nanotube/poly(pyrocatechol violet)/bismuth film for determination of cadmium and lead as environmental pollutants

Abstract: The performance of glassy carbon electrodes (GCE) coated with multi-walled carbon nanotube poly(pyrocatechol violet) composite and bismuth film was investigated as an electrochemical sensor in the simultaneous determination of Cd2+ and Pb2+ ions in a 0.1 M acetate buffer solution at pH = 5.0. The presence of the bismuth film improves the analyte accumulation due to its ability to form a fused alloy with cadmium and lead. It was found that the Bi-film modified electrode shows a better performance than the bare GCE, GCE-MWCNT and GCE-MWCNT/poly(PCV) electrodes. The parameters affecting the stripping current response were investigated and optimized. Under optimal conditions, the electrode showed a good linear response to Cd2+ and Pb2+ in the concentration range of 1.0–300.0 μg L−1 and 1.0–200.0 μg L−1, respectively. The detection limits were 0.20 μg L−1 and 0.40 μg L−1 for Cd2+ and Pb2+, respectively. It was found that the sensor has least interference from most of the common ions due to specific and selective interaction of the modifier functionalities with lead and cadmium ions. The response of the electrode remained constant for at least 3 weeks of successive operation. The proposed method was applied for simultaneous determining Cd2+ and Pb2+ contents in water samples.

A solution-processed, mercaptoacetic acid-engineered CdSe quantum dot photocathode for efficient hydrogen production under visible light irradiation

Abstract: We describe here a simple, efficient and stable CdSe QDs/NiO photocathode engineered using a molecular linker, mercaptoacetic acid (MAA), for H2 generation from neutral water. This protocol does not require any sacrificial reagent, external cocatalyst, protecting layer and buffer solution as well. Upon visible-light irradiation, photocurrent as high as −60 μA cm−2 is achieved at a bias of −0.1 V vs. NHE in 0.1 M Na2SO4 (pH 6.8). Simultaneously, the photocathode evolves H2 consistently for 45 h with ∼100% Faradic efficiency, which is unprecedented in the field of sensitized photocathodes for H2 production. A mechanistic study reveals that the exceptional performance is derived from the efficient hole transfer process.

A terbium(III)-complex-based on-off fluorescent chemosensor for phosphate anions in aqueous solution and its application in molecular logic gates.

Abstract: A new Tb(III) complex based on a tripodal carboxylate ligand has been synthesized for the selective fluorescent recognition of phosphate anions, including inorganic phosphates and nucleoside phosphates (e.g., ATP), in Tris buffer solution. The resulting L·Tb complex shows the characteristic emission bands centered at about 495 and 550 nm from the Tb(III)-centered 5D4 excited state to 7FJ transitions with J = 6 and 5, where the chelating ligand acts only as an “antenna”. Upon the addition of phosphate anions to the aqueous solution of Tb(III) complex, significant “on–off” fluorescence changes were observed, which were attributed to the inhibition of the “antenna” effect between the ligand and Tb(III) after the incorporation of phosphate anions. Furthermore, this unique Tb(III) complex has been successfully utilized to detect phosphate anions with filter papers and hydrogels. Notably, the Tb(III) complex also can be used for the construction of molecular logic gates with TRANSFER and INHIBIT logic functions...

Using isoelectric point to determine the pH for initial protein crystallization trials

Abstract: Motivation: The identification of suitable conditions for crystallization is a rate-limiting step in protein structure determination. The pH of an experiment is an important parameter and has the potential to be used in data-mining studies to help reduce the number of crystallization trials required. However, the pH is usually recorded as that of the buffer solution, which can be highly inaccurate. Results: Here, we show that a better estimate of the true pH can be predicted by considering not only the buffer pH but also any other chemicals in the crystallization solution. We use these more accurate pH values to investigate the disputed relationship between the pI of a protein and the pH at which it crystallizes. Availability and implementation: Data used to generate models are available as Supplementary Material. Contact: ku.ca.kroy@nosliw.eiluj Supplementary information: Supplementary data are available at Bioinformatics online.

pH-dependent and self-healing properties of mussel modified poly(vinyl alcohol) hydrogels in a metal-free environment

Abstract: 3,4-Dihydroxyphenylalanine (DOPA)-based polymers are well-known to form functional hydrogels with self-healing properties by chelating metal ions. However, DOPA-based hydrogels with self-healing properties are difficult to obtain in the absence of the metal ions, as previously reported. Thus, the aim of this study is to prepare a self-healable DOPA-based hydrogel in the absence of metal ions. Firstly, poly(vinyl alcohol)–DOPA (PVA–DOPA) was synthesized by modifying PVA with DOPA through an esterification reaction. The composition of the PVA–DOPA polymer was determined by proton nuclear magnetic resonance (1H NMR) spectroscopy. Then, the PVA–DOPA hydrogel in a metal-free environment could be easily prepared by dissolving the polymer in buffer solution. Rheological analyses showed that the PVA–DOPA polymers had different dynamic moduli depending on the pH of the buffer solutions. The results from the FTIR and UV-vis spectra indicated that there were hydrogen bond interactions between the PVA–DOPA polymers under low pH conditions, while there were both hydrogen bond and covalent interactions under high pH conditions. The PVA–DOPA hydrogel could be rapidly self-healed within 270 s, which was much quicker than the hydrogel prepared in the presence of Fe3+ (about 600 s). The metal-free PVA–DOPA hydrogel has the potential for application in coating and biomedical fields.

Simultaneous determination of hydroquinone and catechol using a modified glassy carbon electrode by ruthenium red/carbon nanotube

Abstract: A decorated glassy carbon (GC) electrode with functionalized multi-walled carbon nanotube (CNTs) and ruthenium red (RR) has been used for simultaneous determination of hydroquinone (HQ) and catechol (CC). The electrocatalytic behaviors of the GC/CNTs–RR were studied in acetate buffer solution with pH 4.5 by differential pulse voltammetry and chronoamperometry techniques. Due to the excellent electrocatalytic activity and enhanced electrical conductivity of the CNTs–RR, the simultaneous determination of HQ and CC with two well-defined peaks was achieved at the GC/CNTs–RR modified electrode. The catalytic peak currents linearly depend on the HQ and CC concentrations in the range of 1.3–433.3 µM with the sensitivity of 5.0 µA µM−1 cm−2 and 7.45 µA µM−1 cm−2, respectively. The detection limits for HQ and CC were obtained 0.21 and 0.18 µM. The diffusion coefficient for the oxidation of HQ and CC at the modified electrode was calculated as 1.06 ± 0.05 × 10−6 and 1.76 ± 0.07 × 10−5 cm2 s−1, respectively. The proposed sensor was successfully examined for real water samples analysis and revealed stable and reliable recovery data.

A new collagen solution with high concentration and collagen native structure perfectly preserved

Abstract: Collagen, the most abundant protein in mammals, is widely used for making biomaterials. Usually, organic solvents, such as 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), or acids (H3PO4, HAc) have been used to disperse collagen to make collagen-based biomaterials. However, the native structure of collagen is often seriously damaged and the concentration of collagen in solution was always relatively low, which greatly limited its application. In this work, we have firstly made a detailed study of the effect of H+ and HAc on collagen dispersal in terms of Zeta potential, particle size and Circular Dichroism (CD), followed by using a benign sodium acetate/acetic acid buffer solution, which is proposed to disperse the collagen. The results showed that the collagen solution from a NaAc/HAc buffer solution at pH = 3.0 had both high concentration (100 mg mL−1) and perfect native structure preservation (up to 94%). We demonstrated that it was the constant concentration of free H+ in the NaAc/HAc buffer solution whose pH was fixed at 3.0 that can maintain an unchanged amount of surface charge on the collagen colloidal particles, which enables the collagen to be dispersed well even at high dose. As an application, the collagen solution from the NaAc/HAc solution at pH 3.0 was successfully electrospun into nanofibers, and the obtained collagen nanofibers can still maintain as much as 57% of its native structure. This study indicated that the novel buffer solution of NaAc/HAc at pH 3.0 could be commonly used in the processing of collagen for a variety of biomaterials based on collagen solutions, and has great potential for use in tissue engineering.

Determination of catecholamines in urine using aminophenylboronic acid functionalized magnetic nanoparticles extraction followed by high-performance liquid chromatography and electrochemical detection.

Abstract: A new method was developed for the simultaneous determination of three catecholamines in urine using aminophenylboronic acid functionalized magnetic nanoparticles extraction followed by high-performance liquid chromatography with electrochemical detection. Novel aminophenylboronic acid functionalized magnetic nanoparticles were prepared by multi-step covalent modification, and characterized by transmission electron microscopy, Fourier-transformed infrared spectroscopy, X-ray diffraction, and vibrating sample magnetometry. With the help of the high affinity between the boronate and cis-diol group, the particles were used for the highly selective separation and enrichment of three major catecholamines, norepinephrine, epinephrine, and dopamine. Effects of the pH of the feed solution, the extraction time, the composition of the buffer solution, the amount of the magnetic particles, the elution conditions, and the recycling of aminophenylboronic acid functionalized magnetic nanoparticles were explored. Under the optimized conditions, 13-17-fold enrichment factors were obtained. The linear ranges were 0.01-2.0 μg/mL for the studied analytes. The limits of detection and quantification were in the range of 2.0-7.9 and 6.7-26.3 ng/mL, respectively. The relative recoveries were in the range of 92-108%, with intraday and interday relative standard deviations lower than 6.8%. This method was successfully applied to analysis of catecholamines in real urine.

Glow discharge electrolysis plasma induced synthesis of cellulose-based ionic hydrogels and their multiple response behaviors

Abstract: Novel ionic hydrogels were prepared successfully from cellulose in the NaOH/urea aqueous system by a glow discharge electrolysis plasma (GDEP) technique. The structure and morphology of the ionic hydrogels were characterized by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM), as well as by determination of swelling and stimuli responses to pH and salts. The results showed that the swelling behavior and the network structure of the ionic hydrogels could be controlled by changing discharge voltage or discharge time, whereas we obtained the maximum absorbency of 898 g g−1 for distilled water at 570 V and 90 s. Shrinkage of the network hydrogels took place at higher or lower pH. Relative to the Na+ buffer solution, hydrogels were more sensitive to Zn2+ and Fe3+ buffer solutions and showed network shrinkage and lower swelling ratio. This work provided a new pathway for preparation of cellulose-based hydrogels with environmental friendliness, high water absorption capacity, and rapid and multiple responses to pH and ions, which may allow their use in the biomaterials area.

Electrochemical tuning of the activity and structure of a copper-cobalt micro-nano film on a gold electrode, and its application to the determination of glucose and of Chemical Oxygen Demand.

Abstract: Micro-nano structured Cu-Co was in situ fabricated on the surface of a gold electrode via electrochemical reduction of CuCl2 and Co(NO3)2. It is shown that the shape of the particles can be controlled by variation of deposition current, deposition time, pH value and the ratio of Cu(II) and Co(II) ions. If prepared under current of −200 μA in 0.1 M, pH 4.0 acetate buffer solution, the film possesses high catalytic activity towards the electrochemical oxidation of glucose at a largely increased oxidation current compared to a non-modified surface. The electrochemical activity of this sensor can be easily tuned. Glucose is a standard compound for evaluating the chemical oxygen demand (COD), and we have therefore studied the application of the sensor to the determination of this parameter. Under optimized conditions, the sensor has linear response to glucose in the 1.92-768 mg L−1 concentration range, and the detection limit is 0.609 mg L−1 (at an S/N ratio of 3). A large number of surface water samples was studied, and the results obtained by this method were found to be linearly correlated to those obtained by the dichromate method (r = 0.995; n = 33).

2nd coordination sphere controlled electron transfer of iron hangman complexes on electrodes probed by surface enhanced vibrational spectroscopy

Abstract: Iron hangman complexes exhibit improved catalytic properties regarding O2 and H2O2 reduction, which are attributed to the presence of a proton donating group in defined vicinity of the catalytic metal centre. Surface enhanced resonance Raman (SERR) and IR (SEIRA) spectro-electrochemistry has been applied concomitantly for the first time to analyse such iron hangman porphyrin complexes attached to electrodes in aqueous solution. While the SERR spectra yield information about the redox state of the central iron, the SEIRA spectra show protonation and deprotonation events of the 2nd coordination sphere. To investigate the influence of a proton active hanging group on the heterogeneous electron transfer between the iron porphyrin and the electrode, two hangman complexes with either an acid or ester functional group were compared. Using time resolved SERR spectroscopy the electron transfer rates of both complexes were determined. Complexes with an acid group showed a slow electron transfer rate at neutral pH that increased significantly at pH 4, while complexes with an ester group exhibited a much faster, but pH independent rate. SEIRA measurements were able to determine directly for the first time a pKa value of 3.4 of a carboxylic hanging group in the immobilized state that shifted to 5.2 in D2O buffer solution. The kinetic data showed an increase of the heterogeneous electron transfer rate with the protonation degree of the acid groups. From these results, we propose a PCET which is strongly modulated by the protonation state of the acid hanging group via hydrogen bond interactions.

Electroanalytical determination of the linuron herbicide using a cathodically pretreated boron-doped diamond electrode: comparison with a boron-doped diamond electrode modified with platinum nanoparticles

Abstract: The determination of linuron using differential-pulse voltammetry (DPV) and a cathodically pretreated boron-doped diamond electrode is proposed. Cyclic voltammetry results showed one irreversible oxidation peak for linuron at 1.29 V (vs. Ag/AgCl (3.0 mol L−1 KCl)) in 0.04 mol L−1 Britton–Robinson (BR) buffer solution (pH 2.0). Under optimized DPV conditions, a linear analytical curve was obtained for the linuron concentration range of 0.61–26.0 μmol L−1 with a detection limit of 0.18 μmol L−1. Similar responses (linearity and sensitivity) were obtained employing a boron-doped diamond electrode modified with platinum nanoparticles. The proposed method was successfully applied in the determination of linuron in natural water samples with recoveries ranging from 90.9% to 104%.

Influence of pH and pH adjustment conditions on photocatalytic oxidation of aqueous ammonia under airflow over Pt-loaded TiO2

Abstract: The influence of pH and pH adjustment conditions on the photocatalytic oxidation of aqueous ammonia in the presence of Pt-TiO 2 under airflow was investigated as a possible treatment for ammonia-containing wastewater. Ammonia oxidation proceeded only under alkaline conditions, and the maximum initial oxidation rate was obtained at pH ∼ 10. The pH of the reaction suspension decreased with the formation of nitrite and nitrate species, stopping completely when the pH fell below 7 for reactions in which the initial pH (pH i ) was adjusted within the range 8.7–11.3 using NaOH(aq). The rate of ammonia oxidation was higher when NaOH(aq) was used to adjust the pH i than that achieved using Na 2 CO 3 –NaHCO 3 buffer solution at the same pH. The maximum ammonia adsorption on Pt-TiO 2 (measured under dark conditions) was obtained at pH 10 and the amount of ammonia adsorbed when the pH i was adjusted with NaOH(aq) was higher than that achieved using the Na 2 CO 3 –NaHCO 3 buffer solution at the same pH; thus, the amount of adsorbed ammonia strongly affected the oxidation rate. Although the selectivity for the sum of the undesired products, nitrite and nitrate was high when the ammonia concentration was low (e.g., 5 mM), the selectivity decreased as the initial ammonia concentration increased for each pH and pH adjustment condition. Suppression of the selectivity was evident when the pH i was adjusted to 10 with NaOH(aq). The selectivity was affected by the changes in the density of N-containing species on the photocatalyst surface as the pH and pH adjustment conditions were varied.

Removal of methylene blue dye in aqueous solution by sorption on a bacterial-g-poly-(acrylic acid) polymer network hydrogel

Abstract: In this study, Bacterial cellulose (BC) grafted with Acrylic acid (AA) was prepared using Co60 γ-rays source (30 KGy). Although many samples were prepared, BC: AA with ratio of 1:1 labelled as A1 and 2:1 labelled as A2 gave the most significant results. Hence these particular ratios have been selected and further investigated. AA was proven grafted onto BC by using ATR-FTIR due to the absent of C-O stretching (1040 cm-1) in both hydrogels. The SEM image of both hydrogels samples showed highly porosity networks structure have been produced. The physical properties of the hydrogels such as equilibrium water content (%) and swelling ratio (%) in different pH buffer solution were measured. It was found that the equilibrium water content (%) of A1 was 93.10% while A2 was 74.83%, respectively. The results indicated that the equilibrium water content (%) increased by gaining the AA concentration. At pH10, the A2 swelling ratio (%) was two folded with 3350% in comparison with the A1. For the removal of methylene blue (MB) from aqueous solution, the results from the UV-VIS spectroscopy demonstrated that the A2 sample hydrogel was also an effective absorbent material.

In vitro toxicity evaluation of hydrogel-carbon nanotubes composites on intestinal cells

Abstract: Composite materials based on carbon nanotubes (CNT) and polymeric hydrogels have become the subject matter of major interest for use as carriers in drug delivery research. The aim of this study was to evaluate the in vitro cytotoxicity of the hydrogel–carbon nanotube–chitosan (hydrogel–CNT–CH) composites on intestinal cells. Oxidized CNT were wrapped with chitosan (CH), Fourier transform infrared (FT-IR) analysis suggest that oxidized CNT interact with CH. Transmission electron microscopy (TEM) images show a CH layer lying around CNT. Chitosan wrapped CNT were incorporated to poly (acrylamide-co-acrylic acid) hydrogels. Swelling behavior in buffers at different pH were evaluated and revealed a significantly lower swelling when it is exposed to a acid buffer solution (pH 2.2). Mechanical properties were evaluated by measurements of elasticity and the material with CNT showed better mechanical properties. The incorporation and liberation of Egg Yolk Immunoglobulin from hydrogel–CNT–CH were also assessed and it revealed an improved performance. To evaluate the effect of these nanocomposites on cellular redox balance, intestinal cells were exposed to hydrogel–CNT–CH composites and antioxidant enzymes were assessed. Cytotoxicity and apoptosis were also evaluated. Hydrogel–CNT–CH composites induce no oxidative stress and there were no evidence of cytotoxicity or cell death. These preliminary findings suggest that hydrogel–CNT–CH composites show improved properties and good biocompatibility in vitro making these biomaterials promising systems for drug delivery purposes. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41370.

In Vitro Study of Temperature and pH-Responsive Gentamycin Sulphate-Loaded Chitosan-Based Hydrogel Films for Wound Dressing Applications

Abstract: Developments in the field of polymer science have led us to the development of Chitosan and PNIPAm mixed pH and temperature responsive hydrogel films. Characterizations were done by Swelling analysis, FTIR, DSC, FESEM and Antibacterial assay. Optimized hydrogel film on swelling analysis does not lose its shape and was not dissolve in to the different buffer solution and at different temperature. FTIR, DSC and FESEM study confirmed the changes in to the hydrogel film after drug absorption. On increasing the temperature and change in pH of the solution, drug absorption increased which was confirmed by zone of inhibition against E. coli.

Structure and solubility behaviour of zinc containing phosphate glasses

Abstract: The structure of phosphate glasses of general composition 10Na2O:(20 + x/2)ZnO:(20 + x/2)CaO:(50 − x)P2O5 (0 ≤ x ≤ 20) has been investigated using IR spectroscopy, 1D 31P and 43Ca MAS Bloch decay, 31P–31P double quantum MAS-NMR and 43Ca and 67Zn static NMR techniques, as well as neutron diffraction analysis. Zinc is shown to aid glass formation in this system. Glass transition temperature and density increase with increasing cation:phosphate ratio. However, free volume calculations show structures becoming significantly more compact from x = 5 to x = 10. The structural data confirm depolymerisation of the glasses with increasing cation:phosphate ratio. Zinc oxide is found to act in a network forming role in the system, with 67Zn NMR and neutron diffraction analysis confirming zinc exhibits predominantly four-coordinate geometry. Solubility in deionised water and tris/HCl buffer solution is seen to decrease significantly with increasing x-value. This is discussed in terms of water ingress and the degree of structural openness, associated with increased cross-linking and a decrease in concentration of P–O–P linkages. pH measurements confirm invert phosphate compositions maintain physiological pH levels on immersion in water and buffer solutions for up to four weeks.

Preparation of chitosan-modified silica nanoparticles and their applications in the separation of auxins by capillary electrophoresis.

Abstract: In recent years, nanoparticles have gained more attention when used in separation science. In this study, chitosan-modified silica nanoparticles were successfully synthesized and characterized by transmission electron microscopy, elemental analysis and zeta potential measurements, etc. When added into the running buffer solution as pseudo-stationary phase in capillary electrophoresis, the separation of four representative auxins, i.e., indole-3-acetic acid, indole butyric acid, 2,4-dichlorophenoxyacetic acid, 1-naphthaleneacetic acid, was carried out. Some important factors, such as the nanoparticles concentration, the pH and concentration of the running buffer solution, were also investigated on the separation. Under optimized experimental conditions, all the auxins investigated can be baseline separated within 5 min with higher column performance. The method established can also be used for quantitative analysis. The relative standard deviations obtained for indole-3-acetic acid, indole butyric acid, 2,4-dichlorophenoxyacetic acid, 1-naphthaleneacetic acid were in the range of 1.6-5.7% for peak area and 0.53-1.60% for migration time. The calibration curves obtained from the peaks areas for auxins were linear in the range of 0.1-80 mg/L with the correlation coefficients of 0.994-0.999. The limit of detection (S/N = 3) was 11-75 μg/L. The developed method was also successfully used for the determination of auxins in fruits and vegetables samples with good recoveries.

Development and Validation of an HPLC Method for Simultaneous Quantification of Clopidogrel Bisulfate, Its Carboxylic Acid Metabolite, and Atorvastatin in Human Plasma: Application to a Pharmacokinetic Study.

Abstract: A simple, sensitive, and specific reversed phase liquid chromatographic method was developed and validated for simultaneous quantification of clopidogrel, its carboxylic acid metabolite, and atorvastatin in human serum. Plasma samples were deproteinized with acetonitrile and ibuprofen was chosen as internal standard. Chromatographic separation was performed on an BDS Hypersil column (250 × 4.6 mm; 5 μm) via gradient elution with mobile phase consisting of 10 mM phosphoric acid (sodium) buffer solution (pH = 2.6 adjusted with 85% orthophosphoric acid) : acetonitrile : methanol with flow rate of 1 mL·min−1. Detection was achieved with PDA detector at 220 nm. The method was validated in terms of linearity, sensitivity, precision, accuracy, limit of quantification, and stability tests. Calibration curves of the analytes were found to be linear in the range of 0.008–2 μg·mL−1 for clopidogrel, 0.01–4 μg·mL−1 for its carboxylic acid metabolite, and 0.005–2.5 μg·mL−1 for atorvastatin. The results of accuracy (as recovery) with ibuprofen as internal standard were in the range of 96–98% for clopidogrel, 94–98% for its carboxylic acid metabolite, and 90–99% for atorvastatin, respectively.