mM In Aqueous Solution Research Articles

Green one-step synthesis of mushroom-derived carbon dots as fluorescent sensors for Fe3+ detection.

Blue photoluminescent carbon dots were synthesized from Lentinus polychrous Lèv. via a simple hydrothermal process without additional chemical reagents or functionalization. The carbon dots (hereafter referred to as LCDs) were quasi-spherical with an average diameter of 6.0 nm. The strong fluorescence emissions of LCDs were utilized as the basis of efficient turn-off probes for Fe3+. The quenching phenomenon could be used to rapidly determine Fe3+ concentrations in the range of 0.0-2.0 mM in aqueous solution, with a limit of detection (LOD) of 16 μM. In the presence of interference, LCDs demonstrated good sensitivity and selectivity towards Fe3+ in both solution-based and paper-based systems. The LCDs also exhibited excellent photostability and an eco-friendly nature, making them an ideal choice for environmental monitoring with significant potential for diagnostic applications.

Modified Cyclodextrins Solubilize Elemental Sulfur in Water and Enable Biological Sulfane Sulfur Delivery

An important form of biological sulfur is sulfane sulfur, or S0, which is found in polysulfide and persulfide compounds as well as in elemental sulfur. Sulfane sulfur, often in the form of S8, functions as a key energy source in the metabolic processes of thermophilic Archaean organisms found in sulfur-rich environments and can be metabolized both aerobically and anaerobically by different archaeons. Despite this importance, S8 has a low solubility in water (∼19 nM), raising questions of how it can be made chemically accessible in complex environments. Motivated by prior crystallographic data showing S8 binding to hydrophobic motifs in filamentous glycoproteins from the sulfur reducing Staphylothermus marinus anaerobe, we demonstrate that simple macrocyclic hydrophobic motifs, such as 2-hydroxypropyl β-cyclodextrin (2HPβ), are sufficient to solubilize S8 at concentrations up to 2.0 ± 0.2 mM in aqueous solution. We demonstrate that the solubilized S8 can be reduced with the common reductant tris(2-carboxyethyl)phosphine (TCEP) and reacts with thiols to generate H2S. The thiol-mediated conversion of 2HPβ/S8 to H2S ranges from 80% to quantitative efficiency for Cys and glutathione (GSH). Moreover, we demonstrate that 2HPβ can catalyze the Cys-mediated reduction of S8 to H2S in water. Adding to the biological relevance of the developed systems, we demonstrate that treatment of Raw 264.7 macrophage cells with the 2HPβ/S8 complex prior to LPS stimulation decreases NO2− levels, which is consistent with known activities of bioavailable H2S and sulfane sulfur. Taken together, these investigations provide a new strategy for delivering H2S and sulfane sulfur in complex systems and more importantly provide new insights into the chemical accessibility and storage of S0 and S8 in biological environments.

P.233 Doxycycline attenuates anxiety and microglia activation induced by repeated lipopolysaccharide

Sodium hyodeoxycholate (NaHDC) is the main component of hog bile salts, which play a role in the absorption of sparingly soluble materials in the intestinal solution. The biosurfactant has an amphiphilic molecular structure, similar to that of ursodeoxycholate from bear gallbladder. Micelle formation from hyodeoxycholate was studied at 308.2 K using pyrene fluorescence probe to determine critical micelle concentrations (cmc) at various NaCl concentrations. The change in the fluorescence spectrum peak ratios with NaHDC concentration indicated two steps for bile salt aggregation. The first step was the formation of small micelles (cmc) at 5 mM, and the second step was the formation of stable aggregates at 14 mM in aqueous solution. The aggregation of hyodeoxycholate, analyzed using the stepwise association model, was found to grow its aggregation number from 4 to 7 with increasing concentration. The aggregation number in aqueous solution was also confirmed by the static light scattering method. The average measured aggregation number of the micelles was 6.7. The micellar size was relatively small as measured by either method, but it was covered by general aggregation number of human bile salts. The degree of counterion binding to the micelles, determined using a sodium ion-selective electrode, was ca. 0.5 for the NaHDC micelles. This value was relatively high among typical bile salts. Moreover, the solubilization capacity of the NaHDC micelles was assessed using cholesterol. It became clear that NaHDC micelles hardly solubilized cholesterol compared to typical human bile salts. The maximum solubilization by NaHDC was equivalent only to that by sodium ursodeoxycholate

In-line sensing of sodium ascorbate using a poly(ferrocenylsilane)-coated microfluidic device

Poly(ferrocenylsilane) (PFS) is a redox-active polymer that can be utilized in a variety of applications, such as sensing, nanoparticle foundries or dual-responsive hydrogels, due to the fact that it can be partially or completely oxidized, reversibly, by (electro)chemical means. In this research, PFS is tethered to a cysteamine-modified gold-coated microchannel electrode via amine alkylation, following a recent published procedure for conventional macro-sized electrodes. The PFS-coated microfluidic device is successfully employed as an electrochemical sensor for sodium l-ascorbate, or vitamin C, with a detection limit of 0.5mM in aqueous solution. The fabrication of the device, that comprises gold-coated electrodes of micrometers in width, is discussed, as well as the static and in-line detection of sodium l-ascorbate. The analyte concentration is sensed through an electrocatalytic process in both static and in-line cases, by cyclic voltammetry and amperometry, respectively. The findings presented in this work open novel opportunities for local surface modification of chip-integrated gold electrodes by redox-responsive polymers used, e.g., as electrochemical sensors.

Molecular Dynamics Simulation of the Aggregation Patterns in Aqueous Solutions of Bile Salts at Physiological Conditions.

Classical molecular dynamics simulations are employed to monitor the aggregation behavior of six bile salts (nonconjugated and glycine- and taurine-conjugated sodium cholate and sodium deoxycholate) with concentration of 10 mM in aqueous solution in the presence of 120 mM NaCl. There are 150 ns trajectories generated to characterize the systems. The largest stable aggregates are analyzed to determine their shape, size, and stabilizing forces. It is found that the aggregation is a hierarchical process and that its kinetics depends both on the number of hydroxyl groups in the steroid part of the molecules and on the type of conjugation. The micelles of all salts are similar in shape-deformed spheres or ellipsoids, which are stabilized by hydrophobic forces, acting between the steroid rings. The differences in the aggregation kinetics of the various conjugates are rationalized by the affinity for hydrogen bond formation for the glycine-modified salts or by the longer time needed to achieve optimum packing for the tauro derivatives. Evidence is provided for the hypothesis from the literature that the entirely hydrophobic core of all aggregates and the enhanced dynamics of the molecules therein should be among the prerequisites for their pronounced solubilization capacity for hydrophobic substances in vivo.

Degradation and mineralization of Bisphenol A (BPA) in aqueous solution using advanced oxidation processes: UV/H2O2 and [formula omitted] oxidation systems

This work reports on the removal and mineralization of an endocrine disrupting chemical, Bisphenol A (BPA) at a concentration of 0.22 mM in aqueous solution using inorganic oxidants (hydrogen peroxide, H2O2 and sodium persulfate, Na2S2O8;S2O82−) under UV irradiation at a wavelength of 254 nm and 40 W power (Io = 1.26 × 10−6 E s−1) at its natural pH and a temperature of 29 ± 3 °C. With an optimum persulfate concentration of 1.26 mM, the UV/S2O82− process resulted in ∼95% BPA removal after 240 min of irradiation. The optimum BPA removal was found to be ∼85% with a H2O2 concentration of 11.76 mM. At higher concentrations, either of the oxidants showed an adverse effect because of the quenching of the hydroxyl or sulfate radicals in the BPA solution. The sulfate-based oxidation process could be used over a wider initial pH range of 3–12, but the hydroxyl radical-based oxidation of BPA should be carried out in the acidic pH range only. The water matrix components (bicarbonate, chloride and humic acid) showed higher scavenging effect in hydroxyl radical-based oxidation than that in the sulfate radical-based oxidation of BPA. UV/S2O82− oxidation system utilized less energy (307 kWh/m3) EE/O in comparison to UV/H2O2 system (509 kWh/m3) under optimum operating conditions. The cost of UV irradiation far outweighed the cost of the oxidants in the process. However, the total cost of treatment of persulfate-based system was much lower than that of H2O2-based oxidation system.

Facilitated Transfer of Alkali and Alkaline‐Earth Metal Ions by a Calix[4]arene Derivative Across Water/1,2‐Dichloroethane Microinterface: Amperometric Detection of Ca2+

AbstractThe host–guest complexation reactions between 5,11,17,23‐tetra‐tert‐butyl‐25,27‐diethoxycarbonylmethoxy‐26,28‐dimethoxy calix[4]arene (BDDC4) and alkali and alkaline‐earth metal ions were investigated by facilitated ion transfer processes across water/1,2‐dichloroethane microinterface by using steady‐state cyclic voltammetry and differential pulse voltammetry. The obtained facilitated transfers for Li+, Na+, K+, Rb+ and Ca2+ were evaluated under the different experimental conditions, at the excess concentrations of metal ions with respect to BDDC4 and vice versa. The association constants having 1 : 1 stoichiometry for Li+, Na+, K+ and Rb+ in 1,2‐DCE were determined. Also, we demonstrated that BDDC4 can play an important role for the development of highly selective chemical sensor for Ca2+ among alkaline‐metal ions in the concentration range of 0.1–1.0 mM in aqueous solution.

Studies of single-step electrodeposition of CuInSe 2 thin films with sodium citrate as a complexing agent

The influences of various parameters in a single-step electrodeposition of CuInSe 2 from aqueous solution containing CuCl 2, InCl 3, and SeO 2, with sodium citrate as the complexing agent, are investigated. Co-deposition of CuInSe 2 from a room temperature, aqueous bath of these electrolytes is accomplished by the aid of sodium citrate. In this work the optimum potential for deposition of CuInSe 2 is found to be −0.5 V vs. Ag/AgCl, the deposition time is 800 s, the concentration ratio of CuCl 2, InCl 3, and SeO 2 is 9 mM:22 mM:22 mM in aqueous solution, and the annealing temperature is 225 °C. Under the optimum conditions, crystalline layers of CuInSe 2 having the chalcopyrite structure can be successfully synthesized. Cyclic voltammetry (CV), scanning electron microscope (SEM), X-ray diffractometer (XRD), and energy dispersive X-ray spectrometer (EDX) were used to examine the electrochemistry, morphologies, structures, and compositions of CuInSe 2 thin films deposited on ITO glass.

Structural Instability of Shell-Like Assemblies of a Keplerate-Type Polyoxometalate Induced by Ionic Strength

We demonstrate a new structural instability of shell-like assemblies of polyoxometalates. Besides the colloidal instability, that is, the formation of aggregates that consist of many single layered POM-shells, these systems also display an instability on a structural scale within the shell-like assemblies. This instability occurs at significantly lower ionic strength than the colloidal stability limit and only becomes evident after a relatively long time. For the polyoxometalate, abbreviated as {Mo(72)Fe(30)}, it is shown that the structural stability limit of POM-shells lies between a NaCl concentration of 1.00 and 5.00 mM in aqueous solution.

Head-to-tail Aggregates of Sulfonatomethylated Calix[4]resorcinarene in Aqueous Solutions

Two amphiphilic water-soluble sulfonatomethylated calix[4]resorcinarene derivatives were studied by various 1H NMR techniques (1H NMR titration, 2D NOESY, NMR diffusion measurements). The derivative with methyl moieties at the lower rim (1) was found to be non-aggregated in the range 0–10 mM in aqueous solutions. Lengthening of the lower rim substituent to pentyl (2) results in self-aggregation of 2 in aqueous solutions with the aggregation number varying from 3 at 1 mM to 20 at 10 mM. The 2D NOESY 1H NMR spectroscopy data reveal an unusual head-to-tail packing mode in aqueous solutions, resulting from the cooperative effect of weak hydrophobic interactions. Binding of guests (tetramethylammonium and N-methylpyridinium) results in additional stabilization of the aggregates whilst the head-to-tail packing mode of the aggregate is retained.

Scavenging of riboflavin-photogenerated oxidative species by uric acid, xanthine or hypoxanthine: A kinetic study

Air-equilibrated aqueous solutions of the purine bases (PBs) uric acid (URA), xanthine (XAN) and hypoxanthine (HXA) have been irradiated with visible light in the presence of riboflavin (Rf) as the only light-absorbing compound, to study to what extent the reactive oxygenated species (ROSs) singlet molecular oxygen, O 2( 1Δ g), and superoxide radical anion, O 2 −, are involved in the observed photodegradation processes. Both reactive species are generated from triplet excited riboflavin ( 3Rf*) by well-known processes: energy transfer from 3Rf* to ground state oxygen to yield O 2( 1Δ g), and electron transfer from each PB to 3Rf* to produce the radical anion Rf − that, after another electron transfer step to ground state oxygen, yields O 2 − and Rf. The kinetics of the involved processes have been studied by polarographic detection of oxygen uptake and time-resolved phosphorescence detection of O 2( 1Δ g), at concentrations in the range 0.05–0.5 mM in aqueous solutions at pH values 5, 7, 9, and 12, to compare the reactivity of the neutral and ionic species of each purine base. By means of Rose Bengal photosensitized reactions, it could be shown that O 2( 1Δ g) is quenched by the three PBs with an overall rate constant decreasing in the order URA > XAN > HXA, with values ranging from 1.16 × 10 9 M −1 s −1 (URA at pH 12) to 5 × 10 6 M −1 s −1 (HXA at pH 7). When Rf is used instead, the quenching process takes place mostly by a chemical mechanism that prevents the oxidation of Rf by O 2( 1Δ g). Experiments with Rf and superoxide dismutase indicate that the PBs also react with O 2 − by a mechanism which is not simple. With URA, largely the most efficient O 2( 1Δ g)-quencher, the major ROS generated is O 2 −, and the process is characterized by the largest rate of oxygen uptake, indicating efficient overall-scavenging and URA oxidation. With HXA, the less efficient O 2( 1Δ g)-quencher, the process shows a relatively high rate of oxygen consumption, especially in alkaline solution, likely as a result of the efficient generation of O 2 − from Rf − and its concomitant reaction with HXA. Finally, with XAN the quenching efficiency takes intermediate values. At physiological pH, URA is the most efficient antioxidant, showing the highest overall rate constant for O 2( 1Δ g) quenching, the lowest efficiency for the reaction with O 2( 1Δ g), and the highest relative rate of oxygen uptake.

Xenon reduces glutamate-, AMPA-, and kainate-induced membrane currents in cortical neurones

The anaesthetic, analgesic, and neuroprotective effects of xenon (Xe) are believed to be mediated by a block of the NMDA (N-methyl-D-aspartate) receptor channel. Interestingly, the clinical profile of the noble gas differs markedly from that of specific NMDA receptor antagonists. The aim of this study was, therefore, to investigate whether Xe might be less specific, also inhibiting the two other subtypes of glutamate receptor channels, such as the alpha-amino-3-hydroxy-5-methyl-4-isoxazolole propionate (AMPA) and kainate receptors. The study was performed on voltage-clamped cortical neurones from embryonic mice and SH-SY5Y cells expressing GluR6 kainate receptors. Drugs were applied by a multi-barreled fast perfusion system. Xe, dissolved at approximately 3.45 mM in aqueous solution, diminished the peak and even more the plateau of AMPA and glutamate induced currents. At the control EC(50) value for AMPA (29 microM) these reductions were by about 40 and 56% and at 3 mM glutamate the reductions were by 45 and 66%, respectively. Currents activated at the control EC(50) value for kainate (57 microM) were inhibited by 42%. Likewise, Xe showed an inhibitory effect on kainate-induced membrane currents of SH-SY5Y cells transfected with the GluR6 subunit of the kainate receptor. Xe reduced kainate-induced currents by between 35 and 60%, depending on the kainate concentration. Xe blocks not only NMDA receptors, but also AMPA and kainate receptors in cortical neurones as well as GluR6-type receptors expressed in SH-SY5Y cells. Thus, Xe seems to be rather non-specific as a channel blocker and this may contribute to the analgesic and anaesthetic potency of Xe.

Molecularly imprinted polymer thin films on quartz crystal microbalance using a surface bound photo-radical initiator

The present work aims to study preparation of thin MIP films on a gold-coated QCM resonator in a well-controlled and reproducible manner. A surface-bound photo-radical initiator was used to furnish an imprinting polymerization in a dilute solution of template, functional monomer and crosslinker. Prior to polymerization, the photo-initiator was covalently coupled to a self-assembled monolayer of carboxyl terminated alkanethiol on a gold surface. With this approach we were able to control the thickness of the MIP film to be below 50 nm, where the selective recognition of target analytes can be easily detected by the underlying quartz crystal resonator. When used in a flow injection analysis system, the assembled QCM sensor generated a large frequency change (>30 Hz) upon encountering a small amount of analyte (0.19 mM). The sensor had a very short response time (<1 min), and displayed certain chiral selectivity towards the original template, ( S)-propranolol at a concentration higher than 0.38 mM in aqueous solution.

Bio-, nano-technology for cellular biosensing

Abstract Cells and tissues transmit various chemical and physical signals. These are response to an extracellular stimulus. All the cellular responses include molecular information as for intracellular biological processes. However, most of cellular signals are very weak and not easily detected with conventional analytical methods. In order to detect cellular signals, two types of tactics to monitor cellular signal under cell culture condition has been studied. First one is the molecular designing of “polymer metal polymer (PMP) complex” as molecular transducer for cellular nitric oxide sensor. The PMP complex is designed and synthesized on the basis of novel ideas on molecular designing. The PMP complex possesses both specific catalytic function and molecular transduceability. The multiproperties are given by peculiar coordinative self-assembled structure that is composed with two (or more) different polymers and metal ion(s). In the present case, PMP complex is designed for cellular NO detection. The PMP complex coated electrode can determine NO concentration from 100 nM to 100 mM in aqueous solution by amperometric measurement. Next one is a genetical construction of postsynapse model cell for an evaluation of extracellular neural transmitter. Postsynaptic function is presented by channel gate receptor on postsynaptic membrane. In the present study, cloned glutamic acid channel gate receptor (GluR-D) gene is transformed into insect cell Sf-9. Sf-9 is easy to cultivate and is able to express GluR-D on its cell surface as same as postsynaptic membrane. Its function can be monitored by outer cell potential. Both of tactics is successfully performed and is applicatable cultured cell-based assay on pharmaceutical screening and chemical safety proofing.

Comparison of the Surface Activity and Bulk Aggregation of Ferrocenyl Surfactants with Cationic and Anionic Headgroups

We report the synthesis and aqueous solution properties of a novel redox-active surfactant, Fc(CH2)11SO3-Na+, where Fc is ferrocene. Electrochemical oxidation of Fc to the ferrocenium cation (Fc+) reversibly transforms the anionic surfactant (Fc(CH2)11SO3-) into a zwitterionic species (Fc+(CH2)11SO3-). When dissolved at concentrations between 0.15 and 0.4 mM in aqueous solutions containing 10 mM Li2SO4, oxidation is accompanied by the reversible transformation of a solution of monomeric species of Fc(CH2)11SO3- into vesicle-like (Dh = 70 ± 8 nm, Rg/Rh = 1.0 ± 0.3) surfactant assemblies of Fc+(CH2)11SO3-. In contrast, at concentrations above 0.4 mM, oxidation reversibly transforms a solution of globular (Dh = 6 ± 2 nm) micelles into vesicle-like assemblies of Fc+(CH2)11SO3-. These various oxidation-induced changes in aggregation are reflected in the interfacial properties of this surfactant system, which are substantially different from those of ferrocenyl surfactants with cationic headgroups (Fc(CH2)11N+(...

Soil Cleanup by In-Situ Surfactant Flushing. VIII. Reclamation of Multicomponent Contaminated Sodium Dodecylsulfate Solutions in Surfactant Flushing

Abstract Solvent extraction with hexane has been studied for use in reclaiming contaminated surfactant solutions for reuse in remediation of hazardous sites. The hexane flow rate, sodium dodecylsulfate (SDS) concentration, and contaminant mixture were varied to determine their effects on the removal of multicomponent mixtures of phenanthrene, naphthalene, and biphenyl. Hexane flow rates greater than 60 mL/min were found to remove greater than 80% of phenanthrene and naphthalene after 1.5 hours of extraction time. The mass transfer rate increased until a hexane flow rate of about 60 mL/min was reached and then remained essentially constant. In experiments in which the SDS concentration was varied from 10 to 100 mM in aqueous solutions of mixtures of phenanthrene and naphthalene, the removal percentages for naphthalene were 98, 91, and 82, respectively, for 10, 50, and 100 mM SDS solutions after 2 hours of extraction, and for phenanthrene were 94, 88, and 75%. The mass transfer rates in these experiments in...

In vivo transcutaneous penetration of nicotinates and sensitive skin

Proclivity to develop irritant reactions and transcutaneous penetration of nicotinates has been investigated in 20 subjects of both sexes, divided into reactors and nonreactors on the basis of the responses to irritant stimuli. 1% sodium lauryl sulphate (patch application for 24 h) and 5% lactic acid in aqueous solutions were used to detect chemical and sensory (subjective) irritation. The vasodilatation induced was measured using a chromameter for 1 h after topical application of the chemical. The area-under-the-curve response and the peak response was used to assess the in vivo penetration of methyl nicotinate (10 mM in aqueous solution). Significant differences were found between reactors and non-reactors. Non-reactors showed a significantly decreased area-under-the-curve response and peak response to methyl nicotinate compared to reactors. Nicotinate-induced vasodilatation has been used as a model to study transcutaneous penetration of chemicals; the correlation between increased penetration of nicotinates and skin hyperreactivity to irritant substances may suggest an increased transcutaneous penetration of water-soluble chemicals in individuals with sensitive skin.

Effect of micellar environment on the photoreduction of azo dyes sensitized by tetraphenyl porphyrin derivatives.

Photoelectron transfer from tris (hydroxymethyl) aminomethane (Tris) to methyl orange (MO) or methyl yellow (MY) as an electron acceptor was studied with α, β, γ, δ-tetraphenyl porphyrin (TPP) and α, β, γ, δ-tetraphenyl porphyrin trisulfonic acid (TPPS) as sensitizers. The reaction efficiency was reduced when the sensitizer was solubilized in heptaethyleneglycol dodecyl ether (HED) micelles. The partitioning of the sensitizers (TPP, TPPS) and the electron acceptors (MO, MY) was estimated by means of absorption spectral measurements in the micellar solution. At HED concentrations above 0.5 mM in aqueous solution, the sensitizers (TPP, TPPS) were completely solubilized in the micellar phase and thus the reaction environment was transferred from the aqueous phase to the micellar phase. The decrease of the reaction rate in the micellar environment can be explained in terms of the lower polarity in the micellar phase which inhibits charge separation in the sensitizer-acceptor excited complex (exciplex). The reaction rate of the TPPS-MO system was the highest and that of the TPP-MY system was the lowest in the micellar phase, because the former system was accommodated in a rather polar micellar environment, while the latter system was located in a less polar micellar environment. It was also observed that an increase in micellar concentration resulted in a decrease of the reaction rate. This was found to be caused by the decreases in the local concentrations of sensitizer and acceptor, not by a change of the reaction environment.