A redox-mediator pathway for enhanced multi-colour electrochemiluminescence in aqueous solution

The classic and most widely used co-reactant electrochemiluminescence (ECL) reaction of tris(2,2′-bipyridine)ruthenium(ii) ([Ru(bpy)₃]²⁺) and tri-n-propylamine is enhanced by an order of magnitude by fac-[Ir(sppy)₃]³⁻ (where sppy = 5′-sulfo-2-phenylpyridinato-C²,N), through a novel ‘redox mediator’ pathway. Moreover, the concomitant green emission of [Ir(sppy)₃]³⁻* enables internal standardisation of the co-reactant ECL of [Ru(bpy)₃]²⁺. This can be applied using a digital camera as the photodetector by exploiting the ratio of R and B values of the RGB colour data, providing superior sensitivity and precision for the development of low-cost, portable ECL-based analytical devices.

A water-soluble Ir(iii) complex is shown to enhance the ‘remote’ mechanism of the most widely used co-reactant ECL reaction of tris(2,2′-bipyridine)ruthenium(ii) with tripropylamine.     

Environment-friendly bio-materials based on cotton-carbon aerogel for strontium removal from aqueous solution

Cotton carbon aerogel was prepared and used as a new water-insoluble adsorbent to remove strontium from aqueous solution. A comprehensive study on adsorption of strontium by cotton carbon aerogel was conducted regarding the effects of initial pH, temperature, initial strontium concentration, and contact time. The adsorbent was characterized by SEM. The results of regression analysis indicated that the adsorption process largely depends on the pH and temperature. The optimum pH range for adsorption process is 5–7. The maximum removal efficiency of strontium from aqueous solution was 60.16%. Moreover, cotton carbon aerogel adsorbent has good reusability before the fifth reuse.     

Differential scanning and titration calorimetric studies of macromolecules in aqueous solution

An enormous amount of detailed information can be obtained concerning macromolecules in aqueous solution using data obtained from differential scanning and titration microcalorimetry. This claim is supported by reference to examples taken from recent work concerned with micelles (e.g. CTAB), vesicles (e.g. DOAB and DDP) and enzymes (e.g. CAT and DNA gyrase).     

Copper removal from aqueous solution using biochar: Effect of chemical activation

The main aim of this study was to test the efficiency of biochar for Cu removal from synthetic and soil solutions, respectively.The biochar was produced from brewers draff via pyrolysis. Additionally, the prepared biochar was also activated using 2 M KOH to enhance its sorption efficiency to remove Cu from both solutions. Two different aqueous solutions were prepared for these experiments: (i) a synthetic using Cu-nitrate salt with 0.01 M NaNO₃ and (ii) soil solution obtained from a Cu-contaminated soil using 0.01 M CaCl₂ leaching procedure. Batch sorption and column experiments were used to evaluate the efficiency of both biochar (BC) and activated biochar (BC_act) to remove Cu from the solutions.Results showed that both biochar samples are pure amorphous carbon and the Cu sorption is thus mainly a result of physical sorption on the biochar surface. Next, chemical activation, using 2 M KOH, significantly increased the total volume of all pores in biochar (from 0.01 ± 0.002 to 8.74 ± 0.18 mL g⁻¹). On the other hand, the BET surface area was similar for both sorbents (BC = 9.80 ± 0.62 m² g⁻¹ and BC_act = 11.6 ± 0.4 m² g⁻¹). Results also demonstrate enhanced sorption efficiency of the BC_act (10.3 mg g⁻¹) in comparison with the BC (8.77 mg g⁻¹). Additionally, enhanced Cu removal during column retention test was observed for the BC_act in both synthetic and soil solutions, respectively.In summary, the results showed that biochar prepared from brewers draff was able to remove Cu from both aqueous solutions.     

Lignite fired fly ash modified by chemical treatment for adsorption of zinc from aqueous solution

The purpose of the study described in this paper was to compare removal of Zn(II) from aqueous solutions by use of two adsorbents—alkali-modified fly ash (FAN) and alkali and dye-modified fly ash (FAN-MO). The effects of four conditions (solution pH, contact time, initial metal ion concentration, and dose of adsorbent) on removal of Zn(II) at 27 ± 5 °C were studied in batch mode. Adsorption of Zn(II) was greater at pH 4.0 for FAN (76.49 %) and at pH 5.0 for FAN-MO (24.72 %). Maximum adsorption of Zn(II) by FAN and FAN-MO was achieved after 50 min. The linear forms of the Langmuir, Freundlich, Tempkin, D–R, Harkin–Jura, and Frenkel–Halsey isotherms were used for experiments with different concentrations of the metals. Adsorption of Zn(II) ions satisfied the Langmuir isotherm model only. The adsorption capacity of both adsorbents was also investigated by column studies. Adsorption of Zn(II) ions on FAN in column studies (45.33 %) was lower than in batch mode studies. For FAN-MO, adsorption was 37.88 % in column studies, again lower than in batch mode studies. Fly ash modified by alkali had a higher adsorption capacity for Zn(II) ions than fly ash modified by alkali followed by addition of dye.     

A simple method for the production of hydrogels based on hemicellulose in aqueous solution

A simple method of bamboo hemicellulose-based hydrogel with multiple responses properties was proposed employing glow discharge electrolysis plasma (GDEP). The network of hydrogels was characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The mechanical properties, swelling, and stimuli responses were also investigated. The results showed that swelling ratio of hydrogel under 570 V and 90 s was 903.6 g/g. Too long discharge time or high discharge voltage indicated high compression stress and modulus. The hydrogels exhibited excellent sensitivity to pH and salts, which indicated their widely application such as adsorption, separation, and drug release systems.     

Aggregation behavior of gemini surfactants and their interaction with macromolecules in aqueous solution

Gemini surfactants are constructed by two hydrophobic chains and two polar/ionic head groups covalently connected by a spacer group at the level of the head groups. Gemini surfactants possess unique structural variations and display special aggregate transitions. Their aggregation ability and aggregate structures can be more effectively adjusted through changing their molecular structures compared with the corresponding monomeric surfactants. Moreover, gemini surfactants exhibit special and useful properties while interacting with polymers and biomacromolecules. Their strong self-aggregation ability can be applied to effectively influence the aggregation behavior of both polymers and biomacromolecules. This short review is focused on the performances of gemini surfactants in aqueous solutions investigated in the last few years, and summarizes the effects of molecular structures on aggregation behavior of gemini surfactants in aqueous solution as well as the interaction of gemini surfactants with polymers and biomacromolecules respectively.     

Quadrupole central transition 17O NMR spectroscopy of biological macromolecules in aqueous solution

We demonstrate a general nuclear magnetic resonance (NMR) spectroscopic approach in obtaining high-resolution (17)O (spin-5/2) NMR spectra for biological macromolecules in aqueous solution. This approach, termed quadrupole central transition (QCT) NMR, is based on the multiexponential relaxation properties of half-integer quadrupolar nuclei in molecules undergoing slow isotropic tumbling motion. Under such a circumstance, Redfield's relaxation theory predicts that the central transition, m(I) = +1/2 ? -1/2, can exhibit relatively long transverse relaxation time constants, thus giving rise to relatively narrow spectral lines. Using three robust protein-ligand complexes of size ranging from 65 to 240 kDa, we have obtained (17)O QCT NMR spectra with unprecedented resolution, allowing the chemical environment around the targeted oxygen atoms to be directly probed for the first time. The new QCT approach increases the size limit of molecular systems previously attainable by solution (17)O NMR by nearly 3 orders of magnitude (1000-fold). We have also shown that, when both quadrupole and shielding anisotropy interactions are operative, (17)O QCT NMR spectra display an analogous transverse relaxation optimized spectroscopy type behavior in that the condition for optimal resolution depends on the applied magnetic field. We conclude that, with the currently available moderate and ultrahigh magnetic fields (14 T and higher), this (17)O QCT NMR approach is applicable to a wide variety of biological macromolecules. The new (17)O NMR parameters so obtained for biological molecules are complementary to those obtained from (1)H, (13)C, and (15)N NMR studies.     

Effect of macromolecules and Triton X-100 on the triplet of aggregated chlorophyll in aqueous solution

Chlorophyll a (Chla) in aqueous solution (2-6% acetone) is present as mono- and dihydrated aggregated forms which are characterized by specific ground state absorption spectra. The amount of dihydrated form is larger in the presence of macromolecules, such as bovine serum albumin (BSA), lysozime and polyvinyl alcohol (PVA), increasing from BSA to lysozime and PVA. Chla in aqueous acetone with and without macromolecules is characterized by low fluorescence and the absence of triplet-triplet (T-T) absorption. The ratio of dihydrated to monohydrated forms is significantly influenced by triton X-100. For lower triton X-100 concentrations, i.e. smaller than the critical micelle concentration of 0.26 mM (cmc), dihydrated forms are converted into monohydrated in both aqueous acetone and the presence of BSA or lysozime. In the presence of PVA dihydrated forms appeared to be resistant to triton X-100 action. Moreover, for triton X-100 concentrations of 2-3 times higher than cmc the amount of these forms is increased with time. T-T absorption of both mono- and dihydrated Chla aggregates was not detected in the presence of [triton X-100] < cmc. The lack of T-T absorption in aqueous acetone solution as well as in the presence of macromolecules implies that the triplet lifetime of the chlorophyll aggregates is short (tauT<10 ns) and/or the quantum yield of intersystem crossing is small (<5 x 10(-3)). The Chla monomers start to be formed as solubilized in the micelle for [triton X-100] larger than cmc, showing substantial fluorescence and T-T absorption.     

A chemical model of catechol-O-methyltransferase. Methylation of 3,4-dihydroxybenzaldehyde in aqueous solution

The reaction of 3,4-dihydroxybenzaldehyde (LH2) and dimethylsulfate (DMS) to form the m- and p-O-methylated products (vanillin and isovanillin, respectively) in aqueous 2-(N-morpholino)ethane sulfonate buffer was studied kinetically. The products were determined by means of high-performance liquid chromatography. The O-methylation occurred principally at the p-hydroxyl group in the absence of divalent metal ions. In the presence of Cu(II), the m-methylation was promoted and became predominant. Zn(II) showed a similar but less pronounced effect. The effects were explained in terms of the complex formation of LH2. The second order rate constants for the m- and p-methylation of the species, LH2, CuL and CuL2-2 by DMS were calculated. The values and their ratio for the m-/p-reactions increased in the order of LH2 less than CuL less than CuL2-2. The reaction may serve as a chemical model for catechol-O-methyltransferase, which requires divalent metals and catalyzes the m-methylation.     

A fluorescent chemosensor for Hg based on naphthalimide derivative by fluorescence enhancement in aqueous solution

Naphthalimide derivative (compound 1) containing hydrophilic hexanoic acid group was synthesized and used to recognize Hg²⁺ in aqueous solution. The fluorescence enhancement of 1 is attributed to the formation of a complex between 1 and Hg²⁺ by 1:1 complex ratio (K = 2.08 × 10⁵), which has been utilized as the basis of fabrication of the Hg²⁺-sensitive fluorescent chemosensor. The comparison of this method with some other fluorescence methods for the determination of Hg²⁺ indicated that the method can be applied in aqueous solution rather than organic solution. The analytical performance characteristics of the proposed Hg²⁺-sensitive chemosensor were investigated. The chemosensor can be applied to the quantification of Hg²⁺ with a linear range covering from 2.57 × 10⁻⁷ to 9.27 × 10⁻⁵ M and a detection limit of 4.93 × 10⁻⁸ M. The experiment results show that the response behavior of 1 toward Hg²⁺ is pH independent in medium condition (pH 4.0–8.0). Most importantly, the fluorescence changes of the chemosensor are remarkably specific for Hg²⁺ in the presence of other metal ions, which meet the selective requirements for practical application. Moreover, the response of the chemosensor toward Hg²⁺ is fast (response time less than 1 min). In addition, the chemosensor has been used for determination of Hg²⁺ in hair samples with satisfactory results, which further demonstrates its value of practical applications.     

Adsorption of naphthalene on zeolite from aqueous solution

Polynuclear aromatic hydrocarbons (PAHs), which are environmental hormones and carcinogens, are viewed as the priority pollutants to deal with by many countries. Most PAHs are hydrophobic with high boiling and melting points and high electrochemical stability, but with low water solubility. Compared with other PAH species, naphthalene has less toxicity and is easily found in the environment. Thus, naphthalene is usually adopted as a model compound to examine the environmental and health aspects of PAHs. This study attempted to use an adsorption process to remove naphthalene from a water environment. The adsorption equilibrium of naphthalene on zeolite from water-butanol solution, which is a surfactant-enriched scrubbing liquid, was successfully evaluated by Langmuir, Freundlich, and linear isotherms. Among the tested kinetics models in this study (e.g., pseudo-first-order, pseudo-second-order, and Elovich rate equations), the pseudo-second-order equation successfully predicted the adsorption.     

Simulation of 59Co NMR chemical shifts in aqueous solution

59Co chemical shifts were computed at the GIAO-B3LYP level for [Co(CN)6]3-, [Co(H2O)6]3+, [Co(NH3)6]3+, and [Co(CO)4]- in water. The aqueous solutions were modeled by Car-Parrinello molecular dynamics (CPMD) simulations, or by propagation on a hybrid quantum-mechanical/molecular-mechanical Born-Oppenheimer surface (QM/MM-BOMD). Mean absolute deviations from experiment obtained with these methods are on the order of 400 and 600 ppm, respectively, over a total delta(59Co) range of about 18,000 ppm. The effect of the solvent on delta(59Co) is mostly indirect, resulting primarily from substantial metal-ligand bond contractions on going from the gas phase to the bulk. The simulated solvent effects on geometries and delta(59Co) values are well reproduced by using a polarizable continuum model (PCM), based on optimization and perturbational evaluation of quantum-mechanical zero-point corrections.     

A radiotracer study of adsorption on activated carbon cloth from aqueous solution

A study has been made on the effect of pH upon the equilibrium adsorption capacity of triethyl phosphate, dimethyl phosphate and orthophosphate on to activated carbon cloth. It is shown that for molecular phosphates no dependence upon pH exists, whilst the adsorption of ionic phosphates exhibit a strong pH dependence. These adsorption trends may be explained in terms of pKa values, ionic strength and the surface charge of the activated carbon cloth is aqueous solution.     

A self-assembled supramolecular organic material for selective extraction of uranium from aqueous solution

Journal of Radioanalytical and Nuclear Chemistry - A supramolecular organic material MA-IPA containing melamine and isophthalic acid was prepared by low-temperature hydrothermal reaction, with an...     

Decontamination of bisphenol A from aqueous solution by graphene adsorption

The decontamination of bisphenol A (BPA) from aqueous solution by graphene adsorption was investigated. The maximum adsorption capacity (q(m)) of graphene for BPA obtained from a Langmuir isotherm was 182 mg/g at 302.15 K, which was among the highest values of BPA adsorption compared with other carbonaceous adsorbents according to the literature. Both π-π interactions and hydrogen bonds might be responsible for the adsorption of BPA on graphene, and the excellent adsorption capacity of graphene was due to its unique sp(2)-hybridized single-atom-layer structure. Therefore, graphene could be regarded as a promising adsorbent for BPA removal in water treatment. The kinetics and isotherm data can be well described by the pseudo-second-order kinetic model and the Langmuir isotherm, respectively. The thermodynamic studies indicated that the adsorption reaction was a spontaneous and exothermic process. Besides, the presence of NaCl in the solution could facilitate the adsorption process, whereas the alkaline pH range and higher temperature of the solution were unfavorable.     

HPLC-DAD-MSn to investigate the photodegradation pathway of nicosulfuron in aqueous solution

The environmental interest of sulfonylurea herbicides was derived from the possibility of diffusion and penetration of these herbicides in the deepest layers of the ground, in particular in sandy or clay-poor soils, up to the ground waters; another interest of the study is their natural degradation pathway which leads to the formation of new species that are potentially more toxic and stable than the precursor herbicides. In this case, a lower persistence in the environment unfortunately does not correspond to a lower toxicity: hence, the importance of the identification of the species can be potentially formed. Here, nicosulfuron, a typical sulfonylurea herbicide, is considered in order to outline the environmental fate of the molecules generating from the simulation of one of the natural processes that can occur, i.e. photoinduced degradation. Aqueous nicosolfuron solutions underwent a simulated sun irradiation: the new species formed during the degradation process were identified by HPLC-DAD-MS/MS and a degradation pathway was proposed. The effect of temperature and the contribution of the hydrolysis were also evaluated. The use of ESI in both positive ion (PI) and negative ion (NI) mode and APCI in PI mode permits to obtain integrated information about the transformation products that can form; moreover, a study of the total ion chromatogram followed by the extraction of the SIM chromatograms of the most intense m/z signals made possible the identification of five possible photodegradation transformation products.     

A methionine-based turn-on chemical sensor for selectively monitoring Hg2+ ions in 100% aqueous solution

Dansyl-labeled methionine is synthesized by solid-phase synthesis, and found to be a highly sensitive and selective sensor for Hg(2+). The sensor sensitively detects Hg(2+) ions in aqueous solution by a turn-on response; however, the sensor detects Hg(2+) ions by a turn-off response in organic and mixed aqueous-organic solutions. We investigated the binding stoichiometry, binding constant, and binding mode of the sensor under various solvent conditions. In 100% aqueous solution, 2 : 1 complexation of the sensor with Hg(2+) ions is more favorable than 1 : 1 complexation, whereas the sensor preferentially forms a 1 : 1 complex in 100% CH(3)CN or in 50% CH(3)CN-aqueous solutions. Results reveal that the stoichiometry of the sensor-Hg(2+) complex plays an important role in the type of response to Hg(2+) ions, and that 2 : 1 complexation is required for a turn-on response to Hg(2+) ions in aqueous solution.     

Adsorption of fluoride on synthetic siderite from aqueous solution

The study has investigated the feasibility of using synthetic siderite for F⁻ removal from aqueous solution. Batch experiments were performed to test effects of adsorbent dosage, contact time, initial F⁻ concentration, temperature, solution pH, and coexisting anions on F⁻ removal. Results show that the kinetic rate of F⁻ adsorption was high in the first 2 h, and thereafter significantly decreased. The kinetic data was better fitted to the pseudo-second order kinetic model than the pseudo-first order kinetic model. In comparison with Langmuir isotherm, both Freundlich and Redlich-Peterson isotherms better described the adsorption process, which indicates that the multilayer adsorption should be involved in the process of F⁻ removal. Thermodynamic study manifests that F⁻ adsorption on synthetic siderite was spontaneous and exothermic in nature. The synthetic siderite had high adsorption capacity for F⁻ removal, which was up to 1.775 mg/g in the batch with an adsorbent dosage of 5 g/L and an initial F⁻ concentration of 20 mg/L at 25 °C. The adsorption was relatively independent on solution pH between 4 and 9. The presence of Cl⁻ and NO₃⁻ had less impact on F⁻ adsorption, while PO₄³⁻ significantly affected F⁻ removal from aqueous solution. Results of X-ray diffraction (XRD) and scanning electron microscopy (SEM) suggest that the high adsorption capacity possibly arose from both coprecipitation of ferric hydroxide with F⁻ and adsorption of F⁻ on the fresh goethite.     

Adsorption of radiocobalt on lead dioxide from aqueous solution

Adsorption of cobalt on lead dioxide from aqueous solutions has been studied in relation to shaking time, amount of adsorbent, pH, and concentration of the adsorbate. The data fitted very well Langmuir, Freundlich, and Dubinin-Radushkevich isotherms and their corresponding constants were calculated. In another set of experiments the influence of different anions and cations on the adsorption of cobalt under the optimum experimental conditions have been determined. EDTA, tartrate, citrate, thiocyanate, oxalate, U(VI), Al(III), Fe(III), Cr(III), and Th(IV), drastically reduced adsorption of cobalt. Therefore these anions and cations should be removed before adsorption of cobalt on lead dioxide. Adsorption of other metal ions on the oxide were measured under identical conditions. TheK _D values indicate that cobalt can be separated successfully from Hg(II), Ag(I), Ta(V), In(III) and Tc(VII).