Sorptive potential of sunflower stem for Cr(III) ions from aqueous solutions and its kinetic and thermodynamic profile

The sorptive potential of sunflower stem (180-300 μm) for Cr(III) ions has been investigated in detail. The maximum sorption (≥85%) of Cr(III) ions (70.2 μM) has been accomplished using 30 mg of high density sunflower stem in 10 min from 0.001 M nitric and 0.0001 M hydrochloric acid solutions. The accumulation of Cr(III) ions on the sorbent follows Dubinin-Radushkevich (D-R), Freundlich and Langmuir isotherms. The isotherm yields D-R saturation capacity X_m = 1.60 ± 0.23 mmol g⁻¹, β = −0.00654 ± 0.00017 kJ² mol⁻², mean free energy E = 8.74 ± 0.12 kJ mol⁻¹, Freundlich sorption capacity K_F = 0.24 ± 0.11 mol g⁻¹, 1/n = 0.90 ± 0.04 and of Langmuir constant K_L = 6800 ± 600 dm³ mol⁻¹ and C_m = 120 ± 18 μmol g⁻¹. The variation of sorption with temperature (283-323 K) gives ΔH = −23.3 ± 0.8 kJ mol⁻¹, ΔS = −64.0 ± 2.7 J mol⁻¹ K⁻¹ and ΔG_298k = −4.04 ± 0.09 kJ mol⁻¹. The negative enthalpy and free energy envisage exothermic and spontaneous nature of sorption, respectively. Bisulphate, Fe(III), molybdate, citrate, Fe(II), Y(III) suppress the sorption significantly. The selectivity studies indicate that Cr(III), Eu(III) and Tb(III) ions can be separated from Tc(VII) and I(I). Sunflower stem can be used for the preconcentration and removal of Cr(III) ions from aqueous medium. This cheaper and novel sorbent has potential applications in analytical and environmental chemistry, in water decontamination, industrial waste treatment and in pollution abatement. A possible mechanism of biosorption of Cr(III) ions onto the sunflower stem has been proposed.     

Liquid-liquid-liquid phase microextraction of aromatic amines in water using crown ethers by high-performance liquid chromatography with monolithic column

Liquid-liquid-liquid phase microextraction (LLLME) coupled with high-performance liquid chromatography (HPLC) for the analysis of some aromatic amines is described. These compounds were extracted from 4.0 mL aqueous sample that adjusted to pH 13 with, NaOH-NaCl buffer solution (donor phase, P₁) into an organic phase (P₂) 150 μl benzyl alcohol and ethyl acetate (2:1) and then back extracted into a microdrop of aqueous acceptor phase (P₃), adjusted at pH 2, with Na₂HPO₄-H₃PO₄ buffer solution. The extraction time, T₁ (from P₁ to P₂) was 20 min and T₂ (from P₂ to P₃) was 1 min. Different crown ethers as complexing agents for amines were added to the acceptor phase to improve the extraction time. Factors such as organic solvents, extraction times, and addition of crown ethers to acceptor phase and stirring rate were optimised. The method was applied for determination of aromatic amines in wastewater samples. Enrichment factors ranged from 184.5 to 389.7. The linearity range was from 3 to 1000 ng/ml and the detection limits varied from 0.8 to 1.80 ng/ml. Relative standard deviations (%, n = 5) were found (at S/N 3) in the range of 1.9 to 10.1. All experiments were carried out at room temperature, 22 ± 0.5 °C.     

Fullerene‐Catalyzed Reduction of Azo Derivatives in Water under UV Irradiation

Metal‐free fullerene (C₆₀) was found to be an effective catalyst for the reduction of azo groups in basic aqueous solution under UV irradiation in the presence of NaBH₄. Use of NaBH₄ by itself is not sufficient to reduce the azo dyes without the assistance of a metal catalyst such as Pd and Ag. Experimental and theoretical results suggest that C₆₀ catalyzes this reaction by using its vacant orbital to accept the electron in the bonding orbital of azo dyes, which leads to the activation of the N?N bond. UV irradiation increases the ability of C₆₀ to interact with electron‐donor moieties in azo dyes.     

Determination of chlorophenols in environmental water samples using directly suspended droplet liquid-liquid-liquid phase microextraction prior to high-performance liquid chromatography

A new sample preparation method named directly suspended droplet liquid-liquid-liquid phase microextraction was used in this research for determination of three chlorophenols in environmental water samples. The analytes (2-chlorophenol, 3-chlorophenol and 4-chlorophenol) were extracted from 4.5?mL acidic donor phase, (pH 2, P1) into an organic phase, 350?µL?of benzene/1-octanol (90?:?10 v/v, P2) and then were back-extracted into a 7?µL droplet of an basic (pH 13) aqueous solution (acceptor phase, P3). In this method, contrary to the ordinary single drop liquid-phase microextraction technique, an aqueous large droplet is freely suspended on the surface of the organic solvent, without using a microsyringe as supporting device. This aqueous microdroplet is delivered at the top-centre position of an immiscible organic solvent which is laid over the aqueous donor sample solution while the solution is being agitated. Then, the acceptor phase containing chlorophenols was withdrawn back into a HPLC microsyringe and neutralised by adding of 7?µL HCl 0.1?M. The total amount was eventually injected into the HPLC system with UV detection at 225?nm for further analysis. Parameters such as the organic solvent, phases volumes, extraction and back-extraction times, stirring rate and pH values were optimised. The calibration graphs are linear in the range of 10–2000?µg?L^?1 with r?≥?0.9973. The enrichment factors were ranged from 115 to 170, and the limit of detection (LOD, n?=?7) varied from 5 to 10?µg?L^?1. The relative standard deviations (RSDs, n?=?5) were found 6.8 to 7.4 at S/N?=?3. All experiments were carried out at room temperature, (22?±?0.5°C).     

On Difference Fields with Quantifier Elimination

This paper proves that a difference field (E, ) admits quantifierelimination if and only if E is an algebraically closed field,and is an integer power of the Frobenius automorphism. 1991Mathematics Subject Classification 03C60, 12H10.     

BEST PROXIMITY POINT THEOREMS FOR SINGLE- AND SET-VALUED NON-SELF MAPPINGS

We study the existence of best proximity points for single-valued non-self map-pings. Also, we prove a best proximity point theorem for set-valued non-self mappings in metric spaces with an appropriate geometric property. Examples are given to support the usability of our results.     

Solving nonlinear parabolic PDEs via extended hybrid BDF methods

The details of new methods based on backward differentiation formulas (BDF) for the MOL solution of one-dimensional nonlinear time dependent PDEs are presented. In these extended hybrid BDF methods, we say EHBDF, one additional stage point (or off-step point) together with one step point have been used in the first derivative of the solution. All presented methods, of order p, p = 2,3,..., 12, are A(α)-stable whereas they have wide stability regions comparing with those of some known methods such as BDF, extended BDF (EBDF) and modified EBDF (MEBDF) methods.     

Proximal Weakly Contractive and Proximal Nonexpansive Non-self-Mappings in Metric and Banach Spaces

In this work, we consider two classes of non-self-mappings, which are called proximal weakly contractive and proximal nonexpansive mappings, and study the existence of solutions of a minimization problem. Existence results of best proximity points for these two classes of non-self-mappings in metric and Banach spaces are also obtained.     

Forced Folding of a Disordered Protein Accesses an Alternative Folding Landscape

Intrinsically disordered proteins (IDPs) are involved in diverse cellular functions. Many IDPs can interact with multiple binding partners, resulting in their folding into alternative ligand‐specific functional structures. For such multi‐structural IDPs, a key question is whether these multiple structures are fully encoded in the protein sequence, as is the case in many globular proteins. To answer this question, here we employed a combination of single‐molecule and ensemble techniques to compare ligand‐induced and osmolyte‐forced folding of α‐synuclein. Our results reveal context‐dependent modulation of the protein′s folding landscape, suggesting that the codes for the protein′s native folds are partially encoded in its primary sequence, and are completed only upon interaction with binding partners. Our findings suggest a critical role for cellular interactions in expanding the repertoire of folds and functions available to disordered proteins.     

Synthesis and application of a novel solid-phase microextraction adsorbent: hollow fiber supported carbon nanotube reinforced sol-gel for determination of phenobarbital

The present study reports the development, validation and application of a new green liquid chromatographic method for the determination of glutathione (GSH) in vegetable samples. In this work we introduce—for the first time—ethyl propiolate (EP) as an advantageous post-column derivatization reagent for thiolic compounds. GSH (t_R = 6.60 min) and N-acetylcysteine (NAC, internal standard) (t_R = 11.80 min) were separated efficiently from matrix endogenous compounds by using a 100% aqueous mobile phase (0.1%, v/v CH₃COOH in 1 mmol L⁻¹ EDTA, Q_V = 0.5 mL min⁻¹) and a Prevail^® reversed phase column that offers the advantage of stable packing material in aqueous mobile phases. The parameters of the post-column reaction (pH, amount concentration of the reagent, flow rates, length of the reaction coil and temperature) were studied. The linear determination range for GSH was 1–200 μmol L⁻¹ and the LOD was 0.1 μmol L⁻¹ (S/N = 3). Total endogenous GSH was determined in broccoli, potato, asparagus and Brussels sprouts using the standards addition approach. The accuracy was evaluated by both recovery experiments (R = 91–110%) and comparison to an o-phthalaldehyde/glycine corroborative post-column derivatization fluorimetric method.