Reagents In Aqueous Solution Research Articles

Immobilization of lipase on hydrophobic MOF synthesized simultaneously with oleic acid and application in hydrolysis of natural oils for improving unsaturated fatty acid production

The hydrolysis of natural oils (vegetable oils and fats) by lipase has significant applications in food and medicine. However, free lipases are usually sensitive to temperature, pH and chemical reagents in aqueous solutions, which hinders their widespread industrial application. Excitingly, immobilized lipases have been widely reported to overcome these problems. Herein, inspired by lipase interface activation, a hydrophobic Zr-MOF (UiO-66-NH2-OA) with oleic acid was synthesized for the first time in an emulsion consisting of oleic acid and water, and the Aspergillus oryzae lipase (AOL) was immobilized onto the UiO-66-NH2-OA through hydrophobic interaction and electrostatic interaction to obtain immobilized lipase (AOL/UiO-66-NH2-OA). 1H NMR and FT-IR data indicated that oleic acid was conjugated with the 2-amino-1,4-benzene dicarboxylate (BDC-NH2) by amidation reaction. As a result, the Vmax and Kcat values of AOL/UiO-66-NH2-OA were 179.61 μM﹒min−1 and 8.27 s−1, which were 8.56 and 12.92 times higher than those of the free enzyme, respectively, due to the interfacial activation. After treated at 70 °C for 120 min, the immobilized lipase maintained 52 % of its original activity, but free AOL only retained 15 %. Significantly, the yield of fatty acids by the immobilized lipase reached 98.3 % and still exceeded 82 % after seven times of recycling.

A New Flow Injection System with Merging-Zone Technique for the Determination of Copper(II) by Neocuproine Reagent in Aqueous Solution

A fast, simple, and high throughput sample merging-zone flow injection design was developed to determine copper(II) in aqueous solution. The procedure is based on the reduction of copper(II) to copper(I) by uric acid followed by a direct reaction with Neocuproine reagent (NC). The orange-yellow complex that forms absorb light at 454 nm. All conditions of the new flow injection unit were investigated. The analytical curve of copper(II) was linear with (r2) value of 0.9978, in the range of 0.4 to 40 mg/L with a detection limit of 0.1 mg/L and a quantification limit of 0.3 mg/L. the molar absorptivity was 1.661 × 105 L/mol cm and the recovery range was between 104.9 and 97%. The homemade acrylic valve was low-cost with zero dead volume and high repeatability (n = 7) with an RSD of 2.31%. The dispersion coefficient values were 1.8,1.62, and 1.31 for the concentrations of 5, 15, and 25 mg/L, respectively. The sample throughput was 69 h–1.

Charge, hydrophobic and spatial matching in the association of fluorescent reagents with ionic surfactants in aqueous solutions

The influence of charge, hydrophobicity, and spatial characteristics on the analytical signal of cationic and anionic surfactants in their association with fluorescent reagents in aqueous solutions is studied. The increase in the analytical signal of the surfactant and the shift in the position of the fluorescence wavelengths maximum with increasing contribution of the role of electrostatic interactions between the reagent particle and the ionic surfactant have been shown. The presence of extrema under conditions of hydrophobic matching in the study of the effect of hydrophobicity of the reagent and ionic surfactants on the surfactant analytical signal has been shown. The manifestation of the spatial matching between the interacting particles in the study of the influence of the spatial characteristics of the reagents and surfactants has also been shown. The influence of colloidal aggregation of associates formed in the reagent-surfactant system on the value of measurement of the analytical signal of the ionic surfactants in the methods of fluorescence and spectrophotometry has been investigated. The obtained effects made it possible to design an analytical system for the determination of sodium dodecyl sulfate with a fluorescent reagent.

Self-assembly of novel manganese (II) compounds based on bifunctional-group ligands: Synthesis, structures, and magnetic properties

Four manganese (II) compounds are obtained by the reaction of manganese salts, triazole-derivatives and auxiliary reagents in aqueous solution or mix-solvents by routine or hydrothermal reactions. X-ray crystal structure analyses reveal that a neutral 0D compound [Mn(Hmctrz)2(H2O)2] (1) (H2mctrz = 1H-1,2,4-triazole-3-carboxylic acid) displays a centro-symmetric mononuclear octahedral entity with two Hmctrz− anions and two water molecules; two neutral 2D clusters [Mn(Hdctrz)(H2O)2]n (2) (H3dctrz = 1H-1,2,4-triazole-3,5-dicarboxylic acid) and [Mn2(pbtrz)(btca)]n·4nH2O (3) (pbtrz = 1,3-bis(1,2,4-triazol-1-yl)-propane&H4btca = benzene-1,2,4,5-tetracarboxylic acid) possess layer structures with Hdctrz2− linkers (2) and Mn(II)-pbtrz-Mn(II) building blocks periodically extended by μ-btca4− connectors (3); [Mn(pbtrz)]n·nOAc·nOH (4) shows a 3D diamond-shaped cationic framework with the anion void volume of 49.2%. Nitrogenous bases are used as the auxiliary ligand in compound 3 and the temple ligand in compounds 1, 2, and 4. Compounds 1–4 show antiferromagnetic coupling that has been fitted by different models with the molecular field approximate with D = − 0.129(1) cm−1 for 1, J = − 0.354(4) cm−1 for 2 and J = − 0.696(6) cm−1 for 3, respectively. The magnetic differences can be related to different superexchange interactions transmitted by the crystal lattice and/or the zero field splitting (ZFS) of the 6A1g single-ion states of 1 and the syn-anti-COO− of 2 as well as the mixed magnetic bridges of μ1-O and μ-pbtrz-μ-COO− of 3.

New diphosphopentamolybdate (VI) ( $$\hbox {C}_{6}\hbox {H}_{14}\hbox {N})_{4}$$ C 6 H 14 N ) 4 ( $$\hbox {NH}_{4})_{2}[\hbox {P}_{2}\hbox {Mo}_{5}\hbox {O}_{23}]\cdot \hbox {H}_{2}\hbox {O}$$ NH 4 ) 2 [ P 2 Mo 5 O 23 ] · H 2 O synthesis, crystal structure, experimental and theoretical studies

The title compound (\(\hbox {C}_{6}\hbox {H}_{14}\hbox {N})_{4}(\hbox {NH}_{4})_{2}[\hbox {P}_{2}\hbox {Mo}_{5}\hbox {O}_{23}]\cdot \hbox {H}_{2}\hbox {O}\) (1) was obtained by solution method using ammonium molybdate tetrahydrate, phosphoric acid and cyclohexylamine reagents in aqueous solution. A single-crystal X-ray diffraction study shows that the compound crystallizes in triclinic crystal system with space group P-1 and cell constants \(a = 10.7178(4)\) Å, \(b= 15.0809(6)\) Å, \(c= 15.7745(9)\) Å, \(\alpha = 71.510(6){^{\circ }}\), \(\beta = 75.508(2){^{\circ }}\) and \(\gamma = 88.493(8){^{\circ }}\). Also, in this article, we report results of thermal, electrochemical and spectral studies. In addition, the majority of theoretical properties were carefully studied.

New β-octamolybdate: [Ba2(H2O)8][Ba0.5(OH)][Mo8O26]·3H2O—synthesis, characterization, Hirshfeld surface and semi-empirical calculations

The title compound [Ba2(H2O)8][Ba0.5(OH)][Mo8O26]·3H2O (1) was obtained by solution method using sodium molybdate dihydrate, ammonium metavanadate and barium chloride dihydrate reagents in aqueous solution. A single-crystal X-ray diffraction study shows that the compound crystallizes in monoclinic crystal system with space group C2/m and cell constants of a = 16.8575(10) A, b = 12.8418(9) A, c = 15.2298(10) A, β = 97.225(5)°. Also in this work, we report results of thermal, electrochemical, spectral and Hirshfeld surface studies. The majority of theoretical properties were carefully studied as well.

Sol-gel synthesis of Er3+:Y3Al5O12/TiO2[sbnd]Ta2O5/MoO2 composite membrane for visible-light driving photocatalytic hydrogen generation

By using TiO2 and Ta2O5 colloids, a stable and efficient visible-light driven photocatalyst, Er3+:Y3Al5O12/TiO2Ta2O5/MoO2 composite membrane, was successfully prepared via sol–gel dip coating method at room temperature. The XRD, FTIR, SEM, TEM and EDX results confirm that approximately spherical Er3+:Y3Al5O12 nanoparticles were embedded in TiO2Ta2O5 matrix. UV–vis absorption and PL spectra of Er3+:Y3Al5O12 were also determined to confirm the visible absorption and ultraviolet emission. The photocatalytic hydrogen generation was carried out by using methanol as sacrificial reagent in aqueous solution under visible-light irradiation. Furthermore, some main influence factors such as heat-treated temperature, heat-treated time and molar ratio of TiO2 and Ta2O5 on visible-light photocatalytic hydrogen generation activity of Er3+:Y3Al5O12/TiO2Ta2O5/MoO2 composite membrane were studied in detail. The experimental results showed that the photocatalytic hydrogen generation activity of Er3+:Y3Al5O12/TiO2Ta2O5/MoO2 composite membrane heat-treated at 550 °C for 3.0 h was highest when the molar ratio of TiO2 and Ta2O5 was adopted as 1.00:0.50. And that a high level photocatalytic activity can be still maintained after four cycles. In addition, a possible mechanism for the visible-light photocatalytic hydrogen generation of the Er3+:Y3Al5O12/TiO2Ta2O5/MoO2 membrane was proposed based on PL spectra.

Spectrophotometric Study and Analytical Applications of Iron (III)-Chelate System with (Mordant Blue-9) Reagent in Aqueous Solution

The reagent 6-(5-chloro-2-hydroxy-3-sulfophenylazo)-5-hydroxy-1-naphthalene sulfonic acid (Mordant blue – 9) is proposed as a spectrophotometric reagent for the determination of trace amounts of iron (III). The proposed chromogenic reagent is sensitive and reacts with iron to form a stable brown 1:2 (Fe (III) – reagent) complex at pH 3.75, Kst = 9.824*109 L2.mol-2. The apparent molar absorptivity of this complex was 16000 l .mol -1 cm-1 at 650 nm in aqueous solutions. Beer's law is obeyed with the range of 6 – 75 μg /25 ml i.e 0.24 – 3 ppm. The reagent is relatively selective for iron III. The importance of this work arises from that it allows quantification and determination of Iron without initial expensive and fatigue separation or extraction procedure. Different analytical validations were determined (accuracy, precision, recovery, stability of the complex, study of interferences, etc.) to demonstrate the suitability of this work for the routine quality control labs. The aim of this work was to determine iron III in aqueous solution specrtophotometrically employing mordant blue-9 reagent. The developed method was applied for the determination of Fe III in urine samples. The results agree with AAS with RSD (±0.74 - ±2.64).

Mechanisms of alkane CH-activation: The 5/6 effect, single-factor compensation effect, strongest reactant and earliest transition state. A puzzle of Shilov reaction

The results on the investigation of alkane activation kinetics and mechanisms in aqueous and acidic media, including theoretical and experimental approaches to the problem, proposed by the author are summarized. The new concepts are introduced: a “direct kinetic study of CH activation”, “visible and hidden reagent preactivation”, the “strongest reactant and earliest transition state” (ETS), the “5/6 effect” (the ratio of CH bonds splitting constant rates in the с-C5H10/с-C6H12 couple), “single-factor compensation effect” (SCE), and a “refined compensation temperature”. The compensation effect (CE) exists in reality, but it is necessary to exclude the influence side factors, for example, to go from rate constants to the 5/6 effect to observe its purest form. The 5/6-CE combination as an example SCE is a new instrument for studying CH-activation mechanisms. Temperature dependences of (5/6) values for the reagents in aqueous solution (PtII, MnO4−, HMnO4, HOCl, HOONO, HVO2 – RuIV, OH, SO4−) and sulfuric acid (PdII, HgII, CrO3, MnIII, CoIII, NO2+, OH+, 1-adamantyl cation, C14H11+, СН2OH+, SO3H+) are found. The only influencing factor on the (5/6) value is conformational strain difference in the C5 and C6 rings, which in a series of one-type reactions decreases with increasing the reagent activity. Four mechanisms are revealed: H-atom abstraction by anionic (I−), uncharged (I0) and cationic (I+) oxygen-centered “O-reactants”, and a bifunctional incorporation into CH bond of electrophilic cation – base adduct (II+). Various SCE lines (the entropy change versus enthalpy changing) for these groups are found. They converge in a “SCE pole” (the first example of ETS). Features of these mechanisms, differences of PtII, PdII, HgII acidocomplexes as the reagents and a surprising similarity between the Shilov reactant PtIICl3(H2O) and OH radicals in the water are discussed. The probable general cause of CEs in various processes is compensation effects in thermodynamics of interparticle interactions.

Enhanced visible-light photocatalytic hydrogen evolution activity of Er3+:Y3Al5O12/PdS–ZnS by conduction band co-catalysts (MoO2, MoS2 and MoSe2)

Several conduction band co-catalysts (CBCOs), MoO2, MoS2 and MoSe2, were prepared to improve the visible-light photocatalytic hydrogen evolution activity of Er3+:Y3Al5O12/PdS–ZnS from water splitting, in which the PdS is a valence band co-catalyst (VBCO) used to facilitate the photo-generated hole transfer and the Er3+:Y3Al5O12 is an up-conversion luminescence agent from visible light to ultraviolet light used to provide the ultraviolet light satisfying the energy demands of wide band-gap ZnS photocatalyst. XRD, SEM, TEM and EDX analyses were employed to confirm the morphology, microstructure and composition of the prepared photocatalysts. UV–vis absorption and PL spectra were also determined to explore luminescence effect of the Er3+:Y3Al5O12. The visible-light photocatalytic hydrogen evolution activity of the prepared photocatalysts was evaluated by using Na2S and Na2SO3 as sacrificial reagents in aqueous solution under visible light irradiation. The influential factors such as contents of CBCOs (MoO2, MoS2 and MoSe2) and visible-light irradiation time on visible-light photocatalytic hydrogen evolution of Er3+:Y3Al5O12/PdS–ZnS–MoX2 (X = O, S and Se) were investigated in detail. Particularly, Er3+:Y3Al5O12/PdS–ZnS–MoSe2 with 0.30 wt% MoSe2 shows the highest photocatalytic hydrogen evolution activity.

Solubilization of 4-(2-Pyridylazo)resorcinol in hydrophobic–hydrophilic ionic liquids and extraction of heavy metal ions from aqueous solutions

The distribution of 4-(2-pyridylazo)resorcinol, PAR (5 × 10–4–1 × 10–2 M) in the systems tetraoctylammonium N-lauroylsarcosinate (TOALS)–water and trioctylmethylammonium salicylate (TOMAS)–water is studied. It is shown that the distribution coefficient of PAR does not depend on the ionic state of the reagent in aqueous solution at pH 2.3–11.8; the logD values are 3.5 and 3.7 (Vo: Vw = 1: 20) for TOALS and TOMAS, respectively. The conditions for quantitative extraction of the ions of cadmium(II), lead(II), cobalt(II), copper(II), and zinc(II) in TOALS and TOMAS in the presence of 4-(2-pyridylazo)resorcinol are determined.

Chemo and regioselective serendipitous electrochemically initiated spirocyclization of caffeic acid esters with barbituric acid derivatives

An interesting sequence of oxidation/Michael addition/oxidation/spirocyclization is observed in the electrolysis of caffeic acid esters in the presence of barbituric acid derivatives leading to the synthesis of a series of novel spirocycles. In an experimentally simple and clean procedure, the electrolyses proceed via a domino of electrochemical (E) and chemical (C) events with employing electrons as the only reagents in aqueous solution without introducing any catalyst or oxidant. From mechanistic point of view, a new type of domino mechanism (ECECi, Ci=spirocyclization) is proven with a unique Ci phenomenon at final step. Also, in light of experimental and theoretical NMR investigations, highly chemo and regioselectivities have been detected in these synthetic electrolyses.

Synthesis of Luminescent Ag Nanoclusters with Antibacterial Activity

This paper focuses on the synthesis of novel Ag nanoclusters (NCs) using DHLA as capping reagents in aqueous solution by a photoreduction method. Luminescence studies indicated that the DHLA‐Ag NCs exhibited strong blue emission with maximum peak at 480 nm. The maximum emission of the NCs can be greatly improved with irradiating time by around 15‐fold from 3 h to 67 h. By means of mycelium growth rate, the results showed that the Ag NCs with smaller sizes had a good antimicrobial effect.

A simple sonochemical approach for synthesis of selenium nanostructures and investigation of its light harvesting application

Selenium (Se) nanostructures were synthesized by a sonochemical method using SeCl4 as a new precursor for Se nanostructures. Moreover, hydrazine, potassium borohydride, and thioglycolic acid were used as reducing reagents in aqueous solution. Ultrasonic power, irradiation time, reducing agent, solvent, HCl, NaOH, and the surfactant were changed in order to investigate the effect of preparation parameters on the morphology and particle size of selenium. The obtained Se with different morphologies and sizes was characterized by XRD, SEM, TEM, EDS, and DRS. The selenium nanostructures exhibited enhanced photocatalytic activity in the degradation of methylene blue (MB) under visible light irradiation. Furthermore, to examine the solar cell application of as-synthesized selenium nanostructure, FTO/TiO2/Se/Pt-FTO and FTO/Se/CdS/Pt-FTO structures were created by deposited selenium film on top of the TiO2 layer and FTO glass prepared by Doctor’s blade method, respectively.

Direct electrosynthesis of a series of novel caffeic acid analogues through a clean and serendipitous domino oxidation/thia-Michael reaction

A series of novel caffeic acid analogues have been synthesized in an experimentally simple electrochemical procedure employing electrons as the only reagents in aqueous solution without introducing any catalyst or oxidant. It has been shown that the reactions proceed via a domino of electrochemical and chemical events (EC mechanism) with an interesting regioselectivity in the formation of arylsulfonyl-functionalized N-caffeoyl amides and caffeate esters. All products were purely obtained at the surface of anode (carbon rods) in excellent yields and no extra purification was needed. Structural characterization of these novel compounds was also performed using various spectroscopic techniques: FT-IR, 1HNMR, 13CNMR and HR-mass.

Visible Spectrophotometric Determination of Ganciclovir in its Pharmaceutical Formulations Using Quinalizarin Reagent

A simple, rapid and sensitive spectrophotometric method for the determination of Ganciclovir was developed. The method is based on the proton transfer reaction of drug with quinalizarin reagent in aqueous solution to form violet product which shows maximum absorbance at 560 nm. Beer's law was obeyed in the concentration range 1-20 µg.mL-1 with an average recovery (accuracy) of 99.02% and precision (RSD) of less than 2.0%. The molar absorbtivity was 8.93x103 l.mol-1.cm-1 with LOD of 0.21 µg.mL-1 and LOQ of 0.71 µg.mL-1. The proposed method was further applied to the determination of the drug in pharmaceutical formulations as an injection and capsule and the results were comparable with the certified values of pharmaceutical formulations.

A quantitative assessment of the production of ˙OH and additional oxidants in the dark Fenton reaction: Fenton degradation of aromatic amines

This paper reports the results of a kinetic study into the transformation of 2,4- and 3,4-dichloroaniline (2,4-DCA, 3,4-DCA) and of methyl yellow (MY) with the Fenton reagent in aqueous solution. All the substrates can be degraded in the presence of Fe(II) + H2O2, but the reaction between Fe(II) and H2O2 causes substrate degradation and Fe(II) oxidation within seconds under the adopted conditions. The HPLC, GC-MS and IC analyses only allow the monitoring of the reaction after all Fe(II) has been consumed, when degradation proceeds more slowly via Fe(III) reduction to Fe(II). Substrate degradation in the first part of the reaction was studied by stopped-flow spectrophotometry, using MY as substrate. The results are consistent with a reaction involving ˙OH, where both Fe(II) and H2O2 compete with MY for the hydroxyl radical. However, the experimental data indicate that ˙OH is unlikely to be the only product of the reaction between Fe(II) and H2O2. Another species, possibly the ferryl ion (FeO2+), is formed as well but has a negligible role in MY degradation. The Fenton reaction would thus yield both ˙OH (about 60% at pH 2) and ferryl (about 40%), and the 60 : 40 branching ratio between ˙OH and the other species is compatible with additional data here reported concerning the degradation of 2,4-DCA and 3,4-DCA in the first ferrous step of the Fenton reaction. The reported findings will hopefully indicate a way out of a long-lasting controversy concerning the mechanism of the Fenton process, also suggesting an approach to quantitatively determine the formation yields of the reactive species as well as a strategy to identify the reactant that is actually involved in substrate transformation.

A New Spectrophotometric Reagent for Fe(III): 2‐(2,3‐Dihydroxy‐4‐oxocyclobut‐2‐enylidene) Hydrozinecarbothiamide and Its Application in Real Samples

A new reagent 2‐(2,3‐dihydroxy‐4‐oxocyclobut‐2‐enylidene) hydrozinecarbothiamide has been synthesized and used for developing a simple spectrophotometric method for the determination of Fe(III) which is based on a 2 : 1 complex formation between Fe(III) and new reagent in aqueous solution. The method is optimized in terms of the pH value, amount of reagent required, ionic strength, and stability of the complex, sensitivity, linearity, and tolerance limits of various foreign ions. The complex is a red‐brown chelate, with λmax = 465 nm at pH = 3 (ε = 1.95 × 103 L·mol−1·cm−1). The ionic strength was kept constant at 0.02 by adding appropriate amounts of NaCl solution. The calibration curve is linear in the concentration range from 0.27–33.50 μg·mL−1. The effects of foreign ions on the determination of Fe(III) were investigated in order to assess the selectivity of the method. The method was applied in determination of Fe(III) in tap water, cow milk, and human serum.

Silver-Catalyzed Decarboxylative Fluorination of Aliphatic Carboxylic Acids in Aqueous Solution

Although fluorinated compounds have found widespread applications in the chemical and materials industries, general and site-specific C(sp(3))-F bond formations are still a challenging task. We report here that with the catalysis of AgNO(3), various aliphatic carboxylic acids undergo efficient decarboxylative fluorination with SELECTFLUOR(®) reagent in aqueous solution, leading to the synthesis of the corresponding alkyl fluorides in satisfactory yields under mild conditions. This radical fluorination method is not only efficient and general but also chemoselective and functional-group-compatible, thus making it highly practical in the synthesis of fluorinated molecules. A mechanism involvinig Ag(III)-mediated single electron transfer followed by fluorine atom transfer is proposed for this catalytic fluorodecarboxylation.

Synthesis, Characterization and Photocatalytic Properties of MnTiO3-Zeolite-Y Nanocomposites

MnTiO3-Zeolite-Y nanocomposites were synthesized with 5-10-20% (w/w) of MnTiO3 by stearic acid gel method. Then, the gels were calcined at 900 °C for 4 hours and the resulted spectra were investigated at 20% (w/w) concentration. Also, the presence of rhombohedral phase of MnTiO3 in Zeolite-Y matrix was confirmed by XRD, SEM, EDX and BET. The VSM results showed the antiferromagnetic properties for the 20% nanocomposite. The photocatalytic activity of the nanocomposites was finally evaluated by degradation of methylene blue and calcon reagents in aqueous solution.