Application of boehmite as a fiber coating for headspace solid-phase microextraction of chlorophenols from aqueous samples.

In this paper, the extraction of chlorophenols from water samples was carried out using high surface area boehmite nanoparticles as a sorbent. The surfactant-free process employed to make the nano-boehmite used in this work was simple, green, and efficient. The proposed approach was based on headspace solid-phase microextraction, followed by GC-ECD for the determination of analytes. In situ derivatization of analytes was performed with acetic anhydride in a basic medium. Various effective parameters, including the amount of derivatization reagent, ionic strength, desorption temperature and time, extraction temperature, equilibrium time, and extraction time were studied. Under optimal conditions, the linear dynamic range was 0.05-5.0 µg L-1 for 2,4-dichlorophenol and 2,6-dichlorophenol and 0.003-0.1 µg L-1 for 2,4,6-trichlorophenol. A low limit of detection (0.75 × 10-3-15 × 10-3 µg L-1), and relative standard deviations for real samples (RSDs) <10% were obtained. The precision (as intra- and inter-day RSDs) was between 1.2 and 9.8%. In comparison to commercial fibers (CAR-PDMS, 85 µm), this fiber showed a greater extraction efficiency. Various water samples were subjected to extraction by the proposed method. The recoveries ranged from 90 to 110%.

Sustainable catalysts for efficient triazole synthesis: an immobilized triazine-based copper-NNN pincer complex on TiO2.

The multistep synthesis of a hybrid material based on a TiO2 core with an immobilized triazine-based copper(II)-NNN pincer complex is reported. The formation of the material was confirmed by FT-IR spectroscopy and elemental and thermogravimetric analyses, and the loading by copper ions was quantified by ICP/OES analysis. The properties of the hybrid material were further investigated by X-ray photoelectron spectroscopy (XPS), contiuous wave electron spin resonance (CW-ESR), UV-vis spectroscopy, and argon sorption. Efficient and regioselective synthesis of 1,4-disubstituted 1,2,3-triazoles was achieved by employing the hybrid material as a catalyst in a mixture of H2O/EtOH as a green solvent with excellent catalytic activity with a TOF up to 495 h-1 at 50 °C. The reusability of the prepared hybrid material in the catalytic reaction was possible over five consecutive runs without significant loss of catalytic activity. The described method represents an effective way to ensure sustainable use of pincer complexes in catalytic systems by immobilizing them on solid supports, resulting in a hybrid organic-inorganic catalyst platform.

AMBER Force Field Parameters for Cobalt-Containing Biological Systems: A Systematic Derivation Study.

In the present work, the parameterization of a set of cobalt-containing systems has been performed to create a comprehensive library for bonding parameters of biological Co-containing systems. A standard process for the extraction and validation of parameters was employed, which could be used to create force field parameters for the other metal-containing systems. All protein data banks were searched to extract common chemical groups in bonding with cobalt, and finally, 16 structures were designed to represent the binding model of the chemical moieties with cobalt. The Hessian matrix of each structure was computed at the B3LYP/6-311++G(2d,2p) level of theory and the Seminario method was employed to compute cobalt bond stretching and angle bending parameters. Validation of the derived parameters was performed using structural minimization and molecular dynamics (MD) simulations of four models. Further validation was performed using an extensive MD simulation on carbonic anhydrase II as a common cobalt-containing metalloprotein. The results demonstrated that among models, the bonded model in combination with the RESP charges can produce the most reliable and accurate structural conformations for the metal site of cobalt-containing systems.

A naphthylamide based fluorescent probe for detection of Al3+, Fe3+, and CN- with high sensitivity and selectivity.

A naphthylamide based fluorescent chemosensor, N,N'-(1,2-phenylene)bis(1-hydroxy-2-naphthamide) (H4L), for detection of Fe3+ and Al3+ cations as well as CN- anion is reported. This compound has been synthesized by a novel and facile synthetic method with high yield and characterized by FT-IR, 1H NMR, elemental analysis, and UV-Vis spectroscopy. It could detect Fe3+ and Al3+ ions in different media with different excitation and emission wavelengths. In DMSO solution, H4L showed selective ON-OFF quenching of its 451 nm emission in the presence of Fe3+. On the other hand, in DMF solution, H4L exhibited selective OFF-ON fluorescence upon the addition of Al3+, the intensity at 429 nm increases drastically by 24-fold. Also, among the anions, the probe can selectively distinguish CN- by deprotonation of OH and NH groups, as proved by 1H NMR titration. TD-DFT calculation supports the UV-Vis and fluorescence measurements of the chemosensor.

Simple and green synthesis of carbon dots (CDs) from valerian root and application of modified mesoporous boehmite (AlOOH) with CDs as a fluorescence probe for determination of imipramine.

A novel, sensitive, rapid, and simple fluorescent probe has been developed based on green-synthesized carbon dots (CDs). In this work, CDs have been synthesized from valerian root by hydrothermal method. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) results confirm the formation of CDs with sizes of less than 10 nm. Fluorescence quenching of CDs was due to the aggregation of the negative charges of CDs with the positive charge of imipramine (IMI) and was then used as the signal for determination of IMI. In addition, the cytotoxicity of CDs was determined using the MTT assay. The probe responses under optimum conditions were linear in the range of 1.0-200.0 ng mL-1 with a limit of detection of 0.6 ng mL-1. Afterwards, mesoporous boehmite (MB) was modified with synthesized CDs (CDs/MB). TEM images confirmed MB modification with CDs. In this case, the variations in the fluorescence signal for different concentrations of IMI increased leading to the higher sensitivity for IMI detection. The limit of detection and linear range for determination of IMI with CDs/MB were obtained as 0.2 and 0.5-200.0 ng mL-1, respectively. To evaluate the fluorescent probe, IMI was measured in real samples. Graphical abstract.

Ultrasonic-assisted synthesis of novel nanocomposite of poly(vinyl alcohol) and amino-modified MCM-41: A green adsorbent for Cd(II) removal.

Amino-modified MCM-41/poly(vinyl alcohol) nanocomposite (M-MCM-41/PVOH NC) was developed for the adsorption of Cd(II) from aqueous media. M-MCM-41/PVOH NC was prepared through ultrasonic-assisted and simple blending procedure with economical and environmentally friendly polymer. The as-prepared adsorbent was characterized by FT-IR, TEM, FE-SEM and TGA. The contact time, solution pH and initial concentration of Cd(II) were found to affect the adsorption of Cd(II) from aqueous media. Kinetic studies were carried out and pseudo-first-order (PFO), pseudo-second-order (PSO), Elovich, and intra-particle diffusion (IPD) reaction kinetic models were examined. The kinetic results revealed that the adsorption of Cd(II) onto M-MCM-41/PVOH NC followed PSO kinetic model and is a chemical adsorption. The equilibrium adsorption data were evaluated by different isotherms viz. Langmuir, Freundlich, and Dubinin Radushkevich (D-R) equations. The equilibrium data fitted better with the Langmuir isotherm and the maximum adsorption capacity of M-MCM-41/PVOH NC at 298K was calculated to be 46.73mgg-1 for Cd(II) on a typical saturated monomolecular layer with a fixed number of localized adsorption sites.

Study on thermal, mechanical and adsorption properties of amine-functionalized MCM-41/PMMA and MCM-41/PS nanocomposites prepared by ultrasonic irradiation.

In this study, two common industrial polymers, poly(methyl methacrylate) (PMMA) and polystyrene (PS), were incorporated into amine-functionalized MCM-41 mesoporous silica as reinforcement agents via an ultrasonic assisted method as a facile, fast, eco-friendly, and versatile synthetic tool. Amino functionalization of MCM-41 were performed by 3-aminopropyl triethoxysilane as a coupling agent and it is denoted as APTS-MCM-41. The obtained nanocomposites (NCs), APTS-MCM-41/PMMA and APTS-MCM-41/PS, were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning and transmission electron microscopies (SEM and TEM), and thermogravimetric analysis (TGA). Their mechanical properties were also probed via stress-strain curves and improved tensile properties were observed in the NCs relative to the neat polymers. Additionally, APTS-MCM-41/PMMA exhibited better mechanical properties than APTS-MCM-41/PS. Sorption studies were carried out on the two NCs and the effect of different process parameters, namely, pH, contact time, and initial Cd(II) concentration investigated in batch mode. Pseudo-second order and intraparticle diffusion models explain the Cd(II) kinetics more effectively for APTS-MCM-41/PMMA and APTS-MCM-41/PS, respectively. The adsorption isotherm data fitted well to Langmuir isotherm for both NCs and the maximum monolayer adsorption capacities were found to be 24.75mg/g and 10.42mg/g for APTS-MCM-41/PMMA and APTS-MCM-41/PS, respectively. The results demonstrate that the NCs show potential for use in adsorption of heavy metal ion such as Cd(II) from aqueous media.

A facile, green and efficient surfactant-free method for synthesis of aluminum nanooxides with an extraordinary high surface area.

Nano boehmite with unprecedented high surface area and pore volume (802 m(2) g(-1), 2.35 cm(3) g(-1)) was prepared using a facile, green and efficient surfactant-free synthesis method. The structure of the material is characterized by the presence of plates with varying thicknesses and morphologies. The calcined samples show curved and rolled plates with a nanotube-like appearance.

Structural and spectroscopic characterizations of aluminum phenoxide.

A synthetic route to obtain crystalline aluminum phenoxide was established. Its molecular structure in solid-state and solution is unambiguously determined by single-crystal X-ray diffraction and (1)H, (13)C and (27)Al NMR spectroscopy. The single-crystal X-ray analysis revealed the presence of the dimeric THF adduct [Al(OPh)3·THF]2 with a disordered trigonal bipyramidal geometry at the aluminum atom which is bonded to a THF ligand, two terminal and two bridging phenoxy groups (OPh). The solution behavior of the title compound was investigated by (27)Al NMR in non-coordinating (CDCl3) as well as coordinating (THF) solvents at different temperatures. The obtained results indicate the presence of four- and five-coordinate species in solution.

Structural and spectroscopic characterizations of tetra-nuclear niobium(V) complexes of quinolinol derivatives.

Reactions between niobium ethoxide and 8-hydroxy-2-methylquinoline or 5-chloro-8-hydroxyquinoline have been explored. Two new tetranuclear heteroleptic niobium complexes containing oxo, ethoxo, and quinolinate chelate rings have been synthesized and characterized by (1)H, (13)C and (93)Nb NMR, UV-Vis, and FT-IR spectroscopies, and single-crystal X-ray diffraction. The molecular structures of the niobium complexes, [Nb4(µ-O)4(µ-OEt)2(ONC10H8)2(OEt)8] (I) and [Nb4(µ-O)4(µ-OEt)2(ONC9H5Cl)2(OEt)8] (II), are composed of a pair of edge-sharing bioctahedral moieties in which connected via two almost linear oxo-bridges, with a large difference in the NbO distances. Single-crystal structures showed both complexes are centrosymmetric and contain two distinct Nb centers, and results confirmed by observation of two niobium signals in the (93)Nb NMR spectra of complexes.

Chiral vanadium(V) complexes with 2-aminoglucose Schiff-base ligands and their solution configurations: synthesis, structures, and DFT calculations.

The sugar-modified Schiff-base ligands derived from benzyl 2-deoxy-2-salicylideneamino-α-D-glucopyranoside (H2L(5-Br) and H2L(3-OMe)) were used to prepare the chiral oxidovanadium(V) complexes [VO(L(5-Br))(OMe)] (1) and [VO(L(3-OMe))(OMe)] (2) which can be isolated from a methanol solution as the six-coordinate complexes with an additional methanol ligand [VO(L(5-Br))(OMe)(MeOH)] (1-MeOH) and [VO(L(3-OMe))(OMe) (MeOH)] (2-MeOH). Both complexes crystallize in the orthorhombic space group P2(1)2(1)2(1) together with two solvent molecules of methanol as 1-MeOH·2MeOH and 1-MeOH·2MeOH. In both crystal structures, only diastereomers with A configuration at the chiral vanadium centre (OC-6-24-A) are observed which corresponds to an cis configuration of the oxido group at the vanadium centre and the benzyl group at the anomeric carbon of the sugar backbone. Upon recrystallization of 2-MeOH from chloroform, the five-coordinate complex 2 was obtained which crystallizes in the monoclinic space group P2(1) with one co-crystallized chloroform molecule (2·CHCl3). For the chiral vanadium centre in 2·CHCl3, a C configuration (SPY-5-43-C) is observed which corresponds to an trans structure as far as the orientations of the oxido and benzyl groups are concerned. (1)H and (51)V NMR spectra of 1 and 2 indicate the presence of two diastereomers in solution. Their absolute configurations can be assigned based on the magnetic anisotropy effect of the oxidovanadium group. This effect leads to significant differences for the (1)H NMR chemical shifts of the H-2 (1.1 ppm) and H-3 protons (0.3 ppm) of the glucose backbone of the two diastereomers, with the downfield shift observed for the H-2 proton of the C-configured and the H-3 proton of the A-configured diastereomer at the vanadium centre. For 1 and 2 the difference between the (51)V NMR chemical shifts of the two diastereomers is 30 and 28 ppm, respectively. Also in the (13)C NMR significant chemical shift differences between the two diastereomers are observed for the carbon atoms C2 (2 ppm) and C3 (4 ppm). DFT calculations of the NMR chemical shift parameters have been performed which are in good agreement with the experimental data. Moreover, the isomerization mechanism between the diastereomers is analysed on the basis of DFT calculations which indicate the required presence of methanol molecules as protic donors.

A single source precursor for low temperature processing of nanocrystalline MgAl2O4 spinel: synthesis and characterization of [MgAl2(µ3-O)(µ2-O(i)Pr)4(O(i)Pr)2]4.

A novel polynuclear single-source precursor was prepared and characterized by single-crystal X-ray diffraction and multinuclear NMR spectroscopy. Nano-crystalline MgAl(2)O(4) spinel was synthesized via sol-gel processing of [MgAl(2)(µ(3)-O)(µ(2)-O(i)Pr)(4)(O(i)Pr)(2)](4). XRD, TGA-DSC and HRTEM confirmed the formation of a spinel phase at 475 °C, a temperature lower than any known processing temperature for MgAl(2)O(4).

Two polymorphs of a lead(II) complex with 8-hydroxy-2-methylquinoline and thiocyanate.

Two distinct polymorphs of bis(mu(2)-methylquinolin-8-olato)-kappa(3)N,O:O;kappa(3)O:N,O-bis[(isothiocyanato-kappaN)lead(II)], [Pb(2)(C(10)H(8)NO)(2)(NCS)(2)], (I), forming dinuclear complexes from a methanolic solution containing lead(II) nitrate, 2-methylquinolin-8-ol (M-Hq) and KSCN, crystallized concomitantly as colourless prisms [form (Ia)] and long thin colourless needles [form (Ib)]. In both cases, the complexes lie across a centre of inversion. The polymorphs differ substantially in their conformation and in their interactions, viz. Pb...S and pi-pi for form (Ia) and Pb...S, Pb...pi and C-H...pi for form (Ib).

Bis(2-methyl-quinolin-8-olato-κN,O)-lead(II).

The Pb(II) atom in the title compound, [Pb(C(10)H(8)NO)(2)], is chelated by two oxine (2-methyl-quinolin-8-olate) anions in a Ψ-trigonal-bipyramidal geometry; the N atoms occupy the axial sites. The mol-ecule lies about a twofold rotation axis.

8-Hydr-oxy-2-methyl-quinolinium tetra-chlorido(quinolin-8-olato-κN,O)stannate(IV) acetonitrile monosolvate.

In the title solvated salt, (C(10)H(10)NO)[SnCl(4)(C(9)H(6)NO)]·CH(3)CN, the Sn(IV) atom is chelated by the N,O-bidentate 8-hydroxy-quinolinate ligand and four chloride ions, generating a distorted SnONCl(4) octa-hedral coordination geometry for the metal. In the crystal, the cations are linked to the anions and the solvent mol-ecules by O-H⋯O and N-H⋯N hydrogen bonds, respectively.

catena-Poly[[(1,10-phenanthroline-κN,N')lead(II)]-µ-azido-κN:N-µ-nitrito-κO,O':O'-[(1,10-phenanthroline-κN,N')lead(II)]-di-µ-azido-κN:N].

The title coordination polymer, [Pb(2)(N(3))(3)(NO(2))(C(12)H(8)N(2))(2)](n), has as the repeat unit a centrosymmetric dinuclear mol-ecule having azide and nitrite groups that bridge adjacent heterocycle-coordinated metal centers. One of the azide group uses its terminal ends to bridge whereas the nitrite group chelates to one metal atom and uses one of its O atoms to bridge. The azide and nitrite groups are disordered with respect to each other in a 1:1 ratio. Adjacent dinuclear mol-ecules are further bridged by the other two azide groups, generating a linear chain motif parallel to [010]. Half of the Pb atoms show a Ψ-dodeca-hedral coordination and the other half show a Ψ-penta-gonal-bipyramidal coordination.

Bis(quinoline-2-carboxyl-ato-κN,O)lead(II).

The Pb(II) atom in the title compound, [Pb(C(10)H(6)NO(2))(2)], is N,O-chelated by two quinoline-2-carboxyl-ate anions in a distorted Ψ-trigonal-bipyramidal environment; four atoms are connected to the Pb(II) atom by regular coordination bonds. The structure also features two somewhat long Pb⋯O inter-actions [2.952 (3) and 3.014 (3) Å]. These long inter-actions give rise to a layer coordination polymer having the lead atom in a distorted Ψ-monocapped octa-hedral geometry.

Bis(µ-quinoline-2-carboxyl-ato)-κN,O:O;κO:N,O-bis-[(acetato-κO,O')(methanol-κO)lead(II)].

The dinuclear title compound, [Pb(2)(C(10)H(6)NO(2))(2)(CH(3)COO)(2)(CH(3)OH)(2)], lies across an inversion center. The methanol-coordinated Pb(II) atom is chelated by the acetate anion as well as by the quinoline-2-carboxyl-ate anion. One O atom of the quinoline-2-carboxyl-ate anion bridges two symmetry-related Pb(II) atoms, forming the dinuclear compound. Aside from the six atoms connected to the Pb(II) atom by regular coordination bonds, the structure features a long Pb⋯O inter-action [3.145 (3) Å] that gives rise to a distorted Ψ-square-anti-prismatic geometry at the metal center. The H atom of the methanol is hydrogen bonded to an O atom of the acetate.

Di-µ-azido-κN:N-bis-[(1,10-phen-anthroline-κN,N')(thio-cyanato-κN)lead(II)].

In the centrosymmetric binuclear title compound, [Pb(2)(N(3))(2)(NCS)(2)(C(12)H(8)N(2))(4)], the N-donor atoms of one N-heterocycle and the N-donor atom of a thio-cyanate anion along with the sterically active lone-pair electrons comprise an approximate square; a plane through three atoms of this square is twisted slightly with respect to the square made up of the other four atoms (two from the other N-heterocycle and one each from the bridging azide anions) at a dihedral angle of 18.7 (1)°. The Pb(II) atom is in a Ψ-square-anti-prismaic coordination.

Bis(acetato-κO)bis-(µ(3)-quinolin-8-olato-κN,O:O:O)tetra-kis(µ(2)-quinolin-8-olato-κN,O:O)tetra-zinc(II) dihydrate.

In the centrosymmetric title compound, [Zn(4)(C(9)H(6)NO)(6)(C(2)H(3)O(2))(2)]·2H(2)O, the Zn(II) atom that is bonded to one O atom of the acetate group is chelated by a quinolin-8-olate anion. This Zn atom is also bonded to the oxide O atoms of two other quinolin-8-olate anions, which themselves engage in chelation to the other Zn(II) atoms. The Zn(II) atom is five-coordinate in a square-pyramidal coordination geometry. The second Zn(II) atom is six-coordinate as it is linked to two oxide O atoms of the anions that chelate to the acetate-bound metal atom, and is chelated by two quinolin-8-olate ligands. The uncoordinated water mol-ecule is disordered over two positions in a 4:1 ratio. O-H⋯O hydrogen bonds between the water molecules and the free O atoms of the carboxylate groups consolidate the crystal packing.