Dye removal from textile industrial effluents by adsorption on exfoliated graphite nanoplatelets: kinetic and equilibrium studies.

The concept of physical adsorption was applied for the removal of direct and reactive blue textile dyes from industrial effluents. Commercial graphite nanoplatelets were used as substrate, and the quality of the material was characterized by atomic force and transmission electron microscopies. Dye/graphite nanoplatelets water solutions were prepared varying their pH and initial dye concentration. Exceptionally high values (beyond 100 mg/L) for adsorptive capacity of graphite nanoplatelets could be achieved without complicated chemical modifications, and equilibrium and kinetic experiments were performed. Our findings were compared with the state of the art, and compared with theoretical models. Agreement between them was satisfactory, and allowed us to propose novel considerations describing the interactions of the dyes and the graphene planar structure. The work highlights the important role of these interactions, which can govern the mobility of the dye molecules and the amount of layers that can be stacked on the graphite nanoplatelets surface.

Synthesis and cholinesterase inhibition of cativic acid derivatives.

Alzheimer's disease (AD) is a neurodegenerative disorder associated with memory impairment and cognitive deficit. Most of the drugs currently available for the treatment of AD are acetylcholinesterase (AChE) inhibitors. In a preliminary study, significant AChE inhibition was observed for the ethanolic extract of Grindelia ventanensis (IC50=0.79 mg/mL). This result prompted us to isolate the active constituent, a normal labdane diterpenoid identified as 17-hydroxycativic acid (1), through a bioassay guided fractionation. Taking into account that 1 showed moderate inhibition of AChE (IC50=21.1 µM), selectivity over butyrylcholinesterase (BChE) (IC50=171.1 µM) and that it was easily obtained from the plant extract in a very good yield (0.15% w/w), we decided to prepare semisynthetic derivatives of this natural diterpenoid through simple structural modifications. A set of twenty new cativic acid derivatives (3-6) was prepared from 1 through transformations on the carboxylic group at C-15, introducing a C2-C6 linker and a tertiary amine group. They were tested for their inhibitory activity against AChE and BChE and some structure-activity relationships were outlined. The most active derivative was compound 3c, with an IC50 value of 3.2 µM for AChE. Enzyme kinetic studies and docking modeling revealed that this inhibitor targeted both the catalytic active site and the peripheral anionic site of this enzyme. Furthermore, 3c showed significant inhibition of AChE activity in SH-SY5Y human neuroblastoma cells, and was non-cytotoxic.

Aripiprazole salts. III. Bis(aripiprazolium) oxalate-oxalic acid (1/1).

The asymmetric unit of the title salt [systematic name: bis(4-(2,3-dichlorophenyl)-1-{4-[(2-oxo-1,2,3,4-tetrahydroquinolin-7-yl)oxy]butyl}piperazin-1-ium) oxalate-oxalic acid (1/1)], 2C(23)H(28)Cl(2)N(3)O(2)(+)·C(2)O(4)(2-)·C(2)H(2)O(4), consists of one protonated aripiprazole unit (HArip(+)), half an oxalate dianion and half an oxalic acid molecule, the latter two lying on inversion centres. The conformation of the HArip(+) cation differs from that in other reported salts and resembles more the conformation of neutral Arip units in reported polymorphs and solvates. The intermolecular interaction linking HArip(+) cations is also similar to those in reported Arip compounds crystallizing in the space group P1, with head-to-head N-H···O hydrogen bonds generating centrosymmetric dimers, which are further organized into planar ribbons parallel to (012). The oxalate anions and oxalic acid molecules form hydrogen-bonded chains running along [010], which 'pierce' the planar ribbons, interacting with them through a number of stronger N-H···O and weaker C-H···O hydrogen bonds, forming a three-dimensional network.

The supramolecular structure of a cadmium complex with the new functionalized terpyridine ligand 4'-[4-(pyrimidin-5-yl)phenyl]-2,2':6',2''-terpyridine (L1): aqua(L1-κ³N,N',N'')(nitrato-κ²O,O')(nitrato-κO)cadmium(II) dihydrate.

The monomeric title compound, aqua(nitrato-κ²O,O')(nitrato-κO){4'-[4-(pyrimidin-5-yl)phenyl]-2,2':6',2''-terpyridine-κ³N,N',N''}cadmium(II) dihydrate, [Cd(NO3)2(C25H17N5)(H2O)]·2H2O, consists of a seven-coordinated CdII centre bound to the novel 4'-[4-(pyrimidin-5-yl)phenyl]-2,2':6',2''-terpyridine (L1) ligand (behaving as a tridentate chelate), two nitrate anions (as chelating-bidentate and monodentate ligands) and a water O atom. Both chelating groups define the base of a slightly deformed pentagonal bipyramid, while the monocoordinated ligands occupy the apices. The four heterocycles in L1 form a planar skeleton, while the central benzene ring is rotated from this planar geometry by more than 30°, probably because of packing effects. Noncovalent interactions lead to the formation of columnar arrays parallel to [100].

A polymorphic form of 4,4-dimethyl-8-methylene-3-azabicyclo[3.3.1]non-2-en-2-yl 3-indolyl ketone, an indole alkaloid extracted from Aristotelia chilensis (maqui).

The title compound [systematic name: (4,4-dimethyl-8-methylene-3-azabicyclo[3.3.1]non-2-en-2-yl)(1H-indol-3-yl)methanone], C20H22N2O, (II), was obtained from mother liquors extracted from Aristotelia chilensis (commonly known as maqui), a native Chilean tree. The compound is a polymorphic form of that obtained from the same source and reported by Watson, Nagl, Silva, Cespedes & Jakupovic [Acta Cryst. (1989), C45, 1322-1324], (Ia). The molecule consists of an indolyl ketone fragment and a nested three-ring system, with both groups linked by a C-C bridge. Comparison of both forms shows that they do not differ in their gross features but in the relative orientation of the two ring systems, due to different rotations around the bridge, as measured by the O=C-C=N torsion angle [130.0 (7)° in (Ia) and 161.6 (2)° in (II)]. The resulting slight conformational differences are reflected in a number of intramolecular contacts being observed in (II) but not in (Ia). Regarding intermolecular interactions, both forms share a similar N-H···O synthon but with differing hydrogen-bonding strength, leading in both cases to C(6) catemers with different chain motifs. There are marked differences between the two forms regarding colour and the (de)localization of a double bond, which allows speculation about the possible existence of different variants of this type of molecule.

(E)-Ethyl 3-(3,4-dihydroxyphenyl)prop-2-enoate: a natural polymorph extracted from Aristotelia chilensis (Maqui).

The natural title compound, C11H12O4, extracted from the Chilean native tree Aristotelia chilensis (Maqui), is a polymorph of the synthetic E form reported by Xia, Hu & Rao [Acta Cryst. (2004), E60, o913-o914]. Both rotational conformers are identical from a metrical point of view, and only differ in the orientation of the 3,4-dihydroxyphenyl ring with respect to the rest of the molecule, which leads to completely different crystal structure arrangements and packing efficiencies. The reasons behind both reside in the different hydrogen-bonding interactions.

Effect of non-covalent self-dimerization on the spectroscopic and electrochemical properties of mixed Cu(i) complexes.

A series of six new Cu(i) complexes with ([Cu(N-{4-R}pyridine-2-yl-methanimine)(PPh3)Br]) formulation, where R corresponds to a donor or acceptor p-substituent, have been synthesized and were used to study self-association effects on their structural and electrochemical properties. X-ray diffraction results showed that in all complexes the packing is organized from a dimer generated by supramolecular π stacking and hydrogen bonding. 1H-NMR experiments at several concentrations showed that all complexes undergo a fast-self-association monomer-dimer equilibrium in solution, while changes in resonance frequency towards the high or low field in specific protons of the imine ligand allow establishing that dimers have similar structures to those found in the crystal. The thermodynamic parameters for this self-association process were calculated from dimerization constants determined by VT-1H-NMR experiments for several concentrations at different temperatures. The values for K D (4.0 to 70.0 M-1 range), ΔH (-1.4 to -2.6 kcal mol-1 range), ΔS (-0.2 to 2.1 cal mol-1 K-1 range), and ΔG 298 (-0.8 to -2.0 kcal mol-1 range) are of the same order and indicate that the self-dimerization process is enthalpically driven for all complexes. The electrochemical profile of the complexes shows two redox Cu(ii)/Cu(i) processes whose relative intensities are sensitive to concentration changes, indicating that both species are in chemical equilibrium, with the monomer and the dimer having different electrochemical characteristics. We associate this behaviour with the structural lability of the Cu(i) centre that allows the monomeric molecules to reorder conformationally to achieve a more adequate assembly in the non-covalent dimer. As expected, structural properties in the solid and in solution, as well as their electrochemical properties, are not correlated with the electronic parameters usually used to evaluate R substituent effects. This confirms that the properties of the Cu(i) complexes are usually more influenced by steric effects than by the inductive effects of substituents of the ligands. In fact, the results obtained showed the importance of non-covalent intermolecular interactions in the structuring of the coordination geometry around the Cu centre and in the coordinative stability to avoid dissociative equilibria.

Correction: Effect of non-covalent self-dimerization on the spectroscopic and electrochemical properties of mixed Cu(i) complexes.

[This corrects the article DOI: 10.1039/D2RA05341A.].

Adsorption of Cd (II) ions and methyl violet dye by using an agar-graphene oxide nano-biocomposite.

In this work, an agar-graphene oxide hydrogel was prepared to adsorb Cd (II) and Methyl Violet (MV) from water. The hydrogel was synthesised and characterised through SEM and EDS. Kinetic, equilibrium and regeneration studies were carried out, in which Langmuir, Freundlich and Sips isotherm models were fitted to the equilibrium experimental data; and regarding the kinetics, studies were conducted by modelling experimental data considering both empirical and phenomenological models. SEM and EDS have shown the composite present a 3D-disordered porous microstructure and that it is mainly constituted of C and O. Sips model fitted well to Cd (II) (R2 = 0.968 and χ2 = 0.176) and MV (R2 = 0.993 and χ2 = 0.783). The qmax values for MV and Cd (II) were 76.65 and 11.70 mg.g-1, respectively. Pseudo-order models satisfactorily described Cd (II) and MV adsorption kinetics with R2 > 0.90. Regeneration experiments revealed an outstanding reuse capacity of the adsorbent after three cycles of adsorption-desorption for both Cd (II) and MV. This study evidences the possibility of a feasible adsorbent for Cd (II) and MV removal from water for successive cycles of use.

Aripiprazole salts. II. Aripiprazole perchlorate.

The molecular structure of aripiprazole perchlorate (systematic name: 4-(2,3-dichlorophenyl)-1-{4-[(2-oxo-1,2,3,4-tetrahydroquinolin-7-yl)oxy]butyl}piperazin-1-ium perchlorate), C(23)H(28)Cl(2)N(3)O(2)(+)·ClO(4)(-), does not differ substantially from the recently published structure of aripiprazole nitrate [Freire, Polla & Baggio (2012). Acta Cryst. C68, o170-o173]. Both compounds have almost identical bond distances, bond angles and torsion angles. The two different counter-ions occupy equivalent places in the two structures, giving rise to very similar first-order `packing motifs'. However, these elemental arrangements interact with each other in different ways in the two structures, leading to two-dimensional arrays with quite different organizations.

Aripiprazole salts. I. Aripiprazole nitrate.

The crystal structure of aripiprazole nitrate (systematic name: 4-(2,3-dichlorophenyl)-1-{4-[(2-oxo-1,2,3,4-tetrahydroquinolin-7-yl)oxy]butyl}piperazin-1-ium nitrate), C(23)H(28)Cl(2)N(3)O(2)(+)·NO(3)(-) or AripH(+)·NO(3)(-), is presented and the molecule compared with the aripiprazole molecules reported so far in the literature. Bond distances and angles appear very similar, except for a slight lengthening of the C-NH distances involving the protonated N atom, and the main differences are to be found in the molecular spatial arrangement (revealed by the sequence of torsion angles) and the intermolecular interactions (resulting from structural elements specific to this structure, viz. the nitrate counter-ions on one hand and the extra protons on the other hand as hydrogen-bond acceptors and donors, respectively). The result is the formation of [100] strips, laterally linked by weak π-π and C-Cl...π interactions, leading to a family of undulating sheets parallel to (010).

Monodentate and bridging behaviour of the sulfur-containing ligand 4'-[4-(methylsulfanyl)phenyl]-4,2':6',4''-terpyridine in two discrete zinc(II) complexes with acetylacetonate.

The Zn complexes bis(acetylacetonato-κ(2)O,O')bis{4'-[4-(methylsulfanyl)phenyl]-4,2':6',4''-terpyridine-κN(1)}zinc(II), [Zn(C(5)H(7)O(2))(2)(C(22)H(17)N(3)S)(2)], (I), and {µ-4'-[4-(methylsulfanyl)phenyl]-4,2':6',4''-terpyridine-κ(2)N(1):N(1'')}bis[bis(acetylacetonato-κ(2)O,O')zinc(II)], [Zn(2)(C(5)H(7)O(2))(4)(C(22)H(17)N(3)S)], (II), are discrete entities with different nuclearities. Compound (I) consists of two centrosymmetrically related monodentate 4'-[4-(methylsulfanyl)phenyl]-4,2':6',4''-terpyridine (L1) ligands binding to one Zn(II) atom sitting on an inversion centre and two centrosymmetrically related chelating acetylacetonate (acac) groups which bind via carbonyl O-atom donors, giving an N(2)O(4) octahedral environment for Zn(II). Compound (II), however, consists of a bis-monodentate L1 ligand bridging two Zn(II) atoms from two different Zn(acac)(2) fragments. Intra- and intermolecular interactions are weak, mainly of the C-H···π and π-π types, mediating similar layered structures. In contrast to related structures in the literature, sulfur-mediated nonbonding interactions in (II) do not seem to have any significant influence on the supramolecular structure.

A triclinic polymorph of cyclo-tetra-µ-thiosaccharinato-κ8S:S-tetrakis[(triphenylphosphane-κP)silver(I)].

The triclinic structure of the title compound, cyclo-tetrakis(µ-1,1-dioxo-1λ(6),2-benzothiazole-3-thiolato-κ(2)S:S)tetrakis[(triphenylphosphane-κP)silver(I)], [Ag(4)(C(7)H(4)NO(2)S(2))(4)(C(18)H(15)P)(4)], is a polymorph of the previously reported monoclinic structure [Dennehy, Mandolesi, Quinzani & Jennings (2007). Z. Anorg. Allg. Chem. 633, 2746-2752]. In both polymorphs, the complex lies on a crystallographic inversion centre and the bond distances are closely comparable. Some differences can be found in the interatomic angles and torsion angles involving the inner Ag(4)S(4) skeleton. The polymorphs contain essentially identical two-dimensional layers, but with different layer stacking arrangements. In the triclinic form, all layers are related by lattice translation, while in the monoclinic form they are arranged around glide planes so that adjacent layers are mirrored with respect to each other.

The conformations of two copper(I) complexes of 1H-benzimidazole-2(3H)-thione and thiosaccharinate.

(Acetonitrile-1κN)[µ-1H-benzimidazole-2(3H)-thione-1:2κ(2)S:S][1H-benzimidazole-2(3H)-thione-2κS]bis(µ-1,1-dioxo-1λ(6),2-benzothiazole-3-thiolato)-1:2κ(2)S(3):N;1:2κ(2)S(3):S(3)-dicopper(I)(Cu-Cu), [Cu(2)(C(7)H(4)NO(2)S(2))(2)(C(7)H(6)N(2)S)(2)(CH(3)CN)] or [Cu(2)(tsac)(2)(Sbim)(2)(CH(3)CN)] [tsac is thiosaccharinate and Sbim is 1H-benzimidazole-2(3H)-thione], (I), is a new copper(I) compound that consists of a triply bridged dinuclear Cu-Cu unit. In the complex molecule, two tsac anions and one neutral Sbim ligand bind the metals. One anion bridges via the endocyclic N and exocyclic S atoms (µ-S:N). The other anion and one of the mercaptobenzimidazole molecules bridge the metals through their exocyclic S atoms (µ-S:S). The second Sbim ligand coordinates in a monodentate fashion (κS) to one Cu atom, while an acetonitrile molecule coordinates to the other Cu atom. The Cu(I)-Cu(I) distance [2.6286 (6) Å] can be considered a strong 'cuprophilic' interaction. In the case of [µ-1H-benzimidazole-2(3H)-thione-1:2κ(2)S:S]bis[1H-benzimidazole-2(3H)-thione]-1κS;2κS-bis(µ-1,1-dioxo-1λ(6),2-benzothiazole-3-thiolato)-1:2κ(2)S(3):N;1:2κ(2)S(3):S(3)-dicopper(I)(Cu-Cu), [Cu(2)(C(7)H(4)NO(2)S(2))(2)(C(7)H(6)N(2)S)(3)] or [Cu(2)(tsac)(2)(Sbim)(3)], (II), the acetonitrile molecule is substituted by an additional Sbim ligand, which binds one Cu atom via the exocylic S atom. In this case, the Cu(I)-Cu(I) distance is 2.6068 (11) Å.

Synthesis and application of graphene oxide as a nanoadsorbent to remove Cd (II) and Pb (II) from water: adsorption equilibrium, kinetics, and regeneration.

In this work, graphene oxide (GO) was synthesized by the modified Hummers method. The nanomaterial was characterized by FTIR and Raman spectroscopy, SEM, and pH at the point of zero charge. GO exhibited typical characteristics of graphene-based materials, indicating that graphite oxidation and exfoliation occurred successfully. Cd (II) and Pb (II) adsorption onto GO was carried out in batch systems, in which the effect of adsorbent dosage, contact time, and initial adsorbate concentration were evaluated. Langmuir, Freundlich, and Sips isotherm models, as well as pseudo order models and Elovich kinetic equation were applied to adsorption experimental data. Results indicated that increasing adsorbent mass, the removal efficiency of Cd (II) and Pb (II) increased. Freundlich isotherm better described Pb (II) adsorption (R2 = 0.96), while Cd (II) isotherm showed linear behavior. From the Akaike's AIC parameter, kinetic data were satisfactorily described by pseudo-first order (Cd (II)) and pseudo-n order (Pb (II)) models. GO was successfully subjected to five regeneration cycles, maintaining high efficiency (> 90%) in all cycles. GO showed high potential for the adsorption of Cd (II) and Pb (II) from aqueous solution, due to its high adsorption capacity, rapid Cd (II) and Pb (II) intakes, and great regeneration performance.

Poly[[tetra-µ3-acetato-hexa-µ2-acetato-diaqua-µ2-oxalato-tetrapraseodymium(III)] dihydrate].

The title complex, {[Pr(4)(C(2)H(3)O(2))(10)(C(2)O(4))(H(2)O)(2)]·2H(2)O}(n), was synthesized under hydrothermal conditions from praseodymium acetate and the ionic liquid 1-butyl-3-methylimidazolium chloride via an in situ oxalate-ligand synthesis. The compound is a two-dimensional polymer and in the structure presents tightly bound planes parallel to (100), which are in turn linked into a three-dimensional network by hydrogen bonds involving both coordinated and solvent water molecules. The oxalate anion lies across an inversion centre and acts as a bridge between pairs of Pr atoms within a tetranuclear segment of the polymer.

1-(9H-Carbazol-4-yloxy)-3-{[2-(2-methoxyphenoxy)ethyl]amino}propan-2-ol hemihydrate: a carvedilol solvatomorph.

In the title racemic hemihydrated solvatomorph of carvedilol (carv), C(24)H(26)N(2)O(4)·0.5H(2)O, the asymmetric unit contains two independent organic moieties and one water molecule. Within this 2(carv)·H(2)O unit, the molecular components are strongly linked by hydrogen bonds and the unit acts as the basic building block for the crystal structure. Interactions parallel to (10 ̅1) generate hydrogen-bonded layers which are further linked by much weaker C-H···N/O interactions. The conformations of the organic molecules, as well as the hydrogen-bonding interactions connecting them, are compared with other related structures in the literature.

Biosorption of heavy fuel oil from aqueous solution by Eichhornia crassipes (Mart.) Solms in natura.

This work investigated the efficiency of bioremediation of heavy fuel oil (HFO) in aqueous solutions by living Eichhornia crassipes (Mart.) Solms, also known as water hyacinth. Possibility of using post-biosorption macrophytes to produce briquettes was also studied. HFO was characterized by its density, viscosity, and Fourier-transform infrared spectroscopy. Water hyacinth was characterized by scanning electron microscope, pH of zero point of charge, buoyancy, and wettability. Experiments were performed to evaluate effects of contact time and initial oil concentration on biosorption. E. crassipes presented a hydrophobic nature, ideal for the treatment of oily effluents. Hollow structures in macrophytes were also identified, which favor capillary rise and retention of oils of high density and viscosity. Biosorption efficiency of HFO reached 94.8% in tests with initial concentration of 160 mg.L-1. A calorific value of 4022 kcal.kg-1 was obtained in briquettes made of water hyacinth post-biosorption. These results reinforce the great potential of E. crassipes as a sustainable and efficient alternative for treatment of oily effluents.

Zoledronate complexes. III. Two zoledronate complexes with alkaline earth metals: [Mg(C(5)H(9)N(2)O(7)P(2))(2)(H(2)O)(2)] and [Ca(C(5)H(8)N(2)O(7)P(2))(H(2)O)](n).

Diaquabis[dihydrogen 1-hydroxy-2-(imidazol-3-ium-1-yl)ethylidene-1,1-diphosphonato-kappa(2)O,O']magnesium(II), [Mg(C(5)H(9)N(2)O(7)P(2))(2)(H(2)O)(2)], consists of isolated dimeric units built up around an inversion centre and tightly interconnected by hydrogen bonding. The Mg(II) cation resides at the symmetry centre, surrounded in a rather regular octahedral geometry by two chelating zwitterionic zoledronate(1-) [or dihydrogen 1-hydroxy-2-(imidazol-3-ium-1-yl)ethylidene-1,1-diphosphonate] anions and two water molecules, in a pattern already found in a few reported isologues where the anion is bound to transition metals (Co, Zn and Ni). catena-Poly[[aquacalcium(II)]-mu(3)-[hydrogen 1-hydroxy-2-(imidazol-3-ium-1-yl)ethylidene-1,1-diphosphonato]-kappa(5)O:O,O':O',O''], [Ca(C(5)H(8)N(2)O(7)P(2))(H(2)O)](n), consists instead of a Ca(II) cation in a general position, a zwitterionic zoledronate(2-) anion and a coordinated water molecule. The geometry around the Ca(II) atom, provided by six bisphosphonate O atoms and one water ligand, is that of a pentagonal bipyramid with the Ca(II) atom displaced by 0.19 A out of the equatorial plane. These Ca(II) coordination polyhedra are ;threaded' by the 2(1) axis so that successive polyhedra share edges of their pentagonal basal planes. This results in a strongly coupled rhomboidal Ca(2)-O(2) chain which runs along [010]. These chains are in turn linked by an apical O atom from a -PO(3) group in a neighbouring chain. This O-atom, shared between chains, generates strong covalently bonded planar arrays parallel to (100). Finally, these sheets are linked by hydrogen bonds into a three-dimensional structure. Owing to the extreme affinity of zoledronic acid for bone tissue, in general, and with calcium as one of the major constituents of bone, it is expected that this structure will be useful in modelling some of the biologically interesting processes in which the drug takes part.

Zoledronate complexes. I. Poly[[mu2-aqua[mu3-1-hydroxy-2-(1H,3H-imidazol-3-ium-1-yl)ethylidenediphosphonato]potassium(I)] monohydrate].

The title compound, {[K(C(5)H(9)N(2)O(7)P(2))(H(2)O)].H(2)O}(n), is polymeric and consists of layers parallel to (001) interconnected by hydrogen-bonding and pi-pi interactions. The K(+) cation is eightfold coordinated in a KO(8) environment by O atoms from three different chelating zoledronate units and two coordinated water molecules. The zoledronate group presents its usual zwitterionic character, with negative charges in the singly protonated phosphonate groups and a positive charge at the protonated imidazole N atom. The anion binds to three different K(+) cations in a (so far unreported) triply chelating manner. Intra- and interplanar interactions are enhanced by a variety of hydrogen bonds involving all available O-H and N-H donors. A strong imidazole-phosphonate C-H...O interaction is present in the structure.