Synthesis and application of imprinted polyvinylimidazole-silica hybrid copolymer for Pb determination by flow-injection thermospray flame furnace atomic absorption spectrometry

A novel ion imprinted polyvinylimidazole-silica hybrid copolymer (IIHC) was synthesized and used as a selective solid sorbent for Pb²⁺ ions preconcentration using an on-line solid phase extraction (SPE) system coupled to TS-FF-AAS. The ionic hybrid sorbent was prepared using 1-vinylimidazole and 3-(trimethoxysilyl)propylmethacrylate as monomers, Pb²⁺ ions as template, tetraethoxysilane as reticulating agent and 2,2′-azobis-isobutyronitrile as initiator. The best on-line SPE conditions concerning sorption behavior, including sample pH (6.46), buffer concentration (9.0 mmol L⁻¹), eluent (HNO₃) concentration (0.5 mol L⁻¹) and preconcentration flow rate (4.0 mL min⁻¹), were optimized by means of full factorial design and Doehlert matrix. The analytical curve ranged from 2.5 to 65.0 μg L⁻¹ (r = 0.999) with limit of detection of 0.75 μg L⁻¹; the precision (repeatability) calculated as relative standard deviation (n = 10) was 5.0 and 3.6% for Pb²⁺ concentration of 10.0 and 60.0 μg L⁻¹, respectively. From on-line breakthrough curve, column capacity was 3.5 mg g⁻¹. Preconcentration factor (PF), consumptive index (CI) and concentration efficiency (CE) were 128.0, 0.16 mL and 25.6 min⁻¹, respectively. The selective performance of the sorbent, based on relative selectivity coefficient, was compared to NIC (non imprinted copolymer) for the binary mixture Pb²⁺/Cd²⁺, Pb²⁺/Cu²⁺ and Pb²⁺/Zn²⁺. The results showed that ion imprinted polyvinylimidazole-silica hybrid polymer had higher selectivity for Pb²⁺ than NIC at 64.9, 16.0 and 8.8 folds. The developed method was successfully applied for highly sensitive and selective Pb²⁺ determination in different kinds of water samples, parenteral solutions and urine. Accuracy was also assessed by analyzing certified reference fish protein (DORM-3) and marine sediment (MESS-3 and PACS-2) with satisfactory results.     

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), C₂₄H₂₆N₂O₄·0.5H₂O, the asymmetric unit contains two independent organic moieties and one water molecule. Within this 2(carv)·H₂O 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) 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.     

Thermal behavior of residues (sludge) originating from the sugarcane industry

The Brazilian sugarcane industry shows a great amount of generated sludge which should be utilized adequately. Two sludge samples, aerobic and anaerobic, were collected. Both were evaluated by thermogravimetry and differential thermal analysis (DTA) as well as X-ray power diffraction. These compounds show variations of mass between 30 and 140 °C due to the dehydration stage. The DTA curves show that the compounds have an exothermic reaction between 450 and 550 °C, which indicates that this can be used as an energy source. Details concerning the kinetic parameters of the dehydration and thermal decomposition have also been described here. The kinetic study of these stages was evaluated in open crucibles under nitrogen atmosphere. The obtained data were evaluated with the isoconversional kinetic method. The results show that different activation energies were obtained for thermal decomposition.     

Thiazole orange (TO) as a light-switch probe: a combined quantum-mechanical and spectroscopic study

A Density Functional Theory (DFT) study of the absorbance and fluorescence emission characteristics of the cyanine thiazole orange (TO) in solution and when intercalated in DNA was carried out in combination with spectrophotometric and spectrofluorometric experiments under different conditions (temperature, concentration, solvent viscosity). T-jump relaxation kinetics of the TO monomer-dimer conversion enabled the thermodynamic parameters of this process to be evaluated. The overall data collected provided information on the features of the "light-switch" by the fluorescent TO and the comparison between experimental and calculated photo-physical properties allowed us to explain and rationalize both shifts and quenching/enhancing effects on fluorescence due to solvation, dimerisation and intercalation in the DNA.     

Molecular association of heteronuclear vibrating square-well dumbbells in liquid-vapor phase equilibrium

Molecular aggregates are formed by heteronuclear vibrating square-well dumbbells. In a recent article [G. A. Chapela and J. Alejandre, J. Chem. Phys., 132(10), 104704 (2010)], it is shown that heteronuclear vibrating square-well dumbbells with a diameter ratio between particles of 1/2 and interacting potential ratio of 4 form micelles of different sizes and shapes which manifest themselves in both the liquid and vapor phases, up to and above the critical point. This means that micellization and phase separation are present simultaneously in this simple model. These systems present a maximum in the critical temperature when plotted against the potential well depth of the second particle ε(2). In the same publication, it was speculated that the formation of micelles was responsible for the appearance of the maximum. A thorough study on this phenomena is presented here and it is found that there is a threshold on the size of the second particle and its corresponding depth of interaction potential, where the micelles are formed. If the diameter and well depth of the second particle are small enough for the first and deep enough for the second, micelles are formed. For σ(2)/σ(1) between 0.25 and 0.65 and ε(2)/ε(1) larger than 5.7, micelles are formed up to and above the critical temperature. Outside these ranges micelles appear only at temperatures lower than the critical point. There is a strong temperature dependence on the formation and persistence of the aggregates. For the deepest wells and large enough second particles, a gel interconnected aggregate is obtained. In this work, the micelles are formed at temperatures as low as the triple point and as high as the critical point and, in some cases, persist well above it. The presence of these maxima in critical temperatures T(c) when plotted against ε(2) as follows. At lower values of ε(2), an increase of T(c) is obtained as is expected by the increase of the attractive volume as indicated by the principle of corresponding states. As ε(2) increases further, the formation of molecular aggregates produce a saturation effect of the deepening of the potential well by encapsulating the particles of the second kind inside the micelles, so the resulting T(c) represents a new poly disperse system of molecular aggregates and not the original heteronuclear vibrating square-well dumbbells. The surface tension is also analyzed for these systems, and it is shown that decreases with increasing attraction due to the formation of molecular aggregates.     

Ionic liquids as recycling solvents for the synthesis of magnetic nanoparticles

This work describes an easy synthesis (one pot) of MFe(2)O(4) (M = Co, Fe, Mn, and Ni) magnetic nanoparticles MNPs by the thermal decomposition of Fe(Acac)(3)/M(Acac)(2) by using BMI·NTf(2) (1-n-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) or BMI·PF(6) (1-n-butyl-3-methylimidazolium hexafluorophosphate) ionic liquids (ILs) as recycling solvents and oleylamine as the reducing and surface modifier agent. The effects of reaction temperature and reaction time on the features of the magnetic nanomaterials (size and magnetic properties) were investigated. The growth of the MNPs is easily controlled in the IL by adjusting the reaction temperature and time, as inferred from Fe(3)O(4) MNPs obtained at 150 °C, 200 °C and 250 °C with mean diameters of 8, 10 and 15 nm, respectively. However, the thermal decomposition of Fe(Acac)(3) performed in a conventional high boiling point solvent (diphenyl ether, bp 259 °C), under a similar Fe to oleylamine molar ratio used in the IL synthesis, does not follow the same growth mechanism and rendered only smaller NPs of 5 nm mean diameter. All MNPs are covered by at least one monolayer of oleylamine making them readily dispersible in non-polar solvents. Besides the influence on the nanoparticles growth, which is important for the preparation of highly crystalline MNPs, the IL was easily recycled and has been used in at least 20 successive syntheses.     

Synthesis and photophysics of silicon phthalocyanine-perylenebisimide triads connected through rigid and flexible bridges

Three new bisperylenebisimide-silicon phthalocyanine triads [(PBI)(2)-SiPcs 1, 2, and 3] connected with either rigid or flexible bridges were synthesized and characterized. A new synthetic approach to connect SiPc and PBI moieties through click chemistry produced triad 3 with an 80% yield. In (PBI)(2)-SiPc 1, PBI and SiPc are orthogonal and were connected with a rigid connector; triads 2 and 3 bear flexible aliphatic bridges, resulting in a tilted (2) or nearly parallel arrangement (3) of PBI and SiPc. Photoinduced intramolecular processes in these (PBI)(2)-SiPcs were studied and the results are compared with those of the reference compounds SiPc-ref and PBI-ref. The occurrence of electron-transfer processes between the SiPc and PBI units was confirmed by time-resolved emission and transient absorption techniques. Charge-separated (CS) states with lifetimes of 0.91, 1.3 and 2.0 ns for triads 1, 2, and 3, respectively, were detected using femtosecond laser flash photolysis. Upon the addition of Mg(ClO(4))(2), an increase in the lifetime of the CS states to 59, 110 and 200 μs was observed for triads (PBI)(2)-SiPcs 1, 2, and 3, respectively. The energy of the CS state (SiPc(·+)-PDI(·-)/Mg(2+)) is lower than the energy of both silicon phthalocyanine ((3)SiPc*-PDI) and perylenebisimide (SiPc-(3)PDI*) triplet excited states, which decelerates the metal ion-decoupled electron-transfer process for charge recombination to the ground state, thus increasing the lifetime of the CS state. The photophysics of the three triads demonstrate the importance of the rigidity of the spacer and the orientation between donor and acceptor units.     

Chemistry of 11-vertex rhodathiaboranes: reactions with monodentate phosphines

The reaction of [8,8-(PPh(3))(2)-nido-8,7-RhSB(9)H(10)] (1) with PR(3) in a 1:2 ratio affords mixtures that contain the mono-substituted bis-PR(3)-ligated rhodathiaboranes [8,8-(PPh(3))(L)-nido-8,7-RhSB(9)H(10)] [L = PMe(2)Ph (5), PMe(3) (6)] and the corresponding tris-PR(3)-ligated compounds [8,8,8-(L)(3)-nido-8,7-RhSB(9)H(10)] [L = PMe(2)Ph (7), PMe(3) (8)]. These latter species are more conveniently prepared from the reaction of 1 with three equivalents of the monodentate phosphines, PMe(2)Ph and PMe(3). Reaction between 1 and PMePh(2) in a 1:2 ratio yields the disubstituted rhodathiaborane [8,8-(PMePh(2))(2)-nido-8,7-RhSB(9)H(10)] (4), whereas the use of three equivalents of phosphine leads to the formation of B-ligated eleven-vertex [8,8,8-(PMePh(2))(2)(H)-nido-8,7-RhSB(9)H(9)-9-(PMePh(2))] (9). Compounds 4-9 have been characterized by NMR spectroscopy, and the structures of 8 and 9 confirmed by X-ray diffraction analyses. The characterization of the cluster compounds has been aided by the use of DFT calculations on some of the species. Variable-temperature NMR studies have demonstrated a lability of the PMePh(2) ligands in compounds 4 and 9, providing mechanistic insights about the ligand substitutional chemistry in these eleven-vertex rhodathiaboranes.     

Gold nanowire networks: synthesis, characterization, and catalytic activity

Gold nanowire networks (AuNWNs) with average widths of 17.74 nm (AuNWN(1)) or 23.54 nm (AuNWN(2)) were synthesized by direct reduction of HAuCl(4) with sodium borohydride powder in deep eutectic solvents, such as ethaline or reline, at 40 °C. Their width and length were dependent on the type of solvent and the NaBH(4)/HAuCl(4) molar ratio (32 in ethaline and 5.2 in reline). High resolution transmission electron microscopy (HR-TEM) analysis of the gold nanowire networks showed clear lattice fringes of polycrystalline nanopowder of d = 2.36, 2.04, 1.44, and 1.23 ? corresponding to the (111), (200), (220), or (311) crystallographic planes of face centered cubic gold. The purified AuNWNs were used as catalysts for the chemical reduction of p-nitroaniline to diaminophenylene with sodium borohydride in aqueous solution. The reaction was monitored in real time by UV-vis spectroscopy. The results show that the reduction process is six times faster in the presence of gold nanowire networks stabilized by urea from the reline (AuNWN(2)) than in the presence of gold nanowire networks stabilized by ethylene glycol from ethaline (AuNWN(1)). This is due to a higher number of corners and edges on the gold nanowires synthesized in reline than on those synthesized in ethaline as proven by X-ray diffraction (XRD) patterns recorded for both types of gold nanowire networks. Nevertheless, both types of nanomaterials determined short times of reaction and high conversion of p-nitroaniline to diaminophenylene. These gold nanomaterials represent a new addition to a new generation of catalysts: gold based catalysts.     

Shedding new light on ZnCl2-mediated addition reactions of Grignard reagents to ketones: structural authentication of key intermediates and diffusion-ordered NMR studies

Building on recent advances in synthesis showing that the addition of inorganic salts to Grignard reagents can greatly enhance their performance in alkylation reactions to ketones, this study explores the reactions of EtMgCl with benzophenone in the presence of stoichiometric or catalytic amounts of ZnCl(2) with the aim of furthering the understanding of the role and constitution of the organometallic species involved in these transformations. Investigations into the metathesis reactions of three molar equivalents of EtMgCl with ZnCl(2) led to the isolation and characterisation (X-ray crystallography and (1)H and (13)C NMR spectroscopy) of novel magnesium "zinc-rich" zincate [{(THF)(6)Mg(2)Cl(3)}(+){Zn(2)Et(5)}(-)] (1), whose complicated constitution in THF solutions was assessed by variable-temperature (1)H DOSY NMR studies. Compound 1 reacted with one equivalent of benzophenone to yield magnesium magnesiate [{(THF)(6)Mg(2)Cl(3)}(+){Mg(2)(OC(Et)Ph(2))(2)Cl(3)(THF)}(-)] (3), whose structure was determined by X-ray crystallography. (1)H NMR monitoring of this reaction showed two equivalents of ZnEt(2) formed as a co-product, which together with the "magnesium only constitution" of 3 provides experimental insights into how zinc can be efficiently recycled in these reactions, and therefore used catalytically. The chemoselectivity of this reaction can be rationalised in terms of the synergic effect of magnesium and zinc and contrasts with the results obtained when benzophenone was allowed to react with EtMgCl in the absence of ZnCl(2), where the reduction of the ketone takes place preferentially. The reduction product [{(THF)(5)Mg(3)Cl(4){OC(H)Ph(CF(3))}(2)] (4) obtained from the reaction of EtMgCl with 2,2,2-trifluoroacetophenone was established by X-ray crystallography and multinuclear ((1)H, (13)C and (19)F) NMR spectroscopy. Compounds 3 and 4 exhibit new structural motifs in magnesium chemistry having MgCl(2) integrated within their constitution, which highlights the new role of this inorganic salt in providing structural support for the newly generated alkoxide ligand.