Ana Rosa Silva

Immobilisation of amine-functionalised nickel(II) Schiff base complexes onto activated carbon treated with thionyl chloride

Abstract Two Schiff base nickel complexes with amine groups, bis[o-[N-(3-aminopropyl)formimidoyl]phenolato-O,N,N′]nickel(II) and bis[4-methoxy-o-[N-(3-aminopropyl)formimidoyl]phenolato-O,N,N′]nickel(II), were anchored onto a chemically oxidised activated carbon treated with thionyl chloride. Complex anchoring was made in three consecutive steps: (i) oxidation of activated carbon with nitric acid, (ii) treatment with thionyl chloride that converts primarily the carboxylic acid carbon surface groups into acyl chloride functionalities, and (iii) reaction between the amine functionalities of the metal complexes with the carbon surface acyl chloride functionalities. The resulting carbon-based materials were characterised by elemental analysis, surface techniques (SEM and XPS), nitrogen adsorption isotherms and thermal analysis (temperature-programmed desorption and thermogravimetry). The data from all the techniques provided evidence that both nickel complexes were anchored onto the activated carbon via an amide ligation originated by the reaction between the acyl chloride carbon surface functionalities and the amine groups of both metal complexes.

Energetics of 6-methoxyquinoline and 6-methoxyquinoline N-oxide: the dissociation enthalpy of the (N-O) bond

Abstract The standard (p o =0.1 MPa ) molar enthalpies of formation, at T=298.15 K , were determined using static-bomb calorimetry for crystalline 6-methoxyquinoline N -oxide (6MeOQUINO), as −(85.6±3.7) kJ · mol −1 and liquid 6-methoxyquinoline (6MeOQUI), −(25.8±2.2) kJ · mol −1 . The standard molar enthalpies of sublimation/vaporization, at T=298.15 K , were measured by microcalorimetry and from the enthalpies of formation of the gaseous compounds, the dissociation enthalpy D m 0 of the (N + –O − ) dative covalent bond was derived, as (269.2±5.0) kJ · mol −1 .

Modulation of the catalytic activity of manganese(III) salen complexes in the epoxidation of styrene: influence of the oxygen source

Several achiral Mn(III) salen complexes with different groups in the diimine bridge and in the aldehyde fragment were synthesised and their catalytic activity in the epoxidation of styrene was studied at room temperature, using two oxygen sources, NaOCl or PhIO, and in two solvents, CH3CN and CH2Cl2. These manganese(III) salen complexes present high chemoselectivities as homogeneous catalysts in the epoxidation of styrene, using either iodosylbenzene or sodium hypochlorite as oxygen sources. In general, when iodosylbenzene is used as oxidant higher styrene epoxide yields and lower yields of by-products, other than benzaldehyde, are obtained than with aqueous sodium hypochlorite solutions. It was possible to tune the catalytic activities of “[Mn(salen)X]” complexes by introduction of substituents in the diimine bridge and in the aldehyde fragment. The presence of bulky substituents in the diimine bridge always increases the catalytic activity of these complexes, regardless of the oxidant, an indication of steric tuning. However, the electronic tuning of the catalytic activity by introducing substituents in the 5 and 3 positions of the aldehyde fragment has different effects depending on the oxygen source. For the one-phase system resulting from the use of PhIO, electron withdrawing groups increase (electron donating groups decrease) the catalytic activity of the complexes, which probably results from destabilisation (stabilisation) of [OMn(V)(salen)X], the identified active species making them more (less) reactive. However, when NaOCl is used, the observed behaviour is the opposite: electron donating groups make the complexes better catalysts. The apparent similarity between the solubility of the complexes in the organic solvent and their catalytic activity seems to suggest that solubility must play a key role in their activity.

Anchoring of a nickel(II) Schiff base complex onto activated carbon mediated by cyanuric chloride

The Schiff base nickel complex functionalised with hydroxyl groups, N,N′-ethylene-bis-(4-hydroxysalicyliminate)nickel(II), [Ni(4-HOsalen)], was anchored onto an air-oxidised activated carbon using cyanuric chloride (CC) as the linking agent. Complex anchoring was made in three consecutive steps: (i) oxidation of activated carbon with a mixture of N2 and air (with 5% O2); (ii) attachment of CC to the air-oxidised carbon surface functionalities, and (iii) reaction between the metal complex functionalised with hydroxyl groups and carbon-bound CC. The carbon-based materials were characterised by elemental analysis, surface techniques (scanning electron microscopy and X-ray photoelectron spectroscopy), X-ray diffraction, nitrogen adsorption isotherms and thermal analysis (temperature-programmed desorption and thermogravimetry). Data from all these techniques provided evidence that the nickel complex was anchored onto the air-oxidised activated carbon via CC.

Activated carbons with immobilised manganese(III)salen complexes as heterogeneous catalysts in the epoxidation of olefins: influence of support and ligand functionalisation on selectivity and reusability

A manganese(III) N2O2 Schiff base complex functionalised with hydroxyl groups on the aldehyde moieties, [Mn(4-HOsalhd)CH3COO], was immobilised onto a commercial activated carbon and on its air and acid oxidised forms: the unfunctionalised manganese(III) salen complex [Mn(salhd)Cl] was also immobilised onto the air oxidised activated carbon. All the materials were characterised by elemental analyses and by XPS and the type of oxygen functionalities present at the surface of the various activated carbons was characterised by TPD. The catalytic activities in the epoxidation of styrene of the manganese(III) salen complexes in homogeneous phase and heterogenised onto the activated carbon based materials were studied, using iodosylbenzene as oxidant and acetonitrile as solvent. All the heterogeneous catalysts are as chemoselective towards the styrene epoxide as their homogeneous counterparts, with the exception of the complex supported onto the nitric acid oxidised activated carbon, which exhibited the lowest values, a consequence of the catalytic role of the support. Catalyst reutilisation studies showed that the hydroxyl functionalised manganese(III) complex supported onto the two oxidised activated carbons kept the catalytic activity, contrasting with the hydroxyl functionalised manganese(III) complex supported onto the untreated activated carbon and the unfunctionalised manganese(III) complex supported onto the air oxidised activated carbon, for which a decrease in styrene epoxide yield was clearly observed. These results indicate that lack of oxygen functionality on the activated carbon or of complex functionalisation results in the deactivation of the manganese(III) salen based heterogeneous catalyst as a consequence of inefficient active phase anchoring. Conversely, the combination of support oxidation and of suitable complex functionalisation leads to the establishment of a covalent attachment of the hydroxyl functionalised Mn(III) complexes onto the carbon surface oxygen groups that retains an efficient site isolation of the complexes, both needed to produce very stable and reusable catalysts.

Physicochemical characterization of silylated functionalized materials

Silylation of several materials where the surface area arises from the internal pores (MCM-41 and FSM-16) or is essentially external (silica gel, and clays) was performed using three organosilanes: (3-aminopropyl)triethoxysilane (APTES), 4-(triethoxysilyl)aniline (TESA) and (3-mercaptopropyl)trimethoxysilane (MPTS). The materials were characterized by nitrogen adsorption-desorption at -196 degrees C, powder XRD, XPS, bulk chemical analysis, FTIR and (29)Si and (13)C MAS NMR. For MCM-41 and FSM-16 the highest amounts of organosilane are obtained for APTES, while for the remaining materials the highest amounts are for MPTS; TESA always anchored with the lowest percentage. In terms of surface chemical analysis, TESA anchored with the highest contents irrespectively of the material, and the opposite is registered for MPTS. Comparison of bulk vs surface contents indicate that TESA is mainly anchored at the material external surface. Moreover, with N or S (surface and bulk) contents expressed per unit of surface area, MCM-41 and FSM-16 (internal porosity) show the lowest amounts of silane; the highest amounts of silane per unit of surface area are obtained for the clays. Grafting of the organosilanes to the surface hydroxyl groups was corroborated by FTIR and (29)Si and (13)C MAS NMR. Furthermore, NMR data suggested that TESA and APTES grafted mostly through a bidentate approach, whereas MPTS grafted by a monodentate mechanism.

Simultaneous aluminium oxide pillaring and copper(II) Schiff base complexes encapsulation in a montmorillonite

Copper(II) acetylacetonate and two complexes with pentadentate N3O2 Schiff-base ligands derived from acetylacetone–bis(acetylacetonate)-3-amino-bis(propyldiimine), ([Cu(acac)2trien]), and bis(acetylacetonate)-3-methylamino-bis(propyldiimine), [Cu(acac)2Metrien], were encapsulated into a pillared clay (PILC) using a new methodology that involves simultaneous oligomer pillaring and complex encapsulation: in the present work the pillaring oligomer was [Al13O4(OH)24+x(H2O)12−x](7−x)+ and the starting clay was a Portuguese montmorilonite. All the materials were characterised by X-ray photoelectron spectroscopy, powder X-ray diffraction, adsorption of nitrogen at low temperature and infrared spectroscopy and, for copper-based materials, by chemical analysis. Data indicate that all three complexes have been immobilised within the matrix, but only for [Cu(acac)2] and [Cu(acac)2trien], did metal complex immobilisation take place concomitantly with aluminium pillar intercalation. Furthermore, the encapsulation of the latter complexes induced an increase in the PILC basal distance when compared with the pillared clay prepared without complex present. Finally, in all the materials the encapsulated complexes exhibit structural properties that are different from those of the free complexes, a consequence of the steric effects imposed by the porous structure of the PILC.

Controlled silver delivery by silver–cellulose nanocomposites prepared by a one-pot green synthesis assisted by microwaves

Controlled silver release from cellulosic nanocomposites was achieved by synthesizing silver nanoparticles, under microwave heating for 1-15 min, in a one-pot, versatile and sustainable process in which microcrystalline cellulose simultaneously functions as reducing, stabilizing and supporting agent in water; chitin, starch and other cellulose derivatives could also be used as reducing, stabilizing and supporting agents for silver nanoparticles and the method was also found to be extensible to the preparation of noble metal (Au, Pt) and metal oxide nanoparticle (ZnO, Cu, CuO and Cu(2)O) nanocomposites.

Evaluation of the sensitivity of genotoxicity and cytotoxicity endpoints in earthworms exposed in situ to uranium mining wastes

Earthworms were exposed for 56 days to a contaminated soil from an abandoned uranium mine and to the natural reference soil LUFA 2.2. The exposure occurred in situ: the containers with contaminated soil were placed near the mine pit; the containers with reference soil were placed in a reference site. For the assessment of metals bioaccumulation, DNA damages, cell-to-cell variation in DNA content, Median Fluorescence Intensity (MFI), coelomocytes frequency and proliferation, organisms were sampled after 0, 1, 2, 7, 14 and 56 days of exposure. For the assessment of radionuclides bioaccumulation, animals were sampled after 0, 14 and 56 days of exposure. As for growth, organisms were sampled after 0, 14, 28 and 56 days of exposure. The reproduction assay was performed according to the OECD (2004) guideline. DNA damages were assessed by comet assay and flow cytometry was used to determine cell-to-cell variation in DNA content, Median Fluorescence Intensity (MFI), coelomocytes frequency and proliferation. Results have shown a myriad of effects in the organisms exposed to the contaminated soil, namely: the inhibition of reproduction, growth reduction, DNA damages, cytotoxicity, changes in eleocytes fluorescence intensity, coelomocytes proliferation and bioaccumulation of metals and radionuclides. Our results showed that the evaluation of genotoxicity and cytotoxicity endpoints, along with other parameters at an individual level in standard reproduction assays conducted in situ, are important to improve the risk assessment process of areas contaminated with uranium and other radioactive mining wastes.

Epoxidation of styrene by a manganese(III) salen complex encapsulated in an aluminium pillared clay

The manganese(III) complex—carboxylate-[N,N′-bis(salicylaldehyde)cyclohexanediaminate]manganese(III), [Mn(salhd)CH3COO]—was encapsulated into an aluminium pillared clay (denoted as Al-WYO) using a two-step liquid phase methodology: (i) adsorption of manganese(II) acetate in ethanolic solution within Al-WYO, followed by (ii) diffusion of N,N′-bis(salicylaldehyde)cyclohexanediamine in ethanolic solution. The new material was characterised by several techniques (ICP-AES, XPS, FTIR, UV–Vis and low temperature nitrogen adsorption) which showed that in situ synthesis of the manganese(III) complex took place within the aluminium pillared clay porous structure. The catalytic activity of the heterogenised [Mn(salhd)CH3COO] in the epoxidation of styrene was studied in acetonitrile, at room temperature, using iodosylbenzene or sodium hypochlorite as oxygen source. With PhIO the new heterogeneous catalyst showed high styrene epoxide chemoselectivity and could be reused at least 3 times without significant loss in styrene epoxide yield, suggesting that no complex leaching took place under the reaction conditions used. When sodium hypochlorite was used as oxidant, high selectivity in by-products was observed, as well as extensive leaching of the catalyst into solution. XPS spectra of the catalyst after the catalytic reaction confirm manganese complex leaching and also show a significant decrease in aluminium content, thus suggesting that partial damage of aluminium pillars took place in this reaction media, inducing complex leaching.