Cristina Freire

Designing Novel Hybrid Materials by One-Pot Co-condensation: From Hydrophobic Mesoporous Silica Nanoparticles to Superamphiphobic Cotton Textiles

This work reports the synthesis and characterization of mesoporous silica nanoparticles (MSNs) functionalized with tridecafluorooctyltriethoxysilane (F13) and their in situ incorporation onto cotton textiles. The hybrid MSNs and the functional textiles were prepared by a one-pot co-condensation methodology between tetraethylorthosilicate (TEOS) and F13, with hexadecyltrimethylammonium chloride (CTAC) as the template and triethanolamine as the base. The influence of the F13 to TEOS molar ratio (1:10, 1:5 and 1:3) on the nanoparticle morphology, porosity, degree of functionalization, and hydro/oleophobic properties is discussed. The hybrid nanosilicas presented high colloidal stability and were spherical and monodispersed with average particle size of ∼45 nm. They also showed high surface areas, large pore volumes, and a wormhole-type mesoporous structure. The increase in the organosilane proportion during the co-condensation process led to a more radially branched wormhole-like mesoporosity, a decrease in the surface area, pore volume, and amount of surface silanol groups, and an enrichment of the surface with fluorocarbon moieties. These changes imparted hydrophobic and oleophobic properties to the materials, especially to that containing the highest F13 loading. Cotton textiles were coated with the F13-MSNs through an efficient and less time-consuming route. The combination between surface roughness and mesoporosity imparted by the MSNs, and the low surface energy provided by the organosilane resulted in superhydrophobic functional textiles. Moreover, the textile with the highest loading of fluorocarbon groups was superamphiphobic.

Electrochemical and structural studies of nickel(II) complexes with N2O2 Schiff base ligands 2. Crystal and molecular structure of N,N′-l,2-ethane-1,2-diyl-bis(2- hydroxyacetophenonylideneiminate)nickel(II), N, N′-1,2-cis cyclohexane-1,2-diyl-bis(2-hydroxyacetophenonylideneiminate)- nickel(II) and N,N′-1,2-benzene-1,2-diyl-bis(3,5-dichlorosalicylideneiminate)nickel(II)

Reductive and oxidative chemistry of three complexes of formula [Ni(L)], where L represents a N2O2 Schiff base pseudomacrocyclic ligand based on salicylaldehyde derivatives and three different diamines, was studied in (CH3)2SO: N,N′-1,2-ethane-1,2-diyl-bis(2-hydroxyacetophenonylideneiminate)nickel(II) (1); N,N′-1,2-cis-cyclohexane-1,2-diyl-bis(2-hydroxyacetophenonylideneiminate)nickel(II) (2); N,N′-1,2-benzene-1,2-diyl-(bis(3,5-dichlorosalicylideneiminate)nickel(II) (3). Electrochemical behavior of the complexes was determined by cyclic voltametry, and EPR spectroscopy was used to characterize the one-electron reduced/oxidized species. Reduction of the complexes 1 and 2 yielded Ni(I) complexes with a dxy ground state (gz>gx, gy), but the reduction of 3 is ligand-centered as suggested from the pseudo-isotropic radicalar EPR signal of frozen electrolyzed solutions. Oxidation of all three complexes is metal-centered and the oxidized products are low spin hexacoordinate Ni(III) species with two solvent molecules coordinated axially, with a dz2 ground state (gx, gy>gz). The crystal structures of the three Ni(II) complexes were determined from single crystal X-ray diffraction data collected with the use of Mo Kα radiation. 1: space group C2/c with a = 25.963(3), b = 7.2973(4), c = 17.357(2) A, β = 107.085(5)°, Z = 8 (R = 0.061); 2: space group P21/a with a = 9.645(6), b = 19.149(16), c = 10.743(5) A, β = 94.66(2)°, Z = 4 (R = 0.085); 3: space group P21/n with a = 13.372(5), b = 8.785(2), c = 16.534(5) A, β = 101.60(3)°, Z = 4 (R = 0.054). Crystal packing of 1 and 3 involves the pairing of two centrosymmetrical related molecules in dimers, but that of 2 shows no systematic parallel orientation of any part of the molecules. X-ray structural data have provided a rationale for the E12 values obtained for the reduction and oxidation processes.

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.

Electrochemical and X-ray studies of nickel(II) Schiff base complexes derived from salicylaldehyde: Structural effects of bridge substituents on the stabilisation of the +3 oxidation state

Abstract The oxidative chemistry of three Ni(II) complexes with Schiff base ligands derived from salicylaldehyde and diamines with different steric demands, N,N′-2-methylpropane-2,3-diyl-bis(salicylideneiminate)nickel(II) (1), N,N′-1,2-cyclohexyl-1,2-dyil-bis(salicylideneiminate)nickel(II) (2) and N,N′-2,3-dimethylbutane-2,3-diyl-bis(salicylideneiminate)nickel(II) (3), was studied by cyclic voltammetry and chronoamperometry in N,N′-dimethylformamide and (CH3)2SO. The electrogenerated species were characterised by EPR spectroscopy. All three complexes exhibited metal-centred oxidised processes and the oxidised products were low-spin six-coordinate Ni(III) species (dz2 ground state) with two solvent molecules axially coordinate. Addition of pyridine resulted in the replacement of solvent molecules with no changes in the ground state. The crystal structures of compounds 1 and 3 were determined from single crystal X-ray diffraction data, and the crystal packing for any of the complexes did not show any systematic parallel orientation of any part of the molecules. X-ray structural data for the Ni(II) complexes provided a rationale for the E1/2 values obtained in the oxidation processes and for the relative energy of the low-lying excited duplets of the electrogenerated Ni(III) species.

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.

Phenolic Profiling of Portuguese Propolis by LC-MS Spectrometry: Uncommon Propolis Rich in Flavonoid Glycosides

INTRODUCTION Propolis is a chemically complex resinous substance collected by honeybees (Apis mellifera) from tree buds, comprising plant exudates, secreted substances from bee metabolism, pollen and waxes. Its chemical composition depends strongly on the plant sources available around the beehive, which have a direct impact in the quality and bioactivity of the propolis. Being as Portugal is a country of botanical diversity, the phenolic characterisation of propolis from the different regions is a priority. OBJECTIVE Extensive characterisation of the phenolic composition of Portuguese propolis from different continental regions and islands. METHOD Forty propolis ethanolic extracts were analysed extensively by liquid chromatography with diode-array detection coupled to electrospray ionisation tandem mass spectrometry (LC-DAD-ESI-MS(n) ). RESULTS Seventy-six polyphenols were detected in the samples and two groups of propolis were established: the common temperate propolis, which contained the typical poplar phenolic compounds such as flavonoids and their methylated/esterified forms, phenylpropanoid acids and their esters, and an uncommon propolis type with an unusual composition in quercetin and kaempferol glycosides - some of them never described in propolis. CONCLUSION The method allowed the establishment of the phenolic profile of Portuguese propolis from different geographical locations, and the possibility to use some phenolic compounds, such as kaempferol-dimethylether, as geographical markers. Data suggest that other botanical species in addition to poplar trees can be important sources of resins for Portuguese propolis.

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.

Synthesis and Characterization of Benzo-15-Crown-5 Ethers with Appended N2O Schiff Bases

New derivatives of benzo-15-crown-5 with flexible appended N2O unsymmetrical Schiff bases were prepared by a two step procedure which involves: (i) preparation of N2O Schiff bases by condensation of hydrazine with salicylaldehyde, 3-methoxysalicylaldehyde or 2-hydroxy-1-naphtaldehyde and (ii) reaction of the resulting NH2 functionalized compounds with 4’-formyl-benzo-15-crown-5.

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.

Novel electrochemical sensor based on N-doped carbon nanotubes and Fe3O4 nanoparticles: simultaneous voltammetric determination of ascorbic acid, dopamine and uric acid.

A new modified electrode based on N-doped carbon nanotubes functionalized with Fe3O4 nanoparticles (Fe3O4@CNT-N) has been prepared and applied on the simultaneous electrochemical determination of small biomolecules such as dopamine (DA), uric acid (UA) and ascorbic acid (AA) using voltammetric methods. The unique properties of CNT-N and Fe3O4 nanoparticles individually and the synergetic effect between them led to an improved electrocatalytic activity toward the oxidation of AA, DA and UA. The overlapping anodic peaks of these three biomolecules could be resolved from each other due to their lower oxidation potentials and enhanced oxidation currents when using the Fe3O4@CNT-N modified electrode. The linear response ranges for the square wave voltammetric determination of AA, DA and UA were 5-235, 2.5-65 and 2.5-85μmoldm(-3) with detection limit (S/N=3) of 0.24, 0.050 and 0.047μmoldm(-3), respectively. These results show that Fe3O4@CNT-N nanocomposite is a promising candidate of cutting-edge electrode materials for electrocatalytic applications.