Electrochemical characterization of a novel salen type modified electrode

The nickel(II) complex with H2saltMe, a N2O2 Schiff base ligand derived from salicylaldehyde, was oxidatively electropolymerized on Pt electrodes in CH3CN/0.1 mol dm-3 tetraethylammonium perchlorate (TEAP) to generate polymer films that exhibit reversible oxidative electrochemical behavior in a wide potential range (0.0-1.3 V), high conductivity, and stability/durability

A voltammetric tool for the evaluation of propolis antioxidant activity

Propolis (bee glue) is a sticky dark-colored material that honeybees collected from parts of plants, buds and exudates, and used as construction and defense material in the hive. This resinous substance is a rich source of phenolic compounds, and its chemical composition is strongly influenced by its phytogeographic origin. This research outlines the evaluation of the redox profile and the quantification of the total antioxidant capacity in Portuguese propolis from different origins and potential floral sources Populus x canadensis Moench and Cistus ladanifer L through cyclic voltammetry and differential pulse voltammetry. Although several oxidation processes were showed by propolis samples, which were dependent of the resin origin, common oxidation potentials within the majority of samples of a region were detected, suggesting an analogous chemical composition in respect of electroactive species. Based on the quantification of the total electroactive antioxidant power, it was found that propolis with higher antioxidant activity was from coast center, followed by north ~ Azores Archipelago > central interior > Madeira Island > south.Soraia I. Falcão thanks Foundation for Science and Technology (FCT) for the PhD grant SFRH/BD/44855/2008, financially supported by POPH-QREN and FSE. Thanks also to FCT for financial support provided to CIMO (PEst-OE/AGR/ UI0690/2011). Thanks to National Federation of Portuguese Beekeepers for propolis samples.info:eu-repo/semantics/publishedVersio

Oxidation of ferrocene derivatives at a Poly[Ni(saltMe)] modified electrode

The characterization of film permeability and mediation properties of poly[Ni(saltMe)] modified electrodes were evaluated by studying the oxidation of ferrocene and 1,1’-dimethylferrocene at these electrodes by rotating-disk voltammetry. The effects of varying the substrate and its solution concentration, film thickness, rotation speed and electrode potential on the limiting current density were analysed using the model of Albery

The volatile composition of Portuguese propolis towards its origin discrimination

The volatiles from thirty six propolis samples collected from six different geographical locations in Portugal (mainland, Azores archipelago and Madeira Island) were evaluated. Populus x canadensis Moenchen leaf-buds and Cistus ladanifer L. branches essential oils were comparatively analysed. The essential oils were isolated by hydrodistillation and analysed by Gas Chromatography (GC) and Gas Chromatography-Mass Spectrometry (GC-MS). Cluster analysis based on propolis samples volatiles chemical composition defined three main clusters, not related to sample site collection. Cluster I grouped 28 samples with high relative amounts of oxygen-containing sesquiterpenes (20-77%), while cluster II grouped 7 samples rich in oxygen-containing monoterpenes (9-65%) and the only sample from cluster III was monoterpene hydrocarbons rich (26%). Although Populus x canadensis and Cistus ladanifer were associated as resin sources of Portuguese propolis, other Populus species as well as plants like Juniperus genus may contribute to the resin in specific geographical locations.Soraia I. Falcão thanks Fundação para a Ciência e a Tecnologia (FCT) for the PhD grant SFRH/BD/44855/2008, financially supported by POPH-QREN and FSE. This study was partially funded by FCT, under Pest-OE/EQB/LA0023/2011 and PTDC/CVT-EPI/2473/2012. Thanks to National Federation of Portuguese Beekeepers for propolis samples.info:eu-repo/semantics/publishedVersio

Spectroelectrochemical characterisation of a poly[Ni(saltMe)] modified electrode

Electrogenerated polymers based on the nickel(II) compIex 2,3-dimetbyl- N,N -bis(salicylidene )butane-2,3- diaminatoniekel(II), poly[Ni(saltMe)], were characterized by in situ FTIR and UV/Vis spectroscopy and ex-situ EPR spectroscopy in order to gain insights into film structure, electronic states and charge conduction. The role of the nickel ions during film oxidation was probed by using EPR to study naturally abundant Ni and 61Ni-enriehed polymers

A combined electrochemical quartz-crystal microbalance probe beam deflection (EQCM-PBD) study of solvent and ion transfers at a poly[Ni(saltMe)]: modified elecrode during redox switching

The oxidative polymerization of the complex2,3-dimelhyl-N,N-bis( salicylidene)butane-2,3-diaminatonickel( n), [Ni(saltMe)], was monitored by the electrochemical quartz microbalance (EQCM) and crystal impedance techniques. Polymerisation efficiency was maintained throughout deposition of a film, which behaved rigidly, on the electrode

Spectroelectrochemical characterisation of copper salen-based polymer modified electrode

Electrogenerated polymers based on copper salen-type complexes were characterised electrochemically and by in situ UV–vis and ex situ EPR spectroscopy. The films, poly[Cu(salen)] and poly[Cu(saltMe)], exhibit reversible oxidative electrochemical behaviour in a wide potential range (0.0–1.5 V). Different regimes for charge transport behaviour are accessed by manipulation of film thickness and experimental time scale: thin films (surface concentration, Γ ca. 90 nmol cm−2) exhibit a changeover from thin-layer to diffusion control regime at a critical scan rate that depends on polymer and film thickness: 0.15–0.20 V s−1 for poly[Cu(salen)], 90 < Γ < 130 nmol cm−2 and 0.20–0.30 V s−1 for poly[Cu(saltMe)], 170 < Γ < 230 nmol cm−2. UV–vis and EPR spectroscopies have allowed the characterisation of electronic states in the reduced and oxidised forms. The role of the copper atom during film oxidation was probed by combining UV–vis data with EPR on copolymers of the copper and nickel complexes. Data from both techniques are consistent and indicate that polymerisation and redox switching are associated with ligand-based processes. EPR of Ni-doped Cu polymers provided evidence for the non-involvement of the metal centre in polymer oxidation; like the analogous nickel polymers, copper polymers behave like delocalised π-system (‘conducting’) rather than discrete site (‘redox’) polymers

Propolis phenolic profile: a study in the Atlantic islands of Azores

Propolis it is a natural resinous substance that honeybees (Apis melifera, L.) collect from buds and exudates of plants and transformed in the presence of bee enzymes. This substance plays an important role in the hive as a construction and defence material due to its chemical and biological properties.[1] Propolis composition is extremely complex and dependent on its vegetal source, geographical location and climatic conditions. Typically this natural product includes resin (50%), beeswax (30%), essential oils (10%), pollen (5%) and other organic compounds (5%).[2] Due to the abundance in phenolic compounds (flavonoids, phenolic acids and their esters) and to its biological and pharmacological properties this group of substances became the target of many research studies in propolis. This work outlines an extensive qualitative and quantitative characterization of the phenolic composition of Azorean islands propolis. For that, eleven samples of propolis, from S. Miguel and Terceira island, were extracted and characterized according to the previous work.[3] The HPLC results show a similar chromatographic profile for all samples, despite their origin, with 37 compounds identified by ESI-MS/MSn analysis and confirmed by HPLC-DAD. Although the samples revealed a similar phenolic composition, significant differences in the concentrations of the different compounds were found, probably due to the differences in flora distribution around the beehive, and therefore resin availability for bees

Propolis phenolic profile: a study in the Atlantic islands of Azores

Propolis it is a natural resinous substance that honeybees (Apis melifera, L.) collect from buds and exudates of plants and transformed in the presence of bee enzymes. This substance plays an important role in the hive as a construction and defence material due to its chemical and biological properties.[1] Propolis composition is extremely complex and dependent on its vegetal source, geographical location and climatic conditions. Typically this natural product includes resin (50%), beeswax (30%), essential oils (10%), pollen (5%) and other organic compounds (5%).[2] Due to the abundance in phenolic compounds (flavonoids, phenolic acids and their esters) and to its biological and pharmacological properties this group of substances became the target of many research studies in propolis. This work outlines an extensive qualitative and quantitative characterization of the phenolic composition of Azorean islands propolis. For that, eleven samples of propolis, from S. Miguel and Terceira island, were extracted and characterized according to the previous work.[3] The HPLC results show a similar chromatographic profile for all samples, despite their origin, with 37 compounds identified by ESI-MS/MSn analysis and confirmed by HPLC-DAD. Although the samples revealed a similar phenolic composition, significant differences in the concentrations of the different compounds were found, probably due to the differences in flora distribution around the beehive, and therefore resin availability for bees

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

The oxidative chemistry of three Ni(II) complexes with Schiff base ligands derived from salicylaldehyde and diamines with different steric demands, N,N9-2-methylpropane-2,3-diyl-bis(salicylideneiminate)nickel(II) (1), N,N9-1,2-cyclohexyl-1,2-dyil-bis(salicylideneiminate)- nickel(II) (2) and N,N9-2,3-dimethylbutane-2,3-diyl-bis(salicylideneiminate)nickel(II) (3), was studied by cyclic voltammetry and chronoamperometry in N,N9-dimethylformamide and (CH3)2SO