Cristiano Giacomelli

Electrochemical oxidation of quercetin in hydro-alcoholic solution

The electrochemistry of quercetin hydro-alcoholic solutions of pH 2.2 to 9.2 was studied by cyclic voltammetry, controlled-potential electrolysis and UV-Vis spectroscopy. Cyclic voltammograms for quercetin showed three oxidation peaks and one reduction peak depending on the experimental conditions. The two-electron two-proton oxidation process at the first peak led to the formation of the corresponding ortho-quinone, which is an electrochemically active and unstable species, as evidenced by the dependence of the cyclic voltammogram profile on the applied scan rate, in agreement with the EC mechanism. Controlled-potential electrolysis yielded three products as characterized by UV-Vis spectroscopy. A reaction scheme comprising electrochemical and chemical steps was proposed for the electro-oxidation of the quercetin in hydro-alcoholic solutions on basis of experimental evidences obtained in this work and elsewhere.

Block Copolymer Systems: From Single Chain to Self-Assembled Nanostructures

Recent advances in the field of macromolecular engineering applied to the fabrication of nanostructured materials using block copolymer chains as elementary building blocks are described in this feature article. By highlighting some of our work in the area and accounting for the contribution of other groups, we discuss the relationship between the physical-chemical properties of copolymer chains and the characteristics of nano-objects originating from their self-assembly in solution and in bulk, with emphasis on convenient strategies that allow for the control of composition, functionality, and topology at different levels of sophistication. In the case of micellar nanoparticles in solution, in particular, we present approaches leading to morphology selection via macromolecular architectural design, the functionalization of external solvent-philic shells with biomolecules (polysaccharides and proteins), and the maximization of micelle loading capacity by the suitable choice of solvent-phobic polymer segments. The fabrication of nanomaterials mediated by thin block copolymer films is also discussed. In this case, we emphasize the development of novel polymer chain manipulation strategies that ultimately allow for the preparation of precisely positioned nanodomains with a reduced number of defects via block-selective chemical reactivity. The challenges facing the soft matter community, the urgent demand to convert huge public and private investments into consumer products, and future possible directions in the field are also considered herein.

Antioxidant activity of phenolic and related compounds: a density functional theory study on the O–H bond dissociation enthalpy

Abstract We report here on calculations at the hybrid DFT/HF (B3-LYP/6-31G(d, p)) level of the O–H bond dissociation enthalpy (O–H BDE) of phenylpropenoic acids (caffeic, ferulic, p-coumaric and cinnamic) and phenolic acids and related compounds (gallic, methylgallate, vanillic and gentisic) in order to gain insight into the understanding of structure–antioxidant activity relationships. The results were correlated and discussed mainly on the basis of experimental data in a companion work (Galato D, Giacomelli C, Ckless K, Susin MF, Vale RMR, Spinelli A. Antioxidant capacity of phenolic and related compounds: correlation among electrochemical, visible spectroscopy methods and structure-antioxidant activity. Redox Report 2001; 6: 243–250). The O–H BDE values showed remarkable dependence on the hydroxyl position in the benzene ring and the existence of additional interaction due to hydrogen bonding. For parent molecules, the experimental antioxidant activity (AA) order was properly obeyed only when intramolecular hydrogen bonding was present in the radicalized structures of o-dihydroxyl moieties. In structurally related compounds, excellent correlation with experimental data was in general observed (0.64 < ρ < 0.99). However, it is shown that excellent correlation can also be obtained for this series of compounds considering p-radicalized structures which were not stabilized by intramolecular hydrogen bonding, but this had no physical meaning. These findings suggested that the antioxidant activity evaluation of phenolic and related compounds must take into consideration the characteristics of each particular compound.

In vivo human electrochemical properties of a NiTi‐based alloy (Nitinol) used for minimally invasive implants

The development of a homemade device for in vivo human determination of the open circuit potential (OCP) of Nitinol is described. Pseudo-reference electrodes (316L stainless steel and Pt) were initially tested and validated in vitro using simulated body fluids. As judged from the excellent electrochemical responses in terms of both accuracy and precision, the most ideal system comprised the combination of sterilized Pt (pseudo-reference) and Nitinol (working) needle-shaped electrodes. The average in vivo human OCP determined from independent measurements on six human patients with indication of direct arterial surgery was -0.334 +/- 0.030 V/SCE. This value was in good agreement with data recorded in vitro using simulated body fluids (-0.313 +/- 0.003 V/SCE in AFNOR S90-701 artificial saliva; -0.334 +/- 0.001 V/SCE in artificial urine; -0.239 +/- 0.007 V/SCE in Ringers solution). The thin surface film protecting the bulk NiTi alloy is therefore not susceptible to active dissolution at rest as long as the break down potentials (>>0.0 V/SCE) so far reported are well above OCP measured in this study. These results highlight the importance of evaluating the corrosion resistance of Nitinol under realistic conditions (mechanical loads, wear and fatigue) in order to establish multifaceted mechanisms that might lead to accelerated dissolution and failure of implanted stents.

Electrochemistry of vitamin E hydro-alcoholic solutions

O comportamento eletroquimico da vitamina E em meio hidro-alcoolico foi estudado na faixa de pH 3,1-12,1 aplicando-se as tecnicas voltametria ciclica, eletrolise com potencial controlado e espectroscopias UV-Vis, IR e 13C RMN. Observou-se que a presenca de agua tem consequencias importantes na estabilidade quimica das especies geradas eletroquimicamente. Em meio hidro-alcoolico e sobre eletrodos de carbono vitreo, a vitamina E apresenta tres picos de oxidacao, enquanto que apenas um pico e observado em outros solventes. Embora a reacao eletroquimica no primeiro pico seja a mesma na presenca e na ausencia de agua, a qual compreende a transferencia de dois eletrons em uma etapa, duas reacoes eletroquimicas e tres quimicas subsequentes ao primeiro pico foram pela primeira vez estabelecidas com base em evidencias eletroquimicas em meio hidro-alcoolico. Estes resultados sao considerados muito importantes levando-se em consideracao o papel mediador na transferencia de eletrons entre a fase aquosa e lipidica que a vitamina E exerce no organismo.

Interaction of poly(4-vinylpyridine) with copper surfaces: electrochemical, thermal and spectroscopic studies

A interacao do polimero poli(4-vinilpiridina) (P4VP) e ions tiocianato com cobre em solucoes acidas foi estudada atraves de voltametria ciclica, termogravimetria, analise elementar e espectroscopia na regiao do infravermelho. Observou-se que os ions Cu(I) eletrogerados em ca. -0,45 V/ECS na superficie do eletrodo promovem uma reacao de complexacao com P4VP e SCN-, ambos presentes em solucao. O complexo polimerico eletroativo resultante cresce sobre a superficie do eletrodo como um filme e o centro metalico e oxidado para Cu(II) numa etapa subsequente em ca. -0,23 V/ECS. De acordo com os resultados termogravimetricos, o complexo obtido e menos estavel do que o P4VP puro, conforme indicado pelo abaixamento da temperatura inicial de degradacao de ca. 400 oC (P4VP) para ca. 200 oC (complexo). A analise elementar do filme revelou uma composicao quimica de 2:1:2 para P4VP:Cu:SCN- e os espectros na regiao do infravermelho indicaram que tal complexo polimerico e formado por um centro metalico de cobre coordenado pelos atomos de nitrogenio dos aneis piridinicos e ions tiocianato.

Behavior of a Co-Cr-Mo biomaterial in simulated body fluid solutions studied by electrochemical and surface analysis techniques

The behavior of a Co-Cr-Mo biomaterial used as dental prosthesis was studied by electrochemical (Open Circuit Potential (OCP) and potentiodynamic polarization) and surface analysis techniques (Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS)) in artificial saliva, artificial saliva with modified temperature (7 °C - 47 °C) and pH (1.4 - 13.4), and containing fluoride (1500 ppm). The results revealed that the surface morphology after potentiodynamic polarization is highly heterogeneous exhibiting three regions of different composition. Soluble metal species such as CrO42- were released to the solution during the potentiodynamic polarization. The electrochemical processes were markedly influenced by solution temperature and pH, whereas the presence of fluoride did not produce changes in the system.

Efficient Condensation of DNA into Environmentally Responsive Polyplexes Produced from Block Catiomers Carrying Amine or Diamine Groups

The intracellular delivery of nucleic acids requires a vector system as they cannot diffuse across lipid membranes. Although polymeric transfecting agents have been extensively investigated, none of the proposed gene delivery vehicles fulfill all of the requirements needed for an effective therapy, namely, the ability to bind and compact DNA into polyplexes, stability in the serum environment, endosome-disrupting capacity, efficient intracellular DNA release, and low toxicity. The challenges are mainly attributed to conflicting properties such as stability vs efficient DNA release and toxicity vs efficient endosome-disrupting capacity. Accordingly, investigations aimed at safe and efficient therapies are still essential to achieving gene therapy clinical success. Taking into account the mentioned issues, herein we have evaluated the DNA condensation ability of poly(ethylene oxide)113-b-poly[2-(diisopropylamino)ethyl methacrylate]50 (PEO113-b-PDPA50), poly(ethylene oxide)113-b-poly[2-(diethylamino)ethyl methacrylate]50 (PEO113-b-PDEA50), poly[oligo(ethylene glycol)methyl ether methacrylate]70-b-poly[oligo(ethylene glycol)methyl ether methacrylate10-co-2-(diethylamino)ethyl methacrylate47-co-2-(diisopropylamino)ethyl methacrylate47] (POEGMA70-b-P(OEGMA10-co-DEA47-co-DPA47), and poly[oligo(ethylene glycol)methyl ether methacrylate]70-b-poly{oligo(ethylene glycol)methyl ether methacrylate10-co-2-methylacrylic acid 2-[(2-(dimethylamino)ethyl)methylamino]ethyl ester44} (POEGMA70-b-P(OEGMA10-co-DAMA44). Block copolymers PEO113-b-PDEA50 and POEGMA70-b-P(OEGMA10-co-DEA47-co-DPA47) were evidenced to properly condense DNA into particles with a desirable size for cellular uptake via endocytic pathways (R(H) ≈ 65-85 nm). The structure of the polyplexes was characterized in detail by scattering techniques and atomic force microscopy. The isothermal titration calorimetric data revealed that the polymer/DNA binding is endothermic; therefore, the process in entropically driven. The combination of results supports that POEGMA70-b-P(OEGMA10-co-DEA47-co-DPA47) condenses DNA more efficiently and with higher thermodynamic outputs than does PEO113-b-PDEA50. Finally, circular dichroism spectroscopy indicated that the conformation of DNA remained the same after complexation and that the polyplexes are very stable in the serum environment.

Formation of annexin-a5 protein/block copolymer micelle complexes: QCM-D and PAGE experiments.

The Annexin-A5 (Anx5) protein is a specific marker of the exposure of phosphatidylserine molecules at the surface of cells, which occurs in processes such as apoptosis and platelet activation. Decoration of self-assembled block copolymer nanostructures by Anx5 is of particular interest in micelle-mediated target drug delivery or in vivo magnetic resonance imaging, the Anx5 imparting (bio)functionality to the system. In this work, the reversible binding of the Anx5 onto polystyrene-b-poly(2-phosphatethyl methacrylate-co-2-hydroxyethyl methacrylate) (PS-b-P(PEMA-co-HEMA)) block copolymer micelles in the presence of Ca2+ ions is described using Quartz crystal microbalance with dissipation monitoring (QCM-D) and polyacrylamide gel electrophoresis (PAGE) analysis. QCM-D experiments confirmed the binding process as well as its reversibility and dependence on the characteristics of macromolecular assemblies, such as the number of phosphonic diacid groups (Pmic) and hydrodynamic diameter (2RH). A linear relationship between the amount of micelles and the amount of protein bound onto the micelle surface until a saturation point was established by QCM-D. The amount of Anx5 bound to PS-b-P(PEMA-co-HEMA) micelles was successfully quantified by PAGE experiments in nondenaturing conditions, which also corroborated that the binding process is mediated by Ca2+ ions. The ability of such surface (bio)-functionalized nanoparticle systems to stabilize and transport hydrophobic loads was highlighted by transmission electron microscopy (TEM) of assemblies with entrapped iron oxide particles.

The effect of oxalic acid on the corrosion of carbon steel

The effect of oxalic acid (OA) on corrosion resistance of carbon steel in sulphuric acid pH=2.5‐6.0 solutions containing 10−7‐10−3M OA was investigated by means of potentiodynamic polarisation measurements and immersion tests. The results suggest that OA is a good corrosion inhibitor for carbon steel, exhibiting inhibition efficiencies (IE) ranging from 50 to 85 per cent in dilute 10−7‐10−5M OA solutions of pH>3.0, whereas for pH≤3.0 solutions, an increase in corrosion rate was found. Non‐accelerated experiments (weight loss tests) carried out by immersing carbon steel specimens into OA‐containing solutions during at least 6 h revealed only positive IE values, regardless of both solution pH and OA content. The results were explained considering the solution composition as function of pH.