Célia M. Ronconi

Nanoreservoir operated by ferrocenyl linker oxidation with molecular oxygen

The fabrication and efficient operation of a redox-driven hybrid nanoreservoir that contains the host–guest pair β-cyclodextrin (β-CD) and a ferrocenyl (–Fc) group attached to MCM-41 nanoparticles loaded with rhodamine B are reported. The operation process is based on the effects of pH that is related to the acid catalyzed oxidation of the ferrocenyl group by molecular oxygen (O2). By a thorough set of experiments, the combined effects of pH and oxygen are exploited to control the releasing process. Such experiments characterize the nanoreservoir at various points along the pathway, and show the level of control achieved over the release of rhodamine B. The results show that the same system can operate under different conditions, i.e., at high O2 levels and pH close to the physiological one, where the drug-like molecules could be rapidly released, or at low O2 levels and slightly acidic conditions (pH 5.5 and 6.5), where the drug will be slowly released. In essence, the work presented herein is a step forward in terms of redox-triggered release drug-like molecules from MCM-41.

Heterogeneous basic catalysts for biodiesel production

Biodiesel is one the main biofuels used as an alternative to fossil sources. It is mainly produced through the transesterification of oils and fats with methanol, under acid, basic or enzymatic catalysis. Today, the majority of the biodiesel production processes employ homogeneous base catalysts, such as NaOH or NaOCH3, which require expeditious purification procedures and yield significant amounts of waste. This review covers recent achievements in the field of basic heterogeneous catalysts for biodiesel production, focusing on the main systems being employed, their advantages and disadvantages. The present drawbacks and future challenges on basic heterogeneous catalytic systems for biodiesel production are also addressed in the concluding remarks.

Modified silica nanoparticles with an Aminonaphthoquinone

The synthesis and characterization of silica nanoparticles (NPs) covalently modified with an aminonaphthoquinone are reported. The aminopropylsilicagelnaphthoquinone (APSGNQ) was obtained by nucleophilic substitution of 2-methoxy-1,4-naphthoquinone with aminopropylsilicalgel (APSG) NPs. Solid state 13 C and 29 Si nuclear magnetic resonance spectra confirmed that the naphthoquinone is covalently bonded to APSG. Due to the solubility of APSGNQ in common organic solvents, solution ultraviolet-visible spectroscopy was used to determine the amount of naphthoquinone on the NPs surface (0.56 mmol of incorporated naphthoquinone per gram of APSGNQ) by comparison with the spectrum of 2-aminobutyl-1,4-naphthoquinone (ABNQ). Elemental analysis indicated that about 8% of the surface propylamine remained unreacted in APSGNQ. These multifunctional silica NPs have potential in medical applications.

Adsorption in a Fixed-Bed Column and Stability of the Antibiotic Oxytetracycline Supported on Zn(II)-[2-Methylimidazolate] Frameworks in Aqueous Media

A metal-organic framework, Zn-[2-methylimidazolate] frameworks (ZIF-8), was used as adsorbent material to remove different concentrations of oxytetracycline (OTC) antibiotic in a fixed-bed column. The OTC was studied at concentrations of 10, 25 and 40 mg L-1. At 40 mg L-1, the breakthrough point was reached after approximately 10 minutes, while at 10 and 25 mg L-1 this point was reached in about 30 minutes. The highest removal rate of 60% for the 10 mg L-1 concentration was reached after 200 minutes. The highest adsorption capacity (28.3 mg g-1) was attained for 25 mg L-1 of OTC. After the adsorption process, a band shift was observed in the UV-Vis spectrum of the eluate. Additional studies were carried out to determine the cause of this band shift, involving a mass spectrometry (MS) analysis of the supernatant liquid during the process. This investigation revealed that the main route of adsorption consisted of the coordination of OTC with the metallic zinc centers of ZIF-8. The materials were characterized by thermal analysis (TA), scanning electron microscopy (SEM), powder X-ray diffraction (XRD), and infrared spectroscopy (IR) before and after adsorption, confirming the presence of OTC in the ZIF-8 and the latter’s structural stability after the adsorption process.

6-Aminocoumarin-naphthoquinone conjugates: design, synthesis, photophysical and electrochemical properties and DFT calculations

Quatro novos conjugados do tipo 6-aminocumarina-naftoquinona foram sintetizados e suas propriedades fotofisicas e eletroquimicas, investigadas. O composto 2-cloro-3-(2-oxo-2H-cromen6-ilamino)-1,4-naftoquinona 1 nao apresentou fluorescencia apreciavel, em comparacao com a 6-aminocumarina, 6-AC. Visando entender as razoes da extincao da fluorescencia neste composto, duas estrategias foram imaginadas. Primeiramente, o composto 1 foi metilado no nitrogenio para remover a interacao eletrostatica intramolecular N-H…O=C que mantem as duas unidades fixas. Entretanto, as propriedades de emissao do produto 2 nao se mostraram significantemente diferentes das do precursor 1. Como os calculos usando a teoria do funcional da densidade dependente do tempo (TD-DFT) dos compostos 1 e 2 indicaram que a supressao da fluorescencia relaciona-se ao carater aceptor no anel naftoquinonico, a segunda estrategia envolveu a substituicao do atomo de cloro na posicao 2 do nucleo naftoquinonico por diferentes grupos doadores de eletrons (compostos 3-5). Novamente nao houve mudancas apreciaveis nas propriedades de emissao. Para explicar estes resultados foram feitos calculos TD-DFT dos estados fundamental (S0) e excitado (S1) de todas as moleculas em solucao, os quais indicaram que o grupo fluorescente (6-AC) doa eletrons para o LUMO da naftoquinona, resultando em uma transferencia de eletron fotoinduzida oxidativa (oxidative-PET). Four novel 6-aminocoumarin-naphthoquinone conjugates were synthesized and their photophysical and electrochemical properties, investigated. 2-Chloro-3-(2-oxo-2H-chromen-6ylamino)-1,4-naphthoquinone 1 did not present appreciable fluorescence in solution in comparison with 6-aminocoumarin, 6-AC. In order to understand the reasons for the fluorescence quenching in this compound, two strategies were attempted. Firstly, compound 1 was N-methylated to remove the intramolecular N-H…O=C electrostatic interaction that maintained the two units fixed, but the emission properties of the product 2 were not significantly different from those of 1. Time-dependent density functional theory (TD-DFT) calculations of compounds 1 and 2 indicate that the fluorescence quenching is related to the electron acceptor character of the naphthoquinone ring. The second strategy, therefore, involved the substitution of the chlorine atom in position 2 of the naphthoquinone nucleus for different electron donor groups (compounds 3-5), but again the emission properties did not change significantly. To explain these experimental findings, TD-DFT calculations of the ground (S0) and excited (S1) states of all molecules in solution were carried out. The results suggest that the energy states in these conjugates are such that the fluorescent group (6-AC) donates electrons to the naphthoquinone LUMO resulting in an oxidative photoinduced electron transfer (oxidative-PET).

Degradation of magnetic nanoparticles mimicking lysosomal conditions followed by AC susceptibility.

Abstract Background: A deeper knowledge on the effects of the degradation of magnetic nanoparticles on their magnetic properties is required to develop tools for the identification and quantification of magnetic nanoparticles in biological media by magnetic means. Methods: Citric acid and phosphonoacetic acid-coated magnetic nanoparticles have been degraded in a medium that mimics lysosomal conditions. Magnetic measurements and transmission electron microscopy have been used to follow up the degradation process. Results: Particle size is reduced significantly in 24 h at pH 4.5 and body temperature. These transformations affect the magnetic properties of the compounds. A reduction of the interparticle interactions is observed just 4 h after the beginning of the degradation process. A strong paramagnetic contribution coming from the degradation products appears with time. Conclusions: A model for the in vivo degradation of magnetic nanoparticles has been followed to gain insight on the changes of the magnetic properties of iron oxides during their degradation. The degradation kinetics is affected by the particle coating, in our case being the phosphonoacetic acid-coated particles degraded faster than the citric acid-coated ones.

Guanidine-functionalized Fe3O4 magnetic nanoparticles as basic recyclable catalysts for biodiesel production

Two organic superbases, 1,5,7-triazabicyclo[4,4,0]dec-5-ene (TBD) and 1,1,3,3-tetramethylguanidine (TMG), were anchored onto silica-coated and uncoated iron oxide nanoparticles, resulting in three (MNP–TBD, MNP–TMG and MNP@SiO2–TBD) recoverable basic nanocatalysts. The nanocatalysts were fully characterized by elemental analysis, infrared and Raman spectroscopies, X-ray diffraction, transmission electron microscopy, N2 adsorption/desorption isotherms, thermogravimetric analysis and magnetic measurements. X-ray diffraction indicated the presence of a spinel-structured iron oxide, and Raman spectroscopy revealed both magnetite and maghemite phases in the prepared nanocatalysts. The average particle sizes of the nanocatalysts were in the range of 11 to 12 nm, and they exhibited superparamagnetic behaviour at 300 K. Infrared spectroscopy indicated the presence of the superbases (TBD and TMG) on the surface of the silica-coated and uncoated iron oxide nanoparticles. The performance of the nanocatalysts was tested in the methanolysis reaction of soybean oil under different conditions. At the end of each reaction, the nanocatalysts were magnetically recovered from the medium, and the product was analysed and quantified by high-performance liquid chromatography (HPLC). MNP–TBD exhibited the best catalytic performance in the first cycle (96% biodiesel conversion); however, MNP@SiO2–TBD exhibited the best reusability.

The effect of the molecular structures of dicyanomethylene compounds on their supramolecular assembly, photophysical and electrochemical properties

Two series of flexible dicyanomethylene compounds, specifically, class 1 and class 2 compounds, have been designed and synthesised. In class 1 compounds, the dicyanomethylene groups are separated by glycol chain spacers of different lengths, whereas, in class 2 compounds, the spacers are alkyl linkers of different lengths. The notion underlying the design of these compounds is that in class 1 molecules, the spacers contain donor oxygen atoms that could not only form hydrogen bonds during the course of crystal packing but also promote withdrawing effects that modify the photophysical and electrochemical properties of these molecules in solution; in contrast, these effects would be absent for class 2 molecules. However, this study revealed that, with respect to crystal packing, the size of the spacers and their even and odd numbers of atoms are more important than their chemical nature. All of the synthesised compounds exhibited blue emission in the solid state and in CH2Cl2 solutions. The photophysical and electrochemical properties of these compounds in solution were not significantly affected by the type and length of the spacer that was used in each molecule. In the solid state, however, the compound with the shortest spacer showed the highest Stokes shift. The electronic transitions for the synthesized compounds in solution were explained by density functional theory and time-dependent density functional theory calculations, which indicated that the methylene moieties control the properties of both classes of compounds and that the spacers do not conjugate with the end groups. These two series of flexible dicyanomethylene compounds could be utilised as molecular building blocks for the development of new solids with novel properties.

A series of coordination networks constructed from the rigid ligand 4,4′-ethynylenedibenzoate: topological diversity, entanglement, supramolecular interactions and photophysical properties

Four coordination networks (CNs), i.e., [Co(edb)(H2O)(Py)2], 3; [Cd(edb)(DMSO)2]·0.5(DMSO), 4; [Er2(edb)3(DMSO)2(H2O)2], 5; and [Gd2(edb)3(H2O)4], 6 (edb2− = 4,4′-ethynylenedibenzoate), were synthesized and structurally characterized, and the luminescence properties of CNs 4 and 5 were investigated. In CN 3, the ligand adopts a bridging coordination mode that connects one Co(II) ion to another, resulting in a 1D CN. CNs 4 and 5 contain binuclear centers that are linked to four ligands in the chelating and bridging coordination modes. CN 4 has a 2D → 3D inclined polycatenated structure, whereas CN 5 exhibits a 3D network because the voids created by the long ligand are stabilized by the π–π stacking interactions, thereby avoiding the entanglement of the structure. CN 6 has a paddle-wheel structure with a two-fold interpenetrated rob topology. The photophysical properties of the compound H2edb and CNs 4 and 5 were studied in the solid state. Compound 2 (H2edb) displays strong absorption bands at 325 and 350 nm and emission at 385 nm. Upon complexation with Er(III), the emission was quenched. The emissions of CN 4 were due to the intraligand transitions.

Studies of the Colloidal Properties of Superparamagnetic Iron Oxide Nanoparticles Functionalized with Platinum Complexes in Aqueous and PBS Buffer Media

The authors would like to thank the Brazilian agencies National Council for Scientific and Technological Development (CNPq: Jovens Pesquisadores em Nanotecnologia grant number 550572/2012-0 and G. B. da Silva was recipient of Science without borders fellowship grant number 279444/2013-9), Brazilian Federal Agency for Support and Evaluation of Graduate Education (CAPES) and Rio de Janeiro Research Foundation (FAPERJ) for financial support. M. D. Vargas and C. M. Ronconi are recipients of CNPq research fellowships. We also thank the Multiuser Laboratory of Material Characterization (http://www.uff.br/lamate/). R. Costo and M. P. Morales would like to thank NANOMAG project (EC FP-7 grant agreement number 604448) for funding. X-ray diffraction, FTIR spectroscopy and thermogravimetric and chemical analysis were carried out in the support laboratories of Instituto de Ciencia de Materiales de Madrid (ICMM/CSIC).