Sergio H. Toma

The coordination chemistry at gold nanoparticles

In gold nanoparticles the surface metal atoms play a major role, determining their chemical and physical properties by interacting with donor-acceptor species or ligands in a similar way as the related metal complexes. In addition, coherent oscillations of the metal electrons in resonance with the frequency of the exciting light give rise to localized surface plasmons responsible for an enhancement of the local electric field and SERS effect, allowing a wide range of applications in chemistry, biology and nanotechnology. Multifunctional bridging ligands can be employed for simultaneously binding metal ions and surface atoms. The attractive point of this approach is the possibility of exploiting the charge controlled stabilization by the metal complexes, while imparting new characteristics and properties to the modified nanoparticles. As a matter of fact, a new, exciting field of coordination chemistry can be envisaged, combining metal nanoparticles and metal complexes, in the light of supramolecular and surface plasmon resonance effects.

A highly efficient redox chromophore for simultaneous application in a photoelectrochemical dye sensitized solar cell and electrochromic devices

We synthesized a novel series of compounds based on a ruthenium(II) dicarboxybipyridine (dcbpy) complex containing chloro and trans-1,4-bis[2-(4-pyridyl)ethenyl]benzene (BPEB) ligands. The binuclear species Na6[{[RuII(dcbpy)2Cl}2(BPEB)] exhibits an electrochromic effect when reduced, which is assigned to the radical BPEB0/˙, similarly as in viologen-based compounds. The carboxylate groups on the 4,4′ positions of bipyridine allow a strong attachment to the TiO2 surface, contributing to an efficient and reversible electron transfer from the oxide to the chromophoric ligand, coloring the oxide film blue. The coloration efficiency CE(λ) at 633 nm was 109 cm2 C−1, which is high compared to TiO2 itself. The complex also exhibits a high photon-to-electron conversion efficiency (IPCE > 70%) when applied as a photoanode in a dye sensitized solar cell (DSSC).

Unravelling the Chemical Morphology of a Mesoporous Titanium Dioxide Interface by Confocal Raman Microscopy: New Clues for Improving the Efficiency of Dye Solar Cells and Photocatalysts

The presence of anatase and rutile domains on nanocrystalline films of P25 TiO2, as well as the distinct coordination modes of carboxylates on those phases, were revealed by confocal Raman microscopy, a technique that showed to be suitable for imaging the chemical morphology down to submicrometric size.

Ultrasmall cationic superparamagnetic iron oxide nanoparticles as nontoxic and efficient MRI contrast agent and magnetic-targeting tool

Fully dispersible, cationic ultrasmall (7 nm diameter) superparamagnetic iron oxide nanoparticles, exhibiting high relaxivity (178 mM−1s−1 in 0.47 T) and no acute or subchronic toxicity in Wistar rats, were studied and their suitability as contrast agents for magnetic resonance imaging and material for development of new diagnostic and treatment tools demonstrated. After intravenous injection (10 mg/kg body weight), they circulated throughout the vascular system causing no microhemorrhage or thrombus, neither inflammatory processes at the mesentery vascular bed and hepatic sinusoids (leukocyte rolling, adhesion, or migration as evaluated by intravital microscopy), but having been spontaneously concentrated in the liver, spleen, and kidneys, they caused strong negative contrast. The nanoparticles are cleared from kidneys and bladder in few days, whereas the complete elimination from liver and spleen occurred only after 4 weeks. Ex vivo studies demonstrated that cationic ultrasmall superparamagnetic iron oxide nanoparticles caused no effects on hepatic and renal enzymes dosage as well as on leukocyte count. In addition, they were readily concentrated in rat thigh by a magnet showing its potential as magnetically targeted carriers of therapeutic and diagnostic agents. Summarizing, cationic ultrasmall superparamagnetic iron oxide nanoparticles are nontoxic and efficient magnetic resonance imaging contrast agents useful as platform for the development of new materials for application in theranostics.

Pushing the surface-enhanced Raman scattering analyses sensitivity by magnetic concentration: a simple non core-shell approach.

A simple and accessible method for molecular analyses down to the picomolar range was realized using self-assembled hybrid superparamagnetic nanostructured materials, instead of complicated SERS substrates such as core-shell, surface nanostructured, or matrix embedded gold nanoparticles. Good signal-to-noise ratio has been achieved in a reproducible way even at concentrations down to 5×10(-11) M using methylene blue (MB) and phenanthroline (phen) as model species, exploiting the plasmonic properties of conventional citrate protected gold nanoparticles and alkylamine functionalized magnetite nanoparticles. The hot spots were generated by salt induced aggregation of gold nanoparticles (AuNP) in the presence of those analytes. Then, the aggregates of AuNP/analyte were decorated with small magnetite nanoparticles by electrostatic self-assembly forming MagSERS hybrid nanostructured materials. SERS peaks were enhanced up to 100 times after magnetic concentration in a circular spot using a magnet in comparison with the respective dispersion of the nanostructured material.

Can mass dissociation patterns of transition-metal complexes be predicted from electrochemical data?

The Cooks kinetic method has been very convenient to correlate the relative dissociation rates obtained by collision-induced fragmentation experiments with the energies of two related bonds in molecules and complexes in the gas phase. Reliable bond energy data are, however, not always available, particularly for polynuclear transition-metal complexes, such as the triruthenium acetate clusters of the general formula [Ru(3) (micro(3)-O)(micro-CH(3)COO)(6)(py)(2)(L)](+), where L = ring substituted N-heterocyclic ligands. Accordingly, their gas-phase collision-induced tandem mass spectrometry (CID MS/MS) dissociation patterns have been analyzed pursuing a relationship with the more easily accessible redox potentials (E(1/2)) and Levers E(L) parameters. In fact, excellent linear correlations of ln(1/2A(L)/A(py)), where A(py) and A(L) are the abundance of the fragments retaining the pyridine (py) and L ligand, respectively, with E(1/2) and E(L) were found. This result shows that those electrochemical parameters are correlated with bond energies and can be used in the analysis of the dissociation data. Such modified Cooks method can be used, for example, to determine the electronic effects of substituents on the metal-ligand bonds for a series of transition-metal complexes.

Self assembled rotaxane and pseudo-rotaxanes based on beta-cyclodextrin inclusion compounds with trans-1,4-bis[(4-pyridyl)ethenyl]benzene-pentacyanoferrate(II) complexes

Inclusion compounds of trans-1,4-bis[(4-pyridyl)ethenyl]benzene (BPEB) and their corresponding pentacyanoferrate(II) complexes with b-cyclodextrin have been studied in aqueous solution by 1H NMR and UV-Visible spectroscopy. All the inclusion compounds exhibit 1:1 stoichiometry is aqueous solution. In the presence of b-cyclodextrin, the binuclear {[Fe(CN)5]2(BPEB)]6- complex is gradually converted into rotaxane species bearing [Fe(CN)5]3-end groups, by a self assembly inclusion mechanism, as confirmed by 1H NMR spectroscopy.

Thermodynamic stabilization of nanostructured alpha-Ni1−xCox(OH)2 for high efficiency batteries and devices

The exceptional stability of FTO electrodes modified with Ni1−xCox(OH)2 in the alpha polymorphic phase was assigned to Co(II) substitution in the Ni(II) reticule, decreasing the basal plane distances and the average grain size, as confirmed by careful analyses of their X-ray diffractograms and thermal behavior as a function of the cobalt content. That phenomenon can be assigned to thermodynamic rather than kinetic factors, reflected by much higher dehydration/dehydroxilation temperatures, as expected for the stabilization of the mixed alpha-phase hydroxides in detriment of the oxides, opening real perspectives for application of alpha-Ni1−xCox(OH)2 in high efficiency batteries and devices.

Correction: Bovine glutamate dehydrogenase immobilization on magnetic nanoparticles: conformational changes and catalysis

Correction for ‘Bovine glutamate dehydrogenase immobilization on magnetic nanoparticles: conformational changes and catalysis’ by Caterina G. C. Marques Netto et al., RSC Adv., 2016, 6, 12977–12992.

Decorated Superparamagnetic Iron Oxide Nanoparticles with Monoclonal Antibody and Diethylene-Triamine-Pentaacetic Acid Labeled with Thechnetium-99m and Galium-68 for Breast Cancer Imaging

AbstractPurposeIn this study we developed and tested an iron oxide nanoparticle conjugated with DTPA and Trastuzumab, which can efficiently be radiolabeled with 99m-Tc and Ga-68, generating a nanoradiopharmaceutical agent to be used for SPECT and PET imaging.MethodsThe production of iron oxide nanoparticle conjugated with DTPA and Trastuzumab was made using phosphorylethanolamine (PEA) surface modification. Both radiolabeling process was made by the direct radiolabeling of the nanoparticles. The in vivo assay was done in female Balb/c nude mice xenografted with breast cancer. Also a planar imaging using the radiolabeled nanoparticle was performed.ResultsNo thrombus and immune response leading to unwanted interaction and incorporation of nanoparticles by endothelium and organs, except filtration by the kidneys, was observed. In fact, more than 80% of 99mTc-DTPA-TZMB@Fe3O4 nanoparticles seems to be cleared by the renal pathway but the implanted tumor whose seems to increase the expression of HER2 receptors enhancing the uptake by all other organs.ConclusionHowever, even in this unfavorable situation the tumor bioconcentrated much larger amounts of the nano-agent than normal tissues giving clear enough contrast for breast cancer imaging for diagnostics purpose by both SPECT and PET technique. Graphical Abstractᅟ