Luca Nodari

Charge binding of rhodamine derivative to OH− stabilized nanomaghemite: Universal nanocarrier for construction of magnetofluorescent biosensors

Superparamagnetic nanoparticles (20-40 nm) of maghemite, γ-Fe(2)O(3), with well-defined stoichiometric structure, are synthesized by the borohydride reduction of ferric chloride at an elevated temperature (100°C) followed by thermal treatment of the reaction product. Prepared maghemite nanoparticles reveal excellent colloidal stability for a long time without the necessity for any additional surface modification. These colloidal features are due to surface stabilizing OH(-) groups, which act as charge barriers preventing a particle aggregation and enabling a reversible binding of various oppositely charged organic substances. Such binding with rhodamine B isothiocyanate results in the fluorescent magnetic nanocarrier providing, at the same time, a spacer arm for covalent immobilization of other biosubstances including enzymes. In this work, we exploit this general applicability of the developed nanocarrier for covalent immobilization of glucose oxidase. This is the first reported example of magnetically drivable fluorescent nanocatalyst. The immobilized enzyme creates a 3-5 nm thick layer on the nanoparticle surface as proved by high-resolution transmission electron microscopy. This layer corresponds to 10 enzyme molecules, which are bound to the nanoparticle surface as found by the fluorimetric determination of flavin adenine dinucleotide. The developed magnetic fluorescent nanocatalyst, showing a rate constant of 32.7s(-1) toward glucose oxidation, can be used as a biosensor in various biochemical, biotechnological, and food chemistry applications. The presence of the nanocatalyst can be simply monitored by its fluorescence; moreover, it can be easily separated from the solution by an external magnetic field and repeatedly used without a loss of catalytic efficiency.

Mineral chemistry of Ti-rich biotite from pegmatite and metapelitic granulites of the Kerala Khondalite Belt (southeast India): Petrology and further insight into titanium substitutions

Abstract Precise chemical composition, including Fe3+ and H, of biotite from a pegmatite dike and its host granulite from the Kerala Khondalite Belt of SE India has been determined using a multi-technique approach involving EMP, SIMS, Mössbauer, and C-H-N elemental analysis. Biotite in these rocks formed at T > 800-850 °C and P = 5 ± 1 kbar. The full analyses were normalized on the basis of [O12-(x+y+z)(OH)xClyFz]. Biotite in the pegmatite is Ti-, F-, and Cl-rich (0.33, 0.46, and 0.16 apfu, respectively), H2O-poor (OH = 0.86 pfu), has XMg = 0.49 and Fe3+/Fetot ≤ 3%. The low octahedral vacancies (0.06 pfu) and the high oxygen content in the hydroxyl site (OH + F + Cl = 1.49 pfu) confirm the role of the Ti-oxy substitution as a major exchange vector in these high-T biotites. In the host granulite, fine-grained biotite is Fe3+-free, has low Cl (0.03 apfu), and more variable composition, with Ti, F, and XMg in the ranges 0.26-0.36, 0.52-0.67, and 0.67-0.77, respectively. The number of octahedral vacancies is relatively large (0.10-0.18 pfu) and the sum of volatiles (OH + F + Cl) varies from 1.71 to 2.06 pfu. Systematic variations of XMg are a function of the microstructural position and are in agreement with retrograde exchange reactions: biotite included in or in contact with garnet has the maximum values, whereas crystals in the matrix have the minima. Titanium has systematic negative correlations with F, XMg, and (OH + F + Cl), whereas Al and octahedral vacancies are virtually constant. These trends indicate that the Ti-vacancy, along with substitutions involving Al, cannot explain the observed short-scale variations. Conversely, the Ti-oxy exchange appears to be active, resulting from combination of two vectors: the more conventional hydroxylation Ti4+ + 2O2- = (Fe,Mg)2+ + 2OH- and the “fluorination” Ti4+ + 2O2- = (Fe,Mg)2+ + 2F-. The systematic retrograde redistribution involves not only Fe and Mg as commonly observed, but also Ti, F, and H, in a way such to eliminate the primary Ti-oxy component of biotite.

Multiple titanium substitutions in biotites from high-grade metapelitic xenoliths (Euganean Hills, Italy): Complete crystal chemistry and appraisal of petrologic control

Abstract Biotites from metapelitic xenoliths included within trachytes from the Euganean Hills (Italy) were analyzed by single-crystal X-ray diffraction (XRD), electron microprobe (EMP), scanning electron microscope (SEM), secondary ion mass spectrometry (SIMS), and Mössbauer spectroscopy. These biotites are Ti-rich and occur in gneissic xenoliths that underwent regional high-T/low-P metamorphism, at about 750 °C, followed by pyrometamorphism during incorporation in the melt at temperatures close to 950 °C. Biotites are zoned, with TiO2 content ranging from 6.79 (cores) to 8.14 wt% (rims). SIMS measurements show that the H2O content is in the range 2.88-4.08 wt%. The simultaneous occurrence of high-Ti and high-H2O contents, and the main cation substitutions based on EMP analyses suggest that the role of Ti-oxy in these biotites is less important than Ti-vacancy and Ti-Tschermak substitutions. Single-crystal XRD confirms that the Ti-oxy exchange was indeed effective but not the dominant substitution mechanism. Based on our data and those taken from literature on petrologically well-constrained systems, we propose that there is a petrologic control on the type of Ti-substitution mechanisms. We consider two types of petrologic groupings for biotites: (1) group A consisting of biotites from H2O-free or H2O-poor petrologic environments (e.g., volcanic rocks, ultrabasic xenoliths, and crustal xenoliths in which biotite underwent incongruent melting): Ti substitution in these biotites occurs via Ti-oxy predominantly, or more specifically Fe3+-Ti-oxy; and (2) group B consisting of biotites from H2O-rich petrologic environments (e.g., metamorphic rocks and crustal granitoids): Ti-vacancy, or more specifically Fe3+-Ti-vacancy, is the dominant mechanism in them. It is concluded that during high-grade metamorphism the dominating type of Ti substitution in biotite is controlled by H2O activity.

Characterization of Synthetic Iron Oxides and their Performance as Support for Au Catalysts.

Gold(0) catalysts supported on ferric oxide are effective catalysts, and so far, the only heterogeneous ones known for the regioselective hydrogenation of α,β‐unsaturated ketones to the corresponding α,β‐unsaturated secondary alcohols. A set of ferric oxide samples, synthesized under strictly controlled conditions and thoroughly characterized (X‐ray powder diffraction, Mössbauer spectroscopy, micro‐Raman spectroscopy, transmission electron microscopy, temperature‐programmed reduction), were employed as supports of gold(0) catalysts for this reaction. The activity and selectivity of the catalysts changed in the same direction from one catalyst to another; increasing fractions of nanostructured ferric oxide phases in the support (with nanoparticles size lower than 10 nm) increased both. With a 4 % gold catalyst supported on the ferric oxide sample containing the highest proportion of nanostructured matter, we achieved a selectivity of 66 % towards the unsaturated alcohol at more than 90 % conversion in the hydrogenation of benzalacetone (ethanol, 60 °C, 103 kPa), which is one of the best performances ever reported for this reaction.

Effects of time and temperature of firing on Fe-rich ceramics studied by Mössbauer spectroscopy and two-dimensional 1H-nuclear magnetic resonance relaxometry

The combined effects of firing temperature and soaking time on the microstructure of iron-rich porous ceramics have been studied by 57Fe-Mossbauer spectroscopy and 2D 1H nuclear magnetic resonance (NMR) relaxometry using a single-sided probe. Examining water-saturated ceramics using the relaxation correlation method, where longitudinal (T1) and transverse (T2) relaxation times are measured concurrently, provides information about firing-induced changes in both porosity (related to T1) and magnetic properties (related to T2). Comparing the information obtained from 1H-NMR analyses with that obtained from Mossbauer spectroscopy (which characterizes changes in iron-bearing species) shows that the T1-T2 NMR correlation technique is very sensitive to even subtle modifications in the magnetic behavior of Fe-bearing species. Moreover, the single-sided NMR approach allows us to perform millimeter-scale depth-resolved measurements, which can be used to non-invasively study the microstructural heterogeneities assoc...

Nanoaggregates of iron poly-oxo-clusters obtained by laser ablation in aqueous solution of phosphonates

Laser ablation in liquid (LAL) emerged as a versatile technique for the synthesis of nanoparticles with various structures and compositions, although the control over products remains challenging in most cases. For instance, it is still difficult to drive the size of metal oxide crystalline domains down to the level of few atom clusters with LAL. Here we demonstrate that laser ablation of a bulk iron target in aqueous solution of phosphonates gives phosphonate-grafted iron oxo-clusters polymerized into nanoaggregates with Fe:ligand ratio of 2:1, instead of the usual nanocrystalline iron oxides. We attribute this result to the strong ability of phosphonate groups to bind iron oxide clusters and prevent their further growth into crystalline iron oxide. These laser generated poly-oxo-clusters are biocompatible and trackable by magnetic resonance imaging, providing interesting features for use in biological environments, such as nano-vehicles for iron administration. Besides, this method is promising for the generation of atom-scale metal-oxide clusters, which are ubiquitary in chemistry and of interest in biochemistry, catalysis, molecular magnetism and materials science.