1,720,970 research outputs found
Low-dimensional magnetic systems for spintronic memories: growth, characterization and modeling
Get PDFL'abstract è presente nell'allegato / the abstract is in the attachmen
Supramolecular chemosensors for the detection of phenethylamines
Get PDFIn this work I described and discussed the results of a research project which focused on both development and application of the NMR-chemosensing technique. This technique is based on the combination of gold nanoparticles 2 nm in diameter coated with specific thiols and particular NMR experiments, and it allows to “extract” from the NMR spectrum of a mixture of substances the single NMR spectrum of the analyte bound by the nanoparticle. Specifically, the main goal of my work was to demonstrate how this technique can be successfully used for designer-drug detection.
The majority of the new drugs that appear on the market every year belong to this category, i.e. they are structural analogs of already well-known drugs. Designer drugs represent a big health issue, because no studies on them are available, therefore the risks and potential long-term adverse effects are not known. Moreover, as reference standards are not available, their sensing with routine techniques is difficult. The technique that I will describe also works on real street samples, with no pretreatment, thus giving the possibility to get from the seizure of the powder to the characterization of the substance in a few hours.
I’ll also show that to improve the potentialities of NMR chemosensing in terms of detection limit and sensitivity one can work from two sides. First, it is possible to improve the design of the coating thiol, obtaining a monolayer with different affinities and different capability of magnetization transfer, both crucial aspects for the technique. On the other hand, it is possible to im-prove sensitivity by acting directly on the type of NMR experiment used as well, also in combination with tricks that exploit magnetization enhancement, such as using the water trapped in the monolayer as an additional magnetization source or using the capability of gold nanoparticles to self-assemble on silica nanospheres, in order to enhance the nanoreceptor’s size. Combining all the various things, I will demonstrate how it is possible to sense inorganic species too, such as K+, which do not have an NMR signal per se.
Finally, as NMR is not, as of now, a technique that is easy to apply for on-field analysis, in the last part of this paper I propose a point-of-care sensor developed in the form of an indicator strip in which a self-assembled supramolecular receptor composed of a cucurbituril and a dye can selectively sense the presence, or not, of a drug in a quick, safe and cheap way
Photogeneration of Hydrogen: Insights from a Pt(II)-Complex Incorporated into a Covalent Organic Framework
No full textPt(II)-based molecular catalysts stand as a prototypical system in hydrogen evolution reactions (HER) owing to their consistently elevated activity levels. Their integration into heterogeneous systems thus provides an ideal platform to develop catalytic materials with optimal atom economy. In this work, by rational molecular design, we have synthesized a novel two-dimensional photoactive Covalent Organic Framework (COF), wherein the pore walls host a quinoline-based alpha-diimine ligand serving as a coordination site for anchoring a Pt(II) molecular catalyst. Thorough structural analyses, employing X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (FT-IR), diffuse reflectance spectroscopy (DR), coupled with DFT calculations, distinctly confirm the Pt(II) complexation through the coordination site of the alpha-diimine ligand. The Pt(II)-metalated COF exhibits photocatalytic activity with a hydrogen evolution rate reaching up to 1300 mu mol g-1 h-1. Nevertheless, the occurrence of platinum nanoparticles in post-catalysis samples, along with reduced photocatalytic activity in the presence of chloride ions, suggests that Pt(II) anchored into the COF backbone might not be the primary catalytic site.|An innovative photoactive covalent organic framework (COF) with pore walls featuring a quinoline-based alpha-diimine ligand as a coordination site was synthesized for anchoring a Pt(II) molecular catalyst for hydrogen evolution reaction (HER). Extensive characterization, supported by DFT calculations, shows that H2 evolution is likely driven by the platinum nanoparticles generated through the photocatalytic processes, rather than by Pt(II) species. imageLR
Luminescent Manganese(II) Iminophosphorane Derivatives
Get PDFThe reaction between the iminophosphorane ligand N-phenyl-1,1,1-triphenylphosphanimine (NPh=PPh3) and anhydrous manganese(II) halides allowed the isolation of complexes with the general formula [MnX2(NPh=PPh3)2] (X = Cl, Br, I). The compounds showed luminescence in the green region attributed to the 4T1(4G)→6A1(6S) transition of the metal centre in the tetrahedral field, which was superimposed in the cases of X = Cl
and X = Br on weak ligand-centred fluorescence. The emission and excitation spectra were compared with those of the free ligand and of the related zinc(II) bromo-complex. DFT calculations on the free ligand and on the manganese(II) bromo-complex helped to rationalise the experimental data. The protonation of NPh=PPh3 led to the formation of the iminium cation [NHPh=PPh3]+, which was used as a building block for the synthesis of organic–inorganic hybrids with the general formula [NHPh=PPh3]2[MnX4] (X = Cl, Br, I). The crystal structure of [NHPh=PPh3]2[MnBr4] was determined by means of X-ray diffraction. Green photoluminescence associated with the metal-centred transition was also observed for the organic–inorganic hybrids, with higher quantum yields with respect to the neutral [MnX2(NPh=PPh3)2] complexes. In the case of X = I, luminescence from the cation was superimposed on that from the tetraiodomanganate anion upon excitation of the compound with near–UV light
Sequence-selective duplex formation and template effect in recognition-encoded oligoanilines
No full textA new family of duplex-forming recognition encoded oligomers, capable of sequence selective duplex formation and template directed synthesis, was developed. Monomers equipped with both amine and aldehyde groups were functionalized with 2-trifluoromethylphenol or phosphine oxide as H-bond recognition units. Duplex formation and assembly properties of homo- and hetero-oligomers were studied by F-19 and H-1 NMR experiments in chloroform. The designed backbone prevents the undesired 1,2-folding allowing sequence-selective duplex formation, and the stability of the antiparallel duplex is 3-fold higher than the parallel arrangement. Dynamic combinatorial chemistry was exploited for the templated synthesis of complementary oligomers, showing that an aniline dimer can template the formation of the complementary imine. The key role of the H-bond recognition confers to the system the ability to discriminate a mutated donor monomer incapable of H-bonding. Sequence selective duplex formation combined with the template effect makes this system an attractive target for further studies
Intracluster ligand rearrangement: an NMR-based thermodynamic study
Get PDFLigand and metal exchange reactions are powerful methods to tailor the properties of atomically precise metal nanoclusters. Hence, a deep understanding of the mechanisms behind the dynamics that rule the ligand monolayer is crucial for its specific functionalization. Combining variable-temperature NMR experiments and dynamic-NMR simulations, we extract the thermodynamic activation parameters of a new exchange reaction: the intracluster ligand rearrangement between the two symmetry-unique positions in [Ag25(DMBT)18]− and [Ag24Au(DMBT)18]− clusters. We report for the first time that this peculiar intracluster modification does not seem to proceed via metal–sulphur bond breaking and follows a first-order rate law, being therefore a process independent from the well-described collisional ligand exchange.</p
Recognition‐Encoded Molecules: A Minimal Self‐Replicator
Get PDFNucleic acids, with their unique duplex structure, which is key for information replication, have sparked interest in self-replication's role in life's origins. Early template-based replicators, initially built on short oligonucleotides, expanded to include peptides and synthetic molecules. We explore here the potential of a class of synthetic duplex-forming oligoanilines, as self-replicators. We have recently developed oligoanilines equipped with 2-trifluoromethylphenol–phosphine oxide H-bond base pairs and we investigate whether the imine formed between aniline and aldehyde complementary monomers can self-replicate. Despite lacking a clear sigmoidal kinetic profile, control experiments with a methylated donor and a competitive inhibitor support self-replication. Further investigations with the reduced aniline dimer demonstrate templated synthesis, revealing a characteristic parabolic growth. After showing sequence selective duplex formation, templated synthesis and the emergence of catalytic function, the self-replication behaviour further suggests that the unique properties of nucleic acids can be paralleled by synthetic recognition-encoded molecules
Selective NMR detection of N-methylated amines using cavitand-decorated silica nanoparticles as receptors
Get PDFWe report a strategy for the realization of NMR chemosensors based on the spontaneous self-assembly of lower rim pyridiniumfunctionalized tetraphopshonate cavitands on commercial silica nanoparticles. These nanohybrids enable the selective detection of physiologically relevant N-methylated amines, with a limit of detection of 31 mM, via STD-based NMR experiments, achieving for the first time fine structural selectivity in nanoparticle-assisted NMR chemosensing
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
