Federico Rastrelli

Predicting the NMR Spectra of Paramagnetic Molecules by DFT: Application to Organic Free Radicals and Transition-Metal Complexes

Nuclear shieldings, including the Fermi contact and pseudocontact terms, have been calculated with DFT methods in a variety of open-shell molecules (nitroxides, aryloxyl and various transition-metal complexes), thereby predicting (1)H and (13)C chemical shifts. In general, when experimental data are reliable a good agreement with experimental values is observed, thus demonstrating the predictive power of DFT also in this context. However, the general accuracy is lower than that for closed-shell species. A few inconsistencies in literature values are reconciled by reassigning some shifts. Structural, magnetic, and dynamic parameters have also been put into the Solomon-Bloembergen equations to predict signal line shapes, in particular those of signals that are difficult to locate or are undetectable. Guidelines are provided to predict the order of magnitude of relaxation rates. It is shown that DFT-predicted paramagnetic shifts can greatly assist in obtaining and understanding the NMR spectra of paramagnetic molecules, which generally require different experimental strategies and exhibit problems in detection and assignment.

Lanthanide-based NMR: a tool to investigate component distribution in mixed-monolayer-protected nanoparticles.

Gd(3+) ions, once bound to the monolayer of organic molecules coating the surface of gold nanoparticles, produce a paramagnetic relaxation enhancement (PRE) that broadens and eventually cancels the signals of the nuclear spins located nearby (within 1.6 nm distance). In the case of nanoparticles coated with mixed monolayers, the signals arising from the different coating molecules experience different PRE, depending on their distance from the binding site. As a consequence, observation of the signal broadening patterns provides direct information on the monolayer organization.

Predicting the 1H and 13C NMR spectra of paramagnetic Ru(III) complexes by DFT

Nuclear shieldings, including the Fermi‐contact and pseudocontact terms, have been calculated with density functional theory (DFT) (nonrelativistic and relativistic) methods in several Ru(III) complexes, thereby predicting 1H and 13C paramagnetic shifts. A fair agreement with experimental values is observed. Structural, magnetic and dynamic parameters have also been input to the Solomon–Bloembergen equation in order to predict signal lineshapes. It is shown that DFT‐predicted paramagnetic shifts can greatly aid in obtaining and understanding NMR spectra of paramagnetic Ru(III) complexes. Copyright

NMR chemosensing using monolayer-protected nanoparticles as receptors.

A new sensing protocol based on NMR magnetization transfer sequences and the molecular recognition abilities of nanoparticles allows the detection and identification of organic molecules in complex mixtures.

Regioselective O-derivatization of quercetin via ester intermediates. An improved synthesis of rhamnetin and development of a new mitochondriotropic derivative.

The regioselective synthesis of several quercetin (3,3’,4’,5,7-pentahydroxy flavone) tetraesters bearing a single free OH on 5-C was achieved in good yield by proper choice of reaction conditions using common esterification procedures. Tetracetylated quercetin with the free OH on 7-C was selectively obtained instead via imidazole-promoted deacylation of the corresponding pentaester. Unambiguous structural characterization of the two isomeric tetraacetyl quercetin derivatives was obtained by combined HSQC and HMBC 2D-NMR analysis. These molecules can be used as starting materials for the regioselective synthesis of other derivatives. High yield syntheses of the natural polyphenol rhamnetin (7-O-methylquercetin) and of the new mitochondriotropic compound 7-(4-triphenylphosphoniumbutyl) quercetin iodide are reported as examples.

Nanoparticle-assisted NMR detection of organic anions: from chemosensing to chromatography.

Monolayer-protected nanoparticles provide a straightforward access to self-organized receptors that selectively bind different substrates in water. Molecules featuring different kinds of noncovalent interactions (namely, hydrophobic, ion pairing, and metal-ligand coordination) can be grafted on the nanoparticle surface to provide tailored binding sites for virtually any class of substrate. Not only the selectivity but also the strength of these interactions can be modulated. Such recognition ability can be exploited with new sensing protocols, based on NMR magnetization transfer and diffusion-ordered spectroscopy (DOSY), to detect and identify organic molecules in complex mixtures.

NMR quantification of trace components in complex matrices by band-selective excitation with adiabatic pulses.

The use of band‐selective excitation with adiabatic pulses to rapidly obtain NMR spectra of trace components in the presence of strong signals is described, along with qualitative and quantitative examples from food matrices like olive oil and honey. Copyright

Ionic liquid crystals based on viologen dimers: tuning the mesomorphism by varying the conformational freedom of the ionic layer

ABSTRACT We investigated the liquid crystal behaviour of newly synthesised bistriflimide salts of symmetric viologen dimers. A smectic A phase was observed for intermediate spacer lengths and for relatively long lateral alkyl chains. The systems were characterised by thermal analysis, polarised optical microscopy, X-ray scattering and solid-state NMR. An intermediate ordered smectic phase was also exhibited by the compounds (except for systems with very short lateral chains) consisting of molten layers of alkyl chains and partially ordered ionic layers. These results, relating to the mesomorphic behaviour of viologen salts, are qualitatively compared to those of the more common imidazolium salts, highlighting the importance of the conformational degrees of freedom of the anions and of the cationic core. It appears that fine tuning of the conformational degrees of freedom of the ionic layer is an important component of mesophase stabilisation. Graphical Abstract

Isocyanides and Arylacetic Acids: Synthesis and Reactivity of 3-Aryl-2-acyloxyacrylamides, an Example of Serendipity-Oriented Synthesis

Research progress is often promoted by unexpected results that open the way to new scenarios. In this communication, an unprecedented condensation of arylacetic acids and isocyanides and the unusual base-mediated rearrangement of the resulting products to give two novel classes of polysubstituted pyrrolones and pyrrolidinediones are reported.

Seeing through Macromolecules: T2-Filtered NMR for the Purity Assay of Functionalized Nanosystems and the Screening of Biofluids

For samples whose NMR spectra are dominated by the broad signals of macromolecules or functionalized nanoparticles, transverse relaxation (T(2)) spectral editing lends itself to a precise identification and determination of small molecules such as metabolites or contaminants. In order to retain the most sensitivity, we propose a method for efficiently removing the interference of spin-spin couplings that typically lead to signal losses in standard pulse schemes designed for T(2) editing.