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Dipartimento di Scienze Chimiche
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Prediction of NMR Spectra by DFT Calculations

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DFT calculations can successfully predict the most relevant molecular properties that determine the appearance of the NMR spectrum, i.e. chemical shifts and spin-spin couplings. We apply these concepts to the structure determination of organic, organometallic and inorganic molecules, with emphasis on natural substances and heavy-atom nuclei.


Paramagnetic NMR

spin density in an iron porphyrin

We pursue the computational modelling of the molecular properties related to the NMR of paramagnetic species. These calculations involve the prediction of contact shifts, hyperfine couplings and g-factor to estimate contact shifts. Along with some dynamic properties (electron and rotational correlation time), these quantities allow to predict the appearance of the NMR spectra of a wide variety of paramagnetic molecules (e.g. nitroxides) and transition-metal complexes.
Weak Noncovalent Interactions

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We investigate by ab initio and DFT methods the changes in NMR spectroscopic parameters (nuclear shielding, spin-spin couplings and electric field gradient) occurring in molecules involved in weak interactions such as hydrogen bonding and van der Waals complexes, and preferential solvation phenomena in solvent mixtures.

Experimental NMR

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We employ high throughput NMR techniques aimed at the investigation of solvation phenomena alongside detection of weak solute-nanosystems (e.g. functionalized gold nanoparticles) interactions. We also develop techniques for the characterisation and quantification of trace-amount molecules in complex matrices, such as oxidation products in edible oils. More recently we have become interested in Solid State NMR, with emphasis on nanosystems and on the study of phase transitions in ionic liquid crystals.


Ionic Liquid Crystals

Ionic Liquid Crystals (ILC) are a new class of materials that are expected to combine the properties and technological applications of Ionic Liquids (IL) and Liquid Crystals (LC), see for example, a book chapter here: DOI. Common systems forming ILC mesophases are constituted by the same type of cations (imidazolium, pyridinium, and other quaternized nitrogen moieties) and anions (halides, BF4-, PF6-, bistriflimide, etc.) forming ionic liquids; however long alkyl chains on the cation, usually C12 and more, are necessary to induce mesomorphism, indeed because the driving force is microphase segregation. We are interested in the synthesis and characterization of viologen-based ILCs, where the viologen unit is the 4,4'-dialkylbipyridinium cation (on the left the formation of fan-textures of the SmA phase of a viologen dimer). We study the effect, on the type and thermal range of stability of the mesophases, of structural changes such as: i) non-symmetric viologen by varying the chain length; ii) non-symmetric viologens by changing the type of chains (alkyl, polyether, polyfluorinated), dimeric viologens, etc. Moreover we investigate the structure and the dynamics, at the microscopic level, of ILCs by Molecular Dynamics (MD) simulations using Coarse-Grained Force Fields (CGFF).

Older Research Topics

Proton Transfer Equilibria and Reaction Mechanisms in Concentrated Acids and bases - Site of Ionization in Polyfunctional Acids and Bases

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We study (a) protonation and deprotonation equilibria of weak bases and acids in concentrated acids and bases with the excess acidity method. (b) The preferred site of protonation or deprotonation in bases and acids possessing multiple sites by monitoring the changes occurring in the NMR longitudinal relaxation rate (1/T1) of all heteronuclei which can act as basic or acid site. For spin-1/2 nuclei (like 15N and 31P) this requires a combined T1 and NOE measurement. For quadrupolar nuclei (like 14N and 17O), the changes observed experimentally are compared with the changes in the electric field gradient calculated by quantum chemical methods. (c) Mechanisms of electrophilic reactions.
The figure depicts the change in the line width of 14N nuclei in neutral (pH 12) and protonated (pH 3) 4-aminopyridine, illustrating the large line narrowing occurring at the pyridine nitrogen signal.