Supervisors: Prof. Lorenzo Di Bari and Prof. Gennaro Pescitelli

Title: Circular Dichroism Spectroscopies and Hyperfine Shift in Metal Complexes and Organic Molecules

Abstract: The determination of the molecular structure in solution is an important target of modern chemistry. In many fields, the knowledge of the solution structure and dynamics is a fundamental piece of information for a complete understanding of chemical processes, from catalytic mechanisms to the biological activities of biopolymers. However, there is not a general strategy to approach the problem of solving solution structures for any type of molecule. The research presented in this thesis concerns the development of new protocols of structural determination using lanthanide properties, but, at the same time, the application or upgrading of well-known experimental methodologies such as ECD (electronic circular dichroism) or VCD (vibrational circular dichroism) and the theoretical simulation of chiroptical properties by means of DFT (density functional theory) and its time-dependent version (TD-DFT). All the substances we took into consideration were chosen for their importance both in inorganic and organic chemistry. In particular, we referred:
(i)   A new benchmark in the pseudocontact shift (PCS) extraction, developing two different methods to achieve the Fermi Contact (or FC)/PCS separation in the analysis of paramagnetic NMR spectra of lanthanide complexes. Our methodology is based on the mathematical analysis of the chemical shift along the series with the same ligand (all-lanthanide protocol) or in an extended range of temperature (temperature-based method);
(ii)  Studies of the near-IR (NIR) emission of the excited states of Yb3+ (around λ=1000 nm) in three different systems. For all the presented cases, a new empirical correction to Richardson equations are introduced in order to improve the prediction of the NIR-emission profile of Yb3+, comparing each results with the experimental ones.  Our results open the way to a new employment of lanthanoid luminescence imaging in vivo;
(iii) Different examples of uses of ECD/TD-DFT, spanning from the study of metal-centered Λ-Δ chirality in some metal  complexes with Schiff bases as ligand (Cu2+ or Ni2+), to conformational/configurational investigations in purely organic systems (i.e. two  enantiomers separated by HPLC of one particular Linezolid, a specific class of new antibiotics). We also report our results on a family of chiral aryl benzyl sulfoxides with perfluorinated aryl or benzyl rings. In this example, only a detailed TD-DFT study allowed us to assign correctly ECD spectra and ultimately the absolute configuration, while a commonly employed empirical assignment of experimental ECD pattern (as reported in literature) is questionable;
(iv) Interpretation of VCD signal enhancement in complexes containing metals with low-lying electronic state (or LEESs). First, we report a self-assembled multicomponent system with d-metals and α-aminoacids, where the enhanced VCD signals allow us to assign the absolute configuration (AC) of the aminoacid component with a very low amount of sample. Second, we analyze a few lanthanide complexes with unpredictable experimental VCD enhancement. Using Richardson’s model, we discuss the CF energies around the lanthanide ion, the geometrical conditions and the electronic state energy of the lanthanoid ion in these systems, in order to justify the anomalous VCD enhancement.

Publications

Oral communications at congress

R. Berardozzi and L. Di Bari. Vibrational Circular Dichroism: Extension to Molecules with Low-Lying Excited Electronic States. Year of Light 2015 - The Chemical Point of View (Pisa, 09/01/2015-10/01/2015).

Poster communications at congress

R. Berardozzi and L. Di Bari. Chiroptical studies on Salen-Type Lanthanides complexes. CD2013, 14th International Conference on Chiroptical Spectroscopy CD2013 (Nashville, 9/06/2013-13/06/2013).

R. Berardozzi and L. Di Bari. Crystal Field Splitting (CFS) and Vibrational Circular Dichroism (VCD) in Lanthanide Complexes. ChirItaly 2014 (Pisa, 18/06/2014-20/06/2014).

R. Berardozzi and L. Di Bari. New Correlation of VCD Enhancement and Crystal Field Splitting on Lanthanide Ions Adducts. CD2015, 15th International Conference on Chiroptical Spectroscopy CD2015 (Sapporo, 30/08/2015-03/09/2015)

R. Berardozzi and L. Di Bari. Optical activity in the near-IR: the 980 nm multiplet of chiral Yb3+ complexes. CD2015, 15th International Conference on Chiroptical Spectroscopy CD2015 (Sapporo, 30/08/2015-03/09/2015)

Journal articles

R. Berardozzi and L. Di Bari. A Simple and General Method to Determine Reliable Pseudocontact Shifts in Lanthanide Complexes. Inorg Chem 2013; 52, 19, 11514-11518.    

M. Enamullah, A. Uddin, G. Pescitelli, R. Berardozzi, G. Makhloufi, V. Vasylyeva, A. Chamayou and C. Janiak. Induced Chirality-at-metal and diastereoselectivity at Δ/Λ-configured distorted square-planar copper complexes by enantiopure Schiff base ligands: combined circular dichroism, DFT and X-ray structural studies. Dalton Trans. 2014; 43, 3313-11518.    

C. G. Fortuna, R. Berardozzi, C. Bonaccorso, G. Caltabiano, L. Di Bari, L. Goracci, A. Guarcello, A. Pace, A. Palumbo Piccionello, G. Pescitelli, P. Pierro, E. Lonati, A. Bulbarelli, C. Cocuzza, G. Musumarra and Rosario Musumeci. New potent antibacterials against Gram-positive multiresistant pathogens: Effects of side chain modification and chirality in linezolid-like 1,2,4-oxadiazoles. Bioorg. Med. Chem. 2014; 22, 6814-6825.

M. Enamullah, M. A. Quddus, M. R. Hasan, G. Pescitelli, R. Berardozzi, G. J. Reiß and C. Janiak. Synthesis, spectroscopy, and structural analyses of dinuclear chiral-at-metal μ-acqua-tetrakis[(R or S)-N-1-(Ar)ethylsalicylaldiminato]di-Λ- or -Δ-nickel(II) complexes. Eur. J. Inorg. Chem. 2015; 16, 2758-2768.

R. Berardozzi and L. Di Bari. Optical Activity In The Near IR: The 980 Nm Multiplet Of Chiral Yb3+ Complexes. ChemPhysChem 2015; 16, 13, 2868-2875.    

R. Berardozzi, C. A. Guido, M. A. M. Capozzi, C. Cardellicchio, L. Di Bari and G. Pescitelli. Circular Dichroism and TDDFT Investigation of Chiral Fluorinated Aryl Benzyl Sulfoxides. Eur. J. Org. Chem. 2015; 2015, 25, 5554-5562.

R. Berardozzi, G. Pescitelli, S. Di Pietro, C. Resta, F. P. Ballistreri, A. Pappalardo, G. A. Tomaselli and L. Di Bari. Synthesis, Structural Characterization and Chiroptical Studies of Bidentate Salen-Type Lanthanide (III) Complexes. Chirality 2015; 27, 12, 857-863.    

I. Gamba, G. Rama, E. Ortega-Carrasco, R. Berardozzi, L. Di Bari, V. Sanchez-Pedregal, J. Maréchal, M. E. Vàzquez and M. Vàzquez Lòpez. The folding of a metallopeptide. Dalton Trans. 2015; early on-line version.

M. Enamullah, M. A. Quddus, M. R. Hasan, G. Pescitelli, R. Berardozzi, G. Makhloufi, V. Vasylyeva, C. Janiak. Chirality at metal and helical ligand folding in optical isomers of chiral bis(napthaldiminato)nickel(II) complexes. Dalton Trans. 2015; early on-line version.

R. Berardozzi, E. Baldini, N. A. Carmos dos Santos, K. Wurst, G. Licini, C. Zonta, L. Di Bari. Enhanced Vibrational CD for the Facile Recognition of α-Aminoacid Chirality. In submission.