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Digital archive of theses discussed at the University of Pisa

 

Thesis etd-11092015-154148


Thesis type
Tesi di dottorato di ricerca
Author
BERARDOZZI, ROBERTO
email address
r.berardozzi@gmail.com
URN
etd-11092015-154148
Thesis title
Circular Dichroism Spectroscopies and Hyperfine Shift in Metal Complexes and Organic Molecules
Academic discipline
CHIM/06
Course of study
SCIENZE CHIMICHE E DEI MATERIALI
Supervisors
tutor Prof. Di Bari, Lorenzo
tutor Prof. Pescitelli, Gennaro
Keywords
  • aminoacids.
  • chirality
  • chiroptical spectroscopies
  • configuration determination
  • conformational distribution
  • DFT calculations
  • diastereoisomers
  • dynamic coupling
  • electronic circular dichroism
  • electronic transition
  • enantiomers
  • Fermi contact
  • iron
  • lantahnides
  • lanthanoids
  • low-lying electronic states
  • metal complexes
  • metal-centered chirality
  • near-IR CD
  • nikel
  • paramagnetic NMR
  • pseudocontact shift
  • richardson model
  • Schiff bases
  • static coupling
  • TD-DFT calculations
  • transition metal
  • vibrational circular dichroism
  • vibrational transition
  • ytterbium
Graduation session start date
06/12/2015
Availability
Full
Summary
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.
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