ETD system

Electronic theses and dissertations repository


Tesi etd-11092015-154148

Thesis type
Tesi di dottorato di ricerca
email address
Circular Dichroism Spectroscopies and Hyperfine Shift in Metal Complexes and Organic Molecules
Settore scientifico disciplinare
Corso di studi
tutor Prof. Di Bari, Lorenzo
tutor Prof. Pescitelli, Gennaro
Parole chiave
  • ytterbium
  • vibrational circular dichroism
  • transition metal
  • TD-DFT calculations
  • static coupling
  • richardson model
  • Schiff bases
  • pseudocontact shift
  • paramagnetic NMR
  • metal-centered chirality
  • near-IR CD
  • nikel
  • metal complexes
  • low-lying electronic states
  • Fermi contact
  • iron
  • lantahnides
  • lanthanoids
  • enantiomers
  • electronic transition
  • electronic circular dichroism
  • vibrational transition
  • dynamic coupling
  • DFT calculations
  • diastereoisomers
  • conformational distribution
  • configuration determination
  • chiroptical spectroscopies
  • chirality
  • aminoacids.
Data inizio appello
Data di rilascio
Riassunto analitico
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.