Silvia Pizzanelli

Phenyl ring dynamics in a liquid crystal polymer through 2H NMR spectroscopy

Abstract The dynamics of a side chain liquid crystal copolymer at two different compositions has been investigated in its smectic A and C phases. J 1 ( ω 0 ) and J 2 (2 ω 0 ) spectral densities have been determined for aromatic deuterium nuclei in the side chains and their interpretation has been carried out by means of several available motional models. The dynamic process mainly contributing to relaxation has been found to be the rotation of the phenyl ring about its para -axis, that is best described by a small step rotational diffusion model, where the diffusion constant has an Arrhenius temperature dependence and a Gaussian distribution of the activation energies is present, indicating a remarkable degree of dynamic heterogeneity of this system.

Cross-polarization for a fluoropolymer involving multiple spin baths of abundant nuclei

The thermodynamic theory of cross-polarization (CP) between one abundant and one rare spin is well understood and widely applied. CP dynamics between several abundant spin baths has some inherent complications that lead to misinterpretation of the CP rates and relaxation parameters if not properly accounted for. A general thermodynamic description of CP dynamics involving up to six spin baths is developed and implemented with MATLAB. The CP dynamics for a fluorinated polymer, (2-perfluorohexylethyl acrylate)–styrene co-polymer, was analysed as a system with five spin baths—four 19F and one 1H. The CP behaviour was successfully simulated above the glass-transition temperature. The CP rates and T1ρs are discussed in terms of the structure and dynamic behaviour of the polymer.

Copper(II) complexes with peptides based on the second cell binding site of fibronectin: metal coordination and ligand exchange kinetics.

Copper(ii) complexes with short peptides based on the second cell binding site of fibronectin, PHSFN and PHSEN, have been characterized by potentiometric, UV-vis, CD, EPR and NMR spectroscopic methods. The histidine imidazole nitrogen is the anchoring site for the metal ion binding. Thermodynamic and spectroscopic evidence is given that the side chain oxygen donor atom of glutamyl residue in Ac-PHSEN-NH2 is also involved in the binding up to physiological pH. To determine ligand exchange kinetic parameters after the imidazole nitrogen anchoring, proton relaxation enhancement NMR data have been collected for the two hydrogen atoms of the imidazole ring in the temperature range 293-315 K at pH 5.2 and globally treated within different kinetic models for ligand exchange. The best fitting model involves two steps. In the first one, which is slow, a water molecule disengages a carbonyl or a carboxylate group coordinated to the metal ion in the complex formed by PHSFN or PHSEN, respectively. This stage is one order of magnitude slower for PHSEN, due to entropic effects. In the second step, which is fast, the complex just formed exchanges with the ligand. In this step, no appreciable differences are found for the two cases examined.

Partially Deuterated Liquid Crystal Polymers: Structure and Orientational Order by X-ray Diffraction and 2 H NMR

The structure, magnetic alignment and orientational order of polysiloxane liquid crystal copolymers were investigated by X-ray diffraction and 2 H NMR spectroscopy. The copolymers incorporated significant amounts of non-mesogenic counits, and the influence of the composition on their properties was studied. The deuterium spectra were analyzed in terms of ordered and Pake disordered components.

Conformation and Orientation of an Oligopeptide in a Lyotropic Mesophase by 1H NMR

The analysis of 1H residual dipolar couplings of zwitterionic tetraalanine in the lyotropic system cesium pentadecafluorooctanoate in water (CsPFO/D2O) showed that the internal peptide residues adopt a polyproline II helix conformation. Moreover, the data allowed an estimate of the dihedral angles of the external residues and suggested that the long molecular axis is tilted by an angle of 56° with respect to the surface of the micelles formed by CsPFO.

Study of the interaction of GFG tripeptide with cesium perfluorooctanoate micelles by means of NMR spectroscopy and MD simulations.

The interaction of glycyl-phenylalanyl-glycine (GFG) with bilayers formed by cesium perfluorooctanoate (CsPFO) in water was investigated in the isotropic phase by means of 1H NMR and molecular dynamics (MD) simulations. Details on the preferential location of the different residues of GFG were obtained from selective variations of chemical shift with peptide concentration and of line width in the presence of the paramagnetic ion Mn2+. The analysis of 1H NMR spectra recorded at different concentrations and temperatures allowed the association constant and the enthalpy change upon binding to be evaluated. MD simulations highlighted the hydrogen bonds formed between the different GFG functional groups and the micelle. Both NMR and MD gave indications of high affinity of GFG with the micelle, with the N-terminal residue anchoring on the surface via hydrogen bonds with the micelle COO(-) groups.