Giorgio Rigatti

Dielectric relaxation theory in nematic liquids

The dipole relaxation behaviour in liquid crystals as a function of the molecular ordering has been interpreted theoretically. The decay function of the electric dipole polarization has been calculated in terms of the correlation function of the Wigner rotation matrices. The orientational potential energy function has been expanded as a series of Legendre polynomials, and the contributions of the various terms investigated.

Absence of water at the sixth co-ordination site in ferric Aplysia myoglobin.

Abstract The acidic ferric form of hemoglobin and myoglobin carries a water molecule as the sixth ligand of the iron atom. On the other hand, Aplysia met myoglobin shows a pentaco-ordinated active site below the p K of the acid-alkaline transition (7.5). This finding rationalizes some peculiar properties of Aplysia myoglobin as compared with sperm whale myoglobin.

Observations on CO trout hemoglobins by 13C NMR

The functional properties of the two major hemoglobin components from trout’s blood (Hb trout IV and I) have been characterized in a number of recent papers (see [ 1 ] for review). The ligand binding equilibrium curve of Hb trout I shows strong homotropic interactions (n=2.3-2.5) but is completely insensitive to changes in proton concentration. On the other hand, Hb trout IV is characterized by marked heterotropic interactions: lowering of pH produces a large decrease both in the overall affinity for ligands such as oxygen and carbon monoxide, and in the heme-heme interactions (the value for Hill’s coefficient n drops from 2.3 at pH = 7.5 to about 1 or less at pH = 6). In the case of oxygen, the affinity of the molecule for the ligand at acid pH values is so dramatically reduced that a large proportion of the oxygen binding sites are deoxygenated even at oxygen pressures above one atomsphere (‘Root’ effect). With the aim of gaining a better insight in the molecular mechanism operative in the hemoglobin components from trout, we have determined the ’ 3C n.m.r. spectra of the 13C0 bound to both I-lb trout I and Hb trout IV.

Dielectric Relaxation Theory in Nematic Liquids

The dipole relaxation behaviour in liquid crystals as a function of the molecular ordering has been interpreted theoretically. The decay function of the electric dipole polarization has been calculated in terms of the correlation function of the Wigner rotation matrices. The orientational potential energy function has been expanded as a series of Legendre polynomials, and the contributions of the various terms investigated.

Effect of the electron spin exchange relaxation on the high-field CIDNP polarization produced by radical pairs☆

Abstract The effect of the electron spin relaxation of the radicals of a radical pair has been examined at the high-field approximation in a reaction whose products display chemically induced nuclear polarization. We have found that the polarization varies noticeably when the relaxation rates are comparable to the singlet-triplet mixing parameter Q , typically of the order of 10 7 rad/sec. Special emphasis has been placed on the relaxation process due to the Heisenberg electron spin exchange between a stable radical and the radicals of the pair since in this case it may be sufficiently fast to affect the extent of the polarization. In the photolysis of a solution of 9,10-phenanthrenequinone and fluorene performed in the presence of di- tert -butyl nitroxide radical, changes of the polarization were obtained for the polarized line of the adduct on varying the concentration of the nitroxide. The experimental and the calculated changes of the polarization were compared and the average value of the rate constants of the collisional dimers formed by the stable radical and the single radicals of the pair could be determined.

Theory of nuclear magnetic resonance paramagnetic shifts in liquid crystalline solvents

The theoretical treatment of paramagnetic chemical shifts in molecules has been reformulated in a general way. The effects of preferential orientational distribution, as found in liquid crystalline solvents, have been included in the treatment.

Carbon-13 nuclear magnetic resonance spectra of 1-p-tolylethyl- and di-p-tolylmethyl-tricarbonylchromium cations

The 13C n.m.r. spectra of 1-p-tolylethyl- and di-p-tolylmethyl-tricarbonylchromium cations and of the analogous complexed alcohols have been obtained. The chemical shifts compared with those of the corresponding uncomplexed cations are explicable in terms of structures in which the positive charge is localized on the tricarbonylchromium system to a great extent. From an analysis of the behaviour upon variations of temperature of the non-equivalent splittings of the ortho- and meta-carbons as well as of the carbonyl resonance one can deduce that two motions, around the aryl–methyl and the metal–ring bonds, characterize the dynamics of the ions.