Obiettivo del Programma di Ricerca:
Obiettivo generale del Programma è migliorare la comprensione della relazione fra struttura e conformazione molecolare e proprietà di ordine e dinamica in vari tipi di cristalli liquidi termotropici e liotropici mediante l' uso di metodologie teoriche, di simulazione al calcolatore, spettroscopiche (NMR, Fluorescenza) con attenzione alle applicazioni. Saranno particolarmente studiati sistemi chirali, sia termotropici (colesterici e smectici C chirali in bulk o confinati) che sistemi liotropici formati da acidi nucleici. Si studierà la relazione fra struttura molecolare e biassialità e organizzazione colesterica. Si studieranno inoltre con tecniche calorimetriche e NMR alcuni sistemi liotropici modello per approfondire il ruolo di interazioni idrofobiche in sistemi di interesse biologico e il problema della stabilità di vescicole fosfolipidiche. Gran parte del programma ha una valenza di base ma le tecniche sviluppate dovrebbero consentire anche la realizzazione di alcuni obiettivi di tipo applicativo, come: (i) simulazioni al calcolatore di display "in plane switching" e a colorante (ii) ottimizzazione di modulatori ottici polymer dispersed liquid crystals (PDLC) (iii) realizzazione di un biosensore per raggi gamma a cristalli liquidi colesterici.
Relazione del Primo Anno
- G. Celebre, N. De Vita, "Solutes Order In Nematics. 1.: A Model For The Description Of The Mechanical Aspects Of The Anisotropic Potential Governing The Orientational Order Of Biaxial Prolate Solutes In Nematic Liquid Crystal Solvents.", to be submitted to J. Chem. Phys. , Abstract: A derivation of analytical form of the short-range mean torque potential for biaxial prolate solutes dissolved in nematic liquid crystals is presented. The development of this model (that will be called Mechanical Model) is based on the mechanics of a rigid body plunged in an anisotropic uniaxial medium. The last part of the paper is devoted to the generalisation of the mechanical result to the statistical mechanics form. Finally, a closed form of the short range potential is given, available to be tested an experimental data, whose main peculiarity is the absence of any undefined parameter to be optimised to fit the experiments.
- G. Celebre, G. De Luca, N. De Vita and M. Longeri, "Solutes Order In Nematics. 2.: A Test of the Mechanical Model For The Prediction Of Solutes Order Parameters In Nematics." , to be submitted to J. Chem. Phys. Abstract: The reliability of a new model, called Mechanical Model (McM), accounting for short range effects in the prediction of solutes order parameters in nematics, has been tested on NMR data of eighteen solutions obtained dissolving three apolar biaxial prolate solutes (1,4-difluorobenzene, 1,4-dichlorobenzene and 1,4-dibromobenzene) in six liquid-crystalline solvents(EBBA, ZLI1132, a 55wt% ZLI1132+EBBA mixture,ZLI1115, I35 and I52) at different temperatures. The McM, that in principle does not need any parameter to be optimised to fit experimental data, calculates the short-range contribution to the order parameter, the missing part being probably due to long-range (electrostatic and dispersive) contribution that the model does not claim to describe. The agreement between experimental and calculated order parameters is good for the solutes in I35 and I52 and excellent for the EBBA solutions; Szz parameters are still quite well reproduced for the remaining solutions, but the McM fails in reproducing the solute biaxiality. A detailed explanation of the results based on the nature of nematic solvents and on a reaction field description of long-range effects is given
- F. Castiglione, G. Celebre, G. De Luca and M. Longeri, "The NMR Spectra of Samples Dissolved In Liquid-Crystalline Phases. Automatic Analysis With The Aid Of Multiple Quantum Spectra: The case of Flexible Molecules.", To be submitted to J. Magn. Reson. Abstract: Homo nS=0 and heteronuclear Multiple Quantum spectra, involving changes in the magnetic number mI by (NI-1), (NI-2) and (NI-3), with NI and NS the number of interacting nuclei of magnetogyric ratio gI and gS, are used for the automatic analysis of 1H NMR spectra of flexible molecules dissolved in liquid-crystalline phases. The automatic procedure has been applied to study molecules of general formula Ph-CH2-X starting from a parameter set having all the spectral parameters set to zero. The results of such an analysis are then used as starting parameters for the analysis of the Single Quantum spectrum. The method was first tested when X=Br and X=H in order to compare strategies differing for the types of parameters used and the applied to the analysis of 3-phenylprop-1-yne and ethylbenzene dissolved in two different nematic solvents.
- C. Algieri, F. Castiglione, G. Celebre, G. De Luca and Marcello Longeri , "An Investigation of The Shape Of Ethylbenzene By Analysis Of The Proton NMR Spectrum Of Samples Dissolved In Nematic Liquid Crystalline Solvents." To be submitted to Physical Chemistry Chemical Physics.
- L. Coppola , U. Olsson (*), R. Muzzalupo, G.A. Ranieri and M. Terenzi, "Microstructures in an Oil-in-Water Microemulsion: A NMR Self-Diffusion Study" We present the accurate measurements of water, oil and surfactant self-diffusion coefficients made in the microemulsion phase of the pentaethylene glycol dodecyl ether (C12E5), water and decane. Fourier Transform NMR self-diffusion experiments provided insights into solution microstructure via investigation of the long-range mobility of the different components. The self-diffusion coefficients of oil and surfactant molecules have been measured using the pulsed gradient stimulated-echo NMR experiment1. We have analysed the microstructure of three microemulsion phases obtained with different surfactant-to-oil volume ratios. Particular attention was focused at the phase boundary where the microemulsions consist of normal oil swollen micelles in equilibrium with excess oil. Increasing the temperature, a micellar growing was supported by self-diffusion results and finally a bicontinuos phase was found. LANGMUIR, submitted
- L. Coppola, U. Olsson (+), C. Oliviero, R. Muzzalupo, G.A. Ranieri and M. Terenzi, NMR studies of a lamellar phase of a nonionic surfactant-oil-water system, Lavoro sottoposto per la pubblicazione, LANGMUIR, submitted NMR techniques have been used in order to study the microstructures of some lyotropic phases in a ternary system with a non-ionic surfactant. The ternary non-ionic system contains pentaethylene glycol dodecyl ether (C12E5), decane and D2O, where the surfactant-to-oil ratio 50/50 (w/w) is kept constant. 2H-NMR line shape measurements have been carried out to follow the formation liquid crystalline phases. The structural sequence of normal spheres to planar bilayers, via cylinders, was observed as a function of decreasing water concentration at a fixed temperature. Special attention was focused on the lamellar microstructures by changing temperature and composition. The phase diagram of this ternary system was found similar to that of the binary surfactant-water system. Accurate measurements of water, oil and surfactant self-diffusion have been performed in lamellar and hexagonal mixtures by using the Fourier Transform Pulsed Gradient Spin-Echo NMR method. The self-diffusion measurements have been interpreted with the one- and two-dimensional diffusional models.
- R. Guzzi, L. Sportelli, C. La Rosa, D. Milardi, D. Grasso, M. Ph. Verbeet, G. W. Canters. A spectroscopic and calorimetric investigation on the thermal stability of the Cys3Ala/Cys26Ala azurin mutant. Biophys. J, in press. Keywords: Thermal unfolding, enzyme, hydrophobic effect, DSC, OD, ESR, thermodynamic.
- L. Sportelli, C. La Rosa, D. Milardi, D. Grasso. Phase transition of DPPC-DPPC:PEG 2000 and DPPC:PEG 350 vesicles by combined microDSC and ESR measurements. ??? Submitted Keywords: Phase transition, hydrophobic effect, phospholipid, lyotropic liquid crystal, DSC, ESR.
- L. Sportelli, C. La Rosa, D. Milardi, D. Grasso. MicroDSC study on DPPC phase transitions: influence of scan rate and deuterium substitution on the polar head. ??? Submitted, Keywords: Phase transition, phospholipid, hydrophobic effect, DSC, computer simulation.