C. Crupi

Absorption spectra and photovoltaic characterization of chlorophyllins as sensitizers for dye-sensitized solar cells.

Dye-sensitized solar cells (DSSCs) based on Chlorine-e6 (Chl-e6), a Chlorophyll a derivative, and Chl-e6 containing Cu, have been investigated by carrying out incident photon to current efficiency (IPCE) and current-voltage (I-V) measurements. The effect of the metallic ion and the influence of the solvent polarity on the dye aggregation and their absorption bands have been analysed by performing electronic absorption measurements. The dependence of the photoelectrochemical parameters of these DSSCs on the electrolyte by the addition of pyrimidine and/or pyrrole has been discussed in details. For the first time I-V curves for a DSSC based on copper Chl-e6 dye have been shown and compared with Zn based chlorophyllin. Furthermore, the performance of a Cu-Chl-e6 based DSSC has been deeply improved by a progressive optimization of the TiO2 multilayer photoanode overcoming the best data reported in literature so far for this dye. Its worth to emphasize that, the analysis reported in this paper supplies very useful information which paves the way to further detailed studies turned to the employment of natural pigments as sensitizers for solar cells.

Multi-component modeling of quasielastic neutron scattering from phospholipid membranes

We investigated molecular motions in the 0.3-350 ps time range of D2O-hydrated bilayers of 1-palmitoyl-oleoyl-sn-glycero-phosphocholine and 1,2-dimyristoyl-sn-glycero-phosphocholine in the liquid phase by quasielastic neutron scattering. Model analysis of sets of spectra covering scale lengths from 4.8 to 30 Å revealed the presence of three types of motion taking place on well-separated time scales: (i) slow diffusion of the whole phospholipid molecules in a confined cylindrical region; (ii) conformational motion of the phospholipid chains; and (iii) fast uniaxial rotation of the hydrogen atoms around their carbon atoms. Based on theoretical models for the hydrogen dynamics in phospholipids, the spatial extent of these motions was analysed in detail and the results were compared with existing literature data. The complex dynamics of protons was described in terms of elemental dynamical processes involving different parts of the phospholipid chain on whose motions the hydrogen atoms ride.

Lipid Diffusion in Alcoholic Environment

We have studied the effects of a high concentration of butanol and octanol on the phase behavior and on the lateral mobility of 1,2-palmitoyl-sn-glycero-3-phosphocholine (DPPC) by means of differential scanning calorimetry and pulsed-gradient stimulated-echo (PGSTE) NMR spectroscopy. A lowering of the lipid transition from the gel to the liquid-crystalline state for the membrane-alcohol systems has been observed. NMR measurements reveal three distinct diffusions in the DPPC-alcohol systems, characterized by a high, intermediate, and slow diffusivity, ascribed to the water, the alcohol, and the lipid, respectively. The lipid diffusion process is promoted in the liquid phase while it is hindered in the interdigitated phase due to the presence of alcohols. Furthermore, in the interdigitated phase, lipid lateral diffusion coefficients show a slight temperature dependence. To the best of our knowledge, this is the first time that lateral diffusion coefficients on alcohol with so a long chain, and at low temperatures, are reported. By the Arrhenius plots of the temperature dependence of the diffusion coefficients, we have evaluated the apparent activation energy in both the liquid and in the interdigitated phase. The presence of alcohol increases this value in both phases. An explanation in terms of a free volume model that takes into account also for energy factors is proposed.

Relation between low-temperature thermal conductivity and the specific heat of cesium borate glasses.

Low-temperature specific heat and thermal conductivity measurements have been performed on cesium borate glasses as a function of cesium oxide content. We have found experimental evidence of a concurrent growth of specific heat and thermal conductivity with increasing Cs(+) content. This finding shows the existence of an uncommon relationship between the peak in C(p)/T(3) and the plateau in thermal conductivity in glasses and represents the most intriguing result for these alkaline borate glasses. The role of local modes associated with heavy cations on the vibrational dynamics in oxide glasses has been considered. Furthermore, a possible correlation between low-temperature thermal properties and the structure on the nanometer length scale of these glasses is put forward.

Raman spectroscopic and low-temperature calorimetric investigation of the low-energy vibrational dynamics of hen egg-white lysozyme

The low-frequency vibrational dynamics of chicken hen egg-white lysozyme were investigated using Raman spectroscopy and low-temperature calorimetry. An amorphous-like behaviour of low-frequency dynamics was observed in this protein. By using inelastic light scattering data and resorting to a fitting procedure, the low-temperature specific heat trend was theoretically reproduced, confirming that, as in disordered systems, the same low-energy excitations give rise to the observed anomalies in low-frequency vibrational and low-temperature thermal properties. A further study of polarised and depolarised Raman spectra has allowed us to infer information about the symmetry of these modes. The frequency dependence of the light–vibrational coupling constant has also been analysed.

Interaction of alcohol with phospholipid membrane: NMR and XRD investigations on DPPC–hexanol system

The investigations of the interaction between phospholipid bilayer and short-chain alcohols are relevant for the potential of lipid bilayer membranes to serve as model systems for studies of various biological processes including permeability of the plasma membrane and molecular mechanisms of anesthesia. Because the hydrophobic portion of an alcohol favorably interacts with lipid hydrocarbon chains, the polar hydroxyl group remains free to form hydrogen bonds with polar lipid atoms that are located near the water/lipid interface. Experiments on phospholipid membranes have shown that alcohols can induce an interdigitated phase and at high concentration even promote the assembly of some lipids into non-bilayer structures within the membrane interior. In this paper we have investigated the DPPC:hexanol system at high alcohol concentration (two molecules per phospholipid) by means of calorimetric, Nuclear Magnetic Resonance, X-ray diffraction and density measurements. We have found that the presence of a high alcohol concentration shifts the membrane transition temperature to lower values, and has a disordering effect on the phospholipid acyl chains in the gel phase. The bilayer spacing and the area of polar head have been also derived for the liquid phase.

Prepeak and First Sharp Diffraction Peak in the Structure Factor of (Cs2O)0.14(B2O3)0.86 Glass: Influence of Temperature

Neutron diffraction measurements on (Cs(2)O)(0.14)(B(2)O(3))(0.86) glass were performed at varying temperature over an extended range from room temperature to 800 K. It was found that, in the same Q range where the first sharp diffraction peak (FSDP) is observed in the static structure factor of almost all glass-forming systems, cesium borate glass shows two peaks. The intensities of these peaks increase with temperature, and their positions shift to lower Q values, in agreement with the peculiarities of the FSDP of network glasses. A description of this anomalous temperature dependence in terms of thermal relaxations of strained bonding arrangements of boron oxide units lying on the boundaries of cages present in the boron skeleton matrix is suggested. By comparing the diffraction patterns of a (Cs(2)O)(0.14)(B(2)O(3))(0.86) sample before and after a high-temperature thermal treatment with the spectra of cesium crystals, a correspondence between the medium-range structure in the glass and the related crystalline phases has been inferred.

Physical study of dynamics in fully hydrated phospholipid bilayers

We studied the thermotropic phase behavior of a phospholipid membrane bilayer of dimyristoylphosphatidylcholine (DMPC) under excess water conditions. We also investigated the effect induced by the antimicrobial peptide, gramicidin D (GrD), when inserted into the membrane bilayer. Several techniques were used to collect information on different properties and various spatial and temporal regimes, including differential scanning calorimetry, fixed energy window neutron scattering, pulsed-field gradient nuclear magnetic resonance and molecular dynamics simulations. We obtained data on the main phase transition (gel–liquid crystalline) temperature of the bilayer system and on the long-range diffusion coefficient for both phospholipids and hydration water. Moreover, we demonstrated the effect of transition on microscopic molecular mobility, perpendicular and parallel to the membrane plane. The influence of gramicidin on these properties is also discussed.

Probing Intermolecular Interactions in Phospholipid Bilayers by Far-Infrared Spectroscopy

Fast thermal fluctuations and low frequency phonon modes are thought to play a part in the dynamic mechanisms of many important biological functions in cell membranes. Here we report a detailed far-infrared study of the molecular subpicosecond motions of phospholipid bilayers at various hydrations. We show that these systems sustain several low frequency collective modes and deduce that they arise from vibrations of different lipids interacting through intermolecular van der Waals forces. Furthermore, we observe that the low frequency vibrations of lipid membrane have strong similarities with the subpicosecond motions of liquid water and suggest that resonance mechanisms are an important element to the dynamics coupling between membranes and their hydration water.

Influence of Alcohols on the Lateral Diffusion in Phospholipid Membranes

The effects of hexanol and octanol on the lateral mobility of 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) bilayer are investigated by means of pulsed-gradient stimulated-echo NMR spectroscopy. Three distinct diffusions are identified for the DMPC/alcohol systems. They are ascribed to the water, the alcohol, and the lipid. We find that the presence of alcohols promotes the lipid diffusion process both in the liquid and in the interdigitated phases. Furthermore, using the Arrhenius approach, the activation energies are calculated. An explanation in terms of a free volume model, that takes into account also the observed increase of the activation energy in both phases, is proposed. The results obtained here are compared with those presented in our previous work on 1,2-palmitoyl-sn-glycero-3-phosphocholine (DPPC) in order to examine the dependence of the lipid translational diffusion process upon the membrane acyl chain length. A peculiar influence of alcohols on different membranes is found.