Summary Small-angle neutron scattering (SANS) measurements on the large 50S ribosomal subunit of... more Summary Small-angle neutron scattering (SANS) measurements on the large 50S ribosomal subunit of the extreme thermophile archaebacterium Sulfolobus solfataricus are presented. The structural effects induced by magnesium ions and temperature are investigated. Supramolecular aggregation was present in all the investigated conditions. Removal of magnesium ions and increase of temperature reduce the intensity of the scattering at Q=0. This reduction is discussed
The thermal response of three proteins with mesophilic, thermophilic and hyperthermophilic charac... more The thermal response of three proteins with mesophilic, thermophilic and hyperthermophilic character hints at the essential role played in thermostability by the protein-water interface. The formation of spanning water clusters enveloping the macromolecule and their resistance to thermal stress is shown to correlate with the charge distribution at the protein surface; in particular our findings suggest an effective role of
Hydration of a spherical micelles of C12E6 in solution is studied by molecular dynamics simulatio... more Hydration of a spherical micelles of C12E6 in solution is studied by molecular dynamics simulation. The interface is found to be separated in an inner part composed of water and hydrophobic and hydrophilic moieties and an outer part with hydrophilic moiety and water only. Hydration numbers in the inner and in the outer parts are in excellent agreement with experimental data from various different methods. Temperature dehydration occurs in the inner region only and is related to the presence of water molecules directly in contact with the hydrophobic core at low temperature.
A model protein and surrounding water have been investigated at different temperatures. We have d... more A model protein and surrounding water have been investigated at different temperatures. We have detected an anomalous compression of the protein near the freezing point of water---a compression not obviously related to the negative thermal expansion of the solvent. Moreover, the physiological protein working temperature (T=300 K) appears to be related to the activation of exchange of vicinal water with
ABSTRACT Aqueous solutions of a nonionic surfactant, n-dodecylhexaoxyethylene glycol [C12H25 (OCH... more ABSTRACT Aqueous solutions of a nonionic surfactant, n-dodecylhexaoxyethylene glycol [C12H25 (OCH2CH2)6 OH], termed C12E6, have been studied in the mole ratio range W0 = 5.6−14.9, where W0 = [D2O]/[C12E6]. There, below a given temperature, a smectic lamellar phase exists. As shown by 1H and 2H NMR spectra, cooling induces the isotropic phase to become an almost completely isooriented lamellar phase when the magnetic field strength is high (14.1 T). In presence of high magnetic fields, the phase diagram is slightly different with respect to the originally reported one, and the coexistence of an isotropic phase and of the isooriented lamellar one can be observed. In a wide temperature range, only the isooriented lamellar phase is present; it is stable out of the magnetic field for several months. A careful study of the 2H splitting as a function of temperature and concentration indicates the onset of fluctuating cylinder inside the lamellar phase and defines their onset and region of existence. Optical polarizing microscopy experiments confirm the above observation, showing the occurrence of fine grained, mosaic optical textures.
Colloids and Surfaces A-physicochemical and Engineering Aspects, 2005
In this article we present a combined analysis of volumetric [1] and molecular dynamics (MD) [2] ... more In this article we present a combined analysis of volumetric [1] and molecular dynamics (MD) [2] determinations of the interfacial properties of non-ionic surfactant aggregates belonging to the family of the oligooxyethylene glycol (CiEj). The volumetric experiments were made on surfactant having i=12 and j ranging from 5 to 8 EO unit and concern the density, and the sound velocity
By means of density, dielectric spectroscopy and sound velocity measurements we perform a systema... more By means of density, dielectric spectroscopy and sound velocity measurements we perform a systematic study on the polyoxyethylene $C_{12}E_{6}$ nonionic surfactant solutions as a function of temperature and concentration. Both density and sound velocity data, at about $34^{\circ}C$, coincide with the value obtained for pure water. Above this temperature the density is lower than the water density whereas below it
ABSTRACT A combined analysis of experiments, small-angle neutron and X-ray scattering, transmissi... more ABSTRACT A combined analysis of experiments, small-angle neutron and X-ray scattering, transmission electron microscopy (TEM), mass density, and thermogravimetric measurements (TGA), was applied to gold nanoparticles (NP) grafted with thiol-terminated poly(ethylene glycol). TEM micrographs indicate that the gold core diameter is ca. 20% polydisperse. The associated polydispersion in volume dictates that the nanoparticle extensive properties thus determined, such as the number of gold atoms and polymer chains, have similar errors (ca. 30%). On the other hand, by combining the results of mass density and TGA the following intensive properties of the nanoparticle can be determined with a precision of 1%: (i) the volume fraction occupied by the gold core, (ii) the density of the nanoparticle, and (iii) the polymer terminations at the interface. An accurate characterization of the structure and hydration of NP is then obtained by fitting the scattering data and use of the density and TGA data to impose constraints on the fits. The scattering data can be fitted with a core−two shell model. The inner core contains only gold atoms and the two shells represent the interfacial region containing the polymer and the hydrating water molecules. The two shells differ in the local solvent−polymer composition: the inner shell is composed almost exclusively of polymer, whereas the outer is hydrated (about 60% of the volume occupied by polymers). Interesting differences have been observed with isotopic substitution in the solvent (H2O/D2O ratio).
Electrical conductivity and dielectric dispersions have been measured on suspensions of 30S, 50S ... more Electrical conductivity and dielectric dispersions have been measured on suspensions of 30S, 50S subunits and 70S ribosomal particles from E. coli, in the presence and absence of magnesium ions. Conductivity measurements show a net contribution due to the disperzed phase. Ribosomal particles act in general as obstructants to the ionic motions in the solution, but besides this effect, there is
... Fabio Sterpone, Giuseppe Briganti, § and Carlo Pierleoni*. ... Methods. Model. We adopt an ... more ... Fabio Sterpone, Giuseppe Briganti, § and Carlo Pierleoni*. ... Methods. Model. We adopt an all-atom model throughout this work. For the C 12 system, we exploited the force field of Tobias, Tu, and Klein 39-41 for the dodecane chains and the SPC model for the water. ...
Summary Small-angle neutron scattering (SANS) measurements on the large 50S ribosomal subunit of... more Summary Small-angle neutron scattering (SANS) measurements on the large 50S ribosomal subunit of the extreme thermophile archaebacterium Sulfolobus solfataricus are presented. The structural effects induced by magnesium ions and temperature are investigated. Supramolecular aggregation was present in all the investigated conditions. Removal of magnesium ions and increase of temperature reduce the intensity of the scattering at Q=0. This reduction is discussed
The thermal response of three proteins with mesophilic, thermophilic and hyperthermophilic charac... more The thermal response of three proteins with mesophilic, thermophilic and hyperthermophilic character hints at the essential role played in thermostability by the protein-water interface. The formation of spanning water clusters enveloping the macromolecule and their resistance to thermal stress is shown to correlate with the charge distribution at the protein surface; in particular our findings suggest an effective role of
Hydration of a spherical micelles of C12E6 in solution is studied by molecular dynamics simulatio... more Hydration of a spherical micelles of C12E6 in solution is studied by molecular dynamics simulation. The interface is found to be separated in an inner part composed of water and hydrophobic and hydrophilic moieties and an outer part with hydrophilic moiety and water only. Hydration numbers in the inner and in the outer parts are in excellent agreement with experimental data from various different methods. Temperature dehydration occurs in the inner region only and is related to the presence of water molecules directly in contact with the hydrophobic core at low temperature.
A model protein and surrounding water have been investigated at different temperatures. We have d... more A model protein and surrounding water have been investigated at different temperatures. We have detected an anomalous compression of the protein near the freezing point of water---a compression not obviously related to the negative thermal expansion of the solvent. Moreover, the physiological protein working temperature (T=300 K) appears to be related to the activation of exchange of vicinal water with
ABSTRACT Aqueous solutions of a nonionic surfactant, n-dodecylhexaoxyethylene glycol [C12H25 (OCH... more ABSTRACT Aqueous solutions of a nonionic surfactant, n-dodecylhexaoxyethylene glycol [C12H25 (OCH2CH2)6 OH], termed C12E6, have been studied in the mole ratio range W0 = 5.6−14.9, where W0 = [D2O]/[C12E6]. There, below a given temperature, a smectic lamellar phase exists. As shown by 1H and 2H NMR spectra, cooling induces the isotropic phase to become an almost completely isooriented lamellar phase when the magnetic field strength is high (14.1 T). In presence of high magnetic fields, the phase diagram is slightly different with respect to the originally reported one, and the coexistence of an isotropic phase and of the isooriented lamellar one can be observed. In a wide temperature range, only the isooriented lamellar phase is present; it is stable out of the magnetic field for several months. A careful study of the 2H splitting as a function of temperature and concentration indicates the onset of fluctuating cylinder inside the lamellar phase and defines their onset and region of existence. Optical polarizing microscopy experiments confirm the above observation, showing the occurrence of fine grained, mosaic optical textures.
Colloids and Surfaces A-physicochemical and Engineering Aspects, 2005
In this article we present a combined analysis of volumetric [1] and molecular dynamics (MD) [2] ... more In this article we present a combined analysis of volumetric [1] and molecular dynamics (MD) [2] determinations of the interfacial properties of non-ionic surfactant aggregates belonging to the family of the oligooxyethylene glycol (CiEj). The volumetric experiments were made on surfactant having i=12 and j ranging from 5 to 8 EO unit and concern the density, and the sound velocity
By means of density, dielectric spectroscopy and sound velocity measurements we perform a systema... more By means of density, dielectric spectroscopy and sound velocity measurements we perform a systematic study on the polyoxyethylene $C_{12}E_{6}$ nonionic surfactant solutions as a function of temperature and concentration. Both density and sound velocity data, at about $34^{\circ}C$, coincide with the value obtained for pure water. Above this temperature the density is lower than the water density whereas below it
ABSTRACT A combined analysis of experiments, small-angle neutron and X-ray scattering, transmissi... more ABSTRACT A combined analysis of experiments, small-angle neutron and X-ray scattering, transmission electron microscopy (TEM), mass density, and thermogravimetric measurements (TGA), was applied to gold nanoparticles (NP) grafted with thiol-terminated poly(ethylene glycol). TEM micrographs indicate that the gold core diameter is ca. 20% polydisperse. The associated polydispersion in volume dictates that the nanoparticle extensive properties thus determined, such as the number of gold atoms and polymer chains, have similar errors (ca. 30%). On the other hand, by combining the results of mass density and TGA the following intensive properties of the nanoparticle can be determined with a precision of 1%: (i) the volume fraction occupied by the gold core, (ii) the density of the nanoparticle, and (iii) the polymer terminations at the interface. An accurate characterization of the structure and hydration of NP is then obtained by fitting the scattering data and use of the density and TGA data to impose constraints on the fits. The scattering data can be fitted with a core−two shell model. The inner core contains only gold atoms and the two shells represent the interfacial region containing the polymer and the hydrating water molecules. The two shells differ in the local solvent−polymer composition: the inner shell is composed almost exclusively of polymer, whereas the outer is hydrated (about 60% of the volume occupied by polymers). Interesting differences have been observed with isotopic substitution in the solvent (H2O/D2O ratio).
Electrical conductivity and dielectric dispersions have been measured on suspensions of 30S, 50S ... more Electrical conductivity and dielectric dispersions have been measured on suspensions of 30S, 50S subunits and 70S ribosomal particles from E. coli, in the presence and absence of magnesium ions. Conductivity measurements show a net contribution due to the disperzed phase. Ribosomal particles act in general as obstructants to the ionic motions in the solution, but besides this effect, there is
... Fabio Sterpone, Giuseppe Briganti, § and Carlo Pierleoni*. ... Methods. Model. We adopt an ... more ... Fabio Sterpone, Giuseppe Briganti, § and Carlo Pierleoni*. ... Methods. Model. We adopt an all-atom model throughout this work. For the C 12 system, we exploited the force field of Tobias, Tu, and Klein 39-41 for the dodecane chains and the SPC model for the water. ...
Uploads
Papers by Giuseppe Briganti