79 research outputs found
Studio dell'idratazione di proteine in miscele acquose: esperimenti di small angle scattering
No full textExplanation of the stability of thermophilic proteins based on unique micromorphology
No full textTwo mesophilic/thermophilic variants of the G-domain of the elongation factor Tu were studied via molecular dynamics simulations. By analyzing the simulation data via the Voronoi space tessellation, we have found that the two proteins have the same macromolecular packing, while the water-exposed surface area is larger for the thermophile. A larger coordination with water is probably due to a peculiar corrugation of the exposed surface of this species. From an enthalpic point of view, the thermophile shows a larger number of intramolecular hydrogen bonds, stronger electrostatic interactions, and a flatter free-energy landscape. Overall, the data suggest that the specific hydration state enhances macromolecular fluctuations but, at the same time, increases thermal stability
NMR DETECTION AT 8.9 mT WITH A GMR BASED SENSOR COUPLED TO A SUPERCONDUCTING Nb FLUX TRANSFORMER
No full textInternational audience—This study presents NMR signal detection by means of a superconducting channel consisting of a Nb surface detection coil inductively coupled to a YBCO mixed sensor. The NMR system operates at a low-field (8.9 mT) in a magnetically shielded room suitable for magnetoencephalographic (MEG) recordings. The main field is generated by a compact solenoid and the geometry of the pickup coil has been optimized to provide high spatial sensitivity * Corresponding author: Raffaele Sinibaldi ([email protected]). 390 Sinibaldi et al. in the NMR field of view. The Nb detection coil is coupled to the mixed sensor through a Nb input coil. The mixed sensor consists of a superconducting YBCO loop with 2-µm constriction above which two Giant MagnetoResistance sensors are placed in a half-bridge configuration to detect changes of the bridge voltage as a function of the flux through the YBCO loop. The sensitivity of the receiving channel is calibrated experimentally. The measured spatial sensitivity is in agreement with the simulations and is ∼10 times better than that of the stand-alone mixed sensor. A NMR echo at 375 kHz shows a SNR only a factor 4 smaller than a tuned room temperature coil tightly wound around the sample, with a noise level which is a factor 3 better than for the volume coil. Our results suggest that mixed sensors are suitable for the integration of low-field MRI and MEG in a hybrid apparatus, where MEG and MRI would be recorded by SQUIDs and mixed sensors, respectively
Hydrophilicity of lysozyme in water–glycerol mixtures
No full textWe performed small angle neutron scattering experiments on lysozyme solvated in glycerol at different water contents to characterize the protein-solvent interface
A new software for dimensional measurements in 3D endodontic root canal instrumentation
No full textThe main issue to be faced to get size estimates of 3D modification of the dental canal
after endodontic treatment is the co-registration of the image stacks obtained through micro
computed tomography (micro-CT) scans before and after treatment. Here quantitative analysis of
micro-CT images have been performed by means of new dedicated software targeted to the analysis
of root canal after endodontic instrumentation. This software analytically calculates the best superposition
between the pre and post structures using the inertia tensor of the tooth. This strategy avoid
minimization procedures, which can be user dependent, and time consuming. Once the co-registration
have been achieved dimensional measurements have then been performed by contemporary
evaluation of quantitative parameters over the two superimposed stacks of micro-CT images. The
software automatically calculated the changes of volume, surface and symmetry axes in 3D occurring
after the instrumentation. The calculation is based on direct comparison of the canal and canal
branches selected by the user on the pre treatment image stack
The Role of Water Coordination in Binary Mixtures. A Study of Two Model Amphiphilic Molecules in Aqueous Solutions by Molecular Dynamics and NMR
No full textTwo binary aqueous mixtures which contain the small amphiphilic molecules TMAO (trimethylamine-Noxide)
and TBA (tert-butyl alcohol) have been investigated by molecular dynamics simulations and NMR
chemical shift and self-diffusion measurements. TMAO is an osmolyte, while TBA is a monohydrate alcohol.
Both possess bulky hydrophobic groups and polar heads, namely, NO in TMAO and OH in TBA. The
hydrophilic/hydrophobic content of these isosteric molecules strongly modulates the structure and dynamics
of the hydration shell, which is thought to be responsible for the effects observed on proteins and phospholipids.
Simulation results, especially on hydrogen-bond networking, spatial correlations, and self-diffusivity, are
consistent with NMR data and agree well with previous numerical studies on similar solutions. The methods
employed allow the elucidation of the microscopic features of the solutions. For TBA solutions, the hydration
shell is found to have a low density and a large spatial spread, and thus, above the molar fraction of 0.03,
reduction of hydrophobic hydration drives self-aggregation of the solute. This effect does not take place in
TMAO solutions, where the hydration shell is more compact and stable, maintaining its structure over a
wider range of solute concentrations
Understanding interaction properties in b-lactoglobulin in solution
No full textWe are studying the effects of increasing pressures on b-lactoglobuline (BLG), a protein belonging to the lipocaline family whose function in vivo is still unclear. Small Angle Neutron and X-Ray Scattering (SANS and SAXS) experiments have been performed to evaluate both structural modification and protein–protein effective interactions in different experimental conditions
Three‐fold increase in admissions for paediatric febrile convulsions during COVID‐19 pandemic could indicate alternative virus symptoms
No full textExperiments and DNS of a round jet with turbulent inlet
No full textExperimental and Direct Numerical Simulation data of a turbulent round jet fed by a turbulent pipe are compared in the near field. The Reynolds number achieved in both the experiment and the simulation, Re = 16000, allows a direct comparison of both the average and the fluctuating velocity statistics. In the experiments the jet is fed with olive oil droplets with a Stokes number St ' 1 whose dynamics is compared against the corresponding DNS simulation to asses the ability of particles to reproduce high order turbulence statistics and to asses the accumulation properties of inertial particles in the near field
Time-Resolved Small-Angle X-Ray Scattering Study of the Early Formation of Amyloid Protofibrils on a Apomyoglobin Mutant
No full textThe description of the fibrillogenesis pathway and the identification of “on-pathwayâ or â off-pathwayâ intermediates are key issues in amyloid research as they are concerned with the mechanism for onset of certain diseases and with therapeutic treatments. Recent results on the fibril formation process revealed an unexpected complexity both in the number and in the types of species involved, but the early aggregation events are still largely unknown, mainly because of their experimental inaccessibility. To provide information on the early stage events of self-assembly of an amyloidogenic protein, during the so-called lag phase, stopped-flow time-resolved small angle x-ray scattering (SAXS) experiments were performed. Using a global fitting analysis, the structural and aggregation properties of the apomyoglobin W7FW14F mutant, which is monomeric and partly folded at acidic pH but forms amyloid fibrils after neutralization, were derived from the first few milliseconds onward. SAXS data indicated that the first aggregates appear in less than 20 ms after the pH jump to neutrality and further revealed the simultaneous presence of diverse species. In particular, worm-like unstructured monomers, very large assemblies, and elongated particles were detected, and their structural features and relative concentrations were derived as a function of time on the basis of our model. The final results show that, during the lag phase, early assembling occurs due to the presence of transient monomeric species very prone to association and through successive competing aggregation and rearrangement processes leading to coexisting on-pathway and off-pathway transient species
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