Antonio Benedetto

Puzzle of Protein Dynamical Transition

Despite recent extensive efforts, the nature of the dynamics of biological macromolecules still remains unclear. In particular, contradicting models have been proposed for explaining the temperature behavior of the mean square displacement, MSD, and of the system relaxation time, τ. To solve this puzzle, different neutron scattering experiments with different instrumental energy resolutions were performed on dry and hydrated lysozyme. The obtained results show that the so called dynamical transition: (i) is a finite instrumental energy resolution effect, and more specifically, it appears when the characteristic system relaxation time intersects the resolution time, (ii) it does not imply any transition in the dynamical properties of the systems, (iii) it is not due to the fragile-to-strong dynamical crossover (FSC) in the temperature behavior of the system relaxation time, differently to what S. H. Chen et al. proposed [Proc. Natl. Acad. Sci. U.S.A.2006, 103, 9012]. Furthermore, the obtained results confirm the change in the τ-temperature dependence at T = 220 K of S. H. Chen et al., and show that it is not due to finite instrumental energy resolution effects and it is not connected to numerical errors in the data analysis protocol, differently to what W. Doster et al. proposed [Phys. Rev. Lett.2010, 104, 098101].

Mean square displacements from elastic incoherent neutron scattering evaluated by spectrometers working with different energy resolution on dry and hydrated (H2O and D2O) lysozyme.

The main aim of the present paper is the evaluation of the effects of the instrumental energy resolution on the mean square displacement (MSD) obtained by elastic incoherent neutron scattering (EINS). In particular, this study is performed in the time domain, through the time-Fourier transform of the elastically scattered neutron intensity, and is mainly focused on the connection between the system MSD and the measured MSD. It is shown how in the case of EINS, the instrumental energy resolution gives rise to the time integration of the time-dependent system MSD function weighted in time by the resolution function. The formulated approach is applied to the data collected on dry and hydrated (H(2)O and D(2)O with h = 0.4) lysozyme samples by two spectrometers working with a different instrumental resolution (the IN10 and IN13 spectrometers of the Institute Laue-Langevin). As a result, the procedure furnishes an excellent agreement for the system MSD evaluated in the low temperature range up to T = 40 K.

Elastic incoherent neutron scattering operating by varying instrumental energy resolution: Principle, simulations, and experiments of the resolution elastic neutron scattering (RENS)

The main aim of this paper is to present the scientific case of the resolution elastic neutron scattering (RENS) method that is based on the collection of elastic neutron scattering intensity as a function of the instrumental energy resolution and that is able to extract information on the system dynamical properties from an elastic signal. In this framework, it is shown that in the measured elastic scattering law, as a function of the instrumental energy resolution, an inflection point occurs when the instrumental energy resolution intersects the system relaxation time, and in an equivalent way, a transition in the temperature behavior of the measured elastic scattering law occurs when the characteristic system relaxation time crosses the instrumental energy resolution time. With regard to the latter, an operative protocol to determine the system characteristic time by different elastic incoherent neutron scattering (EINS) thermal scans at different instrumental energy resolutions is also proposed. The proposed method, hence, is not primarily addressed to collect the measured elastic scattering intensity with a great accuracy, but rather relies on determining an inflection point in the measured elastic scattering law versus instrumental energy resolution. The RENS method is tested both numerically and experimentally. As far as numerical simulations are concerned, a simple model system for which the temperature behavior of the relaxation time follows an Arrhenius law, while its scattering law follows a Gaussian behavior, is considered. It is shown that the system relaxation time used as an input for the simulations coincides with the one obtained by the RENS approach. Regarding the experimental findings, due to the fact that a neutron scattering spectrometer working following the RENS method has not been constructed yet, different EINS experiments with different instrumental energy resolutions were carried out on a complex model system, i.e., dry and D(2)O hydrated lysozyme, in an extended temperature range. The resulting temperature behavior of the system relaxation time, obtained with RENS method, agrees very well with the one obtained in literature, for the same system, following the quasi-elastic neutron scattering (QENS) approach. The proposed scientific case puts into evidence the challenges of an RENS spectrometer working by varying the instrumental energy resolution; in particular, in comparison with QENS, the proposed RENS method requires a smaller amount of sample, which is an important point in dealing with biological and exotic systems; it is not affected by the use of model functions for fitting spectra as in QENS, but furnishes a direct access to relevant information.

Structure and stability of phospholipid bilayers hydrated by a room-temperature ionic liquid/water solution: a neutron reflectometry study.

Neutron reflectometry (NR) measurements were carried out to probe the structure and stability of two model biomembranes consisting of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1,2-dimyristoyl-sn-glycero-3-phosphatidylcholine (DMPC) phospholipid bilayers hydrated by water solutions of two prototypical room-temperature ionic liquids (RTILs), namely, 1-butyl-3-methyl-imidazolium chloride ([bmim][Cl]) and choline chloride ([Chol][Cl]) at concentrations of 0.1 M and 0.5 M, respectively. The raw data were analyzed by fitting a distribution of scattering length densities arising from the different chemical species in the system. The results of this analysis show that (a) for all systems and concentrations that we considered, the thickness of the bilayers shrinks by ∼1 Å upon dissolving the ionic liquid into water and that (b) the RTIL ions enter the bilayer, finding their way to a preferred location in the lipid range that is nearly independent of the lipid and of the [bimim](+) or [Chol](+) choice. The volume fraction of RTIL sorbed in/on the bilayer, however, does depend on the lipid, but, again, is the same for [bmim][Cl] and for [Chol][Cl]. Thus, the RTIL occupies ∼5% of the bilayer volume in POPC, rising to ∼10% in DMPC. Repeating the measurements and data analysis after rinsing in pure water shows that the changes in the bilayer due to the RTIL sorption are irreversible and that a measurable amount of IL remains in the lipid fraction, that is, ∼2.5% of the bilayer volume in POPC and ∼8% in DMPC.

Characterization of molecular motions in biomolecular systems by elastic incoherent neutron scattering

In the present work the role played by the instrumental resolution function in elastic incoherent neutron scattering (EINS) experiment is discussed. An important result consists in the definition of an equivalent time t(*), which depends both on the characteristic system time and on the resolution time, for which the spatial Fourier transform of EINS intensity profile and the self-distribution function (SDF) evaluated at t=t(*) are proportional. Then the equivalent time t(*) is introduced in the SDF procedure, an operational recipe for the mean square displacement determination. The new revised procedure is applied on data of myoglobin in trehalose dry environment and of hydrated homologous disaccharides (sucrose and trehalose).

Elastic Incoherent Neutron Scattering on Systems of Biophysical Interest: Mean Square Displacement Evaluation from Self-Distribution Function

In the present work an operational recipe for the mean square displacement (MSD) determination, highlighting the connection between the self-distribution function and average statistical values, is presented. The determination of the MSD and of its contributions associated with different mechanisms, together with their thermal behavior, is performed by evaluating the self-distribution function derived by elastic incoherent neutron scattering (EINS). The approach is tested on EINS data collected by the backscattering spectrometer IN13 (ILL, Grenoble, France) on two model systems such as dry myoglobin in trehalose and poly(ethylene glycol) with mean molecular weight M(w) = 400 (PEG 400).

Magnesium levels in plasma, erythrocyte, and platelet in hypertensive and normotensive patients with type II diabetes mellitus

The authors, by means of a recently introduced method, evaluated the intraplatelet concentrations of magnesium in 45 normotensive patients with type II diabetes mellitus, in 45 hypertensive diabetics and in 15 healthy controls. They also evaluated plasma and erythrocyte concentrations of the cation through direct current plasma spectrometer. Both normotensive and hypertensive diabetics showed a reduction in plasma, erythrocyte, and platelet concentrations of magnesium compared to controls. On the contrary, no significant difference was found between hypertensive and normotensive diabetics with regard to plasma and erythrocyte magnesium, whereas intraplatelet assay of the ion pointed out significantly lower concentrations of magnesium in hypertensive compared to normotensive patients (56.4±9.0 vs 60.7±10.2 μg/108 cells-p<0.05). The authors believe that intraplatelet assay of magnesium may be the most reliable method for the evaluation of the cation in hypertensive diabetics, probably because platelets share common features with smooth muscle cells, including the α-2-adrenoceptor cyclase system and a coupling mechanism concerning the calcium-dependent contraction.

Motion characterization by self-distribution–function procedure

In the present paper a procedure for the biomolecular motion characterization based on the evaluation of the Mean Square Displacement (MSD), through the Self Distribution Function (SDF), is presented. In particular it will be shown how the MSD, which represents a good observable for the characterization of the dynamical properties in disordered systems, can be decomposed into partial contributions associated to the system dynamical processes within a specific spatial scale. It will be shown how the SDF procedure allows to evaluate both the total MSD and the partial MSDs through the total SFD and the partial SDFs. As a result, the total MSD is the weighed sum of the partial MSD contributions in which the weights are obtained by the fitting procedure of measured EINS intensity data. We apply the SDF procedure at EINS data collected, by the IN13 backscattering spectrometer at the Institute Laue-Langevin, Grenoble, on aqueous mixtures of two homologous disaccharides (sucrose and trehalose) and on dry myoglobin in trehalose environment. It emerges that the hydrogen bond imposed network of the water-trehalose mixture appears to be stronger with respect to that of the water-sucrose mixture and this result can justify the highest bioprotectant effectiveness of trehalose in comparison with sucrose. Furthermore it emerges that, the partial MSD behaviours of sucrose and trehalose are equivalent in the low Q domain (0-1.7) A(-1) whereas they are different in the high Q domain (1.7-4) A(-)(1). This circumstance suggests that the higher structure sensitivity of sucrose in respect to trehalose should be related to the small spatial observation windows.

Response to “Comment on ‘Elastic incoherent neutron scattering operating by varying instrumental energy resolution: Principle, simulations, and experiments of the resolution elastic neutron scattering (RENS)’” [Rev. Sci. Instrum. 83, 107101 (2012)]

Recently [S. Magazu et al., Rev. Sci. Instrum. 82, 105115 (2011)10.1063/1.3641870] we have proposed a new method for characterizing, by neutron scattering, the dynamical properties of complex material systems, such as, the ones of interest in the biophysical field. This approach called Resolution Elastic Neutron Scattering, in short RENS, is based on the detection of the elastically scattered neutron intensity as a function of the instrumental energy resolution. By experimental, theoretical, and numerical findings, we have pointed out that an inflection point occurs in the elastic intensity when the system relaxation time approaches the instrumental energy resolution time. This approach, differently from quasi-elastic neutron scattering (QENS), gives the chance to evaluate the system relaxation times without using pre-defined models that can be wrong and/or misleading. Here, we reply to a Comment on the above-mentioned main paper in which Wuttke proposes a different approach to evaluate the above-mentione...

Self-distribution-function procedure in elastic incoherent neutron scattering for biosystems molecular motion characterization

In the present contribution we present a new procedure for the Mean Square Displacement (MSD) determination from Elastic Incoherent Neutron Scattering (EINS) where the connection between the Self-Distribution Function (SDF) and the measured EINS intensity profile is highlighted. We show how the SDF procedure allows both the total and the partial MSD evaluation, through the total and the partial SDFs. The procedure is applied on EINS data collected, by the IN13 backscattering spectrometer (ILL, Grenoble), on aqueous mixtures of sucrose and trehalose.