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Abstract In the last years, hydrogels from renewable biopolymers and low-cost row materials are a hot topic for biomedical applications. In this context, cellulose nanofibrils are considered suitable building blocks for the synthesis of many biocompatible products, with a variety of chemical-physical properties. Herein we report a multi-technique and multi-scale study, from the molecular to the nanometric length scale, of the sol–gel transition observed in aqueous solutions of TEMPO-oxidized nano-sized cellulose fibrils (TOCNFs), when in the presence of polyvalent cations (Mg2+ and Ca2+). We combine the data from Small Angle Neutron Scattering (SANS), which provide information about the inner structure of the nanofibril, with those from UV Resonant Raman (UVRR) spectroscopy, which is a sensitive probe of the intra- and inter-molecular interactions in the gel and the liquid state. The transition between the gel and the liquid phases is investigated as a function of the concentration of both TOCNFs and cations, the nature of the latter, and the pH at which the phenomenon is observed. SANS analysis reveals that ion concentration induces an anisotropic swelling in the nanofibrils which, at the same time, become more and more flexible. The nanofibrils flexibility is also dependent on TOCNF concentration and pH value. UVRR allows us to elucidate the structural organization and hydrogen-bonding properties of water in aqueous TOCNF dispersions and gels, showing how water molecules partially lose their typical bulk-like tetrahedral organization when ions are added, and the gel phase is formed. Graphical abstract

A method is designed to quickly form protein hydrogels, based on the self-assembly of highly concentrated lysozyme solutions in acidic conditions. Their properties can be easily modulated by selecting the curing temperature. Molecular insights on the gelation pathway, derived by in situ FTIR spectroscopy, are related to calorimetric and rheological results, providing a consistent picture on structure-property correlations. In these self-crowded samples, the thermal unfolding induces the rapid formation of amyloid aggregates, leading to temperature-dependent quasi-stationary levels of antiparallel cross β-sheet links, attributed to kinetically trapped oligomers. Upon subsequent cooling, thermoreversible hydrogels develop by the formation of interoligomer contacts. Through heating/cooling cycles, the starting solutions can be largely recovered back, due to oligomer-to-monomer dissociation and refolding. Overall, transparent protein hydrogels can be easily formed in self-crowding conditions and their properties explained, considering the formation of interconnected amyloid oligomers. This type of biomaterial might be relevant in different fields, along with analogous systems of a fibrillar nature more commonly considered.

We characterize via small-angle neutron scattering the structural properties of a mixture of all-DNA particles with functionalities 4 (A) and 2 (B) constrained by design to reside close to the percolation threshold. DNA base sequences are selected such that A particles can only bind with B ones and that at the studied temperature (10 °C) all AB bonds are formed and long-lived, originating highly polydisperse persistent equilibrium clusters. The concentration dependence of the scattered intensity and its wavevector dependence is exploited to determine the fractal dimension and the size distribution of the clusters, which are found to be consistent with the critical exponents of the 3-D percolation universality class. The value of DNA nanoparticles as nanometric patchy colloids with well-defined functionality, bonding selectivity, and exquisite control of the interaction strength is demonstrated.

G-quadruplexes (G4s) are noncanonical forms of DNA involved in many key genome functions. Here, we exploited UV Resonance Raman scattering to simultaneously explore the vibrational behavior of a human telomeric G4 (Tel22) and its aqueous solvent as the biomolecule underwent thermal melting. We found that the OH stretching band, related to the local hydrogen-bonded network of a water molecule, was in strict relation with the vibrational features of the G4 structure as a function of temperature. In particular, the modifications to the tetrahedral ordering of the water network were strongly coupled to the DNA rearrangements, showing changes in temperature that mirrored the multi-step melting process of Tel22. The comparison between circular dichroism and Raman results supported this view. The present findings provide novel insights into the impact of the molecular environment on G4 conformation. Improving current knowledge on the solvent structural properties will also contribute to a better understanding of the role played by water arrangement in the complexation of G4s with ligands.

Guanine-rich DNA sequences can fold into non-canonical nucleic acid structures called G-quadruplexes (G4s). These nanostructures have strong implications in many fields, from medical science to bottom-up nanotechnologies. As a result, ligands interacting with G4s have attracted great attention as candidates in medical therapies, molecular probe applications, and biosensing. In recent years, the use of G4-ligand complexes as photopharmacological targets has shown significant promise for developing novel therapeutic strategies and nanodevices. Here, we studied the possibility of manipulating the secondary structure of a human telomeric G4 sequence through the interaction with two photosensitive ligands, DTE and TMPyP4, whose response to visible light is different. The effect of these two ligands on G4 thermal unfolding was also considered, revealing the occurrence of peculiar multi-step melting pathways and the different attitudes of the two molecules on the quadruplex stabilization.

Schematic representation of our energy landscape model to describe the fast dynamics of human telomeric G-quadruplex and its change upon ligand complexation.

Telomeric G-quadruplexes (G4s) are promising targets in the design and development of anticancer drugs. Their actual topology depends on several factors, resulting in structural polymorphism. In this study, we investigate how the fast dynamics of the telomeric sequence AG3(TTAG3)3 (Tel22) depends on the conformation. By using Fourier transform Infrared spectroscopy, we show that, in the hydrated powder state, Tel22 adopts parallel and mixed antiparallel/parallel topologies in the presence of K+ and Na+ ions, respectively. These conformational differences are reflected in the reduced mobility of Tel22 in Na+ environment in the sub-nanosecond timescale, as probed by elastic incoherent neutron scattering. These findings are consistent with the G4 antiparallel conformation being more stable than the parallel one, possibly due to the presence of ordered hydration water networks. In addition, we study the effect of Tel22 complexation with BRACO19 ligand. Despite the quite similar conformation in the complexed and uncomplexed state, the fast dynamics of Tel22-BRACO19 is enhanced compared to that of Tel22 alone, independently of the ions. We ascribe this effect to the preferential binding of water molecules to Tel22 against the ligand. The present results suggest that the effect of polymorphism and complexation on the G4 fast dynamics is mediated by hydration water.

The human telomeric G-quadruplex structural motif of DNA has come to be known as a new and stimulating target for anticancer drug discovery. Small molecules that interact with G-quadruplex structures in a selective way have gained impressive interest in recent years as they may serve as potential therapeutic agents. Here, we show how circular dichroism, UV resonance Raman and small angle X-ray scattering spectroscopies can be effectively combined to provide insights into structural and molecular aspects of the interaction between human telomeric quadruplexes and ligands. This study focuses on the ability of berberine and palmatine to bind with human telomeric quadruplexes and provides analysis of the conformational landscape visited by the relevant complexes upon thermal unfolding. With increasing temperature, both free and bound G-quadruplexes undergo melting through a multi-state process, populating different intermediate states. Despite the structural similarity of the two ligands, valuable distinctive features characterising their interaction with the G-quadruplex emerged from our multi-technique approach.

International audience; Nucleic acid sequences rich in guanines can organize into noncanonical DNA G-quadruplexes (G4s) of variable size. The design of small molecules stabilizing the structure of G4s is a rapidly growing area for the development of novel anticancer therapeutic strategies and bottom-up nanotechnologies. Among a multitude of binders, porphyrins are very attractive due to their light activation that can make them valuable conformational regulators of G4s. Here, a structure-based strategy, integrating complementary probes, is employed to study the interaction between TMPyP4 porphyrin and a 22-base human telomeric sequence (Tel22) before and after irradiation with blue light. Porphyrin binding is discovered to promote Tel22 dimerization, while light irradiation of the Tel22-TMPyP4 complex controls dimer fraction. Such a change in quaternary structure is found to be strictly correlated with modifications at the secondary structure level, thus providing an unprecedented link between the degree of dimerization and the underlying conformational changes in G4s.

The maturation of coronavirus SARS-CoV-2, which is the etiological agent at the origin of the COVID-19 pandemic, requires a main protease Mpro to cleave the virus-encoded polyproteins. Despite a wealth of experimental information already available, there is wide disagreement about the Mpro monomer-dimer equilibrium dissociation constant. Since the functional unit of Mpro is a homodimer, the detailed knowledge of the thermodynamics of this equilibrium is a key piece of information for possible therapeutic intervention, with small molecules interfering with dimerization being potential broad-spectrum antiviral drug leads. In the present study, we exploit small angle x-ray scattering (SAXS) to investigate the structural features of the SARS-CoV-2 Mpro monomer-dimer equilibrium, by revealing the corresponding equilibrium dissociation constant and the associated thermodynamic parameters. SAXS is also used to study how the Mpro dissociation process is affected by small inhibitors selected through combinatorial design. Our results show that a clear picture connecting the ability of inhibitors to disrupt the Mpro dimerization with the loss of catalytic activity cannot be provided, thus highlighting the possible role of allosteric effects for the regulation of Mpro functionality.

The maturation of coronavirus SARS-CoV-2, which is the etiological agent at the origin of the COVID-19 pandemic, requires a main protease Mpro to cleave the virus-encoded polyproteins. Despite a wealth of experimental information already available, there is wide disagreement about the Mpro monomer-dimer equilibrium dissociation constant. Since the functional unit of Mpro is a homodimer, the detailed knowledge of the thermodynamics of this equilibrium is a key piece of information for possible therapeutic intervention, with small molecules interfering with dimerization being potential broad-spectrum antiviral drug leads. In the present study, we exploit Small Angle X-ray Scattering (SAXS) to investigate the structural features of SARS-CoV-2 Mpro in solution as a function of protein concentration and temperature. A detailed thermodynamic picture of the monomer-dimer equilibrium is derived, together with the temperature-dependent value of the dissociation constant. SAXS is also used to study how the Mpro dissociation process is affected by small inhibitors selected by virtual screening. We find that these inhibitors affect dimerization and enzymatic activity to a different extent and sometimes in an opposite way, likely due to the different molecular mechanisms underlying the two processes. The Mpro residues that emerge as key to optimize both dissociation and enzymatic activity inhibition are discussed.

Hypotheses Additives are commonly used to tune macromolecular conformational transitions. Among additives, trehalose is an excellent bioprotectant and among responsive polymers, PNIPAM is the most studied material. Nevertheless, their interaction mechanism so far has only been hinted without direct investigation, and, crucially, never elucidated in comparison to proteins. Detailed insights would help understand to what extent PNIPAM microgels can effectively be used as synthetic biomimetic materials, to reproduce and study, at the colloidal scale, isolated protein behavior and its sensitivity to interactions with specific cosolvents or cosolutes. Experiments The effect of trehalose on the swelling behavior of PNIPAM microgels was monitored by dynamic light scattering; Raman spectroscopy and molecular dynamics simulations were used to explore changes of solvation and dynamics across the swelling-deswelling transition at the molecular scale. Findings Strongly hydrated trehalose molecules develop water-mediated interactions with PNIPAM microgels, thereby preserving polymer hydration below and above the transition while drastically inhibiting local motions of the polymer and of its hydration shell. Our study, for the first time, demonstrates that slowdown of dynamics and preferential exclusion are the principal mechanisms governing trehalose effect on PNIPAM microgels, at odds with preferential adsorption of alcohols, but in full analogy with the behavior observed in trehalose-protein systems.

Materials based on ordered protein aggregates have recently received a lot of attention for their application as drug carriers, due to their biocompatibility and their ability to sequester many biological fluids. Bovine serum albumin (BSA) is a good candidate for this use due to its high availability and tendency to aggregate and gel under acidic conditions. In the present work, we employ spectroscopic techniques to investigate the heat-induced BSA aggregation at the molecular scale, in the 12–84 °C temperature range, at pH = 5 where two different isoforms of the protein are stable. Samples at low and high protein concentration are examined. With the advantage of the combined use of FTIR and CD, we recognize the aggregation-prone species and the different distribution of secondary structures, conformational rearrangements and types of aggregates, of millimolar compared to micromolar BSA solutions. Further, as a new tool, we use the Maximum Entropy Method to fit the kinetic curves to investigate the distribution of kinetic constants of the complex hierarchical aggregation process. Finally, we characterize the activation energy of the initial self-assembling step to observe that the formation of both small and large aggregates is driven by the same interactions.

A multi-technique approach, combining circular dichroism spectroscopy, ultraviolet resonance Raman spectroscopy and small angle scattering techniques, has been deployed to elucidate how the structural features of the human telomeric G-quadruplex d[A(GGGTTA)3GGG] (Tel22) change upon thermal unfolding. The system is studied both in the free form and when it is bound to Actinomycin D (ActD), an anticancer ligand with remarkable conformational flexibility. We find that at room temperature binding of Tel22 with ActD involves end-stacking upon the terminal G-tetrad. Structural evidence for drug-driven dimerization of a significant fraction of the G-quadruplexes is provided. When the temperature is raised, both free and bound Tel22 undergo melting through a multi-state process. We show that in the intermediate states of Tel22 the conformational equilibrium is shifted toward the (3+1) hybrid-type, while a parallel structure is promoted in the complex. The unfolded state of the free Tel22 is consistent with a self-avoiding random-coil conformation, whereas the high-temperature state of the complex is observed to assume a quite compact form. Such an unprecedented high-temperature arrangement is caused by the persistent interaction between Tel22 and ActD, which stabilizes compact conformations even in the presence of large thermal structural fluctuations.

Water is a strong self-associated liquid with peculiar properties that crucially depend on H-bonding. As regards its molecular dynamics, only recently has water reorientation been successfully described based on a jump mechanism, which is responsible for the overall H-bonding exchange. Here, using high-resolution broad-band depolarized light scattering, we have investigated the reorientational dynamics of formamide (FA) as a function of concentration from the neat liquid to diluted aqueous solutions. Our main findings indicate that in the diluted regime the water rearrangement can trigger the motion of FA solute molecules, which are forced to reorient at the same rate as water. This highlights an exceptional behavior of FA, which perfectly substitutes water within its network. Besides other fundamental implications connected with the relevance of FA, its water-like behavior provides rare experimental evidence of a solute whose dynamics is completely slaved to the solvent. © 2017 American Chemical Society.

We have studied the high-frequency dynamics of salol by inelastic x-ray scattering over a wide temperature range between 50 and 450 K, across the glass transition. We find that salol efficiently realizes the mechanism of dynamical arrest described by the mode-coupling theory, as manifested by a cusp singularity in the behaviour of the non-ergodicity parameter and a $Q$ dependence of the critical non-ergodicity parameter that is in phase with the static structure factor. These results confront positively the mode-coupling theory with liquids with local order., 7 pages, 6 figures

Smart polymers as poly-N-isopropylacrylamide (PNIPAM) are well known due to their fast response to variations of parameters like temperature, pH, and pressure. [...]

Local and propagating vibrations occurring in DNA in the terahertz domain are essential for processes at the basis of cellular metabolism. Here we report the results of a study on the B-DNA terahertz dynamics where we combined high-resolution inelastic x-ray experiments and incoherent inelastic neutron scattering. By using two different high-hydration conditions we could study the effect of packing interactions between double helices, while by selecting Na and Cs counterions we could inspect how the mass loading affects the DNA low-frequency modes. The pattern of coherent excitation energies is well represented in terms of two branches, an acoustic-like one, with an associated propagation velocity of 3000 ± 100 m/s, and the other almost dispersionless at ~2 meV. This picture is also supported by the vibrational density of states projected on the hydrogen atoms. The acoustic-like mode is assigned to DNA excitations, despite its intriguing similarity with the analogous acoustic mode of bulk water at low wave-vector transfers. We also provide evidence for the intrahelical optic-like character of the low-energy mode, that we ascribe to large scale relative motions of DNA sub-domains.

The present virtual special issue (VSI) of the Journal of Molecular Liquids contains the proceedings of the 4th Conference on Frontiers in Water Biophysics (FWB2017) held in Erice, Sicily (Italy) from 23 to 27 May 2017 at the Ettore Majorana Foundation and Centre for Scientific Culture, in the frame of the V Course of the International School of Sta- tistical Physics (Directors: P. Hanggi, F. Marchesoni).

The response to pH variation of polymeric cyclodextrin-based hydrogels has been investigated by a multi-technique approach based on UV Raman and Brillouin light scattering (BLS) together with Small Angle Neutron Scattering (SANS). By exploiting the complementary information of these three investigation methods, the structural, viscoelastic and molecular modifications of the polymer brought about by the pH changes have been examined, over a spatial range going from mesoscopic to nanoscopic length-scale. The data provide a picture where an increase of pH promotes the change of the characteristic size of the hydrophilic pores when the cross-linker has the suitable structural and acid-base properties, and leads to the reinforcement of the polymer domains interconnections, providing a stiffer gel network on the length-scale probed by BLS. Raman signals are sensitive both to structural changes of the polymer network and to changes of the intermolecular ordering of water due to solvent-polymer interactions. The destructuring effect on the tetrahedral ice-like configurations of water is especially evident at high pH, and might be ascribed to an increased exposition to the solvent of the ionic portions of the polymer surface.

Brillouin spectroscopy is a powerful technique to probe the viscoelastic properties of materials. However, the phenomenon of multiple scattering makes getting information from opaque liquids quite difficult, thus limiting the use of this spectroscopy. In this paper we present a new method that greatly simplifies the problem of analyzing Brillouin spectra affected by multiple scattering from samples of moderate opacity. Our approach is based on the observation that multiple-scattered contributions broaden the spectrum acquired in external backscattering geometry, while preserving in the external side the information related to internally backscattered light. The new strategy avoids unnecessary approximations and requires minimum numerical effort to extract physical information. Here, we show the results of two Brillouin light scattering experiments performed on prototypical hard and soft colloidal systems. First, measurements on latex suspensions as a function of depth are used to validate the method and to derive new relations between the back-scattered and multiple-scattered components of the Brillouin spectrum. Second, measurements on poly-N-isopropylacrylamide (PNIPAM) microgels in water as a function of temperature are used as a testing ground to demonstrate the method's capabilities. Our analysis confirms that sound waves are extremely sensitive to the volume-phase transition of thermoresponsive particles. The presented approach, however, shows that a marked increase of attenuation is accompanied by only a moderate decrease of sound velocity. The study revises the viscoelastic properties of PNIPAM suspensions; more generally, it provides a new guideline in the characterization of moderately opaque media and fosters new theoretical investigations. © 2018 Elsevier B.V.

Brillouin and Raman scattering spectroscopy are established techniques for the nondestructive contactless and label-free readout of mechanical, chemical and structural properties of condensed matter. Brillouin-Raman investigations currently require separate measurements and a site-matching approach to obtain complementary information from a sample. Here we demonstrate a new concept of fully scanning multimodal micro-spectroscopy for simultaneous detection of Brillouin and Raman light scattering in an exceptionally wide spectral range, from fractions of GHz to hundreds of THz. It yields an unprecedented 150 dB contrast, which is especially important for the analysis of opaque or turbid media such as biomedical samples, and a spatial resolution on sub-cellular scale. We report the first applications of this new multimodal method to a range of systems, from a single cell to the fast reaction kinetics of a curing process, and the mechano-chemical mapping of highly scattering biological samples., Comment: 18 pages, 4 figures

We use extended depolarized light scattering spectroscopy to study the dynamics of water in a lysozyme-trehalose aqueous solution over a broad time scale, from hundreds to fractions of picoseconds. We provide experimental evidence that the sugar, present in the ternary solution in quantity relevant for biopreservation, strongly modifies the solvation properties of the protein. By comparing aqueous solutions of lysozyme with and without trehalose, we show that the combined action of sugar and protein produces an exceptional dynamic slowdown of a fraction of water molecules around the protein, which become more than twice slower than in the absence of trehalose. We speculate that this ultraslow water may be caged between the sugar and protein surface, consistently with a water entrapment scenario. We also demonstrate that the dynamics of these water molecules gets slower and slower upon cooling. On the basis of these findings, we believe such ultraslow water close to the lysozyme is likely to be involved in the mechanism of bioprotection.

UV Raman and Brillouin light scattering (BLS) experiments have been used in this study to explore the complex phase change behavior occurring in pH-responsive polysaccharide hydrogels as a function of temperature. Due to the different physical quantities measured by the two techniques, the joint analysis of Raman and BLS spectra has provided an unprecedented large-scale characterization of the molecular rearrangements and of the different kinds of hydrophilic and hydrophobic interactions that cooperate to determine the phase transformation observed in these hydrogels during the heating of the gel. As the main result, the analysis of the Raman and BLS spectra showed the existence of a correlation between the local (molecular) and collective properties of the gels during the phase transformation undergone by the system, which is markedly triggered by pH. The joint set of experimental results suggests a model according to which the mechanism of pH dependence in the hydrogels under investigation is dominated by the interactions involving the hydrophobic parts of the polymer skeleton, whereas the solvation process observed under heating of the gels is driven by the progressive distancing of the polymer domains among them, as monitored by the Brillouin sound velocity.

DNA oligomers with properly designed sequences self-assemble into well defined constructs. Here, we exploit this methodology to produce bulk quantities of tetravalent DNA nanostars (each one composed by 196 nucleotides) and to explore the structural signatures of their aggregation process. We report small-angle neutron scattering experiments focused on the evaluation of both the form factor and the temperature evolution of the scattered intensity at a nano star concentration where the system forms a tetravalent equilibrium gel. We also perform molecular dynamics simulations of one isolated tetramer to evaluate the form factor theoretically, without resorting to any approximate shape. The numerical form factor is found to be in very good agreement with the experimental one. Simulations predict an essentially temperature independent form factor, offering the possibility to extract the effective structure factor and its evolution during the equilibrium gelation., 9 pages, 5 figures

When a solute is dissolved in water, their mutual interactions determine the molecular properties of the solute on one hand, and the structure and dynamics of the surrounding water particles (the so-called hydration water) on the other. The very existence of soft matter and its peculiar properties are largely due to the wide variety of possible water-solute interactions. In this context, water is not an inert medium but rather an active component, and hydration water plays a crucial role in determining the structure, stability, dynamics, and function of matter. This review focuses on the collective dynamics of hydration water in terms of retardation with respect to the bulk, and of the number of molecules whose dynamics is perturbed. Since water environments are in a dynamic equilibrium, with molecules continuously exchanging from around the solute towards the bulk and vice versa, we examine the ability of different techniques to measure the water dynamics on the basis of the explored time scales and exchange rates. Special emphasis is given to the collective dynamics probed by extended depolarized light scattering and we discuss whether and to what extent the results obtained in aqueous solutions of small molecules can be extrapolated to the case of large biomacromolecules. In fact, recent experiments performed on solutions of increasing complexity clearly indicate that a reductionist approach is not adequate to describe their collective dynamics. We conclude this review by presenting current ideas that are being developed to describe the dynamics of water interacting with macromolecules.

Different spectroscopic techniques were applied for studying the structural properties of lysozyme in salt-free aqueous solutions. The results of vibrational and Brillouin scattering measurements were compared to obtain both single-molecule and collective properties of the solutions. The characterization of the protein system, from the conformation of the polypeptide chain to the exposure of side chains to the solvent and the arrangement of the solution network, was then achieved in the range 25–85 °C. Through the analysis of the indole breathing mode, a different environment for the six tryptophan residues of an unfolded lysozyme could be evidenced. Short and long exposures to high temperatures were used to modulate the competition between the thermally induced reversible and irreversible denaturation processes. These different thermal treatments were applied to distinguish between the effects of global unfolding of the single molecule from those of self-aggregation and gel formation. It has been observed that clusterization occurs at melting temperatures with slow kinetics; also, aggregates evolve from the completely unfolded state of the protein and lead to a sensitive increase in viscosity. This effect probably hinders any further conformational rearrangement of the molecules in the aggregate; thus as a consequence, the disordered structure of clusters does not change to give the β-sheet organization, characteristic of filaments or fibrils. Copyright © 2011 John Wiley & Sons, Ltd.

Depolarized light scattering measurements performed on aqueous solutions of α-cyclodextrin are used for investigating the hydration properties of this natural cyclic oligosaccharide, which is well known for its ability to form inclusion complexes with a large variety of guest hydrophobic molecules. The spectral analysis allows the characterization of the solvent relaxation process assigned to hydration water, which is found to be seven to eight times slower than the bulk. As a structural information, the number of water molecules involved in the hydration process is also estimated at about 46. These results are a key step for understanding the role played by water in determining the properties of different forms of cyclodextrins and their derivatives, in turn related to complexation ability of these macrocycles. Copyright © 2011 John Wiley & Sons, Ltd.

Photon correlation spectroscopy and circular dichroism have been used to study the role of hydration in the structure and thermostability of the model protein lysozyme in water-glycerol mixtures. Two cases have been considered: water-rich and glycerol-rich regimes of concentrations. We follow the thermal denaturation both by optical spectral changes and hydrodynamic radius variations. This methodology allows us to emphasize the relevant role played by hydrophobic interactions during the process in aqueous solutions and, in glycerol, to distinguish the non-cooperative melting of secondary structure, supporting the view of a protein transition to a molten globule-like state.

Light scattering spectra on aqueous solutions of trehalose were recorded in a wide frequency range combining the use of a double monochromator and a multipass Fabry-Perot interferometer. Experimental results indicate the presence of a slow relaxation mode related to the solute dynamics, which is clearly separated from the solvent one. The spectral analysis reveals the existence of two separate solvent relaxation processes assigned to hydrating and bulk water molecules. The picosecond dynamics of water molecules directly interacting with the solute (proximal water) is consistently delayed with the corresponding relaxation time increase is about 5-6 times compared to the bulk. The slowing down induced by the sugar on the water dynamics mainly involves a restricted hydration layer constituted of 16-18 water molecules. These results improve our knowledge about the influence of carbohydrates on the fast rearrangement dynamics of water and may serve as a model to gain important insight on basic solvation properties of other biorelevant systems in aqueous media.

Hydrophilic and hydrophobic interactions strongly affect the solvation dynamics of biomolecules. To understand their role, small model systems are generally employed to simplify the investigations. In this study the amphiphile trimethylamine N-oxide (TMAO) is chosen as an exemplar, and studied by means of extended frequency range depolarized light scattering (EDLS) experiments as a function of solute concentration. This technique proves to be a suitable tool for investigating different aspects of aqueous solvation, being able at the same time to provide information about relaxation processes and vibrational modes of solvent and solute. In the case study of TMAO, we find that the relaxation dynamics of hydration water is moderately retarded compared to the bulk, and the perturbation induced by the solute on surrounding water is confined to the first hydration shell. The results highlight the hydrophobic character of TMAO in its interaction with water. The number of molecules taking part in the solvation process decreases as the solute concentration increases, following a trend consistent with the hydration water-sharing model, and suggesting that aggregation between solute molecules is negligible. Finally, the analysis of the resonant modes in the THz region and the comparison with the corresponding results obtained for the isosteric molecule tert-butyl alcohol (TBA) allow us to provide new insights into the different solvating properties of these two biologically relevant molecules.

A Brillouin scattering investigation has been carried out on trehalose-water solutions in a wide range of concentrations (0 < phi < 0.74) in the ultraviolet regime. A complete set of data as a function of temperature (-10 degrees C

We report depolarized light scattering measurements of water-glucose solutions in a wide spectral range from 0.01 to 1000 cm(-1), performed by the combined use of a double monocromator and a multipass Fabry-Perot interferometer. For the first time evidence is given of a low frequency relaxation process related to the glucose dynamics well separated from that of water. This low frequency process has a different origin with respect to the broad relaxation feature detected by dielectric spectroscopy and is interpreted in terms of Stokes-Einstein-Debye rotational diffusion of single glucose molecules. (c) 2007 Elsevier B.V. All rights reserved.

International audience; Brillouin light and x-ray scattering have been used to investigate the dynamic structure factor of supercooled and glassy m-toluidine in the temperature range between 34 and 303 K. In addition to the obiquitous α relaxation, evidence is given of a fast relaxation process active in the ns-ps time region. Information on the activation energy of the fast process is obtained from the attenuation of longitudinal acoustic modes.

Biological interfaces characterized by a complex mixture of hydrophobic, hydrophilic, or charged moieties interfere with the cooperative rearrangement of the hydrogen-bond network of water. In the present study, this solute-induced dynamical perturbation is investigated by extended frequency range depolarized light scattering experiments on an aqueous solution of a variety of systems of different nature and complexity such as small hydrophobic and hydrophilic molecules, amino acids, dipeptides, and proteins. Our results suggest that a reductionist approach is not adequate to describe the rearrangement of hydration water because a significant increase of the dynamical retardation and extension of the perturbation occurs when increasing the chemical complexity of the solute.

The dynamics of the human oligonucleotide AG 3(T2 AG 3)3 has been investigated by incoherent neutron scattering in the sub-nanosecond timescale. A hydration-dependent dynamical activation of thermal fluctuations in weakly hydrated samples was found, similar to that of protein powders. The amplitudes of such thermal fluctuations were evaluated in two different exchanged wave-vector ranges, so as to single out the different contributions from intra- and inter-nucleotide dynamics. The activation energy was calculated from the temperature-dependent characteristic times of the corresponding dynamical processes. The trends of both amplitudes and activation energies support a picture where oligonucleotides possess a larger conformational flexibility than long DNA sequences. This additional flexibility, which likely results from a significant relative chain-end contribution to the average chain dynamics, could be related to the strong structural polymorphism of the investigated oligonucleotides.

New experimental data on vitreous silica, collected in a previously unexplored frequency region between 60 and 120 GHz, are reported. The Brillouin ultraviolet light scattering technique has been used to measure the dynamic structure factor for two exchanged momenta, Q = 0.078 and 0.11 nm−1. The experiment has been performed using the IUVS beam line at the Elettra Synchrotron radiation facility in Trieste. An evidence of a transition between two different dynamical regimes is discussed.

Glasses can be formed in numerous ways, involving very different microscopic processes. Here we report a dielectric and photon-correlation study of chemical vitrification, a process where the slowdown in the dynamics of a liquid system is controlled by the irreversible formation of chemical bonds. We find that vitrification dynamics in chemically reactive systems can be explained in terms of their configurational restrictions in the same manner as in stable glass-forming liquids under cooling or compression.