Observing thermal lensing with quantum light.

The introduction of quantum methods in spectroscopy can provide enhanced performance and technical advantages in the management of noise. We investigate the application of quantum illumination in a pump and probe experiment. Thermal lensing in a suspension of gold nanorods is explored using a classical beam as the pump and the emission from parametric downconversion as the probe. We obtain an insightful description of the behavior of the suspension under pumping with a method known to provide good noise rejection. Our findings are a further step toward investigating the effects of quantum light in complex plasmonic media.

Solar Cookers and Dryers: Environmental Sustainability and Nutraceutical Content in Food Processing.

This work reviewed the state of the art concerning solar cookers and dryers used in food processing. The general description of solar cookers and dryers was presented, with a specific attention to the equipment where the cooking takes place with the contribution of the direct sunlight. Some insight about the history of design and development of devices that use solar light to process food were provided. The possibility to store the heat produced by solar light using Phase Change Materials was analyzed. Moreover, some "case-studies" were revised and discussed, in which solar light is efficiently used to dry or cook food, focusing on the quality of the food in terms of nutraceuticals content. The analyzed literature points out the necessity for further research about the effects produced by direct solar rays on different foods. The reliable data on this aspect will allow assessment of the quality of food transformation by solar cookers and dryers, adding a strong incentive to the development of such devices, up to now primarily motivated by energy-saving and environmental issues.

Hydrogen Bonding and Solvation of a Proline-Based Peptide Model in Salt Solutions.

The hydrogen bonding of water and water/salt mixtures around the proline-based tripeptide model glycyl-l-prolyl-glycinamide·HCl (GPG-NH2) is investigated here by multi-wavelength UV resonance Raman spectroscopy (UVRR) to clarify the role of ion-peptide interactions in affecting the conformational stability of this peptide. The unique sensitivity and selectivity of the UVRR technique allow us to efficiently probe the hydrogen bond interaction between water molecules and proline residues in different solvation conditions, along with its influence on trans to cis isomerism in the hydrated tripeptide. The spectroscopic data suggest a relevant role played by the cations in altering the solvation shell at the carbonyl site of proline., while the fluoride and chloride anions were found to promote the establishment of the strongest interactions on the C=O site of proline. This latter effect is reflected in the greater stabilization of the trans conformers of the tripeptide in the presence of these specific ions. The molecular view provided by UVRR experiments was complemented by the results of circular dichroism (CD) measurements that show a strong structural stabilizing effect on the ß-turn motif of GPG-NH2 observed in the presence of KF as a co-solute.

Hydration of Carboxyl Groups: A Route toward Molecular Recognition?

On Earth, water plays an active role in cellular life, over several scales of distance and time. At a nanoscale, water drives macromolecular conformation through hydrophobic forces and at short times acts as a proton donor/acceptor providing charge carriers for signal transmission. At longer times and larger distances, water controls osmosis, transport, and protein mobility. Neutron diffraction experiments augmented by computer simulation, show that the three-dimensional shape of the hydration shell of carboxyl and carboxylate groups belonging to different molecules is characteristic of each molecule. Different hydration shells identify and distinguish specific sites with the same chemical structure. This experimental evidence suggests an active role of water also in controlling, modulating, and mediating chemical reactions involving carboxyl and carboxylate groups.

Myelin basic protein dynamics from out-of-equilibrium functional state to degraded state in myelin.

Living matter is a quasi-stationary out-of-equilibrium system; in this physical condition, structural fluctuations at nano- and meso-scales are needed to understand the physics behind its biological functionality. Myelin has a simple ultrastructure whose fluctuations show correlated disorder in its functional out-of-equilibrium state. However, there is no information on the relationship between this correlated disorder and the dynamics of the intrinsically disordered Myelin Basic Protein (MBP) which is expected to influence the membrane structure and overall functionality. In this work, we have investigated the role of this protein structural dynamics in the myelin ultrastructure fluctuations in various conditions, by using synchrotron Scanning micro X Ray Diffraction and Small Angle X ray Scattering. We have induced the crossover from out-of-equilibrium functional state to in-equilibrium degeneration changing the pH to values far from physiological condition. The observed compression of the cytosolic layer thickness probes that the intrinsic large MBP fluctuations preserve the cytosol structure also in the degraded state. Thus, the transition of myelin ultrastructure from correlated to uncorrelated disordered state, is principally affected by the deformation of the membrane and extracellular domain.

Exploiting scaling laws for designing polymeric bottle brushes: a theoretical coarse-graining for homopolymeric branched polymers.

Bottle brushes are polymeric macromolecules made of a linear polymeric backbone grafted with side chains. The choice of the grafting density σg, the length ns the grafted side chains and their chemical nature fully determines the properties of each macromolecule, such as its elasticity and its folding behaviour. Typically, experimental bottle brushes are systems made of tens of thousands of monomeric units, rendering a computational approach extremely expensive, especially in the case of bottle brush solutions. A proper coarse graining description of these macromolecules thus appears essential. We present here a theoretical approach able to develop a general, transferable and analytical multi-scale coarse graining of homopolymeric bottle brush polymers under good solvent conditions. Starting from scaling theories, each macromolecule is mapped onto a chain of tethered star polymers, whose effective potential is known from scaling predictions, computational and experimental validations and can be expressed as a function of the number of arms f, and the length na of each arm. Stars are then tethered to one another and the effective potential between them is shown to only depend on the key parameters of the original bottle brush polymer (σg, ns). The generalised form of the effective potential is then used to reproduce properties of the macromolecules obtained both with scaling theories and with simulations. The general form of the effective potentials derived in the current study allows a theoretical and computational description of the properties of homopolymeric bottle brush polymers for all grafting densities and all lengths of both backbone and grafted arms, opening the path for a manifold of applications.

N-Methylacetamide Aqueous Solutions: A Neutron Diffraction Study.

The hydration of N-methylacetamide (NMA) in solution has been determined by neutron diffraction with isotopic Hydrogen/Deuterium substitution (NDIS), augmented by Monte Carlo simulation. This study is representative of the hydration of the peptide bonds characteristic of proteins and might shed light on aggregation phenomena in intrinsically disordered proteins. It is found that NMA forms hydrogen bonds with water at both O and H peptide sites, although of different lengths and strengths. The comparison with the case of tripeptide glutathione evidences differences in both hydration and propensity for aggregation.

Role of Water in Sucrose, Lactose, and Sucralose Taste: The Sweeter, The Wetter?

Natural sugars combine energy supply and, except a few cases, a pleasant taste. On the other hand, exaggerated consumption may impact population health. This has busted the research for the synthesis of increasingly cheaper artificial sweeteners, with low energy content and intense taste. Here, we suggest that studies of the hydration properties of three disaccharides, namely, the natural sucrose and lactose and the artificial sucralose, may explain the difference by orders of magnitude among their sweetness. This is done by analyzing via Monte Carlo simulations the neutron diffraction differential cross sections of aqueous solutions of the three sugars and their isotopes. Our results show that the strength of the sugar-water hydrogen bond interaction is one of the factors influencing sweetness, another being the number of water molecules within the first neighboring shell of the sugar whether bonded or not.

Protection against Dehydration: A Neutron Diffraction Study on Aqueous Solutions of a Model Peptide and Trehalose.

The ability of a wide class of organisms to reversibly go through cycles of suspended life and active metabolism, depending on the turnover of drought and normal water availability conditions, represents a challenging issue. The interest in the natural mechanism for drought survival has grown over time along with the request for always more efficient conservation techniques for biological materials. Carbohydrates, such as trehalose, accumulated in the cytoplasm of drought resistant cells, are considered responsible for desiccation tolerance. Nonetheless, a detailed description of the interaction between trehalose and biomolecules is not yet established. Neutron diffraction experiments show that trehalose entraps a layer of water molecules in the first shell of a model peptide, N-methylacetamide, without direct bonding with it. This evidence contrasts the hypothesis that trehalose substitutes water and supports the opposite view, namely, of trehalose forming a protective shell which entraps a layer of water molecules at the surface of proteins, thus avoiding structural damage due to drought conditions.

Trehalose in Water Revisited.

Trehalose, commonly found in living organisms, is believed to help them survive severe environmental conditions, such as drought or extreme temperatures. With the aim of trying to understand these properties, two recent neutron scattering studies investigate the structure of trehalose water solutions but come to seemingly opposite conclusions. In the first study, which looks at two concentrations of trehalose-water mole ratios of 1:100 and 1:25, the conclusion is that trehalose hydrogen-bonds to water rather weakly and has a relatively minor impact on the structure of water in solution compared to bulk water. On the other hand, for the other, using a mole ratio of 1:38, the conclusion is that the water structure is rather substantially modified by the presence of trehalose and that the hydrogen bonding between water and trehalose hydroxyl groups is significant. In an attempt to try to understand the origin of these divergent views, which arise from similar but independent analyses of different neutron diffraction data, we have performed additional X-ray scattering experiments, which are highly sensitive to water structure, at the same trehalose-water concentrations used in the first study, and combined these with empirical potential structure refinement on the previously collected neutron data. The new analysis unequivocally confirms that trehalose does indeed have only a minor impact on the structure of water, at all three concentrations, and forms relatively weak hydrogen bonds with water. Far from being discrepant with the existing literature, our new analysis of the different datasets suggests a natural explanation for the increased glass-transition temperature of trehalose compared to other sugars and hence its enhanced effectiveness as a protectant against drought stress.

OH Stretching Dynamics in Hydroxide Aqueous Solutions.

The concept of ions being either water "structure makers" or water "breakers" seems to be inconsistent with the existence of a critical number of water molecules per ion dictating the properties of an aqueous solution, independent of the ion identity. To investigate this issue, Raman spectra of hydroxide aqueous solutions in the region of the OH stretching mode have been obtained under ambient conditions and at concentrations ranging from extreme dilution to the solubility limit. Spectra have been analyzed with a relatively model-free approach, in terms of a superposition of contributions due to the vibrations of the OH- ions, with two contributions due to the solvent. One of these latter contributions falls at wavenumbers very close to that of the OH- stretching band, sharing with it its concentration dependence of the full width at half maximum (FWHM). The other contribution due to the solvent is very broad, with increasing FWHM with increasing ion concentration. In the light of these observations, an interpretation of the Raman spectra, based on the possibility of distinguishing the self and distinct contributions, is proposed. The present analysis is supported by structural data on the same solutions and puts into evidence relevant structural and dynamical changes occurring when the number of water molecules available per solute is below ∼20, irrespective of the ion identity.

Dynamical behavior of microgels of interpenetrated polymer networks.

Microgel suspensions of an interpenetrated Polymer Network (IPN) of PNIPAM and PAAc in D2O have been investigated through dynamic light scattering as a function of temperature, pH and concentration across the Volume Phase Transition (VPT). The dynamics of the system is slowed down under H/D isotopic substitution due to different balance states between polymer/polymer and polymer/solvent interactions suggesting the crucial role played by H-bonding. The swelling behavior, reduced with respect to PNIPAM and water, has been described by the Flory-Rehner theory, tested for PNIPAM microgel and successfully expanded to higher order for IPN microgels. Moreover the concentration dependence of the relaxation time at neutral pH has highlighted two different routes to approach the glass transition: Arrhenius and super-Arrhenius (Vogel Fulcher Tammann) respectively below and above the VPT and a fragility plot has been derived. Fragility can be tuned by changing temperature: across the VPT particles undergo a transition from soft-strong to stiff-fragile.

Structure-activity relationships in carbohydrates revealed by their hydration.

One of the more intriguing aspects of carbohydrate chemistry is that despite having very similar molecular structures, sugars have very different properties. For instance, there is a sensible difference in sweet taste between glucose and trehalose, even though trehalose is a disaccharide that comprised two glucose units, suggesting a different ability of these two carbohydrates to bind to sweet receptors. Here we have looked at the hydration of specific sites and at the three-dimensional configuration of water molecules around three carbohydrates (glucose, cellobiose, and trehalose), combining neutron diffraction data with computer modelling. Results indicate that identical chemical groups can have radically different hydration patterns depending on their location on a given molecule. These differences can be linked with the specific activity of glucose, cellobiose, and trehalose as a sweet substance, as building block of cellulose fiber, and as a bioprotective agent, respectively. This article is part of a Special Issue entitled "Recent Advances in Bionanomaterials" Guest Editors: Dr. Marie-Louise Saboungi and Dr. Samuel D. Bader.

Local structure of temperature and pH-sensitive colloidal microgels.

The temperature dependence of the local intra-particle structure of colloidal microgel particles, composed of interpenetrated polymer networks, has been investigated by small-angle neutron scattering at different pH and concentrations, in the range (299÷315) K, where a volume phase transition from a swollen to a shrunken state takes place. Data are well described by a theoretical model that takes into account the presence of both interpenetrated polymer networks and cross-linkers. Two different behaviors are found across the volume phase transition. At neutral pH and T ≈ 307 K, a sharp change of the local structure from a water rich open inhomogeneous interpenetrated polymer network to a homogeneous porous solid-like structure after expelling water is observed. Differently, at acidic pH, the local structure changes almost continuously. These findings demonstrate that a fine control of the pH of the system allows to tune the sharpness of the volume-phase transition.

Water-peptide site-specific interactions: a structural study on the hydration of glutathione.

Water-peptide interactions play an important role in determining peptide structure and function. Nevertheless, a microscopic description of these interactions is still incomplete. In this study we have investigated at the atomic scale length the interaction between water and the tripeptide glutathione. The rationale behind this work, based on the combination between a neutron diffraction experiment and a computer simulation, is twofold. It extends previous studies on amino acids, addressing issues such as the perturbation of the water network brought by a larger biomolecule in solution. In addition, and more importantly, it seeks a possible link between the atomic length scale description of the glutathione-water interaction with the specific biological functionality of glutathione, an important intracellular antioxidant. Results indicate a rather weak hydrogen bond between the thiol (-SH) group of cysteine and its first neighbor water molecule. This -SH group serves as a proton donor, is responsible for the biological activity of glutathione, and it is involved in the formation of glutathione disulfide, the oxidized form of glutathione. Moreover, the hydration shell of the chemically identical carboxylate group on the glutamic acid residue and on the glycine residue shows an intriguing different spatial location of water molecules and coordination numbers around the two CO2(-) groups.

More than one dynamic crossover in protein hydration water.

Studies of liquid water in its supercooled region have helped us better understand the structure and behavior of water. Bulk water freezes at its homogeneous nucleation temperature (approximately 235 K), but protein hydration water avoids this crystallization because each water molecule binds to a protein. Here, we study the dynamics of the hydrogen bond (HB) network of a percolating layer of water molecules and compare the measurements of a hydrated globular protein with the results of a coarse-grained model that successfully reproduces the properties of hydration water. Using dielectric spectroscopy, we measure the temperature dependence of the relaxation time of proton charge fluctuations. These fluctuations are associated with the dynamics of the HB network of water molecules adsorbed on the protein surface. Using Monte Carlo simulations and mean-field calculations, we study the dynamics and thermodynamics of the model. Both experimental and model analyses are consistent with the interesting possibility of two dynamic crossovers, (i) at approximately 252 K and (ii) at approximately 181 K. Because the experiments agree with the model, we can relate the two crossovers to the presence at ambient pressure of two specific heat maxima. The first is caused by fluctuations in the HB formation, and the second, at a lower temperature, is due to the cooperative reordering of the HB network.

Dielectric relaxations in confined hydrated myoglobin.

In this work we report the results of a broadband dielectric spectroscopy study on the dynamics of a globular protein, myoglobin, in confined geometry, i.e. encapsulated in a porous silica matrix, at low hydration levels, where about only one or two water layers surround the proteins. In order to highlight the specific effect of confinement in the silica host, we compared this system with hydrated myoglobin powders at the same hydration levels. The comparison between the data relative to the two different systems indicates that geometrical confinement within the silica matrix plays a crucial role in protein-water dielectric relaxations, the effect of sol-gel encapsulation being essentially a suppression of cooperative relaxations that involve the coherence/cooperativity of solvent motions and solvent-coupled protein dynamics. We also provide direct evidence that protein relaxations inside the gel depend on the hydration level and are "slaved" to the solvent beta-relaxation.

"Similarities" between confined and supercooled water.

Neutron diffraction and deep inelastic neutron scattering experiments performed on bulk stable and supercooled water are compared with the same experiments performed on water confined in silica substrates. Similarities and differences between the two cases clearly show up, as far as both microscopic structure and single proton dynamics are concerned. In particular in both supercooled bulk water and water under confinement we observe a closer average distance between first neighboring oxygen sites and shortening of the H-bonds. In contrast the number of H-bonds per molecule and the number of interstitial water molecules are severely reduced under confinement, and the second peak of the oxygen-oxygen radial distribution function is shifted to shorter distances, compared to the bulk phase. Based on these results a possible scenario for understanding changes evidenced by deep inelastic neutron scattering when water is either confined or supercooled is proposed.

The three-dimensional structure of water confined in nanoporous vycor glass.

Neutron diffraction data, in conjunction with isotopic substitution of deuterium (D) for hydrogen (H), have been analyzed to determine the three-dimensional structure of water confined in vycor, an archetypal hydrophilic porous silica glass containing channels or pores of approximately 40 A diameter. The data have been incorporated into a Monte Carlo computer simulation of the confined water system, and the site-site potentials have been iteratively refined in order to produce a model ensemble which is consistent with both the neutron diffraction data and two possible geometries of the vycor pores (cylindrical and spherical). This approach has allowed us to investigate in detail the contributions to the experimentally accessible partial pair correlation functions, and ascertain whether particular features arise from interactions of the water molecules with the substrate surface, or from purely geometrical confinement effects. We observe a significant decrease in the first shell water oxygen-oxygen co-ordination number, and a decrease in the number of hydrogen bonds per water molecule from approximately 3.6 in bulk water to approximately 2.2 in confinement. In addition, we observe a significant shift inward of the second peak in the water oxygen-water oxygen coordination shell. Overall, we therefore find that the structure of the water in vycor is strongly perturbed relative to the bulk.