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16 pages, 3488 KiB

Open AccessArticle

Protein-Water and Water-Water Long-Time Relaxations in Protein Hydration Water upon Cooling—A Close Look through Density Correlation Functions

by Lorenzo Tenuzzo, Gaia Camisasca and Paola Gallo

Molecules 2020, 25(19), 4570; https://doi.org/10.3390/molecules25194570 - 07 Oct 2020

Cited by 7 | Viewed by 2374

Abstract

We report results on the translational dynamics of the hydration water of the lysozyme protein upon cooling obtained by means of molecular dynamics simulations. The self van Hove functions and the mean square displacements of hydration water show two different temperature activated relaxation [...] Read more.

We report results on the translational dynamics of the hydration water of the lysozyme protein upon cooling obtained by means of molecular dynamics simulations. The self van Hove functions and the mean square displacements of hydration water show two different temperature activated relaxation mechanisms, determining two dynamic regimes where transient trapping of the molecules is followed by hopping phenomena to allow to the structural relaxations. The two caging and hopping regimes are different in their nature. The low-temperature hopping regime has a time scale of tenths of nanoseconds and a length scale on the order of 2–3 water shells. This is connected to the nearest-neighbours cage effect and restricted to the supercooling, it is absent at high temperature and it is the mechanism to escape from the cage also present in bulk water. The second hopping regime is active at high temperatures, on the nanoseconds time scale and over distances of nanometers. This regime is connected to water displacements driven by the protein motion and it is observed very clearly at high temperatures and for temperatures higher than the protein dynamical transition. Below this temperature, the suppression of protein fluctuations largely increases the time-scale of the protein-related hopping phenomena at least over 100 ns. These protein-related hopping phenomena permit the detection of translational motions of hydration water molecules longly persistent in the hydration shell of the protein. Full article

(This article belongs to the Special Issue Physical Chemistry of Aqueous Solutions and Glass Forming Systems)

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9 pages, 1923 KiB

Open AccessFeature PaperArticle

Synthesis of Natural-Like Snow by Ultrasonic Nebulization of Water: Morphology and Raman Characterization

by Ettore Maggiore, Matteo Tommasini and Paolo M. Ossi

Molecules 2020, 25(19), 4458; https://doi.org/10.3390/molecules25194458 - 28 Sep 2020

Cited by 3 | Viewed by 1856

Abstract

The current devices used to produce massive amounts of snow (i.e., snow machines) can be improved with concern to both the energy efficiency and the quality of snow. Here we investigate an alternative snow production method based on the ultrasonic nebulization of water [...] Read more.

The current devices used to produce massive amounts of snow (i.e., snow machines) can be improved with concern to both the energy efficiency and the quality of snow. Here we investigate an alternative snow production method based on the ultrasonic nebulization of water and its subsequent condensation on the cold surfaces of a refrigerator. Inspection of the snow samples with a stereo optical microscope shows both dendritic and granular snow morphologies. The characterization of the samples by Raman spectroscopy shows a behavior consistent with that of a natural, low-density snow. Our results indicate that ultrasonic nebulization of water is an effective strategy for producing natural-like snow at the laboratory scale. Full article

(This article belongs to the Special Issue Physical Chemistry of Aqueous Solutions and Glass Forming Systems)

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15 pages, 4657 KiB

Open AccessArticle

Water-Tree Resistability of UV-XLPE from Hydrophilicity of Auxiliary Crosslinkers

by Jun-Qi Chen, Xuan Wang, Wei-Feng Sun and Hong Zhao

Molecules 2020, 25(18), 4147; https://doi.org/10.3390/molecules25184147 - 10 Sep 2020

Cited by 11 | Viewed by 2427

Abstract

The water-resistant characteristics of ultraviolet crosslinked polyethylene (UV-XLPE) are investigated specially for the dependence on the hydrophilicities of auxiliary crosslinkers, which is significant to develop high-voltage insulating cable materials. As auxiliary crosslinking agents of polyethylene, triallyl isocyanurate (TAIC), trimethylolpropane trimethacrylate (TMPTMA), and N,N′-m-phenylenedimaleimide [...] Read more.

The water-resistant characteristics of ultraviolet crosslinked polyethylene (UV-XLPE) are investigated specially for the dependence on the hydrophilicities of auxiliary crosslinkers, which is significant to develop high-voltage insulating cable materials. As auxiliary crosslinking agents of polyethylene, triallyl isocyanurate (TAIC), trimethylolpropane trimethacrylate (TMPTMA), and N,N′-m-phenylenedimaleimide (HAV2) are individually adopted to prepared XLPE materials with the UV-initiation crosslinking technique, for the study of water-tree resistance through the accelerating aging experiments with water blade electrode. The stress–strain characteristics and dynamic viscoelastic properties of UV-XLPE are tested by the electronic tension machine and dynamic thermomechanical analyzer. Monte Carlo molecular simulation is used to calculate the interaction parameters and mixing energy of crosslinker/water binary systems to analyze the compatibility between water and crosslinker molecules. Water-tree experiments verify that XLPE-TAIC represents the highest ability to inhibit the growth of water-trees, while XLPE-HAV2 shows the lowest resistance to water-trees. The stress–strain and viscoelastic properties show that the concentration of molecular chains connecting the adjacent lamellae in amorphous phase of XLPE-HAV2 is significantly higher than that of XLPE-TAIC and XLPE-TMPTMA. The molecular simulation results demonstrate that TAIC/water and TMPTMA/water binary systems possess a higher hydrophilicity than that of HAV2/water, as manifested by their lower interaction parameters and mixing free energies. The auxiliary crosslinkers can not only increase the molecular density of amorphous polyethylene between lamellae to inhibit water-tree growth, but also prevent water molecules at insulation defects from agglomerating into micro-water beads by increasing the hydrophilicity of auxiliary crosslinkers, which will evidently reduce the damage of micro-water beads on the amorphous phase in UV-XLPE. The better compatibility of TAIC and water molecules is the dominant reason accounting for the excellent water resistance of XLPE-TAIC. Full article

(This article belongs to the Special Issue Physical Chemistry of Aqueous Solutions and Glass Forming Systems)

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24 pages, 775 KiB

Open AccessArticle

Confinement Effects on Glass-Forming Aqueous Dimethyl Sulfoxide Solutions

by Dominik Demuth, Melanie Reuhl, Moritz Hopfenmüller, Nail Karabas, Simon Schoner and Michael Vogel

Molecules 2020, 25(18), 4127; https://doi.org/10.3390/molecules25184127 - 09 Sep 2020

Cited by 6 | Viewed by 2335

Abstract

Combining broadband dielectric spectroscopy and nuclear magnetic resonance studies, we analyze the reorientation dynamics and the translational diffusion associated with the glassy slowdown of the eutectic aqueous dimethyl sulfoxide solution in nano-sized confinements, explicitly, in silica pores with different diameters and in ficoll [...] Read more.

Combining broadband dielectric spectroscopy and nuclear magnetic resonance studies, we analyze the reorientation dynamics and the translational diffusion associated with the glassy slowdown of the eutectic aqueous dimethyl sulfoxide solution in nano-sized confinements, explicitly, in silica pores with different diameters and in ficoll and lysozyme matrices at different concentrations. We observe that both rotational and diffusive dynamics are slower and more heterogeneous in the confinements than in the bulk but the degree of these effects depends on the properties of the confinement and differs for the components of the solution. For the hard and the soft matrices, the slowdown and the heterogeneity become more prominent when the size of the confinement is reduced. In addition, the dynamics are more retarded for dimethyl sulfoxide than for water, implying specific guest-host interactions. Moreover, we find that the temperature dependence of the reorientation dynamics and of the translational diffusion differs in severe confinements, indicating a breakdown of the Stokes–Einstein–Debye relation. It is discussed to what extent these confinement effects can be rationalized in the framework of core-shell models, which assume bulk-like and slowed-down motions in central and interfacial confinement regions, respectively. Full article

(This article belongs to the Special Issue Physical Chemistry of Aqueous Solutions and Glass Forming Systems)

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13 pages, 1641 KiB

Open AccessArticle

On Viscous Flow in Glass-Forming Organic Liquids

by Michael I. Ojovan

Molecules 2020, 25(17), 4029; https://doi.org/10.3390/molecules25174029 - 03 Sep 2020

Cited by 8 | Viewed by 2583

Abstract

The two-exponential Sheffield equation of viscosity η(T) = A₁·T·[1 + A₂·exp(H_m/RT)]·[1 + C·exp(H_d/RT)], where A₁, A₂, H_m, C, and H_m are material-specific constants, is used to analyze the [...] Read more.

The two-exponential Sheffield equation of viscosity η(T) = A₁·T·[1 + A₂·exp(H_m/RT)]·[1 + C·exp(H_d/RT)], where A₁, A₂, H_m, C, and H_m are material-specific constants, is used to analyze the viscous flows of two glass-forming organic materials—salol and α-phenyl-o-cresol. It is demonstrated that the viscosity equation can be simplified to a four-parameter version: η(T) = A·T·exp(H_m/RT)]·[1 + C·exp(H_d/RT)]. The Sheffield model gives a correct description of viscosity, with two exact Arrhenius-type asymptotes below and above the glass transition temperature, whereas near the T_g it gives practically the same results as well-known and widely used viscosity equations. It is revealed that the constants of the Sheffield equation are not universal for all temperature ranges and may need to be updated for very high temperatures, where changes occur in melt properties leading to modifications of A and H_m for both salol and α-phenyl-o-cresol. Full article

(This article belongs to the Special Issue Physical Chemistry of Aqueous Solutions and Glass Forming Systems)

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15 pages, 1292 KiB

Open AccessArticle

Ab Initio Molecular Dynamics Study of Methanol-Water Mixtures under External Electric Fields

by Giuseppe Cassone, Adriano Sofia, Jiri Sponer, A. Marco Saitta and Franz Saija

Molecules 2020, 25(15), 3371; https://doi.org/10.3390/molecules25153371 - 24 Jul 2020

Cited by 16 | Viewed by 3593

Abstract

Intense electric fields applied on H-bonded systems are able to induce molecular dissociations, proton transfers, and complex chemical reactions. Nevertheless, the effects induced in heterogeneous molecular systems such as methanol-water mixtures are still elusive. Here we report on a series of state-of-the-art ab [...] Read more.

Intense electric fields applied on H-bonded systems are able to induce molecular dissociations, proton transfers, and complex chemical reactions. Nevertheless, the effects induced in heterogeneous molecular systems such as methanol-water mixtures are still elusive. Here we report on a series of state-of-the-art ab initio molecular dynamics simulations of liquid methanol-water mixtures at different molar ratios exposed to static electric fields. If, on the one hand, the presence of water increases the proton conductivity of methanol-water mixtures, on the other, it hinders the typical enhancement of the chemical reactivity induced by electric fields. In particular, a sudden increase of the protonic conductivity is recorded when the amount of water exceeds that of methanol in the mixtures, suggesting that important structural changes of the H-bond network occur. By contrast, the field-induced multifaceted chemistry leading to the synthesis of e.g., hydrogen, dimethyl ether, formaldehyde, and methane observed in neat methanol, in 75:25, and equimolar methanol-water mixtures, completely disappears in samples containing an excess of water and in pure water. The presence of water strongly inhibits the chemical reactivity of methanol. Full article

(This article belongs to the Special Issue Physical Chemistry of Aqueous Solutions and Glass Forming Systems)

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21 pages, 4016 KiB

Open AccessArticle

Non-Functionalized Fullerenes and Endofullerenes in Aqueous Dispersions as Superoxide Scavengers

by Ivan V. Mikheev, Madina M. Sozarukova, Elena V. Proskurnina, Ivan E. Kareev and Mikhail A. Proskurnin

Molecules 2020, 25(11), 2506; https://doi.org/10.3390/molecules25112506 - 28 May 2020

Cited by 14 | Viewed by 3296

Abstract

Endohedral metal fullerene are potential nanopharmaceuticals for MRI; thus, it is important to study their effect on reactive oxygen species (ROS) homeostasis. Superoxide anion radical is one of the key ROS. The reactivity of aqueous dispersions of pristine (non-functionalized) fullerenes and Gd@C₈₂ [...] Read more.

Endohedral metal fullerene are potential nanopharmaceuticals for MRI; thus, it is important to study their effect on reactive oxygen species (ROS) homeostasis. Superoxide anion radical is one of the key ROS. The reactivity of aqueous dispersions of pristine (non-functionalized) fullerenes and Gd@C₈₂ endofullerene have been studied with respect to superoxide in the xanthine/xanthine oxidase chemiluminescence system. It was found that C₆₀ and C₇₀ in aqueous dispersions react with superoxide as scavengers by a similar mechanism; differences in activity are determined by cluster parameters, primarily the concentration of available, acting molecules at the surface. Gd endofullerene is characterized by a significantly (one-and-a-half to two orders of magnitude) higher reactivity with respect to C₆₀ and C₇₀ and is likely to exhibit nanozyme (SOD-mimic) properties, which can be accounted for by the nonuniform distribution of electron density of the fullerene cage due to the presence of the endohedral atom; however, in the cell model, Gd@C₈₂ showed the lowest activity compared to C₆₀ and C₇₀, which can be accounted for by its higher affinity for the lipid phase. Full article

(This article belongs to the Special Issue Physical Chemistry of Aqueous Solutions and Glass Forming Systems)

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Review

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33 pages, 2368 KiB

Open AccessReview

Hydrogels for the Delivery of Plant-Derived (Poly)Phenols

by Nicola Micale, Andrea Citarella, Maria Sofia Molonia, Antonio Speciale, Francesco Cimino, Antonella Saija and Mariateresa Cristani

Molecules 2020, 25(14), 3254; https://doi.org/10.3390/molecules25143254 - 16 Jul 2020

Cited by 25 | Viewed by 3557

Abstract

This review deals with hydrogels as soft and biocompatible vehicles for the delivery of plant-derived (poly)phenols, compounds with low general toxicity and an extraordinary and partially unexplored wide range of biological properties, whose use presents some major issues due to their poor bioavailability [...] Read more.

This review deals with hydrogels as soft and biocompatible vehicles for the delivery of plant-derived (poly)phenols, compounds with low general toxicity and an extraordinary and partially unexplored wide range of biological properties, whose use presents some major issues due to their poor bioavailability and water solubility. Hydrogels are composed of polymeric networks which are able to absorb large amounts of water or biological fluids while retaining their three-dimensional structure. Apart from this primary swelling capacity, hydrogels may be easily tailored in their properties according to the chemical structure of the polymeric component in order to obtain smart delivery systems that can be responsive to various internal/external stimuli. The functionalization of the polymeric component of hydrogels may also be widely exploited to facilitate the incorporation of bioactive compounds with different physicochemical properties into the system. Several prototype hydrogel systems have been designed for effective polyphenol delivery and potential employment in the treatment of human diseases. Therefore, the inherent features of hydrogels have been the focus of considerable research efforts over the past few decades. Herein, we review the most recent advances in (poly)phenol-loaded hydrogels by analyzing them primarily from the therapeutic perspective and highlighting the innovative aspects in terms of design and chemistry. Full article

(This article belongs to the Special Issue Physical Chemistry of Aqueous Solutions and Glass Forming Systems)

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