Solvation Shell Water Research Articles

Effects of Hydrogen Peroxide on the Hydrogen Bonding Structure and Dynamics of Water and Its Influence on the Aqueous Solvation of the Insulin Monomer.

The hydrogen bond structure and dynamics of water and hydrogen peroxide (H2O2) in their binary mixtures have been studied at 298 K by classical molecular dynamics simulations. Twelve different concentrations of aqueous-H2O2 solutions are considered for this study. We have analyzed the interactions between water and H2O2 by site-site pair correlation functions and observed that the probability of formation of OW···HP hydrogen bonds are higher compared to OP···HW. The second solvation shell of water is strongly affected by increasing H2O2 concentrations (XP > 0.50), which signifies the destruction of the tetrahedral network structure of water. The translational and rotational dynamics of water and H2O2 do not significantly change up to 25% of H2O2 in aqueous mixtures. The hydrogen bond lifetime of water-water, water-H2O2, and H2O2-H2O2 in the aqueous-H2O2 solutions shows a very minimal change with increasing H2O2 concentrations. In addition to this, we also investigated the effect of H2O2 on the insulin monomer and observed that higher concentrations of H2O2 (XP = 0.10) change the secondary structure. The influence of H2O2 is more on chain-B than that on chain-A in the insulin monomer. The H2O2 occupancy at the protein surface is higher for negatively charged (GLU) and polar (ASN and THR) amino acid residues compared with that for positively charged and neutral residues in the solutions.

All-Atom Molecular Dynamics Simulations of the Temperature Response of Poly(glycidyl ether)s with Oligooxyethylene Side Chains Terminated with Alkyl Groups.

Recently, experimental investigations of a class of temperature-responsive polymers tethered to oligooxyethylene side chains terminated with alkyl groups have been conducted. In this study, aqueous solutions of poly(glycidyl ether)s (PGE) with varying numbers of oxyethylene units, poly(methyl(oligooxyethylene)n glycidyl ether) (poly(Me(EO)nGE)), and poly(ethyl(oligooxyethylene)n glycidyl ether) (poly(Et(EO)nGE) (n = 0, 1, and 2) were investigated by all-atom molecular dynamics simulations, focusing on the thermal responses of their chain extensions, the recombination of intrapolymer and polymer-water hydrogen bonds, and water-solvation shells around the alkyl groups. No clear relationship was established between the phase-transition temperature and the polymer-chain extensions unlike the case for the coil-globule transition of poly(N-isopropylacrylamide). However, the temperature response of the first water-solvation shell around the alkyl group exhibited a notable correlation with the phase-transition temperature. In addition, the temperature at which the hydrophobic hydration shell strength around the terminal alkyl group equals the bulk water density (TCRP) was slightly lower than the cloud point temperature (TCLP) for the methyl-terminated poly(Me(EO)nGE) and slightly higher for the ethyl-terminated poly(Et(EO)nGE). It was concluded that the polymer-chain fluctuation affects the relationship between TCRP and TCLP.

Effect of molecular dynamics water models on flux, diffusivity, and ion dynamics for polyamide membrane simulations

While molecular dynamics (MD) models for reverse osmosis (RO) and nanofiltration (NF) membranes are useful for studying water filtration processes, the specific water model and force-field parameters have a profound impact on key measures such as flux and diffusivity. Moreover, ensemble related parameters such as temperature and how it is controlled via a thermostat also affect simulation results. To quantify these effects, we investigate the performance of three commonly used water models, SPC/E, TIP3P, and TIP4P, in simulating an NF membrane system at varying temperatures and thermostat settings. All three water models successfully capture the Arrhenius relationship between water diffusivity and temperature as well as the linear relationship between water flux through the membrane and water diffusivity in the membrane. However, SPC/E underpredicts, TIP3P overpredicts, and TIP4P most accurately reproduces the water dynamics, especially water self-diffusivity, compared to experiments. We also investigate the effect of the water model on common salt solutions at various concentrations. TIP4P generally outperforms the other two water models when describing ion diffusivities and water solvation shells around ions. These findings indicate that TIP4P is an appropriate water model to use in polyamide membrane MD simulations.

Metal-organic frameworks for high performance desalination through thickness control and structural fine-tuning

Two-dimensional nanoporous membranes hold great promise for the design of state-of-the-art desalination architectures to alleviate the increasing global water scarcity. Herein, by employing molecular dynamics simulations, we demonstrate the great potential of two recently reported metal-organic frameworks (MOF) membranes, namely NiIT and NiAT, as efficient desalination membranes that reach super high water flux and high salt rejection. The desalination performance of the MOF membrane is highly tunable through controlling the membrane thickness from one layer to five layers. Double layer NiIT membrane exhibits excellent salt rejection of 100% for NaCl, and meanwhile achieving high water permeability of ∼45 L/cm2/MPa/day. While for the convertible double-layer NiAT, it effectively rejects ∼96% ions with an improved water permeation of over 70 L/cm2/MPa/day. Quantitative analysis of water distribution reveals a denser water solvation shell around NiAT membrane than NiIT and a higher water velocity through the nanopore of NiAT than that of NiIT, contributing to the enhanced water permeability. Through calculating free energy for water/ions translocating through two membranes, a clear energy barrier is observed for ions to penetrate through the sub-nanosized pores in both membranes, leading to the high salt rejection. The present study suggests that these two MOF membranes can serve as a promising semipermeable membrane for energy-efficient desalination which is highly prospective in industrial applications.

Pilot Aquaphotomic Study of the Effects of Audible Sound on Water Molecular Structure.

Sound affects the medium it propagates through and studies on biological systems have shown various properties arising from this phenomenon. As a compressible media and a “collective mirror”, water is influenced by all internal and external influences, changing its molecular structure accordingly. The water molecular structure and its changes can be observed as a whole by measuring its electromagnetic (EMG) spectrum. Using near-infrared spectroscopy and aquaphotomics, this pilot study aimed to better describe and understand the sound-water interaction. Results on purified and mineral waters reported similar effects from the applied 432 Hz and 440 Hz frequency sound, where significant reduction in spectral variations and increased stability in water were shown after the sound perturbation. In general, the sound rearranged the initial water molecular conformations, changing the samples’ properties by increasing strongly bound, ice-like water and decreasing small water clusters and solvation shells. Even though there was only 8 Hz difference in applied sound frequencies, the change of absorbance at water absorbance bands was specific for each frequency and also water-type-dependent. This also means that sound could be effectively used as a perturbation tool together with spectroscopy to identify the type of bio, or aqueous, samples being tested, as well as to identify and even change water functionality.

Direct and Water-Mediated Adsorption of Stabilizers on SERS-Active Colloidal Bimetallic Plasmonic Nanomaterials: Insight into Citrate-AuAg Interactions from DFT Calculations.

In previous studies, AuAg colloidal nanostar formulations were developed with the two-fold aim of producing optimized surface-enhanced Raman spectroscopy (SERS) substrates and investigating the nature of the capping process itself. Findings demonstrated that the nanoparticle metals are alloyed and neutral, and capping by stabilizers occurs via chemisorption. This study utilizes citrate as the model stabilizer and investigates the mechanistic aspects of its interaction with mono- (Au20) and bimetallic (Au19Ag) surfaces by density functional theory (DFT) calculations. Citrate was modeled according to the colloid's pH and surrounded by a water and sodium first solvation shell. A population of stable cluster-citrate structures was obtained, and energies were refined at the uB3LYP//LANL2TZ(f)/cc-pVTZ level of theory. Solvation was accounted for both explicitly and implicitly by the application of the continuum model SMD. Results indicate that both direct binding and binding by water proxy through the charge-transfer complex formation are thermodynamically favorable. Water participation in citrate adsorption is supported by the adsorption behavior observed experimentally and the comparison between experimental and DFT-simulated IR spectra. Vibrational mode analysis suggests the possible presence of water within a crystal in dried nanostar residues. All ΔGads(aq) indicate a weak chemisorptive process, leading to the hypothesis that citrate could be displaced by analytes during SERS measurements.

β-lactoglobulin and resveratrol nanocomplex formation is driven by solvation water release

Despite some thermodynamics studies about β-lactoglobulin (βLG) and resveratrol (RES) interactions, there is a gap regarding kinetics data about βLG-RES complex formation. Here, we determined the kinetic and thermodynamic parameters of βLG-RES interactions by using surface plasmon resonance (SPR). The kinetic association parameters were dependent on the 3D water structure present on the solvation shell of both interacting molecules. At lower temperature (285.15 K), all activation energies were positive (Eacta‡= 82.86 kJ.mol−1,TΔSa‡= 32.26 kJ.mol−1, and ΔCpa‡= 4.15 kJ.mol−1K−1) due to the higher water structuration on the RES and βLG solvation shell. All these energetic barriers become mainly from the energetic cost for the desolvation process of RES and βLG. At higher temperature (301.15 K), the solvation water structure decreases and all the above activation energies become negative (Eacta‡=-121.58 kJ.mol−1,TΔSa‡=-173.59 kJ.mol−1, and ΔCpa‡=-29.92 kJ.mol−1K−1) because the direct interaction between desolvated RES and βLG molecules released more energy than it is absorbed by desolvation process. However, kinetic dissociation parameters were not dependent on the hydrogen bond density of the water solvation shell as showed by the temperature independence of dissociation energetic parameters. This non-dependence of the dissociation process from the desolvation step probably is because the water molecules interacting with the βLG-RES complex is not concentrated around/inside the protein site of interaction. The association of free molecules was 1.5 times faster than the dissociation of the thermodynamically stable complex (ΔG(a)‡ ≅ 48.15 kJ.mol−1, ΔG(d)‡ ≅ 73.10 kJ.mol−1). The lower free energy barrier observed for the association came from an isokinetic process where entropic and enthalpic parameters compensated for each other. The ΔG° values indicate that the thermodynamically stable complex predominates over free molecules. At low temperature (285.15 K), the hydrophobic interaction (ΔH° = 73.06 kJ.mol−1; TΔS° = 99.60 kJ.mol−1) drove the βLG-RES complex formation while at high temperature (301.15 K), hydrophilic interactions became dominant (ΔH° = −142.50 kJ.mol−1; TΔS° = −118.18 kJ.mol−1).

Structure and rotational dynamics of water around hydrogen peroxide

The density functional theory-based molecular dynamics simulations were induced to study various properties of water around different solvation pockets around hydrogen peroxide(H2O2). Our study aims to understand water behavior in the vicinity of H2O2 molecule through analyzing structure, hydrogen bond statistics, orientational and non-diffusive jump profile. A water-like peroxide molecule can form four hydrogen bonds with nearby water molecules: two as a proton donor and two as a proton acceptor, which must disturb the local structure and dynamics of the surrounding water. The presence of two different peak maxima in radial distribution function (RDF) allows us to resolve the solvation environment into three solvation sites: solvation shell I, solvation shell II, and bulk. The probability distribution of the average distance of central water molecule from 4 nearest water molecules shows a shift in the peak for solvation shell I water molecules towards a ∼0.3Å higher value compared to two other solvation shells. This further affects tetrahedral order parameters as water molecules shift from the regular tetrahedron. For the first solvation layer, the water molecules lose their tetrahedrality to a significant extent as qtet probability distribution peaks at 0.5 and broaden in the higher values of qtet without any shoulder. For the second solvation layer, we find the qtet peak at 0.87 with a minor shoulder appearing at qtet = 0.55, a sign of slight loss of tetrahedrality in the unstructured water compared to undisturbed water. Loss of tetrahedrality hints at the change of orientation of H2O molecules in the vicinity of H2O2 and affects the water-water hydrogen bond (HB) formation. A noteworthy reduction in the HB donor/acceptor account and per water HB count shows interference of H2O2. The water molecules prefer H2O2 compared to neighboring water molecules for HB formation. The orientation autocorrelation function provides the rotational pace of water molecules in the different solvation layers. The reorientation time constant difference in the solvation shells I and II fluctuate by mere 0.20 ps, showcasing the trivial nature of hydrogen peroxide and water HBs. Using the HB descriptors, we also report the non-diffusive jump profile involving vicinal water molecules of H2O2. The jump angle profile of solvation shell water molecules is in line with bulk water.

Local structure in lithium chloride solution: a Monte-Carlo simulation study

ABSTRACT Monte-Carlo simulations and the nearest neighbour approach have been employed in the present study to investigate the structural properties of aqueous solutions of LiCl salt at ambient conditions. The calculations are performed at increasing concentration of LiCl starting from c = 0.1 m up to 10 m. The analysis shows that increasing salt concentration results in a reduction of the tetrahedral arrangement of water in favour of a non-tetrahedral arrangement characterised by an O–O–O angle between the reference oxygen and two of its four closest oxygen neighbours at 60°. Moreover, the LiCl concentration has a considerable effect on the hydrogen-bonding structure of water. By correctly choosing the nearest neighbours, it is found that the deviation in water structure is due to the presence of chloride ion, not lithium ion, in the first solvation shell of water. It is also demonstrated that in concentrated LiCl solution Cl− ions can substitute the fourth water neighbour which leads to a tetrahedral network formed by water molecules and Cl− ions around a central water molecule. The analysis of the effect of concentration increase on the arrangement of the four closest water molecules neighbours from a reference lithium cation allows us to elucidate a structural maker role of Lithium ion.

Bridging the 12-6-4 Model and the Fluctuating Charge Model.

Metal ions play important roles in various biological systems. Molecular dynamics (MD) using classical force field has become a popular research tool to study biological systems at the atomic level. However, meaningful MD simulations require reliable models and parameters. Previously we showed that the 12-6 Lennard-Jones nonbonded model for ions could not reproduce the experimental hydration free energy (HFE) and ion-oxygen distance (IOD) values simultaneously when ion has a charge of +2 or higher. We discussed that this deficiency arises from the overlook of the ion-induced dipole interaction in the 12-6 model, and this term is proportional to 1/r 4 based on theory. Hence, we developed the 12-6-4 model and showed it could solve this deficiency in a physically meaningful way. However, our previous research also found that the 12-6-4 model overestimated the coordination numbers (CNs) for some highly charged metal ions. And we attributed this artifact to that the current 12-6-4 scheme lacks a correction for the interactions among the first solvation shell water molecules. In the present study, we considered the ion-included dipole interaction by using the 12-6 model with adjusting the atomic charges of the first solvation shell water molecules. This strategy not only considers the ion-induced dipole interaction between ion and the first solvation shell water molecules but also well accounts for the increased repulsion among these water molecules compared to the bulk water molecules. We showed this strategy could well reproduce the experimental HFE and IOD values for Mg2+, Zn2+, Al3+, Fe3+, and In3+ and solve the CN overestimation issue of the 12-6-4 model for Fe3+ and In3+. Moreover, our simulation results showed good agreement with previous ab initio MD simulations. In addition, we derived the physical relationship between the C 4 parameter and induced dipole moment, which agreed well with our simulation results. Finally, we discussed the implications of the present work for simulating metalloproteins. Due to the fluctuating charge model uses a similar concept to the 12-6 model with adjusting atomic charges, we believe the present study builds a bridge between the 12-6-4 model and the fluctuating charge model.

Differential Hydration of Ice‐Binding Surface of Globular and Hyperactive Antifreeze Proteins

AbstractLike hyperactive antifreeze proteins (AFPs), globular AFPs also illustrate thermal hysteresis by specific binding to ice. The ice‐binding surface (IBS) topology and residue preferences are different between globular AFPs and hyperactive AFPs. This study explores the hydration water ordering and its temperature and length‐scale dependencies for type‐III AFPs, and the results with hyperactive AFP and non‐AFPs are compared. The hydration layer of the IBS of globular AFP is semiclathrate‐like, which is different from the hyperactive AFPs, as it is reported to be ice‐like. In a similar environment, the solvation water surrounding the non‐ice‐binding surface (non‐IBS) is mostly liquid‐like. Surprisingly, the non‐IBS is appreciably dissimilar from the non‐AFP in terms of hydration pattern. The amino acid compositions of the non‐IBS are in contrast with the IBS. Protein–water hydrogen bonding patterns between the IBS and non‐IBS of AFP are also different. These consequences suggest the collective function of non‐IBS and IBS in the antifreeze activity. The different nature of the first solvation shell water ordering around the IBS of type‐III AFP and hyperactive insect AFP implicates a differential design of IBS that may account for their observed difference in antifreeze activity.

Transfer free energy of micro-hydrated ion clusters from water into acetonitrile solvent

The transfer free energies of micro-hydrated alkali ions (Li+, Na+, K+, and Cs+) and halide ions (F-, Cl-, Br-, and I-) clusters from bulk water to bulk acetonitrile are investigated within the framework of reaction density functional theory (RxDFT), in which the formation of micro-hydrated ion clusters containing one to four water molecules is treated as associated reaction. By analyzing the free energy of hydration and solvation, we show that the micro-hydrated ion clusters, [M(H2O)n]+, exist stably in both water and acetonitrile and a larger percentage of the total electrostatic interactions of ions is contributed by their first solvation shell water molecules. For the transfer free energy of bare ions, the calculated results agree well with the values of experimental observation. The transfer free energy significantly decreases as the size of bare ions and the number of water molecules in the cluster increase. This dependence is stronger for small ions than for large ions. Moreover, the lowest transfer free energy is correspond to the different coordinated number of water molecule (Nw). For Li+, Na+, F-, Cl-, Br-, and I- ion, the lowest transfer free energy are correspond to Nw = 4, while for K+ and Cs+ ion, Nw with the lowest transfer free energy are 3 and 2, respectively. Our findings provide not only the framework to predict transfer free energy but also theoretical guidance for solvent extraction, ion-selective electrodes, biological ion channels, and phase transfer catalysis.

Probing the structural properties of the water solvation shell around gold nanoparticles: A computational study.

While subjected to radiation, gold nanoparticles (GNPs) have been shown to enhance the production of radicals when added to aqueous solutions. It has been proposed that the arrangement of water solvation layers near the water-gold interface plays a significant role. As such, the structural and electronic properties of the first water solvation layer surrounding GNPs of varying sizes were compared to bulk water using classical molecular dynamics and quantum and semi-empirical methods. Classical molecular dynamics was used to understand the change in macroscopic properties of bulk water in the presence of different sizes of GNP, as well as by including salt ions. The analysis of these macroscopic properties has led to the conclusion that larger GNPs induce the rearrangement of water molecules to form a 2D hydrogen-bond network at the interface. Quantum methods were employed to understand the electronic nature of the interaction between water molecules and GNPs along with the change in the water orientation and the vibrational density of states. The stretching region of vibrational density of states was found to extend into the higher wavenumber region, as the size of the GNP increases. This extension represents the dangling water molecules at the interface, as a result of reorientation of the water molecules in the first solvation shell. This multi-level study suggests that in the presence of GNP of increasing sizes, the first water solvation shell undergoes a rearrangement to maximize the water-water interactions as well as the water-GNP interactions.

Determining Sonication Effect on E. coli in Liquid Egg, Egg Yolk and Albumen and Inspecting Structural Property Changes by Near-Infrared Spectra.

In this study, liquid egg, albumen, and egg yolk were artificially inoculated with E. coli. Ultrasound equipment (20/40 kHz, 180/300 W; 30/45/60 min) with a circulation cooling system was used to lower the colony forming units (CFU) of E. coli samples. Frequency, absorbed power, energy dose, and duration of sonication showed a significant impact on E. coli with 0.5 log CFU/mL in albumen, 0.7 log CFU/mL in yolk and 0.5 log CFU/mL decrease at 40 kHz and 6.9 W absorbed power level. Significant linear correlation (p < 0.001) was observed between the energy dose of sonication and the decrease of E. coli. The results showed that sonication can be a useful tool as a supplementary method to reduce the number of microorganism in egg products. With near-infrared (NIR) spectra analysis we were able to detect the structural changes of the egg samples, due to ultrasonic treatment. Principal component analysis (PCA) showed that sonication can alter C–H, C–N, –OH and N–H bonds in egg. The aquagrams showed that sonication can alter the properties of H2O structure in egg products. The observed data showed that the absorbance of free water (1412 nm), water molecules with one (1440 nm), two (1462 nm), three (1472 nm) and four (1488 nm) hydrogen bonds, water solvation shell (1452 nm) and strongly bonded water (1512 nm) of the egg samples have been changed during ultrasonic treatment.

Boosting the performance by the water solvation shell with hydrogen bonds on protonic ionic liquids: insights into the acid catalysis of the glycosidic bond

Hydrogen-bonding (HB) of protonic ionic liquids induced by the water solvation shell is proposed to dominate in the acid catalysis of the glycosidic bond in hydrolysis.

Ab initio molecular dynamics simulations and experimental speciation study of levofloxacin under different pH conditions.

Levofloxacin is an extensively employed broad-spectrum antibiotic belonging to the fluoroquinolone class. Despite the extremely wide usage of levofloxacin for a plethora of diseases, the molecular characterization of this antibiotic appears quite poor in the literature. Moreover, the acid-base properties of levofloxacin - crucial for the design of efficient removal techniques from wastewaters - have never extensively been investigated so far. Here we report on a study on the behavior of levofloxacin under standard and diverse pH conditions in liquid water by synergistically employing static quantum-mechanical calculations along with experimental speciation studies. Furthermore, with the aim of characterizing the dynamics of the water solvation shells as well as the protonation and deprotonation mechanisms, here we present the unprecedented quantum-based simulation of levofloxacin in aqueous environments by means of state-of-the-art density-functional-theory-based molecular dynamics. This way, we prove the cooperative role played by the aqueous hydration shells in assisting the proton transfer events and, more importantly, the key place held by the nitrogen atom binding the methyl group of levofloxacin in accepting excess protons eventually present in water. Finally, we also quantify the energetic contribution associated with the presence of a H-bond internal to levofloxacin which, on the one hand, stabilizes the ground-state molecular structure of this antibiotic and, on the other, hinders the first deprotonation step of this fluoroquinolone. Among other things, the synergistic employment of quantum-based calculations and speciation experiments reported here paves the way toward the development of targeted removal approaches of drugs from wastewaters.

Evaluating Simple Ab Initio Models of the Hydrated Electron: The Role of Dynamical Fluctuations.

Despite its importance in electron transfer reactions and radiation chemistry, there has been disagreement over the fundamental nature of the hydrated electron, such as whether or not it resides in a cavity. Mixed quantum/classical simulations of the hydrated electron give different structures depending on the pseudopotential employed, and ab initio models of computational necessity use small numbers of water molecules and/or provide insufficient statistics to compare to experimental observables. A few years ago, Kumar et al. (J. Phys. Chem. A 2015, 119, 9148) proposed a minimalist ab initio model of the hydrated electron with only a small number of explicitly treated water molecules plus a polarizable continuum model (PCM). They found that the optimized geometry had four waters arranged tetrahedrally around a central cavity, and that the calculated vertical detachment energy and radius of gyration agreed well with experiment, results that were largely independent of the level of theory employed. The model, however, is based on a fixed structure at 0 K and does not explicitly incorporate entropic contributions or the thermal fluctuations that should be associated with the room-temperature hydrated electron. Thus, in this paper, we extend the model of Kumar et al. by running Born-Oppenheimer molecular dynamics (BOMD) of a small number of water molecules with an excess electron plus PCM at room temperature. We find that when thermal fluctuations are introduced, the level of theory chosen becomes critical enough when only four waters are used that one of the waters dissociates from the cluster with certain density functionals. Moreover, even with an optimally tuned range-separated hybrid functional, at room temperature the tetrahedral orientation of the 0 K first-shell waters is entirely lost and the central cavity collapses, a process driven by the fact that the explicit water molecules prefer to make H-bonds with each other more than with the excess electron. The resulting average structure is quite similar to that produced by a noncavity mixed quantum/classical model, so that the minimalist 4-water BOMD models suffer from problems similar to those of noncavity models, such as predicting the wrong sign of the hydrated electron's molar solvation volume. We also performed BOMD with 16 explicit water molecules plus an extra electron and PCM. We find that the inclusion of an entire second solvation shell of explicit water leads to little change in the outcome from when only four waters were used. In fact, the 16-water simulations behave much like those of water cluster anions, in which the electron localizes at the cluster surface, showing that PCM is not acceptable for use in minimalist models to describe the behavior of the bulk hydrated electron. For both the 4- and 16-water models, we investigate how the introduction of thermal motions alters the predicted absorption spectrum, vertical detachment energy, and resonance Raman spectrum of the simulated hydrated electron. We also present a set of structural criteria that can be used to numerically determine how cavity-like (or not) a particular hydrated electron model is. All of the results emphasize that the hydrated electron is a statistical object whose properties are inadequately captured using only a small number of explicit waters, and that a proper treatment of thermal fluctuations is critical to understanding the hydrated electron's chemical and physical behavior.

Raman Spectra of Glycine and Their Modeling in Terms of the Discrete–Continuum Model of Their Water Solvation Shell

Raman spectra of glycine in a crystalline form and in a water environment have been obtained. B3LYP/6-311++G(3df,2p) quantum-chemical calculations have shown that an adequate description of the Raman spectra of glycine is achieved using the discrete–continuum model of its water solvation shell. A model is proposed for the stabilization of the zwitterionic state of glycine involving the inclusion of a single water molecule that is hydrogen-bonded with the –СOO– and –NH $$_{3}^{ + }$$ groups. Calculations of the Raman spectra of glycine complexes Gly + nH2O (where n = 1–3), as well as of a glycine dimer, yield good agreement with experiment.

Making Advanced Electrogravimetry as an Affordable Analytical Tool for Battery Interface Characterization.

Numerous sophisticated diagnostic techniques have been designed to monitor electrode-electrolyte interfaces that mainly govern the lifetime and reliability of batteries. Among them is the electrochemical quartz crystal microbalance (EQCM) that offers valuable insights of the interfaces once the required conditions of the deposited film in terms of viscoelastic and hydrodynamic properties are fulfilled. Herein, we propose a friendly protocol that includes the elaboration of a homogeneous deposit by spray coating followed by QCM measurements at multiharmonic frequencies to ensure the film flatness and rigidity for collecting meaningful data. Moreover, for easiness of the measurements, we report the design of a versatile and airtight EQCM cell setup that can be used either with aqueous or non-aqueous electrolytes. We also present, using a model battery material, LiFePO4, how dual frequency and motional resistance monitoring during electrochemical cycling can be used as a well-suitable indicator for achieving reliable and reproducible electrogravimetric measurements. We demonstrate through this study the essential role of the solvent assisting lithium-ion insertion at the LiFePO4 interface with a major outcome of solvent-dependent interfacial behavior. Namely, in aqueous media, we prove a near-surface desolvation of lithium ions from their water solvation shell as compared with organic molecules. This spatial dissimilarity leads to a smoother Li-ion transport across the LFP-H2O interface, hence accounting for the difference in rate capability of LFP in the respective electrolytes. Overall, we hope our analytical insights on interfacial mechanisms will help in gaining a wider acceptance of EQCM-based methods from the battery community.

Solubility of water in perfluoroalkylalkanes surfactants: Evidence of specific interaction between water and the surfactant molecule

The solubility of water in five liquid perfluoroalkylalkanes was measured as a function of temperature (283 K–313 K) and the thermodynamic functions of solution and solvation were calculated. The studied perfluoroalkylalkanes cover a range of relative lengths of the hydrogenated and perfluorinated segments.This is the first time the solubility of water in these substances has been measured, which is surprising given their pharmaceutical and medical relevance. The new data thus fills an important gap in the literature.The liquid organization of the water-in-PFAAs solutions was further investigated using atomistic molecular dynamics simulations, providing structural and energetic evidence about the solvation shell of water within the different solvents.The results indicate the existence of a specific interaction between the water molecule and the dipole located at the centre of the surfactant molecules, which explains the increased solubility of water in these solvents, relatively to alkanes and perfluoroalkanes. These findings also help to interpret the formation of nano-patterned molecular films of PFAA at the surface of water and of wet silicon wafers.