Minimal Hydration Research Articles

In-silico investigation of mechanical behavior of hydrated Na-montmorillonite tactoid

Swelling clay minerals, exemplified by Na-montmorillonite (Na-Mt), are vital constituents in expansive soils and hold significant relevance in geotechnical engineering. Comprehending their distinctive swelling behavior upon hydration is imperative for managing potential damage to civil infrastructure. Conversely, this swelling property gives rise to numerous advantageous applications, including using these clays in barrier materials and nanocomposites. The hierarchical structure of montmorillonite, consisting of clay mineral layers, tactoids, aggregates, and assemblies of aggregates, plays a pivotal role in the swelling behavior of expansive clays. This investigation employs molecular dynamics (MD) and steered molecular dynamic (SMD) simulations to explore the nanomechanical properties of hydrated Na-Mt tactoids at various hydration levels. It provides insights into their responses to compression, tensile, and shear deformation. This study reveals increased hydration levels increase interlayer spacing in clay structures, resulting in higher average d‐values. Water molecules drive attractive electrostatic interactions with clay mineral layers, predominantly mediated by sodium ions, highlighting the complex interplay between interlayer hydration and tactoid stability. Higher hydration enhances tactoid compressibility, reducing the stress required for deformation by compressing water molecules and clay mineral layers in the interlayer space. The study also demonstrates a notable reduction in tensile modulus with increasing hydration, signifying the significant impact of even minimal hydration on interlayer cation-clay layer interactions. Hydrated tactoids exhibit altered mechanical responses in shear deformation compared to dry ones, requiring lower shear stress to detach the top clay layer from the tactoid. The presence of water molecules impedes the locking of clay mineral layers, further influencing mechanical properties. The results and insight provided by this work will contribute to a better understanding of the impact of interlayer hydration on the stability and response of swelling clay minerals.

Scanning electron microscopy results of the vitreous body in asteroid hyalosis

To evaluate the structure of vitreous body in asteroid hyalosis by low vacuum scanning electron microscopy. The material of the study was samples of the vitreous body obtained from 7 patients aged from 62 to 72 years with vitreomacular traction syndrome during vitrectomy. In all cases, clinical manifestations of asteroid hyalosis (the presence of multiple point-like echo-positive inclusions) were identified during the preoperative examination. Samples for scanning electron microscopy and chemical microanalysis were prepared without using fixation elements, total dehydration, staining or centrifugation, and according to the so-called principle of bougienage, which consists in partial separation of fractions of the gel-like tissue with a stream of saline. The conducted examinations made it possible to identify various types of local accumulations of mineral elements in the vitreous body in asteroid hyalosis - called asteroid bodies - that is, multiple complex rounded formations consisting of needle-shaped crystals of a radial fibrous structure. The developed algorithm, which includes intraoperative sampling of the vitreous body in conditions of its minimal hydration and a special technique for preparing samples for scanning electron microscopy and chemical microanalysis, provides the capability for the in vivo assessment of morphological changes in hyaloid elements of the vitreous body. With that, asteroid bodies can be considered as markers of the vitreous structures that are difficult to visualize.

Effect of education on preference of parenteral nutrition for patients in palliative care unit: quantitative and qualitative study with an anthropological approach.

Patients and their family have resistance in withholding parenteral nutrition (PN) when patient become unable to intake food in the end-of-life. We aimed to investigate whether the preference for PN is changed after receiving an individual education about the risk and benefit of PN. Additionally, we focused on the preferences of patients and their family and why they prefer it about the nutritional support in the end of life. This is prospective study. Patients are eligible if they cannot tolerate oral intake and enteral feeding and have Palliative Performance Scale (PPS) ≤50% due to progressive cancer. After informed consent, investigators educated patients and family for an hour using the handouts. Then, patients decided if they will receive PN. Quality of life (QOL) was checked by European Organization for Research and Treatment of Cancer Quality of Life Questionnaire (EORTC QLQ-C15-PAL) weekly during 3 weeks. Symptoms related to fluid overloading or dehydration was surveyed weekly also. A social anthropologist participated as an observer or interviewer during whole process of this study. After education, 12 patients (80%) chose to keep receiving PN and 3 patients (20%) changed their decision from PN to minimal hydration among the 15 patients. More calories were administered to patients who chosen PN (median 1,042.2 vs. 324.3 Kcal/day, P<0.001) for initial 7 days. Overall survival, scores of QLQ-C15-PAL, and symptoms were not different with or without PN. According to the anthropologist, medical staffs regard PN as complex medical treatments, while patients and family recognize it as meal rather than medicine. Most patients and family prefer to receive PN despite its potential harm and marginal benefit. An in-depth discussion about prognosis and aim of care must be preceded before a decision whether to receive PN can be made.

Silica surface states and their wetting characteristics

The wetting characteristics of silica (SiO2) surfaces can be described by molecular dynamics (MD) and ab initio simulations, including comparison of silica surfaces (talc (001), siloxanated quartz, tridymite (001) and quartz (001)), some of which have not been considered previously in the literature. Classic MD and ab initio simulation methods have been used to determine the contact angle, interfacial water structure, hydroxylation reaction and hydration energy, the results of which are compared with experimental results reported in the literature. Wetting of silica surfaces depends on surface polarity and extent of hydroxylation. The non-polar siloxane surfaces are characterized by a contact angle of about 80°, an MD ‘water exclusion zone’ of about 3 Å, a relaxed interfacial water orientation, inertness to hydroxylation and minimal hydration energy. The polar silica surfaces can be wetted by water and have a more ordered interfacial water structure. Silanol groups form at the polar silica surface during hydroxylation reactions, and the calculated hydration energy of −1·2 and −1·6 eV matches the experimental heat of immersion measurements reported in the literature, which correspond to hydrogen (H) bonding with interfacial water. Fundamental understanding of silica surfaces is important for understanding flotation phenomena and fluid flow in silica nanopores.

Quantum Mechanics Study on Hydrophilic and Hydrophobic Interactions in the Trivaline-Water System.

With the aim to elucidate hydrophobic effects in the unfolded state of peptides, DFT-M062X computations on the Val3H+· nH2O ( n up to 22) clusters have been accomplished. As far as the main chain is concerned, four conformers with β-strand and/or polyproline type II conformations, PPII (indicated as β-β, β-PPII, PPII-β, and PPII-PPII), have been found by changing the ϕ and ψ angles. For bare peptide, the side chain (isopropyl) of each residue can independently take on three different orientations with negligible effects on energetics. The great isopropyl spatial separations in β-β and β-PPII conformers allow for the construction of synergic and extensive water-water and water-peptide H-bonding in the minimal hydration Val3H+·22H2O models without significant steric encumbrance. Conversely, due to the proximity of the isopropyl of the central residue with the other two, some restrictions in the water shell construction around the peptide become evident for the PPII-PPII conformer and the number of energetically accessible structures decreases. This is indicative of correlated motion involving isopropyls and backbone mediated by water molecules, the origin of the nearest neighbor effects. Comparing the thermodynamic data of Ala3H+·22H2O and Val3H+·22H2O, what emerges is that both hydration enthalpy and entropy drive the β-strand stability of the latter.

The influence of the cationic form and degree of hydration on the structure of Nafion™

FT-IR ATR spectroscopy has been undertaken to elucidate how the structure of Nafion™ membranes is affected by the cationic form (i.e., H+, D+, and Na+) and water content. Three distinct hydration levels were considered: (a) completely dry (λ ≡ Η2Ο/ – SO3− ≅ 0); (b) minimal hydration (λ ≅ 2); and (c) fully hydrated (λ ≅ 22). The measured spectra reveal that the associated cation and degree of hydration have a significant effect on the vibrational modes of the perfluoroether side chains of the ionomer. Two peaks ascribed to the SO3X terminal groups and the features attributed to the COC linkages were clearly identified. The latter were studied in detail, and are shown to be diagnostic of the conformation of the side chains. A comprehensive framework of interpretation of the experimental results is proposed, with emphasis on: (a) the role played by the interactions between the SO3X terminal groups of the different side chains; and (b) how the latter interactions are affected by the amount of H2O or D2O in the samples. In particular, reference is made to the formation and spatial distribution of the positively-charged species characterized by significantly different structural features.

Theory of collective proton motion at interfaces with densely packed protogenic surface groups

We present a theoretical study of collective proton transport at a 2D array of end-grafted protogenic surface groups with sulfonic acid head groups. The graft positions of the surface groups form a regular hexagonal lattice. We consider the interfacial array at a high packing density of the surface groups and under minimal hydration with one water molecule added per head group. For these conditions, the stable interfacial conformation consists of a bicomponent lattice of hexagonally ordered sulfonate anions and interstitial hydronium cations. Hydronium ion motion occurs as a travelling solitary wave. We analyse the microscopic parameters of the solitons and study the influence of different potential profiles on the proton motion created by rotation and tilting of sidechains and sulfonate anions. Using soliton solutions of the equation of motion, we establish relations between the energy and mobility of the solitons and the microscopic structural and interaction parameters of the array.

Water Sorption and Transport Properties of Polymer Electrolyte Membranes: New Insights from Theory

Pertinent polymer electrolyte membranes (PEM) channel protons through random networks of water-filled pores. Their operation hinges on sufficient amounts of water for proton conduction. This requirement affects structure and properties on > 6 scales. Theoretical research on PEM employs a hierarchy of physical models to address these multiscale challenges. The first part of this contribution focuses on recent progress in ab initio calculations of structural correlations and proton dynamics at dense interfacial arrays of protogenic surface groups. These results have vital implications for the design of PEM that could attain high proton conductivity at minimal hydration. The second part explores the realms of equilibrium and dynamic water sorption and swelling of PEM. The outlined approaches in modeling provide capabilities to predict the membrane response to changing external conditions and to extract parameters of bulk water transport in PEM and vaporization exchange at the membrane surfaces from measured water fluxes through the membrane.

Hydration Effect on Low-Frequency Protein Dynamics Observed in Simulated Neutron Scattering Spectra

Hydration effects on protein dynamics were investigated by comparing the frequency dependence of the calculated neutron scattering spectra between full and minimal hydration states at temperatures between 100 and 300 K. The protein boson peak is observed in the frequency range 1–4 meV at 100 K in both states. The peak frequency in the minimal hydration state shifts to lower than that in the full hydration state. Protein motions with a frequency higher than 4 meV were shown to undergo almost harmonic motion in both states at all temperatures simulated, whereas those with a frequency lower than 1 meV dominate the total fluctuations above 220 K and contribute to the origin of the glass-like transition. At 300 K, the boson peak becomes buried in the quasielastic contributions in the full hydration state but is still observed in the minimal hydration state. The boson peak is observed when protein dynamics are trapped within a local minimum of its energy surface. Protein motions, which contribute to the boson peak, are distributed throughout the whole protein. The fine structure of the dynamics structure factor is expected to be detected by the experiment if a high resolution instrument (<∼20 μeV) is developed in the near future.

Hydration-Dependent Protein Dynamics Revealed by Molecular Dynamics Simulation of Crystalline Staphylococcal Nuclease

Molecular dynamics simulations of crystalline Staphylococcal nuclease in full and minimal hydration states were performed to study hydration effects on protein dynamics at temperatures ranging from 100 to 300 K. In a full hydration state (hydration ratio in weight, h=0.49), gaps are fully filled with water molecules, whereas only crystal waters are included in a minimal hydration state (h=0.09). The inflection of the atomic mean-square fluctuation of protein as a function of temperature, known as the glass-like transition, is observed at approximately 220 K in both cases, which is more significant in the full hydration state. By examining the temperature dependence of residual fluctuation, we found that the increase of fluctuations in the loop and terminal regions, which are exposed to water, is much greater than that in other regions in the full hydration state, but the mobilities of the corresponding regions are relatively restricted in the minimal hydration state by intermolecular contact. The atomic mean-square fluctuation of water molecules in the full hydration state at 300 K is 1 order of magnitude greater than that in the minimal hydration state. Above the transition temperature, most water molecules in the full hydration state behave like bulk water and act as a lubricant for protein dynamics. In contrast, water molecules in the minimal hydration state tend to form more hydrogen bonds with the protein, restricting the fluctuation of these water molecules to the level of the protein. Thus, intermolecular interaction and solvent mobility are important to understand the glass-like transition in proteins.

Hydrated Arrays of Acidic Surface Groups as Model Systems for Interfacial Structure and Mechanisms in PEMs

We utilize ab initio quantum mechanical calculations in order to explore structural conformations and cooperative mechanisms at a minimally hydrated 2D array of flexible acidic surface groups. This system serves as a model for rationalizing interactions and correlations of protons and water with ionized side chains that are affixed to hydrophobic polymer aggregates in polymer electrolyte membranes (PEMs). The model exhibits two basic minimum energy configurations upon varying the separation of surface groups from 5 to 12 A. In the "upright" structure at small separation, surface groups are fully dissociated and oriented perpendicular to the basal plane. Together with hydronium ions (H3O+) they form a highly ordered network with long-range correlations. At larger separations we found the transition to a "tilted" structure with cluster-like conformation of surface groups. This structure retains only short-range correlations. Moreover, we investigated the strength of water binding to the minimally hydrated structures. At small separations between surface groups, an additional water molecule interacts only weakly with the minimally hydrated array (binding energy < 0.1 eV) while the energy needed to remove one water molecule exceeds 1 eV. This shows that the minimally hydrated systems are very stable. Ideally, these studies would expedite the design of cheap, highly performing PEMs for fuel cells, with a major focus on membranes that could operate stably at minimal hydration and elevated temperatures (>120 degrees C).

The effects of backbone conformation on hydration and proton transfer in the ‘short-side-chain’ perfluorosulfonic acid membrane

Presented here is a first principles based molecular modeling investigation of the effects of conformational changes in the backbone on hydration and proton transfer in the short-side-chain perfluorosulfonic acid fuel cell membrane under minimal hydration conditions. Extensive searches for minimum energy structures (at the B3LYP/6-311G ⁎⁎ level) of the two pendant side chain polymeric fragment: CF 3CF(–O(CF 2) 2SO 3H)–(CF 2) 7–CF(–O(CF 2) 2SO 3H)CF 3 with from 4 to 7 explicit water molecules revealed that the perfluorocarbon backbone may adopt both an elongated geometry with all carbons in a trans configuration and also a folded conformation as a result of the hydrogen bonding of the terminal sulfonic acids with the water. Our calculations show that the fragments displaying the latter ‘kinked’ backbone possessed stronger binding of the water to the sulfonic acid groups and also effect proton dissociation with fewer water molecules. These calculations point to the importance of the flexibility of the backbone in the transport of protons for membranes with low water content.

Optimisation and characterisation of bioadhesive controlled release tetracycline microspheres

A Box-Behnken experimental design was employed to statistically optimise the formulation parameters of a tetracycline microsphere preparation for maximum bioadhesivity and controlled drug release. The quantitative effect of the formulation parameters at different levels on bioadhesion and drug release could be predicted using polynomial equations. A formulation comprising of 3% (w/w) chitosan, 10% (w/w) tetracycline HCl and 9% (w/v) tripolyphosphate was identified for maximising bioadhesivity and obtaining controlled drug release. The optimal microsphere preparation was subsequently characterised in terms of hydration dynamics, release kinetics, antimicrobial activity, thermal properties, morphology and surface pH. Kinetic models revealed that drug release followed Fickian diffusion while textural analysis showed minimal hydration over the test period. Antimicrobial studies showed that the drug concentrations in the in vitro release samples were above the minimum concentration of drug required for inhibition of Staphylococcus aureus growth. Thermal analyses showed a possible interaction between the drug and polymer. Scanning electron microscopy confirmed the integrity of the microspheres and identified the morphological changes following drug release. Surface pH of the microspheres was similar to salivary pH and did not show extremes in changes over the test period.

Molecular Modeling of the Short-Side-Chain Perfluorosulfonic Acid Membrane

Presented here is a first principles based molecular modeling investigation of the possible role of the side chain in effecting proton transfer in the short-side-chain perfluorosulfonic acid fuel cell membrane under minimal hydration conditions. Extensive searches for the global minimum energy structures of fragments of the polymer having two pendant side chains of distinct separation (with chemical formula: CF(3)CF(O(CF(2))(2)SO(3)H)(CF(2))(n)CF(O(CF(2))(2)SO(3)H)CF(3), where n = 5, 7, and 9) with and without explicit water molecules have shown that the side chain separation influences both the extent and nature of the hydrogen bonding between the terminal sulfonic acid groups and the number of water molecules required to transfer the proton to the water molecules of the first hydration shell. Specifically, we have found that fully optimized structures at the B3LYP/6-311G** level revealed that the number of water molecules needed to connect the sulfonic acid groups scaled as a function of the number of fluoromethylene groups in the backbone, with one, two, and three water molecules required to connect the sulfonic acid groups in fragments with n = 5, 7, and 9, respectively. With the addition of explicit water molecules to each of the polymeric fragments, we found that the minimum number of water molecules required to effect proton transfer also increases as the number of separating tetrafluoroethylene units in the backbone is increased. Furthermore, calculation of water binding energies on CP-corrected potential energy surfaces showed that the water molecules bound more strongly after proton dissociation had occurred from the terminal sulfonic acid groups independent of the degree of separation of the side chains. Our calculations provide a baseline for molecular results that can be used to assess the impact of changes of polymer chemistry on proton conduction, including the side chain length and acidic functional group.

Esterase catalysis of substrate vapour: enzyme activity occurs at very low hydration

It has been generally accepted that enzyme activity requires a minimal hydration of about 0.2 g H 2O g −1 protein. This fits well with evidence that hydration above this level is associated with the onset of intramolecular motions. The influence of enzyme hydration on the hydrolysis of substrate by Candida rugosa Lipase B and pig liver esterase was investigated. Each enzyme was studied as a powder at various hydration levels, using vapour phase ethyl butyrate as substrate. This procedure allows the separation of those effects that are due to hydration from those arising from diffusional constraints. We found hydrolytic activity in both enzymes at all hydration levels above zero (between 0.054–0.47 and 0.029–0.60 g H 2O g −1 protein, respectively) that were investigated. The lowest hydration level investigated, <0.03 g H 2O g −1 enzyme, corresponded to a water/enzyme mole ratio of 100 and a coverage of about 10% of the enzyme surface by water molecules. The hydrolytic activity of both enzymes was dependent on protein hydration. However, since the hydrolysis of ethyl butyrate requires water as a second substrate, the absence of activity at zero hydration does not rule out the possibility of enzyme activity in the absence of water. These results suggest that the properties conferred on proteins by water, at least above 10% surface coverage (in this case corresponding to a hydration level of 0.03 g H 2O g −1 protein), are not a requirement for enzyme catalysis.

8] Using cosolvents to stabilize protein conformation for crystallization

Publisher Summary This chapter focuses on the use of cosolvents to stabilize protein conformation for crystallization. Polyols can be used in crystallization by simply adding glycerol or a concentrated sugar solution to a crystallization mixture. It is also important to add a polyol to a reservoir to maintain the same ratio of the polyol to precipitant in both the reservoir and crystallization solutions. Otherwise, it will be impossible to predict the approximate equilibrium concentrations of the precipitant and the polyol in the crystallization drop. When crystallizing a particular protein under conditions of minimal hydration, care must be taken to avoid the induction of salt-crystal formation in the crystallization solution because the salt may become supersaturated in the crystallization drop. This can happen when the drop is disturbed for seeding or crystal harvest. When this occurs, the precipitant concentration in the solution drops and the protein crystals may dissolve. These issues are only problematic when maximally saturated solutions of salts and glycerol are being used for crystallization.

Solution structure of papain as studied by molecular mechanics and molecular dynamics techniques.

In this paper, we report the molecular mechanics and molecular dynamics studies of the hydration of papain using the AMBER and CHARMm programs. We studied papain in an environment with minimal hydration involving only the X-ray waters and also in the hydrated environment by adding an extra 9 Å layer of water around the residues. The effect of nonbond cutoff was studied by performing minimizations with 8 Å and 15 Å nonbond cutoffs using the program AMBER. Two different solvent models-a constant dielectric and a distance-dependent dielectric-were considered. The AMBER-minimized structure and the average structure obtained from the CHARMm simulations for papain solvated with X-ray waters are presented and compared with the X-ray crystal structure results. Results of a similar comparison of the hydrated structures were also presented. The calculated root mean square deviation between the minimized structure and the X-ray structure is smaller for the hydrated system than for the system hydrated with only the X-ray waters. Results of the molecular mechanics and molecular dynamics simulations were presented for the various regions of papain. The hydration of the active site of papain and the effect of hydration on the torsional motion of the active site residues are presented. © 1996 by John Wiley & Sons, Inc.

Unibase/glycol as an electrolyte medium for recording the electrodermal duct filling response.

ABSTRACTTwo experiments with 12 subjects each compared electrodermal recordings taken simultaneously with four different electrolyte media. These were polyethylene glycol, Unibase/glycol, Unibase, and hydrated agar (i.e., a site recorded with agar electrolyte which had been attached to the skin long enough to attain a high degree of hydration). The primary purpose was to compare the electrolyte containing a mixture of Unibase/glycol with the other electrolytes. The glycol and the hydrated agar were assumed to reflect low and high levels of epidermal hydration, respectively. These comparisons were made for monophasic negative SPRs and slow recovery SCRs (and their associated prestimulus levels), which are believed to reflect the endosomatic and exosomatic manifestations of the epidermal duct filling response.Unibase/glycol was quite similar to glycol alone with the exception of the prestimulus SPL associated with negative SPRs. Taken in conjunction with previous findings, the results suggest that for most aspects of electrodermal activity Unibase/glycol is a convenient electrolyte medium for use when minimal hydration is required. It is argued on theoretical grounds that minimal hydration is preferable for skin potential recordings.

A convenient, non-hydrating electrolyte medium for the measurement of electrodermal activity.

ABSTRACTTwo experiments with 12 subjects each compared electrodermal recordings taken simultaneously with four different electrolyte media. These were polyethylene glycol, Unibase/glycol, Unibase, and hydrated agar (i.e., a site recorded with agar electrolyte after presoaking it with water). The primary purpose was to compare the electrolyte containing a mixture of Unibase/glycol with the other electrolytes. The glycol and the hydrated agar were assumed to reflect low and high levels of epidermal hydration, respectively, while Unibase provided a comparison with Unibase alone. These comparisons were made for positive SPRs and rapid recovery SCRs (and their associated prestimulus levels), which are believed to reflect the endosomatic and exosomatic manifestations of the epidermal membrane response.Unibase/glycol was quite similar to glycol alone; thus it offers a more convenient electrolyte for use when minimal hydration is required. The results were interpreted as indicating that Unibase/glycol is preferable for skin potential recordings, while Unibase is to be preferred for skin conductance recordings.

Effect of pH on Water Vapor Sorption by Caseins

Abstract Water vapor sorption by whole casein and micellar casein was measured by isopiestic techniques in the water activity range of .2 to .98 as a function of pH. At high water activities, whole casein revealed minimal hydration near its isoelectric point (approximately pH 4.6). Water sorption by micellar casein increased on either side of a pH close to that of the original milk serum. Results are interpreted in terms of ion hydration, binding, and solubility equilibria. The changes in water sorption capacity of micellar casein upon acidification suggest that water activity during lactic acid fermentation in milk products is decreased significantly.