Low Hydration Levels Research Articles

(Invited) Macroscopic Models of Ion-Nafion Interations: Influence of Counter Ion Density on Network Morphology

We develop a continuum energy formulation for an ionomer membrane with a multicomponent counter-ion electrolye, such as occur in Vanadium redox flow batteries. At low hydration levels the high electrolyte molarity induces strong interactions between tethered and counter ions, as well as competition for solvation among ionic groups. Through-membrane variation in composition of the counter-ion density can lead to changes in the ionomer membrane network morphology, which in turn couple to the counter ion mobility. We consider a gradient flow model which couples electrolyte motion, solvation, ionomer network morphology and present both analytical and numerical simulations.

The Effect of Water upon Deep Eutectic Solvent Nanostructure: An Unusual Transition from Ionic Mixture to Aqueous Solution.

The nanostructure of a series of choline chloride/urea/water deep eutectic solvent mixtures was characterized across a wide hydration range by neutron total scattering and empirical potential structure refinement (EPSR). As the structure is significantly altered, even at low hydration levels, reporting the DES water content is important. However, the DES nanostructure is retained to a remarkably high level of water (ca. 42 wt % H2O) because of solvophobic sequestration of water into nanostructured domains around cholinium cations. At 51 wt %/83 mol % H2O, this segregation becomes unfavorable, and the DES structure is disrupted; instead, water–water and DES–water interactions dominate. At and above this hydration level, the DES–water mixture is best described as an aqueous solution of DES components.

The Effect of Water upon Deep Eutectic Solvent Nanostructure: An Unusual Transition from Ionic Mixture to Aqueous Solution

AbstractThe nanostructure of a series of choline chloride/urea/water deep eutectic solvent mixtures was characterized across a wide hydration range by neutron total scattering and empirical potential structure refinement (EPSR). As the structure is significantly altered, even at low hydration levels, reporting the DES water content is important. However, the DES nanostructure is retained to a remarkably high level of water (ca. 42 wt % H2O) because of solvophobic sequestration of water into nanostructured domains around cholinium cations. At 51 wt %/83 mol % H2O, this segregation becomes unfavorable, and the DES structure is disrupted; instead, water–water and DES–water interactions dominate. At and above this hydration level, the DES–water mixture is best described as an aqueous solution of DES components.

Effect of oil and shortening in rice bread quality: Relationship between dough rheology and quality characteristics

This study showed that the type and quantity of fat added in rice based breads affect the bread quality in a different way. In general, it can be said that the incorporation of up to 20% oil improved rice based breads. Oil increased the specific volume, the a* and b* parameters of the crust and the cell density. It also decreases hardness, cohesiveness, springiness, resilience, and the L* parameter. Converse to breads made with oil, the addition of shortening can negatively affect the quality of the breads. Moreover, the correlation analysis has demonstrated that the study of dough rheology could be a good predictor of gluten-free bread quality.

Body composition measurements using bioelectrical impedance analysis (BIA) in pediatric patients with hepatic glycogen storage disease – Preliminary data

Summary Background Patients with hepatic glycogen storage diseases (GSDs) are prone to accumulation of an excessive body fat due to dietary therapy with frequent meals and addition of uncooked cornstarch. The aim of this study was to estimate body composition, in particular body fat in Polish pediatric patients with GSDs using BIA. Patients and methods Twenty four patients with hepatic GSDs: I, III/VI/IX,0: 9,14,1, respectively, aged 8.5 years (SD = 2.8) were included into the study. The average fasting time preceding BIA was 2.7 h (SD = 0.9). Patient was weighed, then height, age, gender, weight, and round the waist and hips were entered into computer. Results Median weight was (median [interquartile range]) 25.3 kg [13.7; 60.5] and median height was 119 cm [89; 157]. An average BMI was 18.8 (SD = 3.4) and 81.7 (SD = 3.4) percentile. An average round the waist and hips were 65.4 (SD = 13.3) and 67.2 (SD = 15.0), respectively, and average waist/hips ratio was 0.99 (SD = 0,2). An average body fat percentage was 36.7% (SD = 5.7) and 11.6 kg (SD = 5.7). An average lean body mass (bm) was 17,0 kg (SD = 8.8) and dry lean bm 4.7 kg (SD = 2.2). An average body water percentage was 48.6% (SD = 4.2) and 11.9 kg (SD = 6.5). Conclusion Polish patients with GSD have excessive body fat percentage which may be due to a very high calorie diet/excessive cornstarch intake. It may also be affected by their low hydration levels.

Adsorption of Chromium (VI) on Calcium Phosphate: Mechanisms and Stability Constants of Surface Complexes

The adsorption of chromate on octacalcium phosphate (OCP) was investigated as a function of contact time, surface coverage, and solution pH [...]

Nanoscale Structure and Morphology of Sulfonated Polyphenylenes via Atomistic Simulations

We performed atomistic simulations on a series of sulfonated polyphenylenes systematically varying the degree of sulfonation and water content to determine their effect on the nanoscale structure, particularly for the hydrophilic domains formed by the ionic groups and water molecules. We found that the local structure around the ionic groups depended on the sulfonation and hydration levels, with the sulfonate groups and hydronium ions less strongly coupled at higher water contents. In addition, we characterized the morphology of the ionic domains employing two complementary clustering algorithms. At low sulfonation and hydration levels, clusters were more elongated in shape and poorly connected throughout the system. As the degree of sulfonation and water content were increased, the clusters became more spherical, and a fully percolated ionic domain was formed. These structural details have important implications for ion transport.

Internal Hydration Properties of Single Bacterial Endospores Probed by Electrostatic Force Microscopy.

We show that the internal hydration properties of single Bacillus cereus endospores in air under different relative humidity (RH) conditions can be determined through the measurement of its electric permittivity by means of quantitative electrostatic force microscopy (EFM). We show that an increase in the RH from 0% to 80% induces a large increase in the equivalent homogeneous relative electric permittivity of the bacterial endospores, from ∼4 up to ∼17, accompanied only by a small increase in the endospore height, of just a few nanometers. These results correlate the increase of the moisture content of the endospore with the corresponding increase of environmental RH. Three-dimensional finite element numerical calculations, which include the internal structure of the endospores, indicate that the moisture is mainly accumulated in the external layers of the endospore, hence preserving the core of the endospore at low hydration levels. This mechanism is different from what we observe for vegetative bacterial cells of the same species, in which the cell wall at high humid atmospheric conditions is not able to preserve the cytoplasmic region at low hydration levels. These results show the potential of quantitative EFM under environmental humidity control to study the hygroscopic properties of small-scale biological (and nonbiological) entities and to determine its internal hydration state. A better understanding of nanohygroscopic properties can be of relevance in the study of essential biological processes and in the design of bionanotechnological applications.

THz dynamics of nanoconfined water by ultrafast optical spectroscopy

We investigated the vibrational dynamics and structural relaxation of water nanoconfined in porous silica samples with a pore size of 4 nm at different levels of hydration and temperature. We used the time-resolved optical Kerr effect (OKE), a spectroscopic technique that enables investigation of ultrafast water dynamics in a wide time (0.1–10 ps) or frequency (10–0.1 THz) window. At low hydration levels corresponding to two complete superficial water layers, no freezing occurs and the water remains mobile at all investigated temperatures. Meanwhile, at full hydration we witness a partial ice formation at about 248 K that coexists with the surface water remaining in the supercooled state. At low hydration, both structural and vibrational dynamics show significant modifications compared to bulk liquid water. This is due to the strong interaction of the water molecules with silica surfaces. Inner water, however, reveals relaxation dynamics very similar to bulk water.

STRUCTURE-TRANSPORT RELATIONSHIP OF PERFLUOROSULFONIC-ACID MEMBRANES IN DIFFERENT CATIONIC FORMS

Perfluorosulfonic-acid (PFSA) ionomers are widely used as solid electrolytes and ion-exchange membranes in electrochemical devices, wherein their properties are impacted by the interactions among the anionic sulfonate groups, mobile counter-ions (cations), and hydration levels. Cation-form and humidity collectively affect the structure/transport-property relationship, yet their interplay is still not well known. In this paper, we report changes in water uptake and conductivity of cation-exchanged PFSA in both vapor and liquid water, which are then correlated with changes in mechanical properties and nanostructure (hydrophilic-domain spacing and phase-separation). It is found that the magnitude of changes depends significantly on the membrane water content, with master curves in terms of water volume fraction and water per charge realized. Moreover, membrane nanostructure and dynamical-mechanical behavior is examined to establish structure/transport and transport/stability relationships. It is found that with increasing cation size (radius) and valence, the storage modulus increases, while the water uptake and conductivity decrease. In addition, regardless of the cation type, a universal relationship is found between the conductivity and modulus, indicative of a transport/stability tradeoff. The extent to which the cations impact the transport properties depends on the water content: at low hydration levels the controlling factor is the cation (and its interaction with the sulfonate sites), at increasing hydration the dominant factor becomes water volume fraction, although it is also controlled by the cations. Similarly, the decrease in hydrophilic domain spacing of PFSA exchanged with larger cations scales with cation radius at low water contents, but with Lewis acid strength (LAS) at higher hydration levels. The findings reported here not only provide valuable insights into the interaction between sulfonate groups, cations, and water surrounding these ionic groups, but also for understanding cation contamination in fuel cells and redox flow batteries.

Coarse-grained simulations of hemolytic peptide δ-lysin interacting with a POPC bilayer

δ-lysin, secreted by a Gram-positive bacterium Staphylococcus aureus, is a 26-residue membrane active peptide that shares many common features with antimicrobial peptides (AMPs). However, it possesses a few unique features that differentiate itself from typical AMPs. In particular, δ-lysin has zero net charge, even though it has many charged residues, and it preferentially lyses eukaryotic cells over bacterial cells. Here, we present the results of coarse-grained molecular dynamics simulations of δ-lysin interacting with a zwitterionic membrane over a wide range of peptide concentrations. When the peptides concentration is low, spontaneous dimerization of peptides is observed on the membrane surface, but deep insertion of peptides or pore formation was not observed. However, the calculated free energy of peptide insertion suggests that a small fraction of peptides is likely to be present inside the membrane at the peptide concentrations typically seen in dye efflux experiments. When the simulations with multiple peptides are carried out with a single pre-inserted transmembrane peptide, spontaneous pore formation occurs with a peptide-to-lipid ratio (P/L) as low as P/L=1:42. Inter-peptide salt bridges among the transmembrane peptides seem to play a role in creating compact pores with very low level of hydration. More importantly, the transmembrane peptides making up the pore are constantly pushed to the opposite side of the membrane when the mass imbalance between the two sides of membrane is significant. Thus, the pore is very dynamic, allowing multiple peptides to translocate across the membrane simultaneously.

Computational study of inelastic neutron scattering vibrational spectra of water clusters and their relevance to hydration water in proteins

BackgroundInelastic neutron scattering (INS) vibrational spectra for hydration water in proteins can be obtained from spectral differences, but their interpretation has mainly been limited to comparisons with various forms of ice at high hydration levels without making use of available structural information from neutron protein crystallography. MethodsThe INS vibrational spectra of free and partially constrained water clusters (up to n=17) were calculated with DFT methods using published energy-minimized structures. ResultsReference is made to neutron diffraction studies of hydrated proteins, which contain a wealth of structural information both on individual water molecules and small clusters in the inner “shell” in order to select representative clusters to serve as models for bound, rather than free clusters as they would occur in a protein. ConclusionsINS spectra of the water librational region calculated for a combination of model bound clusters provide a qualitative account of the essentially featureless experimental spectra on water in proteins at very low hydration levels, but do indicate that the well-known rise in intensity near 500cm−1 is connected to increasing numbers of four-coordinate water molecules in larger clusters. General significanceThe combination of structural information of hydration water from neutron protein crystallography with much more sophisticated computational methods than used herein should lead to a much more detailed picture of the hydration of proteins. This article is part of a Special Issue entitled "Science for Life" Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo.

Cladode growth dynamics in Opuntia ficus-indica under drought

Cactus pear (Opuntia ficus-indica L. Miller) is a CAM plant with an extraordinary capacity to store water in its succulent stems (cladodes). However, the daily variations of cladode thickness is unknown. Studying cladode thickness fluctuations may be useful for the early prediction of plant dehydration stress. The objective of this study was to determine if age, water availability and temperature influence diel cladode shrinkage and enlargement dynamics in cactus pear. The experiment was conducted in a greenhouse from April to July 2014, using cactus pear plants, equally split into irrigated and unirrigated treatments, and unrooted cladodes detached from mother plants. Soil moisture content (SMC), soil water depletion over 24-h, cladode relative water content (RWC), cladode thickness, stomatal conductance (gs), cladode growth rates (area increase) and nocturnal malic acid accumulation were monitored in plants of various ages. Cladode shrinkage and enlargement dynamics were assessed using stem gauges and expressed as absolute growth rate (AGRthickness, μmmin−1). In unirrigated pots, drought decreased SMC, RWC,cladode thickness, cladode growth rate and gs. Younger cladodes lost water later than older ones. Detached cladodes exhibited gs activity 3–4 months after detachment. Trends of AGRthickness showed that there was a progressive reduction of diel swelling and shrinkage fluctuations as cladodes aged. Such fluctuations were minimized under severe drought when 1-year-old cladodes reached 8mm thickness and a RWC of about 45%. A positive correlation was found between SMC and AGRthickness. Temperatures were also directly correlated with AGRthickness, although this relationship was gradually lost as SMC decreased. Overall, cactus pears were able to maintain some growth at very low hydration levels, and cladode growth was highly responsive to rehydration after long periods of drought.

Photochemistry and Photobiology of the Spore Photoproduct: A 50-Year Journey.

Fifty years ago, a new thymine dimer was discovered as the dominant DNA photolesion in UV-irradiated bacterial spores [Donnellan, J. E. & Setlow R. B. (1965) Science, 149, 308-310], which was later named the spore photoproduct (SP). Formation of SP is due to the unique environment in the spore core that features low hydration levels favoring an A-DNA conformation, high levels of calcium dipicolinate that acts as a photosensitizer, and DNA saturation with small, acid-soluble proteins that alters DNA structure and reduces side reactions. In vitro studies reveal that any of these factors alone can promote SP formation; however, SP formation is usually accompanied by the production of other DNA photolesions. Therefore, the nearly exclusive SP formation in spores is due to the combined effects of these three factors. Spore photoproduct photoreaction is proved to occur via a unique H-atom transfer mechanism between the two involved thymine residues. Successful incorporation of SP into an oligonucleotide has been achieved via organic synthesis, which enables structural studies that reveal minor conformational changes in the SP-containing DNA. Here, we review the progress on SP photochemistry and photobiology in the past 50 years, which indicates a very rich SP photobiology that may exist beyond endospores.

Ring-Tailed Lemur (Lemur catta) Health Parameters across Two Habitats with Varied Levels of Human Disturbance at the Bezà Mahafaly Special Reserve, Madagascar

The health of 36 wild, free-ranging ring-tailed lemurs (Lemur catta) at the Bezà Mahafaly Special Reserve was assessed across 2 habitats of varied human impact: a reserve riverine gallery forest, and a degraded mixed dry deciduous and Alluaudia-dominated spiny forest. While there were no statistically significant differences in leukocyte count or differential between habitats, female lemurs in the reserve gallery forest had significantly higher percentages of monocytes and eosinophils than male lemurs in the gallery forest. Lemurs from the degraded spiny habitat had significantly higher mean packed cell volume, hematocrit, hemoglobin, total protein, blood urea nitrogen, chloride, ionized calcium and urine specific gravity than lemurs from the reserve gallery forest. These findings may reflect lower hydration levels in lemurs living in degraded habitat, providing evidence that environmental degradation has identifiable impacts on the physiology and health of wild, free-ranging ring-tailed lemurs living in nearby habitats. Given the greater evidence of human impact in the mixed dry deciduous/spiny forest habitat, a pattern seen throughout southern Madagascar, biomedical markers suggestive of decreased hydration can provide empirical data to inform new conservation policies facilitating the long-term survival of this lemur community.

Supercooling and freezing processes in nanoconfined water by time-resolved optical Kerr effect spectroscopy

Using heterodyne-detected optical Kerr effect (HD-OKE) measurements, we investigate the vibrational dynamics and the structural relaxation of water nanoconfined in Vycor porous silica samples (pore size ≃ 4 nm) at different levels of hydration and temperatures. At low levels of hydration corresponding to two complete superficial water layers, no freezing occurs and the water remains mobile at all the investigated temperatures with dynamic features similar, but not equal to, the bulk water. The fully hydrated sample shows the formation of ice at about 248 K. This process does not involve all the contained water; a part of it remains in a supercooled phase. The structural relaxation times measured from the decay of the time-dependent HD-OKE signal shows the temperature dependence largely affected by the hydration level; the low frequency (ν < 500 cm−1) vibrational spectra obtained by the Fourier transforms of the HD-OKE signal appear less affected by confinement.

Dominant Alcohol-Protein Interaction via Hydration-Enabled Enthalpy-Driven Binding Mechanism.

Water plays an important role in weak associations of small drug molecules with proteins. Intense focus has been on binding-induced structural changes in the water network surrounding protein binding sites, especially their contributions to binding thermodynamics. However, water is also tightly coupled to protein conformations and dynamics, and so far little is known about the influence of water-protein interactions on ligand binding. Alcohols are a type of low-affinity drugs, and it remains unclear how water affects alcohol-protein interactions. Here, we present alcohol adsorption isotherms under controlled protein hydration using in situ NMR detection. As functions of hydration level, Gibbs free energy, enthalpy, and entropy of binding were determined from the temperature dependence of isotherms. Two types of alcohol binding were found. The dominant type is low-affinity nonspecific binding, which is strongly dependent on temperature and the level of hydration. At low hydration levels, this nonspecific binding only occurs above a threshold of alcohol vapor pressure. An increased hydration level reduces this threshold, with it finally disappearing at a hydration level of h ≈ 0.2 (g water/g protein), gradually shifting alcohol binding from an entropy-driven to an enthalpy-driven process. Water at charged and polar groups on the protein surface was found to be particularly important in enabling this binding. Although further increase in hydration has smaller effects on the changes of binding enthalpy and entropy, it results in a significant negative change in Gibbs free energy due to unmatched enthalpy-entropy compensation. These results show the crucial role of water-protein interplay in alcohol binding.

Quantum chemical analysis of the deprotonation of sulfonic acid in a hydrocarbon membrane model at low hydration levels

We conducted a quantum chemical analysis of the deprotonation reaction of the sulfonic group (SO3H) in a model of a hydrocarbon (HC) membrane, which has been proposed as a new proton conductor for polymer electrolyte membranes (PEMs) of polymer electrolyte fuel cells (PEFCs). By comparison with perfluorosulfonic acid (PFSA) species, activation energies are higher at all hydration levels. When deprotonation occurs in the PFSA at hydration level three, the activation energy in the model HC is still higher than the thermal energy of the PEFC operation temperature and therefore it is difficult or impossible to overcome it. Moreover, at hydration level three, the deprotonated state is not stable, in contrast to PFSA, and deprotonation of SO3H and protonation of the sulfonate (SO3−) should occur with the same probability. Because the activation energy is high and the deprotonation state is unstable, it is difficult to deprotonate the SO3H of the model HC to SO3− at hydration level three. Moreover, a bond-order analysis shows that SO3− is more strongly connected to H3O+ than it is for PFSA. These appear to be the main causes of the remarkably reduced proton conductivity in HC membranes at low hydration levels.

Vertical ordering sensitivity of solid supported DPPC membrane to alamethicin and the related loss of cell viability

BackgroundExperimental studies of antimicrobial peptides interacting with lipid membranes recently attracted growing interest due to their numerous biomedical applications. However, the influence of such peptides on the structural organisation of lipid membranes in connection with the actual cell response still remains an elusive issue. MethodsX-ray diffraction was employed on detecting the sensitivity of the periodical spacing of dipalmitoyl-phosphatidyl-choline stacked as solid-supported bilayers to the presence of varying amounts of the peptide alamethicin in a wide range of peptide-to-lipid molar ratios. These results were then correlated with the effects of alamethicin on biological membranes in vitro as observed by optical microscopy and microculture tetrazolium assay on the tumour cells HeLa to provide a comprehensive and quantitative analysis of these effects, based on a dose–response relationship. ResultsThe experiments allowed correlating the periodical spacing and the peptide-to-lipid molar ratio on alamethicin-dipalmitoyl-phosphatidyl-choline samples. Two different trends of periodical spacing vs. peptide-to-lipid molar ratio clearly appeared at low and high hydration levels, showing intriguing non-linear profiles. Unexpected correspondences were observed between the peptide-to-lipid molar ratio range where the changes in dipalmitoyl-phosphatidyl-choline structure occur and the alamethicin doses which alter the viability and the plasma membrane morphology of HeLa. ConclusionsAlamethicin might induce either mechanical or phase changes on dipalmitoyl-phosphatidyl-choline bilayers. Such easily accessible ordering information was well-calibrated to predict the alamethicin doses necessary to trigger cell death through plasma membrane alterations. General significanceThis benchmark combined study may be valuable to predict bioeffects of several antimicrobial peptides of biomedical relevance.

Controlled release of a sparingly water-soluble anticancer drug through pH-responsive functionalized gold-nanoparticle-decorated liposomes.

The binding and detachment of carboxyl-modified gold nanoparticles from liposomes is used for controlled drug delivery. This study reveals that the binding and detachment of nanoparticles from liposomes depends on the degree of hydration of the liposomes. Liposomes with a lower hydration level undergo stronger electrostatic interactions with negatively charged gold nanoparticles, thus leading to a slower detachment of the carboxyl-modified gold nanoparticles under gastric conditions. Therefore, under gastric conditions, gold-nanoparticle-decorated dipalmitoylphosphatidylcholine (DPPC) liposomes exhibit an at least ten-times-slower drug release compared to gold-nanoparticle-decorated 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes, although both liposomes in the bare state fail to pursue controlled release. Our study also reveals that one can modulate the drug-release rate by simply varying the concentration of nanoparticles. This study highlights a novel strategy for the controlled release of drug molecules from liposomes.