Low Hydration Levels Research Articles

Vibrational excitation induced proton transfer in hydrated Nafion membranes.

We study the energy relaxation and structural relaxation dynamics of hydrated protons in Nafion membranes at different hydration levels using femtosecond infrared transient absorption spectroscopy. At low hydration levels we observe that the excitation of the proton vibration of an Eigen-like proton hydration structure leads to a structural relaxation process in which the Eigen-like structure evolves to a Zundel-like proton hydration structure. This reorganization leads to a transfer of the proton charge and closely follows the mechanism of infrared-induced adiabatic proton transfer that has been proposed by S. Hammes-Schiffer, J. T. Hynes, and others. At high hydration levels, the spectral dynamics are dominated by vibrational energy relaxation and subsequent cooling of the proton hydration structures and the surrounding water molecules. Using a kinetic analysis of the transient spectral data, we determine the rates of proton transfer, vibrational energy relaxation, and cooling as a function of hydration level. We find that infrared-induced proton transfer occurs at all hydration levels but becomes less observable at high hydration levels due to the increasingly dominant influence of the vibrational energy relaxation.

Effects of Topical N-Acetylcysteine on Skin Hydration/Transepidermal Water Loss in Healthy Volunteers and Atopic Dermatitis Patients.

Dear Editor: Atopic dermatitis (AD) is a relapsing chronic inflammatory pruritic skin disorder that has been partially attributed to skin barrier dysfunction. Skin barrier function was previously estimated by measuring skin hydration and transepidermal water loss (TEWL), and low levels of skin hydration along with high levels of TEWL were reported in AD patients1,2. N-acetylcysteine (NAC) is a thiol derivative that stimulates the synthesis of glutathione, an internal antioxidant. NAC has been clinically used as a mucolytic agent as well as an antidote for acetaminophen toxicity. NAC was previously reported to be useful in the treatment of skin diseases including toxic epidermal necrolysis and lamellar ichthyosis3,4. NAC may exert beneficial effects in skin diseases by: (1) reacting with oxidative intermediates and replenishing intracellular cysteine levels; (2) inhibiting the production of proinflammatory cytokines and factors; and (3) regulating epidermal proliferation. In the present study, we assessed the clinical effects of topical NAC on skin hydration and TEWL in healthy volunteers and AD patients. We enrolled 10 healthy volunteers (6 males and 4 females, age range: 28 to 76 years) and 11 AD patients (6 males and 5 females, age range: 31 to 73 years). AD patients had been receiving topical treatments including corticosteroids and tacrolimus ointment. Patients were not receiving cyclosporine or methotrexate. Patients with severe co-existing conditions as well as those with a heavy smoking status and/or high alcohol consumption were excluded. Informed consent was obtained from all patients. This study was approved by the Ethics Committee of the Faculty of Medicine, Kagawa University (No. 20-14). A NAC solution (20 w/v%; Senju Pharmaceutical Co., Ltd., Osaka, Japan) or its control vehicle was applied to the forearm skin twice a day for 4 weeks. Forearm skin hydration and TEWL were measured before and after the topical NAC application. Skin hydration and TEWL were measured using a Corneometer and Tewameter (Courage+Khazaka Electronic GmbH, Cologne, Germany). The topical application of NAC for 4 weeks increased skin hydration in 9/10 healthy volunteers (Fig. 1A, increase from 36.2±9.9 to 48.8±15.7 arbitrary units, p=0.001) and decreased TEWL in 8/10 healthy volunteers (Fig. 1B, decrease from 13.5±8.9 to 10.1±6.1 g/hm2, p= 0.0341). Topical application of the control vehicle for 4 weeks decreased skin hydration in 8/11 AD patients (Fig. 1C, decrease from 39.3±15.1 to 33.3±11.6 arbitrary units, p=0.0409). The topical application of NAC increased skin hydration in 9/11 AD patients (Fig. 1C, increase from 35.6±12.0 to 44.7±13.9 arbitrary units, p=0.0262) and decreased TEWL in 9 AD patients (Fig. 1D, decrease from 18.1±15.1 to 10.8±11.2 g/hm2, p=0.0409). Fig. 1 (A, B) Effects of the topical application of N-acetylcysteine (NAC) (for 4 weeks) on skin hydration and transepidermal water loss (TEWL) in healthy volunteers. (C, D) Effects of the topical application of NAC on skin hydration and TEWL in atopic dermatitis ... In a mouse model of AD, NAC was reported to restore the expression of some cell adhesion molecules that contribute to skin barrier formation by reducing oxidative stress5. Therefore, the topical application of NAC may increase skin hydration and decrease TEWL by strengthening the function of this barrier. Lamellar ichthyosis exhibits abnormal keratinization due to TGM1 gene mutations and a differential pattern of filaggrin expression, which implies that the success of NAC treatment in lamellar ichthyosis may be attributed to NAC-induced amelioration of abnormal keratinization and improvements in skin barrier function. Our results also support the possibility of skin barrier function restoration by NAC. Although AD patients generally have low levels of skin hydration and high levels of TEWL1,2, we could not obtain consistent results. Some AD patients have been shown to have normal skin barrier function6, and these values can be affected by various factors such as seasonality, exercise, and lifestyle. Thus, future studies involving a larger number of patients and excluding skin barrier-deteriorating factors are required to accurately assess the effects of NAC on AD.

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.

Investigating Lipid Phase Changes from Liquid Crystalline to Ripple to Gel Phases with All-Atom Molecular Dynamics Simulations

Lipid mixed with water can exist in many different phases that depends on various factors, such as hydration, temperature and pressure (J. Chem. Theory Comput.,6 (8): 2488 (2010)). The liquid crystalline (chain-disordered state) is a well-studied phase for single lipid bilayers both experimentally and computationally. At low enough temperatures or hydration levels, this chain-disordered state can change to a gel state with high chain order and a certain chain tilt with respect to the membrane normal. Depending on the lipid, an intermediate phase can exist between the gel and liquid crystalline phase, which is known as the ripple phase. The main objective of this study was probing the accuracy of the CHARMM36 (C36) force field (FF) (J. Phys. Chem. B.,114 (23): 7830 (2010)) in predicting phase changes in lipid bilayers. Pure and mixed lipid bilayers at different compositions of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) were studied using molecular dynamics (MD) simulations. Based on the pure gel-phase transition temperature of each lipid, a range of temperatures was selected (from 200C to 400C) (Biochem. 18: 3280 (1979)). MD simulations were able to capture ripple phase in %25 DMPC and %75 DPPC mixture and pure DMPC at 250C. Simulations were run for 200-300 ns. MD simulations also show either a gel state or gel-like state depending on if the system gets trapped (gel-like is a state without proper leaflet alignment). Phase diagram was compared to that obtained from experimental data such as NMR. Based on the phase diagram and our transition temperatures, C36 FF accurately predicts the phase transitions of this fully saturated PC lipids. Therefore, studies on phase coexistence of liquid ordered and liquid disordered domains are likely to be accurate using the C36 FF.

Characterising the biophysical properties of normal and hyperkeratotic foot skin.

BackgroundPlantar foot skin exhibits unique biophysical properties that are distinct from skin on other areas of the body. This paper characterises, using non-invasive methods, the biophysical properties of foot skin in healthy and pathological states including xerosis, heel fissures, calluses and corns.MethodsNinety three people participated. Skin hydration, elasticity, collagen and elastin fibre organisation and surface texture was measured from plantar calluses, corns, fissured heel skin and xerotic heel skin. Previously published criteria were applied to classify the severity of each skin lesion and differences in the biophysical properties compared between each classification.ResultsCalluses, corns, xerotic heel skin and heel fissures had significantly lower levels of hydration; less elasticity and greater surface texture than unaffected skin sites (p < 0.01). Some evidence was found for a positive correlation between hydration and elasticity data (r ≤ 0.65) at hyperkeratotic sites. Significant differences in skin properties (with the exception of texture) were noted between different classifications of skin lesion.ConclusionsThis study provides benchmark data for healthy and different severities of pathological foot skin. These data have applications ranging from monitoring the quality of foot skin, to measuring the efficacy of therapeutic interventions.

Mass spectrometry to quantify and compare the gas barrier properties of radiation grafted membranes and Nafion®

This study describes a method using mass spectrometry (MS) to quantify the gas barrier properties of different classes of ionomer membranes and the base film used in radiation grafted membranes for polymer electrolyte fuel cells. The effects of relative humidity (RH), temperature and graft level are investigated for different types of radiation grafted membrane with dissimilar chemical compositions. The results show that the radiation grafted membranes and Nafion® 212 share the same trend of increasing gas permeability with RH, while the ETFE base film does not show RH dependency. With addition of nitrile-containing comonomer units in the grafted chains, the permeability of reactant gases in the membranes can be remarkably reduced. On the basis of experimental results, a physical model is proposed to describe the effect of water contents on the gas transport in the radiation grafted membranes and to explain the effect of graft level on gas barrier properties and the difference of gas barrier properties at high and low hydration levels between Nafion® membranes and radiation grafted membranes. Using helium as a tracer, the deterioration of the gas barrier properties of the radiation grafted membrane during an accelerated stress test at open circuit voltage (OCV) is recorded in situ.

Quantum Chemical Analysis about Deprotonation Reaction of Sulfonic Group of Modeled Hydrocarbon Membrane in Low Hydration Level

Ease of deprotonation what is called acidity about sulfonic group of model molecules of perfluorosulfonic acid (PFSA) membrane and hydrocarbon (HC) membrane was focused on in this study. The deprotonation reaction of sulfonic group by water molecules were analyzed by density functional theory in low hydration levels. Target hydration levels were one to three. Calculation level was B3LYP/6-311+G(d,p). As a result, sulfonic group of model molecules of PFSA is deprotonated in hydration level three via low activation energy. In addition, deprotonated state (SO3 - group, H3O+ and two water molecules) is more stable than the protonated state (sulfonic group and three water molecules). On the other hand, deprotonated state of model molecule of HC in hydration level three is unstable. In addition, activation energy is relatively high. Those properties indicate sulfonic group of HC membrane is relatively hard to deprotonate in comparison with PFSA membrane in the same hydration level.

An Improved EVB Model for Proton Transport in Polymer Electrolyte Membrane

We have performed a detailed analysis of proton solvation and transport properties in hydrated Nafion using molecular dynamics simulation. The revised EVB model predicts a significantly enhanced transport in comparison with the classical hydronium models, which largely improves the agreement with the available experimental data. The excess proton was found to have weaker interaction with the sulfonate groups in comparison with the classical hydronium ion, reflecting the delocalization nature of the proton charge defects in the EVB model. Our results suggest that the hopping transport has a large contribution to the proton diffusion even at lower hydration levels, as low as 3. It was also found that the Grotthuss component becomes more important and its contribution increases linearly as the hydration level increases.

Quantum Chemical Analysis about Deprotonation Reaction of Sulfonic Group of Modeled Hydrocarbon Membrane in Low Hydration Level

Hydrocarbon membranes (HC) are expected as a new polymer electrolyte membrane (PEM) of polymer electrolyte fuel cell (PEFC) by its high durability and low synthetic cost. There is one weak point in HC. That is low proton conductivity especially in low hydration level1 in comparison with perfluorosulfonic acid (PFSA) membrane. This difference between HC and PFSA is considered to be caused by high probability of deprotonation as well as membrane flexibility2. Thus, activation energy of deprotonation reaction (ΔEa) and energy difference before and after deprotonation (ΔH) are very important information to estimate the performance of membrane in the low hydration level. However, deprotonation mechanism of HC by water molecule(s) was not clarified yet. For PFSA, deprotonation process of sulfonic group by three water molecules has been already clarified by our study3. We showed characteristic reaction process in hydration level three. In this hydration level, sulfonic group of PFSA should be deprotonated smoothly by three water molecules via low ΔEa. ΔH in this reaction is enough low to prevent the reverse reaction. Thus, PFSA shows strong acidity. However, deprotonation mechanism and its properties about HC membrane are still unknown.Then, we attempted to clarify the deprotonation reaction about HC species by some water molecules in the same manner as PFSA. Benzenesulfonic acid (C6H5SO3H) was adopted as a model molecule of HC. A relative configuration between sulfonic group and water molecules in reactant, transition state and product for each hydration level was set in the same manner of the analysis of PFSA3. Each geometries, that is, reactant, transition state and product, were calculated by B3LYP/6-311+G(d,p) level of theory. The basis set super position error was corrected by counterpoise method. All of calculations were performed by Gaussian094, installed on super computer systems of Institute of Fluid Science, Tohoku University. All of geometries were confirmed as appropriate stable state or transition state by the normal vibration analysis.Energy changes along the reaction in hydration level from one to three were depicted in Fig. 1. All of energies were treated as relative energy; reactants are set as 0 kcal/mol.Fig. 1. Energy changes along the reaction in each hydration levels.The predicted ΔEas for hydration level one, two and three were 12.95, 10.02 and 4.16 kcal/mol, respectively. ΔEas were obviously decreased with increasing hydration level. ΔEas in these hydration levels were much higher than the heat energy around the 350K (≈ 0.7 kcal/mol), which was the operation temperature of PEFC. In hydration level three, predicted electronic energy of product was slightly larger than the reactant, which means that the product geometry which indicates SO3 - group, H3O+ and two water molecules is barely unstable by 0.55 kcal/mol. Considering the computational error of this study, however, it is hard to evaluate this slightly large ΔH Only we can conclude that deprotonated state in HC is not favorable qualitatively. In HC, thus, ΔEa of deprotonation reaction of sulfonic group and protonation reaction of SO3 - group are almost same. Then, those two reactions occur in the same probability. These results are different from PFSA’s results. ΔEas in PFSA species were 10.94, 5.24 and 0.70 kcal/mol in hydration level one, two and three, respectively. And ΔH in PFSA was - 3.72 kcal/mol in hydration level three. Compared with those results, both ΔEas and ΔH of HC are higher than those of PFSA. This difference is caused by the difference of its constituent. PFSA mainly consists of fluorocarbon which hasis strong electron withdrawing moiety. Due to the strong electronegativity electron withdrawing of fluorocarbon, both ΔEas and ΔH are very low. On the other hand, HC consists of phenyl group. Electron withdrawing ability of phenyl group is not so strong as fluorocarbon then both ΔEas and ΔHof HC are higher than those of PFSA.AcknowledgementThis work was financially supported by the New Energy and Industrial Technology Development Organization (NEDO). And authors also thank to the super computer systems of Institute of Fluid Science, Tohoku University.References (1) Rikukawa, M.; Sanui, K. Prog. Polym. Sci. 2000, 25, 1463. (2) Kopitzke, R. W.; Linkous, C. A.; Anderson, H. R.; Nelson, G. L. J. Electrochem. Soc. 2000, 147, 1677. (3) Sakai, H.; Tokumasu, T. The Journal of Physical Chemistry A 2014, 118, 275. (4) Frisch, M. J. et. al.; Revision C.01 ed.; Gaussian, Inc.: 2010.

The abundance and stability of “water” in type 1 and 2 carbonaceous chondrites (CI, CM and CR)

Carbonaceous chondrites record processes of aqueous alteration in the presence of hydrated and hydroxylated minerals, which could have provided a source of water in the inner solar system (Alexander et al., 2012, 2013). In this study, thermogravimetric analysis (TGA) was performed on 26 CM chondrites, which cover a range of degree of aqueous alteration from 2.0, such as Meteorite Hills (MET) 01070, to 2.6, such as Queen Alexandra Range (QUE) 97990, in order to quantify their water content. In addition, by measuring the release of volatile elements as a function of temperature, we obtained information on the mineralogy of water-bearing phases and provide indicators of aqueous alteration based on water released by phyllosilicates. These analyses are combined with infrared spectroscopy (IR) made on meteorite pellets heated up to 300°C. The infrared features (–OH band at 3-μm and SiO4 around 10-μm) revealed a correlation with TGA. The two techniques are in agreement with the scheme of aqueous alteration proposed by Rubin et al. (2007) and Alexander et al. (2013) based on phyllosilicate abundance.The low temperature (200–400°C) mass loss observed in TGA is attributed to Fe-oxy-hydroxydes (ferrihydrite, goethite). However, the proportion of these minerals formed by terrestrial alteration remains unknown. TGA also revealed two anomalous CM chondrites, Pecora Escarpment (PCA) 02012 and PCA 02010. Their TGA curves are significantly different from those of “regular” CMs with little mass loss, which can be related to the dehydration history of these meteorites in response to a heating event (Raman measurements also point toward a thermal event, Quirico et al., 2013). In the case of more mildly heated chondrites, such as with Wisconsin Range (WIS) 91600, the TGA curve presents similar mass loss to the other CMs.Seven bulk measurements of CR chondrites and 3 measurements of matrix-enriched parts of CR meteorites were also studied by TGA, and confirm the low hydration level of chondrules and a significant alteration of the matrix. The water content of the matrix of the CM 2.6 QUE 97990 was estimated and compared to TGA of the matrix enriched portion of the CR2 EET 92159 and that of Orgueil.Results suggest a similar aqueous alteration degree between Orgueil and the matrix of CMs (around 25wt.%) and a lower alteration of the CR2 matrix (11wt.% of H2O).

Characteristic differences in barrier and hygroscopic properties between normal and cosmetic dry skin. II. Depth profile of natural moisturizing factor and cohesivity

In a previous paper (Lu et al., International Journal of Cosmetic Science, in press), we reported that in comparison with normal skin, cosmetic dry skin characteristically has a thicker stratum corneum (SC) with weaker barrier quality. Our goal here was to obtain a more complete picture of the difference between normal and cosmetic dry skin, by further analysing the data collected from the same clinical study to address two additional aspects of skin: the amount and depth profile of natural moisturizing factor (NMF) and the cohesivity of the SC. The SC samples were collected by sequential tape stripping in a clinical study consisting of 64 healthy Caucasian female subjects with either normal or cosmetic dry skin. Protein and free amino acids (FAA) on tape strips were extracted and analysed using high-throughput methods. The level of pyrrolidone carboxylic acid (PCA), the prominent component of NMF, was detected using HPLC analysis. It was found that dry skin had significantly lower ratios of FAA/protein and PCA/protein across the stripped SC depth, corresponding to a lower hydration level compared with the normal skin. Our results indicated that filaggrin to FAA hydrolysis occurred deeper in dry skin and at a lower level compared with normal skin. In addition, the mass of proteins stripped from dry skin subjects was significantly higher than that from the normal skin counterpart, especially for the first 10-12 tape strips. Our results showed that, compared with normal skin, cosmetic dry skin had a lower NMF level across the SC depth and a lower cohesivity. Such results suggested that NMF levels are critical for cosmetic skin conditions, and lower NMF production may be associated with dry skin. In addition, the NMF level and its depth profile and the SC cohesivity are useful clinical end points for assessing the efficacy of dry skin treatments such as skin moisturizers.

Does a Dry Protein Undergo a Glass Transition?

Bovine serum albumin (BSA) with extremely low hydration level 0.04, which is usually defined as dry, has been investigated in the temperature range between 200 and 340 K by incoherent inelastic neutron scattering using the neutron time-of-flight spectrometer FOCUS (PSI, Switzerland). Anomalous temperature behavior has been revealed for relaxational and low-frequency vibrational dynamics of BSA in the vicinity of 250 K. The mean-square atomic displacement has been shown to exhibit a change in the slope of temperature dependence near the same temperature. The presented results point out that the glass-like transition occurs in the dry protein.

Boson peak as a probe of quantum effects in a glassy state of biomolecules: the case of L-cysteine.

Some physical properties of hydrated biomolecules, e.g., the occurrence of a boson peak, have been recognized to resemble those of glassy states. The present work shows that quantum fluctuations play a fundamental role in describing the glassy state of biomolecules, particularly at lower hydration levels. There is a linear relationship between the quantumness and the slope of the temperature dependence of the boson peak frequency, which is used to classify the extent of quantum contributions to the glassy state of glasses in general. Lastly, we demonstrate that the boson peak two-band spectral structure that is observed in some cases can be directly linked to the anisotropy of the elastic properties of the material. The amino acid L-cysteine is studied in detail. The findings are compared with previously reported data for other macromolecules.

Characteristic differences in barrier and hygroscopic properties between normal and cosmetic dry skin. I. Enhanced barrier analysis with sequential tape‐stripping

Cosmetic dry skin often has a lower hydration level but a similar apparent barrier function, as measured by transepidermal water loss (TEWL), than that of the normal skin. To investigate the intrinsic difference in barrier property and moisture-holding ability between the cosmetic dry and normal skin, we developed a new clinical and data analysis procedure based on sequential tape-stripping with TEWL measurement, coupled with chemical analysis for protein and natural moisturizing factors (NMF) in the stratum corneum. A clinical study consisting of 64 healthy Caucasian female subjects with normal and cosmetic dry skin was conducted according to our clinical and data collection protocols. After the baseline visual dryness assessment, 20 tape-strips were placed and removed on each test site using D-Squame tapes. TEWL was measured at baseline and after the 5th, 10th, 15th and 20th tape-strips. All tapes were analysed for protein mass via chemical extraction and the Pierce BCA protein assay, as well as using an infrared densitometry device SquameScan 850A. The stratum corneum thickness and barrier quality (water transport resistance per thickness of the stratum corneum) were decoupled from the apparent barrier function using the TEWL and protein data. A linear relationship between 1/TEWL and cumulative protein removal was observed for both normal and cosmetic dry skin. However, the slope of the linear relation was significantly steeper for normal skin, and significantly more protein was removed from cosmetic dry skin. The results showed that on average, the barrier quality of the stratum corneum of the normal skin is about 40% higher than that of the dry skin, whereas the stratum corneum of the dry skin is about 30% thicker than that of the normal skin. In addition, the amount of SC removal in sequential tape-stripping is generally non-uniform. Our results demonstrated that there are characteristic differences in the barrier property between normal and cosmetic dry skin. In comparison to the normal skin, the stratum corneum of the cosmetic dry skin is considerably thicker, however, with a lower barrier quality. The results also showed that the amount of the SC removal in sequential tape-stripping is generally non-uniform. Therefore, the number of tape strips is not a good indicator for the tape-stripping depth.

Ab initio molecular dynamics simulations of aqueous triflic acid confined in carbon nanotubes.

Ab initio molecular dynamics simulations were performed to investigate the effects of nanoscale confinement on the structural and dynamical properties of aqueous triflic acid (CF3SO3H). Single-walled carbon nanotubes (CNTs) with diameters ranging from ∼11 to 14 Å were used as confinement vessels, and the inner surface of the CNT were either left bare or fluorinated to probe the influence of the confined environment on structural and dynamical properties of the water and triflic acidic. The systems were simulated at hydration levels of n = 1-3 H2O/CF3SO3H. Proton dissociation expectedly increased with increasing hydration. Along with the level of hydration, hydrogen bond connectivity between the triflic acid molecules, both directly and via a single water molecule, played a role on proton dissociation. Direct hydrogen bonding between the CF3SO3H molecules, most commonly found in the larger bare CNT, also promoted interactions between water molecules allowing for greater separation of the dissociated protons from the CF3SO3(-) as the hydration level was increased. However, this also resulted in a decrease in the overall proportion of dissociated protons. The confinement dimensions altered both the hydrogen bond network and the distribution of water molecules where the H2O in the fluorinated CNTs tended to form small clusters with less proton dissociation at n = 1 and 2 but the highest at n = 3. In the absence of nearby hydrogen bond accepting sites from H2O or triflic acid SO3H groups, the water molecules formed weak hydrogen bonds with the fluorine atoms. In the bare CNT systems, these involved the CF3 groups of triflic acid and were more frequently observed when direct hydrogen bonding between CF3SO3H hindered potential hydrogen bonding sites. In the fluorinated tubes, interactions with the covalently bound fluorine atoms of the CNT wall dominated which appear to stabilize the hydrogen bond network. Increasing the hydration level increased the frequency of the OH···F (CNT) hydrogen bonding which was highly pronounced in the smaller fluorinated CNT indicating an influence on the confinement dimensions on these interactions.

Reaction Analysis for Deprotonation of the Sulfonic Group of Perfluorosulfonic Acid Molecules at Low Hydration Levels

A reaction analysis for deprotonation of the sulfonic group in a model molecule of perfluorosulfonic acid (PFSA) at low hydration levels was performed. PFSA is usually adopted as a polymer electrolyte membrane in polymer electrolyte fuel cells. In hydration level three, the deprotonation reaction certainly occurs. The deprotonated state produced is more stable than the predeprotonated state by 3.72 kcal/mol. In addition, its activation energy is very low. Although quantitative discussion of this activation energy is difficult considering the computational error, it can be said qualitatively that H(+) is abstracted smoothly from the sulfonic group because of a low activation energy. From the results of bond-order analysis, the produced H3O(+) is strongly bound by the SO3(-) group. Thus, diffusivity of H3O(+) would be low. In hydration level four or more, we found a possibility that the diffusivity of H3O(+) increases because the hydrogen-bond strength between H3O(+) and SO3(-) is lower or SO3(-) cannot bind H3O(+) directly by forming an Eigen cation.

Vibrational spectroscopy of water in hydrated lipid multi-bilayers. III. Water clustering and vibrational energy transfer

Water clustering and connectivity around lipid bilayers strongly influences the properties of membranes and is important for functions such as proton and ion transport. Vibrational anisotropic pump-probe spectroscopy is a powerful tool for understanding such clustering, as the measured anisotropy depends upon the time-scale and degree of intra- and intermolecular vibrational energy transfer. In this article, we use molecular dynamics simulations and theoretical vibrational spectroscopy to help interpret recent experimental measurements of the anisotropy of water in lipid multi-bilayers as a function of both lipid hydration level and isotopic substitution. Our calculations are in satisfactory agreement with the experiments of Piatkowski, Heij, and Bakker, and from our simulations we can directly probe water clustering and connectivity. We find that at low hydration levels, many water molecules are in fact isolated, although up to 70% of hydration water forms small water clusters or chains. At intermediate hydration levels, water forms a wide range of cluster sizes, while at higher hydration levels, the majority of water molecules are part of a large, percolating water cluster. Therefore, the size, number, and nature of water clusters are strongly dependent on lipid hydration level, and the measured anisotropy reflects this through its dependence on intermolecular energy transfer.

Ultrafast Two-Dimensional Infrared Spectroscopy of Guanine–Cytosine Base Pairs in DNA Oligomers

NH and OH stretching excitations of hydrated double-stranded DNA oligomers containing guanine-cytosine (GC) base pairs in a Watson-Crick geometry are studied by two-dimensional (2D) infrared spectroscopy. The 2D spectra measured at a low hydration level (∼4 water molecules/base pair) are dominated by NH stretch contributions from the NH2 groups of G and C and the NH group of G. Partially hydrated NH2 groups display red-shifted NH stretch frequencies and a mixing of the wave functions of the two local NH oscillators via the mechanical vibrational coupling. The NH stretch lifetimes are of the order of 200-300 fs. Weak couplings exist between NH stretch oscillators within a base pair, while interactions between neighboring GC pairs in the double helix are negligible. The absence of spectral diffusion on a 1 ps time scale suggests a relatively rigid structure of the hydrogen bonds between DNA and residual water molecules. 2D spectra recorded with fully hydrated DNA oligomers exhibit NH and OH stretch contributions with a weak influence of water fluctuations on the NH stretch lineshapes. The femtosecond spectral diffusion of OH stretch excitations is slower than that in bulk H2O and originates from structural fluctuations of the water shell and the formation of a vibrationally hot ground state by vibrational relaxation. We compare our findings with measurements on hydrated adenine-thymine DNA oligomers and anhydrous GC base pairs in solution.

Quantum Chemical Analysis about Deprotonation Reaction of Sulfonic Group of Perfluorosulfonic Acid Species in the Low Hydration Level

In this study, we focused on the chemical feature about sulfonic group of perfluorosulfonic acid (PFSA) by first principle calculation in low hydration levels. Our study could elucidate two facts about the chemical property of PFSA, the one is why deprotonation reaction of sulfonic group of PFSA is not occurred in hydration level one and two and the other is notable feature of deprotonation reaction in hydration level three by B3LYP/6-311+G(d,p) level calculation. In the hydration level three, activation energy of deprotonation reaction of sulfonic group was 0.70 kcal/mol. Although this activation energy includes computational error, it is considered that this deprotonation reaction would proceed in the operation temperature of polymer electrolyte fuel cell smoothly. And total energy of product was lower than the reactant by 3.72 kcal/mol. From these results, deprotonation reaction of sulfonic group in hydration level three would proceed to product efficiently. In addition, reverse reaction is hard to occur by the thermal energy of 350 K which is operation temperature of polymer electrolyte fuel cell.

FTIR Analysis of the State of Water in Radiation Grafted ETFE Anion Exchange Membrane for Fuel Cell Applications

Infrared study of water in a poly(ethylene-co-tetrafuloroethylene) anion exchange membrane at different level of hydration (%RH 0, 25, 50, 75 and 100) was performed using a Fourier transform infrared (FTIR) microscope. FTIR spectra showed at least two different states of water present in the membrane. The presence of both the non-hydrogen bonded water molecules at the lower hydration level and the hydrogen bonded water molecules at the higher hydration level, unambiguously, are altered with changing humidity.