The relationship between charge and molecular dynamics in viscous acid hydrates.

Oscillatory shear rheology has been employed to access the structural rearrangements of deeply supercooled sulfuric acid tetrahydrate (SA4H) and phosphoric acid monohydrate, the latter in protonated (PA1H) and deuterated (PA1D) forms. Their viscoelastic responses are analyzed in relation to their previously investigated electric conductivity. The comparison of the also presently reported dielectric response of deuterated sulfuric acid tetrahydrate (SA4D) and that of its protonated analog SA4H reveals an absence of isotope effects for the charge transport in this hydrate. This finding clearly contrasts with the situation known for PA1H and PA1D. Our analyses also demonstrate that the conductivity relaxation profiles of acid hydrides closely resemble those exhibited by classical ionic electrolytes, even though the charge transport in phosphoric acid hydrates is dominated by proton transfer processes. At variance with this dielectric simplicity, the viscoelastic responses of these materials depend on their structural compositions. While SA4H displays a "simple liquid"-like viscoelastic behavior, the mechanical responses of PA1H and PA1D are more complex, revealing relaxation modes, which are faster than their ubiquitous structural rearrangements. Interestingly, the characteristic rates of these fast mechanical relaxations agree well with the characteristic frequencies of the charge rearrangements probed in the dielectric investigations, suggesting appearance of a proton transfer in mechanical relaxation of phosphoric acid hydrates. These findings open the exciting perspective of exploiting shear rheology to access not only the dynamics of the matrix but also that of the charge carriers in highly viscous decoupled conductors.

Tuning the dynamics of imidazolium-based ionic liquids via hydrogen bonding. I. The viscous regime.

Combining results from impedance spectroscopy and oscillatory shear rheology, the present work focuses on the relation between the mass and charge flows and on how these are affected by the H-bonding in viscous ionic liquids (ILs). In particular, we compare the relaxational behaviors of the paradigmatic IL 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) and its OH-functionalized counterpart 1-(2-hydroxyethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (OHEMIM-TFSI). Our results and their analysis demonstrate that the presence of cationic OH-groups bears a strong impact on the overall dynamics of OHEMIM-TFSI, although no signatures of suprastructural relaxation modes could be identified in their dielectric and mechanical responses. To check whether at the origin of this strong variation is the H-bonding or merely the difference between the corresponding cation sizes (controlling both the hydrodynamic volume and the inter-charge distance), the present study includes 1-propyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (PMIM-TFSI), mixtures of EMIM-TFSI and PMIM-TFSI with lithium bis(trifluoromethylsulfonyl)imide (Li-TFSI), and mixtures of OHEMIM-TFSI with PMIM-TFSI. Their investigation clearly reveals that the dynamical changes induced by H-bonding are significantly larger than those that can be attributed to the change in the ion size. Moreover, in the mixtures of OHEMIM-TFSI with PMIM-TFSI, a dilution of the OH-groups leads to strong deviations from ideal mixing behavior, thus highlighting the common phenomenological ground of hydroxy-functionalized ILs and other H-bonded liquids.

Structure and dynamics of short-chain polymerized ionic liquids.

Combining experimental results obtained with X-ray scattering and field-gradient nuclear magnetic resonance (NMR) and an assessment of new and previous dielectric and rheology data, our study focuses on the molecular weight (Mw) evolution of local structure and dynamics in a homologous series of covalently bonded ionic liquids. Performed on a family of electrolytes with a tailored degree of ionic decoupling, this study reveals the differences between monomeric and oligomeric melts with respect to their structural organization, mass and charge transport, and molecular diffusion. Our study demonstrates that for the monomeric compound, the broadband conductivity and mechanical spectra reflect the same underlying distribution of activation barriers and that the Random Barrier Model describes fairly well both the ionic and structural relaxation processes in these materials. Moreover, the oligomers with chains comprising ten segments only exhibit both structural and dynamical fingerprints of a genuine polymer. A comparison of conductivity levels estimated using the self-diffusion coefficients probed via NMR and those probed directly with dielectric spectroscopy reveals the emerging of ion correlations which are affecting the macroscopic charge transport in these materials in a chain-length dependent manner.

Influence of Chain Rigidity and Dielectric Constant on the Glass Transition Temperature in Polymerized Ionic Liquids.

Polymerized ionic liquids (PolyILs) are promising candidates for a wide range of technological applications due to their single ion conductivity and good mechanical properties. Tuning the glass transition temperature (Tg) in these materials constitutes a major strategy to improve room temperature conductivity while controlling their mechanical properties. In this work, we show experimental and simulation results demonstrating that in these materials Tg does not follow a universal scaling behavior with the volume of the structural units Vm (including monomer and counterion). Instead, Tg is significantly influenced by the chain flexibility and polymer dielectric constant. We propose a simplified empirical model that includes the electrostatic interactions and chain flexibility to describe Tg in PolyILs. Our model enables design of new functional PolyILs with the desired Tg.

Quantum effects in dynamics of water and other liquids of light molecules.

Nuclear quantum effects in atomic motions are well known at low temperatures [Formula: see text] K, but analyses of structural relaxation in liquids and description of the glass transition traditionally neglect quantum effects at higher temperatures, [Formula: see text] K. Recent studies, however, suggested that nuclear quantum effects in systems of light molecules (e.g., water) might play an important role in structural dynamics and provide non-negligible contributions at such temperatures, and even up to ambient temperature. In this article, we discuss experimental evidences of the quantum effects in glass transition in liquids of light molecules and possible theoretical descriptions of these effects. We show that quantum effects may qualitatively change the temperature behavior of the structural relaxation time in supercooled liquids leading to deviations of some well-established properties of the glass transition when it happens at low temperatures. We also demonstrate that unusual behavior of water dynamics at low temperatures, including apparent fragile-to-strong crossover, can be ascribed to nuclear quantum effects.

Role of quantum fluctuations in structural dynamics of liquids of light molecules.

A possible role of quantum effects, such as tunneling and zero-point energy, in the structural dynamics of supercooled liquids is studied by dielectric spectroscopy. The presented results demonstrate that the liquids, bulk 3-methyl pentane and confined normal and deuterated water, have low glass transition temperature and unusually low for their class of materials steepness of the temperature dependence of structural relaxation (fragility). Although we do not find any signs of tunneling in the structural relaxation of these liquids, their unusually low fragility can be well described by the influence of the quantum fluctuations. Confined water presents an especially interesting case in comparison to the earlier data on bulk low-density amorphous and vapor deposited water. Confined water exhibits a much weaker isotope effect than bulk water, although the effect is still significant. We show that it can be ascribed to the change of the energy barrier for relaxation due to a decrease in the zero-point energy upon D/H substitution. The observed difference in the behavior of confined and bulk water demonstrates high sensitivity of quantum effects to the barrier heights and structure of water. Moreover, these results demonstrate that extrapolation of confined water properties to the bulk water behavior is questionable.

Proton Conductivity in Phosphoric Acid: The Role of Quantum Effects.

Phosphoric acid has one of the highest intrinsic proton conductivities of any known liquids, and the mechanism of this exceptional conductivity remains a puzzle. Our detailed experimental studies discovered a strong isotope effect in the conductivity of phosphoric acids caused by (i) a strong isotope shift of the glass transition temperature and (ii) a significant reduction of the energy barrier by zero-point quantum fluctuations. These results suggest that the high conductivity in phosphoric acids is caused by a very efficient proton transfer mechanism, which is strongly assisted by quantum effects.

Why many polymers are so fragile: A new perspective.

Many polymers exhibit much steeper temperature dependence of their structural relaxation time (higher fragility) than liquids of small molecules, and the mechanism of this unusually high fragility in polymers remains a puzzle. To reveal additional hints for understanding the underlying mechanism, we analyzed correlation of many properties of polymers to their fragility on example of model polymer polystyrene with various molecular weights (MWs). We demonstrate that these correlations work for short chains (oligomers), but fail progressively with increase in MW. Our surprising discovery is that the steepness of the temperature dependence (fragility) of the viscosity that is determined by chain relaxation follows the correlations at all molecular weights. These results suggest that the molecular level relaxation still follows the behavior usual for small molecules even in polymers, and its fragility (chain fragility) falls in the range usual for molecular liquids. It is the segmental relaxation that has this unusually high fragility. We speculate that many polymers cannot reach an ergodic state on the time scale of segmental dynamics due to chain connectivity and rigidity. This leads to sharper decrease in accessible configurational entropy upon cooling and results in steeper temperature dependence of segmental relaxation. The proposed scenario provides a new important insight into the specifics of polymer dynamics: the role of ergodicity time and length scale. At the end, we suggest that a similar scenario can be applicable also to other molecular systems with slow intra-molecular degrees of freedom and to chemically complex systems where the time scale of chemical fluctuations can be longer than the time scale of structural relaxation.

Mechanism of Conductivity Relaxation in Liquid and Polymeric Electrolytes: Direct Link between Conductivity and Diffusivity.

Combining broadband impedance spectroscopy, differential scanning calorimetry, and nuclear magnetic resonance we analyzed charge and mass transport in two polymerized ionic liquids and one of their monomeric precursors. In order to establish a general procedure for extracting single-particle diffusivity from their conductivity spectra, we critically assessed several approaches previously employed to describe the onset of diffusive charge dynamics and of the electrode polarization in ion conducting materials. Based on the analysis of the permittivity spectra, we demonstrate that the conductivity relaxation process provides information on ion diffusion and the magnitude of cross-correlation effects between ionic motions. A new approach is introduced which is able to estimate ionic diffusivities from the characteristic times of conductivity relaxation and ion concentration without any adjustable parameters. This opens the venue for a deeper understanding of charge transport in concentrated and diluted electrolyte solutions.

Correlation between temperature variations of static and dynamic properties in glass-forming liquids.

Detailed analysis of the static structure factor S(Q) in several glass-forming liquids reveals that the temperature variations of the width of the main diffraction peak ΔQ(T) correlate with the fragility of these liquids. This observation suggests a direct connection between rather subtle structural changes and sharp slowing down of structural relaxation in glass-forming liquids. We show that this observation can be rationalized using the Adam-Gibbs approach, through a connection between temperature variations of structural correlation length, l_{c}∼2π/ΔQ, and the size of cooperatively rearranging regions.

Protein dynamics: from rattling in a cage to structural relaxation.

We present an overview of protein dynamics based mostly on results of neutron scattering, dielectric relaxation spectroscopy and molecular dynamics simulations. We identify several major classes of protein motions on the time scale from faster than picoseconds to several microseconds, and discuss the coupling of these processes to solvent dynamics. Our analysis suggests that the microsecond backbone relaxation process might be the main structural relaxation of the protein that defines its glass transition temperature, while faster processes present some localized secondary relaxations. Based on the overview, we formulate a general picture of protein dynamics and discuss the challenges in this field.

[DIETARY SUPPLEMENT REKECEN IMPROVES SAFETY AND EFFICACY OF CHRONIC PROSTATITIS ANTIBACTERIAL THERAPY].

This randomized comparative study was carried out to estimate efficacy and safety of the natural complex of fermented food fibers and short chain fatty acids (dietary supplement rekicen-RD®) in antibacterial therapy of 64 patients with chronic infectious prostatitis. 32 patients of the treatment group received 8 week standard antibacterial therapy for chronic prostatitis in combination with dietary supplement rekicen-RD® and 32 patients of the control group were treated only with antibacterial therapy. Short-term and long-term results were estimated after 8 weeks and 6 months follow-up, respectively. It was found, that addition of dietary supplement rekicen- RD® to antibacterial therapy resulted in statistically significant improvement of the treatment efficacy. Compared to patients of the control group, patients of the treatment group had more pronounced positive changes of all indicators of treatment efficacy (NIH-CPSI total score, quality of life, echo-structure of prostate, the number of leukocytes in prostatic secretions). Long-term (after 6 months) clinical efficacy of the combination of antibacterial therapy with dietary supplement rekicen-RD® was 96,9%, bacteriological efficacy after 8 weeks - 87,5%, after 6 months - 81%. Notably, there was 4,5-fold reduction in the rate of antibiotics adverse side effects in the treatment group patients without a single gastro-intestinal side effect.

[Properties of unrelated salicylate hydroxylases in bacteria of the genus pseudomon].

The unrelated salicylate hydroxylases NahG and NahU of the strains Pseudomonasfluorescens 142 NF and P. Putida BS3701 were extracted and purified by ion-exchange and hydrophobic and gel permeation chromatography. The extracted enzymes differed in kinetic and catalyst performance during salicylate hydrolysis. For NahU salicylate hydroxylase, Km and Vmax were found to be higher (3.1 +/- 0.6 microM and 7.7 +/- 0.4 microM/min, respectively) than for NahG salicylate hydroxylase (1.3 +/- 0.1 microM and 4.7 +/- 0.1 microM/min, respectively). The activity of both enzymes toward substituted salicylates was higher in cases where the substituent groups were in para position than in cases with those in meta position. The activity toward substituted salicylates with substituent groups in meta position was different. The activity of salicylate hydroxylase NahG was higher toward salicylates with substituent groups in position 3; salicylate hydroxylase NahU activity was higher toward those with substituent groups in position 5. This suggests a difference in the spatial configuration of active sites in extracted unrelated salicylate hydroxylases.

Quantum effects in the dynamics of deeply supercooled water.

Despite its simple chemical structure, water remains one of the most puzzling liquids with many anomalies at low temperatures. Combining neutron scattering and dielectric relaxation spectroscopy, we show that quantum fluctuations are not negligible in deeply supercooled water. Our dielectric measurements reveal the anomalously weak temperature dependence of structural relaxation in vapor-deposited water close to the glass transition temperature T(g)∼136K. We demonstrate that this anomalous behavior can be explained well by quantum effects. These results have significant implications for our understanding of water dynamics.

Qualitative change in structural dynamics of some glass-forming systems.

Analysis of the temperature dependence of the structural relaxation time τ(α)(T) in supercooled liquids revealed a qualitatively distinct feature-a sharp, cusplike maximum in the second derivative of logτ(α)(T)at some T(max). It suggests that the super-Arrhenius temperature dependence of τ(α)(T) in glass-forming liquids eventually crosses over to an Arrhenius behavior at T

Decoupling of ionic conductivity from structural dynamics in polymerized ionic liquids.

Charge transport and structural dynamics in low molecular weight and polymerized 1-vinyl-3-pentylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquids (ILs) are investigated by a combination of broadband dielectric spectroscopy, dynamic mechanical spectroscopy and differential scanning calorimetry. While the dc conductivity and fluidity exhibit practically identical temperature dependence for the non-polymerized IL, a significant decoupling of ionic conduction from structural dynamics is observed for the polymerized IL. In addition, the dc conductivity of the polymerized IL exceeds that of its molecular counterpart by four orders of magnitude at their respective calorimetric glass transition temperatures. This is attributed to the unusually high mobility of the anions especially at lower temperatures when the structural dynamics is significantly slowed down. A simple physical explanation of the possible origin of the remarkable decoupling of ionic conductivity from structural dynamics is proposed.

High pressure as a key factor to identify the conductivity mechanism in protic ionic liquids.

In this Letter we report the relation between ionic conductivity and structural relaxation in supercooled protic ionic liquids (PILs) under high pressure. The results of high-pressure dielectric and volumetric measurements, combined with rheological and temperature-modulated differential scanning calorimetry experiments, have revealed a fundamental difference between the conducting properties under isothermal and isobaric conditions for three PILs with different charge transport mechanisms (Grotthuss vs vehicle). Our findings indicate a breakdown of the fractional Stokes-Einstein relation and Walden rule when the ionic transport is controlled by fast proton hopping. Consequently, we demonstrate that the studied PILs exhibit significantly higher conductivity than one would expect taking into account that they are in fact a mixture of ionic and neutral species. Thus, the examined herein samples represent a new class of "superionic" materials desired for many advanced applications.

Effect of temperature and density fluctuations on the spatially heterogeneous dynamics of glass-forming Van der Waals liquids under high pressure.

In this Letter, we show how temperature and density fluctuations affect the spatially heterogeneous dynamics at ambient and elevated pressures. By using high-pressure experimental data for van der Waals liquids, we examine contributions of the temperature and density fluctuations to the dynamics heterogeneity. We show that the dynamic heterogeneity decreases significantly with increasing pressure at a constant structural relaxation time (isochronal condition), while the broadening of the relaxation spectrum remains constant. This observation questions the relationship between spectral broadening and dynamic heterogeneity.

Coherent neutron scattering and collective dynamics on mesoscale.

By combining, and modestly extending, a variety of theoretical concepts for the dynamics of liquids in the supercooled regime, we formulate a simple analytic model for the temperature and wavevector dependent collective density fluctuation relaxation time that is measurable using coherent dynamic neutron scattering. Comparison with experiments on the ionic glass-forming liquid Ca-K-NO3 in the lightly supercooled regime suggests the model captures the key physics in both the local cage and mesoscopic regimes, including the unusual wavevector dependence of the collective structural relaxation time. The model is consistent with the idea that the decoupling between diffusion and viscosity is reflected in a different temperature dependence of the collective relaxation time at intermediate wavevectors and near the main (cage) peak of the static structure factor. More generally, our analysis provides support for the ideas that decoupling information and growing dynamic length scales can be at least qualitatively deduced by analyzing the collective relaxation time as a function of temperature and wavevector, and that there is a strong link between dynamic heterogeneity phenomena at the single and many particle level. Though very simple, the model can be applied to other systems, such as molecular liquids.

Role of quantum effects in the glass transition.

It is shown that quantum effects lead to a significant decrease of the glass transition temperature T(g) with respect to the melting temperature T(m), so that the ratio T(g)/T(m) can be much smaller than the typical value of 2/3 in materials where T(g) is near or below ~60 K. Furthermore, it is demonstrated that the viscosity or structural relaxation time in such low temperature glass formers should exhibit highly unusual temperature dependence, namely a decrease of the apparent activation energy upon approaching T(g) (instead of traditional increase).