Local chemistry of the surfactant's head groups determines protein stability in reverse micelles.

When comparing protein folding in vitro and in vivo significant differences have been found. This has been attributed to crowding and confinement effects. Using a combination of GHz- and THz-dielectric relaxation spectroscopy and MD simulations, we studied hydration dynamics and reviewed protein stability data inside sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and cetyltrimethylammonium bromide (CTAB) reverse micelles which are model systems for confinement.

The temperature dependence of the Hofmeister series: thermodynamic fingerprints of cosolute-protein interactions.

The Hofmeister series is a universal homologous series to rank ion-specific effects on biomolecular properties such as protein stability or aggregation propensity. Although this ranking is widely used, outliers and exceptions are discussed controversially and a molecular level understanding is still lacking. Studying the thermal unfolding equilibrium of RNase A, we here show that this ambiguity arises from the oversimplified approach to determine the ion rankings.

Dissecting ion-specific from electrostatic salt effects on amyloid fibrillation: A case study of insulin.

Diseases like Alzheimer, type II diabetes mellitus, and others go back to fibril formation of partially unfolded proteins. The impact of sodium, potassium, choline, guanidinium, and 1-ethyl-3-methylimidazolium chloride on the fibrillation kinetics of insulin in an acid-denaturing solvent environment is studied by fluorescence spectroscopy using thioflavin T as a fibril-specific stain. The fibrillation kinetics reveal a sigmoidal behavior, characterized by the lag time τlag and the maximum elongation rate k of the fibrils.

Orientational alignment of amyloidogenic proteins in pre-aggregated solutions.

In the present study we combine dielectric relaxation spectroscopy with generalized Born simulations to explore the role of orientational order for protein aggregation in solutions of bovine pancreatic insulin at various pH conditions. Under aggregation-prone conditions at low pH, insulin monomers prefer antiparallel dipole alignments, which are consistent with the orientation of the monomeric subunits in the dimer structure. This alignment is also true for two dimers, suggesting that already at moderate protein concentrations the species assemble in equilibrium clusters, in which the molecules adopt preferred orientations also found for the protomers of the corresponding oligomers.

Relaxation stretching, fast dynamics, and activation energy: a comparison of molecular and ionic liquids as revealed by depolarized light scattering.

Depolarized light scattering (DLS) spectra of a series of 16 molecular and 6 room temperature ionic liquids are investigated by applying tandem-Fabry-Pérot interferometry, double monochromator, and photon correlation spectroscopy. Temperatures up to well above the melting point, in some cases, even up to the boiling point, are covered, and all liquids can be supercooled. The accessed time constants are between 1 ps and 10 ns; in some cases, even longer times are reached.

Pair dynamics and the intermolecular nuclear Overhauser effect (NOE) in liquids analysed by simulation and model theories: application to an ionic liquid.

Combining simulation and model theories, this paper analyses the impact of pair dynamics on the intermolecular nuclear Overhauser effect (NOE) in liquids. For the first time, we give a distance resolved NOE. When applied to the ionic liquid 1-ethyl-3-methyl-imidazolium tetrafluoroborate the NOE turns out to be of long-range nature.

The ion speciation of ionic liquids in molecular solvents of low and medium polarity.

The ion speciation of ionic liquids dissolved in molecular liquids of low and medium polarity is studied experimentally and theoretically. The ion speciation in some representative systems is characterized by dielectric relaxation spectroscopy and electrical conductance measurements. A corresponding-states approach is used to compare the experimental results with predictions for a reference system of charged hard spheres in a dielectric continuum.

Steering the enzymatic activity of proteins by ionic liquids. A case study of the enzyme kinetics of yeast alcohol dehydrogenase.

We explore ion-specific effects exerted by ionic liquids (ILs) on the enzyme kinetics of yeast alcohol dehydrogenase. The Michaelis-Menten reaction scheme is used to parameterize the observed kinetics in terms of the apparent dissociation constant of the substrate (Michaelis-Menten constant) K(M), the turnover number k(cat), which reflects the number of product molecules per enzyme molecule per second, and the enzymatic efficiency k(cat)/K(M) of the reaction. Results for fifteen salts are used to deduce Hofmeister anion and cation series.

How ionic liquids can help to stabilize native proteins.

The native state of a globular protein is essential for its biocatalytic function, but is marginally stable against unfolding. While unfolding equilibria are often reversible, folding intermediates and misfolds can promote irreversible protein aggregation into amorphous precipitates or highly ordered amyloid states. Addition of ionic liquids-low-melting organic salts-offers intriguing prospects for stabilizing native proteins and their enzymatic function against these deactivating reaction channels.

Ion speciation driving chirality transfer in imidazolium-based camphorsulfonate ionic liquid solutions.

The underlying principle of the chirality transfer in imidazolium-based camphorsulfonate ionic liquids is rationalized by linking catalytic results from the hydrogenation of [N-(3'-oxobutyl)-N-methylimidazolium] [(+)-camphorsulfonate] to [N-(3'-hydroxybutyl)-N-methylimidazolium] [(+)-camphorsulfonate] in tetrahydrofuran with electrolyte theory by the help of dielectric relaxation spectroscopy. Using this approach we are able to explain why the maximum of the enantiomeric excess of the hydrogenation reaction in tetrahydrofuran is found at a medium concentration of 0.15 mol L(-1), whereas it declines at both, lower and higher concentrations.

Synthesis of room-temperature ionic liquids with the weakly coordinating [Al(ORF)4]- anion (RF=C(H)(CF3)2) and the determination of their principal physical properties.

A large series of ionic liquids (ILs) based on the weakly coordinating alkoxyaluminate [Al(hfip)(4)](-) (hfip: hexafluoroisopropoxy) with classical as well as functionalized cations were prepared, and their principal physical properties determined. Melting points are between 0 ([C(4)MMIM][Al(hfip)(4)]) and 69 °C ([C(3)MPip][Al(hfip)(4)]); three qualify as room-temperature ILs (RTILs). Crystal structures for six ILs were determined; their structural parameters and anion-cation contacts are compared here with known ILs, with a special focus on their influence on physical properties.

Communication: Are hydrodynamic models suited for describing the reorientational dynamics of ions in ionic liquids? A case study of methylimidazolium tetra(hexafluoroisopropoxy)aluminates.

We report on dielectric relaxation spectra of six homologous ionic liquids (ILs) with tetra(hexafluoroisopropoxy)aluminate ([Al(hfip)(4)](-)) as a common anion. The dominating mode on the time scale of several 100 ps mainly results from cation reorientation. Because the viscosities are low and cation modification does not substantially change the viscosity, these ILs are interesting candidates for testing hydrodynamic models of rotational dynamics.

Communications: Polarity fluctuations of the protic ionic liquid ethylammonium nitrate in the terahertz regime.

We have measured the complex dielectric function of the protic ionic liquid ethylammonium nitrate in the frequency range between 0.15 and 1.8 THz with a terahertz time domain spectrometer.

Patterns of protein unfolding and protein aggregation in ionic liquids.

The objective of this study is to characterize the effect of ionic liquids (ILs) on the stability of proteins with regard to denaturation, protein aggregation and the formation of folding intermediates. Ribonuclease A was used as a model protein. A variety of ILs were tested.

Application of a new statistical mechanical model for calculating Kirkwood factors in self associating liquid systems to alkanol + CCl4 mixtures.

A recently developed statistical-mechanical model for calculating Kirkwood correlation factors g(K) in self associating liquids and liquid mixtures has been applied for the simultaneous description of g(K) derived from dielectric constant data, the molar enthalpy of mixing H, and the infrared absorbtion of monomeric alcoholic species as function of the composition in alkanol + CCl(4) mixtures. The alkanols are methanol, ethanol, propanol, butan-1-ol, pentan-1-ol, hexan-1-ol, octan-1-ol, sec-butanol, tert-butanol and pentan-3-ol. The majority of parameters involved in the theory are obtained by independent quantum mechanical ab initio calculations of molecular clusters consisting of up to four alcohol molecules.

Solvation dynamics of model peptides probed by terahertz spectroscopy. Observation of the onset of collective network motions.

We have studied the solvation of model peptides at low hydration levels by terahertz absorption spectroscopy. We have recorded the concentration-dependent terahertz absorption coefficients of N-acetyl-glycine-amide (NAGA), N-acetyl-glycine-methylamide (NAGMA), N-acetyl-leucine-amide (NALA), N-acetyl-leucine-methylamide (NALMA), and N-acetyl-tryptophan-amide (NATA) in aqueous solution. We find a dramatic decrease in the THz absorption, if the number of water molecules per solute is less than 18-20.

Small-angle X-ray scattering and near-infrared vibrational spectroscopy of water confined in aerosol-OT reverse micelles.

The state of water confined in Aerosol-OT-hydrocarbon-water reverse micelles with cyclohexane, n-pentane, n-octane, and n-dodecane as apolar solvents is investigated by small-angle X-ray scattering and near-infrared vibrational spectroscopy of the first overtone of the OH stretching mode of water. The experiments focus on water/AOT molecular ratios W(0)=2-20, where water is strongly affected by the confinement and surface-water interactions. The pair-distance distribution functions derived from the small-angle scattering patterns allows a detailed characterization of the topology of these systems, and they indicate deviations from monodisperse, spherical water pools for some of these hydrocarbon systems.

Hydration dynamics of water near an amphiphilic model peptide at low hydration levels: a dielectric relaxation study.

A dielectric relaxation study of aqueous solutions of the amphiphilic model peptide N-acetyl-leucine amide (NALA) at 298 K over a wide range of hydration levels is presented. The experiments range from states where water builds up several hydration layers to states where single water molecules or small water clusters are shared by several NALA molecules. The dielectric spectra reveal two modes on the 10 and 100 ps timescales.

Understanding ionic liquids at the molecular level: facts, problems, and controversies.

Ionic liquids (ILs) are organic salts with melting points near room temperature (or by convention below 100 degrees C). Recently, their unique materials and solvent properties and the growing interest in a sustainable, "green" chemistry has led to an amazing increase in interest in such salts. A huge number of potential cation and anion families and their many substitution patterns allows the desired properties for specific applications to be selected.

Memory deficits among alcoholics: performance on a selective reminding task.

This article compared alcoholics and healthy controls on the Buschke Selective Reminding Task. Alcoholics demonstrated deficits in memory and learning when compared to healthy controls, even when controlling for age. Examination of the alcoholic sample initially showed that age predicted memory deficits; however, age was no longer a significant predictor once the number of years of heavy drinking was entered into the regression equation.

Collective rotational dynamics in ionic liquids: a computational and experimental study of 1-butyl-3-methyl-imidazolium tetrafluoroborate.

The aim of this study is the analysis of the rotational motion in ionic liquids, in particular, 1-butyl-3-methyl-imidazolium tetrafluoroborate. By comparing single-particle and collective motion it is found that the Madden-Kivelson relation is fairly fulfilled in long-term simulation studies (>100 ns), i.e.