Changes In Hydration Structure Research Articles

Influence of TMAO and Pressure on the Folding Equilibrium of TrpCage.

Trimethylamine-N-oxide (TMAO) is an osmolyte known for its ability to counteract the pressure denaturation of proteins. Computational studies addressing the molecular mechanisms of TMAO's osmolyte action have however focused exclusively on its protein-stabilizing properties at ambient pressure, neglecting the changes that may occur under high-pressure conditions where TMAO's hydration structure changes to that of increased water binding. Here, we present the first study on the combined effect of pressure and TMAO on a mini-protein, TrpCage. The results showed that at high pressures, nonpolar residues packed less tightly and the salt bridge of TrpCage was destabilized. This effect was mitigated by TMAO which was found to be strongly depleted from the protein/water interface at 1 kbar than at 1 bar ambient pressure, thus counterbalancing the thermodynamically unfavorable effect of elevated pressure in the free energy of folding. TMAO was depleted from charged groups, like the salt bridge-forming ones, and accumulated around hydrophobic groups. Still, it stabilized both kinds of interactions. Furthermore, enthalpically favorable TrpCage-water hydrogen bonds were reduced in the presence of TMAO, causing a stronger destabilization of the unfolded state than the folded state. This shifted the protein-folding equilibrium toward the folded state. Therefore, TMAO showed stabilizing effects on different kinds of groups, which were partially enhanced at high pressures.

Differentiating the Structure and Dynamics of Solute-Bound Vs. Bulk Water in Deep-Eutectic Aqueous AlCl3 Solutions

Aqueous solutions of aluminum chloride exhibit a deep eutectic (-52˚C) that is likely due to solute-directed formation of complex network structures in the solvent. It is well known that the solute-bound solvent must have a distinct chemical environment from that of the bulk solvent. Commonly used vibrational spectroscopic measurements of aqueous salt solutions are not selective enough to directly identify distinct water environments in solution. However, variable-temperature 1H-NMR spectroscopy of aqueous solutions, specifically those with high charge density salts, can distinguish water directly bound to the cation from water of the bulk solution. This unique ability to resolve characteristic water peaks by NMR spectroscopy affords the opportunity to explore the hydration structure and dynamics of deep-eutectic aqueous solutions. The aqueous AlCl3 system is an excellent model to study solution structure since we can exploit the high charge density of the ions for which strong ion-dipole interactions are structure-directing to the solvent waters, allowing resolution of distinct water chemical environments. We conducted a thorough investigation of the composition- and temperature-dependent solution structure of the AlCl3 : water system using 1H-NMR spectroscopy, and X-ray and neutron diffraction. The room-temperature proton chemical shift of water proceeds downfield with increasing salt concentration until AlCl3•22H2O, the eutectic composition, after which further increasing concentration results in an upfield chemical shift (see Figure.) Using VT-NMR, we can resolve the first-nearest neighbor water signals from the bulk signal upon cooling. 1H-NMR T1 and T2 relaxation measurement of the distinct water environments reveal stark differences in proton mobility for compositions on the water-rich versus AlCl3-rich sides of the eutectic, implying significant changes in hydration structure. To evaluate the extent to which these changes are structural, a parallel set of composition- and temperature-dependent neutron and X-ray diffraction experiments demonstrate that both cations and anions exhibit significant structure-directing influences on the solution, which we hypothesize underlies deep eutectic behavior in aqueous solutions. Figure 1

From amino acids to dipeptide: The changes in thermal stability and hydration properties of β-alanine, L-histidine and L-carnosine

The changes in hydration structure of β-alanine and L-histidine through dipeptide formation were studied and discussed from experimentally measured values of densities, viscosities and computational investigations of amino acids diluted aqueous solutions, β-alanine and L-histidine, and the final dipeptide, L-carnosine over the temperature range from 283.15 K to 313.15 K. The apparent molar volume (Vϕ), apparent molar volume at infinite dilution (Vϕo), Masson's experimental slope (Sv), limiting apparent molar expansibility, (Eϕo), Hepler's coefficient, hydration number, and viscosity B coefficient have been evaluated using the experimental density and viscosity values. The formation of the peptide bond has been examined in terms of water structuring nature around dipeptide and starting amino acids, and how it is linked with dipeptide self-interactions. Also, L-carnosine solubility in water was determined, as well as the thermal decomposition of the investigated compounds was examined by simultaneous thermogravimetric (TG) and DSC measurement. For the evaluation of their decomposition, the data obtained by coupled TG–mass spectrometric (MS) measurements were used.

Hydration Structures and Water Chemistry at Zirconia-Water Interface

The life cycle of zirconium cladding is a key safety factor and design parameter for higher fuel burnups in pressurized water reactors. The degradation of the metal alloy is primarily attributed to interactions of native oxide with water. Here we probe the detailed interfacial hydration structures at the 8 mol% yttria-stabilized cubic zirconia (YSZ) surfaces as a model system using synchrotron-based high-resolution X-ray reflectivity technique. Interfacial hydration structures in the major crystallographic orientations, (100), (110), and (111), were determined with sub-angstrom resolution and compared with each other to identify common features as well as different surface chemistry effects on the interfacial processes. All three surfaces terminate with significant number of point defects originating from the metal depletion and the intrinsic oxygen vacancies. Water molecules fill those vacancies, forming an ordered, layered structure on the top surface. Above the termination layer on each surface, two additional adsorbed layers form characteristic interfacial hydration structures. The first adsorbed layers likely include metal species based on the observed local densities, whereas the second layers consist of pure water. The current results provide valuable references for future studies of water chemistry effect on the interfacial hydration structure and the high temperature stability test of the zirconia in pressurized water conditions simulating realistic environment in pressurized water reactors of nuclear power plants. We also studied the effect of zinc adsorption on the interfacial hydration structure in zinc acetate solutions. Zinc injection into the reactor coolant system has been known to be effective in reducing the radioactive wastes as well as stabilizing crud oxide layers of the cladding materials. Our X-ray reflectivity data qualitatively reveal that there are obvious hydration structure changes at (100) and (111) surfaces while (110) surface show little changes. The interfacial electron density profiles were derived from the structure factor analysis of the measured reflectivity data. The structure factor analysis indicated an inner-sphere adsorption of Zn2+ layer at YSZ (111)-water interface, while there appeared to be an outer-sphere adsorption of Zn2+ layer at YSZ (100)-water interface. We further confirmed the detailed element specific adsorption profile of Zn2+ ions on YSZ (110) and (111)-water interfaces with resonant anomalous X-ray reflectivity measurements.

Changes in hydration structure are necessary for collective motions of a multi-domain protein.

Conformational motions of proteins are necessary for their functions. To date, experimental studies measuring conformational fluctuations of a whole protein structure have revealed that water molecules hydrating proteins are necessary to induce protein functional motions. However, the underlying microscopic mechanism behind such regulation remains unsolved. To clarify the mechanism, multi-domain proteins are good targets because it is obvious that water molecules between domains play an important role in domain motions. Here, we show how changes in hydration structure microscopically correlate with large-amplitude motions of a multi-domain protein, through molecular dynamics simulation supported by structural analyses and biochemical experiments. We first identified collective domain motions of the protein, which open/close an active-site cleft between domains. The analyses on changes in hydration structure revealed that changes in local hydration in the depth of the cleft are necessary for the domain motion and vice versa. In particular, ‘wetting’/‘drying’ at a hydrophobic pocket and ‘adsorption’/‘dissociation’ of a few water molecules at a hydrophilic crevice in the cleft were induced by dynamic rearrangements of hydrogen-bond networks, and worked as a switch for the domain motions. Our results microscopically demonstrated the importance of hydrogen-bond networks of water molecules in understanding energy landscapes of protein motions.

High-pressure protein crystallography of hen egg-white lysozyme.

Crystal structures of hen egg-white lysozyme (HEWL) determined under pressures ranging from ambient pressure to 950 MPa are presented. From 0.1 to 710 MPa, the molecular and internal cavity volumes are monotonically compressed. However, from 710 to 890 MPa the internal cavity volume remains almost constant. Moreover, as the pressure increases to 950 MPa, the tetragonal crystal of HEWL undergoes a phase transition from P43212 to P43. Under high pressure, the crystal structure of the enzyme undergoes several local and global changes accompanied by changes in hydration structure. For example, water molecules penetrate into an internal cavity neighbouring the active site and induce an alternate conformation of one of the catalytic residues, Glu35. These phenomena have not been detected by conventional X-ray crystal structure analysis and might play an important role in the catalytic activity of HEWL.

Communication: Coordination structure of bromide ions associated with hexyltrimethylammonium cations at liquid/liquid interfaces under potentiostatic control as studied by total-reflection X-ray absorption fine structure

Total-reflection X-ray absorption fine structure (TR-XAFS) technique was applied for the first time to an interface between two immiscible electrolyte solutions under potentiostatic control. The hydration structure of bromide ions was investigated at polarized 2-octanone/water interfaces. TR-XAFS spectra at Br K-edge measured in the presence of hexyltrimethylammonium bromide (C6TAB) were slightly modified depending on the Galvani potential difference (Δ(o)(w)φ). The extended X-ray absorption fine structure analysis exposed hydration structure changes of bromide ions at the polarized interface. The coordination structure of bromide ions at the interface could be analyzed as compared with bromide ions dissolved in aqueous solution and Br(-)-exchanged resin having quaternary ammonium groups. The results indicated that bromide ions were associated with C6TA(+) at the polarized interface. The relative contribution of ion association form of bromide ions with quaternary ammonium groups was enhanced at a potential close to the ion transfer of C6TA(+), where the interfacial concentration of C6TA(+) is increased as a function of Δ(o)(w)φ.

1D-RISM study of glycine zwitterion hydration and ion-molecular complex formation in aqueous NaCl solutions

Structural aspects of the hydration of glycine zwitterion (Gly-ZW) in NaCl(aq) were studied over a wide concentration range of NaCl (c=0–5M) with the 1D-RISM integral equation method. Analysis of the structural data revealed that increasing salt concentration leads only to minor changes in hydration structure of Gly-ZW with the maximum effect occurring for the NH3+ and COO− groups where the number of H-bonds is decreased. On the other hand, increasing salt concentration stimulates the formation of ion-molecular complexes like (NH3+:Cl−)aq and (COO−:Na+)aq. On the basis of the obtained data a structural mechanism for this process is suggested.

Hydration structure changes around proteins at work

Hydration structure changes around proteins at work

Proton transfer pathways in the mutant His‐64–Ala of human carbonic anhydrase II

We have investigated the possible proton transfer pathways from the surface of the protein to the zinc-bound water molecule in the mutant His-64-Ala of human carbonic anhydrase II. Starting with an input of known crystallographic structures of the mutant, we model the proton pathways as hydrogen-bonded networks of proton conducting groups and bound solvent molecules. No proton path is detected in the mutant, in close agreement with the experimental observation of a 20-fold decrease in its catalytic efficiency compared to the wild-type enzyme. We also investigate in detail changes in hydration structure at the active site of the mutant and the resulting proton paths in the presence of an exogenous proton donor 4-methylimidazole (4-MI). The proton transfer pathways thus detected are correlated to the observed chemical rescue of catalytic activity by 4-MI.

The effects of temperature on the hydration structure around Ni2+ in concentrated aqueous solution

A preliminary investigation has been made of the effects of temperature on the hydration structure around Ni2+ in a concentrated (nominally 4 m) aqueous solution of nickel (II) chloride using the technique of neutron diffraction with isotope substitution. The scattering from two heavy water solutions containing, respectively, nickel in natural abundance and enriched in the Ni62 isotope, were measured at temperatures of 90, 175, and 230 °C using the general liquids and amorphous materials diffractometer at the intense pulsed neutron source, Argonne National Laboratory. The Ni2+ hydration structure was seen to become progressively weaker and broader with increasing temperature, consistent with the findings of previous experiments. A more subtle effect of temperature on hydration structure has also been highlighted for the first time, namely, gradual shifts in the first hydration peak positions in the real-space difference function. Our findings point to the importance of following changes in hydration structure closely by measuring as many state points as possible, and the desirability of complementary approaches such as EXAFS (extended x-ray absorption fine structure) and quasielastic neutron scattering. Our initial study has also demonstrated the successful performance of a new sample cell designed at Oak Ridge National Laboratory for handling corrosive aqueous solutions under conditions of elevated temperatures and pressures.

Difference Spatial Distribution Function Analysis of Aqueous Solutions. IV. Hydration Structure Changes of Ethylene Glycol Solutions throughout Conformational Change Process from gGg' to tGg' Conformers.

Monte Carlo (MC) simulations were carried out for an infinitely dilute aqueous solution of two stable conformers (gGg' and tGg') and of three conformations between gGg' and tGg' conformers of ethylene glycol (EG) at 298K. Based on the spatial distribution function (SDF) goo(x,y,z), obtained from the MC simulation in the above conformations in liquid water, the high distribution of hydration water molecules could be divided into hydrogen acceptor (HA), hydrogen donor (HD), MIX (overlapped distribution of HA and HD), and hydrophobic hydration (HH) regions. The spatial orientations of hydrogen-bonded water molecules were found to be of a linear type with a triple-layer structure in the HA region and HA part (in the MIX region), and double-layer structures in the HD region and HD part (in the MIX region). In addition, it was apparent that the spatial orientations of these water molecules were of the linear type throughout the conformational change process from gGg' to tGg' conformers in liquid water. From the difference SDF (DSDF), deltagoo(x,y, z), between the SDFs of two conformations, we concluded that the distribution of hydration water molecules in the HA and HD parts of the MIX region are governed by the competition of internal hydrogen bonds between the hydrogen atom and two lone-pair electrons on the oxygen atom of an EG molecule.

Hydration of ions at various temperatures: The role of electrostriction

A new statistical approach to the electric properties of water at elevated temperatures is proposed. The local permittivity and electrostriction pressure in hydration shells of Sr2+ and Ni2+ ions at ambient conditions, and of Ni2+ ion at elevated temperatures are calculated. The insensitivity of Ni2+ hydration characteristics to the applied pressure is explained by the role played by the much higher local electrostriction pressure. A correlation between the temperatures at which destroyed hydration structures have been observed in recent neutron scattering experiments and the calculated local electrostriction pressures on the one hand, and the melting line of H2O on the other hand, is pointed out. Temperatures at which analogous changes in hydration structure may be expected are predicted for several ions.

Large hydration structure changes on hydrolysing ATP.

Es wurde die Hydrolyse von ATP in wassrigen Losungen IR-spektroskopisch untersucht. Innerhalb kleiner Hydrolysegrad-Bereiche treten enorme Veranderungen an den Banden der Wassermolekule, insbesondere an der Torsionsschwingung auf. Die Bedeutung dieses Effekts wird diskutiert.