Water Molecules In Layer Research Articles

Resolving the Negative Potential Side (n-side) Water-accessible Proton Pathway of F-type ATP Synthase by Molecular Dynamics Simulations

The rotation of F(1)F(o)-ATP synthase is powered by the proton motive force across the energy-transducing membrane. The protein complex functions like a turbine; the proton flow drives the rotation of the c-ring of the transmembrane F(o) domain, which is coupled to the ATP-producing F(1) domain. The hairpin-structured c-protomers transport the protons by reversible protonation/deprotonation of a conserved Asp/Glu at the outer transmembrane helix (TMH). An open question is the proton transfer pathway through the membrane at atomic resolution. The protons are thought to be transferred via two half-channels to and from the conserved cAsp/Glu in the middle of the membrane. By molecular dynamics simulations of c-ring structures in a lipid bilayer, we mapped a water channel as one of the half-channels. We also analyzed the suppressor mutant cP24D/E61G in which the functional carboxylate is shifted to the inner TMH of the c-protomers. Current models concentrating on the "locked" and "open" conformations of the conserved carboxylate side chain are unable to explain the molecular function of this mutant. Our molecular dynamics simulations revealed an extended water channel with additional water molecules bridging the distance of the outer to the inner TMH. We suggest that the geometry of the water channel is an important feature for the molecular function of the membrane part of F(1)F(o)-ATP synthase. The inclination of the proton pathway isolates the two half-channels and may contribute to a favorable clockwise rotation in ATP synthesis mode.

Nonequilibrium molecular dynamics simulation of water transport through carbon nanotube membranes at low pressure

Nonequilibrium molecular dynamics (NEMD) simulations are used to investigate pressure-driven water flow passing through carbon nanotube (CNT) membranes at low pressures (5.0 MPa) typical of real nanofiltration (NF) systems. The CNT membrane is modeled as a simplified NF membrane with smooth surfaces, and uniform straight pores of typical NF pore sizes. A NEMD simulation system is constructed to study the effects of the membrane structure (pores size and membrane thickness) on the pure water transport properties. All simulations are run under operating conditions (temperature and pressure difference) similar to a real NF processes. Simulation results are analyzed to obtain water flux, density, and velocity distributions along both the flow and radial directions. Results show that water flow through a CNT membrane under a pressure difference has the unique transport properties of very fast flow and a non-parabolic radial distribution of velocities which cannot be represented by the Hagen-Poiseuille or Navier-Stokes equations. Density distributions along radial and flow directions show that water molecules in the CNT form layers with an oscillatory density profile, and have a lower average density than in the bulk flow. The NEMD simulations provide direct access to dynamic aspects of water flow through a CNT membrane and give a view of the pressure-driven transport phenomena on a molecular scale.

Structural Effects of an Atomic-Level Layer of Water Molecules around Proteins Solvated in Supra-Molecular Coarse-Grained Water

Atomistic molecular dynamics simulations of proteins in aqueous solution are still limited to the multinanosecond time scale and multinanometer range by computational cost. Combining atomic solutes with a supra-molecular solvent model in hybrid fine-grained/coarse-grained (FG/CG) simulations allows atomic detail in the region of interest while being computationally more efficient. A recent comparison of the properties of four proteins in CG water versus FG water showed the preservation of the secondary and tertiary structure with a computational speed-up of at least an order of magnitude. However, an increased occurrence of hydrogen bonds between side chains was observed due to a lack of hydrogen-bonding partners in the supra-molecular solvent. Here, the introduction of a FG water layer around the protein to recover the hydrogen-bonding pattern of the atomistic simulations is studied. Three layer thicknesses of 0.2, 0.4, and 0.8 nm are considered. A layer thickness of 0.8 nm is found sufficient to recover the behavior of the proteins in the atomistic simulations, whereas the hybrid simulation is still three times more efficient than the atomistic one and the cutoff radius for nonbonded interactions could be increased from 1.4 to 2.0 nm.

Water at hydrophobic interfaces delays proton surface-to-bulk transfer and provides a pathway for lateral proton diffusion

Fast lateral proton migration along membranes is of vital importance for cellular energy homeostasis and various proton-coupled transport processes. It can only occur if attractive forces keep the proton at the interface. How to reconcile this high affinity to the membrane surface with high proton mobility is unclear. Here, we tested whether a minimalistic model interface between an apolar hydrophobic phase (n-decane) and an aqueous phase mimics the biological pathway for lateral proton migration. The observed diffusion span, on the order of tens of micrometers, and the high proton mobility were both similar to the values previously reported for lipid bilayers. Extensive ab initio simulations on the same water/n-decane interface reproduced the experimentally derived free energy barrier for the excess proton. The free energy profile G(H(+)) adopts the shape of a well at the interface, having a width of two water molecules and a depth of 6±2RT. The hydroniums in direct contact with n-decane have a reduced mobility. However, the hydroniums in the second layer of water molecules are mobile. Their in silico diffusion coefficient matches that derived from our in vitro experiments, (5.7±0.7)10(-5)cm(2)s(-1). Conceivably, these are the protons that allow for fast diffusion along biological membranes.

Regularities and mechanisms of hydrogen trapping in graphitized carbon composite upon irradiation by atoms with thermal velocities

Experiments are performed to study particle trapping in a graphitized carbon composite upon its exposure to a flux of deuterium atoms. It is shown that irradiation by deuterium atoms with thermal velocities ensures trapping according to a potential mechanism: atoms of the irradiating flux and hydrogen atoms from a layer of water molecules sorbed on the surface are both trapped. Mechanisms of trapping are discussed. Based on the experimental results, the contribution to deuterium-atom trapping in CFC irradiated in deuterium plasma is determined for each component-ions, electrons, and atoms.

1H MRI study of small-diameter silk vascular grafts in water

Small-diameter vascular grafts (VG) made from silk fibroin (SF) fibers by a double-raschel knitting method were prepared by coating their interior and exterior with different materials, such as SF or polyurethane (PU). The 1H spin density, 1H spin–spin relaxation time (T2) and diffusion coefficient (D) of the water molecules in the layer of the VG coated by these materials were non-destructively observed in water using 1H NMR imaging. The inner and outer coating materials significantly affected the amount and mobility of water molecules in the VG. The water content of the SF-coated VG was considerably higher than that of PU-coated VG. The T2 value of the water molecules in the SF-coated VG layer was smaller than that of the PU-coated VG, which means that the rotational motion of the water molecules in the layer of the SF-coated VG was restricted by the intermolecular interaction between the SF and water molecules. The diffusion coefficient (D) of the water molecules in the SF-coated VG layer was larger than that of the PU-coated VG, indicating that the water molecules were confined to the pores in the graft layer of the PU-coated VG. The images of 1H spin density, 1H T2 and diffusion coefficient (D) of water molecules in the layer of silk-based vascular grafts (VG) coated by different materials that are silk fibroin or polyurethane were non-destructively observed in water using 1H MR imaging. The inner and outer coating materials affect significantly the amount and mobility of water molecules in the VG.

Coadsorption of n-Propanol and Water on SiO2: Study of Thickness, Composition, and Structure of Binary Adsorbate Layer Using Attenuated Total Reflection Infrared (ATR-IR) and Sum Frequency Generation (SFG) Vibration Spectroscopy

The thickness and structure of the binary adsorbate layer of n-propanol and water molecules formed on fused silica at near equilibrium vapor pressure at room temperature were studied using attenuated total reflectance infrared spectroscopy (ATR-IR) and sum frequency generation (SFG) vibration spectroscopy. The thickness of the binary adsorbate layer on silica is kept relatively constant at ∼0.9 nm when the n-propanol vapor fraction (ypropanol) is between 0.6 and 1 and then gradually increases up to ∼6.5 nm as ypropanol decreases from 0.6 to 0 (ywater increasing from 0.4 to 1). The composition of the binary adsorbate layer as well as the n-propyl group at the adsorbate/air interface shows a drastic change at the azeotrope composition of the vapor mixture (ypropanol = 0.36). The binary mixture is propanol-rich at ypropanol > 0.36 and water-rich at ypropanol < 0.36, which is consistent with the vapor–liquid equilibrium. However, the vapor composition dependence of the adsorbate/air interface structure appears drastically different from that of the liquid/air interface. The n-propanol SFG signal at the adsorbate/air interface gradually decreases as ypropanol decreases from 1 and suddenly drops at ypropanol = 0.36, while the n-propanol SFG signal increases to a maximum value at ypropanol = 0.36 for the liquid/air interface. Comparison of the ATR-IR and SFG results suggests that the binary adsorbate layer of n-propanol and water assumes a layered structure in which n-propanol is at the adsorbate/vapor interface and water is inside the adsorbate layer, and unlike the liquid/vapor interface, the propanol molecules do not form a paired dimer-like structure at the adsorbate/vapor interface.

Rare‐Earth Melonates LnC6N7(NCN)3·xH2O (Ln = La, Ce, Pr, Nd, Sm, Eu, Tb; x = 8–12): Synthesis, Crystal Structures, Thermal Behavior, and Photoluminescence Properties of Heptazine Salts with Trivalent Cations

AbstractThe rare‐earth melonates LnC6N7(NCN)3·xH2O (Ln = La, Ce, Pr, Nd, Sm, Eu, Tb; x = 8–12) have been synthesized by metathesis reactions in aqueous solution and characterized by single‐crystal and powder XRD, FTIR spectroscopy, thermal analysis, and photoluminescence studies. Powder XRD patterns revealed isotypism of the La–Sm compounds. The structure of LaC6N7(NCN)3·8H2O has been solved and refined from single‐crystal diffraction data and those of the remaining salts have been refined from powder XRD data by Rietveld refinement. In the crystal structures, the melonate entities are arranged in corrugated layers, which alternate with layers of crystal water molecules. The lanthanide ions are coordinated by two melonate and six water molecules. LnC6N7(NCN)3·xH2O (Ln = Eu, Tb; x = 9–12) have also been investigated by photoluminescence studies. Neither hydrated nor dehydrated europium melonate exhibits luminescence under UV excitation, whereas photoluminescence studies of terbium melonate showed green emission with a maximum at 545 nm due to the 5D4→7F5 transition. Thermal analysis revealed rather low thermal stability of the rare‐earth melonates, which is probably due to the tight binding of crystal water that results in hydrolytic decomposition at elevated temperatures.

Free Energy Barriers for Escape of Water Molecules from Protein Hydration Layer

Free energy barriers separating interfacial water molecules from the hydration layer at the surface of a protein to the bulk are obtained by using the umbrella sampling method of free energy calculation. We consider hydration layer of chicken villin head piece (HP-36) which has been studied extensively by molecular dynamics simulations. The free energy calculations reveal a strong sensitivity to the secondary structure. In particular, we find a region near the junction of first and second helix that contains a cluster of water molecules which are slow in motion, characterized by long residence times (of the order of 100 ps or more) and separated by a large free energy barrier from the bulk water. However, these "slow" water molecules constitute only about 5-10% of the total number of hydration layer water molecules. Nevertheless, they play an important role in stabilizing the protein conformation. Water molecules near the third helix (which is the important helix for biological function) are enthalpically least stable and exhibit the fastest dynamics. Interestingly, barrier height distributions of interfacial water are quite broad for water surrounding all the three helices (and the three coils), with the smallest barriers found for those near the helix-3. For the quasi-bound water molecules near the first and second helices, we use well-known Kramers' theory to estimate the residence time from the free energy surface, by estimating the friction along the reaction coordinate from the diffusion coefficient by using Einstein relation. The agreement found is satisfactory. We discuss the possible biological function of these slow, quasi-bound (but transient) water molecules on the surface.

Free vibration of the fluid-filled single-walled carbon nanotube based on a double shell-potential flow model

A double shell-potential flow model is developed to study the free vibration of single-walled carbon nanotube (SWCNT) conveying water. Water is divided into the absorbed layer of water molecules and the water flow in the center of the SWCNT. The SWCNT and the internally absorbed layer of water are modelled as two-layer thin shells coupled via the interlayer van der Waals (vdW) interaction. It is shown that the vdW interaction is responsible for an upshift in the frequency of the SWCNT and an improvement of the system stability. Results also reveal that the internal moving water plays an important role in the instability of system whereas it has very little influence on the dynamic characteristics of the SWCNT. It is hoped that the paper can provide a new and efficient approach for the study of the general dynamic behavior of fluid-filled nanodevices.

1,4-Diazabicyclo[2.2.2]octane (DABCO) 5-aminotetrazolates

The crystal structures of four salts of 1,4-diazabicyclo[2.2.2]octane (DABCO) and 5-aminotetrazole are described. Anhydrous 1:1 (Pbca, Rgt = 0.041) and 1:2 (P, Rgt = 0.038) salts form hydrogen-bonded layers of anions and cations. The monohydrate of the 1:1 compound (P21/c, Rgt = 0.038) shows infinite chains of DABCO cations and an undulated layer of anions and water molecules. The octahydrate of the 3:2 compound (P21/c, Rgt = 0.042) features DABCO triples and clusters of four tetrazolate ions in a network of water molecules.

Nonintercalating nanosubstrates create asymmetry between bilayer leaflets.

The physical properties of lipid bilayers can be remodeled by a variety of environmental factors. Here we investigate using molecular dynamics simulations the specific effects of nanoscopic substrates or external contact points on lipid membranes. We expose palmitoyl-oleoyl phosphatidylcholine bilayers unilaterally and separately to various model nanosized substrates differing in surface hydroxyl densities. We find that a surface hydroxyl density as low as 10% is sufficient to keep the bilayer juxtaposed to the substrate. The bilayer interacts with the substrate indirectly through multiple layers of water molecules; however, despite such buffered interaction, the bilayers exhibit certain properties different from unsupported bilayers. The substrates modify transverse lipid fluctuations, charge density profiles, and lipid diffusion rates, although differently in the two leaflets, which creates an asymmetry between bilayer leaflets. Other properties that include lipid cross-sectional areas, component volumes, and order parameters are minimally affected. The extent of asymmetry that we observe between bilayer leaflets is well beyond what has been reported for bilayers adsorbed on infinite solid supports. This is perhaps because the bilayers are much closer to our nanosized finite supports than to infinite solid supports, resulting in a stronger support-bilayer electrostatic coupling. The exposure of membranes to nanoscopic contact points, therefore, cannot be considered as a simple linear interpolation between unsupported membranes and membranes supported on infinite supports. In the biological context, this suggests that the exposure of membranes to nonintercalating proteins, such as those belonging to the cytoskeleton, should not always be considered as passive nonconsequential interactions.

Density minimum of confined water at low temperatures: a combined study by small-angle scattering of X-rays and neutrons

A simple explanation is given for the low-temperature density minimum of water confined within cylindrical pores of ordered nanoporous materials of different pore size. The experimental evidence is based on combined data from in-situ small-angle scattering of X-rays (SAXS) and neutrons (SANS), corroborated by additional wide-angle X-ray scattering (WAXS). The combined scattering data cannot be described by a homogeneous density distribution of water within the pores, as was originally suggested from SANS data alone. A two-step density model reveals a wall layer covering approximately two layers of water molecules with higher density than the residual core water in the central part of the pores. The temperature-induced changes of the scattering signal from both X-rays and neutrons are consistent with a minimum of the average water density. We show that the temperature at which this minimum occurs depends monotonically on the pore size. Therefore we attribute this minimum to a liquid-solid transition of water influenced by confinement. For water confined in the smallest pores of only 2 nm in diameter, the density minimum is explained in terms of a structural transition of the surface water layer closest to the hydrophilic pore walls.

Hydration dynamics of protein molecules in aqueous solution: Unity among diversity#

Dielectric dispersion and NMRD experiments have revealed that a significant fraction of water molecules in the hydration shell of various proteins do not exhibit any slowing down of dynamics. This is usually attributed to the presence of the hydrophobic residues (HBR) on the surface, although HBRs alone cannot account for the large amplitude of the fast component. Solvation dynamics experiments and also computer simulation studies, on the other hand, repeatedly observed the presence of a non-negligible slow component. Here we show, by considering three well-known proteins (lysozyme, myoglobin and adelynate kinase), that the fast component arises partly from the response of those water molecules that are hydrogen bonded with the backbone oxygen (BBO) atoms. These are structurally and energetically less stable than those with the side chain oxygen (SCO) atoms. In addition, the electrostatic interaction energy distribution (EIED) of individual water molecules (hydrogen bonded to SCO) with side chain oxygen atoms shows a surprising two peak character with the lower energy peak almost coincident with the energy distribution of water hydrogen bonded to backbone oxygen atoms (BBO). This two peak contribution appears to be quite general as we find it for lysozyme, myoglobin and adenylate kinase (ADK). The sharp peak of EIED at small energy (at less than 2 k B T) for the BBO atoms, together with the first peak of EIED of SCO and the HBRs on the protein surface, explain why a large fraction (~ 80%) of water in the protein hydration layer remains almost as mobile as bulk water. Significant slowness arises only from the hydrogen bonds that populate the second peak of EIED at larger energy (at about 4 kBT). Thus, if we consider hydrogen bond interaction alone, only 15–20% of water molecules in the protein hydration layer can exhibit slow dynamics, resulting in an average relaxation time of about 5–10 ps. The latter estimate assumes a time constant of 20–100 ps for the slow component. Interestingly, relaxation of water molecules hydrogen bonded to back bone oxygen exhibit an initial component faster than the bulk, suggesting that hydrogen bonding of these water molecules remains frustrated. This explanation of the heterogeneous and non-exponential dynamics of water in the hydration layer is quantitatively consistent with all the available experimental results, and provides unification among diverse features. This study reveals a bimodal electrostatic energy distribution of protein–water hydrogen bonds involving side chain oxygen and faster than bulk water hydrogen bond breaking dynamics of protein–water hydrogen bond involving backbone oxygen.

Local heterogeneous dynamics of water around lysozyme: a computer simulation study

Water present near the surface of a protein exhibits dynamic properties different from that of water in the pure bulk state. In this work, we have carried out atomistic molecular dynamics simulation of an aqueous solution of hen egg-white lysozyme. Attempts have been made to explore the correlation between the local heterogeneous mobility of water around the protein segments and the rigidity of the hydration layers with the microscopic dynamics of hydrogen bonds formed by water molecules with the protein residues. The kinetics of breaking and reformation of hydrogen bonds involving the surface water molecules have been calculated. It is found that the reformations of broken hydrogen bonds are more frequent for the hydration layers of those segments of the protein that are more rigid. The calculation of the low-frequency vibrational modes of hydration layer water molecules reveals that the protein influences the transverse and longitudinal degrees of freedom of water around it in a differential manner. These findings can be verified by appropriate experimental studies.

More than one dynamic crossover in protein hydration water.

Studies of liquid water in its supercooled region have helped us better understand the structure and behavior of water. Bulk water freezes at its homogeneous nucleation temperature (approximately 235 K), but protein hydration water avoids this crystallization because each water molecule binds to a protein. Here, we study the dynamics of the hydrogen bond (HB) network of a percolating layer of water molecules and compare the measurements of a hydrated globular protein with the results of a coarse-grained model that successfully reproduces the properties of hydration water. Using dielectric spectroscopy, we measure the temperature dependence of the relaxation time of proton charge fluctuations. These fluctuations are associated with the dynamics of the HB network of water molecules adsorbed on the protein surface. Using Monte Carlo simulations and mean-field calculations, we study the dynamics and thermodynamics of the model. Both experimental and model analyses are consistent with the interesting possibility of two dynamic crossovers, (i) at approximately 252 K and (ii) at approximately 181 K. Because the experiments agree with the model, we can relate the two crossovers to the presence at ambient pressure of two specific heat maxima. The first is caused by fluctuations in the HB formation, and the second, at a lower temperature, is due to the cooperative reordering of the HB network.

Novel Alkali Triazine Tricarboxylates Li3[C3N3(CO2)3]·4H2O, Rb3[C3N3(CO2)3]·2H2O and Cs3[C3N3(CO2)3]·2H2O – Synthesis, Crystal Structure and Thermal Behavior

AbstractThe alkali 1,3,5‐triazine‐2,4,6‐tricarboxylates Li3[C3N3(CO2)3]·4H2O, Rb3[C3N3(CO2)3]·2H2O and Cs3[C3N3(CO2)3]·2H2O were synthesized by saponification of the respective triethyl ester in aqueous solution. In the crystal structure, the triazine tricarboxylate (TTC) units and metal ions are arranged in layers alternating with layers of crystal water molecules. Within the layers the triazine tricarboxylate entities form either strands in Li3[C3N3(CO2)3]·4H2O or a hexagonal arrangement in Rb3[C3N3(CO2)3]·2H2O and Cs3[C3N3(CO2)3]·2H2O. Perpendicular to the layers, the triazine cores exhibit varying degrees of π–π stacking dependent on the metal ions resulting in the formation of rods in Rb3[C3N3(CO2)3]·2H2O and Cs3[C3N3(CO2)3]·2H2O. Additionally, the thermal behavior of the alkali triazine tricarboxylates was investigated by means of FT‐IR spectroscopy, TG and DTA measurements. Differences and similarities regarding structural features and thermal behavior are discussed for the obtained novel alkali triazine tricarboxylates and potassium triazine tricarboxylate dihydrate.

Surface Hydrophilicity-Dependent Water Adsorption on Mixed Self-Assembled Monolayers of C7–CH3 and C7–COOH Residues. A Grand Canonical Monte Carlo Simulation Study

Grand Canonical Monte Carlo (GCMC) simulations are used to study the adsorption and organization of gas-phase water molecules on two-component self-assembled monolayers (SAMs) of eight-carbon alkanethiols bound to a flat virtual carrier, as the character of the SAM surface is changing from completely hydrophobic to completely hydrophilic by randomly replacing methyl-terminated (C7–CH3) alkanethiol chains with carboxylic acid-terminated (C7–COOH) chains. At low chemical potentials (low relative humidity), a synergistic effect of nearby COOH functional groups on water adsorption is observed. In particular, clusters of nearby surface COOH groups are found to attract considerably more water molecules than the same amount of COOH groups if they are isolated from each other. By promoting lateral water–water interactions, such surface COOH clusters thus act as condensation nuclei for water. With increasing water chemical potential, the possibility of the formation of new water–water hydrogen bonds gradually becomes an increasingly important driving force of the adsorption, in addition to the formation of new water–COOH hydrogen bonds. Further, as the relative humidity increases, the growing number of water–water hydrogen bonds clearly overcompensates the effect of the decreasing average number of water–COOH hydrogen bonds per (first layer) water molecules. These findings are supported by the adsorption isotherms, by the preferential orientation of the surface COOH groups and first layer water molecules, and by the binding energy distributions of the water molecules being in direct contact with the SAM surface as obtained from the simulation. The atmospheric relevance of our results is also considered.

Glass transition and dynamics in BSA–water mixtures over wide ranges of composition studied by thermal and dielectric techniques

Protein–water dynamics in mixtures of water and a globular protein, bovine serum albumin (BSA), was studied over wide ranges of composition, in the form of solutions or hydrated solid pellets, by differential scanning calorimetry (DSC), thermally stimulated depolarization current technique (TSDC) and dielectric relaxation spectroscopy (DRS). Additionally, water equilibrium sorption isotherm (ESI) measurements were performed at room temperature. The crystallization and melting events were studied by DSC and the amount of uncrystallized water was calculated by the enthalpy of melting during heating. The glass transition of the system was detected by DSC for water contents higher than the critical water content corresponding to the formation of the first sorption layer of water molecules directly bound to primary hydration sites, namely 0.073 (grams of water per grams of dry protein), estimated by ESI. A strong plasticization of the Tg was observed by DSC for hydration levels lower than those necessary for crystallization of water during cooling, i.e. lower than about 0.3 (grams of water per grams of hydrated protein) followed by a stabilization of Tg at about −80°C for higher water contents. The α relaxation associated with the glass transition was also observed in dielectric measurements. In TSDC a microphase separation could be detected resulting in double Tg for some hydration levels. A dielectric relaxation of small polar groups of the protein plasticized by water, overlapped by relaxations of uncrystallized water molecules, and a separate relaxation of water in the crystallized water phase (bulk ice crystals) were also recorded.

Synthesis of Aligned Polyaniline Belts by Interfacial Control Approach

Aligned polyaniline (PANI) belts doped with dodecatungstosilic acid (H4SiW12O40, abbreviated as SiW12) are synthesized by interfacial control method without surfactants or templates. The structure and morphology of the PANI are characterized by Fourier transform infrared (FT-IR) spectra, X-ray diffraction (XRD) patterns, and scanning electron microscope images (SEM). SiW12, as a doping-acid replacing HCl and offering a strong adhesive action between itself and water molecules, plays an important role in controlling aniline in interface system by the ordering character of water molecule layers along the interface. The alignment of the molecules or particles in the polymer nanostructures has a great influence on its performance. The conductivity of SiW12-doped and HCl-doped PANI prepared under the same conditions is tested. As compared to HCl-doped PANI, SiW12-doped PANI has a superior performance on the conductivity.