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Molecular reorientation dynamics in liquid water are typically probed using either infrared (IR) pump-probe anisotropy experiments or the NMR spin-echo technique. While it is widely appreciated that the two yield different reorientation times based on the nature of the measurements, little attention has been paid to the implications for the corresponding activation energies. Here, the activation energies associated with reorientation of the OH bond vector in liquid water are calculated to high accuracy directly from simulations at a single temperature using a recently developed method [Z. A. Piskulich et al., J. Chem. Phys.147, 134103 (2017)]. The results indicate that the reorientation times obtained from IR anisotropy and NMR measurements have different activation energies that, with improved accuracy, should be experimentally distinguishable. The origins of the differences in the two activation energies are examined in detail, including by a decomposition into the contributions to the activation energies due to the kinetic energy and the intermolecular interactions. [ABSTRACT FROM AUTHOR]

We perform a complete classical molecular dynamics study of the dielectric heating of water in the microwave (MW) region. MW frequencies ranging from 1.0 to 15.0 GHz are used together with a series of well-known empirical force fields. We show that the ability of an empirical force field to correctly predict the dielectric response of liquids toMWradiation should be evaluated on the basis of a joint comparison of the predicted and experimental static dielectric constant, frequency-dependent dielectric spectra, and heating profiles. We argue that this is essential when multicomponent liquids are studied. We find that both the three-site OPC3 and four-site TIP4P-ε empirical force fields of water are equally superior for reproducing dielectric properties at a range of MW frequencies. Despite its poor prediction of the static dielectric constant, the well-known SPCE force field can be used to accurately describe dielectric heating of water at lowMWfrequencies. [ABSTRACT FROM AUTHOR]

At physiological conditions, myriads of biomolecules (e.g., amino acids, peptides, and proteins) exist predominantly in the zwitterionic structural form and their biological functions will result in these conditions. However these geometrical structures are inaccessible energetically in the gas phase, and at this point, stabilization of amino-acids in physiological conditions is still under debate. In this paper, the electronic properties of a glycine molecule in the liquid environment were studied by performing a relaxation of the glycine geometry in liquid water using the free energy gradient method combined with a sequential quantum mechanics/molecular mechanics approach. A series of Monte Carlo Metropolis simulations of the glycine molecule embedded in liquid water, followed by only a quantum mechanical calculation in each of them were carried out. Both the local and global liquid environments were emphasized to obtain nuclear magnetic resonance (NMR) parameters for the glycine molecule in liquidwater. The results of the equilibrium structure in solution and the systematic study of the hydrogen bonds were used to discard the direct proton transfer from the carboxyl group to the ammonium group of the glycine molecule in water solution. The calculations of the Density Functional Theory (DFT) were performed to study the polarization of the solvent in the parameters of nuclear magnetic resonance of the glycine molecule in liquid water. DFT calculations predicted isotropic chemical changes on the H, C, N, andOatoms of glycine in liquidwater solution which agree with the available experimental data. [ABSTRACT FROM AUTHOR]

In this article, we present a novel adaptive enhanced sampling molecular dynamics (MD) method for the accelerated simulation of protein folding and aggregation. We introduce a path-variable L based on the un-biased momenta p and displacements dq for the definition of the bias s applied to the system and derive 3 algorithms: general adaptive bias MD, adaptive path-sampling, and a hybrid method which combines the first 2 methodologies. Through the analysis of the correlations between the bias and the un-biased gradient in the system, we find that the hybrid methodology leads to an improved force correlation and acceleration in the sampling of the phase space. We apply our method on SPC/E water, where we find a conservation of the average water structure. We then use our method to sample dialanine and the folding of TrpCage, where we find a good agreement with simulation data reported in the literature. Finally, we apply our methodologies on the initial stages of aggregation of a hexamer of Alzheimer's amyloid β fragment 25-35 (Aβ 25-35) and find that transitions within the hexameric aggregate are dominated by entropic barriers, while we speculate that especially the conformation entropy plays a major role in the formation of the fibril as a rate limiting factor. [ABSTRACT FROM AUTHOR]

Water confined to nanoscale widths in two dimensions between ideal planar walls has been the subject of ample study, aiming at understanding the intrinsic response of water to confinement, avoiding the consideration of the chemistry of actual confining materials. In this work, we study the response of such nanoconfined water to the imposition of a periodicity in the confinement by means of computer simulations, both using empirical potentials and from first-principles. For that we propose a periodic confining potential emulating the atomistic oscillation of the confining walls, which allows varying the lattice parameter and amplitude of the oscillation. We do it for a triangular lattice, with several values of the lattice parameter: one which is ideal for commensuration with layers of Ih ice and other values that would correspond to more realistic substrates. For the former, the phase diagram shows an overall rise of the melting temperature. The liquid maintains a bi-layer triangular structure, however, despite the fact that it is not favoured by the external periodicity. The first-principles liquid is significantly affected by the modulation in its layering and stacking even at relatively small amplitudes of the confinement modulation. Beyond some critical modulation amplitude, the hexatic phase present in flat confinement is replaced by a trilayer crystalline phase unlike any of the phases encountered for flat confinement. For more realistic lattice parameters, the liquid does not display higher tendency to freeze, but it clearly shows inhomogeneous behaviour as the strength of the rugosity increases. In spite of this expected inhomogeneity, the structural and dynamical response of the liquid is surprisingly insensitive to the external modulation. Although the first-principles calculations give a more triangular liquid than the one observed with empirical potentials (TIP4P/2005), both agree remarkably well for the main conclusions of the study. [ABSTRACT FROM AUTHOR]

We investigate collective molecular motion and the self-diffusion coefficient Ds of water molecules in the mobile interfacial layer of the secondary prismatic plane (1120) of hexagonal ice by molecular dynamics simulation based on the TIP4P/2005 water potential and a metrology of collective motion drawn from the field of glass-forming liquids. The width ξ of the mobile interfacial layer varies from a monolayer to a few nm as the temperature is increased towards the melting temperature Tm, in accordance with recent simulations and many experimental studies, although different experimental methods have differed in their precise estimates of the thickness of this layer. We also find that the dynamics within this mobile interfacial ice layer is "dynamically heterogeneous" in a fashion that has many features in common with glass-forming liquids and the interfacial dynamics of crystalline Ni over the same reduced temperature range, 2/3 < T/Tm < 1. In addition to exhibiting non-Gaussian diffusive transport, decoupling between mass diffusion and the structural relaxation time, and stretched exponential relaxation, we find string-like collective molecular exchange motion in the interfacial zone within the ice interfacial layer and colored noise fluctuations in the mean square molecular atomic displacement 〈u²〉 after a "caging time" of 1 ps, i.e., the Debye-Waller factor. However, while the heterogeneous dynamics of ice is clearly similar in many ways to molecular and colloidal glass-forming materials, we find distinct trends between the diffusion coefficient activation energy Ea for diffusion Ds and the interfacial width ξ from the scale of collective string-like motion L than those found in glass-forming liquids. [ABSTRACT FROM AUTHOR]

The unique properties of liquid water apparently arise from more than just the tetrahedral bond angle between the nuclei of a water molecule since simple three-site models of water are poor at mimicking these properties in computer simulations. Four- and five-site models add partial charges on dummy sites and are better at modeling these properties, which suggests that the shape of charge distribution is important. Since a multipole expansion of the electrostatic potential describes a charge distribution in an orthogonal basis set that is exact in the limit of infinite order, multipoles may be an even better way to model the charge distribution. In particular, molecular multipoles up to the octupole centered on the oxygen appear to describe the electrostatic potential from electronic structure calculations better than four- and five-site models, and molecular multipole models give better agreement with the temperature and pressure dependence of many liquid state properties of water while retaining the computational efficiency of three-site models. Here, the influence of the shape of the molecular charge distribution on liquid state properties is examined by correlating multipoles of non-polarizable water models with their liquid state properties in computer simulations. This will aid in the development of accurate water models for classical simulations as well as in determining the accuracy needed in quantum mechanical/molecular mechanical studies and ab initio molecular dynamics simulations of water. More fundamentally, this will lead to a greater understanding of how the charge distribution of a water molecule leads to the unique properties of liquid water. In particular, these studies indicate that p-orbital charge out of the molecular plane is important. [ABSTRACT FROM AUTHOR]

We propose a water-immersed geometrically oblique grating structure patterned with a 1D periodic array of oblique rhombuses. Twin acoustic-induced mutual forces (both repulsive and attractive) between coupled steel plates were realized in this system when the external plane wave normally impacted the plates. Calculations showed that the emerging forces are more than an order of magnitude larger than the corresponding induced force of a conventional grating structure. We also found that the strong acoustic-induced mutual forces stem from the resonant excitation of nonleaky flexural Lamb modes in the coupled plates, and that these forces couple more strongly with the external incident acoustic waves. Furthermore, the amplitudes and resonant wavelengths of these forces can be coarsely controlled by changing the symmetry of the system and finely adjusted by varying the slant angle and the edge-length of the oblique rhombus. The proposed acoustic system could potentially be applied in sensors and in the ultrasonic detection of weak signals in water. [ABSTRACT FROM AUTHOR]

Infrared vibrational spectroscopy is a valuable tool for probing molecular structure and dynamics. However, obtaining an unambiguous molecular-level interpretation of the spectral features is made difficult, in part, due to the complex interplay of the dipole moment with the underlying vibrational structure. Here, we disentangle the contributions of the potential energy surface (PES) and dipole moment surface (DMS) to the infrared spectrum of liquid water by examining three classes of models, ranging in complexity from simple point charge models to accurate representations of the many-body interactions. By decoupling the PES from the DMS in the calculation of the infrared spectra, we demonstrate that the PES, by directly modulating the vibrational structure, primarily controls the width and position of the spectroscopic features. Due to the dependence of the molecular dipole moment on the hydration environment, many-body electrostatic effects result in a ~100 cm-1 redshift in the peak of the OH stretch band. Interestingly, while an accurate description of many-body collective motion is required to generate the correct (vibrational) structure of the liquid, the infrared intensity in the OH stretching region appears to be a measure of the local structure due to the dominance of the one-body and short-ranged two-body contributions to the total dipole moment. [ABSTRACT FROM AUTHOR]

Threespine stickleback exhibit a row of superficial neuromasts that project through the bony plates on each side of the trunk and which constitute an important sensory modality for detection of near-field water motion. Previously, we have shown that numbers of neuromasts on each structural plate are highly variable among populations. In the current paper, we expand this study to evaluate the extent of deviation from bilateral symmetry of 4344 fish in 57 natural and three transplant populations of threespine stickleback from lakes, streams and oceanic habitats of coastal British Columbia, predicting that neuromasts would be largely bilaterally symmetrical for optimal detection of external stimuli. In contrast, we found asymmetry in all populations, the greatest amount occurring on the anterior buttressing lateral plates and on populations with the fewest neuromasts. We found no consistent trends of signed (directional) asymmetry (SA) among the populations while relative absolute asymmetry (RAA) is lower in dystrophic (stained) habitats than in clearwater habitats (p < 0.001), except for fish with few neuromasts. Sexual dimorphism in RAA is also greater in dystrophic habitats (p < 0.001). Transplants from stained lakes to unstained ponds resulted in a 0.1% to 14% difference in RAA from the source population in less than 12 generations but varied in direction among experiments. Our data suggest a widespread tendency for populations exposed to reduced photic information to exhibit reduced asymmetry in their lateral line system, which can change rapidly in response to a new environment. [ABSTRACT FROM AUTHOR]

The structure, equation of state, IR, Raman, and inelastic neutron scattering (INS) spectra of high-pressure, proton-ordered phase VIII of ice are calculated by the second-order many-body perturbation and coupled-cluster singles and doubles methods. Nearly all the observed features of the pressure-dependence of the structures and spectra are reproduced computationally up to 60 GPa insofar as the anharmonic effects can be neglected. The calculations display no sign of the hypothetical isostructural transition in 2-3 GPa to phase VIII', the existence of which has been a matter of controversy for over a decade, while they do not contradict the interpretation of the spectral anomaly at 10-14 GPa as a precursor of the VIII-X phase transition. The calculated INS spectra correct a systematic error in the peak positions of the observed spectra. [ABSTRACT FROM AUTHOR]

Atmospheric water has a complex behaviour partly due to the influence of precipitation. Consequently, it is challenging to explain properties of water such as the scale-dependence of its variance, for which a range of spectral exponents has been identified in observational data. Here, a precipitating quasi-geostrophic (PQG) model is explored as a possible prototype for contributing to understanding of water spectra, in an idealised setting. Geostrophic turbulence is examined in numerical simulations, where precipitation is included to explore its effect on the water spectrum, but where phase changes are neglected to allow corresponding theoretical analysis. The water spectral exponent is seen to range from approximately −1.4 to approximately −5 depending on the rainfall speed parameter, V r , which indicates a significant influence of precipitation on the water spectrum. The limiting values of this range are explained through asymptotic analyses for large and small values of V r . To obtain this theoretical understanding of the model, a key observation is that water can be written as a linear combination of two other tracers (equivalent potential temperature and a moist variable M), which themselves have theoretically tractable spectra. These two other tracers are linked to distinct modes of the PQG equations–the vortical mode and a moist mode – and the analysis here highlights the usefulness of wave or mode decompositions for understanding water in a saturated domain. [ABSTRACT FROM AUTHOR]

Inelastic X-ray and neutron scattering techniques were jointly used to investigate the dynamics of water-glycerol mixtures at different concentrations and temperatures. It was observed that even relatively low concentrations of glycerol increase the damping of shear modes, as a consequence of the known ability of glycerol to disrupt the hydrogen bond network of water. A similar trend was observed when increasing the temperature, which suggests the presence of a locus in the concentration-temperature plane marking a crossover in the shear modulus. [ABSTRACT FROM AUTHOR]

Guided by theoretical predictions, the rotational spectrum of HD17O was recorded and assigned for the first time, while the measurements for D217O were extended up to the THz region. For both isotopic species, a large portion of the rotational spectrum, from 65 GHz (from 200 GHz for the bideuterated isotopologue) up to 1.6 THz, was investigated, thus allowing the accurate determination of the ground-state rotational and centrifugal-distortion constants. Considering that the rotational spectra of water isotopologues are characterized by a very low density of lines and strong centrifugal-distortion effects, the accurate quantum-chemical prediction of the relevant spectroscopic parameters played a crucial role in the line search and assignment as well as in supporting the fitting procedure. In addition to rotational and centrifugal-distortion constants, the knowledge of the oxygen quadrupole-coupling constants was essential, as the corresponding interaction leads to characteristic features (hyperfine structure) that enabled proper line assignments. [ABSTRACT FROM AUTHOR]

Hydrocarbon-bearing zone identification of tight reservoirs plays a crucial role in hydrocarbon exploration and development. However, tight carbonate reservoirs are generally characterized by complex lithology, low porosity, strong heterogeneity, and weak fluid logging responses, which present a major challenge to detect hydrocarbon-bearing zones using conventional methods. To address this challenge, this paper develops a new method defined as R wa spectrum, taking advantage of the high vertical resolution and borehole coverage of the image logs. The R wa spectra can be derived from the histogram distribution of the apparent resistivity values of formation water (R wa) in a sliding window, combining the Simandoux equation and the triple-porosity model. The results show that a very broad R wa spectrum with long tails corresponds to hydrocarbon-bearing zones, and the peak shape of it is flat. In contrast, the narrow R wa spectrum corresponds to water-bearing zones, and the peak shape of it is a sharp spike. Furthermore, two R wa spectrum parameters, namely AVERAGE (reflects the size of main peak values) and VARIANCE (reflects shape changes of the R wa spectra) are defined to quantificationally detect hydrocarbon-bearing zones. For oil zones in Yingxi field, the AVERAGE had a value higher than 10 and the VARIANCE was higher than 10. And for water zones, the AVERAGE had a value lower than 4.5 and the VARIANCE was lower than 5. The resistivity values decrease linearly with the increase in pyrite content of the reservoirs of high pyrite content, which disturbs the response to resistivity values from different fluid types (oil, gas or water). Hence, this method is suitable for the formation of no or little pyrite contents (lower than 0.2), and the case where the salinity value of drilling mud is similar to that of formation water. Moreover, the method has been validated by production test data, providing unusual perspectives on the identification of fluid types in tight carbonate reservoirs. • Changed traditional application of image logging which only based on image analysis. • The R wa spectrum is derived from image logs combining Simandoux equation and the triple-porosity model. • The effect of pyrite on resistivity is greater than that of fluid within pores in formation in some cases. [ABSTRACT FROM AUTHOR]

• First high-resolution spectrum of the 2 ν 2 band of HT16O measured. • Line-by-line analysis of 488 lines at an accuracy up to a few 10 − 4 cm − 1. • Differences to ab-initio line positions of the order of 0.1 cm − 1. • Spectroscopic constants determined in A-reduced Watson Hamiltonian. The high-resolution infrared spectrum of tritiated water vapor has been recorded at room temperature using a Fourier-transform spectrometer with a resolution of 0.0075 cm − 1. We report 488 new experimental line positions in the 2450 to 2950 cm − 1 range that were assigned to the 2 ν 2 band of HT16O, with rotational quantum numbers up to J = 14 and K a = 5. The assigned lines were used to determine the spectroscopic constants of the 2 ν 2 band of HT16O in the A-reduced Watson Hamiltonian. No perturbations were observed. The comparison with variational calculations of line positions and intensities of HTO from the Tomsk database shows differences of up to several 0.1 cm − 1 concerning the line positions, while the (relative) line intensities agree with the observed values within a few percent. The line list from this study may be useful for detection of gaseous traces of HTO using laser-based methods in the future. [ABSTRACT FROM AUTHOR]

Abstract In the IR spectra of water on polyethylene, polypropylene and polytetrafluoroethylene frequent and substantial negative peaks occurred and are explained by a theoretical analysis. New states, FEXs, Fast-formed EXcited states are formed by the combination of an IR photon and water and are now made manifest by inefficient energy transfer to the polymer combined with limited energy transfer to the small (0.5–1.0 μL) water sample. Graphical abstract Unlabelled Image Highlights • Infra-red electromagnetic absorption minima in water upon some organic polymers are observed and explained. • New excited states are created as products of an excited electronic state and an oligomer state. • The absorption minima change to absorption maxima upon increase of the ambient temperature. [ABSTRACT FROM AUTHOR]

Abstract Water structures of hydrated polymers have been suggested to directly influence the biomolecules' adsorption. We conducted a serial of molecular dynamics simulations to investigate the water structures of hydrated poly(2-methoxyethyl acrylate) (PMEA). According to the calculated IR spectra of water molecules categorized into four binding sites in hydrated PMEA, most of water molecules at water content less than 3 wt% are water molecules interacting with two carbonyl groups, corresponding to experimental observed non-freezing water. In addition, we found two-stage variation of the non-bound water content with increasing the water content. The turnover point can be regarded as the saturation point and be used to estimate the equilibrium water content (EWC). Furthermore, the ratio of bound water content to polymer oxygen content was found to be a possible index for predicting the platelet adhesion of polymers. The findings will be useful for developing new biomaterials containing oxygen moieties in the medical applications. Graphical abstract Image 1 Highlights • Two-stage variation of the non-bound water content with water content is found. • The turnover point can be used to estimate the equilibrium water content. • The relationship between the bound water (BW) and platelet adhesion is found. • The ratio of BW to polymer oxygen is a potential predictor of platelet adhesion. [ABSTRACT FROM AUTHOR]

Infrared spectroscopy with medium to high spectral resolution is essential to characterize the gas content of circumstellar disks. Unfortunately, conducting continuum and line radiative transfer of thermochemical disk models is too time-consuming to carry out large parameter studies. Simpler approaches using a slab model to fit continuum-subtracted spectra require the identification of either the global or local continuum. Continuum subtraction, particularly when covering a broad wavelength range, is challenging but critical in rich molecular spectra as hot (several hundreds K) molecular emission lines can also produce a pseudo continuum. In this work, we present CLIcK, a flexible tool to simultaneously fit the continuum and line emission. The continuum model presented by Dullemond, Dominik, and Natta, and a plane-parallel slab of gas in local thermodynamic equilibrium are adopted to simulate the continuum and line emission, respectively, both of them are fast enough for homogeneous studies of large disk samples. We applied CLIcK to fit the observed water spectrum of the AA Tau disk and obtained water vapor properties that are consistent with literature results. We also demonstrate that CLIcK properly retrieves the input parameters used to simulate the water spectrum of a circumstellar disk. CLIcK will be a versatile tool for the interpretation of future James Webb Space Telescope spectra. [ABSTRACT FROM AUTHOR]

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Broadband dielectric spectra of water and ice reveal similar temperature run of the static permittivity, ε(0), and spectral shape of the Debye relaxation. We suggest an approach to describe these features uniformly. We extend to ice the model recently developed by us for water. The model explains the 6 orders magnitude difference between the Debye relaxation time in water and ice, as well as alike temperature behavior of ε(0), by bipolar diffusion of counter charges. [ABSTRACT FROM AUTHOR]

Antifreeze proteins (AFPs) inhibit ice growth in organisms living in cold environments. Hyperactive insect AFPs are particularly effective, binding ice through "anchored clathrate" motifs. It has been hypothesized that the binding of hyperactive AFPs to ice is facilitated by preordering of water at the ice-binding site (IBS) of the protein in solution. The antifreeze protein TmAFP displays the best matching of its binding site to ice, making it the optimal candidate to develop ice-like order in solution. Here we use multiresolution simulations to unravel the mechanism by which TmAFP recognizes and binds ice. We find that water at the IBS of the antifreeze protein in solution does not acquire ice-like or anchored clathrate-like order. Ice recognition occurs by slow diffusion of the protein to achieve the proper orientation with respect to the ice surface, followed by fast collective organization of the hydration water at the IBS to form an anchored clathrate motif that latches the protein to the ice surface. The simulations suggest that anchored clathrate order could develop on the large ice-binding surfaces of aggregates of ice-nucleating proteins (INP). We compute the infrared and Raman spectra of water in the anchored clathrate motif. The signatures of the OH stretch of water in the anchored clathrate motif can be distinguished from those of bulk liquid in the Raman spectra, but not in the infrared spectra. We thus suggest that Raman spectroscopy may be used to probe the anchored clathrate order at the ice-binding surface of INP aggregates. [ABSTRACT FROM AUTHOR]

A water soluble chloro bridged binuclear copper(II) complex (3) and mononuclear complex (4) have been synthesized from chloro substituted 2‐oxo‐1,2‐dihydroquinolin‐3‐yl‐methylene‐2 hydroxybenzohydrazide 1 and 2 and CuCl2·2H2O. The structures of the complexes have been determined by single crystal X‐ray diffraction. The binding interactions of the ligands and complexes with CT‐DNA and protein have been evaluated by absorption and emission spectroscopic method. CT‐DNA and ethidium bromide (EB) competitive studies revealed that the compounds could interact with CT‐DNA through intercalation binding mode. Interactions of the compounds with BSA were also studied by UV−visible, fluorescence and synchronous fluorescence spectroscopic methods which showed that the compounds had a strong binding affinity with BSA through static quenching process. The cytotoxic effect of the compounds examined on cancer cell lines, such as A549 (lung cancer) and MCF7 (breast cancer) cell lines showed that all four compounds exhibited substantial cytotoxic activity. [ABSTRACT FROM AUTHOR]

Luminescence of water during irradiations of proton-beams or X-ray photons lower energy than the Cerenkov-light threshold is promising for range estimation or the distribution measurements of beams. However it is not yet obvious whether the intensities and distributions are stable with the water conditions such as temperature or addition of solvable materials. It remains also unclear whether the luminescence of water linearly increases with the irradiated proton or X-ray energies. Consequently we measured the luminescence of water during irradiations of proton-beam or X-ray photons lower energy than the Cerenkov-light threshold with different water conditions and energies to evaluate the stability and linearity of luminescence of water. We placed a water phantom set with a proton therapy or X-ray system, luminescence images of water with different conditions and energies were measured with a high-sensitivity cooled charge coupled device (CCD) camera during proton or X-ray irradiations to the water phantom. In the stability measurements, imaging was made for different temperatures of water and addition of inorganic and organic materials to water. In the linearity measurements for the proton, we irradiated with four different energies below Cerenkov light threshold. In the linearity measurements for the X-ray, we irradiated X-ray with different supplied voltages. We evaluated the depth profiles for the luminescence images and evaluated the light intensities and distributions. The results showed that the luminescence of water was quite stable with the water conditions. There were no significant changes of intensities and distributions with the different temperatures. Results from the linearity experiments showed that the luminescence of water linearly increased with their energies. We confirmed that luminescence of water is stable with conditions of water. We also confirmed that the luminescence of water linearly increased with their energies. [ABSTRACT FROM AUTHOR]

Self-assembly of proteins often gives rise to interesting quasi-stable structures that serve important biological purposes. Insulin hexamer is such an assembly. While monomer is the biologically active form of insulin, hexamer serves as the storehouse of the hormone. The hexamer also prevents the formation of higher order aggregates. While several studies explored the role of bivalent metal ions like Zn2+, Ca2+, etc., in the stabilization of the hexameric form, the role of water molecules has been ignored. We combine molecular dynamics simulations, quantum calculations and X-ray analyses to discover that a team of approximately 10 water molecules confined inside a barrel-shaped nanocavity at the center of insulin hexamer is one of the major causes that account for the unusual stability of the biomolecular assembly. These cavity water molecules exhibit interesting dynamical features like intermittent escape and reentrance. We find that these water molecules are dynamically slower than the bulk and weave an intricate hydrogen bond network among themselves and with neighboring protein residues to generate a robust backbone at the center of the hexamer that holds the association strongly from inside and maintains the barrel shape. [ABSTRACT FROM AUTHOR]

Alternating water/flooding is known to be very efficient for enhanced oil recovery, but is often economically infeasible for smallsources. A similar effect can be achieved indirectly via injection of water–mixture with low molecular-weight emulsifiers with affinity for polar segments of residual hydrocarbons. To investigate the potential of this approach, we have performed molecular simulations of N-acetyl morpholine (NAM) and N-formyl morpholine (NFM) surfactants in liquid–systems atK andAtm. The surfactants were modelled by means of the OPLSAA force field, with quantum mechanical calculations used to obtain the partial charges. Our simulations clearly showed the affinity of both NAM and NFM for the–interface, providing extensive evidence of their interfacial activity. We also present an intuitive technique aiming to find and analyse intrinsic surfaces that define liquid-liquid interfaces by utilizing instantaneous and time averaged atomic configurations. This analysis allowed us to quantify the impact of NAM and NFM on the intrinsic surface structure ofin liquid–systems. Our results indicate that the instantaneous structure of intrinsicsurface will be significantly roughened by the presence of NAM and NFM. [ABSTRACT FROM PUBLISHER]

Here, we study quasi-chemical theory (QCT) for the free energies of divalent alkaline earth ions (Ba, Sr, Ca, Mg) in water, emphasizing that: (a) interactions between metal ions and proximal water molecules are as strong as traditional chemical effects; (b) QCT builds directly from accessible electronic structure calculations but rests on fully elaborated molecular statistical thermodynamics; (c) QCT offers choices of convenience in identifying coordination numbers for analysis. We investigate utilisation of direct QCT with inner-shell conditioning, alternative to the traditionalconditioning motivated by a generalised van der Waals view. The alternativeworks well: deleterious non-Gaussian effects of van der Waals repulsive interactions are not serious, and the alternative conditioning improves the convenience of QCT calculations. Comparison betweenab initioand force field molecular dynamics (AIMD and FFMD) with standard models suggests that FFMD likely exaggerates the anharmonicity in the thermal motion of inner-shell ion-water clusters. Together with the general encouraging support for the harmonic approximations implied by theconditioning, that observation helps explain the remarkable success of the cluster-based QCT solution free energies, which do not require assessment of all inner-shell occupancies by simulation. [ABSTRACT FROM PUBLISHER]

Remote sensing of inland and sea waters depends on the quality of the retrieval of the water-leaving radiance from the top-of-atmosphere measurements. The water-leaving radiance can be difficult to observe due to the reflection of direct sunlight on the air-water interface (sunglint) in the direction of the satellite field of view. The viewing geometry of Sentinel-2 satellite ( European Space Agency ) makes it vulnerable to sunglint contamination. In this paper, an original method is proposed to correct Sentinel-2-like imagery for sunglint contamination. The sunglint contribution is first estimated from the shortwave-infrared (SWIR) part of the spectrum and then extrapolated toward the near-infrared and visible bands. The spectral variation of the sunglint signal is thus revisited for a wide spectral range (from 350 to 2500 nm). The bidirectional reflectance distribution function related to the sunglint is shown to vary by > 28% from the SWIR to the blue bands of Sentinel-2. The application of the proposed algorithm on actual Sentinel-2 data demonstrates that sunglint patterns are satisfactorily removed over the entire images whatever the altitude of the observed target. Comparison with in situ data of water-leaving radiances (AERONET-OC) showed that our proposed algorithm significantly improves the correlation between satellite and in situ data by 55% (i.e., from R 2 = 0.56 to R 2 = 0.87). In addition, the discrepancies between satellite and in situ measurements are reduced by 60%. It is also shown that the aerosol data provided by the Copernicus Atmosphere Monitoring Service (CAMS) can be safely used within the proposed algorithm to correct the Sentinel-2-like satellite data for both sunglint and atmospheric radiances. Improvements of the proposed method potentially rely on simultaneous retrievals of the aerosol optical properties. The proposed method is applicable to any satellite sensor which is able to measure in SWIR spectral bands over aquatic environments. [ABSTRACT FROM AUTHOR]

With the aid of differential phonon spectrometrics (DPS) and surface stress detection, we show that HI and NaI solvation transforms different fractions of the H O stretching phonons from the mode of ordinary water centred at ∼3200 to the mode of hydration shell at ∼3500 cm −1 . Observations suggest that an addition of the H ↔ H anti-hydrogen-bond to the Zundel notion, [H(H 2 O) 2 ] + , would be necessary as the H O bond due H 3 O + has a 4.0 eV energy, and the H ↔ H fragilization disrupts the solution network and the surface stress. The I − and Na + ions form each a charge centre that aligns, stretches, and polarize the O:H O bond, resulting in shortening the H O bond and its phonon blue shift in the hydration shell or at the solute-solvent interface. The solute capabilities of bond-number-fraction transition follow: f H = 0, f Na ∝ C, and f I ∝ 1 − exp(−C/C 0 ) toward saturation, with C being the solute molar concentration and C 0 the decay constant. The f H = 0 evidences the non-polarizability of the H + because of the H ↔ H formation. The linear f Na (C) suggests the invariance of the Na + hydration shell size because of the fully-screened cationic potential by the H 2 O dipoles in the hydration shell but the nonlinear f I (C) fingerprints the I − ↔ I − interactions at higher concentrations. Concentration trend consistency between Jones–Dole’s viscosity and the f NaI (C) coefficient may evidence the same polarization origin of the solution viscosity and surface stress. [ABSTRACT FROM AUTHOR]

We have used continuous-wave cavity ring-down spectroscopy to record the spectrum of H 2 O Kr in the 2OH excitation range of H 2 O. 11 sub-bands have been observed for the main krypton isotope, 84 Kr. Their rotational structure ( T rot = 18 K) is analyzed and the lines fitted together with literature microwave data, with a unitless standard deviation σ = 0.86 and 1.32 for ortho and para species, respectively. 4 more sub-bands are observed for the three other isotopes and are also analyzed. The upper state vibrational predissociation lifetime is estimated to 4 ns from observed spectral linewidths. [ABSTRACT FROM AUTHOR]

Ab initio calculations of water intensities are becoming mature and are claimed to have 1% accuracy in many cases. Experimental intensities with 1% accuracy can be achieved with some care. An intercomparison of ab initio against experimental water intensities is presented for a variety of infrared bands for H 2 16 O and some for H 2 18 O and H 2 17 O. A new calculated H 2 16 O line list is presented for which uncertainties in the ab initio line intensities are evaluated. Much of the data show agreement within 2% between ab initio and experiment, however, for some bands, notably those involving excitation of some stretching modes, there are larger offsets of up to 8% attributed to ab initio calculation errors but still within the uncertainty of the ab initio calculation. In the ν 1 fundamental band differences of between + 5 % and − 13 % are found which show systematic dependence on wavenumber, Δ K a , and Δ J , again attributable to ab initio calculation errors. In the ν 2 band, intensity-dependent differences up to 2% originate from the analysis of the experimental data. At present experiments are important to validate ab initio calculations but ab initio predictions can be very useful in validating the experiment. As the two procedures display significantly different systematic errors, it is suggested that combining both gives the best results; this study will also facilitate further improvements of the theoretical methodology. [ABSTRACT FROM AUTHOR]

A Bruker IFS 125 HR Fourier transform spectrometer was used to measure several pure water transmittance spectra in the spectral range 1850–4000 cm −1 . A total of 15 measurements with absorption path lengths between 24.9 cm and 174.6 m and sample gas pressures from 0.1 to 20 mbar were performed at 296 K. The transmittance spectra were corrected for various error sources and were analyzed in the spectral ranges 1850–2280 cm −1 and 2390–4000 cm −1 for the majority of intensities between 3×10 –26 and 3×10 –19 cm molecule −1 . A multispectrum fitting approach was used applying a quadratic speed-dependent Voigt model extended to account for line mixing in the Rosenkranz first order perturbation approximation. Line positions, intensities, self-broadening widths, their speed-dependence and in some cases line mixing had to be adjusted for fitting the measurements to noise level. An extensive error estimation calculation was performed propagating several instrumental and measurement errors into individual parameter inaccuracies. The determined parameters are compared to HITRAN12 and independent experimental values while intensities are compared to recent ab initio calculations performed at UCL. The overall agreement between ab initio calculations and experimental values is remarkable and below 1% in most cases. The determined line parameters are provided as a supplement to this publication. [ABSTRACT FROM AUTHOR]

Water-mediated ion-pair dissociation is studied by molecular dynamics simulations of NaCl in water. Multidimensional free-energy analysis clarifies the relation between two essential solvent coordinates: the water coordination number and water-bridge formation. These two are related in a complex way. Both are necessary to describe ion-pair dissociation. The mechanism constructed with both solvent variables clearly shows the individual roles. The water coordination number is critical for starting ion-pair dissociation. Water-bridge formation is also important because it increases the likelihood of ion-pair dissociation by reducing the dissociation free-energy barrier. Additional Ca–Cl and NH4–Cl calculations show that these conclusions are unaffected by changes in the ion charge and shape. The present results will contribute to future explorations of many other molecular events such as surface water exchange and protein-ligand dissociation because the same mechanism is involved in such events. [ABSTRACT FROM PUBLISHER]

Stability of Ag2S@ZnS QDs in water is a crucial concern for their application in biology. In this work, both physical sustainability and emission stability of Ag2S QDs were enhanced using parameter optimization of a pulsed microwave irradiation (MI) method up to 105 days after their preparation. UV-Vis and photoluminescence spectroscopies depicted an absorption and emission about 817 nm and 878 nm, respectively. X-ray diffraction (XRD) analysis showed a growth of Ag2S acanthite phase. Transmission Electron Microscopy (TEM) images revealed a clear formation of Ag2S@ZnS core-shell structure. [ABSTRACT FROM AUTHOR]

The possibility of laboratory X-ray reflectometry study of the structure of dimyristoyl phosphatidylserine (DMPS) phospholipid monolayers on the water surface in various phase states has been demonstrated. [ABSTRACT FROM AUTHOR]

Turbidity of water due to the presence of suspended sediment is measured and interpreted in a variety of ways, which can lead to the misinterpretation of data. This paper re-examines the physics of light scattering in water, and exposes the extent to which the reporting of turbidity data is inconsistent. It is proposed that the cause of this inconsistency is the fact that the accepted turbidity standards USEPA Method 180.1, ISO 7027 and GLI Method 2 are mutually inconsistent, as these standards give rise to a large number of measurement units that are not based on the optical properties of light absorption and scattering by suspensions in water, but by the arbitrary definition of the degree of turbidity being due to a concentration of formazin or other similar polymer-based calibration standard. It is then proposed that all turbidity-measuring devices should be calibrated with precise optical attenuators such as neutral density filters. Such calibration would allow for the definition of a beam attenuation coefficient for every turbidity-measuring instrument which would be crosscomparable with any other instrument calibrated in the same way. The units for turbidity measurements should be based on attenuation and reported as dB m-1. It is also proposed that a new standard should be drafted according to this attenuation-based method, and this new standard should also define the nomenclature for reporting data collected at any specific scattering angle in terms of an attenuation in dB m-1. The importance of multi-parameter turbidity measurements for the improvement of the quality of turbidity data and the application of parameter-rich data sets to new methods of sediment characterization are discussed. It is suggested that more research into multi-parameter turbidity measurements is needed, as these new methods will facilitate an increase in parity between turbidity and suspended sediment concentration, a relationship that is subjective. [ABSTRACT FROM AUTHOR]

Quantum chemical electronic energy of a molecular system depends on the level of the employed basis functions. The inverse power laws describing the convergences of the calculated Hartree-Fock ( HF) and electronic correlation energies of water molecules have been determined by fitting the energies predicted by the CCSD(T) theory with various levels of correlation consistent basis functions. The law was applied to calculate the energies of a few simple water clusters by varying the OH bond distance of a molecule in order to understand how the two parts of the potential energy subject to the stretching motion of water molecules depend on the variation of local environments. It is found that the HF energy strongly depends on the environments of a local OH bond while the correlation energy is almost insensitive to the neighboring molecules. This suggests that the HF theory may have a great advantage in saving computation time for efficient calculations of vibrational frequencies widely distributed due to the inhomogeneity in the local environments of water molecules in the condensed phases. [ABSTRACT FROM AUTHOR]

To investigate the dynamics of a bubble induced on a finite rigid boundary in water, a simple experimental method based on laser beam transmission probe is developed to measure the time dependence of the bubble’s radius on a finite metallic surface under different incident laser energies, and a numerical method is employed to simulate the bubble’s first collapse. A correction factor based on the Raleigh collapse time formula is proposed to describe the collapse time of the bubble induced on a finite rigid boundary. The experimental and simulation results show that the correction factor is slightly different for the bubble’s first and subsequent two oscillations, and its detailed expression is obtained from the experimental and simulation results. The experimental results show that the conversion efficiency of the incident laser energy into bubble energy increases with the former, and the ratio of the energy left for subsequent bubble oscillation increases with the number of bubble oscillation. [ABSTRACT FROM AUTHOR]

Here, we demonstrate a phosphorodiamidate morpholino oligos (PMO)-functionalized nanochannel biosensor for label-free detection of microRNAs (miRNAs) with ultrasensitivity and high sequence specificity. PMO, as a capture probe, was covalently anchored on the nanochannel surface. Because of the neutral character and high sequence-specific affinity of PMO, hybridization efficiency between PMO and miRNAs was enhanced, thus largely decreasing background signals and highly improving the detection specificity and sensitivity. The miRNAs detection was realized through observing the change of surface charge density when PMO/miRNAs hybridization occurred. Not only could the developed biosensor specifically discriminate complementary miRNAs (Let-7b) from noncomplementary miRNAs (miR-21) and one-base mismatched miRNAs (Let-7c), but also it could detect target miRNAs in serum samples. In addition, this nanochannel-based biosensor attained a reliable limit of detection down to 1 fM in PBS and 10 fM in serum sample, respectively. It is expected that such a new method will benefit miRNA detection in clinical diagnosis. [ABSTRACT FROM AUTHOR]

The paper has analyzed relationships between lengths of covalent and hydrogen bonds and characteristic distances between oxygen atoms in water and ice, and also density of water and its isobaric and isothermal compressibility on temperature and pressure. It is shown that regularities of changes in properties of water are determined by the features of covalent and hydrogen bonds and electrostatic repulsion between oxygen atoms. [ABSTRACT FROM AUTHOR]

The spatial scale dependence of midlatitude water vapor variability in the high-resolution limited-area model COSMO is evaluated using diagnostics of scaling behavior. Past analysis of airborne lidar measurements showed that structure function scaling exponents depend on the corresponding airmass characteristics, and that a classification of the troposphere into convective and nonconvective layers led to significantly different power-law behaviors for each of these two regimes. In particular, scaling properties in the convective air mass were characterized by rough and highly intermittent data series, whereas the nonconvective regime was dominated by smoother structures with weaker small-scale variability. This study finds similar results in a model simulation with an even more pronounced distinction between the two air masses. Quantitative scaling diagnostics agree well with measurements in the nonconvective air mass, whereas in the convective air mass the simulation shows a much higher intermittency. Sensitivity analyses were performed using the model data to assess the impact of limitations of the observational dataset, which indicate that analyses of lidar data most likely underestimated the intermittency in convective air masses due to the small samples from single flight tracks, which led to a bias when data with poor fits were rejected. Though the quantitative estimation of intermittency remains uncertain for convective air masses, the ability of the model to capture the dominant weather regime dependence of water vapor scaling properties is encouraging. [ABSTRACT FROM AUTHOR]

In this study, a new method was proposed for calibrating hygrometers. The moisture permeation cylinder, which was used to measure the water vapor permeability of fabrics, was used to generate various levels of relative humidity. A dry nitrogen stream was employed to sweep the water vapor away. It was deduced that the relative humidity of the outgoing nitrogen stream was negatively correlated to the volumetric flow rate of nitrogen stream, i.e., the lower the volumetric flow rate, the higher the relative humidity. The hygrometer HMT 333 was chosen to measure the relative humidity of the outgoing nitrogen stream at five levels. The test data indicated that good agreement was observed between the measured humidity and the observed humidity from the Vaisala, Inc. Moreover, this method offers high sensitivity and fast response. Therefore, the relative humidity of the outgoing nitrogen stream can be used as a secondary humidity reference. [ABSTRACT FROM AUTHOR]

Water vapor transmission rate (WVTR) measuring devices with a quadrupole mass spectrometer (QMS) have an advantage in measuring low WVTRs because measurements are taken under an extremely low background of water vapor by realizing ultrahigh vacuum conditions. Here, the reliability of the QMS measurements was improved by including a porous plug with known molecular conductance in the device to generate a reference molar flux for in situ QMS calibration. Then, standard gas barrier (SGB) films made from a clay-polyimide nanocomposite film were also developed and used to validate the measurement. The measurement results for the SGB films were on the extrapolated calibration curve obtained with the porous plug down to WVTR at the 10-6 g m-2 day-1 level within the estimated measurement uncertainty. [ABSTRACT FROM AUTHOR]

To date, existing urban land surface models (ULSMs) have been mostly evaluated and optimized for mid- and high-latitude cities. For the first time, we provide a comparative evaluation of four ULSMs for a tropical residential neighbourhood in Singapore using directly measured energy balance components. The simulations are performed offline, for an 11 month period, using the bulk scheme TERRA_URB and three models of intermediate complexity (CLM, SURFEX and SUEWS). In addition, information from three different parameter lists are used to quantify the impact (interaction) of (between) external parameter settings and model formulations on the modelled urban energy balance components. Encouragingly, overall results indicate good model performance for most energy balance components and align well with previous findings for midlatitude regions, suggesting the transferability of these models to (sub)tropical regions. Similar to results from midlatitude regions, the outgoing long-wave radiation and latent heat flux remain the most problematic fluxes. In addition, the various combinations of models and different parameter values suggest that error statistics tend to be dominated more by the choice of the latter than the choice of model. Finally, our intercomparison framework enabled the attribution of common deficiencies in the different model approaches found previously in midlatitude regions: the simple representation of water intercepted by impervious surfaces leading to a positive bias in the latent heat flux directly after a precipitation event; and the positive bias in modelled outgoing long-wave radiation that is partly due to neglecting the radiative interactions of water vapour between the surface and the tower sensor. These findings suggest that future developments in urban climate research should continue the integration of more physically based processes in urban canopy models, ensure the consistency between the observed and modelled atmospheric properties and focus on the correct representation of urban morphology, water storage and thermal and radiative characteristics. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulations are used to investigate 1 H nuclear magnetic resonance (NMR) relaxation and diffusion of bulk n - C 5 H 12 to n - C 17 H 36 hydrocarbons and bulk water. The MD simulations of the 1 H NMR relaxation times T 1 , 2 in the fast motion regime where T 1 = T 2 agree with measured (de-oxygenated) T 2 data at ambient conditions, without any adjustable parameters in the interpretation of the simulation data. Likewise, the translational diffusion D T coefficients calculated using simulation configurations agree with measured diffusion data at ambient conditions. The agreement between the predicted and experimentally measured NMR relaxation times and diffusion coefficient also validate the forcefields used in the simulation. The molecular simulations naturally separate intramolecular from intermolecular dipole-dipole interactions helping bring new insight into the two NMR relaxation mechanisms as a function of molecular chain-length (i.e. carbon number). Comparison of the MD simulation results of the two relaxation mechanisms with traditional hard-sphere models used in interpreting NMR data reveals important limitations in the latter. With increasing chain length, there is substantial deviation in the molecular size inferred on the basis of the radius of gyration from simulation and the fitted hard-sphere radii required to rationalize the relaxation times. This deviation is characteristic of the local nature of the NMR measurement, one that is well-captured by molecular simulations. [ABSTRACT FROM AUTHOR]

In this study composite mixed matrix membranes containing hydrophilic microphase-separated block copolymer (Pebax ® 1657) and graphene oxide nanosheets were prepared using a dip coating method. Water vapor and N 2 gas permeation were measured as a function of different parameters: (i) layer thickness, (ii) content of graphene oxide (GO), and (iii) content of reduced GO. Surprisingly, a concentration of only 2 wt% of GO nanosheets well dispersed in the Pebax layer boosted the selectivity 8 times by decreasing the water vapor permeance by only 12% whereas N 2 gas permeance decreased by 70%. Using reduced GO instead, the water vapor permeance declined by up to 16% with no influence on the N 2 gas permeance. We correlated the permeation properties of the mixed matrix membranes with different models and found, that both the modified Nielsen model and the Cussler model give good correlation with experimental findings. [ABSTRACT FROM AUTHOR]