Molecular Properties Of Water Research Articles

Ecology of freshwaters: a view for the twenty-first century

Ecology of freshwaters: a view for the twenty-first century

Influence of Exchangeable Cations on Water Adsorption by Soil Clays

The interaction of water with the clay fractions (<2 μm) from two midwestern soils was studied using Fourier transform infrared (FTIR) spectroscopy and gravimetric methods. The soil clay fractions were obtained from a Blount loam (fine, illitic, mesic Aeric Epiaqualfs) and a Fayette silty clay loam (fine‐silty, mixed, mesic, superactive Typic Hapludalfs). These clay fractions were exchanged with Mg2+, 50:50 Ca2+/Mg2+, Ca2+, Na+, and K+ to determine the influence of the exchangeable cation on their water sorption behavior. Water sorption isotherms and FTIR spectra of the clays were collected simultaneously using a gravimetric‐spectroscopic cell. Overall, the amount of water sorbed by the samples increased as the ionic potential of the exchangeable cation increased and was strongly correlated to the hydration energy of the cations (P > F < 0.0001). The position of the H–O–H bending band (ν2 mode) also increased with increasing ionic potential of the exchangeable cation indicating strengthening of water H bonds. In addition, it was observed that the position of this band decreased with increasing water content for the Mg‐exchanged clays compared with an overall increase for the Ca‐exchanged samples. X‐ray diffraction patterns indicated an expansion of the phyllosilicate clay minerals as the water activity increased; however, no differences were observed between the Ca‐ and Mg‐exchanged samples. This study shows that the molecular properties of water on Ca‐ and Mg‐exchanged soil clays are similar to that on specimen clays and provides new insight about the role of exchangeable cations in soils.

Effect of high pressure processing and addition of glycerol and salt on the properties of water in corn tortillas

The effects of high pressure processing (HPP) at 500 and 800 MPa for 1 and 10 min, and the addition of glycerol (4% w/w) and salt (1% w/w) on the properties of water in corn tortillas were investigated. Moisture content and water activity were not affected by either HPP or addition of glycerol/salt. Thermal analysis techniques (such as differential scanning calorimetry and thermogravimetric analysis) and nuclear magnetic resonance spectroscopy ( 1 H cross-relaxation and 1 H T1 and T2 relaxation times) were used to characterize these samples at a structural and molecular level, respectively. Addition of glycerol and salt significantly decreased the ‘freezable’ water content of the tortillas while HPP had little effect on the measured structural properties. The proton mobility was significantly decreased by HPP but not affected by addition of glycerol and salt. These results show that both composition and HPP may alter the structural and molecular properties of water in corn tortillas. q 2003 Elsevier Ltd. All rights reserved.

Properties of saccharides and saccharide derivatives in the dry and partially hydrated states

This study investigates the correlation (if any) between the surface properties of dry mannitol, sorbitol and glucose, as determined using inverse gas chromatography (IGC) and other techniques, with microwave dielectric analysis of the molecular polarisability of water in the hydrated material. Microwave dielectric analysis of the hydrated material (using a circular resonant cavity) showed a transition (ht) in the gradient of imaginary permittivity (e″ at 2.2 GHz) vs. water content for all materials. This transition reflects the appearance of another population of water with enhanced mobility. The gradient below ht (m1) reflects the reorientation mobility of water close to the surface of the solid, and therefore provides one measure of the strength of interaction with each material. Estimates for ht and m1 parallel the IGC data by giving a rank order of affinity as glucose ≥ mannitol ≥ sorbitol. This link suggests that the molecular properties of water and the strength of interaction with the hydrated material are most certainly governed by the acceptor/donor properties of the surface (as determined by IGC). Moreover, it can be inferred that the presence of mobile water (up to the relatively high levels defined by ht) does not change the surface energy of the material.

Time resolved measurements of proton diffusion in HexII water-phospholipids mixture

Under well defined conditions, water and phospholipids are spontaneously assembled into a well-ordered structure, where the lipids form long tubes, of known diameter, filled with water. This structure is referred to as HexII. In our study, we dissolved Pyranine (8-hydroxy 1,3,6 trisulfonate) in the aqueous phase of HexII, and by monitoring the dynamics of proton dissociation, gauged the physical-chemical properties of the aqueous matrix, organized as long tubes with diameter varying between 16 A ̊ < 2r w < 50 A ̊ . The measurements, based on real time detection of proton dissociation, indicate that the lipid-water interface is characterized by diminished capacity of water to bind protons and intensified electrostatic interactions. Both properties varied with the diameter of the tubes. These observations are explained by considering the molecular properties of water at the hydration layer and by the effect of dielectric discontinuity at the water-lipid junction.

A polarizable, dissociating molecular dynamics model for liquid water

We describe a molecular dynamics model for dissociable, polarizable water. The model, which describes both the static and dynamic properties of real water quite reasonably, contains the following features: Self-consistent local fields are calculated in an extension of an earlier algorithm in which the dipole moments of the water are treated as dynamical variables. An intramolecular three-body potential assures that the molecular properties of water are in agreement with experiment. Ewald methods are used to take account of monopole–dipole and dipole–dipole as well as monopole–monopole interactions. The model was optimized using a Monte Carlo procedure in the parameter space which is described.

Solvent properties and thier effects on gradient elution high-performance liquid chromatography: I. Bulk and molecular properties of water and acetonitrile

The most common baseline anomalies observed in gradient elution high-performance liquid chromatography can be explained by the non-ideal behaviour of the solvents used. The bulk and molecular properties of mixed solvents, as they affect the perfomance of the liquid chromatograph, are explored. The concept of mole flow-rate, useful in heat balance and partition mechanism studies, is introduced and put to use in a preliminary heat balance study which could be sued to size heat exchange equipment useful in thermostatting a liquid chromatograph. The inter-dependecne of these properties is shown to produce cumulative effects in the pumping system, the column and the detector of the liquid chromatograph. The properrties of water-acetonitrile mixtures are used for illustration.

Molecular properties of water

Extended basis set configuration interaction calculations have been performed on the 1A 1 ground state of water at the experimental geometry. Using a wavefunction which yielded the lowest variational energy to date, a variety of molecular properties have been evaluated and their convergence with respect to basis set discussed.