Solvent Packing Research Articles

Paramagnetic Effects in NMR Spectroscopy of Transition-Metal Complexes: Principles and Chemical Concepts.

ConspectusMagnetic resonance techniques represent a fundamental class of spectroscopic methods used in physics, chemistry, biology, and medicine. Electron paramagnetic resonance (EPR) is an extremely powerful technique for characterizing systems with an open-shell electronic nature, whereas nuclear magnetic resonance (NMR) has traditionally been used to investigate diamagnetic (closed-shell) systems. However, these two techniques are tightly connected by the electron-nucleus hyperfine interaction operating in paramagnetic (open-shell) systems. Hyperfine interaction of the nuclear spin with unpaired electron(s) induces large temperature-dependent shifts of nuclear resonance frequencies that are designated as hyperfine NMR shifts (δHF).Three fundamental physical mechanisms shape the total hyperfine interaction: Fermi-contact, paramagnetic spin-orbit, and spin-dipolar. The corresponding hyperfine NMR contributions can be interpreted in terms of through-bond and through-space effects. In this Account, we provide an elemental theory behind the hyperfine interaction and NMR shifts and describe recent progress in understanding the structural and electronic principles underlying individual hyperfine terms.The Fermi-contact (FC) mechanism reflects the propagation of electron-spin density throughout the molecule and is proportional to the spin density at the nuclear position. As the imbalance in spin density can be thought of as originating at the paramagnetic metal center and being propagated to the observed nucleus via chemical bonds, FC is an excellent indicator of the bond character. The paramagnetic spin-orbit (PSO) mechanism originates in the orbital current density generated by the spin-orbit coupling interaction at the metal center. The PSO mechanism of the ligand NMR shift then reflects the transmission of the spin polarization through bonds, similar to the FC mechanism, but it also makes a substantial through-space contribution in long-range situations. In contrast, the spin-dipolar (SD) mechanism is relatively unimportant at short-range with significant spin polarization on the spectator atom. The PSO and SD mechanisms combine at long-range to form the so-called pseudocontact shift, traditionally used as a structural and dynamics probe in paramagnetic NMR (pNMR). Note that the PSO and SD terms both contribute to the isotropic NMR shift only at the relativistic spin-orbit level of theory.We demonstrate the advantages of calculating and analyzing the NMR shifts at relativistic two- and four-component levels of theory and present analytical tools and approaches based on perturbation theory. We show that paramagnetic NMR effects can be interpreted by spin-delocalization and spin-polarization mechanisms related to chemical bond concepts of electron conjugation in π-space and hyperconjugation in σ-space in the framework of the molecular orbital (MO) theory. Further, we discuss the effects of environment (supramolecular interactions, solvent, and crystal packing) and demonstrate applications of hyperfine shifts in determining the structure of paramagnetic Ru(III) compounds and their supramolecular host-guest complexes with macrocycles.In conclusion, we provide a short overview of possible pNMR applications in the analysis of spectra and electronic structure and perspectives in this field for a general chemical audience.

Disclosing the Interfacial Electrolyte Structure of Na-Insertion Electrode Materials: Origins of the Desolvation Phenomenon.

Among a variety of promising cathode materials for Na-ion batteries, polyanionic Na-insertion compounds are among the preferred choices due to known fast sodium transfer through the ion channels along their framework structures. The most interesting representatives are Na3V2(PO4)3 (NVP) and Na3V2(PO4)2F3 (NVPF), which display large Na+ diffusion coefficients (up to 10-9 m2 s-1 in NVP) and high voltage plateaux (up to 4.2 V for NVPF). While the diffusion in the solid material is well-known to be the rate-limiting step during charging, already being thoroughly discussed in the literature, interfacial transport of sodium ions from the liquid electrolyte toward the electrode was recently shown to be important due to complex ion desolvation effects at the surface. In order to fill the blanks in the description of the electrode/electrolyte interface in Na-ion batteries, we performed a molecular dynamics study of the local nanostructure of a series of carbonate-based sodium electrolytes at the NVP and the NVPF interfaces along with careful examination of the desolvation phenomenon. We show that the tightness of solvent packing at the electrode surface is a major factor determining the height of the free energy barrier associated with desolvation, which explains the differences between the NVP and the NVPF structures. To rationalize and emphasize the remarkable properties of this family of cathode materials, a complementary comparative analysis of the same electrolyte system at the carbon electrode interface was also performed.

Temperature-dependent solvent reorganization entropies, free energies, and transition dipole strengths for the photoexcitation of Reichardt's dye B30.

Absorption spectra of the solvatochromic dye 2,6-diphenyl-4-2,4,6-triphenyl-1-pyridinophenolate (B30) were measured in seven solvents of varying polarity over temperature ranging from each solvent's freezing point to 300K. The excitation energies and their variances allowed calculations of the solvent reorganization energies, reorganization free energies and reorganization entropies as functions of temperature. The entropies of solvent packing around the chromophore are found to make major contributions to the reorganization free energies. The variances of the excitation energies depend only weakly on temperature, in disagreement with an expression that is often used for solvent reorganization free energies. Polar solvents reduce the transition dipole strength of B30's long-wavelength absorption band, probably because interactions with the solvent enhance the charge-transfer character of the transition. The dipole strength drops further at low temperatures.

Effective electrostatic interaction between columnar colloids: roles of solvent steric hindrance, polarity, and surface geometric characteristics

In the present work, coupling between the electrostatic interaction and solvent steric hindrance, and solvent polarity are studied by classical density functional theory with emphasis on their influence on the effective electrostatic potential between two similarly charged and parallel cylinder surfaces immersed in electrolyte solution.Several conclusions are confirmed. First, solvent steric hindrance always enhances the effective electrostatic potential curve oscillation and its first potential well depth or induces the potential well formation even in +1:−1 electrolyte; the enhancing effects are positively correlated with the solvent packing fraction. The curve oscillation is weakened anomalously with the surface charge density strength. Second, with a certain packing fraction of the crowding agent, its diameter has no distinct effect on the oscillation intensity of the effective electrostatic potential curves, but the oscillation period is always equal to the diameter. Third, influences of solvophilicity or solvophobicity of counter- and co-ions on the effective electrostatic potential are different in strength and mode. Strong counter-ion solvophobicity greatly raises the like-charge attraction strength with a simultaneously weakening of the effective electrostatic potential oscillation, and vice versa; solvophobicity or solvophilicity of co-ion influences the effective electrostatic potential curve in a less obvious way by translating it up/down, respectively; more specifically, the curve morphology is rarely changed. Fourth, it is illustrated that high counter-ion valence and high surface charge are not necessary conditions (confirmed in previous literature) of the surface charge reversal occurrence; counter-ion solvophobicity induces the charge reversal at far milder conditions: univalent counter-ion, lower bulk concentration, and lower surface charge strength. Fifth, by comparing with previous two works on the effects of solvent granularity on the effective electrostatic potential in flat and spherical slits, we conclude that the flat slit contact potential is always repulsive, the spherical slit contact potential can be very attractive, and the present cylinder slit contact potential is between the two.

Structure and Na Ion Transport in NaPF6/Carbonate Electrolyte inside Carbon Nanopores: A Molecular Dynamics Study

Sodium-ion batteries (NIBs) are in the spotlight as highly promising energy storage applications due to the low cost and wide availability of Na sources. To date, computational studies of Na storage and transport in carbon electrodes have been carried out without considering the realistic structural and dynamic properties of a carbon anode - electrolyte, which could be critical to battery performance. Using combined molecular dynamics (MD) simulation and density functional theory (DFT) calculations, we describe the behavior of a Na-based electrolyte, consisting of sodium hexafluorophosphate (NaPF6), ethylene carbonate (EC), and dimethyl carbonate (DMC), near the confined structures of nanoporous carbon electrodes. In our simulation, nanoporous carbons with an average pore size of 8.9 Å were first generated using the Mimetic porous carbon model by quench MD simulation. We also adopted the constant potential method (CPM) to model the electrode carbon to account for the fluctuation of the local charges that are characteristic of realistic battery systems. We investigated the distribution of electrolyte molecules and their microstructures at 0 V and 2 V potentials to provide molecular insights on properties such as solvent packing, degree of confinement (DoC), preferential adsorption sites, and solvation sheath structure. Under the influence of applied potential, we report a good wettability of the electrode by electrolyte molecules as a result of the interconnectivity of nanopores, with the accumulation of electrolyte compounds at the electrode/electrolyte interface as they diffuse into the nanopores. Also, Na+ intercalates into highly confined carbon structures while PF6 - occupies weakly confined carbon nanostructures by forming ion pairs with Na+. We show that nanoporous carbon structures reduce the adsorption distance of Na+ by ~29 % compared to planar electrodes and consequently identify a hydrogen-terminated edge of porous carbon as a preferential adsorption site for Na+ of favorable adsorption energy of -0.27 eV compared to the adsorption energy of 0.02 eV for Na+ insertion onto a basal surface. Finally, an investigation of the solvation sheath structure as a function of DoC shows decreased solvation shell, shortened adsorption distances, and increased counter-charge with increasing DoC.

A Molecular Dynamics Study of Na Ion Transport and Storage inside Nanoporous Carbon Electrode for Na-Ion Batteries

Hard carbon has emerged as an attractive anode material for sodium ion batteries (NIBs) because of its low cost, high initial coulombic efficiency, high specific capacity, and steady cycling performance. Based on combined molecular dynamics (MD) simulation and density functional theory (DFT) calculations, we present an atomistic description of the electrolyte-electrode interaction of sodium hexafluorophosphate (NaPF6) in mixed ethylene (EC) and dimethyl carbonate (DMC) electrolyte inside nanoporous carbon electrode. We investigate the microstructure of electrolyte in carbon nanopores with an average pore size of 8.9 Å and a specific surface area of 1794 m2g-1 at 0 V and 2 V to gain molecular insight into electrolyte behavior such as solvent packing, preferential adsorption sites, and solvation structure. Our simulation suggests good accessibility of carbon nanopores by electrolyte molecules upon charging. At 2 V, Na+ is desolvated and intercalates into highly confined carbon structures as a result of the strong interaction between Na+ and charged carbon atoms while PF6 - occupies weakly confined carbon nanostructures by forming ion pairs with Na+. Also, we examined the various levels of confinement of electrolyte components using a degree of confinement (DoC) analysis, and present the effects of confinement on electrolyte properties. Our calculations show a 29 % reduction in Na+ adsorption distance for a nanoporous structure compared to a planar structure of carbon, and the preferential adsorption of Na+ at a hydrogen-terminated edge of porous carbon with an adsorption energy of -0.27 eV compared to a basal site with a higher adsorption energy of 0.02 eV. Finally, an investigation of the solvation sheath structure as a function of DoC shows decreased solvation shell, shortened adsorption distances, and increased counter-charge with increasing DoC.

Observing Solvent Dynamics in Porous Carbons by Nuclear Magnetic Resonance

The adsorption and diffusion of species in activated carbons is fundamental to many processes in catalysis and energy storage. Nuclear magnetic resonance (NMR) gives an insight into the molecular-level mechanisms of these phenomena thanks to the unique magnetic shielding properties of the porous carbon structure, which allows adsorbed (in-pore) species to be distinguished from those in the bulk (ex-pore). In this work we investigate exchange dynamics between ex-pore and in-pore solvent species in microporous carbons using a combination of one-dimensional (1D) and two-dimensional (2D) NMR experiments. We systematically compare the effects of four variables: particle size, porosity, solvent polarity and solvent viscosity to build up a picture of how these factors influence the exchange kinetics. We show that exchange rates are greater in smaller and more highly activated carbon particles, which is expected due to the shorter in-pore–ex-pore path length and faster diffusion in large pores. Our results also show that in-pore–ex-pore exchange of apolar solvents is slower than water, suggesting that the hydrophobic chemistry of the carbon surface plays a role in the diffusion kinetics, and that increased viscosity also reduces the exchange kinetics. Our results also suggest the importance of other parameters, such as molecular diameter and solvent packing in micropores.

Electric Double Layers with Surface Charge Regulation Using Density Functional Theory.

Surprisingly, the local structure of electrolyte solutions in electric double layers is primarily determined by the solvent. This is initially unexpected as the solvent is usually a neutral species and not a subject to dominant Coulombic interactions. Part of the solvent dominance in determining the local structure is simply due to the much larger number of solvent molecules in a typical electrolyte solution.The dominant local packing of solvent then creates a space left for the charged species. Our classical density functional theory work demonstrates that the solvent structural effect strongly couples to the surface chemistry, which governs the charge and potential. In this article we address some outstanding questions relating double layer modeling. Firstly, we address the role of ion-ion correlations that go beyond mean field correlations. Secondly we consider the effects of a density dependent dielectric constant which is crucial in the description of a electrolyte-vapor interface.

Intrinsic characteristics of cellulose dissolved in an ionic liquid: the shape of a single cellulose molecule in solution

Although cellulose is the oldest macromolecule we have known, its intrinsic properties are still not well understood because of the lack of suitable solvents. The recent development of ionic liquids enables preparation of cellulose solutions in which cellulose molecules are supposed to be dispersed molecularly. Conventionally a semi-flexible-chain model or a worm-like chain model has been applied to describe the dilute solution properties of cellulose. A semi-flexible chain model is specified in terms of a persistent length to determine the chain stiffness of a solute molecule, completely neglecting details of the solvent–solute interaction, and the discussion is mainly focusing on the conformation of a solute molecule. In this paper we adapt a cylinder model which at least specifies the local shape of a solute molecule. Since the ionic liquids are now available as a new solvent of cellulose, we have prepared cellulose/ionic liquid solutions for small-angle X-ray scattering (SAXS) measurements which provide information on the local structure of cellulose molecules in the restricted range. The SAXS measurements were performed on the cellulose/ionic liquid solutions at two independent synchrotron facilities and confirmed the consistency of the observed scattering profile. Standard methods were applied to analyze the scattered data first, and afforded a model for representing a cellulose molecule in ionic liquid solutions. Two types of ionic liquids were used, and it was ascertained that cellulose was not degraded under the conditions used. The solution characteristic was found to change by heating during the preparation of each solution. The heating effect on the conformational change of cellulose was discussed in terms of the solute–solvent interaction from the simulation with a coaxial double layer cylinder model. The state of solvent packing was considered as well from the thickness and relative electron density of the sheath in the simulated coaxial double layer cylinder model.

Relationships between residue Voronoi volume and sequence conservation in proteins

BackgroundFunctional and biophysical constraints can cause different levels of sequence conservation in proteins. Previously, structural properties, e.g., relative solvent accessibility (RSA) and packing density of the weighted contact number (WCN), have been found to be related to protein sequence conservation (CS). The Voronoi volume has recently been recognized as a new structural property of the local protein structural environment reflecting CS. However, for surface residues, it is sensitive to water molecules surrounding the protein structure. Herein, we present a simple structural determinant termed the relative space of Voronoi volume (RSV); it uses the Voronoi volume and the van der Waals volume of particular residues to quantify the local structural environment. MethodsRSV (range, 0–1) is defined as (Voronoi volume−van der Waals volume)/Voronoi volume of the target residue. The concept of RSV describes the extent of available space for every protein residue. ResultsRSV and Voronoi profiles with and without water molecules (RSVw, RSV, VOw, and VO) were compared for 554 non-homologous proteins. RSV (without water) showed better Pearson's correlations with CS than did RSVw, VO, or VOw values. The mean correlation coefficient between RSV and CS was 0.51, which is comparable to the correlation between RSA and CS (0.49) and that between WCN and CS (0.56). ConclusionsRSV is a robust structural descriptor with and without water molecules and can quantitatively reflect evolutionary information in a single protein structure. Therefore, it may represent a practical structural determinant to study protein sequence, structure, and function relationships.

Polymorphism-dependent aggregation-induced emission of pyrrolopyrrole-based derivative and its multi-stimuli response behaviors

Bis(4-cyanophenyl)-4,4′-(2,5-diphenylpyrrolo[3,2-b] pyrrole-1,-4-diyl) dibenzoate (DPPCN) was synthesized and exhibited aggregation-induced emission properties. DPPCN was cultivated in different solvents getting three kinds of crystals, A, B and C. Crystals of A and B were respectively blue and cyan-blue emissive, while C was yellow-green emissive. They all displayed crystalline-induced emission behaviors. According to X-ray single crystal diffraction analysis, the intermolecular interactions account for restricted internal rotations, leading to fluorescence enhancement. The different kinds of co-effects of the solvent, intermolecular forces, molecular conformations and molecular packing modes endow DPPCN polymorphisms with multi-color emissions (from blue to yellow and up to 60 nm) and different fluorescence efficiencies. The fluorescence of A can be reversibly tuned by grinding and exposing to chloroform vapor with a 46 nm wavelength change. The crystal of C can blue shifted the fluorescence that matches with B upon fumed by chloroform for about 12 h and further blue shifted the fluorescence emission that matches with A when fumed by chloroform for about 24 h. Multi-color fluorescence tuning and switching is attributed to the nature of polymorphs, that is, a change of molecular conformation and intermolecular packing modes. The crystal of A also exhibited thermo-stimulus fluorescence switching behavior due to the co-crystallization with solvent chloroform. The properties of A show promising applications in temperature monitoring and volatile organic compound detecting devices.

Evolution of off-lattice model proteins under ligand binding constraints

We investigate protein evolution using an off-lattice polymer model evolved to imitate the behavior of small enzymes. Model proteins evolve through mutations to nucleotide sequences (including insertions and deletions) and are selected to fold and maintain a specific binding site compatible with a model ligand. We show that this requirement is, in itself, sufficient to maintain an ordered folding domain, and we compare it to the requirement of folding an ordered (but otherwise unrestricted) domain. We measure rates of amino acid change as a function of local environment properties such as solvent exposure, packing density, and distance from the active site, as well as overall rates of sequence and structure change, both along and among model lineages in star phylogenies. The model recapitulates essentially all of the behavior found in protein phylogenetic analyses, and predicts that amino acid substitution rates vary linearly with distance from the binding site.

Crystal structure of bis-[tetra-kis-(tri-phenyl-phosphane-κP)silver(I)] (nitrilo-tri-acetato-κ(4) N,O,O',O'')(tri-phenyl-phosphane-κP)argentate(I) with an unknown amount of methanol as solvate.

The structure of the title compound, [Ag(C18H15P)4]2[Ag(C6H6NO6)(C18H15P)], exhibits trigonal (P-3) symmetry, with a C 3 axis through all three complex ions, resulting in an asymmetric unit that contains one third of the atoms present in the formula unit. The formula unit thus contains two of the cations, one anion and disordered mol-ecules of methanol as the packing solvent. Attempts to refine the solvent model were unsuccessful, indicating uninter-pretable disorder. Thus, the SQUEEZE procedure in PLATON [Spek (2015 ▸). Acta Cryst. C71, 9-18] was applied, accounting for 670 electrons per unit cell, representing approximately 18 mol-ecules of methanol in the formula unit. The stated crystal data for M r, μ etc do not take these into account.

Too packed to change: side-chain packing and site-specific substitution rates in protein evolution.

In protein evolution, due to functional and biophysical constraints, the rates of amino acid substitution differ from site to site. Among the best predictors of site-specific rates are solvent accessibility and packing density. The packing density measure that best correlates with rates is the weighted contact number (WCN), the sum of inverse square distances between a site’s Cα and the Cα of the other sites. According to a mechanistic stress model proposed recently, rates are determined by packing because mutating packed sites stresses and destabilizes the protein’s active conformation. While WCN is a measure of Cα packing, mutations replace side chains. Here, we consider whether a site’s evolutionary divergence is constrained by main-chain packing or side-chain packing. To address this issue, we extended the stress theory to model side chains explicitly. The theory predicts that rates should depend solely on side-chain contact density. We tested this prediction on a data set of structurally and functionally diverse monomeric enzymes. We compared side-chain contact density with main-chain contact density measures and with relative solvent accessibility (RSA). We found that side-chain contact density is the best predictor of rate variation among sites (it explains 39.2% of the variation). Moreover, the independent contribution of main-chain contact density measures and RSA are negligible. Thus, as predicted by the stress theory, site-specific evolutionary rates are determined by side-chain packing.

Toward rapid preparation of capillary columns for electrochromatography use

CEC is a high performance electrodriving liquid phase separation technique. It does not need complex and sophisticated high pressure instrumentation for nanoflow driving. This is attractive for parallel multicolumn analysis. To this end, high throughput methods for column preparation are needed to support the use of multiple columns. In this study, we directly used CEC mobile phase solution as the packing solvent, and realized rapid preparation of capillary columns based on a single particle fritting technology. The method presented high preparation throughput compared with other reported methods based on various fritting technologies. The single particle fritting approach promoted column preparation throughput to 1 column/h, including all the fritting, packing and conditioning steps. The rapidly prepared columns showed consistently high efficiency of up to 150 000 plates per meter, and usefulness in reversed phase CEC of neutral, charged and biomolecules. With standard peptides as the sample, excellent long term reproducibility (better than 0.8%RSD, ten days, for retention times) was observed.

Intermolecular interactions in mixtures of poly (ethylene glycol) with methoxybenzene and ethoxybenzene: Volumetric and viscometric studies

The density and viscosity values of the binary mixtures of {poly (ethylene glycol) (PEG400)+methoxybenzene, or+ethoxybenzene} have been measured at T=(298.15, 308.15, and 318.15)K. From these experimental values, the excess molar volume, apparent specific volume, partial specific volume of solute, partial specific volume of solvent and excess Gibbs free energy of activation have been computed over the entire range of composition at three temperatures. From the experimental data, the thermodynamic functions of activation have been estimated for each binary mixture. The obtained results have been interpreted in light of polymer–solvent interactions and packing effects. The signs of excess molar volume and deviations of excess Gibbs free energy of activation have been used to obtain some information in regard to existence of specific interactions between PEG400 and solvents molecules. The changes in entropy and enthalpy of activation from the initial state to the transition state were also calculated in order to see which one of these functions controls viscous flow process in the studied polymer solutions. The excess molar volume and excess Gibbs free energy of activation values have been adequately fitted to the Redlich–Kister polynomial. Apparent specific volume values were correlated with the suitable equation. The different models proposed for correlating the viscosity of polymer solutions or liquid mixtures (segment-based-Eyring–NRTL, segment-based-Eyring–Wilson, Grunbreg–Nissan, Frenkel, Hind et al., Katti–Chauddhri, Tamura–Kurata, Auslander and McAllister) have also been used to fit the viscosity values.

Determining the Performance of an Efficient Nonaqueous CO2 Capture Process at Desorption Temperatures below 373 K

Efficient CO2 capture by chemical absorption is currently gaining interests for the control greenhouse gas emissions. In this work, a nonaqueous process was developed to regenerate CO2 below 373 K by removing methanol first after the hybrid solvent of monoethanolamine (MEA) and methanol had absorbed CO2. A model was accordingly developed to analyze the performance of the desorption process. Experiments were performed to determine the missing reaction kinetics of nonaqueous solvent regeneration of CO2 to help develop the model. The predicted gas concentration, axial velocity, energy consumption, and desorption efficiency agreed well with the stripper experimental data. A parametric analysis was conducted to investigate the effects of temperature, pressure, lean solvent loading, gas/liquid ratio, packing, and internals on the energy consumption and desorption efficiency. All analyses were performed under three defined desorption conditions: N2, methanol vapor, and steam as purge gases. Major energy savings ...

Cation exchange, solvent free synthesis and packing patterns of quinolinium nickel(II) dipicolinates

Nickel dipicolinate complexes (HQ)2[NiL2]·5H2O (1) and (H5AQ)2[NiL2]·4H2O (2) (where L=pyridine-2,6-dicarboxylate anion, Q=quinoline, 5AQ=5-aminoquinoline) are synthesized in solution and also through solvent free cation exchange reactions of H2[NiL2]·3H2O. The crystal structures of the complexes 1 and 2 are determined. The strong π–π interactions between the quinolinium cations disrupt the conventional π-stacking interactions of the nickel–dipicolinate anions. The quinolinium cations of these complexes exchanges with alkali metal cations in basic medium and only at an extreme acidic condition the pyridine-2,6-dicarboxylate can be replaced from these complexes by halide ions.

The effect of urea on aqueous hydrophobic contact-pair interactions

Urea is perhaps the most common denaturant used for studying proteins. However the mechanism of denaturation is still not well understood. Recent theoretical work suggests that van der Waals interactions between urea and non-polar amino acid residues are a major contributor to the protein denaturation process. However, there are few experimental data measuring the effect of urea on hydrophobic interactions. In this work we have determined how the addition of urea to the aqueous solvent affects the contact-pair formed between alkyl and phenyl groups in model compounds: the data indicate that for solutes having a radius smaller than 2.87 Å cavity formation energetics dominate, therefore the addition of urea promotes the formation of hydrophobic contact pairs; while for larger solutes, van der Waals interactions have the largest magnitude, causing urea to disrupt the formation of contact pairs. The influence of urea on hydrophobic interactions is shown to be continuous in the 1-8 M concentration range and is well-correlated with the predictions of scaled particle theory. This demonstrates that the effect of urea on hydrophobic contact pairs can be explained by the changes observed in the solvent packing density, without having to invoke changes in the hydrogen bonding network of water.

ChemInform Abstract: Control of Nanospaces with Molecular Devices

AbstractReview: 32 refs.