Size Of Solvent Molecules Research Articles

New Heterometallic Carboxylate Frameworks: Synthesis, Structure, Robustness, Flexibility, and Porosity

Solvothermal reactions of cobalt acetate, alkali metal hydroxide, and isophthalic acid (H(2)ipa) in H(2)O/alcohol produce five new three-dimensional (3D) heterometallic carboxylate frameworks, namely, [Na(2)Co(ipa)(2)(MeOH)(2)](n) (1), [Na(2)Co(ipa)(2)(EtOH)(2)](n) (2), [Na(2)Co(ipa)(2)(H(2)O)(EtOH)](n) (3), [Li(2)Co(ipa)(2)(EtOH)](n) (4), and {[Li(2)Co(ipa)(2)(H(2)O)].H(2)O}(n) (5). Compounds 1-5 are all based on anionic [Co(ipa)(2)](n) square grids, which are linked by alkali metal ions in various manners to generate closely related but quite different 3D architectures. In addition to the carboxylate oxygen donors of the anionic [Co(ipa)(2)](n) square grids, the alkali metal ions are also coordinated by the MeOH, EtOH, or H(2)O ligands. The prototypical compound 1 shows interesting solid-state structural transformations and sorption properties. The coordinated MeOH molecules in 1 can be easily substituted by moist H(2)O, accompanying a structural transformation from the chiral phase 1 to centrosymmetric phase 3. Further, thermal liberation of all MeOH ligands causes significant structural change and gives rise to a non-porous framework [CoNa(2)(ipa)(2)](n) (1'), which adsorbs MeOH, EtOH, and MeCN but not acetone based on the sizes of solvent molecules. Moreover, 1' can also selectively absorb CO(2) over N(2), H(2), and C(2)H(2), demonstrating the importance of oxophilic Na(I) ion in controlling the gate-opening behavior.

Solvent Effects On Protein Mechanical Stability: A Steered Molecular Dynamics Study

The solvent is an integral component in all cellular processes and solvent composition is actively regulated in the living cell. Changes in solvent environment constitute a chemical signal that is transduced into a mechanical response: a chemically induced change of mechanical properties of a protein system. In this study, steered molecular dynamics simulations are used to stretch mechanical proteins set in non-aqueous solvent environment to reveal details and mechanism of protein - solvent interactions. We explore the atomic level mechanism and measure the effect of solvent substitution on the mechanical properties of proteins. We investigate the distance to the transition state during force induced unfolding as a function of solvent molecule size and the atomistic detail and timescale of participation of solvent molecules in the transition state structure. Resulting constant velocity and constant force extension profiles showed increased stability and resistance to unfolding force by proteins solvated in deuterium oxide vs. proteins solvated in water. Solvent molecules were found present the transition state structure and involved in forming a stabilizing bridge between the force-bearing sheer topology elements. Features of the simulations were also matched with previously reported experimental results.

Chirality-Controlled and Solvent-Templated Catenation Isomerism in Metal−Organic Frameworks

A family of highly porous homochiral, racemic, and meso metal-organic frameworks (MOFs) were synthesized based on a new elongated tetra-carboxylate ligand and the copper paddle-wheel building units. These MOFs exhibited remarkable catenation isomerism that is controlled by both chirality of the bridging ligand and the size of solvent molecules. The ability to manipulate framework interpenetration is key to future synthesis of mesoporous homochiral MOFs which hold great promise in heterogeneous asymmetric catalysis and chiral separations.

Diffusion of solvents in thin porous films

Porous films are used nowadays as dielectrics with low dielectric constant (so-called low- k dielectrics). Knowing the porous structure of such films is important for successful integration in the semiconductor manufacturing technology. We developed a simple characterization method based on diffusion of solvents inside a porous film. In our experiments toluene as a non-polar solvent and ethanol as a polar solvent were used. A porous film is covered with a barrier impermeable for solvent so the solvent only can enter the film from the side. The barrier is transparent that allows observation of diffusion as a color change of the film. Measuring diffused distance as a function of diffusion time, diffusion coefficients can be calculated. It was found that the diffusion coefficients strongly depend on the porous structure of the films. Small pores (with the size comparable with the solvent molecule size) show low diffusion coefficients with high activation energies comparable with the enthalpy of evaporation. Bigger pores exhibit high diffusion coefficients with low activation energies corresponding to the activation energy of the solvent viscosity. Measuring diffusion coefficients as functions of porosity/pore size it is possible to evaluate the interconnectivity of the porous structure of a film in question.

How does solvent molecular size affect the microscopic structure in polymer solutions?

Monte Carlo simulation has been used to investigate the effects of linear solvent molecular size on polymer chain conformation in solutions. Increasing the solvent molecular size leads to shrinkage of the polymer chains and increase of the critical overlap concentrations. The root-mean-square radius of gyration of polymer chains (R(g)) is less sensitive to the variation of polymer concentration in solutions of larger solvent molecules. In addition, the dependency of R(g) on polymer concentration under normal solvent conditions and solvent molecular size is in good agreement with scaling laws. When the solvent molecular size approaches the ideal end-to-end distance of the polymer chain, an extra aggregation of polymer chains occurs, and the solvent becomes the so-called medium-sized solvent. When the size of solvent molecules is smaller than the medium size, the polymer chains are swollen or partially swollen. However, when the size of solvent molecules is larger than the medium size, the polymer coils shrink and segregate, enwrapped by the large solvent molecules.

Reply to “Comment on ‘Hydrophobic effects on partial molar volume’ ” [J. Chem. Phys. 123, 167103 (2005)

In the Comment on our paper [J. Chem. Phys. 123, 167103 (2005), preceding paper], Graziano argues based on the scaled particle theory that the partial molar volume change in the transfer of a hydrophobic solute from “hypothetical nonpolar water” to water can be explained simply by the difference in the effective size of solvent molecules. Opposing to the argument, we clarify using the reference interaction site model theory that the attractive interactions represented by the hydrogen bonding play an essential role for the volume change, and that the explanation given by Graziano replaces the real physics by a fake model based on an “effective” molecular diameter. We also make a general argument against the use of hard-sphere models when one considers the properties of hydration.

Anomalous diffusivity and electric conductivity for low concentration electrolytes in nanopores.

We apply equilibrium and nonequilibrium molecular dynamics simulations to study the dynamic properties of electrolytes in nanopores. The realistic primitive model and the restrictive primitive model widely used in the statistical mechanics of liquid-state theory are applied to model the electrolytes. The electrolytic ions are immersed in water, treated in this work as either a dielectric continuum ignoring the size of solvent molecules or a macroscopic dielectric continuum (polar property) plus neutral soft spheres, and the aqueous electrolyte is put in a confined space. To simulate a condition mimicking closely processes of practical interest and yet maintaining the simulation computationally manageable, we consider an infinitely long and uncharged cylindrical tube. The equilibrium property of the self-diffusion coefficient D and the nonequilibrium property of electric conductivity sigma are computed in terms of electrolyte concentration, particle size, and cylindrical pore radius. The simulation results for the continuum solvent restrictive primitive model and continuum solvent primitive model show normal behavior for D versus pore radius R at ionic concentration 0.1M -i.e., D decreases with decreasing R -display an R independence of D at a certain threshold concentration and undergo an anomalous increase in D with reducing R at a lower value 0.025 M. The mechanism of the anomaly at the ionic concentration 0.025 M was sought for and interpreted in this work to arise from the energetic and entropic factors. Our simulated data of sigma at this same concentration follow the same trend as D. To delve further into the transport properties, we perform simulation studies for the discrete solvent primitive model and make a detailed analysis of the characteristic of the ion radial density functions. Comparison of the latter functions with those in the continuum solvent primitive model sheds light on the simulated diffusion coefficient within the context of discrete solvent primitive model which is about two orders of magnitude less. This difference in D is naturally attributed to the solvent effect. Similar disparities were reported by others for the discrete and continuum restrictive primitive models.

Solvation thermodynamics of xenon in n-alkanes, n-alcohols and water

Experimental thermodynamic data for the solvation of xenon in n-alkanes, water and n-alcohols, from different sources, are analysed by means of a general theory of solvation. The standard solvation Gibbs energy change is given by the sum of the work spent to create a cavity suitable to host xenon and the energy gained to turn on xenon-solvent attractive interactions. The latter contribution is larger in magnitude than the former in both n-alkanes and n-alcohols; the reverse holds in water. This finding is due to the fact that liquid water is characterized by the largest work of cavity creation, because of the smallness of its molecules. Since the two contributions to the solvation Gibbs energy change are both larger in magnitude in n-alcohols with respect to n-alkanes of the same number of heavy atoms, the xenon solubility is not so different between the two classes of solvents. The H-bonds play an indirect role, being important to determine the density of the liquid. It is also shown that there is no clear correlation between the cohesive energy density of the liquid and the solubility of xenon in the liquid itself. The present study confirms that the effective molecular size of solvent molecules is the principal factor in controlling the solvation Gibbs energy changes.

Coordination and Chemistry of Stable Cu(II) Complexes in the Gas Phase

A technique has been developed that provides a solution to the very considerable technical problem of preparing gas-phase complexes from transition metals in their higher oxidation states, i.e., Cu(II), Cr(III), Fe(II), etc. Charge transfer prevents complexes, such as [Cu·(H2O)n]2+, from being prepared via nucleation about an ion core, and yet these ions are pivotal to an understanding of transition metal chemistry. Discussed here are new results from a technique that appears capable of producing complexes from a wide variety of metals and ligands. Data are presented for copper(II) in association with 20 different ligands, including water, ammonia, pyridine, tetrahydrofuran, and benzene. For each [Cu·Ln]2+ system, two important quantities are identified: (i) the minimum number of ligands required to form a stable unit and (ii) the value of n for which the intensity distribution reaches a maximum. The data show considerable variation as a function of the composition and size of solvent molecule, with evidence of stable coordination shells containing between 2 and 8 molecules. In most instances, coordination shells containing more than four molecules can be attributed to the formation of an extended network of hydrogen bonds. Collisional activation of size-selected clusters reveals the presence of extensive ligand-to-metal electron transfer in the smaller complexes, and in several cases, charge transfer is also accompanied by chemical reactivity. The extent of charge transfer is frequently observed to be determined by the stability of the singly charged metal-containing product.

Charging Processes in Electroactive C60/Pd Films: Effect of Solvent and Supporting Electrolyte

The electrochemical properties of solid films deposited on an electrode surface by simultaneous electrochemical reduction of C60 and palladium(II) acetate trimer in an acetonitrile/toluene mixture have been studied using cyclic voltammetry. The electrochemical switching between the doped (conducting) and undoped (nonconducting) states involves both electron and ion transport within the film. The overall control of charge percolation through the C60/Pd electroactive material is governed by the transport of cations. The ion transport depends both on the nature of solvent and supporting electrolyte. The size of solvent molecule is the major factor determining the degree of solvent swelling of the layer. In the case of small solvent molecules, the C60/Pd film exhibits a reversible redox behavior. For larger molecule solvents, the voltammograms show a departure from reversibility. The reduction of the layer is accompanied by changes in its morphology allowing for the solvent swelling of the film also in the case of large molecule solvents. The electrochemical response of the layer is not affected by the anions of the supporting electrolyte. However, a strong influence of both nature and concentration of supporting electrolyte cations on the redox properties of the layer is observed, since these cations are incorporated into the C60/Pd layer. The redox ability in solutions containing large cations is considerably reduced. The activation of the film at negative potentials results in an increase of the doping level. The stability of the films is affected by the potential range over which they are examined. Scanning to highly negative potentials results in the loss of redox activity due to removal of the film from the electrode surface.

Polarizability and inductive effect contributions to solvent–cation binding observed in electrospray ionization mass spectrometry

Electrospray ionization (ESI) mass spectrometry (MS) has been used in conjunction with computer modeling to investigate binding tendencies of alkali metal cations to low molecular weight solvents. Intensities of peaks in ESI mass spectra corresponding to solvent-bound alkali metal cations were found to decrease with increasing ionic radii (Li + > Na + > K + > Cs +) in either dimethylacetamide (DMAc) or dimethylformamide (DMF). When a lithium or sodium salt was added to an equimolar mixture of DMF, DMAc, and dimethylpropionamide (DMP), the intensities of gas-phase [solvent + alkali cation] + peaks observed in ESI mass spectra decreased in the order DMP > DMAc ≫ DMF. A parallel ranking was obtained for alkali metal cation affinities in ESI-MS/MS experiments employing the kinetic method. These trends have been attributed to a combination of at least three factors. An inductive effect exhibited by the alkyl group adjacent to the carbonyl function on each solvent contributes through-bond electron donation to stabilize the alkali metal cation attached to the carbonyl oxygen. The shift in the partial negative charge at the oxygen binding site with increasing n-alkyl chain length (evaluated via computer modeling), however, cannot fully account for the mass spectrometric data. The increasing polarizability and the augmented ability to dissipate thermal energy with increasing size of the solvent molecule are postulated to act in conjunction with the inductive effect. Further evidence of these contributions to solvent–cation binding in ESI-MS is given by the relative intensities of [solvent + Li] + peaks in mixtures containing equimolar quantities of alcohols, indicating preferential solvation of Li + in the order n-propanol > ethanol > methanol. These experiments suggest a combined role of polarizability, the inductive effect, and solvent molecule size in determining relative intensities of solvated cation peaks in ESI mass spectra of equimolar mixtures of homologous solvents.

Correlation dimension as a measure of surface roughness of protein molecules

We propose to use the correlation dimension as a measure of surface roughness of protein molecules which varies with the size of guest molecules. Smaller guest molecules can probe the finer details of surface corrugation than the larger ones. Hence the correlation dimension has the larger value for smaller guest molecules. Molecular dynamics simulations of a protein molecule at constant temperature and pressure show that the magnitude of structural fluctuation and the coefficient of self-diffusion vary with the size of solvent molecules and correlate nicely with the correlation dimension.

Kinetics of polymerization-induced phase separation

We have studied a Monte Carlo computer simulation on a model for polymerization-induced phase separation. The time evolution of the structure factor are found to preserve the scaling law obtained from teh thermally quenched phase separation. A novel peaking behavior of the mean cluster size of solvent molecules has been found and can be explained by the irreversibility of polymerization. The simulation results are in agreement with experimental observations.

Structure of solvent affects enantioselectivity of lipase-catalyzed transesterification

Lipase-catalyzed transesterification of ( rac)-6-methyl-5-hepten-2-ol (sulcatol) with vinyl acetate has been studied in various solvents and the effect of solvent on the enantioselectivity has been discussed from the viewpoint of molecular shape of the solvent. Alkanes and ethers are selected as solvents. Enantioselectivity of a reaction in a structurally linear solvent is higher than that in the corresponding branched chain solvent. Furthermore, the enantioselectivity decreases specifically with the increase in the ring size of solvent molecule. Thus, lipase recognizes not only the structure of substrate but also that of solvent.

Solvent effects on the magnetic field dependent recombination kinetics of the Zn-porphyrin—viologen dyad radical ion pair state

Magnetic field dependent recombination kinetics of the triplet radical pair state (RIPS) of the semirigid Zn-porphyrin—viologen (PPhVi 2+) dyad in which Zn-porphyrin (P) and viologen (Vi 2+) linked by the semirigid spacer (Ph) containing a 1,4-phenylene moiety has been studied by nanosecond laser flash photolysis technique in sixteen solvents of widely varying properties. The influence of solvent viscosity, the size of solvent molecules and the specific solvation on the triplet RIPS recombination kinetics in an external magnetic field has been found and discussed in terms of the hyperfine coupling mechanism including an exchange interaction modulated by the stochastic spacer motion in low magnetic fields and the spin—orbit coupling induced intersystem electron transfer in high magnetic fields.

The second‐generation polysulfone gas‐separation membrane. I. The use of lewis acid: Base complexes as transient templates to increase free volume

AbstractThe second‐generation polysulfone (PSU) gas‐separation membrane is seen as a trilayer that is considerably more permeable and at least as selective as the first‐generation bilayer that it has replaced. In air separation, a fourfold increase in oxygen permeabiliy has been obtained with no loss in oxygen/nitrogen selectivity. The enhanced performance is the result of a membrane skin that is not only thinner, but also exhibits increased free volume and a graded density. The key to the emergency of the trilayer morphology was the discovery of a hitherto unsuspected relationship between the size of solvent molecules within a sol and the free volume and permeability in the resultant gel! Solvent molecules with a molar volume V > ˜ 147 cc/mol function as transient templates (spacers) that decrease macromolecular packing density. As a practical matter, the low diffusivity (difficult extractibility) of large solvent molecules is circumvented by the use of 1:1 Lewis acid: base (A:B) complexes such as propionic acid: N‐methyl pyrrolidone instead of neat solvents. Complexes whose acid and base strengths, respectively, lie between (Gutmann 47 < AN < 53 and 27 < DN < 28) are sufficiently stable to function as templates, while at the same time exhibiting the hydrolytic instability that leads to their ready disassociation and extraction by water. Selectivity is maintained by the use of A:B complexes whose Hildebrand solubility parameters differ from that of PSU by less than ˜ 1.3 (cal/cc)½. The emergence of the trilayer membrane is considered to be the second decoupling of permeability from selectivity. By the formation of an anisotropic (graded density) skin, permeability has been increased and selectivity maintained. This is analogous to the first decoupling by Loeb and Sourirajan who essentially replaced a thick dense monolayer film with a bilayer consisting of a thin skin of uniform density in series with a thick porous substructure.

Case II diffusion: effect of solvent molecule size

Rutherford back-scattering spectrometry has been used to examine the detailed composition vs. depth profile for polystyrene exposed at 25°C to the vapour (activity = 0.45) of a series of 1-iodo-n-alkanes ranging from iodopropane ( n = 3) to iodooctane ( n = 8), where n is the number of carbon atoms on the alkane chain. All the iodoalkanes tested exhibit case II diffusion. The velocity V of the case II front decreases exponentially with n. The diffusion coefficient D in the glass, which is determined from the concentration profile of the iodoalkanes ahead of the front using the measured value of V, decreases exponentially with increasing n; D decreases by approximately a factor of 4 for each carbon atom added to the alkane chain. These data are compared with previous studies, which show that D decreases exponentially with the molecular diameter d, calculated from the density of the pure liquid solvent: D = D 0 e − δd , where δ is a constant for spherically symmetric solvent molecules. For the linear iodoalkanes D shows a similar exponential decrease but with a 20% lower value of δ, resulting in D for these non-spherical molecules being as much as three orders of magnitude larger than that for spherical molecules with an equivalent d. At the critical concentration ф c for case II diffusion to begin, the swelling rate dф dt at the surface of the sample also decreases approximately exponentially with increasing n. The swelling rate decreases strongly with the osmotic pressure P os, while P os at ф c decreases with the molecular volume (and thus with n). The change in dф dt with n, inferred from the corresponding change in P os, can account for nearly all of the observed dependence of dф dt on n. The Thomas and Windle model of case II diffusion leads to the following prediction for V: V = [( D ф c )( dф dt )| ф c ] 1 2 . We find that the front velocities derived from this equation using the measured values of D and ( dф dt )| ф c are in quantitative agreement with the experimental values of V for the entire series of iodoalkanes, a result that provides strong confirmation of the Thomas and Windle model.

Flory theory of polymeric fractals - intersection, saturation and condensation

Abstract We consider swelling effects of polymeric fractals, recently introduced by Cates, by usual simple Flory arguments for the free energy. The Flory arguments can be formulated to give a unified view for all polymers, linear, branched, or percolation clusters, as long they are of fractal connectivity. If the size of solvent molecules, being fractals themselves, is comparable to the given cluster, new values of the fractal dimensions can be found. The upper critical dimension is reduced. This is due to usual screening of the excluded volume. By standing overlap and repulsive energies of fractals of different fractal dimensions we find condensation to non-fractal objects depending on the value of the fracton dimension. A melt of polymeric fractals of the same fractal dimension and the same size becomes compact if the spectral dimension exceeds a “critical” value. These considerations are of relevance concerning recent experiments, considering static and dynamic properties of mixtures of microgels and linear polymers of different or equal sizes.

Rhenium carbonyl biradicals. Formation, recombination, and halogen atom transfer

The organometallic biradicals (OC)/sub 4/ReLLRe(CO)/sub 4/ (LL = R/sub 2/P(CH/sub 2/)/sub n/PR/sub 2/; R = Me, Ph, Cy; n = 2-6 or cis-Ph/sub 2/PCH=CHPPh/sub 2/) have been observed as transient species following laser flash photolysis of the bridging ligand substituted dirhenium octacarbonyls, in which homolytic metal-metal bond cleavage is a dominant primary photoprocess and CO dissociation is negligible. The intramolecular recombination of these biradicals follows simple first-order kinetics. The rate constants for recombination show a slight solvent dependence probably related to viscosity and the sizes of solvent molecules. The rate constants are affected by steric requirements of the substituents on phosphorus atoms and geometry in the ligand backbone. The rate constants for halogen atom transfer to the biradicals, determined either by laser flash photolysis or by continuous photolysis, are characteristic of mononuclear rhenium carbonyl radicals with similar substituent environments. The metal-centered biradicals thus show typical monoradical behavior in their reactions such as recombination, halogen atom transfer, and electron transfer.

Molecular theory of solvated ion dynamics. II. Fluid structure and ionic mobilities

Calculations of ionic mobility based on a molecular theory of solvated ion dynamics [J. Chem. Phys. 68, 473 (1978)] are presented. We develop approximation schemes for the equilibrium averages needed in the theory. The results for ions in water are in remarkably good agreement with experiment. The importance of fluid structure, arising from the finite size of solvent molecules, is clearly illustrated.