Solutes Of Different Sizes Research Articles

Pressure-Enhanced Liquid Chromatography, a Proof of Concept: Tuning Selectivity with Pressure Changes and Gradients.

Many chromatographers have observed that the operating pressure can dramatically change the chromatographic retention of solutes. Small molecules show observables changes, yet even more sizable effects are encountered with large biomolecules. With this work, we have explored the use of pressure as a method development parameter to alter the reversed-phase selectivity of peptide and protein separations. An apparatus for the facile manipulation of column pressure was assembled through a two-pump system and postcolumn flow restriction. The primary pump provided an eluent flow through the column, while the secondary pump provided a pressure-modulating flow at a tee junction after the column but ahead of a flow restrictor. Using this setup, we were able to quickly program various constant pressure changes and even pressure gradients. It was reconfirmed that pressure changes impact the retention of large molecules to a much greater degree than small molecules, making it especially interesting to consider the use of pressure to selectively separate solutes of different sizes. The addition of pressure to bring the column operating pressure beyond 500 bar was enough to change the elution order of insulin (a peptide hormone) and cytochrome C (a small serum protein). Moreover, with the proposed setup, it was possible to combine eluent and pressure gradients in the same analytical run. This advanced technique was applied to improve the separation of insulin from one of its forced degradation impurities. We have referred to this method as pressure-enhanced liquid chromatography and believe that it can offer unseen selectivity, starting with peptide and protein reversed-phase separations.

Dust Acoustic Solitons in Saturn\u2019s Dust-Filled Magnetosphere

The possibility is considered of propagation of localized wave structures, such as dust acoustic solitons, in the plasma of the dust-filled Saturn’s magnetosphere, which contains electrons of two sorts (hot and cold) subject to kappa distribution, ions, and charged dust grains. The ranges of possible velocities and amplitudes of the solitons are determined. Soliton solutions for different sizes and concentrations of dust grains in the dust-filled Saturn’s magnetosphere are found.

Understanding fast diffusion of solutes in solid solutions: A molecular dynamics study of solutes in body centered cubic solid.

In some binary alloys, the solute exhibits high or fast diffusion with low activation energy. In order to understand this, diffusion of solute atoms through a lattice of body centered cubic solvent atoms has been investigated with molecular dynamics technique. Surprisingly, solutes exhibit two distinct diffusivity maxima. Solutes migrate through the lattice mainly by diffusion from one tetrahedral void to another (tt) and, less frequently, by diffusion from a tetrahedral to an octahedral void (to) or reverse jumps (ot). Solutes with maximum diffusivity show smooth decay of the velocity autocorrelation function without backscattering. The average force on the solutes of various diameters correlates well with the position and intensity of the diffusivity maxima exhibited by the solutes. This suggests that the explanation for the diffusivity maxima lies in the levitation effect, which suggests a lowered force on the solute at the diffusivity maxima. The activation energy computed for the solutes of different sizes confirms this interpretation as it is lower for the solutes at the diffusivity maxima. Calculations with blocking of octahedral voids show that the second diffusivity maximum has significant contributions from the to diffusion path. These findings obtained here explain the fast solute/impurity atom diffusivity and low activation energies seen in the literature in many of the alloys, such as Co in γ-U and β-Zr, Cu in Pr, or Au in Th.

Neat Protein-Polymer Surfactant Bioconjugates as Universal Solvents.

Solvents, particularly those having low volatility, are of great interest for the biocatalytic synthesis of utility chemicals and fuels. We show novel and universal solvent-like properties of a neat and water-less polymer surfactant-bovine serum albumin (BSA) conjugated material (WL-PS pBSA). This highly viscous, nonvolatile material behaves as a liquid above its solid-liquid transition temperature (∼25-27 °C) and can be used as a solvent for variety of completely dry solutes of different sizes and surface chemistries. We show using a combination of optical microscopy and steady -state and time-resolved fluorescence spectroscopy that dry and powdered dyes (hydrophobic Coumarin 153 (C153)), enzymes (α-chymotrypsin (α-Chy)), or even 1 μm microparticles (diffusion coefficient ca. three orders slower than C153), can be solubilized and completely dispersed in the WL-PS pBSA solvent above 25 °C. While C153, irrespective of its mode of addition to WL-PS pBSA, binds similarly to BSA, α-Chy can be stabilized and activated to perform its hydrolysis function, even at 100 °C. This work therefore provides insights into the form of universal solvent characteristic property for this new class of nonaqueous, nonvolatile, biodegradable protein-polymer surfactant-based conjugated materials and suggests potential new avenues that can have a huge impact on biocatalysis, bionanotechnology, drug delivery, and other applications.

A revised correlation between molecular weight between crosslinks and equilibrium degree of swelling of hydrogel networks

Event Abstract Back to Event A revised correlation between molecular weight between crosslinks and equilibrium degree of swelling of hydrogel networks Dany J. Munoz-Pinto1 and Mariah S. Hahn2 1 Trinity University, Engineering Science, United States 2 Rensselaer Polytechnic Institute, Biomedical Engineering, United States Introduction: Among hydrogels properties, characterization of their capacity to transport solutes of different sizes is of great relevance for the biomedical community. Their diffusional capacity has been commonly estimated using the average molecular weight between crosslinks (Mc) which is calculated using equilibrium degree of swelling data[1]. However, the current correlation lacks of sensitivity and fails to accurately reflect the diffusional properties of more highly crosslink hydrogel networks[2]. To address this limitation, the present work first evaluated the robustness of the standard swelling correlation using poly(ethylene glycol) diacrylate (PEGDA) as a material model. The strength of the correlation was assessed by contrasting swelling and mechanical behavior as functions of hydrogel crosslink density (ρx).Second, an independent assessment of hydrogel mesh size (ξ) by molecular size exclusion (MSE) was utilized to calculate ρx. The resulting set of data followed more general trends for swelling and modulus. Finally, using the MSE data, an improved correlation between Mc and degree of swelling was generated. Material and Methods: Hydrogel Preparation. Hydrogels were prepared by the photopolymerization of aqueous solutions of 3.4, 6.0, 10.0 and 20.0 kDa PEGDA. For each PEGDA MW, six distinct polymer concentrations ranging from 8 to 30 wt% were characterized. Swelling Measures. The volumetric swelling ratios at the swollen and relaxed states (Q and Q’) were calculated from the hydrogel initial, swollen and dry weights. Mc and ρx for each hydrogel formulation were then determined using swelling data correlations[1]. Mesh Size Evaluation. Mesh size was independently estimated by molecular size exclusion experiments[3],[4]. The measured ξ was then used to back calculate Mc and ρx. Tensile Modulus (E) Evaluation. The modulus of each formulation was determined from the slope of the linear portion of the stress-strain curve using a ring test method and an Instron 3342 mechanical tester[5]. New Swelling Correlation Model. To generate a new model to correlate Mc and swelling data, the value 1/Mc from the MSE data and the effective number of chain per unit volume (Vc) from swelling data were fit to the linear model: 1/Mc=a+bVc'. Where Vc'=f(Q,Q')*Vc. Results and Discussion: As expected, Q and E of PEGDA hydrogels as functions of ρx exhibited a tradeoff behavior for both sets of data (Fig. 1A and 1B).However only the ρx estimates based on MSE-based mesh size measures (Fig. 1B) resulted in a general ρx-Q trend, which was independent of PEGDA MW. Furthermore, the data from MSE model was used to derive an improved correlation between Mc and degree of swelling of hydrogel networks (Fig. 1C). Conclusions: The current data shows that the values of 1/Mc can potentially be calculated from swelling data using a modified version of the current correlation. Although in this work we used PEGDA as a model, this correlation can potentially be extended to other polymer networks.

Correlation of macromolecular permeability to network characteristics of multivinyl poly(vinyl alcohol) hydrogels

ABSTRACTModulation of the structural parameters of multivinyl hydrogels allows optimization of their permeability, which is a prerequisite for different biomedical applications. However, only a few studies to date have been reported regarding macromolecular diffusion within divinyl and multivinyl systems, and even less provide information about the correlation of diffusion to the network characteristics. Therefore, this study aimed to understand the permeability performance of tailored poly(vinyl alcohol) (PVA) multivinyl hydrogels and correlating it to the network characteristics using two common theories: rubber elasticity and equilibrium swelling. A systematic increase in the number of functional groups per PVA backbone successfully modulated the PVA physicomechanical properties. These modifications resulted in varying the hydrogel permeability performance to solutes of different sizes and shapes. Correlating the network characteristics to macromolecular permeability of hydrogels proved the reliability of applying the equilibrium swelling theory for hydrogel mesh size estimation over the rubber elasticity theory. © 2013 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2014, 52, 63–72

An evolutionary approach for multi-objective optimization of the integrated location–inventory distribution network problem in vendor-managed inventory

Vendor-managed inventory (VMI) is one of the emerging solutions for improving the supply chain efficiency. It gives the supplier the responsibility to monitor and decide the inventory replenishments of their customers. In this paper, an integrated location–inventory distribution network problem which integrates the effects of facility location, distribution, and inventory issues is formulated under the VMI setup. We presented a Multi-Objective Location–Inventory Problem (MOLIP) model and investigated the possibility of a multi-objective evolutionary algorithm based on the Non-dominated Sorting Genetic Algorithm (NSGA2) for solving MOLIP. To assess the performance of our approach, we conduct computational experiments with certain criteria. The potential of the proposed approach is demonstrated by comparing to a well-known multi-objective evolutionary algorithm. Computational results have presented promise solutions for different sizes of problems and proved to be an innovative and efficient approach for many difficult-to-solve problems.

Communication: On the locality of Hydrogen bond networks at hydrophobic interfaces

The formation of structured hydrogen bond networks in the solvation shells immediate to hydrophobic solutes is crucial for a large number of water mediated processes. A long lasting debate in this context regards the mutual influence of the hydrophobic solute into the bulk water and the role of the hydrogen bond network of the bulk in supporting the solvation structure around a hydrophobic molecule. In this context we present a molecular dynamics study of the solvation of various hydrophobic molecules where the effect of different regions around the solvent can be analyzed by employing an adaptive resolution method, which can systematically separate local and nonlocal factors in the structure of water around a hydrophobic molecule. A number of hydrophobic solutes of different sizes and two different model potential interactions between the water and the solute are investigated.

Molecular Simulations of Solute Transport in Xylose Isomerase Crystals

Cross-linked enzyme crystals (CLECs) enclose an extensive regular matrix of chiral solvent-filled nanopores, via which ions and solutes travel in and out. Several cross-linked enzyme crystals have recently been used for chiral separation and as biocatalysts. We studied the dynamics of solute transport in orthorhombic d-xylose isomerase (XI) crystals by means of Brownian dynamics (BD) and molecular dynamics (MD) simulations, which show how the protein residues influence the dynamics of solute molecules in confined regions inside the lattice. In the BD simulations, coarse-grained beads represent solutes of different sizes. The diffusion of S-phenylglycine molecules inside XI crystals is investigated by long-time MD simulations. The computed diffusion coefficients within a crystal are found to be orders of magnitude lower than in bulk water. The simulation results are compared to the recent experimental studies of diffusion and reaction inside XI crystals. The insights obtained from simulations allow us to understand the nature of solute-protein interactions and transport phenomena in CLECs, which is useful for the design of novel nanoporous biocatalysts and bioseparations based on CLECs.

Hydration Structure and Interfacial Properties of Water near a Hydrophobic Solute from a Fundamental Measure Density Functional Theory

Using a density functional theory (DFT) based on Rosenfeld's formalism for hard spheres, we investigate the influence of model solutes of different sizes on the structure and interfacial properties...

DFT and TD‐DFT investigation of IR and UV spectra of solvated molecules: Comparison of two SCRF continuum models

AbstractWe report the calculation of liquid‐phase infrared (IR) and ultraviolet (UV) spectra in the framework of the solute's response to the reaction field of several solvents. In particular, we compare these two properties for the multipolar expansion model developed in the Nancy continuum model (NCM) and the polarized continuum model (PCM) scheme developed in Pise and Naples. All calculations are carried out at the (TD‐)DFT/6–311G(2d,2p) level of theory. The cavity size used for modeling the solute effects on the IR and UV spectra are examined. To calibrate the solute cavity size, we have investigated the IR spectra of coumarin and of a set of 14 additional solutes of different size and polarity in several dielectrical surroundings. It turns out that: (i) PCM and NCM present an identical behavior when a common cavity is used to calibrate the models; and (ii) for both NCM and PCM models, the IR spectra are highly sensitive to the solute and solvent polarity. The UV/VIS investigation of coumarin derivatives demonstrates that both models provide close estimates of λmax independent of the solute cavity size. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007

Combining Small Angle Neutron Scattering (SANS) and Fluorescence Correlation Spectroscopy (FCS) Measurements To Relate Diffusion in Agarose Gels to Structure

Small angle neutron scattering (SANS) and fluorescence correlation spectroscopy (FCS) measurements were carried out on agarose hydrogels to link their microscopic structure to the diffusivity of solutes at different scales. SANS allowed for the determination of the distribution of void volumes within the gels. They were shown to be compatible with a random network of cylindrical fibers as described by the Ogston model. FCS measured solute diffusivity in spaces similar in size to the void volumes, and thus, the results reflected the gel heterogeneity. Solute diffusivity was predicted by modeling the gel as microscopic geometrical cells. Variations in the diffusivity of solutes of different sizes could be predicted from the structural parameters of the gel using theory, taking into account obstruction by cylindrical cells and solute hydrodynamics. Prediction of the FCS autocorrelation functions for solutes from a cell model demonstrated a lack of sensitivity of this technique for multicomponent analysis.

A sensitive in vivo model for quantifying interstitial convective transport of injected macromolecules and nanoparticles

Effective interstitial transport of particles is necessary for injected drug/diagnostic agents to reach the intended target; however, quantitative methods to estimate such transport parameters are lacking. In this study, we develop an in vivo model for evaluating interstitial convection of injected macromolecules and nanoparticles. Fluorescently labeled macromolecules and particles are coinfused with a reference solute at constant infusion pressure intradermally into the mouse tail tip, and their relative convection coefficients are determined from spatial and temporal interstitial concentration profiles. Quantifying relative solute velocity with a coinfused reference solute eliminates the need to estimate interstitial fluid velocity profiles, greatly reducing experimental variability. To demonstrate sensitivity and usefulness of this model, we compare the effects of size (dextrans of 3, 40, 71, and 2,000 kDa and 40-nm diameter particles), shape (linear dextran 71 kDa vs. 69 kDa globular protein albumin), and charge (anionic vs. neutral dextran 3 kDa) on interstitial convection. We find significant differences in interstitial transport rates between each of these molecules and confirm expected transport phenomena, testifying to sensitivity of the model in comparing solutes of different size, shape, and charge. Our data show that size exclusion (within a specific size range) dominates molecular convection, while mechanical hindrance slows larger molecules and nanoparticles; proteins convect slower than linear molecules of equal molecular mass, and negative surface charges increase convection through matrix repulsion. Our in vivo model is presumably a sensitive and reliable tool for evaluating and optimizing potential drug/diagnostic vehicles that utilize interstitial and lymphatic delivery routes.

A quadra-directional decomposition heuristic for a two-dimensional, non-equidistant machine-cell location problem

After the development of numerous cell formation techniques, machine-cell location (MCL) problems have been the focus of many researchers in cellular manufacturing systems. With the cost cutting strategy, locating machines within the cell itself has not only been the major concern of management, but also the location of cells with respect to each other on a spatial coordinate system to minimize the transportation cost or job movement costs. For lack of being able to solve a large problem optimally, a number of heuristics have been developed for one-dimensional machine and MCL problems. The problem still exists for locating machine-cells on spatial coordinates, which has been addressed in this research. The location coordinates have been decomposed into four movements, backward, forward, upward and downward; and the MCL problem is formulated as a linear combination of these four decomposed (partitioned) objective functions subject to other boundary conditions. A quadra-directional decomposition heuristic (QDDH) is developed to find a sub-optimal solution to the MCL problem. The decomposition procedure for four objective functions is presented and the performance of the heuristic is tested on a set of well-known data. Empirical tests show that the solution procedure produces efficient, good quality solutions for different sizes of the problem instances.

A cohesion/tension mechanism explains the gating of water channels (aquaporins) in Chara internodes by high concentration.

Isolated internodes of Chara corallina have been used to study the gating of aquaporins (water channels) in the presence of high concentrations of osmotic solutes of different size (molecular weight). Osmolytes were acetone and three glycol ethers: ethylene glycol monomethyl ether (EGMME), diethylene glycol monomethyl ether (DEGMME), and triethylene glycol monoethyl ether (TEGMEE). The 'osmotic efficiency' of osmolytes was quite different. Their reflection coefficients ranged between 0.15 (acetone), 0.59 (EGMME), 0.78 (DEGMME), and 0.80 (TEGMEE). Bulk water permeability (Lp) and diffusive permeabilities (Ps) of heavy water (HDO), hydrogen peroxide (H2O2), acetone, and glycol ethers (EGMME, DEGMME, and TEGMEE) were measured using a cell pressure probe. Cells were treated with different concentrations of osmotic solutes of up to 800 mM ( approximately 2.0 MPa of osmotic pressure). Inhibition of aquaporin activity increased with both increasing concentration and size of solutes (reflection coefficients). As cell Lp decreased, Ps increased, indicating that water and solutes used different passages across the plasma membrane. Similar to earlier findings of an osmotic gating of ion channels, a cohesion/tension model of the gating of water channels in Chara internodes by high concentration is proposed. According to the model, tensions (negative pressures) within water channels affected the open/closed state by changing the free energy between states and favoured a distorted/collapsed rather than the open state. They should have differed depending on the concentration and size of solutes that are more or less excluded from aquaporins. The bigger the solute, the lower was the concentration required to induce a reversible closure of aquaporins, as predicted by the model.

Do Molecules as Small as Neopentane Induce a Hydrophobic Response Similar to That of Large Hydrophobic Surfaces?

This is the first of two papers aimed at understanding, from an atomistic perspective, hydrophobicity at different length scales and how properties such as local densities and angular profiles change for hydrophobic solutes of different sizes. In a subsequent publication we will describe the hydrophobic hydration and hydrophobic interaction of platelike molecules of nanoscale size. Molecular dynamics is used to compute radial and orientational distribution functions of water around three different molecules: argon, methane, and neopentane. In addition, the potential of mean force between two neopentane molecules is computed. The results for the full OPLS/AA1 force field are compared with the solute−solvent WCA truncated OPLS/AA force field for these systems. This work addresses the question of whether a molecule of the size of neopentane is large enough to induce a hydrophobic response similar to that of large hydrophobic molecules or paraffin walls. We answer this question in the affirmative. The orient...

Estimation of the Krichevskii parameter for aqueous nonelectrolytes

The Krichevskii parameter determines the sign and magnitude of the near-critical divergence of the partial molar thermodynamic properties of infinitely dilute solutions. Estimation of the values of the Krichevskii parameter, A Kr, would be helpful in improving the quality of predictions of the infinite dilution partial molar properties of aqueous nonelectrolytes at near-critical and supercritical conditions. In this paper, we discuss the methods to obtain values of A Kr from various types of experimental information on the thermodynamic properties of binary systems, and use these methods to evaluate the Krichevskii parameter for more than 30 aqueous nonelectrolytes. The possibility of calculating the values of the Krichevskii parameter for solutes at infinite dilution in water from the van der Waals and Peng–Robinson equations of state was also checked. It is shown that the classical cubic equations of state may be used to predict the values of A Kr for small nonpolar solutes in water, but grossly overestimate A Kr for larger compounds. As an alternative, we propose an empirical correlation between the Krichevskii parameter and the Gibbs energy of hydration at 298.15 K and 0.1 MPa for the corresponding compound. This correlation seems to hold for solutes with values of the Krichevskii parameter ranging from −200 to +200 MPa, and values of the Gibbs energy of hydration extending over 100 kJ mol −1, and appears to be useful for estimating values of the Krichevskii parameter for many solutes of different sizes and polarities, from inert gases to aqueous silica. Predictions, related to the sign of the Krichevskii parameter for a number of aqueous inorganic and organic nonelectrolytes, are made, which can be verified experimentally.

On-line separation of solute mixtures using reciprocating size exclusion chromatography

Solutes of different size in a mixture solution were separated on-line, using a semi-continuous reciprocating size exclusion chromatography. The band of fast-moving large molecules was isolated during the first half cycle, while the band of slow-moving small molecules was isolated during the second half cycle. After 7 cycles of frontal mode operation, 89% of the Blue Dextran in the feed was isolated as a pure solution. Vitamin B12 of constant concentration was also isolated as a pure solution.

The role of solvent structure in perturbation methods applied to the dissolution of an apolar solute in water

In view of recent experimental and simulation studies which show that solvent reorientation does not play a significant role in the dissolution of small apolar solutes in water, the performance of first order perturbation theories (FOPT) has been reassessed. A contribution which cannot be obtained from classical FOPT is the many-body effect of the instantaneous solvent electric field which induces a dipole on the apolar solute and contributes an attractive term. The average square electric field was determined by molecular dynamics for solutes of different size and its effect upon the solute's chemical potential was calculated from it with an appropriate extension of the test-particle method. The contribution of this term to the thermodynamic quantities of dissolution is discussed.

A Study on the Solute Separation and the Pore Size Distribution of a Montmorillonite Membrane

Abstract A montmorillonite membrane with a thickness of 0.5 mm was prepared, and reverse osmosis experiments were conducted for various inorganic and organic solutes of different sizes under an operating pressure of 3 MPa. The mean pore size and pore size distribution were determined by a log-normal probability plot between the solute separation and the Einstein-Stokes radius of the solute molecules for which reverse osmosis and ultrafiltration performance was investigated. The relationships between the pore size and the pore size distribution and the structure of montmorillonite are discussed. A comparison is also made between the pore size and the thickness of the electrical double layer.