Excluded volume effect of linear polymer molecules

An approximate closed expression for the excluded volume effect of linear polymer molecules is developed with the aid of a uniform expansion model of perturbed chains. The linear expansion factor α for the end-to-end distance is given by (α³ ? 1) + (3/8) (α⁵ ? α³) = (5/2)z where z is the excluded volume parameter. This equation is numerically close to the Ptitsyn equation in the ordinary range of α; i.e., for 1 ≤ α ≤ 2.     

Excluded volume scaling for polymers

The excluded volume of several polymers in the dilute solution regime is calculated using the Monte Carlo integration. The calculated scaling exponent, λ, for the excluded volume for a polymer chain with another chain of the same length is 1.74±0.02. This exponent is consistent with the idea that the interaction of chains with one another in a good solvent is similiar to the interaction of two hard spheres. The effective radius of the hard sphere is proportional to the radius of gyration which has a scaling exponent of ν=0.595±0.005. This result is close to the theoretical value of 0.589. This study establishes the relationship λ=3ν.     

Excluded volume for polydisperse spheroplatelets

Mulder's derivation of the excluded volume between a pair of identical biaxial spheroplatelets is extended to the case of non-identical particles. This result will be useful in the application of scaled particle theory to the monodisperse spheroplatelet fluid or in the study of a bidisperse spherocylinder—'square' spheroplatelet fluid mixture or a generally polydisperse spheroplatelet fluid.     

Excluded volume effect on the electrophoretic mobility of colloidal particles

In a recent work [J. Colloid Interface Sci. 316 (2007) 196] we studied the influence of the excluded volume effect on spatial distributions of ionic species and electrostatic potential in the neighborhood of a suspended spherical particle. It was shown that the excluded volume effect considerably increases the surface potential (for a given value of the particle charge) as compared to the case when ideal ion behavior is assumed. In the present work we extend our previous equilibrium results to the perturbed/nonequilibrium problem and analyze the effect of ion size constraints on the electrophoretic mobility of a rigid spherical particle immersed in a general electrolyte solution. We find that the electrophoretic mobility always increases with the excluded volume effect, which might broaden the range of experimental data that can be interpreted, including those cases where the measured mobility exceeded the theoretical maximum value predicted by the standard model.     

Excluded volume effect for solutions of cellulose derivatives evaluated by wormlike chain model

Third-power law type equations of the linear expansion factor α_s and of the excluded volume effect $\text{z}$h($\text{z}$), expressed by a conventional notation, are derived for a wormlike chain as an extension of the Yamakawa and Stockmayer theory [J. chem. Phys.57, 2843(1972)], in which the corresponding fifth-power law type equations were obtained. The literature data on 11 systems of solutions of cellulose and its derivatives are analysed, by using a penetration function method based on the derived equations, to evaluate an excluded volume effect for a wormlike chain model. The results are compared with those deduced for a pearl necklace model.     

Polymer translocation through a nanopore. II. Excluded volume effect

Following our previous study of a Gaussian chain translocation, we have investigated the transport of a self-avoiding chain from one sphere to another sphere through a narrow pore, using the self-consistent field theory formalism. The free energy landscape for polymer translocation is significantly modified by excluded volume interactions among monomers. The free energy barrier for the placement of one of the chain ends at the pore depends on the chain length N nonmonotonically, in contrast to the N-independence for Gaussian chains. This results in a nonmonotonic dependence of the average arrival time [tau0] on N for self-avoiding chains. When the polymer chain is partitioned between the donor and recipient spheres, a local free energy minimum develops, depending on the strength w of the excluded volume interaction and the relative sizes of the donor and recipient spheres. If the sizes of spheres are comparable, the average translocation time tau (the average time taken by the polymer, after the arrival at the pore, to convert from the donor to the recipient) increases with an increase in w for a fixed N value. On the other hand, for the highly asymmetric sizes of the donor and recipient spheres, tau decreases with an increase in w. As in the case of Gaussian chains, tau depends nonmonotonically on the pore length.     

Excluded volume effect on confined polymer translocation through a short nanochannel

We simulated the translocation process of a polymer chain from a source container to a drain container through a short nanochannel. We utilized the bond fluctuation model coupled with Monte Carlo dynamics in our simulations. The calculation results show that the excluded volume effect significantly affects the polymer's translocation time tau. This time depends nonmonotonically on the polymer length N. For a fixed nanochannel length, tau decreases when the polymer length increases. tau, however, increases when the polymer length exceeds a certain threshold. This observation differs from those predicated for a Gaussian chain. In this paper, we will further present our findings to explain this phenomenon. The knowledge we gain from this research can enhance the understanding of complex transport processes in many biological systems.     

Effect of small solutes on the water populations in inverted micelles

Different types of water are present in the core of inside-up vesicles; their relative populations are modified when small molecules like aminoacids or oligopeptides are dissolved in the aqueous compartment. I.R. spectroscopy allows the monitoring of the water organization in terms of greater or lesser molecular freedom.     

Excluded volume effects in macromolecular forces and ion-interface interactions

A charged Yukawa liquid confined in a slit nanopore is studied in order to understand excluded volume effects in the interaction force between the pore walls. A previously developed self-consistent scheme [S. Buyukdagli, C. V. Achim, and T. Ala-Nissila, J. Stat. Mech. 2011, P05033] and a new simpler variational procedure that self-consistently couple image forces, surface charge induced electric field, and pore modified core interactions are used to this aim. For neutral pores, it is shown that with increasing pore size, the theory predicts a transition of the interplate pressure from an attractive to a strongly repulsive regime associated with an ionic packing state, an effect observed in previous Monte Carlo simulations for hard core charges. We also establish the mean-field theory of the model and show that for dielectrically homogeneous pores, the mean-field regime of the interaction between the walls corresponds to large pores of size d > 4 ?. The role of the range of core interactions in the ionic rejection and interplate pressure is thoroughly analyzed. We show that the physics of the system can be split into two screening regimes. The ionic packing effect takes place in the regime of moderately screened core interactions characterized with the bare screening parameter of the Yukawa potential b ? 3/l(B), where l(B) is the Bjerrum length. In the second regime of strongly screened core interactions b ? 3/l(B), solvation forces associated with these interactions positively contribute to the ionic rejection driven by electrostatic forces and enhance the magnitude of the attractive pressure. For weakly charged pores without a dielectric discontinuity, core interactions make a net repulsive contribution to the interplate force and also result in oscillatory pressure curves, whereas for intermediate surface charges, these interactions exclusively strengthen the external pressure, thereby reducing the magnitude of the net repulsive interplate force. The pronounced dependence of the interplate pressure and ionic partition coefficients on the magnitude and the range of core interactions indicates excluded volume effects as an important ion specificity and a non-negligible ingredient for the stability of macromolecules in electrolyte solutions.     

Excluded volume effect of rat intestinal mucin on taurocholate/phosphatidylcholine mixed micelles

The interaction of bile salt/phospholipid mixed micelles with an intestinal mucin has been investigated to provide the foundation for the transport of ingested fat and poorly water-soluble drugs through the intestinal mucous layer. Egg phosphatidylcholine (PC) was equilibrated with sodium taurocholate (TC) to generate several series of solutions, which had different intermicellar concentrations of TC. Within each series, each solution had the same IMC and thereby micelle sizes, but varied with respect to micelle concentration. These solutions were combined with isolated rat intestinal mucin, equilibrated, and then separated by centrifugation. The supernatant and mucin pellet were assayed for PC and TC, and the diffusion coefficient of PC was measured in the supernatant by PFG-SE NMR spectroscopy. For each series, four linear relationships were found; TC supernatant concentration plotted as a function of PC supernatant concentration; TC pellet concentration plotted as a function of PC pellet concentration; TC pellet concentration plotted as a function of TC supernatant concentration; and PC pellet concentration plotted as a function of PC supernatant concentration. Theoretical analysis of these results indicated that mucin excludes from 25 to 80% of the bile salt/phospholipid mixed micelles with greater exclusion observed with larger micelle size. There is preferential association of the taurocholate with intestinal mucin, when present in the mixed micelle region of the phase diagram. The association coupled with exclusion would allow mucin to modulate the concentration of bile salt at the epithelial surface.     

Excluded volume study of a sulfonate-containing polyelectrolyte in salt solutions

Chain characteristics of a linear sulfonate-containing homopolymer, sodium poly(3-methacryloyloxypropane-1-sulfonate), in aqueous salt solutions (ionic strength, C_s = 0.01N to 5N NaCl) have been investigated by light scattering and intrinsic viscosity. The molecular weight (M?_w)–viscosity relation can be well described by the Mark–Houwink and the Stockmayer–Fixman equations. The coil is highly expanded even in the most concentrated NaCl solution (6N), and no 1:1 electrolyte was found to precipitate this polymer. A linear relation was observed between the viscosity expansion factor, α^3η, and (M?_w/C_s)^1/2. Examination of the data in terms of theories for excluded volume and hydrodynamic interaction suggests that the coil experiences dominant hydrodynamic interaction, corresponding to a nondraining coil, and the second virial coefficient and coil expansion at high C^s can be correlated by the Flory–Krigbaum–Orofino equation. Results for this polymer are compared with those for other polyelectrolytes, and are discussed in terms of chain structure, flexibility, and hydrophobicity.     

Convergence of retention for small solutes in reversed-phase liquid chromatography

Summary It is shown theoretically that when the concentration of organic solvent in the mobile phase increases, or solute size decreases, log k values of small solutes in reversed-phase liquid chromatography (RPLC) will tend to have a minimum value called the convergence point. A theoretical model for evaluating the convergent coordinates of small solutes is presented by using a stoichiometric displacement model for retention (SMDR). The physical meaning of the coordinates of each kind of convergence are also elucidated. The convergence points have either two-dimensional coordinates with a common ordinate (the logarithm of the phase ratio of the column, log ) or threedimensional corrdinates with two common axes: — log and the logarithm of the molar concentration of the pure displacing agent in mobile phase, log a_D. The other axis relates to the nature of the solutes, such as carbon number of a homolog, van der Waal's surface area, hydrophobic fragment constant etc. for the latter and those and/or concentration axis for the former. The model was tested with published data and found to give a good fit.     

Theory for the solvation of nonpolar solutes in water

We recently developed an angle-dependent Wertheim integral equation theory (IET) of the Mercedes-Benz (MB) model of pure water [Silverstein et al., J. Am. Chem. Soc. 120, 3166 (1998)]. Our approach treats explicitly the coupled orientational constraints within water molecules. The analytical theory offers the advantage of being less computationally expensive than Monte Carlo simulations by two orders of magnitude. Here we apply the angle-dependent IET to studying the hydrophobic effect, the transfer of a nonpolar solute into MB water. We find that the theory reproduces the Monte Carlo results qualitatively for cold water and quantitatively for hot water.     

Excluded volume effect for various chain models. II. Application to optical anisotropy and end-to-end distance of branched polymers

Monte Carlo simulation has been used to investigate the excluded volume problem for branched polymers. The mean-square optical anisotropy and mean-square end-to-end distance were examined for two models including short-range intramolecular interactions. Molecules of regular-comb and random-comb type were studied. The various effects found are discussed.     

Excluded volume entropic effects on protein unfolding times and intermediary stability

The dynamics of protein folding result from both enthalpic and entropic contributions to the free energy. In this paper we focus on entropic volume exclusion effects. We carry out computer simulations using a model that allows us to independently change the size or biochemical properties of amino acid residues. To determine the importance of excluded volume effects, we investigate the effects of changing the size of side chains on the unfolding dynamics of a model four-helix bundle protein. In addition, we also investigate the effects of changing the thickness of the chain's backbone. This has relevance to the behavior of synthetic polymers where the size of the constituent units can be varied. We find that entropic excluded volume effects are crucially important for stabilizing the organized native state relative to the molten globule.     

Relative log P and solution structure for small organic solutes in the chloroform/water system using monte carlo methods

Relative log P values of dimethylether to methanol and dimethylamine to methylamine were calculated in the chloroform/water system using Monte Carlo simulations and statistical perturbation theory. Correct ordering of the calculated relative log Ps was obtained for the two pairs although the method leads to an overestimation of these values. In aqueous solution, both dimethyl ether and dimethylamine solutes are proton acceptors forming a single hydrogen bond to water. Dimethylamine forms a stable N? H-Ow hydrogen bond while the water hydrogen is poorly localized in the O? H-Ow bond to the ether. In chloroform, the solvent molecules are less ordered around the solutes than was found around methanol and methylamine.     

Effect of large volume injection of hydrophobic solvents on the retention of less hydrophobic pharmaceutical solutes in RP-LC

Injection of large volumes of samples in solvents other than mobile phase composition has been proved for some less hydrophobic compounds. Thus, the retention behavior of several compounds of pharmaceutical interest (isosorbide-2-nitrate, isosorbide-5-nitrate, tropicamide, pentoxifylline, and methyl p-hydroxybenzoate) was studied by using different hydrophobic solvents (n-hexane, n-heptane, or i-octane) as sample solvents. Two types of stationary phases were used: octyl and octadecyl modified silica (both of Zorbax Eclipse type). The experiments showed a linear dependence between capacity factor of each solute and sample injection volume, up to maximum volume values of about 680 microL for C8 stationary phase and 580 microL for C18 stationary phase, when the solutes are no longer retained in stationary phase. Injection of large volumes of these hydrophobic solvents is thus possible in RP-LC with a gradual reduction of retention and peak efficiency. Two major conditions are however necessary in order to apply such an injection approach: the solutes must have a proper solubility in hydrophobic solvents and meanwhile they have to be less hydrophobic than the sample solvent in order to avoid competition with solvent molecules in partitioning between mobile and stationary phases.     

Comparison of two ICP-MS set-ups for measuring 99Tc in large volume water samples

Large volume fjord and seawater samples have been radiochemically prepared for ICP-MS analysis in order to test the robustness of the procedure and to carry out a comparison of two ICP-MS set-ups. A sector field instrument (MicroMass PT2) coupled with an ultrasonic nebuliser and a quadrupole ICP-MS (Perkin-Elmer Elan 6000) coupled with an electrothermal vaporisation (ETV) unit were used. The results showed that the radiochemical procedure was robust, removing Ru and Mo to acceptable levels, and that the two set-ups gave results that were in agreement. The correlation coefficient between the sets of 11 results was 1.0 +/- 0.05. The importance of establishing the matrix effect when using an ETV is discussed.