Contribution Of Polar Interactions Research Articles

Transport properties and fouling issues of membranes utilized for the concentration of dairy products by air-gap membrane distillation and microfiltration

The work contains results related to the application of membrane separation processes (i.e., membrane distillation and microfiltration) in dairy products processing. The performance of titania ceramic membranes (pristine as well as hydrophobized) was studied in the microfiltration process of whey and lactose solutions. On the other hand, polymeric porous hydrophobic membranes, (polypropylene—PP and polytetrafluoroethylene—PTFE) were tested in the air-gap membrane distillation (AGMD) process in contact with whey and lactose solutions. The extended material and physiochemical characterization (including fouling issues) of membrane materials before and after the separation process was performed. Transport of lactose solution across the membranes was characterized by higher effectiveness comparing with whey solution. Lactose played an important role and reduced the interactions with membrane material. Lactose solution possessed lower adhesion ability than whey what influenced the fouling and reduction of permeate flux. Membrane distillation was found to be a process that generates high-quality water with retention > 99% while simultaneously concentrating whey or lactose solutions. Microfiltration process was characterized by a rejection of lactose in the range of 80–90% for pristine ceramic membrane and hydrophobized one, respectively. The tendency to fouling in the case of AGMD process was associated with the higher contribution of polar part (29%) of the surface free energy SFE for PTFE membrane. The lowest value of normalized flux decline was observed for PP membrane, and that was correlated with the smallest contribution of polar interaction in SFE, the lowest value of roughness (RSM), contact angle (CA), and contact angle hysteresis (HCA), determined for the membrane after its utilization in the separation process.

Exploring the Molecular Basis of dsRNA Recognition by Mss116p Using Molecular Dynamics Simulations and Free-Energy Calculations

DEAD-box proteins are the largest family of helicase that are important in nearly all aspects of RNA metabolism. However, it is unclear how these proteins recognize and bind RNA. Here, we present a detailed analysis of the related DEAD-box protein Mss116p-RNA interaction, using molecular dynamics simulations with MM-GBSA calculations. The energetic analysis indicates that the two strands of double strands RNA (dsRNA) are recognized asymmetrically by Mss116p. The strand 1 of dsRNA provides the main binding affinity. Meanwhile, the nonpolar interaction provides the main driving force for the binding process. Although the contribution of polar interaction is small, it is vital in stabilizing the protein-RNA interaction. Compared with the wild type Mss116p, two studied mutants Q412A and D441A have obviously reduced binding free energies with dsRNA because of the decreasing of polar interaction. Three important residues Lys409, Arg415 and Arg438 lose their binding affinity significantly in mutants. In conclusion, these results complement previous experiments to advance comprehensive understanding of Mss116p-dsRNA interaction. The results also would provide support for the application of similar approaches to the understanding of other DEAD-box protein-RNA complexes.

Characterization of biomaterials polar interactions in physiological conditions using liquid–liquid contact angle measurements: Relation to fibronectin adsorption

Wettability of biomaterials surfaces and protein-coated substrates is generally characterized with the sessile drop technique using polar and apolar liquids. This procedure is often performed in air, which does not reflect the physiological conditions. In this study, liquid/liquid contact angle measurements were carried out to be closer to cell culture conditions. This technique allowed us to evaluate the polar contribution to the work of adhesion between an aqueous medium and four selected biomaterials widely used in tissue culture applications: bacteriological grade polystyrene (PS), tissue culture polystyrene (tPS), poly(2-hydroxyethyl methacrylate) film (PolyHEMA), and hydroxypropylmethylcellulose-carboxymethylcellulose bi-layered Petri dish (CEL). The contributions of polar interactions were also estimated on the same biomaterials after fibronectin (Fn) adsorption. The quantity of Fn adsorbed on PS, tPS, PolyHEMA and CEL surfaces was evaluated by using the fluorescein-labeled protein. PolyHEMA and CEL were found to be hydrophilic, tPS was moderately hydrophilic and PS was highly hydrophobic. After Fn adsorption on PS and tPS, a significant increase of the surface polar interaction was observed. On PolyHEMA and CEL, no significant adsorption of Fn was detected and the polar interactions remained unchanged. Finally, an inverse correlation between the polarity of the surfaces and the quantity of adsorbed Fn was established.

Interpretation of the influence of temperature on the solvation properties of gas chromatographic stationary phases using Abraham's solvation parameter model

Abraham's solvation parameter model is used to interpret the influence of temperature on the contribution of cavity formation and solute—solvent intermolecular interactions to the solvation of a varied group of 62 solutes on ten representative stationary phases used in gas chromatography. It was observed that the magnitude of polar interactions increased at lower temperatures and that the change in the characteristic phase constants deduced from Abraham's model as a function of temperature could be described by a second-order polynomial function. Since the susceptibility of a solvent for a particular intermolecular interaction changes in a phase-specific manner as a function of temperature the observed ranking of phases for a particular intermolecular interaction at one temperature cannot be used to predict phase rankings at another temperature for the same interaction. A comparison of Abraham's model with an alternative cavity model proposed by Poole for the sum of the cavity and dispersion contributions to solvation shows similar trends as a function of temperature but differences in the magnitude of the contribution of the cavity—dispersion term to the overall free energy change for the solvation process. Agreement for the contribution of polar interactions to the solvation process is only qualitative for the two models unless a correction is made for the difference in magnitude for the cavity—dispersion contribution. A correction can be made by dividing the c term in Abraham's model into two contributions; a constant term independent of temperature which is assigned to the cavity-dispersion contribution to solvation and a temperature dependent term which is assigned to the polar interaction contribution to solvation. With this construct the two solvation models agree within experimental error for the relative contribution made by the cavity—dispersion term and solute—solvent polar interaction forces to the solvation process.