Binding Behavior of Crystalline and Noncrystalline Phases: Evaluation of the Enthalpic and Entropic Contributions to the Separation Selectivity of Nonpolar Solutes with a Novel Chromatographic Sorbent

In this paper, we describe studies of the retention characteristics of nonpolar molecules with a novel liquidcrystalline, silica-supported, comb-shaped polymer chromatographic phase, Sil-ODA 18 . These results extend and amplify previous reports of the roles of enthalpic-and entropic-driven processes in the modulation of the selectivity of nonpolar and polar compounds in reversed-phase high-performance liquid chromatography (RP-HPLC). The investigations reveal that phase reorganization is the most important factor controlling selectivity enhancement with silica-supported, comb-shaped polymer phases as the temperature, T, of the system is varied. Moreover, these studies demonstrate that contributions from the stationary and the mobile phases can be independently fine-tuned to achieve enhanced selectivity via partition and/or adsorption binding processes. The relevant thermodynamic parameters, namely, the changes in enthalpy, entropy, and heat capacity for various nonpolar solutes with this comb-shaped polymeric sorbent, have also been determined using recently developed analytical procedures for the evaluation of nonlinear van't Hoff plots. These investigations into the thermodynamic properties of the comb-shaped polymeric sorbent in its ordered crystalline and noncrystalline states clearly delineate the differences in binding behavior compared to conventional types of monolayer n-alkylsilica sorbents and thus should facilitate wider application of this new class of reversed-phase sorbents in the separation sciences. Introduction Reversed-phase chromatography (RPC) is currently the most widely used of all of the high-performance liquid chromatographic (HPLC) modes of separations. The evaluation of the physicochemical basis of the retention mechanisms of different classes of solutes in RPC has received extensive attention, with the experimental results often interpreted in terms of the solvophobic model proposed by Horvath et al. 1,2 A central question pertaining to all RPC separations is, What drives the retention process? This question has been the subject of considerable debate and investigation since the concept of RPC was first used in 1950 as an analytical separation method by Howard and Martin. 3 Two primary RPC mechanisms can be considered, namely, the solvation/desolvation model, 1,2 whereby expulsion of solutes from a polar mobile phase dominates the free energy of transfer with nonpolar sorbents acting as receptive but passive surfaces, and the partitioning model, 4-6 where the stationary phase contributes in a much more significant way to the overall distribution process. On the basis of solvophobic considerations that encompass the solvation/desolvation model, Horvath and co-workers 1 have proposed that the interaction between the solute and the mobile phase provides the primary driving force. According to this model, retention in the high-performance modes of RPC can then be attributed to adsorption rather than partitioning processes between the solutes and the nonpolar sorbent. 1,2 In the solvation/desolvation model, the contributio

Thermodynamic assessment of the stability of thrombin receptor antagonistic peptides in hydrophobic environments.

In this paper, a general procedure is described to determine thermodynamic parameters associated with the interaction of thrombin receptor antagonistic peptides (TRAPs) with immobilized nonpolar ligands. The results show that these interactions were associated with nonlinear van't Hoff dependencies over a wide temperature range. Moreover, changes in relevant thermodynamic parameters, namely the changes in Gibbs free energy of interaction, DeltaG(0)assoc, enthalpy of interaction, DeltaH(0)assoc, entropy of interaction, DeltaS(0)assoc, and heat capacity, DeltaC(0)p, have been related to the structural properties of these TRAP analogs. The implications of these investigations for the design of thrombin receptor agonists/antagonists with structures stabilized by intramolecular hydrophobic interactions are discussed

Lateral force contrast for the detection of hydrophillc beads embedded within a PDMS surface

Abstract not available

Steel protection using sol-gel coatings in simulated concrete pore solution contaminated with chloride

This work compares the anticorrosion features of polysiloxane hybrid films deposited on carbon steel substrates by dip-coating. To assess the influence of the components, sol-gel coatings were prepared from condensation and polymerization of TEOS and MPTS, TEOS and MTES, TMOS and MPTS or TMOS and MTES mixtures in three molar ratios. The corrosion protection of the coatings was evaluated by means of polarization curves and electrochemical impedance spectroscopy measurements. The coatings' thickness was quantified by field emission-scanning electron microscopy. The results indicate that all the coatings improved the corrosion resistance of carbon steel in an alkaline environment contaminated with 3. wt.%NaCl solution and show that the protective properties of the coating were especially improved when MTES was added to the formulations and when the TMOS/MPTS mixture was used, probably due to a highly cross-linked network and a greater coating thickness, capable of delaying the corrosion process. © 2014 Elsevier B.V.M. Criado expresses her gratitude to the Spanish Ministry of Science and Innovation for the Juan de la Cierva contract (Ref. JDC-2010)Peer Reviewe