Dynamics of Water/Methanol Mixtures at Functionalized Chromatographic Interfaces

Abstract

Fully atomistic simulations of water/methanol mixtures of varying compositions (80/20 and 50/50) at chromatographic interfaces with different functionalizations are presented. The dynamical properties in terms of equilibration times and solvent exchange dynamics are characterized and found to depend on the different systems on the nanosecond time scale. The solvent density profile and the structuring of the stationary phase differ for derivatizations including (-CN, NO(2), -NH(2), -C(6)H(5)) of the C(18) chain. The time scale and intensity of the water exchange dynamics differs for the different realizations of the chromatographic systems and ranges from 200 to 500 ps. Water exchange rates depend on solvent composition as well as on the functionalization of alkyl chains. Simulations with acridine as a probe molecule provide atomistic insight into the slot model.

From in silica to in silico: retention thermodynamics at solid–liquid interfaces

“…During US, the analytes' height above the surface z is constrained to within a window of 1 Å but it is free to rotate. It is evident that the C 18 chains are not fully extended but in a partially collapsed state as was already found in previous simulations 3,7,20,21 . The typical average extent is found to be 10 Å and 12 Å above the solid support for 20:80 and 50:50 MeOH/H 2 O solvent mixtures, respectively.…”

“…The water model in the present work is the transferable intermolecular potential three point (TIP3P) 48 model. For the methanol (MeOH) molecule, parameters are taken from previous work 3 with an OH-equilibrium bond length of 0.96 Å. 49 The CT3-OH1 bond, the HA-CT3-OH1 and HA-OH1-CT3 angles, and the dihedrals 49…”

“…Solute retention in reversed-phase liquid chromatography is an important process dominated by intermolecular interactions and has received considerable attention during the past decade. [1][2][3][4][5][6][7][8] Due to the molecular complexity of the system and because QSAR (quantitative structure activity relationship)-like interpretations of experimental data remained largely inconclusive, it is of major importance to improve the understanding of solute retention using computational modelling so that the composition, functionalization and other physico-chemical properties of specific columns can be quantitatively predicted. [9][10][11] Extensions of molecularly-resolved pictures to the mesoscale for liquid chromatography are particularly relevant as they have the potential to reduce development times and potentially improved selectivity of such columns.…”

“…Despite the seemingly simple chemical composition of such systems, the atomistic understanding underlying the separation process remains elusive since the system is highly dynamical, heterogeneous and disordered [1][2][3][4] . Use of computational and experimental spectroscopic techniques such as IR [12][13][14] , Raman 15 and NMR [16][17][18] has provided important insights concerning the water/methanol mixture and proved to be useful in order to characterize these highly heterogeneous systems at the molecular level 1,7,[19][20][21][22][23] .…”

Single‐Molecule and Ensemble Diffusivities in Individual Nanopores with Spatially Dependent Mobility

“…In recent years, MD simulations have become ap owerful tool in the analysis of diffusion processes for both solventa nd solute molecules in confined systems. [33][34][35][36][37][38][39][40] For example, the RPLC characteristics were elucidated from MD simulations [39,[41][42][43][44][45] and Monte Carlo computations, particularly by Siepmannand co-workers. [46] Using MD simulations,single-molecule and ensembled iffusivities can be directly recorded in the same nanopore used as am odel geometry with full flexibility on the chemical-surface modification, pore size, and choice of the solute molecules.…”