Density Functional Theory Analysis of the Impact of Steric Interaction on the Function of Switchable Polarity Solvents

Abstract

A density functional theory (DFT) analysis has been performed to explore the impact of steric interactions on the function of switchable polarity solvents (SPS) and their implications on a quantitative structure-activity relationship (QSAR) model previously proposed for SPS. An X-ray crystal structure of the N,N-dimethylcyclohexylammonium bicarbonate (Hdmcha) salt has been solved as an asymmetric unit containing two cation/anion pairs, with a hydrogen bonding interaction observed between the bicarbonate anions, as well as between the cation and anion in each pair. DFT calculations provide an optimized structure of Hdmcha that closely resembles experimental data and reproduces the cation/anion interaction with the inclusion of a dielectric field. Relaxed potential energy surface (PES) scans have been performed on Hdmcha-based computational model compounds, differing in the size of functional group bonded to the nitrogen center, to assess the steric impact of the group on the relative energy and structural properties of the compound. Results suggest that both the length and amount of branching associated with the substituent impact the energetic limitations on rotation of the group along the N-R bond and NC-R bond, and disrupt the energy minimized position of the hydrogen bonded bicarbonate group. The largest interaction resulted from functional groups that featured five bonds between the ammonium proton and a proton on a functional group with the freedom of rotation to form a pseudo six membered ring which included both protons.

1-Cyclohexylpiperidine as a thermolytic draw solute for osmotically driven membrane processes

“…The QSAR model indicated including ring systems which are near or included the nitrogen such as cyclohexyl groups, pyrrolidines, and piperidines facilitates reaching high concentrations in the polar form [20]. Density functional theory (DFT) studies demonstrated that the ring system constrains the organic groups preventing steric disruption at the amine proton [21]. In response we investigated 1-cyclohexylpiperidine (CHP), featuring two ring systems around the nitrogen center.…”

Energy requirements of the switchable polarity solvent forward osmosis (SPS-FO) water purification process

“…Our initial demonstration of the SPS FO process used dimethylcyclohexylamine (DMCA) [4]. While DMCA is a potential SPS draw solute an SPS optimized for SPS FO process has been sought [15][16][17][18] and suggest 1-cyclohexylpiperidine is an especially promising candidate. Regardless of the SPS employed in the process DMCA is an excellent model SPS and was used to develop the process energy model.…”

Electrochemical production of syngas from CO2 captured in switchable polarity solvents

“…CO 2 capture and utilization cycle 1-Cyclohexylpiperidine (CHP) was tested as SPS for the capture and electrochemical reduction of CO 2 based on high CO 2 absorption capacities, up to 189.63 g/L, compatibility with polymeric systems, and expected low production cost. [29][30][31] As capture-electrolyte media for the utilization of CO 2 , CHP presents additional ideal characteristics, such as low volatility, effective polar-to-nonolar phase transition, low membrane permeability, and compatibility with a wide range of materials. 27 A buffer-layer-type cell with a cation exchange (CEM), inspired in the work of Delacourt et al, 23 was used to perform the electrochemical release and reduction of captured CO 2 .…”