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. 2021 Nov 19;6(48):32460-32474.
doi: 10.1021/acsomega.1c03864. eCollection 2021 Dec 7.

Exploring the Interactions of Ionic Liquids with Bio-Organic Amphiphiles Using Computational Approaches

Rachel E Daso  1 , Saige M Mitchell  1 , Charlotta G Lebedenko  1 , Ryan M Heise  1 , Ipsita A Banerjee  1
Affiliations

Exploring the Interactions of Ionic Liquids with Bio-Organic Amphiphiles Using Computational Approaches

Rachel E Daso et al. ACS Omega. .

Abstract

Bio-organic amphiphiles have been shown to effectively impart unique physicochemical properties to ionic liquids resulting in the formation of versatile hybrid composites. In this work, we utilized computational methods to probe the formation and properties of hybrids prepared by mixing three newly designed bio-organic amphiphiles with 14 ionic liquids containing cholinium or glycine betaine cations and a variety of anions. The three amphiphiles were designed such that they contain unique biological moieties found in nature by conjugating (a) malic acid with the amino acid glutamine, (b) thiomalic acid with the antiviral, antibacterial pyrazole compound [3-(3,5-dimethyl-1H-pyrazol-1-yl)benzyl]amine, and (c) Fmoc-protected valine with diphenyl amine. Conductor-like screening model for real solvents (COSMO-RS) was used to obtain sigma profiles of the hybrid mixtures and to predict viscosities and mixing enthalpies of each composite. These results were used to determine optimal ionic liquid-bio-organic amphiphile mixtures. Molecular dynamics simulations of three optimal hybrids were then performed, and the interactions involved in the formation of the hybrids were analyzed. Our results indicated that cholinium-based ILs interacted most favorably with the amphiphiles through a variety of inter- and intramolecular interactions. This work serves to illustrate important factors that influence the interactions between bio-organic amphiphiles and bio-ILs and aids in the development of novel ionic liquid-based composites for a wide variety of potential biological applications.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Top row: two-dimensional (2D) structures of the designed amphiphiles (a) MG, (b) TMC, and (c) Fmoc-Val-DP. Second row: (i) choline and (ii) glycine betaine are the IL cation components; and (iii) IL anion component bicarbonate. Third row: anion components of IL utilized (iv) citrate, (v) dihydrogen phosphate, and (vi) glucuronate. Fourth row: additional anion components of IL utilized (vii) levulinate, (viii) serine, and (ix) chloride.
Figure 2
Figure 2
Three-dimensional (3D) sigma surfaces of (a) MG, (b) TMC-PY, and (c) Fmoc-Val-DP calculated by COSMO-RS methods; (d) corresponding sigma profiles of the three amphiphiles.
Figure 3
Figure 3
Sigma profiles showing the density of electrostatic potential over the surface of the molecule for IL cations and anions, as calculated by the COSMO-RS method.
Figure 4
Figure 4
Predicted change in viscosity (ln(η)) with an increase in temperature by 1 K for all 14 IL combinations. Solid bars are indicative of ILs with cholinium containing cations, while striped bars are indicative of glycine betaine ILs. Each of these contains different anions, as indicated in Table 1.
Figure 5
Figure 5
Estimated total excess enthalpy, HmE, of binary mixtures of ILs and amphiphiles: (a) MG, (c) TMC-PY, and (e) Fmoc-Val-DP at 298.15 K plotted against the mole fraction of the amphiphile. Predicted contribution of electrostatic misfit interactions (Hm,MFE), hydrogen-bonding interactions (Hm,HBE), and van der Waals forces (Hm,VDWE) to the total excess enthalpy of the IL-amphiphile mixtures at a 50% mole ratio at 298.15 K for (b) MG, (d) TMC-PY, and (f) Fmoc-Val-DP. All IL combinations 1–14 are indicated in Table 1.
Figure 6
Figure 6
Comparison of trajectory snapshots of MD simulations of neat amphiphiles and composites of amphiphile-IL mixtures at 0, 25, and 50 ns. Green, amphiphile; red, choline; blue, levulinate; purple, serine; and yellow, chloride. Simulations were carried out in water, but water molecules were hidden for ease of viewing. Top row is indicative of neat assembly formation. Rows 2–4 are indicative of interactions of assemblies with cholinium levulinate (IL9), cholinium serine (IL11), and cholinium chloride (IL13), respectively.
Figure 7
Figure 7
Total solvent-accessible surface area of the amphiphiles over 50 ns. Runs were conducted in a solvated box of 60 Å at STP. Charts show runs of (a) MG with and without the addition of ILs, (b) TMC-PY with and without the addition of ILs, and (c) Fmoc-Val-DP with and without the addition of ILs (IL9, cholinium levulinate; IL11, cholinium serine; IL13, cholinium chloride).
Figure 8
Figure 8
Comparison of the total number of hydrogen bonds between the ILs and ILs with amphiphiles over 50 ns. Runs were conducted in a solvated box of 60 Å at STP. Charts show runs of (a) MG with ILs, (b) TMC-PY with ILs, (c) Fmoc-Val-DP with ILs, and (d) neat ILs for comparison (IL9, cholinium levulinate; IL11, cholinium serine; IL13, cholinium chloride).
Figure 9
Figure 9
Radial distribution functions from MD simulations for (a) neat amphiphiles calculated between the center of mass of each amphiphile molecule, (b) neat ILs 9, 11, and 13 calculated between the center of mass of all IL components (cation and anion), (c) hybrids calculated between the center of mass of all molecules in the hybrid system (amphiphiles, cations, and anions), (d) hybrids calculated between the center of mass of each amphiphile molecule, and (e) hybrids calculated from the center of mass of cation and anion molecules to the center of mass of amphiphile molecules.
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