Iranian Journal of Chemical Engineering (IJChE)
Scientific Journal

Atomistic Molecular Dynamics Simulation of Pyridinium Bromide Ionic Liquids: Quantitative Insights into Alkyl Chain Length Effects on Ion Transport and Microstructure

Articles in Press

Document Type : Regular Article

Authors

Zahra Fakhri
Azim Soltanabadi

Faculty of Chemistry, Razi University, Kermanshah, Iran

10.22034/ijche.2026.572366.1584
Abstract
This study employs classical molecular dynamics simulations using the OPLS-AA force field to systematically investigate the influence of alkyl chain length on the structural, thermodynamic, and dynamical properties of a homologous series of pyridinium-based ionic liquids (methyl- to pentyl-pyridinium bromide). The main objective is to elucidate how gradual alkyl chain elongation affects intermolecular interactions and ion transport behavior at the molecular level. The model demonstrates good agreement with available experimental density data, confirming its reliability for predicting physicochemical trends in these systems. The results indicate that increasing alkyl chain length weakens electrostatic interactions and enhances free volume, leading to a systematic reduction in density and cohesive energy density. Structural analysis reveals well-defined cation–anion coordination shells, reflecting strong local ionic organization across all systems. Dynamical analysis shows a consistent decrease in ionic mobility with chain elongation due to stronger van der Waals interactions and steric effects, which in turn reduces diffusion and ionic conductivity. Importantly, ionic transference numbers calculated from ion mobilities clearly demonstrate that cations contribute more to charge transport than anions in all investigated systems. This cation-dominated transport behavior provides a direct molecular-level explanation for the observed decrease in ionic conductivity with increasing alkyl chain length.

Keywords

Pyridinium-based ionic liquids
RDF
Heats of vaporization
Diffusion coefficient
Subjects
[1] Ahluwalia VK (2021) Green chemistry: Environmentally benign reactions. Springer Nature. https://doi.org/10.1007/978-3-030-58513-6.
[2] Jiménez-González C, Constable DJ (2011) Green chemistry and engineering: a practical design approach. John Wiley & Sons. ISBN: 978-0-470-17087-8.
[3] Dunn PJ (2012) The importance of green chemistry in process research and development. Chem Soc Rev 41:1452-1461. http://dx.doi.org/10.1039/c1cs15041c.
[4] Sheldon RA (2012) Fundamentals of green chemistry: efficiency in reaction design. Chem Soc Rev 41:1437-1451. http://dx.doi.org/10.1039/c1cs15219j.
[5] Capello C, Fischer U, Hungerbühler K (2007) What is a green solvent? A comprehensive framework for the environmental assessment of solvents. Green Chem 9:927-934. http://dx.doi.org/10.1039/b617536h.
[6] Slater CS, Savelski M (2007) A method to characterize the greenness of solvents used in pharmaceutical manufacture. J Environ Sci Health A 42:1595-1605. http://dx.doi.org/10.1080/10934520701517747.
[7] Imam HT, Krasňan V, Rebroš M, Marr AC (2021) Applications of ionic liquids in whole-cell and isolated enzyme biocatalysis. Molecules 26:4791. https://doi.org/10.3390/molecules26164791.
[8] Bedrov D, Piquemal JP, Borodin O, MacKerell AD Jr, Roux B, Schröder C (2019) Molecular dynamics simulations of ionic liquids and electrolytes using polarizable force fields. Chem Rev 119:7940−7995. http://dx.doi.org/10.1021/acs.chemrev.8b00763.
[9] Begić S, Jónsson E, Chen F, Forsyth M (2017) Molecular dynamics simulations of pyrrolidinium and imidazolium ionic liquids at graphene interfaces. Phys Chem Chem Phys 19:30010-30020. https://doi.org/10.1039/C7CP03389C.
[10] Reddy TDN, Mallik BS (2020) Ionic dynamics of hydroxylammonium ionic liquids: a classical molecular dynamics simulation study. J Phys Chem B 124:4960-4974. https://doi.org/10.1021/acs.jpcb.0c01388.
[11] Sedghamiz E, Moosavi M (2017) Tricationic ionic liquids: structural and dynamical properties via molecular dynamics simulations. J Phys Chem B 121:1877-1892. https://doi.org/10.1021/acs.jpcb.6b10766.
[12] Zhu X, Mu L, Zhu J, Lu X, Ji Y (2024) The role of hydrogen bonding in solubilizing camptothecin in hydrophilic and hydrophobic ionic liquids. Green Chem Eng 5:489-500. https://doi.org/10.1016/j.gce.2023.12.002.
[13] Liu H, et al. (2012) Thermal and transport properties of six ionic liquids: an experimental and molecular dynamics study. Ind Eng Chem Res 51:7242-7254. https://doi.org/10.1021/ie300222a.
[14] Panbo P, Thubsuang U, Payaka A (2025) Molecular dynamics simulations of hydrogen-bonded network structures of polybenzoxazines in the gas phase and aqueous solution. J Mol Graph Model 134:10883. https://doi.org/10.1016/j.jmgm.2024.108893.
[15] Dhakal P, Das SK, Shah JK (2022) Revealing hydrogen bond dynamics between ion pairs in binary and reciprocal ionic liquid mixtures. J Mol Liq 368:120515. https://doi.org/10.1016/j.molliq.2022.120515.
[16] Fedorova IV, Krestyaninov MA, Safonova LP (2021) Structure and ion-ion interactions in trifluoroacetate-based ionic liquids: quantum chemical and molecular dynamics simulation studies. J Mol Liq 328:115449. https://doi.org/10.1016/j.molliq.2021.115449.
[17] Tong B, Liu QS, Tan ZC, Welz-Biermann U (2010) Thermochemistry of alkyl pyridinium bromide ionic liquids: calorimetric measurements and calculations. J Phys Chem A 114:3782–3787. https://doi.org/10.1021/jp9047538.
[18] Sowmiah S, Esperança JMSS, Rebelo LPN, Afonso CAM (2018) Pyridinium salts: from synthesis to reactivity and applications. Org Chem Front 5:453–493. https://doi.org/10.1039/c7qo00836h.
[19] Zhang Q, He H, Wang H, Zhang Z, Chen C (2019) Efficient catalytic oxidation of methyl aromatic hydrocarbon with N-alkyl pyridinium salts. RSC Adv 9:38891–38896. https://doi.org/10.1039/c9ra08185b.
[20] Yang J, Chen Q, Afsar NU, Ge L, Xu T (2023) Poly (alkyl-biphenyl pyridinium)-Based Anion Exchange Membranes with Alkyl Side Chains Enable High Anion Permselectivity and Monovalent Ion Flux. Membranes 13:188. https://doi.org/10.3390/membranes13020188.
[21] Mahmood Fatemi S, Foroutan M (2015) Recent findings about ionic liquids mixtures obtained by molecular dynamics simulation. Nanostruct Chem 5:243–253. https://doi.org/10.1007/s40097-015-0155-0.
[22] Zhua G, Zhoua S, Maa Z, Xua J (2025) Molecular dynamics simulation of the interaction between ionic liquid [OPy][BF4] and SO2. Fluid Phase Equilib 589:114257. https://doi.org/10.1016/j.fluid.2024.114257
[23] Forester TR, Smith W (1995) DL_POLY. Warrington: CCLRC, Daresbury Laboratory. Available from http://www.stfc.ac.uk/CSE/randd/ccg/software/DL_POLY/25526.aspx.
[24] McLean AD, Chandler GS (1980) Contracted Gaussian basis sets for molecular calculations. I. Second row atoms, Z= 11–18. J Chem Phys 72:5639–5648. http://dx.doi.org/10.1063/1.438980.
[25] Krishnan R, Binkley JS, Seeger R, Pople JA (1980) Self consistent molecular orbital methods. XX. A basis set for correlated wave functions. J Chem Phys 72:650–654. http://dx.doi.org/10.1063/1.438955.
[26] Grimme S, Ehrlich S, Goerigk L (2011) Effect of the damping function in dispersion corrected density functional theory. J Comput Chem 32:1456–1465. https://doi.org/10.1002/jcc.21759.
[27] Frisch MJ, et al. (2009) Gaussian 09, Revision D.01. Gaussian, Inc.: Wallingford, CT.
[28] Jorgensen WL, Maxwell DS, Tirado-Rives J (1996) Development and testing of the OPLS all-atom force field on conformational energetics and properties of organic liquids. J Am Chem Soc 118:11225–11236. https://doi.org/10.1021/ja9621760.
[29] Hoover WG (1985) Canonical dynamics: Equilibrium phase-space distributions. Phys Rev A 31:1695. https://doi.org/10.1103/PhysRevA.31.1695.
[30] Allen MP, Tildesley DJ (1987) Computer simulation of liquids. Clarendon: Oxford. https://doi.org/10.1093/oso/9780198803195.001.0001.
[31] Fakhri Z, Soltanabadi A (2025) An experimental-computational analysis of molecular interactions and its effect on thermodynamic properties of mixtures of isobutanol and ethylbenzene. Results Chem 15:102286. https://doi.org/10.1016/j.rechem.2025.102286
[32] Meng X, He J, Xu C (2022) Preparation of Ionic Liquid 1-Propylpyridinium Bromide [C3py] Br and the Molar Surface Quasi-Gibbs Energy Model of Its Aqueous Solution. J Chem Eng Data 67:23–27. https://doi.org/10.1021/acs.jced.1c00569.
[33] Shaikh VR, Terdale SS, Gupta GR, Hundiwale DG, Patil KJ (2013) Thermodynamic studies of ionic interactions in aqueous solutions of N-butyl-pyridinium bromide at 298.15 K. J Mol Liq 186:14–22. https://doi.org/10.1016/j.molliq.2013.04.027.
[34] van Leeuwen ME, Smit B (1995) Molecular simulation of the vapor-liquid coexistence curve of methanol. J Phys Chem 99:1831–1833. https://doi.org/10.1021/j100007a006.
[35] Fakhri Z, Soltanabadi A (2024) A Combined Experimental, DFT and Molecular Dynamics Simulation Study of Binary Mixture of Ethylbenzene and Aniline. ChemistrySelect 9:e202401340. https://doi.org/10.1002/slct.202401340.
[36] Soltanabadi A, Fakhri Z (2025) DFT study of 1, 4-diazabicyclo [2.2. 2] octane (DABCO) based ionic liquids: Effect of alkyl chain and anion types. Results Chem 15:102285. https://doi.org/10.1016/j.rechem.2025.102285.
[37] Ferreira ML, Pastoriza-Gallego MJ, Araújo JMM, Canongia Lopes JN, Rebelo LPN, Piñeiro MM, Shimizu K, Pereiro AB (2017) Influence of Nanosegregation on the Phase Behavior of Fluorinated Ionic Liquids. J Phys Chem C 121:5415–5427. https://doi.org/10.1021/acs.jpcc.7b00516.
[38] Shimizu K, et al. (2010) Three commentaries on the nano-segregated structure of ionic liquids. J Mol Struct THEOCHEM 946:70–76. https://doi.org/10.1016/j.theochem.2009.11.034.
[39] Feng G, Chen M, Bi S, Goodwin ZAH, Postnikov EB, Brilliantov N, Urbakh M, Kornyshev AA (2019) Free and bound states of ions in ionic liquids, conductivity, and underscreening paradox. Phys Rev X 9:021024. https://doi.org/10.1103/PhysRevX.9.021024.
[40] Koishi T, Fujikawa S (2010) Static and dynamic properties of ionic liquids. Mol Simul 36:1237–1242. https://doi.org/10.1080/08927020903536358.
 
 
 
 
 
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Available Online from 08 June 2026

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