FTIR fingerprints discriminate ionic liquids’ antibacterial activity

Abstract

Ionic liquids (ILs) are those organic salts which exist in liquid form below 100 ​°C. ILs have drawn attention of scientific community due to their increased industrial applications in variety of sectors. In the present study Fourier transform infrared (FTIR) spectroscopy has been utilized to discriminate the antibacterial activities of ILs having different cations and anions against various microorganisms found in the environment. Imidazolium, Pyridinium, Quaternary ammonium and Tetraalkylphosphonium were used as cations in the study whereas, Bromide, Methane sulphonate, Bis(trifluoromethanesulfonyl)imide, Dichloroacetate, Tetrafluoroborate and Hydrogen sulphate were used as anionic parts. High and low ILs relative to antibacterial activity is obtained through m-clust clustering. Mostly ILs formed with Octyl methyl imidazolium (OMIm) and butyl methyl imidazolium (BMIm) show high antibacterial activity against the considered microbes. Spectral base line is corrected through modified polynomial fitting (MPF) with smoothing parameter λ ​= ​1. For discrimination of ILs i.e. high and low antibacterial groups through FTIR spectral data sparse partial least squares discriminant analysis (sPLS-LDA) and jackknife partial least squares logistic regression (jPLS-LR) are used. Spectral wavenumbers selection and model parameters are optimized by maximizing the crossvalidation accuracy. Based on 100 Monte Carlo simulation runs, sPLS-LDA best discriminate ILs groups with 90% validated accuracy. Influential wavelength extracted by sPLS-LDA are used to identify the influential functional compounds i.e. C–Br, C = N, C = CH2, C = CH, C–O and O–H, which discriminate the ILs groups. The results indicated that FTIR fingerprints could be used as a rapid method to discriminate antibacterial activities of ionic liquids.