Amino Acid Anions in Organic Ionic Compounds. An ab Initio Study of Selected Ion Pairs

Abstract

The combination of amino acids in their deprotonated and thus anionic form with a choline cation gives origin to a new and potentially important class of organic ionic compounds. A series of such neutral ion pairs has been investigated by first principle methods. The results reveal intriguing structural motives as well as regular patterns in the charge distribution and predict a number of vibrational and optical properties that could guide the experimental investigation of these compounds. The replacement of choline with its phosphocholine analogue causes the spontaneous reciprocal neutralization of cations and anions, taking place through the transfer of a proton between the two ions. Systems of this kind, therefore, provide a wide and easily accessible playground to probe the ionic/polar transition in organic systems, while the easy transfer of H(+) among neutral and ionic species points to their potential application as proton conductors. The analysis of the ab initio data highlights similarities as well as discrepancies from the rigid-ions force-field picture and suggests directions for the improvement of empirical models.

Room-temperature ionic liquids meet bio-membranes: the state-of-the-art

“…Maginn and co-workers did not observe inter-leaflet diffusion of [bmim][Cl] in POPC, and S.K. Wiedmer and co-workers did observe inter-leaflet diffusion of different RTILs in POPC, we can conclude that the disagreement is due to the important role played by the RTIL chemistry, in line with our neutron reflectivity results (Benedetto et al 2014b). …”

“…This article is part of a Special Issue on 'IUPAB Edinburgh Congress' edited by Damien Hall (v) Penetrate, create pores, and destroy biomembranes (Benedetto et al 2014b, Bhattacharya et al 2017, Evans 2008, Yoo et al 2014, b, Wang et al 2015a, b, 2016Drücker et al 2017; and (vi) Dissolve cellulose and other complex polysaccharides (Youngs et al 2011, Zhang et al 2017, Cheng et al 2011, Liu et al 2010.…”

“…To the best of our knowledge, these are the first chemical-physical investigations of the interactions between RTILs and model biomembranes. However, the first molecular level experimental study to characterize the penetration of RTILs into model biomembranes has been done by means of neutron scattering (Benedetto et al 2014b). More specifically, the density distribution of the chemical species ( Fig.…”

“…3 Density distribution profiles as a function of height z from the surface of the substrate obtained by fitting the neutron reflectivity data taken from (Benedetto et al 2014b). Neutron reflectometry has allowed us to model each single supported phospholipid bilayers with four different density distributions accounting for: (i) the inner lipid heads layer (cyan), (ii) the inner lipid tail layer (blue), (iii) the outer lipid tail layer (blue), (iv) the outer lipid heads layer (cyan); and also (v) the density distribution of the cations (red), whereas the anion (Cl − ) is almost .5%, and 11% of the lipid bilayer volume respectively.…”

Electronic Structure, NMR, Spin–Spin Coupling, and Noncovalent Interactions in Aromatic Amino Acid Based Ionic Liquids

“…[20][21][22][23][24][25] On the theoretical front, molecular dynamics (MD) simulations on the ILs composed of deprotonated amino acid anions and choline cation revealed that their formation is facilitated through proton transfer involving the hydrogen bond effectively neutralizing cation and anion. 26 Fileti and coworkers 27 A molecular level understanding of noncovalent interactions encompassing hydrogen bonding, steric repulsion, aromatic ring stacking and electrostatic interactions should prove useful 5 for designing of task specific ILs. To this direction interactions arising from aromatic rings or π-stacking have received significant attention in the recent years.…”