New Subsidiary Interaction Mode of Counteranions with the Periphery Cavity of Calix[4]pyrroles Binding with the Anion Subunits

The solution binding properties of calix[4]pyrroles with anion （as tetraalkylammonium salts） were investigated using UV-Vis spectroscopic techniques. The obvious red-shift of absorption maximum band of calix[4]pyrrole in EtOH in the presence of the tetramethylammonium （TMA^＋） salts or tetraethylammonium （TEA^＋） salts were observed, due to the charge-transfer interactions between the electron-rich pyrrole rings of calix[4]pyrroles and TMA^＋ or TEA^＋ cation subunit. The results indicated that calix[4]pyrrole receptors, which link the anionic species through multiple hydrogen bonding interactions, can use the periphery cavity for selectively binding cation subunits by cation-π charge-transfer interaction. The subsidiary interaction mode helps to further stabilize the calix[4]pyrrole-anion complex.

Interaction Energies of Tetraalkylphosphonium Cation- and Amino Acid Anion- Based Ionic Liquids

Ab initio calculations were performed using the Gaussian 03 software package to obtain the optimized structure, interaction energy and infrared spectrum of ionic liquids （ILs） containing a tetraalkylphosphonium cation and an amino acid anion. In order to investigate the effect of the presence of nitrogen in the cation, the tetraalkylphosphonium cation was replaced by a tetraalkylammonium cation, while amino acids were retained as anions in the ionic liquid. The amino acids studied here included glycine, alanine, serine, lysine, and glutamine. Optimized structures of several ILs in the gas phase were determined at the levels of Hartree-Fock （HF/6-3＋G（d）） and 1density functional theory （B3LYP/6-3 1＋＋G（d,p））. At high-level estimations, MP2/6-31＋G（d） and MP2/6-31＋＋G（d,p）, the interaction energies between the cations and anions of the ILs were determined. In order to investigate the effect of alkyl-chain length on interaction energy, the alkyl groups were varied from methyl to ethyl and propyl in the tetraalkylphosphonium functional groups. This procedure revealed that there is a considerably stronger interaction between the alkylphosphonium cations and amino acids than between alkylammonium cations and amino acids. Vibrational spectroscopy of ILs shows that a significant -OH vibration peak occurs at 4124 cmt in serine-containing ILs, and a prominent C=O vending peak occurs at 1626 cm^-1 in amino acids.

Electrostatic interaction mechanism on the separation of phenols by non-aqueous capillary electrophoresis

The electrostatic interaction between additive and analyte is of great importance to non-aqueous cap- illary electrophoresis(NACE)separation.Three tetraalkylammonium bromides and acetonitrile were applied as additives and running solvent respectively.The effect of alkyl chain length and concentra- tion of additive on electrostatic interactions was investigated by the separation of phenols.The sepa- ration ability was found to increase with decreasing alkyl chain length of the additive,and the resolu- tion values were increased with increasing additive concentration.The separation was seriously dete- riorated after a little amount of water was added in the running solution.Furthermore,the electrostatic interaction is strong under the conditions of low electron cloud density,weak steric hindrance and multi-interaction sites.Thus,the separation result can be predicted by theoretical analysis,which is helpful for the separation of other substances in NACE based on electrostatic interaction.