Bonding of Aqueous Citrate with Zn2+ and ZnO Nanoclusters: A Theoretical Study. Issue 6 (24th February 2017) - Sutton, Catherine C. R.
Abstract: To gain insight into how citrate bonds to ZnO, we have studied how aqueous citrate bonds to zinc cations (Zn 2+ ) as well as zinc oxide nanoclusters [(ZnO) n, n =8 to 12] through density functional theory modelling. The infrared (IR) spectra of each complex in water has been calculated at the M05‐2X/cc‐pVTZ level of theory with the SMD solvent model and is presented over the region of 1700 cm −1 to 1250 cm −1 ; this region corresponds to the stretching modes of the carboxylate group, which change when bonding occurs. Citrate forms bidentate chelating and monodentate bonds with Zn 2+ ; bidentate bonds result in antisymmetric stretching modes of lower wavenumber, while monodentate bonds result in higher wavenumber modes. The most stable structures involve bonds between multiple carboxylate groups and the Zn 2+ and sometimes involve the hydroxyl group. Carboxylate groups not involved in bonding generally do not exhibit shifts in their infrared spectra. Similar trends are also observed in complexes of (Zn)2 ‐citrate, (Zn)3 ‐citrate and (Zn)‐citrate2 . Citrate bonds weakly with the nanoclusters, forming one or two monodentate bonds to different zinc atoms; the IR spectra are not as strongly affected as when bonding occurs with Zn 2+ . Abstract : Modelling suggests that when citrate bonds to Zn 2+ via one terminal and the center carboxylates in monodentate configurations as well as the hydroxyl, the predicted IR spectra most closely matches that found when citrate bonds to the ZnO basal plane.