Hg2+ detection by new anthracene pendant-arm derivatives of mixed N/S-, and N/S/O-donor macrocycles: Fluorescence, matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and DFT studies

The optical response of four new anthracenylmethyl pendant-arm derivatives (L1-L4) of the macrocyclic ligands [12]aneNS3, [12]aneNS2O, [15]aneNS2O2, and [12]aneN2SO toward the metal ions Zn(II, Cd(II),Pb(II), Cu(II),Hg(II), Ag(I),Fe(II),Co(II),Ni(II),Mn(II)Ca(II),Na(I),Mg(II) , and K(I) was investigated in 1:1 (v/v) MeCN/H2O solutions. A strong chelation enhancement of quenching effect was observed on the fluorescent emission intensity of L2 as a consequence of the host-guest interaction with Hg(II) and the formation of a 1:2 metal-to-ligand complex. Density functional theory calculations confirmed the formation of a sandwich-type complex between L2 and Hg(II) as a favorable process. A matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry study using the four ligands as active MALDI probes was also performed. L1-L4 have also been explored as fluorescence chemosensors in microsamples using NANODROP technology

Importance of Off-Cycle Species in the Acid-Catalyzed Aza-Piancatelli Rearrangement

The observed rate of reaction in the dysprosium triflate catalyzed aza-Piancatelli rearrangement is controlled by a key off-cycle binding between aniline and catalyst. Deconvoluting the role of these ancillary species greatly broadens our understanding of factors affecting the productive catalytic pathway. We demonstrate that the rate of reaction is controlled by initial competitive binding between the furylcarbinol and nitrogen nucleophile using either a Brønsted or Lewis acid catalyst and that the resulting rearrangement proceeds without involving the Brønsted and Lewis acid catalyst. This shows conclusively that the rate-controlling step and selectivity of reaction are decoupled