Ion-Pairing Stereodynamic Probes for Circular Dichroism Chiral Sensing of Amines

Tris(2-pyridylmethyl)amine (TPMA) and tris(2-phenolmethyl)amine (TPA) metal complexes have been extensively used for catalysis and molecular recognition applications. In particular, due to their ability to form stereodynamic complexes through the helical arrangement of the ligand around the metal in a propeller shape, chiroptical sensing has been extensively investigated. In particular, the capability of the analyte, usually a Lewis base, to bind the metal complex has been the predominant recognition motif. Herein, we report the synthesis and application of a zinc TPA-based stereodynamic probe for the sensing of chiral amines and amino-alcohols in which an ion-pair interaction between the anionic metal complexes and the ammonium ions is responsible for the recognition.

Circular Dichroism Sensing: Strategies and Applications

The analysis of the absolute configuration, enantiomeric composition, and concentration of chiral compounds are frequently encountered tasks across the chemical and health sciences. Chiroptical sensing methods can streamline this work and allow high-throughput screening with remarkable reduction of operational time and cost. During the last few years, significant methodological advances with innovative chirality sensing systems, the use of computer-generated calibration curves, machine learning assistance, and chemometric data processing, to name a few, have emerged and are now matched with commercially available multi-well plate CD readers. These developments have reframed the chirality sensing space and provide new opportunities that are of interest to a large group of chemists. This review will discuss chirality sensing strategies and applications with representative small-molecule CD sensors. Emphasis will be given to important milestones and recent advances that accelerate chiral compound analysis by outperforming traditional methods, conquer new directions, and pioneering efforts that lie at the forefront of chiroptical high-throughput screening developments. The goal is to provide the reader with a thorough understanding of the current state and a perspective of future directions of this rapidly emerging field.

Tripodal gold(i) polypyridyl complexes and their Cu+ and Zn2+ heterometallic derivatives. Effects on luminescence

Three gold(i) tripodal complexes containing the tris(2-pyridylmethyl)amine (TPA) ligand coordinated to Au-PR₃ moieties (PR₃ = 1,3,5-triaza-7-phosphatricyclo[3.3.1.13.7]decane, PTA (1), 3,7-diacetyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane, DAPTA (2) and triphenylphosphane (3)) were prepared together with a cage-like structure containing triphosphane 1,1,1-tris(diphenylphosphinomethyl)ethane (4). The luminescence of these complexes has been studied and they show a red shift upon the formation of heterometallic complexes by reaction with Zn(NO₃)₂, CuCl and [Cu(CH₃CN)₄]BF₄. The different coordination motifs of the Zn²⁺ and Cu⁺ heterometallic species and the resulting changes in the recorded absorption, emission and NMR spectra were analysed and supported by TD-DFT calculations.

Tris-pyridylmethylamine (TPMA) complexes functionalized with persistent nitronyl nitroxide organic radicals

The chance to have persistent organic radicals in combination with metals has attracted much interest since it offers the possibility of having new functional molecules with multiple open-shell elements. In this study, we report the synthesis of two tripodal tris(2-pyridyl)methylamine ligands (TPMA) functionalized with nitronyl nitroxide persistent radicals. The newly formed ligands have been used to coordinate zinc(ii), copper(ii), iron(ii) and cobalt(ii). The resulting complexes have been investigated by means of electron paramagnetic resonance (EPR), ESI-MS, FT-IR spectroscopy and X-ray diffraction. An electron reduction of the N-O radical moiety has been observed, depending on the metal used for the formation of the complex and the reaction conditions. We have observed small differences in the EPR spectra depending on the meta or para position of the radical moiety in the complex structure and some antiferromagnetic interactions between the paramagnetic M(ii) ions and the radical species.