Design, synthesis, photophysics and self-assembly study of platinum (II) terpyridine complexes and their utilization as stimuli-responsive smart materials and probes for molecules and macromolecules of biological interest

Abstract

A series of water-soluble platinum(II) terpyridine complexes with functionalized alkynyl ligands and a boronic acid-containing polymer, PAAPBA, have been synthesized and characterized. The photophysical and electrochemical properties of all the platinum(II) complexes have been studied. Some of the complexes have been demonstrated to show ground-state aggregation in organic solvents and aqueous solutions at high concentrations, leading to Pt…Pt and/or π–π interactions and hence the emergence of metal-metal-to-ligand charge transfer (MMLCT) transitions in both the UV−visible and emission spectra. The induced self-assembly of [Pt(tpy)(C≡CC6H4−CH2NMe3-4)](OTf)2 by PAAPBA has been explored for the development of glucose sensing protocols and α-glucosidase assay by monitoring the triplet metal-metal-to-ligand charge transfer (3MMLCT) emission in the near-infrared (NIR) region. [Pt(tpy){C≡CC6H4− {NHC(=NH2+)(NH2)}-4}](OTf)2 has been observed to undergo induced aggregation in the presence of citrate, with good selectivity over other mono- and dicarboxylates in the tricarboxylic acid (TCA) cycle. Enzymatic activity of citrate lyase has also been probed by the emission spectral changes of the complex in the NIR region.

A series of water-soluble alkynylplatinum(II) terpyridine complexes and water-soluble conjugated polyelectrolytes (CPEs) have been synthesized and characterized. The UV–vis absorption and emission properties of the platinum(II) complexes and CPEs have been investigated in organic solvents and/or aqueous buffer solutions. The electrochemical properties and ground-state aggregation at high concentrations of the platinum(II) complexes have also been examined. Two-component ensembles containing selected platinum(II) complexes and PPE-SO3− have been studied, and Förster resonance energy transfer (FRET) has been demonstrated from the PPE-SO3− donor to the aggregated complexes as acceptors. The ensemble containing PPE-SO3− and [Pt(tpy)(C≡CC6H4CH2NMe3-4)](OTf)2 has been employed for a “proof-of-principle” label-free detection of human serum albumin (HSA) in pH 3 buffer solutions with high selectivity and sensitivity, while another ensemble containing PPE-SO3− and [Pt{tpy(C6H4CH2NMe3-4)-4’}(C≡CC6H5)](OTf)2 has been utilized for selective label-free detection of G-quadruplex structure of the human telomeric DNA in physiological buffer solutions.

A series of water-soluble platinum(II) terpyridine complexes with stimuli-responsive alkynyl ligands and a series of water-soluble platinum(II) metallosupramolecular triblock copolymers have been synthesized and characterized. The photophysical and electrochemical properties as well as the ground-state aggregation of the complexes have been investigated. Some of them have been found to show different electronic absorption and emission properties in aqueous solution at different pHs due to aggregation/deaggregation of the complexes. One of the complexes has been employed for live-cell imaging experiments to locate acidic organelles, such as lysosomes, in MDCK cells. The water-soluble platinum(II) metallosupramolecular triblock copolymers have been found to show an increase in 3MMLCT emission intensity in the red-NIR region with temperature, which has been attributed to the formation of spherical polymeric micelles. The platinum(II) triblock copolymer with pH-responsive –CH2NMe2 moieties has been demonstrated as a NIR-emitting dual sensor for pH and temperature through the changes in hydrophilicity and hence the emission properties with pH and temperature simultaneously.