Design and synthesis of heterobimetallic complexes as optical chemodosimetric ensembles for the detection of biological and environmental substrates in aqueous media

Abstract

Molecules and ions play numerous crucial roles in biological systems, chemical processes and environmental pollution. Design and synthesis of receptors capable of recognizing molecular and ionic analytes and communicating the recognition events via visual signals are particularly important. Traditionally, most synthetic molecular sensors are designed according to the receptor – signaling unit covalent attachment approach. However, the requirement of covalent linkage of the receptor and signaling units usually poses considerable constraints on the development of molecular sensors. In chapter one, an alternative design of molecular sensors known as the “displacement approach” is introduced. A brief review on molecular sensors based on such “displacement approach” is also given. Components, properties, advantages and examples involved are discussed. In accordance with this approach, a novel “heterobimetallic chemodosimetric ensemble” design, where one metal center acting as a functional-specific binding site for analytes is coordinately bridged to another coordination metal center responsible for signal transduction is described. In chapter two, a neutral trinuclear heterobimetallic cyano-bridged Ru(II)/Pt(II) complex, cis-Ru(phen)2[CN⎯Pt(DMSO)Cl2]2 (phen = 1,10-phenanthroline) (Ru-Pt-1) capable of functioning as a chemodosimetric ensemble for the ratiometric determination of sulfur-containing amino acids and peptides is described. Synthesis, characterization and spectroscopic properties of Ru-Pt-1 are given. Binding properties of Ru-Pt-1 with common amino acids and peptides revealed that it is very selective for sulfur-containing amino acids and peptides (L-cysteine, DL-homocysteine, L-methionine and glutathione) with binding constants ranging from 2.91 ± 0.19 × 104 to 1.73 ± 0.15 × 105 M-1. The sensing mechanism of Ru-Pt-1 involves the cleavage of its cyano-bridges by the coordination of the thiols to the Pt(II) receptor and hence restoration of the characteristic orange-red 3MLCT luminescence of the Ru(II)-diimine chromophore. In chapter three, a series of new trinuclear heterobimetallic cyano-bridged complexes, cis-Fe(bpy)2[CN⎯Pt(DMSO)Cl2]2 (Fe-Pt-2), cis-Ru(bpy)2[CN⎯Pt(DMSO)Cl2]2 (Ru-Pt-3) and cis-Os(bpy)2[CN⎯Pt(DMSO)Cl2]2 (Os-Pt-4) are synthesized and characterized. Binding properties of Fe-Pt-2, Ru-Pt-3 and Os-Pt-4 with common amino acids and peptides revealed that all of the heterobimetallic complexes are very selective to sulfur-containing amino acids and peptides (L-cysteine, DL-homocysteine, L-methionine and glutathione). Systematic variation of the chromotropic signal transducer results different visual responses to the sulfur-containing amino acids and peptide. A systematic study on how the relative stability of the donor-acceptor ensemble (reporter-receptor ensemble) to that of the adduct formed between the accepting metal center (receptor) and the analyte affects the analyte-selectivity of such a chemodosimetric design is also carried out. Results indicate that of the interaction between the receptor and the reporter unit is too weak, analyte-specificity of the resultant ensemble will not be good as it may respond to a lot of different analytes. On the other hand, if the interaction is too strong, the ensemble may not be responsive to any analyte at all. In chapter four, a new Ru(II)/Cu(II) heterobimetallic complex, {RuII(tBubpy)(CN)4-[CuII(dien)]2}(ClO4)2 (tBubpy = 4,4’-di-tert-butyl-2,2’-bipyridine; dien = diethylenetriamine) (Ru-Cu-8), as a chemodosimetric ensemble for the specific dual luminescent/colorimetric detection of cyanide anion is described. Synthesis, characterization and spectroscopic properties of Ru-Cu-8 are reported. Binding properties of Ru-Cu-8 with common anions revealed that this heterobimetallic complex is very selective to cyanide with binding constant 7.39 ± 0.23 × 106 M-2 and sensitivity reaching 1.2 μM (0.03 ppm) in aqueous DMF at pH 7.4.

Date of Award	15 Feb 2005
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Hon Wah Michael LAM (Supervisor)