Synthesis and Structural and Spectroscopic Studies of a pH-Neutral Argentic Chelate Complex: Tribasic Silver (III) Bisperiodate

The preparation of stable hypervalent metal complexes containing Ag(III) has historically been challenging due to their propensity for reduction under ambient conditions. This work explores the preparation of a tripotassium silver bisperiodate complex as a tetrahydrate via chemical oxidation of the central silver atom and orthoperiodate chelation. The isolation of the chelate complex in high yield and purity was achieved via acidimetric titration. The comprehensive physiochemical characterization of the tribasic silver bisperiodate included single crystal X-ray diffraction, thermogravimetric and differential scanning calorimetry, and infrared and ultraviolet-visible spectroscopy. Infrared and UV-visible absorption spectra (λ_max 255 and 365 nm) were in good agreement with historically prepared pentabasic diperiodatoargentate chelate complexes. The C2/c monoclinic distorted square planar structure of the bis-chelate complex affords a mutually supportive framework to both Ag(III) and I(VII), conferring stability under both thermal and long-term ambient conditions. Thermal analysis of the tribasic silver bisperiodate complex identified an endothermic mass loss, ΔH = +278.35 kJ/mol, observed at 139.0 °C corresponding to a solid-state reduction of silver from Ag(III) to Ag(I). Under ambient conditions, no significant degradation was observed over a 12 month period (P = 0.30) for the silver bisperiodate complex in a solid state, with an observed half-life of τ_1/2 = 147 days in a pH-neutral aqueous solution.

Self-assembly of an anion receptor with metal-dependent kinase inhibition and potent in vitro anti-cancer properties

One topical area of supramolecular chemistry is the binding of anionic species but despite the importance of anions in diverse cellular processes and for cancer development, anion receptors or 'binders' have received little attention as potential anti-cancer therapeutics. Here we report self-assembling trimetallic cryptands (e.g. [L₂(Metal)₃]⁶⁺ where Metal = Cu²⁺, Zn²⁺ or Mn²⁺) which can encapsulate a range of anions and which show metal-dependent differences in chemical and biological reactivities. In cell studies, both [L₂Cu₃]⁶⁺ and [L₂Zn₃]⁶⁺ complexes are highly toxic to a range of human cancer cell lines and they show significant metal-dependent selective activity towards cancer cells compared to healthy, non-cancerous cells (by up to 2000-fold). The addition of different anions to the complexes (e.g. PO₄³-, SO₄²- or PhOPO₃²-) further alters activity and selectivity allowing the activity to be modulated via a self-assembly process. The activity is attributed to the ability to either bind or hydrolyse phosphate esters and mechanistic studies show differential and selective inhibition of multiple kinases by both [L₂Cu₃]⁶⁺ and [L₂Zn₃]⁶⁺ complexes but via different mechanisms.

Self-Assembled Anion-Binding Cryptand for the Selective Liquid-Liquid Extraction of Phosphate Anions

The ligands L1 and L2 form trinuclear self-assembled complexes with Cu2+ (i.e. [(L1 )2 Cu3 ]6+ or [(L2 )2 Cu3 ]6+ ) both of which act as a host to a variety of anions. Inclusion of long aliphatic chains on these ligands allows the assemblies to extract anions from aqueous media into organic solvents. Phosphate can be removed from water efficiently and highly selectively, even in the presence of other anions.