Buffering Heavy Metal Ions with Photoactive CrownCast Cages

Abstract

Historically, caged compounds have been used to interrogate the biological activity of organic molecules by using light; however, R. Tsien and others have developed methodologies over the last three decades for using nitrobenzyl-derived caged complexes to study the signaling behavior of Ca 2+. A series of cation-selective N-phenyl-azamacrocyclic receptors integrated with a 4,5-dimethoxy-2-nitrobenzyl (DMNB) photoactive group act as cages for divalent metal ions. The uncaging mechanism of these complexes involves a photoreaction that converts the nitrobenzhydrol, which is para to the aniline nitrogen atom, into the corresponding nitrosobenzophenone. Resonance delocalization of the aniline into the distal carbonyl group of the photoproduct attenuates the ability of the nitrogen atom to interact with the guest. CrownCast-1 (3) utilizes a 13-phenyl-1,4,7,10-tetraoxa-13-azacyclopentadecane (A15C5, 2) receptor. Binding studies with CrownCast-1 revealed a modest selectivity for Ca 2+ ; however, differences in the measured binding affinity upon photolysis suggest that CrownCast-1 is better suited to cage

Understanding the Relationship Between Photolysis Efficiency and Metal Binding Using ArgenCast Photocages

“…As demonstrated previously, the ca 350 nm absorption feature of the uncaged ligand is a well‐behaved benzophenone charge‐transfer band. The absorption band at ca 270 nm of the unphotolyzed photocage appears to be a complicated combination of transitions that do not change linearly with metal ion binding (7). The Δ K d < 1 measured for ArgenCast instead suggests that there is only a minimal change in binding affinity when uncaged, similar to CrownCast‐3.…”

“…ArgenCast‐3 ( 5 ) was prepared with the TMSOTf promoted reaction between 1 and 3‐nitro‐2‐naphthaldehyde (13), which was prepared as previously described. ArgenCast‐4 ( 7 ) was synthesized in an analogous manner using 1‐nitro‐2‐naphthaldehyde. The yield of ArgenCast‐2 was 58% and ArgenCast‐3 was prepared in 72% yield (Scheme 2).…”

“…In addition to the various photocaged complexes that have elucidated the roles of Ca 2+ in neurotransmission, we have developed several tools for controlling the release of Mg 2+ (4), Fe 3+ (5,6), Hg 2+ (7) and Zn 2+ (8) that utilize analogous uncaging strategies. We have dubbed the class of photocaged complexes based on the nitrobenzhydrol to benzophenone conversion Cast complexes, because the metal ion is cast off after photolysis.…”

Mix‐&‐Read Determination of Mercury(II) at Trace Levels with Hybrid Mesoporous Silica Materials Incorporating Fluorescent Probes by a Simple Mix‐&‐Load Technique

“…meso ‐Receptor‐substituted BODIPY dyes are principally very potent probes, because they allow for strong switching of the fluorescence upon analyte binding . The complexation behavior of I was thus investigated in more detail in the presence of the thiophilic metal ions Hg II and Ag I and their closest paramagnetic competitors, Cu II and Ni II .…”

Synthesis and spectroscopic–electrochemical properties of novel ratiometric Hg (II) chemosensor containing Bodipy and the N-phenylaza-15-crown-5 moiety

“…Due to their intense fluorescence, Bodipy’s have been found useful in the synthesis of novel fluorescent sensor for Hg 2+ cation and the energy transfer from Bodipy-terminal to metal ion detected. Binding of the analyte to Bodipy as fluorescent sensor can be caused in either enhancement or quenching of the emission [21, 22]. The Bodipy-terminal behaves as an antenna complex capable of light harvesting and other units serve as fluorophore (by the binding of analyte) [23, 24].…”