Synthesis and metal complexation properties of bisbenzospiropyran chelators in water

Abstract

As a step towards developing a light-controlled reversible binding switch based on photochromic bisbenzospiropyran for investigating intracellular calcium signaling, substituted bisbenzospiropyran and phenolic chelators were synthesized and examined for metal binding strength. The complexation of these compounds with alkaline earth and zinc ions in methanol and buffer was characterized using NMR and luminescence spectroscopy. An increased length of convergent ligands on the rigid scaffold maintained binding affinity for Ca 2+ but decreased selectivity for Ca 2+ over Mg 2+ . Results indicate that at least three carboxylate ligands are required for significant binding, and increased length of the ligands will result in a fully water-soluble photoswitch that exhibits two states with approximately 300-fold difference in binding affinity for Ca 2+ .

Isomerization between 2-(2,4-Dihydroxystyryl)-1-benzopyrylium and 7-Hydroxy-2-(4-hydroxystyryl)-1-benzopyrylium

“…One possible explanation is the formation of a bis(benzospiropyran) intermediate (SP), as recently reported in the literature (Scheme 4). 30,31 Formation of the SP intermediate is compatible with the observed decrease in absorbance in the visible, as well as with the increase of the rate and amplitude of the faster process with increasing pH. Any other isomer or rotamer from the 2-(2,4dihydroxystyryl)-1-benzopyrylium would absorb in the visible and would not explain the behavior of Figure 6A.…”

“…The nature of the intermediate is a matter of discussion. One possible explanation is the formation of a bis­(benzospiropyran) intermediate (SP), as recently reported in the literature (Scheme ). , …”

Synthesis and metal binding properties of N-alkylcarboxyspiropyrans

“…Broadly speaking, the effects upon metal binding of incremental increase in alkylcarboxylate chain length were subtle. The general trends were: (i) compounds bearing longer tethers produced higher concentrations of MC–M 2+ complex per unit metal ion (presumably on the basis that carboxylates on longer tethers with greater conformational flexibility are able to interact more effectively with cations, despite their inherent entropic penalty [ 35 ]); (ii) affinity for metals was in the order Zn 2+ > Mg 2+ > Co 2+ > Ni 2+ . Binding to Ni 2+ was considerably less effective than for other divalent metal cations and this was particularly pronounced for non-carboxylate 9 , wherein 9 –Ni 2+ complexation did not exceed background [merocyanine].…”

Photochromic properties of 1′,3′,3′‐trimethyl‐6‐nitrospiro[2H‐1‐benzopyran‐2,2′‐indoline] doped in PMMA and epoxy resin thin films

“…SPs, one of the promising families of organic photochromic compounds, have found various applications in ophthalmic lenses, display and communication systems, and optoelectronic devices, such as memories and switches (Raschella et al , 2006; Katsonis et al , 2007), and nonlinear optics (Berkovic et al , 2000). SPs have been recently used as nucleic acid hybridisation probes (Guo et al , 2005), as photoswitching of protein activity (Tomizaki et al , 2005), and as optical control of ion penetration through biological membranes (Kumar et al , 2008). The recent interest in the photochromism of SPs is due to their fast colouration rate under UV irradiation, fast thermal fading and excellent fatigue resistance which are crucial for their use.…”