Mechanochemical versus sol-gel silica loading of phenolate- and acetate-bridged dizinc complexes: toward instant and inexpensive hybrids for controlled binding and release of Zn~(2+) in pure water

摘要

Herein, we have explored expeditious and lowered expense SiO2-loading in the context of fluorescent "off-on" and "on-off" Zn~(2+) ion detection/controlled release. A simple racemic ligand (H2rlys) (1) prepared in situ can be mechanically SiO2-loaded so as to induce surface sites that allow for "off-on" aqueous fluorescence (λ_(em,max) = ～450 nm) detection of Zn~(2+); with Cu~(2+) as a competing input, "inhibit" logic gate behaviour is present. Oppositely, dimeric, chiral fluorescent zinc complexes (Φ _F = ～0.20) prepared in a "one pot" method, and bearing different Zn···Zn internuclear spacings, can be incorporated into silica by two methods. Specifically, the chiral Zn2(slysH)2Cl2 (2) and racemic Zn2(rslysH)2(μ-OAc)2 species (3) [slys or rslys = 6-amino-2-{(2-hydroxybenzylidene)amino}hexanoate] were mechanochemically loaded. An adsorption constant was 1.99 x 10~(-4) (molecules of 2/units SiO2)(min)~(-1) for times of 5-20 min, as determined by extensive SEM-EDS data. These confirmed the highly selective "on-off" rapid aqueous fluorescent Cu~(2+) detection (versus, Li~+, Na~+, Cs~+, Mg~(2+), Ca~(2+), Mn~(2+), Fe~(2+), Co~(2+), Ni~(2+), Ag~+, Cd~(2+), Hg~(2+), Pb~(2+)) through direct Zn~(2+) displacement under bulk neat water flow (pH = 7.4) as verified by an authentic sample of [Cu2(slysH)2(N03)2]-silica (4-silica). With the use of 2SiO2, Na4EDTA and Cu~(2+) "inhibit" logic gate behaviour was also found. Sol-gel techniques allowed for loadings of 2 (20-890 mg) up to 1 : 1 (by wt). The preparation of these inorganic hybrids are extremely inexpensive and rapid to prepare from commercial starting materials and can be extended to variegated forms of SiO2; alumina gel was also functionalized with 2. Cu~(2+) and Zn~(2+) are metals pertinent to human neurological health promotion and in neurodegenerative diseases.