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

Abstract

Herein, we have explored expeditious and lowered expense SiO2-loading in the context of fluorescent "off-on" and "on-off" Zn2+ ion detection/controlled release. A simple racemic ligand (H(2)rlys) (1) prepared in situ can be mechanically SiO2-loaded so as to induce surface sites that allow for "off-on" aqueous fluorescence (lambda(em,max) = similar to 450 nm) detection of Zn2+; with Cu2+ as a competing input, "inhibit'' logic gate behaviour is present. Oppositely, dimeric, chiral fluorescent zinc complexes (Phi(F) = similar to 0.20) prepared in a "one pot'' method, and bearing different Zn center dot center dot center dot Zn internuclear spacings, can be incorporated into silica by two methods. Specifically, the chiral Zn-2(slysH)(2)Cl-2 (2) and racemic Zn-2(rslysH)(2)(mu-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 Cu2+ detection (versus, Li+, Na+, Cs+, Mg2+, Ca2+, Mn2+, Fe2+, Co2+, Ni2+, Ag+, Cd2+, Hg2+, Pb2+) through direct Zn2+ displacement under bulk neat water flow (pH = 7.4) as verified by an authentic sample of [Cu-2(slysH)(2)(NO3)(2)]-silica (4-silica). With the use of 2 center dot SiO2, Na(4)EDTA and Cu2+ "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. Cu2+ and Zn2+ are metals pertinent to human neurological health promotion and in neurodegenerative diseases.