Fluorescence
recognition of d-glucose in water with excellent
sensitivity, selectivity, and chiral selectivity is desired because d-glucose is an essential component in biological and pathological
processes. We report an innovative approach that exploits the 1:2
stoichiometric inclusion complexes of γ-cyclodextrin (γ-CyD)
with two molecules of fluorescent monoboronic acid-based receptors,
which form a pseudo-diboronic acid moiety as the
recognition site for d-glucose in water. Two monoboronic
acids (1F and 2N) were easily synthesized
without heating or column purification. The 1:2 stoichiometric inclusion
complexes (1F/γ-CyD and 2N/γ-CyD) were prepared in a mixture of dimethyl sulfoxide/water (2/98 in
v/v) by mixing γ-CyD and the corresponding monoboronic acids.
Both 1F/γ-CyD and 2N/γ-CyD exhibited
strong turn-on response to d-glucose with excellent selectivity
over nine other saccharides in the water-rich solvent at pH 7.4 owing
to the ditopic recognition of d-glucose by the pseudo-diboronic acid moieties. The limits of detection of 1F/γ-CyD and 2N/γ-CyD for d-glucose were 1.1
and 1.8 μM, respectively, indicating the remarkable sensitivity
for the detection of d-glucose at μM levels. 1F/γ-CyD and 2N/γ-CyD also demonstrated
chiral-selective recognition of d-glucose, which is apparent
from the 2.0- and 6.3-fold enhancement of fluorescence by the addition
of d-glucose relative to l-glucose addition, owing
to the chiral pseudo-diboronic acid moieties produced
by the chiral γ-CyD cavity. To the best of our knowledge, 2N/γ-CyD has the highest d/l selectivity
among hitherto reported fluorescent diboronic acid-based receptors.
The electrodeposition of Zn-Al alloys was investigated using AlCl3-ZnCl2-dimethylsulfone (DMSO2) molten electrolytes at 110°C. The alminum contents of electrodeposites obtained at constant current densities between 30 and 100 mA/cm 2 ranged from 1 to 8 at%. With the decrease in ZnCl2 concentrations of the electrolyte and with the increase in current densities, the intensity of the diffraction peaks of Zn decreased suggesting low crystallinity of zinc. Electrodeposition was carried out at constant potentials from-0.8V to-1.5 V vs Zn in DMSO2 / ZnCl2, on the basis of the cyclic voltammogram, and deposits with Al contents ranging from 1-90 at% were obtained.
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