The development of gate-like
sy
stem
s able to perform certain programmed function
s i
s anintere
sting way of taking chemi
stry to the frontier
s of nano
science. In relation to thi
s field, we report acomplete
study of the behavior of a pH-driven and anion-controlled nano-
supramolecular gate-like en
sembleobtained by anchoring
suitable polyamine
s on the pore outlet
s of me
soporou
s material
s of the type MCM-41 (
solid
N3-S). The relea
se of an entrapped dye (Ru(bipy)
32+) from the pore void
s into the bulk
solutionallow
s u
s to
study the gating effect. A pH-driven open/clo
se mechani
sm wa
s ob
served that ari
se
s from thehydrogen-bonding interaction between amine
s at neutral pH (open gate) and Coulombic repul
sion
s at acidicpH between clo
sely located polyammonium
s at the pore opening
s (clo
sed gate). Molecular dynamic
ssimulation
s u
sing force field method
s have been carried out to explain the pH-driven open/clo
se mechani
sm.For thi
s purpo
se, a me
soporou
s silica
structure wa
s con
structed, taking a
s ba
se the (1
![](/image<font color=)
s/entitie
s/onemacr.gif">1) plane of the
![](/image<font color=)
s/gifchar
s/beta2.gif" BORDER=0 ALIGN="middle">-cry
stoballite
structure on which large hexagonal nanopore
s and anchored polyamine
s were included.From the
se calculation
s, it wa
s ob
served how completely unprotonated amine
s di
splay poor coverage ofthe pore (fully open gate), wherea
s completely protonated amine
s (
simulating a pH 2 or lower) re
sult in aclear reduction of the pore aperture, in agreement with the experimental re
sult
s. In additional to the pH-driven protocol, opening/clo
sing of the gate-like en
semble can al
so be modulated via an anion-controlledmechani
sm. Thi
s study wa
s carried out by monitoring the dye relea
sed from the pore void
s of the
N3-Ssolid at a certain pH in the pre
sence of a range of anion
s with different
structural dimen
sion
s and charge
s,including chloride,
sulfate, pho
sphate, and ATP (
Canion = 1 × 10
-2 mol dm
-3). The choice of a certainanionic gue
st re
sult
s in a different gate-like en
semble behavior, ranging from ba
sically no action (chloride)to complete (ATP) or partial pore blockage, depending on the pH (
sulfate and pho
sphate). The remarkableanion-controllable re
spon
se of the gate-like en
semble can be explained in term
s of anion complex formationwith the tethered polyamine
s. The
se experimental
studie
s are al
so in agreement with computational
simulation
s with fluoride, chloride, iodide, and dihydrogen pho
sphate anion
s. In the model, larger anion
spu
sh the tethered polyamine
s toward the pore opening
s more efficiently, and therefore the pore aperturedecrea
se
s. The
studie
s al
so
show that, for anion
s showing a
strong tendency to form hydrogen-bondingnetwork
s (e.g., pho
sphate), complete pore blockage wa
s ob
served at acidic pH. Finally,
selectivity pattern
shave been di
scu
ssed in term
s of kinetic rate
s of the liberation of the Ru(bipy)
32+ dye from the amine-functionalized dye-containing material
N3-S.