The development of gate-like
system
s able to perform certain programmed function
s i
s anintere
sting wa
y of taking chemi
str
y to the frontier
s of nano
science. In relation to thi
s field, we report acomplete
stud
y of the behavior of a pH-driven and anion-controlled nano-
supramolecular gate-like en
sembleobtained b
y anchoring
suitable pol
yamine
s on the pore outlet
s of me
soporou
s material
s of the t
ype MCM-41 (
solid
N3-S). The relea
se of an entrapped d
ye (Ru(bip
y)
32+) from the pore void
s into the bulk
solutionallow
s u
s to
stud
y the gating effect. A pH-driven open/clo
se mechani
sm wa
s ob
served that ari
se
s from theh
ydrogen-bonding interaction between amine
s at neutral pH (open gate) and Coulombic repul
sion
s at acidicpH between clo
sel
y located pol
yammonium
s at the pore opening
s (clo
sed gate). Molecular d
ynamic
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">-cr
ystoballite
structure on which large hexagonal nanopore
s and anchored pol
yamine
s were included.From the
se calculation
s, it wa
s ob
served how completel
y unprotonated amine
s di
spla
y poor coverage ofthe pore (full
y open gate), wherea
s completel
y 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 stud
y wa
s carried out b
y monitoring the d
ye 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
sicall
y 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 pol
yamine
s. The
se experimental
studie
s are al
so in agreement with computational
simulation
s with fluoride, chloride, iodide, and dih
ydrogen pho
sphate anion
s. In the model, larger anion
spu
sh the tethered pol
yamine
s toward the pore opening
s more efficientl
y, and therefore the pore aperturedecrea
se
s. The
studie
s al
so
show that, for anion
s showing a
strong tendenc
y to form h
ydrogen-bondingnetwork
s (e.g., pho
sphate), complete pore blockage wa
s ob
served at acidic pH. Finall
y,
selectivit
y pattern
shave been di
scu
ssed in term
s of kinetic rate
s of the liberation of the Ru(bip
y)
32+ d
ye from the amine-functionalized d
ye-containing material
N3-S.