Polyaminocyclodextrin nanosponges: synthesis,
characterization and pH-responsive sequestration
abilities
Marco Russo,
a
Maria Luisa Saladino,
ab
Delia Chillura Martino,
ab
Paolo Lo Meo
*
a
and Renato Noto
a
New pH-responsive nanosponges were obtained by reacting four different polyaminocyclodextrins with
heptakis-(6-bromo)-(6-deoxy)-b-cyclodextrin. The materials obtained were characterized by various
techniques (FT-IR, potentiometric titration, differential scanning calorimetry (DSC), porosimetry (BET),
13
C
{
1
H} CP-MAS NMR). Their adsorption abilities at different pH values were verified towards a suitable set of
model guests, and seem mainly controlled by electrostatic interactions, as a function of the protonation/
charge status of the polymer matrix. By contrast, data positively point out a lesser importance assumed
by the induced-fiteffect, important in affecting the formation of host–guest complexes in solution. The
frequency-switched Lee-Goldburg (FSLG) heteronuclear correlation solid-state NMR technique was
exploited in order to assess the possible location of the guests within the polymer matrix.
Introduction
Nanosponges (NSs) are a class of hyper-reticulated polymeric
material,
1
which have attracted increasing interest during the
past years, due to their adsorption or controlled release abilities
towards various organic molecules, such as drugs,
1,2
conserva-
tion agents
3
and pollutants.
4
These materials can be obtained by
polymerizing or co-polymerizing macrocyclic species able to act
as supramolecular hosts. Great attention has been devoted in
particular to cyclodextrin-based NSs, which are usually obtained
by treating native b-cyclodextrin (bCD) with double electro-
philes such as epichlorohydrin,
5
carbonic acid derivatives
6
or
bis-isocyanates.
7
The reaction, of course, exploits the nucleo-
philic reactivity of the hydroxyl groups (both primary and
secondary) on the bCD scaffold, whereas the electrophile resi-
dues function as linkers between the bCD subunits. Very
recently, we have succeeded in exploiting a different approach,
8
i.e. a CuAAC reaction
9
between heptakis-(6-azido)-(6-deoxy)-bCD
and a tetrakis-propargyloxy-calix[4]arene derivative. This
procedure affords mixed co-polymers, having different average
compositions depending on the combination ratio of the reac-
tants. The potential use of these materials takes advantage of
the somehow complementary binding abilities possessed by the
two diverse macrocyclic hosts, and we veried that their
adsorption abilities largely vary as a function of their actual
composition.
An interesting aspect related to the latter issue is the
potential tunability of the co-polymers obtained, which can be
hardly achieved for NSs based on bCD only. Sensitivity to
external stimuli is an appealing goal in materials science.
10
In
particular, systems able to change their properties in response
to pH variations constitute an expanding area of research.
11
Just
to cite a few examples, pH-tunable nanochannels for selective
transmembrane ion transport have been built by means of
polyelectrolyte brushes
12
or functionalized carbon nanotubes.
13
Molecular shuttles triggered by pH variations can mimic
“molecular muscles”.
14
Reversible pH-dependent emulsifying
action has been reported for chitosan.
15
Mesoporous silica
containers equipped with supramolecular nanovalves have
been used for drug delivery into acid generating cells.
16
In this
context, the synthesis of pH-responsive NSs may constitute
a very interesting task, in particular for the construction of drug
carrier/delivery systems or pollutant removal devices.
In the present work we report on the preparation, charac-
terization, and sequestering abilities of a new class of NS
materials, namely aminocyclodextrin nanosponges (ACN),
Fig. 1 Structures of polyamines A1–A4.
a
Universit` a degli Studi di Palermo-Dipartimento di Scienze e Tecnologie Biologiche,
Chimiche e Farmaceutiche, V.le delle Scienze, Parco d’Orleans, pad. 17, 90128
Palermo, Italy. E-mail: paolo.lomeo@unipa.it
b
CGA-ATeN Center – Universit` a di Palermo, Via F. Marini, 14, 90128 Palermo, Italy
Cite this: RSC Adv. , 2016, 6, 49941
Received 10th March 2016
Accepted 15th May 2016
DOI: 10.1039/c6ra06417e
www.rsc.org/advances
This journal is © The Royal Society of Chemistry 2016 RSC Adv. , 2016, 6, 49941–49953 | 49941
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