23 research outputs found
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Selective and highly efficient dye scavenging by a pH-responsive molecular hydrogelator
A structurally simple low molecular weight hydrogelator derived from isophthalic acid forms robust pH-responsive hydrogels capable of highly efficient and selective dye adsorption
HRMAS 1H NMR as a tool for the study of supramolecular gels
HRMAS 1H NMR is reported for the first time as a useful technique to gain insight into the dynamic properties of aggregates present in supramolecular gels. The study of several low molecular weight gelators with this technique in toluene and acetonitrile is described
Supramolecular Autoregulation
Enzyme activity in biological systems is often governed by control mechanisms in which the catalytic properties are made sensitive or insensitive to differences in enzyme or substrate concentration. Here, we report the first supramolecular system where the catalytic activity is made concentration independent through the use of newly designed inhibitor molecules. The precise concentration dependence of coupled supramolecular equilibriums between free catalyst, inhibited catalyst, active inhibitor, and inactive inhibitor allows to keep the concentration of free catalyst at 1 mM in a broad concentration range, yielding an autoregulated catalytic system
Mechanically induced gelation of a kinetically trapped supramolecular polymer
The stimuli-induced gelation of a urethane-functionalized ditopic ureidopyrimidinone (UPy) compound is presented, and the mechanism by which the gelation proceeds is proposed. In a 40–120 mM solution in chloroform, the compound can exist in two different aggregated states, namely a low viscous mixture of (cyclic) oligomers or a fibrous gel. As evidenced by IR, NMR, and WAXS, the liquid state is stabilized by hydrogen bonds between the UPy and the back-folded chain, while the fibrous gel is stabilized by lateral hydrogen bonds within stacked UPy dimers. Controlled preparation techniques allow for pathway selection to arrive at one of both states. The remarkable long-term stability of the low viscous state (over 2 months for a 80 mM solution) is in contrast to the fast transformation into a gel by stirring in a few hours. Other mechanical stimuli like shaking, sonicating, and stirring for a shorter period, as well as freezing and thawing the solution, yield weaker gels than those obtained by long stirring. Heating the gels and slow cooling reversibly yield the nonviscous solution. This shows that the formation of UPy–urethane hydrogen bonds kinetically traps the UPy polymers, thereby preventing their lateral aggregation. The application of mechanical stress or freezing disrupts this interaction, allowing for the formation of a stacked nucleus on which further material can grow, eventually leading to gelation of the solution
Microfluidic assisted self-assembly of pH-sensitive low-molecular weight hydrogelators close to the minimum gelation concentration
\u3cp\u3eThe fibrillation and subsequent gelation of low molecular hydrogelators is usually triggered by external stimuli. Generally, strong acids are employed to trigger the self-assembly mechanism in pH-responsive supramolecular systems. However, the generation and design of novel stable gels with performing mechanical properties is a challenging task as a result of the uneven self-assembled networks formed. Here, we report the study of the self-assembly process of a low molecular weight hydrogelator (LMWG) in the proximity of its minimum gelation concentration (MGC = 0.3 mg/ml). At such high dilution, the generation of homogeneous gels with good mechanical properties by turning pH by strong acids is a demanding task as a result of the lack of monodisperse 1D self-assembled rod-like aggregates. A microfluidic device is employed here to gradually and homogeneously change the pH. We show that self-assembly of LMWG in well-defined structures can be enhanced by using the diffusive mixing occurring in the microfluidic reactor channel. For very short mixing times, aggregates with 2 nm cross-section are found in the region adjacent to the focused LMWG solution in contact with the low pH buffer solution streams, where the pH reaches values below the pKa of the LMWG and triggers the supramolecular self-assembly. For longer mixing times, aggregates grow in size and occupy homogeneously the micro channel. The results presented here show that better controlled self-assembly can be achieved using microfluidic mixing devices and early stages of self-assembly can be efficiently studied by coupling synchrotron SAXS with microfluidics.\u3c/p\u3
Mechanically induced gelation of a kinetically trapped supramolecular polymer
The stimuli-induced gelation of a urethane-functionalized ditopic ureidopyrimidinone (UPy) compound is presented, and the mechanism by which the gelation proceeds is proposed. In a 40–120 mM solution in chloroform, the compound can exist in two different aggregated states, namely a low viscous mixture of (cyclic) oligomers or a fibrous gel. As evidenced by IR, NMR, and WAXS, the liquid state is stabilized by hydrogen bonds between the UPy and the back-folded chain, while the fibrous gel is stabilized by lateral hydrogen bonds within stacked UPy dimers. Controlled preparation techniques allow for pathway selection to arrive at one of both states. The remarkable long-term stability of the low viscous state (over 2 months for a 80 mM solution) is in contrast to the fast transformation into a gel by stirring in a few hours. Other mechanical stimuli like shaking, sonicating, and stirring for a shorter period, as well as freezing and thawing the solution, yield weaker gels than those obtained by long stirring. Heating the gels and slow cooling reversibly yield the nonviscous solution. This shows that the formation of UPy–urethane hydrogen bonds kinetically traps the UPy polymers, thereby preventing their lateral aggregation. The application of mechanical stress or freezing disrupts this interaction, allowing for the formation of a stacked nucleus on which further material can grow, eventually leading to gelation of the solution
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Self-assembly studies of a chiral bisurea-based superhydrogelator
A chiral bisurea-based superhydrogelator
that is capable of forming
supramolecular hydrogels at concentrations
as low as 0.2 mm is reported. This
soft material has been characterized by
thermal studies, rheology, X-ray diffraction
analysis, transmission electron
microscopy (TEM), and by various
spectroscopic techniques (electronic
and vibrational circular dichroism and
by FTIR and Raman spectroscopy).
The expression of chirality on the molecular
and supramolecular levels has
been studied and a clear amplification
of its chirality into the achiral analogue
has been observed. Furthermore, thermal
analysis showed that the hydroACHTUNGTRENUNGgel-
ACHTUNGTRENUNGation of compound 1 has a high response
to temperature, which corresponds
to an enthalpy-driven self-assembly
process. These particular thermal
characteristics make these
materials easy to handle for soft-application
technologie