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

Enantioselective component selection in multicomponent supramolecular gels

We investigate a two-component acid-amine gelation system in which chirality plays a vital role. A carboxylic acid based on a second generation l-lysine dendron interacts with chiral amines and subsequently assembles into supramolecular gel fibers. The chirality of the amine controls the assembly of the resulting diastereomeric complexes, even if this chirality is relatively "poor quality". Importantly, the selective incorporation of one enantiomer of an amine over the other into the gel network has been demonstrated, with the R amine that forms complexes which assemble into the most stable gel being primarily selected for incorporation. Thermodynamic control has been proven by forming a gel exclusively with an S amine, allowing the R enantiomer to diffuse through the gel network, and displacing it from the "solidlike" fibers, demonstrating that these gels adapt and evolve in response to chemical stimuli to which they are exposed. Excess amine, which remains unincorporated within the solidlike gel fiber network, can diffuse out and be reacted with an isocyanate, allowing us to quantify the enantioselectivity of component selection but also demonstrating how gels can act as selective reservoirs of potential reagents, releasing them on demand to undergo further reactions; hence, component-selective gel assembly can be coupled with controlled reactivity

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

The 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

Structural and morphological studies of the dipeptide based L-Pro-L-Val organocatalytic gels and their rheological behaviour

Organocatalytic gels based on the dipeptide sequence L-Pro-L-Val have been studied by two different FTIR techniques. This suggests a different arrangement of the gelator molecules in the self-assembled fibers depending on the organic solvent employed. In acetonitrile and nitromethane the structure of the supramolecular aggregates is similar and provides similar catalytic properties (supramolecularenhancement of basicity). In contrast, the self-assembled fibers obtained in toluene clearly presented a different molecular arrangement consistent with its different catalytic behaviour (enamine-based catalysis). In addition these gels have been studied by microscopy and rheology

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