Mechanically Induced Gelation of a Kinetically Trapped Supramolecular Polymer

Abstract

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.

Finely Controlled Circularly Polarized Luminescence of a Mechano‐Responsive Supramolecular Polymer

“…[14,15] Mechano-responsive materials also usually exhibit emission properties under mechanical stress. [16][17][18] In most cases, this effect results from the formation of supramolecular nanostructures;m echanical stimulus triggers transitions between several crystalline and amorphous phases or between an aggregated and am onomeric state,w hich are responsible for changes in the luminescence emission. [19][20][21][22][23][24][25] Although mechano-responsive materials have been developed for mechanical stress sensing [20] and security tag applications, [21] owing to the limit of expression of both chirality and luminescence properties,m echano-responsive materials that enable control of CPL characteristics have been only two studies reported by Kawai [24] and Yamashita [25] groups.Inprevious studies,the researchers have reported the control of chirality in hydrogels composed of two components and al uminescence dissymmetry factor of two difluoroboron-b-diketonate complexes.I nc ontrast, the kinetically controlled mechano-responsive chiral supramolecular polymerization through the control of CPL property has not been reported, despite their benefits as the seed and building block in living supramolecular co-polymerizations.T herefore,t he investigation of CPL supramolecular polymerization generated by af inely tuned external stimulus (for example, rotation, pressure,a nd light) still remains as ignificant challenge.H erein, we report kinetic controlled CPL supramolecular polymerization with four l-o rd-a lanine branch side chains formed by the fine-tuning of am echanical stimulus.I nterestingly,C Da nd CPL signals were able to be finely tuned by controlling rotational speed;i ncreasing the rotational speed led to the acceleration of al arge enhancement of CD and CPL signals.…”

Gels with sense: supramolecular materials that respond to heat, light and sound

“…379 Infrared and NOESY NMR experiments suggest that lateral stacking of the initial linear assemblies is obstructed by urethane-ureidopyrimidinone interactions, but prolonged agitation causes these kinetically trapped structures to dissociate, allowing for the formation of larger aggregates linked by a continuous network of urethane- urethane motifs.…”

Supramolecular Buffering by Ring–Chain Competition

“…To this end, we probed the 1 H-NMR signal of the urethane proton resulting in a concentration-dependent splitting that is assigned to either monomeric cycles, oligomeric cycles or linear chains ( Figure 2; for assignment details see ESI). 22 With the aggregation states assigned, the concentration-dependent fractions are analyzed using the ring-chain theory employing the reported value of K UPy-UPy in CHCl 3 (K UPy-UPy = 6 . 10 7 M -1 ) as a fixed constant.…”

“…Indeed, this increase in stability is in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 line with a measured intramolecular hydrogen bond between the urethane proton and the carbonyl of the pyrimidinone in monomeric rings formed by 1b. 22,24 Although the model employing two EM values gives a slightly better description of the ringchain competition of ditopic UPy's 1b and 1c, the generality of supramolecular ring-chain buffering, which is based on the use of a single EM value, is not affected. Upon addition of NaPy, oligomeric rings are formed in very low amounts, which reduces the sensitivity of the buffering towards changes in EM 2 (for details, see ESI).…”