Detailed Approach to Investigate Thermodynamically Controlled Supramolecular Copolymerizations

Abstract

Elucidating the microstructure of supramolecular copolymers remains challenging, despite the progress in the field of supramolecular polymers. In this work, we present a detailed approach to investigate supramolecular copolymerizations under thermodynamic control. Our approach provides insight into the interactions of different types of monomers and hereby allows elucidating the microstructure of copolymers. We select two monomers that undergo cooperative supramolecular polymerization by way of threefold intermolecular hydrogen bonding in a helical manner, namely, benzene-1,3,5-tricarboxamide (BTA) and benzene-1,3,5-tris(carbothioamide) (thioBTA). Two enantiomeric forms and an achiral analogue of BTA and thioBTA are synthesized and their homo- and copolymerizations are studied using light scattering techniques, infrared, ultraviolet, and circular dichroism spectroscopy. After quantifying the thermodynamic parameters describing the homopolymerizations, we outline a method to follow the self-assembly of thioBTA derivatives in the copolymerization with BTA, which involves monitoring a characteristic spectroscopic signature as a function of temperature and relative concentration. Using modified types of sergeants-and-soldiers and majority-rules experiments, we obtain insights into the degree of aggregation and the net helicity. In addition, we apply a theoretical model of supramolecular copolymerization to substantiate the experimental results. We find that the model describes the two-component system well and allows deriving the hetero-interaction energies. The interactions between the same kinds of monomers (BTA–BTA and thioBTA–thioBTA) are slightly more favorable than those between different monomers (BTA–thioBTA), corresponding to a nearly random copolymerization. Finally, to study the interactions of the monomers at the molecular level, we perform density functional theory-based computations. The results corroborate that the two-component system exhibits a random distribution of the two monomer units along the copolymer chain.

Selenoamides modulate dipole–dipole interactions in hydrogen bonded supramolecular polymers of 1,3,5-substituted benzenes

“…By fitting the experimental data to a nucleationelongation model, 35 we determined enthalpy (DH e ) and entropy (DS e ) of elongation equal to À75 kJ mole À1 and À97 J mole À1 K À1 , respectively, and a nucleation penalty of 21 kJ mole À1 . The latter corresponds to a cooperativity factor, s, of 2 Â 10 À4 at 293 K. Compared to the supramolecular polymers of c-SBTA (DH e = À65.7 kJ mole À1 ), 30,36 the enthalpic contribution in the supramolecular polymerization of c-SeBTA was slightly more favorable, suggesting stronger intermolecular interactions in the case of the selenoamides. The entropic penalty of the supramolecular polymerization of c-SeBTA (DS e = À97 J mole À1 K À1 ) was comparable to that of c-SBTA 30,36 (DS e = À102.6 J mole À1 K À1 ), instead, and we speculate similar ordering between the homopolymers of c-SeBTA and c-SBTA.…”

“…The latter corresponds to a cooperativity factor, s, of 2 Â 10 À4 at 293 K. Compared to the supramolecular polymers of c-SBTA (DH e = À65.7 kJ mole À1 ), 30,36 the enthalpic contribution in the supramolecular polymerization of c-SeBTA was slightly more favorable, suggesting stronger intermolecular interactions in the case of the selenoamides. The entropic penalty of the supramolecular polymerization of c-SeBTA (DS e = À97 J mole À1 K À1 ) was comparable to that of c-SBTA 30,36 (DS e = À102.6 J mole À1 K À1 ), instead, and we speculate similar ordering between the homopolymers of c-SeBTA and c-SBTA. We rationalize these thermodynamic parameters with an increased dipole-dipole and charge transfer character of the diffuse Se-NH hydrogen bond, 21,37 which ultimately affords the increased thermal stability of the supramolecular polymers of c-SeBTA (more favorable DH e and very similar DS e compared to c-SBTA).…”

“…In the past we have extensively investigated the self-assembly of C 3 -symmetrical N,N 0 ,N 0 0 0 -trialkylbenzene-1,3,5-tricarboxamides (OBTAs) in apolar alkane solvents (achiral OBTA and chiral c-OBTA, Scheme 1) and more recently also of N,N 0 ,N 0 0 0trialkylbenzene-1,3,5-trithioamides (S-BTAs) (achiral SBTA and c-SBTA, Scheme 1). 29,30 Stimulated by the increased dipolar character of the interactions between thioamides as compared to normal amides, [31][32][33] we hypothesized that moving one row further down the periodic table to selenoamides would affect the stability of the formed cooperative supramolecular polymers. In addition, we anticipated that in copolymerizations the microstructure of the copolymers could be modulated.…”

“…This is in strong contrast to the lower cooperativity of c-SBTA compared to c-OBTA (s o 10 À6 ). 30,36 Next to VT-CD spectroscopy, the supramolecular polymerization of c-SeBTA was also investigated by changing the solvent quality in a denaturation experiment. Analogously to a previous study on c-SBTA 38 discrete aliquots of CHCl 3 (good solvent) were added to 20 mM solutions of c-SeBTA in MCH and the intensity of the CD signal was monitored ( Fig.…”

“…We applied the model developed by Markvoort and ten Eikelder 10,39 to quantify the heterointeraction of c-SeBTA with OBTA and SBTA in the sergeants and soldiers experiment. These heterointeractions are dependent on the two homopolymerizations through an a-parameter (eqn (1)), 30 DG hetero ¼ 1 2 Á a Á DG e;SeBTA þ DG e;XBTA À Á…”