Supramolecular polymers in action

Abstract onl

Supramolecular polymers from linear telechelic siloxanes with quadruple- hydrogen- bonded units

Telechelic oligo- and poly(dimethylsiloxanes) with two ureidopyrimidone (UPy) functional groups and 2 (I) and 100 (II) dimethylsiloxy repeating units, were prepd. via hydrosilylation reaction of poly(dimethylsiloxane). The compds. were characterized in soln. by 1H NMR and viscometry and in the solid state by 1H NMR and 13C NMR, FTIR, and rheol. measurements. The measurements show that the UPy groups of the polymers are assocd. via quadruple hydrogen bonds in a donor-donor-acceptor-acceptor (DDAA) array. In many aspects, the materials behave like entangled, high mol. wt. polymers. Compd. II has a Tg of -119 Deg and shows melting of microcryst. domains of assocd. UPy units at -25 Deg. Compd. I has a cryst. form (Tm = 112 Deg) and an amorphous modification with a Tg of 25 Deg. Solid-state NMR was used to study the mobility of these phases; wide-line sepn. [WISE] spectra show a higher mobility of the UPy groups in the amorphous phase than in the crystals of I. Amorphous I and II behave like entangled polymers. The mech. behavior is characterized by a rubbery plateau and a relatively high activation enthalpy for stress relaxation (DH = 127 kJ/mol for I; DH = 54 kJ/mol for II), which was derived from the temp. dependence of the zero-shear viscosity. Ests. for the d.p. of I and II, based on the mech. properties, give DP > 100 for I and approx. 20 for I. Like in condensation polymn., the DP of reversible supramol. polymers is presumably limited by the presence of small amts. of monofunctional impuritie

Resolutely pure helices

Helical coordination compounds that show promising antibiotic activity in aqueous media have been assembled directly in their optically pure form, without the need for a resolution step

Potential enthalpic energy of water in oils exploited to control supramolecular structure

Water directs the self-assembly of both natural 1,2 and synthetic 3-9 molecules to form precise yet dynamic structures. Nevertheless, our molecular understanding of the role of water in such systems is incomplete, which represents a fundamental constraint in the development of supramolecular materials for use in biomaterials, nanoelectronics and catalysis 10 . In particular, despite the widespread use of alkanes as solvents in supramolecular chemistry 11,12, the role of water in the formation of aggregates in oils is not clear, probably because water is only sparingly miscible in these solvents - typical alkanes contain less than 0.01 per cent water by weight at room temperature 13 . A notable and unused feature of this water is that it is essentially monomeric 14 . It has been determined previously 15 that the free energy cost of forming a cavity in alkanes that is large enough for a water molecule is only just compensated by its interaction with the interior of the cavity; this cost is therefore too high to accommodate clusters of water. As such, water molecules in alkanes possess potential enthalpic energy in the form of unrealized hydrogen bonds. Here we report that this energy is a thermodynamic driving force for water molecules to interact with co-dissolved hydrogen-bond-based aggregates in oils. By using a combination of spectroscopic, calorimetric, light-scattering and theoretical techniques, we demonstrate that this interaction can be exploited to modulate the structure of one-dimensional supramolecular polymers