‘Click’ functionalised polymer resins: a new approach to the synthesis of surface attached bipyridinium and naphthalene diimide [2]rotaxanes

Abstract

Herein we describe the design and synthesis of a series of solid-tethered [2]rotaxanes utilising crown ether-naphthalene diimide or crown ether-bipyridinium host guest interactions. TentaGel polystyrene resins were initially modified in a two-stage procedure to azide functionalised beads before the target supramolecular architectures were attached using a copper catalysed "click" procedure. The final assembly was examined using IR spectroscopy and gel-phase (1)H High Resolution Magic Angle Spinning (HR MAS) NMR spectroscopy. The HR MAS technique enabled a direct comparison between the solid-tethered architectures and the synthesis and characterisation of analogous solution-based [2]rotaxanes to be made.

Dynamic Covalent Synthesis of Donor–Acceptor Interlocked Architectures in Solution and at the Solution:Surface Interface

“…This red coloration is indicative of a charge-transfer phenomenon between the p-rich dialkoxynaphthalene motifs of the macrocycle and the p-deficient naphthalene diimide motif in the thread, and has been seen in related solution and surface-bound rotaxanes. [28,30,31] This qualitatively suggests at least some rotaxane assembly at the beadsolvent interface. 1 H HR-MAS NMR analysis indicated that rotaxane formation had occurred on the surface as evidenced by the diimide peak at 8.03 ppm; however, peaks for the macrocycle napthoquinone protons were obscured under the bead and stopper aromatic protons (see Figure 7).…”

“…The bound diimide proton chemical shift is consistent with that seen in related surface-bound diimide-containing rotaxanes. [30,31] Nevertheless, it is clear that significant amounts of uncomplexed diimide thread remain on the surface, and future work will look at optimizing reaction conditions to favor the formation of interlocked architectures at the solution:surface interface. …”

“…We have previously reported the controlled self-assembly of rotaxane and pseudorotaxane systems on polystyrene TentaGel resins. [30,31] This work highlighted two important issues; firstly, surface functionalization using kinetically controlled bond formation can result in mixtures of the desired interlocked and undesired non-interlocked products on the surface, and secondly, the dynamic behavior of supramolecular architectures deposited on surfaces is not always directly comparable to that observed in solution, highlighting the importance of using characterization tools such as Naphthalene diimide functionalized beads 16 (1 equiv) were added to a solution of 1,5-dialkoxynaphthalene dithiol 2.1 (2 equiv) in CHCl 3 , and disulfide exchange was initiated by the addition of DBU (1 equiv). The reaction was left to stir at ambient conditions for 14 days to ensure that thermodynamic equilibrium was reached.…”

“…[23,24] Likewise, the synthesis of the dinapthocrown 4, diimide stoppered thread 5, and diimide-functionalized TentaGel resins 16 have all been previously reported. [28,31] The synthesis of the thiol building blocks can be found in the Supporting Information.…”

1H HR-MAS NMR spectroscopy as a simple tool to characterize peptide – Functionalized hydrogels as a function of cross linker density

“…It could be shown that HR-MAS can provide significant line narrowing by using a magnetic-susceptibility-matching probe technology [17]. While first HR-MAS examples included the investigation of resins for combinatorial chemistry [18], solvent swollen polystyrene gels [19], and lipid systems [20], more recent examples used this technique for the direct monitoring of hydrolytic degradation of biodegradable cross linked polymer network [21], estimation of cross link density of poly (dimethyl siloxane) (PDMS) networks [22], analysis of the polymer resins functionalization [23], or the study of water/polymer interactions in a poly(amidoamine) hydrogel [24].…”