la6b01549_si_001.pdf (1.12 MB)
Structural Implications on the Properties of Self-Assembling Supramolecular Hosts for Fluorescent Guests
journal contribution
posted on 2016-08-04, 00:00 authored by Sicheng Tang, Bryan Donaphon, Marcia Levitus, Françisco
M. RaymoNine
amphiphilic macromolecules with decyl and oligo(ethylene glycol)
side chains, randomly distributed along a common poly(methacrylate)
backbone, were synthesized from the radical copolymerization of appropriate
methacrylate monomers. The resulting amphiphilic constructs differ
in (1) the ratio between their hydrophobic and hydrophilic components,
(2) the length of their oligo(ethylene glycol) chains, and/or (3)
the molecular weight. When the ratio between hydrophobic and hydrophilic
segments is comprised between 6:1 and 1:2, the macromolecules assemble
spontaneously into particles with nanoscaled dimensions in neutral
buffer and capture hydrophobic borondipyrromethene chromophores in
their interior. However, the critical concentration required for the
assembly of these supramolecular hosts as well as their hydrodynamic
diameter, supramolecular weight, and number of constituent macromolecular
building blocks all vary monotonically with the ratio between hydrophobic
and hydrophilic components. Specifically, the critical concentration
decreases and the other three parameters increase as the relative
hydrophobic content raises. Furthermore, an increase in the relative
hydrophobic content also discourages interchromophoric interactions
between entrapped guests in both ground and excited states as well
as delays access of potential quenchers. In fact, these observations
demonstrate that the hydrophobic components must be in excess over
their hydrophilic counterparts for optimal supramolecular hosts to
assemble. Indeed, a ratio of 6:1 between the numbers of decyl
and oligo(ethylene glycol) side chains appears to be ideal for this
particular structural design. Under these conditions, supramolecular
hosts assemble spontaneously even at relatively low polymer concentrations
and their fluorescent guests do not escape into the bulk aqueous solution,
despite the reversibility of the noncovalent interactions holding
the supramolecular container together. Thus, these systematic investigations
provide invaluable structural guidelines to design self-assembling
supramolecular hosts with optimal composition for the effective encapsulation
of fluorescent guests and can lead to ideal delivery vehicles for
the transport of imaging probes to target locations in biological
samples.