Communication
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to quantify these interactions within the NP-bound monolayer,
and link molecular-level understanding of the dynamic covalent
process to aggregation mechanism and assembly morphology.
In summary, we have developed a new category of dynamic
covalent NP building block. In situ spectroscopic characterization
has revealed that NP-bound boronate ester exchange on a homo-
geneous monolayer of boronic acids proceeds rapidly and rever-
sibly; high degrees of surface functionalization can be achieved;
and mixed-monolayer compositions are tuneable under thermo-
dynamic control. Dynamic covalent NP-bound monolayers open
up a vast new region of chemical space for engineering respon-
sive nanomaterials, unrestricted by the structural or stability
constraints of biomolecules or noncovalent systems. They raise
the exciting prospect of assembling NPs under error-correcting
conditions, yet exploiting stable, structurally unambiguous
covalent links. Simple bifunctional linkers produce covalently
connected NP assemblies displaying morphologies that are
sensitive to molecular structure. Remarkably, despite being
linked by covalent bonds, these solid-state aggregates can be
disassembled on application of molecular stimuli; the assembly
and disassembly processes are quantitative; and both states are
indefinitely stable. The ability to characterize NP-bound dynamic
covalent processes in situ promises a predictive understanding
of how molecular-level details can be manipulated to control
assembly morphology. We foresee that this will ultimately lead to
a modular and flexible route to responsive NP assemblies where
structure on several size-scales is tuned by molecular-level features,
and can be remotely reconfigured by applying chemical or physical
stimuli.
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This work was supported by the EPSRC (EP/K016342/1 and
EP/J500549/1), the University of St Andrews and by a Royal Society
of Edinburgh/Scottish Government Fellowship (E. R. K.). We thank
Dr Lorna Eades for ICP-OES measurements, and are grateful to
Mr Ross Blackley for assistance with TEM imaging. Mass spectro-
metry was carried out at the EPSRC UK National Mass Spectro-
metry Facility (NMSF) at Swansea University. We thank Professor
Douglas Philp for helpful discussions. The research data supporting
463d9de9-a8c3-44b4-9eb2-bbc63f9364a6.
Notes and references
‡ A high concentration of base (900 mM, 100 equivalents with respect
to 1) was used to ensure quantitative consistency across all NMR
experiments. However, the same behaviour is observed at much lower
base concentrations (see ESI† Section 4).
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17 (a) E. Aznar, M. Dolores Marcos, R. Martınez-Manez, F. Sancenon,
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§ At no stage was a shift in the NP plasmon resonance observed. This is
not unexpected for small NPs (d E 3.4 nm) connected by molecular
linkers that restrict interparticle distances to values significantly greater
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suspension (see ESI† Section 5.1).
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Chem. Commun.
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