A homochiral naphthalenediimide-based building block forms in water a disulfide library of macrocycles containing topological isomers. We attempted to identify each of these isomers, and explored the ...mechanisms leading to their formation. The two most abundant species of the library were assigned as a topologically chiral Solomon link (60% of the library, as measured by high-performance liquid chromatography (HPLC)) and a topologically achiral figure eight knot (18% by HPLC), competing products with formally different geometries but remarkably similar 4-fold symmetries. In contrast, a racemic mixture of building blocks gives the near-quantitative formation of another new and more stable structure, assigned as a meso figure eight knot. Taken together, these results seem to uncover a correlation between the point chirality of the building block used and the topological chirality of the major structure formed. These and the earlier discovery of a trefoil knot also suggest that the number of rigid components in the building block may translate into corresponding knot symmetry and could set the basis of a new strategy for constructing complex topologies.
Discovery of an Organic Trefoil Knot Ponnuswamy, Nandhini; Cougnon, Fabien B. L.; Clough, Jessica M. ...
Science (American Association for the Advancement of Science),
11/2012, Volume:
338, Issue:
6108
Journal Article
Peer reviewed
Molecular knots remain difficult to produce using the current synthetic methods of chemistry because of their topological complexity. We report here the near-quantitative self-assembly of a trefoil ...knot from a naphthalenediimide-based aqueous disulfide dynamic combinatorial library. The formation of the knot appears to be driven by the hydrophobic effect and leads to a structure in which the aromatic components are buried while the hydrophilic carboxylate groups remain exposed to the solvent. Moreover, the building block chirality constrains the topological conformation of the knot and results in its stereoselective synthesis. This work demonstrates that the hydrophobic effect provides a powerful strategy to direct the synthesis of entwined architectures.
Subphthalocyanine (SubPc)-stoppered 2rotaxanes were synthesized for the first time. The rotaxane bearing unsubstituted SubPc as a stopper exhibited an equilibrium of slipping-on and slipping-off, ...whereas a perfluorinated SubPc stopper completely blocked slippage of the ring due to its slightly larger size. Kinetic studies revealed the Gibbs free energy of activation for the slipping-on and slipping-off processes. The optical properties of the rotaxanes, including photoinduced electron transfer, were also revealed.
Amino-acid functionalized naphthalenediimides self-assemble into hydrogen-bonded supramolecular helical nanotubes via a noncooperative, isodesmic process; the self-assembly of ordered helical systems ...is usually realized through a cooperative process. This unexpected behavior was rationalized as a manifestation of entropy–enthalpy compensation. Fundamental insights into the thermodynamics governing this self-assembly were obtained through the fitting of the isodesmic model to 1H NMR spectrometry and circular dichroism spectroscopy measurements. Furthermore, we have extended the application of this mathematical model, for the first time, to quantitatively estimate the effect of guests, solvents, and side chains on the stability of the supramolecular nanotube; most significantly, we demonstrate that C60 acts as a template to stabilize the nanotube assembly and thereby substantially increase the degree of polymerization.
The discovery through dynamic combinatorial chemistry (DCC) of a new generation of donor−acceptor 2catenanes highlights the power of DCC to access unprecedented structures. While conventional ...thinking has limited the scope of donor−acceptor catenanes to strictly alternating stacks of donor (D) and acceptor (A) aromatic units, DCC is demonstrated in this paper to give access to unusual DAAD, DADD, and ADAA stacks. Each of these catenanes has specific structural requirements, allowing control of their formation. On the basis of these results, and on the observation that the catenanes represent kinetic bottlenecks in the reaction pathway, we propose a mechanism that explains and predicts the structures formed. Furthermore, the spontaneous assembly of catenanes in aqueous dynamic systems gives a fundamental insight into the role played by hydrophobic effect and donor−acceptor interactions when building such complex architectures.
Two donor−acceptor 2catenanes have been synthesized and characterized from a single dynamic combinatorial library in water. One of these catenanes is different from earlier related interlocked ...molecules in that two donor units stack on each other in an unexpected order. Shifting the equilibrium by choosing the right conditions resulted in a significant increase in the yields of the individual catenanes.
Chirality is omnipresent in the living world. As biomimetic nanotechnology and self-assembly advance, they too need chirality. Accordingly, there is a pressing need to develop general methods to ...characterize chiral building blocks at the nanoscale in liquids such as waterthe medium of life. Here, we demonstrate the chiroptical second-harmonic Tyndall scattering effect. The effect was observed in Si nanohelices, an example of a high-refractive-index dielectric nanomaterial. For three wavelengths of illumination, we observe a clear difference in the second-harmonic scattered light that depends on the chirality of the nanohelices and the handedness of circularly polarized light. Importantly, we provide a theoretical analysis that explains the origin of the effect and its direction dependence, resulting from different specific contributions of “electric dipole–magnetic dipole” and “electric dipole–electric quadrupole” coupling tensors. Using numerical simulations, we narrow down the number of such terms to 8 in forward scattering and to a single one in right-angled scattering. For chiral scatterers such as high-refractive-index dielectric nanoparticles, our findings expand the Tyndall scattering regime to nonlinear optics. Moreover, our theory can be broadened and adapted to further classes where such scattering has already been observed or is yet to be observed.
The design and synthesis of water soluble, amino‐acid‐functionalised naphthalenediimides (NDIs) as potential ligands of native G‐quadruplexes is reported. The NDIs were tested on a panel of oncogene ...promoters, on the human telomeric sequence h‐telo, and on double‐stranded DNA. Out of the ligands tested, NDI 3 (Nϵ‐Boc‐l‐lysine NDI) exhibited a highly discriminating nature by only stabilising the oncogene promoter c‐kit2, which is up‐regulated up to 80 % in ovarian, gastrointestinal, and breast malignancies.
Selective oncogene stablilisation: Water‐soluble, amino acid functionalised naphthalenediimides are potential ligands of native G‐quadruplexes, and they are tested on a panel of oncogene promoters and against double‐strand DNA. One of the ligands, NDI 3, exhibits a highly discriminating nature by stabilising only the oncogene promoter c‐kit2, which is upregulated up to 80 % in ovarian, gastrointestinal, and breast malignancies (see figure).
Templated Dynamic Synthesis of a [3]Catenane Cougnon, Fabien B. L.; Jenkins, Nicholas A.; Pantoş, G. Dan ...
Angewandte Chemie (International ed.),
February 6, 2012, Volume:
51, Issue:
6
Journal Article
Peer reviewed
Three rings: The self‐assembly of a water‐soluble 3catenane from a library composed of two linear building blocks, both terminated by cysteine components, is promoted either by a high salt ...concentration or by the presence of spermine. The spermine‐templated synthesis of the 3catenane shows that such structures can exhibit strong binding interactions with a biologically relevant target in water under near‐physiological conditions.
PDF
