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Self-Assembled Organic Nanotubes: Novel Bionanomaterials for Orthopedics and Tissue Engineering
Published in Tuan Vo-Dinh, Nanotechnology in Biology and Medicine, 2017
Rachel L. Beingessner, Baljit Singh, Thomas J. Webster, Hicham Fenniri
With this in mind, the heterobicyclic base G∧C (Figure 2.4a) was designed and synthesized to be a hydrophobic base unit possessing the Watson–Crick donor–donor–acceptor (DDA) H-bond array of guanine and acceptor–acceptor–donor (AAD) of cytosine. Because of the asymmetry of its hydrogen bonding arrays, their spatial arrangement, and the hydrophobic character of the bicyclic system, G∧C undergoes a hierarchical self-assembly process fueled by hydrophobic effects in water to form a six-membered supermacrocycle maintained by 18 H-bonds (rosette, Figure 2.4b). The resulting and substantially more hydrophobic aggregate self-organizes into a linear stack defining an open central channel 1.1 nm across, running the length of the assembly, and up to several millimeters long (Figure 2.4c). A covalently attached functional group, such as an amino acid moiety, dictates the supramolecular chirality of the resulting assembly. This tri-block design endows the modules with elements essential for the sequential self-assembly into stable nanotubular architectures (Figure 2.4c). The inner diameter is directly related to the distance separating the hydrogen bonding arrays within the G∧C motif while the peripheral diameter and its chemistry are dictated by the choice of the functional groups appended to this motif.
Chiral Metamaterials and Their Applications
Published in Song Sun, Wei Tan, Su-Huai Wei, Emergent Micro- and Nanomaterials for Optical, Infrared, and Terahertz Applications, 2023
Yidong Hou, Xuannan Wu, Xiu Yang
Chiral SPR biosensor. In principle, the chiral SPR biosensor relies on the super-chiral near-field of chiral structures to reduce the space mismatch between the twisted circularly polarized electromagnetic field and the chiral molecules. The shift of chiroptical resonance peak is often measured to indicate the molecular chirality. To obtain a high-performance chiral biosensor, the employed chiral structures should simultaneously own the super-chiral near-field, high refractive index sensitivity, and high-quality chiroptical resonance. Among which, the super-chiral near-field is considered to be the most important factor for chiral biosensor. Researchers have proposed and investigated lot of structures that can support the super-chiral near-field, including the nano-helix, two- or four-armed chiral structures, chiral plasmonic oligomer, the offset nano-slit, and the diagonal slit on mirror. In fact, the chiral near-field depends on both electric and magnetic components of light, but the metallic materials can only response to the electric component. Thus, a specific plasmonic geometry should be included to improve the response to the magnetic field, and hence the chiral field. One of the most interested designs is the nano-cub dimer on mirror, which theoretically shows a super-chiral near-field enhancement of up to 3000-times. In 2010, M. Kadodwala and his groups demonstrated the ultrasensitive detection and characterization of supramolecular chirality by using superchiral field excited near the planar chiral nanostructures, yielding a high detection sensitivity that is 106 times of that without chiral nanostructures [86]. To date, researchers have successfully detected the chirality of both the micromolecules, such as the L- and D-cysteine [93], and the macromolecules, such as the proteins. Various types of chiral structures have been proposed and investigated, such as six-armed chiral structure [94,95] and -shaped chiral structure [86]. We believe that the continuous efforts will be devoted on this direction to provide an effective method for detecting molecular chirality.
Langmuir and Langmuir–Blodgett films of aromatic amphiphiles
Published in Soft Materials, 2022
Lopez and coworkers have reported a chiral azobenezene amphiphile 64 and studied the supramolecular chiral structures formed at the air–water interface and LB films by multiple techniques .[112] The amphiphile formed stable monolayers with Alift, Ac, πc values of 45 Å2/molecule, 28 Å2/molecule, 25 mmN/m, respectively Beyond the collapse point (overshoot region), the authors proposed the formation of trilayer structures which were also supported by BAM imaging showing the presence of numerous bright spots and domains. Langmuir films were also analyzed by UV-vis reflection spectroscopy. The absorption peak centered around 354 nm at the start of the compression process which decreased to 342 nm at ~ 31 Å2/molecule just before the overshoot indicating H-aggregate formation. On further compression to ~ 15 Å2/molecule, the situation became drastically different. A red-shift (50 nm) was observed suggesting that J-aggregates have formed between molecules in adjacent layers. A quantitative analysis of the reflection spectra established the formation of trilayer structures beyond the overshoot. A similar formation of J-aggregates was also observed in the LB films (3/5 layers) using similar conditions. AFM investigations showed that the monolayer transferred before the overshoot had a coarse morphology with defects while those transferred after the overshoot (trilayer) displayed a smooth and uniform morphology. The thickness was determined to be 2.3 nm for the monolayer and 5.8 nm for the trilayer and a model was provided to account for this discrepancy in layer thickness. The authors proposed that the second layer is inserted ~1 nm into the first layer favoring interactions between the azobenezene moieties. The second and third layers interact through H-bonding. CD studies were performed to understand the supramolecular chirality of these structures. One layer LB film did not show any CD signal while 3-layer LB film showed a substantial signal. Similarly, the trilayer formed at the air–water interface when transferred onto a solid surface also exhibited CD signal indicating the formation of ordered multilayer structures in the LB films.