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Carbon Nanotubes
Published in Sourav Bhattacharjee, Principles of Nanomedicine, 2019
Carbon nanotubes (CNTs) are nanoscale cylindrical structures that appear to be single or multiple graphene sheets rolled to form single-walled CNTs (SWCNTs) and multiwalled CNTs (MWCNTs), respectively (Fig. 6.1) [1, 2]. CNTs exhibit very high aspect ratios, with some of the CNTs reported to reach a length of ~0.5 m [3]. The minimal internal diameter of a CNT is 0.3 nm, while CNTs with higher internal diameters are also known [4]. Typical to graphene, CNTs bear sp2-hybridized C-atoms arranged in aromatic rings, which demonstrate excellent thermal and electrical conductivity apart from being the strongest material discovered so far (tensile strength of up to 100 GPa) [5]. The π-electrons of the aromatic rings interact (π-stacking). Hence, multiple CNTs can naturally align sideways due to the van der Waals force in order to form rope-like structures [6]. The significant strength of CNTs was utilized to synthesize nanotubes with a very high aspect ratio, 132,000,000:1 [7], which is an impossible task in any other known material. Hence, CNTs have been used as strengthening materials in various structures, including automobile parts, sports equipment, and Damascus steel [8].
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
π–π interactions involve London dispersion forces and the hydrophobic effect. This form of stabilizing interaction is commonly found in DNA where the vertical base stacking contributes a significant stabilizing force to the double helix. In an aqueous environment, an unfavorable entropy effect occurs as a result of polar solvent molecules trying to order themselves around apolar (or hydrophobic) molecules. This unfavorable entropy provides a driving force for hydrophobic solute aggregation to reduce the total hydrophobic surface area accessible to polar solvent molecules. This form of binding can thus be described as the association of nonpolar regions of molecules in polar media, resulting from the tendency of polar solvent molecules to assume their thermodynamically favorable states. The hydrophobic effect is a salient force in, for instance, micelle formation, protein–protein interactions, and protein folding.
Strategies to Synthesize Biodegradable Conducting Polymers
Published in Ram K. Gupta, Conducting Polymers, 2022
Shagun Kainth, Piyush Sharma, Pawan Kumar Diwan
It was observed that the behavior of self-assembly was distinct in dendritic polymers in comparison to block polymers [68]. The dendritic polymers were made of ester dendron and AT and self-assembled in the presence of THF. The self-assembly of these polymers significantly depends on various factors such as amphiphilic interactions, intermolecular interactions, and the intermolecular π-π stacking among oligomers. The amphiphilic interactions and intermolecular interactions occurred due to building blocks and easter dendrons, respectively. Later, a block oligomer of aniline having a dendron-rod-dendron dumbbell shape was synthesized [69]. In this case, the morphology was changed from fibrils to flat single-layer films. In addition, there was the formation of a porous network due to the conformational transition of the conductive oligomer during oxidation. There are some grafted biodegradable CPs that can undergo self-assembly [70]. For example, AP grafted chitosan self-assemble into micelles of size 200–300 nm. The reason behind self-assembly was associated with variation in pH and the presence of salt. It was also found that multialdehyde sodium alginate-graft-tetraaniline copolymer possesses a tendency to self-assemble in the nanosphere having a hydrophilic part as shell and hydrophobic part as a core. The aggregation of micelle was prevented by a negatively charged surface of micelle due to the presence of large-sized carboxylic ions in the multialdehyde sodium alginate-graft-tetraaniline copolymer [71]. These fascinating results open new doors to couple drugs or biomolecules in the presence of salt.
Synthesis, characterization, and crystal structure analysis of group IIB coordination compounds containing N,N′-bidentate chelating Schiff-base ligand
Published in Journal of Coordination Chemistry, 2020
Taraneh Hajiashrafi, Roghayeh Zekriazadeh, Maciej Kubicki
The crystal packing analysis of 1 reveals that discrete neutral units of [ZnL4-OH Br2] are connected to each other along the crystallographic a-direction viapyridylπ···πphenyl stacking interaction (Table 3 and Figure 2). These units are further linked to each other through O–H···Br and C–H···Br non-classical hydrogen bonding interactions in the bc-plane (Table 4). In the crystal structure of 2, adjacent binuclear units of [Hg2(L4-OH)2I4] are linked to each other through a combination of π-interactions, chelateπ···πpyridyl and pyridylπ···πphenyl, in the crystallographic a-direction (Table 3 and Figure 3(a)). Recent studies have revealed that aromaticity might not be the key feature of stacking interactions and those nonaromatic cyclic systems such as chelate rings with delocalized π-bonds can form stacking interactions [42]. The methanol molecules of crystallization link discrete molecular units, in the bc-plane, via O–H···O hydrogen bonding interactions, which is further assisted by imineC–H···I and C–H···O interactions to generate the three-dimensional 3D crystal network (Table 4 and Figure 3(b)).
On the nature of trapped states in an MoS2 two-dimensional semiconductor with sulfur vacancies
Published in Molecular Physics, 2019
Gabriela Ben-Melech Stan, Maytal Caspary Toroker
The electronic states of two-dimensional materials have attracted a lot of interest in recent years [1,2]. Two-dimensional materials are characterised by atomic layer arrangements stacked together by van der Waals forces. The large versatility of stacking arrangements and atomic composition position these materials as potentially useful for downscaling electronic devices. The state-of-the-art field effect transistor that is made out of two-dimensional materials contains graphene as source and drain metallic electrodes and molybdenum sulfide (MoS2) as the main semiconducting channel [3]. Characterising the electronic properties of MoS2 is important for understanding the functionality of this device, especially under realistic conditions where material defects such as vacancies are dominant.
Synthesis and structure of organoplatinum(II) complexes containing aryl olefins and 8-hydroxyquinolines
Published in Journal of Coordination Chemistry, 2019
Le Thi Hong Hai, Nguyen Thi Ngoc Vinh, Luu Thi Tuyen, Luc Van Meervelt, Tran Thi Da
Of only two complexes with identical Pt(II) coordination sphere the crystal structure is known. The first one, {4,5-dimethoxy-2-[(2,3-η)-2-prop-2-en-1-yl]phenyl-κC1}(8-hydroxyquinolato-κN,O)platinum(II) (complex A [23]), only differs from 9 by the substitution of both rings. Only the Pt-N distances differ significantly [2.188(2) Å in 9vs. 2.109(2) Å in complex A], which is caused by the sterical hindrance of the methyl substituent on the quinoline ring and the vinyl group C21 = C22 in 9. The dihedral angle between both aromatic rings is 39.87(10)°. The packing of complex A shows similar C-H…O interactions as in 9. No π…π stacking interactions are observed, but they are replaced by C-H…π interactions between parallel chains of molecules. In the second one, {5-(2-ethoxy-2-oxoethoxy)-4-methoxy-2-[(2,3-η)-prop-2-en-1-yl]phenyl-κC1}(quinoline-2-carboxylato–κN,O)platinum(II) (complex B, [13]), the Pt(II) coordination distances are identical (compared to 9) despite that the coordinating O atom now comes from a carboxylate group. As this O atom belongs to the carboxylate substituent at position 2 instead of at position 8 in 9, the ethyl eugenoxyacetate ligand is also rotated by about 180°. The best planes through both aromatic rings make an angle of 28.06(13)°.