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1. Threading carbon nanotubes through a self-assembled nanotube

   https://doi.org/10.1039/c9sc02313e  

   Ji, Mingyang; Mason, McKensie L.; Modarelli, David A.; Parquette, Jon R. (August 2019, Chemical Science)

   Achieving the co-assembly of more than one component represents an important challenge in the drive to create functional self-assembled nanomaterials. Multicomponent nanomaterials comprised of several discrete, spatially sorted domains of components with high degrees of internal order are particularly important for applications such as optoelectronics. In this work, single-walled carbon nanotubes (SWNTs) were threaded through the inner channel of nanotubes formed by the bolaamphiphilic self-assembly of a naphthalenediimide-lysine (NDI-Bola) monomer. The self-assembly process was driven by electrostatic interactions, as indicated by ζ -potential measurements, and cation–π interactions between the surface of the SWNT and the positively charged, NDI-Bola nanotube interior. To increase the threading efficiency, the NDI-Bola nanotubes were fragmented into shortened segments with lengths of <100 nm via sonication-induced shear, prior to co-assembly with the SWNTs. The threading process created an initial composite nanostructure in which the SWNTs were threaded by multiple, shortened segments of the NDI-Bola nanotube that progressively re-elongated along the SWNT surface into a continuous radial coating around the SWNT. The resultant composite structure displayed NDI-Bola wall thicknesses twice that of the parent nanotube, reflecting a bilayer wall structure, as compared to the monolayer structure of the parent NDI-Bola nanotube. As a final, co-axial outer layer, poly( p -phenyleneethynylene) (PPE-SO 3 Na, M W = 5.76 × 10 4 , PDI – 1.11) was wrapped around the SWNT/NDI-Bola composite resulting in a three-component (SWNT/NDI-Bola/PPE-SO 3 Na) composite nanostructure. 

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2. Using Preformed Meisenheimer Complexes as Dopants for n‐Type Organic Thermoelectrics with High Seebeck Coefficients and Power Factors

   https://doi.org/10.1002/adfm.202010567  

   Han, Jinfeng; Ganley, Connor; Hu, Qin; Zhao, Xingang; Clancy, Paulette; Russell, Thomas_P; Katz, Howard_E (February 2021, Advanced Functional Materials)

   Abstract A pre‐formed Meisenheimer complex of a naphthalenediimide (NDI) with tetrabutylammonium fluoride (TBAF) is obtained in a simple way by mixing dibrominated 4,9‐dibromo‐2,7‐bis(2‐octyldodecyl)benzo[lmn][3,8]phenanthroline‐1,3,6,8(2H,7H)‐tetraone and TBAF in solution and used as a dopant for n‐type organic thermoelectrics. Two n‐type polymers PNDIClTVT and PBDOPVTT are synthesized, n‐doped, and characterized as conductive and thermoelectric materials. PNDIClTVT doped with NDI‐TBAF presents a high σ value of 0.20 S cm^–1, a Seebeck coefficient (S) of −1854 µV K^–1, and a power factor (PF) of 67 µW m^–1K^–2, among the highest reported PF in solution‐processed conjugated n‐type polymer thermoelectrics. Using 4‐(1,3‐dimethyl‐2,3‐dihydro‐1H‐benzoimidazol‐2‐yl)phenyl)dimethylamine and NDI‐TBAF as co‐dopants, PNDIClTVT has a PF > 35 µW m^–1K^–2; while for PBDOPVTT σ = 0.75 S cm^–1and PF = 58 µW m^–1K^–2. In this study it is found that an ionic adduct together with a neutral dopant improves the performance of n‐type organic thermoelectrics leading to an enhanced power factor, and more generally, the role of such an adduct in polymer doping is also elucidated. 

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3. pH-Responsive Rhodamine Nanotube Capable of Self-Reporting the Assembly State

   https://doi.org/10.1021/acsami.4c07280  

   Meng, Ziyuan; Taneja, Sagarika; Hassan, Reham; Parquette, Jon R (September 2024, ACS Applied Materials & Interfaces)

   Nanomaterials that respond to intracellular signals, such as pH, have potential for many biomedical applications, such as drug delivery, because the assembly/disassembly process can be tailored to respond to a stimulus characteristic of a specific subcellular location. In this work, two rhodamine-peptides that form stable nanotubes at physiological pH but dissociate into highly fluorescent monomers within the acidified interior of endosomal/lysosomal cellular compartments has been developed. The rhodamine dipeptide conjugates, NH2-KK(RhB)-NH2 (RhB-KK) and NH2-EK(RhB)-NH2 (RhB-KE) with rhodamine B chromophores appended at the ε-amino position of a lysine residue, were shown to assemble into well-defined nanotubes at pH values above ~4-5 and to dissociate into a fluorescent monomer state at lower pH values. The pH-dependence of the assembly process was investigated using CD and fluorescence spectroscopy along with TEM, AFM and confocal imaging. Although the ring opening/closing transition of the rhodamine chromophore took place at pH 4.1 for both peptides, the onset of assembly began at pH 4.6 for RhB-KE and at a comparatively more basic pH (5.8) for RhB-KK. Accordingly, the rhodamine-peptides interconverted between three, pH-dependent states: an open-ring, monomeric state (max 580 nm, 𝜆ex 550 nm) at pH values at or below ~4.6; a closed-ring, nanotube form that exhibits AIEE (max 460 nm, 𝜆ex = 330 nm) at higher pH values and a closed-ring, non-emissive monomeric state that emerged below the CMC. The pH-responsive features of the peptides were evaluated by live-cell imaging in three cancer cell lines using confocal laser scanning microscopy (CLSM). Visualizing the cells after incubation with either RhB-KE or RhB-KK produced CLSM images with a punctate appearance in the Texas Red channel that colocalized with the lysosomes. These experiments indicating that the nanotubes were rapidly trafficked into the acidic lysosomal compartments within the cells, which induced dissociation into a monomeric, open state. Uptake inhibition studies suggested that cellular uptake was mediated by either or both caveolae- and clathrin-mediated endocytosis, depending on the cell line studied. 

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4. Tying the alkoxides together: an iron complex of a new chelating bulky bis(alkoxide) demonstrates selectivity for coupling of non-bulky aryl nitrenes

   https://doi.org/10.1039/C9CC05319K  

   Kurup, Sudheer S.; Wannipurage, Duleeka; Lord, Richard L.; Groysman, Stanislav (September 2019, Chemical Communications)

   New chelating bis(alkoxide) ligand H 2 [OO] Ph and its iron( ii ) complex Fe[OO] Ph (THF) 2 are described. The coordination of the ligand to the metal center is reminiscent of the coordination of two monodentate alkoxides in previously reported Fe(OR) 2 (THF) 2 species. Fe[OO] Ph (THF) 2 catalyzes selective and efficient dimerization of non-bulky aryl nitrenes to yield the corresponding azoarenes. 

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5. Selective host–guest chemistry, self-assembly and conformational preferences of m -xylene macrocycles probed by ion-mobility spectrometry mass spectrometry

   https://doi.org/10.1039/C9CP06938K  

   Link, Benjamin A.; Sindt, Ammon J.; Shimizu, Linda S.; Do, Thanh D. (May 2020, Physical Chemistry Chemical Physics)

   We demonstrated ion-mobility spectrometry mass spectrometry (IMS-MS) as a powerful tool for interrogating and preserving selective chemistry including non-covalent and host–guest complexes of m -xylene macrocycles formed in solution. The technique readily revealed the unique favorability of a thiourea-containing macrocycle MXT to Zn 2+ to form a dimer complex with the cation in an off-axis sandwich structure having the Zn–S bonds in a tetrahedral coordination environment. Replacing thiourea with urea generates MXU which formed high-order oligomerization with weak binding interactions to neutral DMSO guests detected at every oligomer size. The self-assembly pathway observed for this macrocycle is consistent with the crystalline assembly. Further transformation of urea into squaramide produces MXS, a rare receptor for probing sulfate in solution. Tight complexes were observed for both monomeric and dimeric of MXS in which HSO 4 − bound stronger than SO 4 2− to the host. The position of HSO 4 − at the binding cavity is a 180° inversion of the reported crystallographic SO 4 2− . The MXS dimer formed a prism-like shape with HSO 4 − exhibiting strong contacts with the 8 amine protons of two MXS macrocycles. By eliminating intermolecular interferences, we detected the low energy structures of MXS with collisional cross section (CCS) matching cis – trans and cis – cis squaramides-amines, both were not observed in crystallization trials. The experiments collectively unravel multiple facets of macrocycle chemistry including conformational flexibility, self-assembly and ligand binding; all in one analysis. Our findings illustrate an inexpensive and widely applicable approach to investigate weak but important interactions that define the shape and binding of macrocycles. 

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