Selective Homocysteine Assay with Cucurbit[7]uril by pH Regulation

We report the effect of pH on the supramolecular complexation of two biothiols, viz., homocysteine (Hcy) and cysteine (Cys), with cucurbit[7]uril (CB[7]). Under basic pH conditions, Cys did not complex with CB[7], whereas Hcy efficiently complexed with CB[7], as confirmed by ¹H NMR spectroscopy and Ellman's reagent (5,5'-dithio-bis(2-nitrobenzoic acid), DTNB) assay. ¹H NMR and Raman spectroscopic studies revealed that, in the absence of CB[7], Hcy auto-oxidized slowly (~36 h) to homocystine (HSSH) under basic pH conditions. However, the rate of Hcy oxidation increased by up to 150 fold in the presence of CB[7], as suggested by the DTNB assay. Thus, supramolecular complexation under basic pH conditions led to the formation of a HSSH-CB[7] complex, and not Hcy-CB[7]. The results indicate that Hcy is rapidly oxidized to HSSH under the catalysis of CB[7], which acts as a reaction chamber, in basic pH conditions. Our studies suggest that Hcy concentration, a risk factor for cardiovascular disease, can be selectively and more easily quantified by supramolecular complexation with CB [7].

Supramolecular Surface Functionalization of Iron Oxide Nanoparticles with α-Cyclodextrin-Based Cationic Star Polymer for Magnetically-Enhanced Gene Delivery

Supramolecular polymers formed through host-guest complexation have inspired many interesting developments of functional materials for biological and biomedical applications. Here, we report a novel design of a non-viral gene delivery system composed of a cationic star polymer forming supramolecular complexes with the surface oleyl groups of superparamagnetic iron oxide nanoparticles (SPIONs), for magnetically enhanced delivery of DNA into mammalian cells. The cationic star polymer was synthesized by grafting multiple oligoethylenimine (OEI) chains onto an α-cyclodextrin (α-CD) core. The SPIONs were synthesized from iron(III) acetylacetonate and stabilized by hydrophobic oleic acid and oleylamine in hexane, which were characterized in terms of their size, structure, morphology, and magnetic properties. The synthesized magnetic particles were found to be superparamagnetic, making them a suitable ferrofluid for biological applications. In order to change the hydrophobic surface of the SPIONs to a hydrophilic surface with functionalities for plasmid DNA (pDNA) binding and gene delivery, a non-traditional but simple supramolecular surface modification process was used. The α-CD-OEI cationic star polymer was dissolved in water and then mixed with the SPIONs stabilized in hexane. The SPIONs were "pulled" into the water phase through the formation of supramolecular host-guest inclusion complexes between the α-CD unit and the oleyl surface of the SPIONs, while the surface of the SPIONs was changed to OEI cationic polymers. The α-CD-OEI-SPION complex could effectively bind and condense pDNA to form α-CD-OEI-SPION/pDNA polyplex nanoparticles at the size of ca. 200 nm suitable for delivery of genes into cells through endocytosis. The cytotoxicity of the α-CD-OEI-SPION complex was also found to be lower than high-molecular-weight polyethylenimine, which was widely studied previously as a standard non-viral gene vector. When gene transfection was carried out in the presence of an external magnetic field, the α-CD-OEI-SPION/pDNA polyplex nanoparticles greatly increased the gene transfection efficiency by nearly tenfold. Therefore, the study has demonstrated a facile two-in-one method to make the SPIONs water-soluble as well as functionalized for enhanced magnetofection.

Initiating Electron Transfer in Doubly-curved Nanographene Upon Supramolecular Complexation of C60

The formation of supramolecular complexes between C₆₀ and a molecular nanographene endowed with both positive and negative curvatures is described. The presence of a corannulene moiety and the saddle shape of the molecular nanographene allows the formation of complexes with 1:1, 1:2, and 2:1 stoichiometries. The association constants for the three possible supramolecular complexes were determined by ¹H NMR titration. Furthermore, the stability of the three complexes was calculated by theoretical methods that also predict the photoinduced electron transfer from the curved nanographene to the electron acceptor C₆₀. Time‐resolved transient absorption measurements on the ns‐time scale showed that the addition of C₆₀ to NG‐1 solutions and photo‐exciting them at 460 nm leads to the solvent‐dependent formation of new species, in particular the formation of the one‐electron reduced form of C₆₀ in benzonitrile was observed.

Facile Synthesis of Fluorescent Hyper-Cross-Linked β-Cyclodextrin-Carbon Quantum Dot Hybrid Nanosponges for Tumor Theranostic Application with Enhanced Antitumor Efficacy

Fluorescent hyper-cross-linked β-cyclodextrin-carbon quantum dot (β-CD-CQD) hybrid nanosponges of about 200 nm with excellent biocompatibility and strong bright blue fluorescence excited at 365 nm with a high photoluminescence quantum yield (PLQY) of 38.0% were synthesized for tumor theranostic application by facile condensation polymerization of carbon quantum dots (CQDs) with β-cyclodextrin (β-CD) at a feeding ratio of 1:5. The DOX@β-CD-CQD theranostic nanomedicine, around 300 nm with DOX-loading capacity of 39.5% by loading doxorubicin (DOX) via host-guest complexation, showed a pH responsive controlled release and released DOX in the simulated tumor microenvironment in a sustained release mode, owing to the formation constant in the supramolecular complexation of DOX with the β-CD units in the β-CD-CQD nanosponges. The proposed DOX@β-CD-CQD theranostic nanomedicine could be internalized into HepG2 cells, and the released DOX was accumulated into the cell nuclei, demonstrating an antitumor efficacy more enhanced than that of the free drug.

Isorecticular Synthesis of Dissectible Molecular Bamboo Tubes of Hexarhenium(I) Benzene-1,2,3,4,5,6-hexaolate Complexes

A family of bamboo-like metal-organic nanotubes consisting of in situ synthesized macromolecular blocks (MB) is reported. The MBs are composed of six fac-(CO)3 Re cores, one benzene-1,2,3,4,5,6-hexaolate plate, and six pyridine-derivative pillar ligands, which have a doubly tri-legged geometry and can be mutually assembled, piece by piece. This entire system is characterized as a simple but precise supramolecular complexation of these macromolecular blocks and further introduces an archetypal approach to systematically constructing a tunable form of dissectible molecular bamboo tubes.

Supramolecular Inhibition of Neurodegeneration by a Synthetic Receptor

Cucurbit[7]uril (CB[7]) was found in vitro to sequester the neurotoxins MPTP (N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and MPP(+) (N-methyl-4-phenylpyridine). The CB[7]/neurotoxin host-guest complexes were studied in detail with (1)H NMR, electrospray ionization mass spectrometry, UV-visible spectroscopic titration, and molecular modeling by density functional theory. The results supported the macrocyclic encapsulation of MPTP and MPP(+), respectively, by CB[7] in aqueous solutions with relatively strong affinities and 1:1 host-guest binding stoichiometries in both cases. More importantly, the progression of MPTP/MPP(+) induced neurodegeneration (often referred to as a Parkinson's disease model) was observed to be strongly inhibited in vivo by the synthetic CB[7] receptor, as shown in zebrafish models. These results show that a supramolecular approach could lead to a new preventive and/or therapeutic strategy for counteracting the deleterious effects of some neurotoxins leading to neurodegeneration.

Supramolecular Complexation of Carbohydrates for the Bioavailability Enhancement of Poorly Soluble Drugs

In this review, a comprehensive overview of advances in the supramolecular complexes of carbohydrates and poorly soluble drugs is presented. Through the complexation process, poorly soluble drugs could be efficiently delivered to their desired destinations. Carbohydrates, the most abundant biomolecules, have diverse physicochemical properties owing to their inherent three-dimensional structures, hydrogen bonding, and molecular recognition abilities. In this regard, oligosaccharides and their derivatives have been utilized for the bioavailability enhancement of hydrophobic drugs via increasing the solubility or stability. By extension, polysaccharides and their derivatives can form self-assembled architectures with poorly soluble drugs and have shown increased bioavailability in terms of the sustained or controlled drug release. These supramolecular systems using carbohydrate will be developed consistently in the field of pharmaceutical and medical application.

Targeting the blind spot of polycationic nanocarrier-based siRNA delivery

Polycationic nanocarriers attract increasing attention to the field of siRNA delivery. We investigated the self-assembly of siRNA vs pDNA with polycations, which are broadly used for nonviral gene and siRNA delivery. Although polyethyleneimine (PEI) was routinely adopted as siRNA carrier based on its efficacy in delivering pDNA, it has not been investigated yet why PEI efficiently delivers pDNA to cells but is controversially discussed in terms of efficacy for siRNA delivery. We are the first to investigate the self-assembly of PEI/siRNA vs PEI/pDNA and the steps of complexation and aggregation through different levels of hierarchy on the atomic and molecular scale with the novel synergistic use of molecular modeling, molecular dynamics simulation, isothermal titration calorimetry, and other characterization techniques. We are also the fist to elucidate atomic interactions, size, shape, stoichiometry, and association dynamics for polyplexes containing siRNA vs pDNA. Our investigation highlights differences in the hierarchical mechanism of formation of related polycation-siRNA and polycation-pDNA complexes. The results of fluorescence quenching assays indicated a biphasic behavior of siRNA binding with polycations where molecular reorganization of the siRNA within the polycations occurred at lower N/P ratios (nitrogen/phosphorus). Our results, for the first time, emphasize a biphasic behavior in siRNA complexation and the importance of low N/P ratios, which allow for excellent siRNA delivery efficiency. Our investigation highlights the formulation of siRNA complexes from a thermodynamic point of view and opens new perspectives to advance the rational design of new siRNA delivery systems.