A Bimodal, Cationic, and Water-Soluble Calix[4]arene Conjugate: Design, Synthesis, Characterization, and Transfection of Red Fluorescent Protein Encoded Plasmid in Cancer Cells

Calix[4]arene Polyamine Triazoles: Synthesis, Aggregation and DNA Binding

Artificial gene delivery systems are in great demand from both scientific and practical biomedical points of view. In this paper, we present the synthesis of a new click chemistry calix[4]arene precursor with free lower rim and new water-soluble calixarene triazoles with 12 amino-groups on the upper rim (one with free phenol hydroxyl groups and two another containing four butyl or tetradecyl fragments). Aggregation in the series of amino-triazole calixarenes of different lipophilicity (calixarene with free phenol hydroxyl groups or butyl and tetradecyl fragments on the lower rim) was studied using dynamic light scattering and fluorescent pyrene probe. It was found that calix[4]arene with a free lower rim, like alkyl-substituted butyl calix[4]arene, forms stable submicron aggregates 150-200 nm in size, while the more lipophilic tetradecyl -substituted calix[4]arene forms micellar aggregates19 nm in size. Using UV-Vis spectroscopy, fluorimetry and CD, it was shown that amino-triazole calix[4]arenes bind to calf thymus DNA by classical intercalation. According to DLS and TEM data, all studied macrocycles cause significant DNA compaction, forming stable nanoparticles 50-20 nm in size. Among all studied calix[4]arenes the most lipophilic tetradecyl one proved to be the best for both binding and compaction of DNA.

Fluorescent cyclophanes and their applications

With the serendipitous discovery of crown ethers by Pedersen more than half a century ago and the subsequent introduction of host-guest chemistry and supramolecular chemistry by Cram and Lehn, respectively, followed by the design and synthesis of wholly synthetic cyclophanes-in particular, fluorescent cyclophanes, having rich structural characteristics and functions-have been the focus of considerable research activity during the past few decades. Cyclophanes with remarkable emissive properties have been investigated continuously over the years and employed in numerous applications across the field of science and technology. In this Review, we feature the recent developments in the chemistry of fluorescent cyclophanes, along with their design and synthesis. Their host-guest chemistry and applications related to their structure and properties are highlighted.

Synthesis of novel calix[4]arene p-benzazole derivatives and investigation of their DNA binding and cleavage activities with molecular docking and experimental studies

In this study, novel p-benzimidazole-derived calix[4]arene compounds with different structures, and a benzothiazole-derived calix[4]arene compound, were synthesized by a microwave-assisted method and their structures were determined by FTIR, 1H NMR, 13C NMR, MALDI-TOF mass spectroscopy, and elemental analysis. The effects of functional calixarenes against bacterial (pBR322 plasmid DNA) and eukaryotic DNA (calf thymus DNA = CT-DNA) were investigated. The studies with plasmid DNA have shown that compounds 6 and 10 containing methyl and benzyl groups, respectively, have DNA cleavage activity at the highest concentrations (10 000 μM). Interactions with plasmid DNA using some restriction enzymes (BamHI and HindIII) were also investigated. The binding ability of p-substituted calix[4]arene compounds towards CT-DNA was examined using UV-vis and fluorescence spectroscopy and it was determined that some compounds showed efficiency. In particular, it was observed that the functional compounds (10 and 5) containing benzyl and chloro-groups had higher activity (K b binding constants were found to be 7.1 × 103 M-1 and 9.3 × 102 M-1 respectively) on DNA than other compounds. Competitive binding experiments using ethidium bromide also gave an idea about the binding properties. Docking studies of the synthesized compounds with DNA were performed to predict the binding modes, affinities and noncovalent interactions stabilizing the DNA-compound complexes at the molecular level. Docking results were in good agreement with the experimental findings on the DNA binding activities of compounds. Based on these results, this preliminary study could shed light on future experimental antibacterial and/or anticancer research.

1,3-Di-naphthalimide Conjugate of Calix[4]arene as a Sensitive and Selective Sensor for Trinitrophenol and This Turns Reversible when Hybridized with Carrageenan as Beads

A fluorescent naphthalimide conjugate of calix[4]arene (L₁ ) has been synthesized and characterized. The selective and efficient detection of trinitrophenol (TNP) by L₁ among nine other different nitroaromatic compounds was demonstrated using absorption and fluorescence spectroscopy. The minimum detection limit is 29 nM, which is the lowest reported so far by any conjugate of calixarene toward TNP. The fluorescence quenching is associated with a high Stern-Volmer constant of 3.3 ± 0.4 × 10⁵ M^-1. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) data revealed a network structure with pores having a weighted average size of 0.66 ± 0.08 μm for L₁ . When incubated with TNP, the pores were filled with fibril structures, as supported by both SEM and TEM data. In order to demonstrate the real time applications, the L₁ has been coated onto a Whatman filter paper and the imprint of TNP contaminated thumb has been detected upon physical contact. The ¹HNMR titration and the studies carried out using the control molecule support the necessity of both the naphthalimide moiety and the calixarene platform for sensing. In order to mend L₁ as a reversible sensor for TNP, the same is incorporated into carrageenan beads (L₁ @C_b ) and the reversible sensing has been shown for three cycles by reusing the same material upon recovery followed by washing it. The solid-state detection of TNP has also been demonstrated using the lyophilized L₁ @C_b bead powder. The fluorescence intensity of L₁ was quenched upon addition of solid TNP to the lyophilized bead powder of L₁ @C_b as studied by fluorescence microscopy. The computational studies show that one of the arms of the calixarene takes a bent conformation, and the 1:1 TNP complex of L₁ is stabilized by exhibiting differential extents of hydrogen bonding interactions with the two arms owing to their conformational difference. The result of such complexation was already felt through the shifts observed in the experimentally measured ¹HNMR spectra.

Binding of Fe(ii)-complex of phenanthroline appended glycoconjugate with DNA, plasmid and an agglutinin protein

A phenanthroline appended glycoconjugate and its Fe(ii) complex have been synthesized and characterized thoroughly. The Fe-complex interacts with DNA and WGA protein and alter their structures as studied by spectroscopy and microscopy.

A luminescent on–off probe based calix[4]arene linked through triazole with ruthenium(ii) polypyridine complexes to sense copper(ii) and sulfide ions

The supramolecular sensor Ru2L was designed by joining a bis-ruthenium(ii) polypyridyl complex with a p-tert-butyl calix[4]arene platform through a 1,2,3-triazole linker and used for sensing of copper(ii) and sulfide ions by fluorescence.

Surface Functionalization and Patterning by Multifunctional Resorcinarenes

Plant phenolic compounds and catecholamines have been widely used to obtain substrate-independent precursor nanocoatings and adhesives. Nevertheless, there are downsides in using such phenolic compounds for surface modification such as formation of nonuniform coatings, need for multistep modification, and restricted possibilities for postfunctionalization. In this study, inspired by a strong binding ability of natural polyphenols found in plants, we used three different macrocyclic polyphenols, known as resorcin[4]arenes, to modify the surface of different substrates by simple dip-coating into the dilute solution of these compounds. Eight hydroxyl groups on the large rim of these resorcin[4]arenes provide multiple anchoring points to the surface, whereas the lower rim decorated with different appending groups introduces the desired chemical and physical functionalities to the substrate's surface. Deposition of a uniform and transparent resorcinarene layer on the surface was confirmed by several surface characterization techniques. Incubation of the modified substrates in different environments indicated that the stability of the resorcinarene layer was dependent on the type of substrate and the pH value. The most stable resorcinarene layer was formed on amine-functionalized substrates. The surface was modified with alkenyl functional groups in one step using a resorcinarene compound possessing four alkenyl appending groups on its small rim. Thiol-ene photoclick chemistry was used to site-selectively postfunctionalize the surface with hydrophilic and hydrophobic micropatterns, which was confirmed by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. Thus, we demonstrate that resorcin[4]arenes extend the scope of applications of plant polyphenol and mussel-inspired precursors to tailor-made multifunctional nanocoatings, suitable for a variety of potential applications in biotechnology, biology, and material science.

Plasmid-Templated Control of DNA-Cyclodextrin Nanoparticle Morphology through Molecular Vector Design for Effective Gene Delivery

Engineering self-assembled superstructures through complexation of plasmid DNA (pDNA) and single-isomer nanometric size macromolecules (molecular nanoparticles) is a promising strategy for gene delivery. Notably, the functionality and overall architecture of the vector can be precisely molded at the atomic level by chemical tailoring, thereby enabling unprecedented opportunities for structure/self-assembling/pDNA delivery relationship studies. Beyond this notion, by judiciously preorganizing the functional elements in cyclodextrin (CD)-based molecular nanoparticles through covalent dimerization, here we demonstrate that the morphology of the resulting nanocomplexes (CDplexes) can be tuned, from spherical to ellipsoidal, rod-type, or worm-like nanoparticles, which makes it possible to gain understanding of their shape-dependent transfection properties. The experimental findings are in agreement with a shift from chelate to cross-linking interactions on going from primary-face- to secondary-face-linked CD dimers, the pDNA partner acting as an active payload and as a template. Most interestingly, the transfection efficiency in different cells was shown to be differently impacted by modifications of the CDplex morphology, which has led to the identification of an optimal prototype for tissue-selective DNA delivery to the spleen in vivo.

Silica-Calix Hybrid Composite of Allyl Calix[4]arene Covalently Linked to MCM-41 Nanoparticles for Sustained Release of Doxorubicin into Cancer Cells

An inorganic-organic hybrid material, MCM-allylCalix, was synthesized by covalent modification of an MCM-41 surface with a tetra-allyl calixarene conjugate. The synthesized hybrid was characterized by ¹³C and ²⁹Si MAS-NMR, Fourier transform infrared (FT-IR), Brunauer-Emmett-Teller surface area, thermogravimetric analysis (TGA), and transmission electron microscopy (TEM) analyses. The application of this MCM-allylCalix hybrid has been demonstrated for loading and in vitro release of doxorubicin (Dox) in phosphate-buffered saline (PBS) buffer as well as in the cancer cells, viz., MCF7, HeLa, and MDA-MB231. The Dox-loaded hybrid, MCM-allylCalix-Dox, was characterized by TEM, FT-IR, TGA, N₂ sorption, diffuse refectance spectroscopy-UV, and fluorescence microscopy to confirm the presence of the drug. The release study of the drug from MCM-allylCalix-Dox was carried out in PBS buffer at pH 5 and 7.4. The results showed ∼140% increase in the release of Dox at pH 5 compared to that at pH 7.4 in 144 h, suggesting a pH-triggered release of the drug. MCM-allylCalix-Dox releases a greater amount of Dox compared to that released from unmodified MCM-Dox. Cytotoxicity studies suggested that MCM-allylCalix-Dox exhibits anticancer activity that is dependent on the nature of the cell. The Dox-loaded hybrid shows more cytotoxicity for MCF7 compared to that for the HeLa and MDA-MB231 cells. This was further supported by ∼120% more internalization of Dox into MCF7 cells compared to that in the other two cell lines. Both fluorescence microscopy and fluorescence-activated cell sorting studies suggested concentration-dependent internalization of Dox into the MCF7 and HeLa cells. The results suggested that the inorganic-organic hybrid can be useful in sustained drug delivery into cancer cells.