Electrochemical DNA-Sensor Based on Macrocyclic Dendrimers with Terminal Amino Groups and Carbon Nanomaterials

The assembling of thiacalix[4]arene-based dendrimers in cone, partial cone, and 1,3-alternate configuration on the surface of a glassy carbon electrode coated with carbon black or multiwalled carbon nanotubes has been characterized using cyclic voltammetry, electrochemical impedance spectroscopy, and scanning electron microscopy. Native and damaged DNA were electrostatically accumulated on the modifier layer. The influence of the charge of the redox indicator and of the macrocycle/DNA ratio was quantified and the roles of the electrostatic interactions and of the diffusional transfer of the redox indicator to the electrode interface indicator access were established. The developed DNA sensors were tested on discrimination of native, thermally denatured, and chemically damaged DNA and on the determination of doxorubicin as the model intercalator. The limit of detection of doxorubicin established for the biosensor based on multi-walled carbon nanotubes was equal to 1.0 pM with recovery from spiked human serum of 105-120%. After further optimization of the assembling directed towards the stabilization of the signal, the developed DNA sensors can find application in the preliminary screening of antitumor drugs and thermal damage of DNA. They can also be applied for testing potential drug/DNA nanocontainers as future delivery systems.

Oxyethylated Fluoresceine-(thia)calix[4]arene Conjugates: Synthesis and Visible-Light Photoredox Catalysis in Water-Organic Media

Fluorescent derivatives attract the attention of researchers for their use as sensors, photocatalysts and for the creation of functional materials. In order to create amphiphilic fluorescent derivatives of calixarenes, a fluorescein derivative containing oligoethylene glycol and propargyl groups was obtained. The resulting fluorescein derivative was introduced into three different (thia)calix[4]arene azide derivatives. For all synthesized compounds, the luminescence quantum yields have been established in different solvents. Using UV-visible spectroscopy, dynamic light scattering, as well as transmission and confocal microscopy, aggregation of macrocycles was studied. It was evaluated that calixarene derivatives with alkyl substituents form spherical aggregates, while symmetrical tetrafluorescein-containing thiacalix[4]arene forms extended worm-like aggregates. The macrocycle containing tetradecyl fragments was found to be the most efficient in photoredox ipso-oxidation of phenylboronic acid. In addition, it was shown that in a number of different electron donors (NEt₃, DABCO and iPr₂EtN), the photoredox ipso-oxidation proceeds best with triethylamine. It has been shown that a low molecular weight surfactant Triton-X100 can also improve the photocatalytic abilities of an oligoethylene glycol fluorescein derivative, thus showing the importance of a combination of micellar and photoredox catalysis.

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.