Interaction of acridine-calix[4]arene with DNA at the electrified liquid|liquid interface

Electroactivity of Aptamer at Soft Microinterface Arrays

The electrochemical behavior of a synthetic oligonucleotide, thrombin-binding aptamer (TBA, 15-mer), was explored at a liquid-organogel microinterface array. TBA did not display any response when only background electrolytes were present in both phases. On the basis of literature reports that surfactants can influence nucleic acid detection, the response in the presence of cetyltrimethylammonium (CTA⁺) was examined. With both TBA and CTA⁺ in the aqueous phase, the transfer current for CTA⁺ was diminished, signifying the interaction of CTA⁺ with TBA. Experiments with CTA⁺ spiked into the organic phase revealed a sharp current peak, consistent with the interfacial formation of a CTA⁺-TBA complex. However, use of CTA⁺ as the organic phase electrolyte cation, as the salt with tetrakis(4-chlorophenyl)borate, greatly improved the response to TBA. In this case, a distinctive peak response (at ca. -0.25 V) was attributed to the transfer of CTA⁺ across the soft interface to complex with aqueous phase TBA. Employing this process as a detection step enabled a detection limit of 0.11 μM TBA (by cyclic voltammetry). Furthermore, the presence of magnesium cations at physiological concentration resulted in the disappearance of the TBA response because of Mg²⁺-induced folding of TBA. Also, the current response of TBA was decreased by the addition of thrombin, indicating TBA interacted with this binding partner. Finally, the interfacial surfactant-aptamer interaction was explored in a synthetic urine matrix that afforded a detection limit of 0.29 μM TBA. These results suggest that aptamer-binding interactions can be monitored by electrochemistry at aqueous-organic interfaces and open up a new possibility for detection in aptamer-binding assays.

Electroanalytical Opportunities Derived from Ion Transfer at Interfaces between Immiscible Electrolyte Solutions

This review presents an introduction to electrochemistry at interfaces between immiscible electrolyte solutions and surveys recent studies of this form of electrochemistry in electroanalytical strategies. Simple ion and facilitated ion transfers across interfaces varying from millimetre scale to nanometre scales are considered. Target detection strategies for a range of ions, inorganic, organic, and biological, including macromolecules, are discussed.

The effect of the functionalization and molecular weight of cationic dextran polyelectrolytes on their electrochemical behavior at the water/1,2-dichloroethane interface

The functionalization and molecular weight of cationic dextran polyelectrolytes have an impact on their adsorption and electrochemical behavior at the water/1,2-dichloroethane interface.

N-substituted phenoxazine and acridone derivatives: structure-activity relationships of potent P2X4 receptor antagonists

P2X4 receptor antagonists have potential as drugs for the treatment of neuropathic pain and neurodegenerative diseases. In the present study the discovery of phenoxazine derivatives as potent P2X4 antagonists is described. N-Substituted phenoxazine and related acridone and benzoxazine derivatives were synthesized and optimized with regard to their potency to inhibit ATP-induced calcium influx in 1321N1 astrocytoma cells stably transfected with the human P2X4 receptor. In addition, species selectivity (rat, mouse, human) and receptor subtype selectivity (versus P2X1,2,3,7) were investigated. The most potent P2X4 antagonist of the present series was N-(benzyloxycarbonyl)phenoxazine (26, PSB-12054) with an IC(50) of 0.189 μM and good selectivity versus the other human P2X receptor subtypes. N-(p-Methylphenylsulfonyl)phenoxazine (21, PSB-12062) was identified as a selective P2X4 antagonist that was equally potent in all three species (IC(50): 0.928-1.76 μM). The compounds showed an allosteric mechanism of action. The present study represents the first structure-activity relationship analysis of P2X4 antagonists.

Interactions of Calix[n]arenes with Nucleic Acids

DNA interaction with artificial binders is of great interest, especially in light of the broad range of possible biomedical applications. The growing understanding of replication, transcription and translation opened the path for new approaches to target pathological effects at a very early stage. Meanwhile, the competitive binding to nucleic acids by designed molecules, which, for example, block certain sequences for natural binders, such as transcription factors, has become a promising concept in the context of gene therapy. On the other extreme, the transport of nucleic acids over the cell membrane into the nucleus by transfection agents opens the possibility to reprogram protein biosynthesis within host cells.

In the past decades several substance classes have been developed for a noncovalent specific DNA binding with predictable biological effects, such as peptide nucleic acids or polyamide ligands. Calixarenes have not received so much attention, although they consist of a compact aromatic core tuneable in size, and allow the introduction of cationic functionalities at their upper and lower rims. Formerly being utilized as receptor moieties due to the possibility of complexating guests in their cavities, calixarenes are now also used as molecular scaffolds for multivalent ligands and are, therefore, suitable tools for cooperative DNA complexation.

This review surveys specific supramolecular interactions between calixarene derivatives and nucleic acids, with an emphasis on structural elements in the calixarenes and the biological consequences of their complex formation with DNA strands.