ESI-MS characterization of a novel pyrrole-inosine nucleoside that interacts with guanine bases

Based on binding studies undertaken by electrospray ionization-mass spectrometry, a synthetic pyrrole-inosine nucleoside, 1, capable of forming an extended three-point Hoogsteen-type hydrogen-bonding interaction with guanine, is shown to form specific complexes with two different quadruplex DNA structures [dTG₄T]₄ and d(T₂G₄)₄ as well as guanine-rich duplex DNA. The binding interactions of two other analogs were evaluated in order to unravel the structural features that contribute to specific DNA recognition. The importance of the Hoogsteen interactions was confirmed through the absence of specific binding when the pyrrole NH hydrogen-bonding site was blocked or removed. While 2, with a large blocking group, was not found to interact with virtually any form of DNA, 3, with the pyrrole functionality missing, was found to interact non-specifically with several types of DNA. The specific binding of 1 to guanine-rich DNA emphasizes the necessity of careful ligand design for specific sequence recognition.     

Binuclear fluoro-bridged zinc and cadmium complexes of a schiff base expanded porphyrin: fluoride abstraction from the tetrafluoroborate anion

Reactions of the Schiff base oligopyrrolic octaazamacrocycle 1 with BF4- salts of divalent zinc and cadmium result in fluoride anion abstraction and the formation of difluoride-bridged metal complexes. X-ray diffraction analyses provide support for the notion that hydrogen-bonding interactions, involving the N-H groups of the macrocycle and the coordinated fluoride ions, play an important role in stabilizing these new complexes.     

A facile synthesis of cyclononatripyrroles

A facile synthesis of a functionalized cyclononatripyrrole derivative is described. It involves the iodine-catalyzed cyclotrimerization of ethyl 3,3-dimethyl-5,7-dihydro[1,3]dioxepino[5,6-c]pyrrole-6-carboxylate in methanol. The product obtained in this way exists solely in the crown conformation typical of cyclononatripyrroles. However, in contrast to previously reported compounds of this class, it possesses three labile methoxymethyl arms that can be further functionalized under acidic conditions.     

Palladium induced macrocyclic preorganization for stabilization of a tetrathiafulvalene mixed-valence dimer

Ditopic metalation of a flexible "Pacman"-like tetrathiafulvalene (TTF) modified Schiff-base-calixpyrrole results in the stabilization upon oxidation of an otherwise difficult-to-access mixed-valence TTF radical dimer. EPR and optical spectroscopies were used to characterize the mixed-valence species.     

High-order tunneling processes in single-porphyrin transistors

Cotunneling and the Kondo effect are observed in single-electron transistors incorporating cobalt-porphyrins. These effects are attributed to high-order tunneling and strong coupling between the electrodes and the intervening porphyrin.     

Decoration of Gold Nanoparticles by a Double‐Armed Calix[4]pyrrole: A Receptor‐Decorated Nanoensemble for Anion Sensing and Extraction

Gold nanoparticles decorated with a double‐armed, deep‐cavity calix[4]pyrrole were prepared and fully characterized. Transmission electron microscopy imaging revealed that the average diameter of the particles was approximately 4 nm both before and after attachment of the receptor to the surface. The calix[4]pyrrole‐functionalized nanoparticles exhibited highly elevated sensing behavior (approximately 1000 times in dichloromethane) relative to its monomeric congener while maintaining its guest selectivity. The receptor–nanoparticle conjugate (nanoreceptor) showed significant aggregation upon addition of the biphenolate anion, an effect ascribed to anion‐mediated interparticle linking. The receptor–nanoparticle conjugate is also capable of extracting the fluoride anion (as its tetrabutylammonium salt) from an aqueous layer to an organic medium. Control experiments revealed that this extraction is not possible when using the analogous monomeric receptor.     

Stochasticity in many-dimensional nonlinear oscillating systems

Qualitative analytic estimates of the stochasticity limit of one- and many-dimensional nonlinear oscillating systems are derived using the overlapping of first-order resonances as a criterion for stochasticity. Computational results obtained with several very simple transformations are compared with the analytic estimates. Numerical studies significantly below the stochasticity limit of a many-dimensional nonlinear system reveal an example of a very slow instability, the first, to the best of our knowledge.