β‐Cyclodextrin Duplexes That Are Connected through Two Disulfide Bonds: Potent Hosts for the Complexation of Organic Molecules

New tubular host molecules, which are composed of two β‐cyclodextrin macrocycles that are connected through two disulfide bonds, have been prepared by the air‐promoted oxidation of 6^I,6^IV‐dideoxy‐6^I,6^IV‐disulfanyl‐β‐cyclodextrin in aqueous solution. This reaction leads to three products: monomeric intramolecular disulfide and two dimeric species, which are termed as “non‐eclipsed” and “eclipsed” cyclodextrin duplexes. Oxidation at a concentration of the starting thiol of 0.1 mM gave the intramolecular disulfide as the major product whereas a concentration in the millimolar range afforded the dimeric species as the dominant products. The tubular structure of the “non‐eclipsed” isomer was unequivocally determined by X‐ray analysis. The binding affinities of the duplexes to a wide range of compounds, including fluorescent dyes and clinically used drugs Imatinib and Esomeprazol, were studied in water by ITC. For most guest compounds, the experimentally determined K_a values were in the range 10⁷–10⁸ M ^?1. These binding affinities are significantly higher than those found in the literature for analogous complexes with native cyclodextrins. In cases of binding of neutral or anionic guest molecules cyclodextrin duplexes outperformed cucurbiturils. A complex between a duplex and Nile blue was used to investigate its ability to penetrate the cytoplasmic membrane of HeLa cells. We found that the complex accumulated in the cell membrane but did not pass into cytosol. Importantly, the complex did not decompose to a significant extent under high dilution in the cellular environment.     

Optimisation of the dipole-Coulomb approximation for high-l Rydberg states of polar molecules

ABSTRACT

The present work deals with the question of the origin choice to get the maximal accuracy of the dipole-Coulomb approximation in the theory of molecular Rydberg states with high orbital momentum l. Concerning birefringence in polar molecules, the question of adequate origin choice has first been raised in the classical work by Buckingham & Longuet-Higgins in 1968, where it has been taken into account that the dipole moment of a polar molecular core (cation) depends on the origin choice. This dependence also leads to inseparability of dipole and quadrupole corrections to the Rydberg electron spectra in polar molecules. In the present work a new option for the problem is proposed as applied to the dipole-Coulomb approximation. Considering a simplified model of a molecular core as a system of N effective fixed point charges, we show both analytically and numerically that the optimal choice of origin, at least for a linear core, is the geometric centre of the core. On the other hand, results of the present work as well as previous publications show that the problem raised by Buckingham and Longuet-Higgins does not have a universal solution.

Abbreviations: RS: Rydberg state; RSs: Rydberg states; ZEKE: zero electron kinetic energy; MATI: mass-analysed threshold ionisation; QDT: quantum defect theory; DCA: dipole-Couloumb approximation; CD: centre of dipole; CC: centre of charge; GC: geometric centre; DCAGC: dipole-Couloumb approximation with origin in the geometric centre; DCACD: dipole-Couloumb approximation with origin in the centre of dipole     

Flash memory cells data loss caused by total ionizing dose and heavy ions

The paper provides experimental results of flash memory loss data investigation. Possible mechanisms of charge loss from storage element are reviewed. We provide some guidelines for flash memory evaluation to space application.     

Synthesis of Novel Saccharide Hydrazones

Synthesis of important heterocyclic hydrazine derivatives N-aminopyrrolidine, N-aminopiperidine, and N-aminoazepane from hydrazine hydrate and dihalogenides were examined and optimized. These heterocyclic hydrazine derivatives were used in condensation reactions with six different monosaccharides to form corresponding hydrazones. Biological evaluations of these novel compounds, which are simple acyclic nucleoside analogs, were done. L-Arabinose N-aminoazepane hydrazone showed minor anti-HIV activity, giving a starting point for further structural modifications.     

Impedimetric DNA Sensor Based on Poly(proflavine) for Determination of Anthracycline Drugs

Electropolymerization is often used as a tool for immobilization of charged biopolymers and their electric wiring in the biosensor assembly. In this work, electropolymerization of proflavine has been for the first time used for the physical adsorption of DNA and measurement of anthracycline drugs (doxorubicin and daunorubicin) able to intercalate DNA. Redox properties of the proflavine polymers on the glassy carbon electrode and DNA deposition were characterized with cyclic voltammetry, scanning electron microscopy and electrochemical impedance spectroscopy. It was shown that DNA decreased the peak currents on voltammogram but increased the charge transfer resistance. The latter effect is pronounced with the following drug application. The impedimetric response regularly increased with the drugs concentration in the range 1 nM to 0.1 μM for doxorubicin and 1 pM–10 nM for daunorubicin (limit of detections 0.3 and 0.001 nM, respectively). The biosensor was tested on pharmaceutical preparations and spiked solution simulating the plasma electrolytes and possible interference of serum proteins.