Correlation between Hydrogen Bonding Association Constants in Solution with Quantum Chemistry Indexes: The Case of Successive Association between Reduced Species of Quinones and Methanol

The functional M05-2X together with the SMD solvent model have been used to calculate hydrogen bonding association constants in dimethylsulfoxide (DMSO) solution. Data of equilibrium constants in DMSO for the case of electrochemically generated dianions interacting with methanol have been considered to test the reliability of the chemistry theoretical approach. From this approach, it was found that the successive association constants involved in the formation of the complexes depend on a linear combination of three quantum chemistry indexes which are the ionization energy, the electron affinity, and the charge on the oxygen atom receiving the methanol molecule. Under this perspective, the stoichiometry of all the dianion–methanol complexes was explained on the basis of the relative strength of the hydrogen bonding interaction compared to that of the methanol–DMSO and methanol dimer complexes. This linear combination seems to be valid regardless of the nature of the dianion structure and the number of methanol molecules in the complex, which is a relevant finding to generalize the applicability of both the functional M05-2X and the SMD solvent model, to calculate association constants for any other neutral or anionic molecules interacting by hydrogen bonding with proton donors

Tacticity Influence on the Electrochemical Reactivity of Group Transfer Polymerization-Synthesized PTMA

Spectroscopic, thermal, and electrochemical characterization results are presented for the redox active polymer poly­(2,2,6,6-tetramethyl-1-piperinidyloxy-4-yl methacrylate) or PTMA, synthesized by group transfer polymerization (GTP), and its precursors 4-hydroxy-tetramethylpiperidine-<i>N</i>-oxyl (HO-TEMPO) and 4-methacryloyloxy-tetramethylpiperidine-<i>N</i>-oxyl (MO-TEMPO). DSC analysis of synthesized PTMA showed that the glass transition temperature (<i>T</i>_g) of the polymer structure occurs at 155 °C, corroborated by dynamic mechanical analysis (DMA), which is higher when compared with <i>T</i>_g data for PTMA synthesized by other methods. Also, the amount of radical species present in PTMA synthesized by GTP reactions (100%) is higher than the values typically upon synthesizing PTMA by radical polymerization. Electrochemical and spectroelectrochemical-electron spin resonance studies in acetonitrile revealed two redox events in the PTMA polymer, one of which is reversible, accounting for ca. 80% of the spins in the polymer and giving rise to the battery behavior. The other redox event is irreversible, accounting for the remaining ca. 20% of spins, which has not previously been reported. These two redox events are linked to a structural property associated with the tacticity of the polymer, where the reversible feature (responsible for cathode behavior) is the dominant species. This corresponds to a number of isotactic domains of the polymer (determined by high temperature ¹H NMR). The second feature accounts for the three-line impurity observed in the ESR, which has been reported previously but poorly explained, associated to the number of heterotactic/syndiotactic triads

MDN-0185, an Antiplasmodial Polycyclic Xanthone Isolated from <i>Micromonospora</i> sp. CA-256353

A potent antiplasmodial polycyclic xanthone, MDN-0185 (<b>1</b>), was isolated from an unidentified species of the genus <i>Micromonospora</i>. The planar structure of <b>1</b> was established as a seven-ring polycyclic xanthone with partial structures very similar to two known natural products, namely, xantholipin and Sch 54445. Using ROESY correlations, the relative stereochemistry of the two independent stereoclusters of compound <b>1</b> could be determined. Mosher analysis and comparison of the specific rotation of compound <b>1</b> with that of xantholipin allowed the determination of its absolute configuration. Compound <b>1</b> exhibited an IC₅₀ of 9 nM against <i>Plasmodium falciparum</i> 3D7 parasites