Supramolecular inter-ionic charge-transfer complexes between derivatives of pyridinium-4-oxime cations and hexacyanoferrate(ii) anions

Abstract

Mono- and bis-pyridinium-4-oxime compounds are introduced as new electron acceptors for the formation of colored, supramolecular, inter-ionic charge-transfer complexes with hexacyanoferrate(ii) as a donor.

Novel Insights into the Thioesterolytic Activity of N-Substituted Pyridinium-4-oximes

“…The final single-point energies were attained with a highly flexible 6-311++G(2df,2pd) basis set using the M06-2X functional, which was designed to provide highly accurate thermodynamic and kinetic parameters for various organic systems. To account for the effects of the aqueous solution we included, during both the geometry optimization and the single-point energy evaluation, a conductor-like polarizable continuum model (CPCM) with all of the parameters for pure water, giving rise to the (CPCM)/M06-2X/6-311++G(2df,2pd)//(CPCM)/M06-2X/6-31+G(d) model employed here, being in line with our earlier reports on similar systems [11,14,34,35]. Additionally, no basis set superposition error correction was employed as both the size and the flexibility of the utilized 6-311++G(2df,2pd) basis set warrants that such corrections would only be marginal.…”

“…Moreover, the reaction with both oximes is exergonic (∆G R COMP = −12.1 kJ•mol −1 for PAM4 and ∆G R COMP = −10.0 kJ•mol −1 for BPA4), the difference being only 2.1 kJ•mol −1 in favor of PAM4. The similar reactivity, that is, electronic properties of these two pyridinium-4-oximes has been recently established by the analysis of the corresponding frontier orbitals where it becomes clear that no significant electron density is observed in the additional phenyl ring in the LUMO of BPA4 + , while the majority of the electron density is located in the pyridinium-4-oxime moiety, just as in PAM4 + [14]. As was previously recognized for the reactivity of pyridinium-oximes toward the AcSCh + , the reactivity differences did not origin from different electron density on the oxygen of the oximate but was caused with the steric hindrance of the oxime group by the rest of the molecule, resulting in higher reactivity of the oxime group in para-position than those in ortho-position [8,9,22].…”

“…However, these pharmacological compounds possess multiple modes of action and alternative bioactivities are an active research topic. A particular focus is placed on electron and charge transfer processes where pyridinium-4-oxime cations are recognized as new electron acceptors for the formation of colored, supramolecular, inter-ionic charge-transfer complexes with hexacyanoferrate(II) anion [14].…”

“…To provide insights into the role of pyridinium oximes such as pseudo-hydrolases (thioesterases), two well-defined pyridinium-4-oximes, N-methylpyridinium-4-oxime iodide (PAM4 + I − ) and N-benzylpyridinium-4-oxime chloride (BPA4 + Cl − ) [14,24], have been tested as oximolytic agents toward the AcSCh + . To complete the cycle of the pyridinium-4-oximate promoted reactions, the hydrolytic susceptibility of the newly synthetized pyridinium-4-oxime-ester, O-acetyl-N-methylpyridinium-4-oxime iodide (AcPAM4 + I − ), has been separately investigated.…”

Supramolecular Solid Complexes between Bis-pyridinium-4-oxime and Distinctive Cyanoiron Platforms

“…The enhanced bioactivity of bis-pyridinium salts, like TOXO itself, has been attributed to improved binding orientation, but from the electrochemical viewpoint, a second electroactive pyridinium-4-oxime moiety might elicit an enhanced electrical response [3]. Focused on electron-and charge-transfer processes, pyridinium-4-oxime cations have recently been recognized as new electron acceptors for the formation of colored, supramolecular, inter-ionic charge-transfer complexes, with the hexacyanoferrate(II) anion as a donor [8]. The use of highly charged cyanoiron donors and N-heterocyclic mono-and dications to build supramolecular charge-transfer complexes has attracted much attention, especially with the 4,4 ′ -dipyridinium dication (viologen) and its derivatives [9].…”