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Origin and Scope of Long-Range Stabilizing Interactions and Associated SOMO–HOMO Conversion in Distonic Radical Anions

Abstract (Expand)

High-level quantum-chemical methods have been used to study the scope and physical origin of the significant long-range stabilizing interactions between nonmutually conjugated anion and radical moieties … in SOMO–HOMO converted distonic radical anions. In such species, deprotonation of the acid fragment can stabilize the remote radical by tens of kilojoules, or, analogously, formation of a stable radical (by abstraction or homolytic cleavage reactions) increases the acidity of a remote acid by several pKa units. This stabilization can be broadly classified as a new type of polar effect that originates in Coloumbic interactions but, in contrast to standard polar effects, persists in radicals with no charge-separated (i.e., dipole) resonance contributors, is nondirectional, and hence of extremely broad scope. The stabilization upon deprotonation is largest when a highly delocalized radical is combined with an initially less stable anion (i.e., the conjugate base of a weaker acid), and is negligible for highly localized radicals and/or stable anions. The effect is largest in the gas phase and low-polarity solvents but is quenched in water, where the anion is sufficiently stabilized. These simple rules can be employed to design various switchable compounds able to reversibly release radicals in response to pH for use in, for example, organic synthesis or nitroxide-mediated polymerization. Moreover, given its wide chemical scope, this effect is likely to influence the protonation state of many biological substrates under radical attack and may contribute to enzyme catalysis.

Authors: Ganna Gryn’ova, Michelle L. Coote

Date Published: 3rd Oct 2013

Publication Type: Journal

Organism-Adapted Specificity of the Allosteric Regulation of Pyruvate Kinase in Lactic Acid Bacteria

Abstract

Not specified

Authors: Nadine Veith, Anna Feldman-Salit, Vlad Cojocaru, Stefan Henrich, Ursula Kummer, Rebecca C. Wade

Date Published: 25th Jul 2013

Publication Type: Journal

Regulation of the Activity of Lactate Dehydrogenases from Four Lactic Acid Bacteria

Abstract

Not specified

Authors: Anna Feldman-Salit, Silvio Hering, Hanan L. Messiha, Nadine Veith, Vlad Cojocaru, Antje Sieg, Hans V. Westerhoff, Bernd Kreikemeyer, Rebecca C. Wade, Tomas Fiedler

Date Published: 19th Jul 2013

Publication Type: Journal

Brownian dynamics simulation of protein diffusion in crowded environments

Abstract

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Authors: Paolo Mereghetti, Rebecca C. Wade

Date Published: 18th Jul 2013

Publication Type: Proceedings

Dynamic enzyme docking to the ribosome coordinates N-terminal processing with polypeptide folding

Abstract

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Authors: Arzu Sandikci, Felix Gloge, Michael Martinez, Matthias P Mayer, Rebecca Wade, Bernd Bukau, Günter Kramer

Date Published: 1st Jul 2013

Publication Type: Journal

Learning morphological maps of galaxies with unsupervised regression

Abstract

Not specified

Authors: Oliver Kramer, Fabian Gieseke, Kai Lars Polsterer

Date Published: 1st Jun 2013

Publication Type: Journal

Switching Radical Stability by pH-Induced Orbital Conversion

Abstract (Expand)

In most radicals the singly occupied molecular orbital (SOMO) is the highest-energy occupied molecular orbital (HOMO); however, in a small number of reported compounds this is not the case. In the … present work we expand significantly the scope of this phenomenon, known as SOMO–HOMO energy-level conversion, by showing that it occurs in virtually any distonic radical anion that contains a sufficiently stabilized radical (aminoxyl, peroxyl, aminyl) non-π-conjugated with a negative charge (carboxylate, phosphate, sulfate). Moreover, regular orbital order is restored on protonation of the anionic fragment, and hence the orbital configuration can be switched by pH. Most importantly, our theoretical and experimental results reveal a dramatically higher radical stability and proton acidity of such distonic radical anions. Changing radical stability by 3–4 orders of magnitude using pH-induced orbital conversion opens a variety of attractive industrial applications, including pH-switchable nitroxide-mediated polymerization, and it might be exploited in nature.

Authors: Ganna Gryn'ova, David L. Marshall, Stephen J. Blanksby, Michelle L. Coote

Date Published: 1st Jun 2013

Publication Type: Journal

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