Abstract
ABSTRACTThe quinone compound 2,6-dimethoxy-1,4-benzoquinone is hydroxylated in alkaline aqueous solution with pH above 12. Electron paramagnetic resonance experiments showed that two transient radicals are formed in this reaction. The radical appearing first is assigned to a one electron reduced 2,6-dimethoxy-1,4-benzoquinone, receiving the electron from an intermediate anionic hydroxylated species. For this primary radical, all proton couplings were determined (quinoid ring protons: 1.453 G, methyl protons: 0.795 G). The density functional theory method was applied to obtain electronic and structural information of the primary radical and a solution structure is suggested. For approaching the experimental hyperfine couplings in theoretical models, it was necessary to consider effects of external polarisation arising from water molecules near one carbonyl group, and the orientation of methoxy groups towards the quinone ring. With this approach, the secondary radical formed in the hydroxylation reaction, and the transient radicals found for other biologically important quinones (including coenzymes Q) and their hydroxylated species may become accessible.
Highlights
Quinones have received great attention in chemistry because these compounds are involved in many fundamental processes ranging from simple organic reactions [1,2] to industrially applied polymerisation reactions [3,4,5,6]
We focus on spectroscopic properties as well as the electronic structure and hyperfine couplings of the primary radical which is formed in the initial phase of the hydroxylation reaction, and which plays a pivotal role in the transformation of 2,6-DBQ
The primary radical of 2,6-dimethoxy-1,4benzoquinone generated by a single electron transfer in alkaline medium was analysed in detail by density functional theory (DFT) methods to obtain insights into the structure of this transient species
Summary
Quinones have received great attention in chemistry because these compounds are involved in many fundamental processes ranging from simple organic reactions [1,2] to industrially applied polymerisation reactions [3,4,5,6]. Bennett et al [13] demonstrated that synthetic 2-palmytoylhydroquinone (2PHQ) is capable to transfer calcium ions across a liposome bilayer in a redox dependent manner. Mirceski et al [14] have shown mainly by voltammetric techniques that reduced 2PHQ can bind and transfer Ca2+, and other divalent ions such as Ba2+, Sr2+ or Mg2+ Both studies revealed the crucial role of two adjacent oxygen atoms for providing a redox dependent complexation site. Such a structural configuration is not present in naturally occurring coenzymes like Q10 or the related compound Q1. We have recently shown that in alkaline aqueous solutions or upon action of cytochrome P450, hydroxylated derivatives of Q1 and Q10 are formed which bind
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
