ENDOR Spectroscopic and Molecular Orbital Study of the Dynamical Properties of the Side Chain in Radical Anions of Ubiquinones Q-1, Q-2, Q-6, and Q-10

Lehtovuori, Pekka; Joela, Heikki

doi:10.1006/jmre.2000.2099

Cited by 9 publications

(9 citation statements)

References 22 publications

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“…4 Earlier we calculated and measured similar side chain dynamics of ubiquinones Q-n, which have an isoprenic side chain like that of tocotrienol. 15,16 Dynamic processes were measured as dependence of temperature in the region of 200-330 K in liquid solutions. The fact that the primary radical reacts very sensitively to subsequent radical species causes additional difficulties.…”

Section: Resultsmentioning

confidence: 99%

Radical cations of vitamin E

Lehtovuori

Joela

2002

Phys. Chem. Chem. Phys.

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Radical cations of vitamin E compounds (a-, b-, gand d-tocopherols and a-, b-, gand d-tocotrienols) were for the first time successfully prepared in different solvents. Their unpaired electron distribution was solved by means of EPR and ENDOR spectroscopy and assignment of isotropic hyperfine couplings was performed. The isotropic hyperfine coupling constants calculated theoretically (UB3LYP) were comparable to those studied experimentally. Radical cations were observed to exist as an intermediate product in the formation of the neutral radical. Moreover, loosening the proton from the radical cation of a-tocopherol and from a-tocotrienol produced the neutral radical, which was detected in the ENDOR spectrum. The potency of the hydroxyl proton of the radical cation for further reactions as a measure of the biological activity of various tocopherol and tocotrienol compound is discussed.

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Section: Resultsmentioning

confidence: 99%

Radical cations of vitamin E

Lehtovuori

Joela

2002

Phys. Chem. Chem. Phys.

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“…Because of the intrinsic asymmetry of CoQ1, the CH 3 -protons of the methoxy-group(s) have rather small couplings that were not resolved in the EPR spectra. 39,40 In strong alkaline solutions (0.1 M NaOH), but in the absence of a reducing agent, an identical 9-line spectrum appeared. This radical signal showed a pronounced time dependence, with increasing intensity (i.e., radical concentration) after a short lag time (∼5 min at pH of 13) ( Figure 2B) for about 2 h, and was stable for several hours afterward.…”

Section: ' Materials and Methodsmentioning

confidence: 94%

Calcium Binding and Transport by Coenzyme Q

et al. 2011

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Coenzyme Q10 (CoQ10) is one of the essential components of the mitochondrial electron-transport chain (ETC) with the primary function to transfer electrons along and protons across the inner mitochondrial membrane (IMM). The concomitant proton gradient across the IMM is essential for the process of oxidative phosphorylation and consequently ATP production. Cytochrome P450 (CYP450) monoxygenase enzymes are known to induce structural changes in a variety of compounds and are expressed in the IMM. However, it is unknown if CYP450 interacts with CoQ10 and how such an interaction would affect mitochondrial function. Using voltammetry, UV–vis spectrometry, electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), fluorescence microscopy and high performance liquid chromatography–mass spectrometry (HPLC–MS), we show that both CoQ10 and its analogue CoQ1, when exposed to CYP450 or alkaline media, undergo structural changes through a complex reaction pathway and form quinone structures with distinct properties. Hereby, one or both methoxy groups at positions 2 and 3 on the quinone ring are replaced by hydroxyl groups in a time-dependent manner. In comparison with the native forms, the electrochemically reduced forms of the new hydroxylated CoQs have higher antioxidative potential and are also now able to bind and transport Ca2+ across artificial biomimetic membranes. Our results open new perspectives on the physiological importance of CoQ10 and its analogues, not only as electron and proton transporters, but also as potential regulators of mitochondrial Ca2+ and redox homeostasis.

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“…In our studies on ubiquinones, , we noticed strange lines in the LF region of the ENDOR spectrum. When certain EPR lines were radiated, prominent lines or line pairs (couplings) in the LF region were present that could not be assigned properly.…”

Section: Introductionmentioning

confidence: 52%

Two-Photon Transitions in CW-ENDOR Spectra of Radicals in Fluid Solution

Lehtovuori

Joela

2002

J. Phys. Chem. A

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The radical anion of duroquinone (2,3,5,6-tetramethyl-1,4-benzoquinone) was used as a model compound to describe the low-frequency (LF) ENDOR lines observed in many radical systems. These LF lines are shown to arise from two-photon transitions, and they occur because of the rapid cross-relaxation rates and dynamical processes of the system. The LF lines occur when the radio frequency (RF) and microwave frequency match the energy of an adjacent EPR transition. In practical work, LF ENDOR lines disturb the determination of nuclei such as 2H, 13C, Na, and K, whose Larmor frequencies are in that region. Under certain conditions, two-photon transitions were also observed in the normal proton coupling region. A method for distinguishing normal ENDOR lines from two-photon transitions is given. The method is based on the different shape of an ENDOR-induced EPR spectrum when it is measured from two-photon-transition ENDOR lines.

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ENDOR Spectroscopic and Molecular Orbital Study of the Dynamical Properties of the Side Chain in Radical Anions of Ubiquinones Q-1, Q-2, Q-6, and Q-10

Cited by 9 publications

References 22 publications

Radical cations of vitamin E

Radical cations of vitamin E

Calcium Binding and Transport by Coenzyme Q

Two-Photon Transitions in CW-ENDOR Spectra of Radicals in Fluid Solution

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