Quantifying methyl tunneling induced (de)coherence of nitroxides in glassy <i>ortho</i>-terphenyl at low temperatures

Eggeling, Andrea; Soetbeer, Janne; Ibáñez, Luis Fábregas; Klose, Daniel; Jeschke, Gunnar

doi:10.1039/d3cp01299a

Cited by 12 publications

(22 citation statements)

References 64 publications

(134 reference statements)

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“…As a plausible explanation of these experimental results, we suggest that the low-temperature dynamics of methyl (and potentially amino) groups govern decoherence in photosynthetic proteins. This is in agreement with several experimental and theoretical studies on the model systems, where methyl group rotation, libration, and tunneling have been shown to substantially enhance decoherence at low temperatures. − It is quite likely that similar factors also limit the coherence time in other photosynthetic RC proteins.…”

Section: Introductionsupporting

confidence: 88%

“…Less intuitively, methyl groups can still enhance decoherence at low temperatures via tunneling, which is observed even at very low temperatures such as a few kelvin. 44,45,47,48,64,65 As a plausible explanation of our experimental results, we suggest that this low-temperature dynamics of methyl groups, and potentially similar dynamics involving amino groups, in protein microenvironments surrounding the spin-carrying donor/acceptor cofactors provides an additional mechanism for decoherence and leads to the short times observed here. Analysis of the crystal structure of PSI revealed that many methyl groups in the close surrounding of the cofactors P 700 and A 1 are present.…”

Section: The Journal Of Physical Chemistry B Pubsacsorg/jpcb Articlesupporting

confidence: 62%

“…Instead, we speculate that the observed unusually short coherence times and their almost independence of isotopic composition of PSI (protonated or deuterated) can be explained by the protein microenvironment of the electron spins, which is substantially different from the commonly used protonated vitrified solutions. Indeed, it was reported previously 39,44,45,47,48,64,65 that in the solvents containing methyl groups, the echo decay of stable organic radicals is much faster than in solvents without methyl groups, even at low temperatures. This was explained by the particular molecular dynamics of methyl groups.…”

Section: The Journal Of Physical Chemistry B Pubsacsorg/jpcb Articlementioning

confidence: 97%

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Coherences of Photoinduced Electron Spin Qubit Pair States in Photosystem I

Bindra,

Niklas,

Jeong

et al. 2023

J. Phys. Chem. B

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This publication presents the first comprehensive experimental study of electron spin coherences in photosynthetic reaction center proteins, specifically focusing on photosystem I (PSI). The ultrafast electron transfer in PSI generates spin-correlated radical pairs (SCRPs), which are entangled spin pairs formed in well-defined spin states (Bell states). Since their discovery in our group in the 1980s, SCRPs have been extensively used to enhance our understanding of structure−function relationships in photosynthetic proteins. More recently, SCRPs have been utilized as tools for quantum sensing. Electron spin decoherence poses a significant challenge in realizing practical applications of electron spin qubits, particularly the creation of quantum entanglement between multiple electron spins. This work is focused on the systematic characterization of decoherence in SCRPs of PSI. These decoherence times were measured as electron spin echo decay times, termed phase memory times (T M ), at various temperatures. Decoherence was recorded on both transient SCRP states P 700 + A 1 − and thermalized states. Our study reveals that T M exhibits minimal dependence on the biological species, biochemical treatment, and paramagnetic species. The analysis indicates that nuclear spin diffusion and instantaneous diffusion mechanisms alone cannot explain the observed decoherence. As a plausible explanation we discuss the assumption that the low-temperature dynamics of methyl groups in the protein surrounding the unpaired electron spin centers is the main factor governing the loss of the spin coherence in PSI.

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Section: Introductionsupporting

confidence: 88%

Section: The Journal Of Physical Chemistry B Pubsacsorg/jpcb Articlesupporting

confidence: 62%

Section: The Journal Of Physical Chemistry B Pubsacsorg/jpcb Articlementioning

confidence: 97%

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Coherences of Photoinduced Electron Spin Qubit Pair States in Photosystem I

Bindra,

Niklas,

Jeong

et al. 2023

J. Phys. Chem. B

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“…Nitroxide radicals, including piperidine nitroxides, have important applications in biophysics as spin labels, especially for EPR distance measurements in biomolecules. − The distance measurements, especially few-nm long, require spin labels with long electron spin coherence times T m of the order of a few μs, preferably at temperatures above 80 K. In typical gem -dimethyl nitroxides, the onset of rotation of methyl groups on the EPR time scale at T > 80 K lowers T m significantly. − To solve this problem, a number of “methyl-less” spin labels were prepared; − for example, Spiro-IA enabled EPR distance measurements in immobilized proteins at room temperature, and diazaadamantane derivative IA-DZD was used to demonstrate the supramolecular approach to EPR distance measurement in proteins up to 150 K (Figure ). …”

Section: Persistent and Stable Monoradicals As Spin Centersmentioning

confidence: 99%

From Stable Radicals to Thermally Robust High-Spin Diradicals and Triradicals

Shu,

Yang,

Rajca

2023

Chem. Rev.

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Stable radicals and thermally robust high-spin di-and triradicals have emerged as important organic materials due to their promising applications in diverse fields. New fundamental properties, such as SOMO/HOMO inversion of orbital energies, are explored for the design of new stable radicals, including highly luminescent ones with good photostability. A relation with the singlet−triplet energy gap in the corresponding diradicals is proposed. Thermally robust high-spin di-and triradicals, with energy gaps that are comparable to or greater than a thermal energy at room temperature, are more challenging to synthesize but more rewarding. We summarize a number of high-spin di-and triradicals, based on nitronyl nitroxides that provide a relation between the experimental pairwise exchange coupling constant J/k in the high-spin species vs experimental hyperfine coupling constants in the corresponding monoradicals. This relation allows us to identify outliers, which may correspond to radicals where J/k is not measured with sufficient accuracy. Double helical high-spin diradicals, in which spin density is delocalized over the chiral π-system, have been barely explored, with the sole example of such high-spin diradical possessing alternant π-system with Kekuléresonance form. Finally, we discuss a high-spin diradical with electrical conductivity and derivatives of triangulene diradicals.

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“…Tremendous efforts have been made to probe macromolecules in natural biological systems that can provide insight into their structures and functions. Site-directed spin labeling (SDSL) pulsed electron paramagnetic resonance (EPR) dipolar spectroscopy (PDS), which includes double electron–electron resonance (DEER) and double quantum coherence (DQC), is among the best techniques for accurate measurement of the conformations of flexible regions of biomolecules. − The advantages include high sensitivity, wide dynamic range, absolute distance distributions, and minimal structural perturbation from relatively small-size nitroxide spin labels. , The most widely used spin label for SDSL is methane thiosulfonate pyrroline nitroxide (MTSL), which selectively binds to cysteine, that can be introduced at selected locations by mutagenesis to provide doubly labeled proteins. , Using nitroxides, these measurements require cryogenic temperatures because of the dynamic averaging effects associated with methyl group rotation, which shorten the electron spin coherence time ( T m ) between about 80 and 300 K. − …”

Section: Introductionmentioning

confidence: 99%

Cucurbit[7]uril Enhances Distance Measurements of Spin-Labeled Proteins

Yang,

Stein,

Pink

et al. 2023

J. Am. Chem. Soc.

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We report complex formation between the chloroacetamide 2,6-diazaadamantane nitroxide radical (ClA-DZD) and cucurbit[7]uril (CB-7), for which the association constant in water, K a = 1.9 × 106 M–1, is at least 1 order of magnitude higher than the previously studied organic radicals. The radical is highly immobilized by CB-7, as indicated by the increase in the rotational correlation time, τrot, by a factor of 36, relative to that in the buffer solution. The X-ray structure of ClA-DZD@CB-7 shows the encapsulated DZD guest inside the undistorted CB-7 host, with the pendant group protruding outside. Upon addition of CB-7 to T4 Lysozyme (T4L) doubly spin-labeled with the iodoacetamide derivative of DZD, we observe the increase in τrot and electron spin coherence time, T m, along with the narrowing of interspin distance distributions. Sensitivity of the DEER measurements at 83 K increases by a factor 4–9, compared to the common spin label such as MTSL, which is not affected by CB-7. Interspin distances of 3 nm could be reliably measured in water/glycerol up to temperatures near the glass transition/melting temperature of the matrix at 200 K, thus bringing us closer to the goal of supramolecular recognition-enabled long-distance DEER measurements at near physiological temperatures. The X-ray structure of DZD-T4L 65 at 1.12 Å resolution allows for unambiguous modeling of the DZD label (0.88 occupancy), indicating an undisturbed structure and conformation of the protein.

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Quantifying methyl tunneling induced (de)coherence of nitroxides in glassy ortho-terphenyl at low temperatures

Abstract: The low-temperature Hahn echo decay signal of the pyrroline-based nitroxide H-mNOHex in ortho- terphenyl (OTP) shows two contributions on distinct time scales. Tunneling of the nitroxide’s methyl groups cause electron...

Cited by 12 publications

References 64 publications

Coherences of Photoinduced Electron Spin Qubit Pair States in Photosystem I

Coherences of Photoinduced Electron Spin Qubit Pair States in Photosystem I

From Stable Radicals to Thermally Robust High-Spin Diradicals and Triradicals

Cucurbit[7]uril Enhances Distance Measurements of Spin-Labeled Proteins

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