Predicting the paramagnet-enhanced NMR relaxation of H<sub>2</sub>encapsulated in endofullerene nitroxides by density-functional theory calculations

Rastrelli, Federico; Frezzato, Diego; Lawler, Ronald G.; Li, Yongjun; Turro, Nicholas J.; Bagno, Alessandro

doi:10.1098/rsta.2011.0634

Cited by 5 publications

(10 citation statements)

References 46 publications

(74 reference statements)

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“…As mentioned above, this approach is questionable for H 2 @C 60 . Nevertheless, in a related work in this Theo Murphy Meeting Issue [42], we have demonstrated that, at least at room temperature, the error involved in treating the motion of H 2 classically is negligible. A final issue concerns the open-shell nature of the species.…”

Section: Density Functional Theory Calculations Of the Hyperfine Intementioning

confidence: 99%

Probing the C ₆₀ triplet state coupling to nuclear spins inside and out

Filidou

Mamone

Simmons

et al. 2013

Phil. Trans. R. Soc. A.

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The photoexcitation of functionalized fullerenes to their paramagnetic triplet electronic state can be studied by pulsed electron paramagnetic resonance (EPR) spectroscopy, whereas the interactions of this state with the surrounding nuclear spins can be observed by a related technique: electron nuclear double resonance (ENDOR). In this study, we present EPR and ENDOR studies on a functionalized exohedral fullerene system, dimethyl[9-hydro (C60-Ih)[5,6]fulleren-1(9 H )-yl]phosphonate (DMHFP), where the triplet electron spin has been used to hyperpolarize, couple and measure two nuclear spins. We go on to discuss the extension of these methods to study a new class of endohedral fullerenes filled with small molecules, such as H 2 @C 60 , and we relate the results to density functional calculations.

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Section: Density Functional Theory Calculations Of the Hyperfine Intementioning

confidence: 99%

Probing the C ₆₀ triplet state coupling to nuclear spins inside and out

Filidou

Mamone

Simmons

et al. 2013

Phil. Trans. R. Soc. A.

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“…We previously assumed that τ c is only slightly affected by the C 60 functionalization , an assumption that is supported by DFT calculations . Here, as explained below, we consider that the impact of the peptide‐TOAC moiety on τ c is also negligible.…”

Section: Resultsmentioning

confidence: 77%

“…(1) is negligible. As values of τ c for the fullerene nitroxides are longer than 10 −11 s , 1/ T 1,p should therefore be approximately proportional to τ c . .…”

Section: Resultsmentioning

confidence: 99%

“…1, which only refers to the dipolar contribution to the relaxation rate :

\frac{1}{T_{1, p}} = \frac{2}{15} {()(, \frac{μ_{0}}{4 π})}^{2} [\frac{γ_{I}^{2} g^{2} μ_{B}^{2} S (S + 1)}{r^{6}}] [\frac{3 τ_{c}}{1 + ω_{I}^{2} τ_{c}^{2}} + \frac{7 τ_{c}}{1 + ω_{S}^{2} τ_{c}^{2}}] = \frac{A}{r^{6}}

where γ I is magnetogyric ratio of the nucleus that is being relaxed (H), g is the electronic g factor, μ B is the Bohr magneton, r is the distance between the proton and the unpaired electron in the complex, S is the spin quantum number (1/2 for nitroxide), ω I and ω S are the nuclear and electronic Larmor frequencies, respectively, and τ c is the global correlation time. τ c essentially corresponds to the rotational correlation time of the molecule, τ r .…”

Section: Resultsmentioning

confidence: 99%

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Interaction of H₂@C₆₀ and Nitroxide through Conformationally Constrained Peptide Bridges

Garbuio

Antonello

et al. 2013

Photochem & Photobiology

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We synthesized two molecular systems, in which an endofullerene C 60 , incarcerating one hydrogen molecule (H 2 @C 60 ) and a nitroxide radical are connected by a folded 3 10 -helical peptide. The difference between the two molecules is the direction of the peptide orientation. The nuclear spin relaxation rates and the para ? ortho conversion rate of the incarcerated hydrogen molecule were determined by 1 H NMR spectroscopy. The experimental results were analyzed using DFT-optimized molecular models. The relaxation rates and the conversion rates of the two peptides fall in the expected distance range. One of the two peptides is particularly rigid and thus ideal to keep the H 2 @C 60 /nitroxide separation, r, as large and controlled as possible, which results in particularly low relaxation and conversion rates. Despite the very similar optimized distance, however, the rates measured with the other peptide are considerably higher and thus are compatible with a shorter effective distance. The results strengthen the outcome of previous investigations that while the para ? ortho conversion rates satisfactorily obey the Wigner's theory, the nuclear spin relaxation rates are in excellent agreement with the Solomon-Bloembergen equation predicting a 1/r 6 dependence.

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“…The effect of unpaired electrons on the nuclear relaxation of endohedral H 2 in solution is investigated by Rastrelli et al [17]. DFT calculations are conducted on endofullerenes with attached nitroxide moieties.…”

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confidence: 99%

Nanolaboratories: physics and chemistry of small-molecule endofullerenes

Levitt

Horsewill

2013

Phil. Trans. R. Soc. A.

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This Theo Murphy Meeting Issue contains papers presented at a Discussion Meeting held at the Kavli Centre of the Royal Society in March 2012. The meeting brought together a wide variety of scientists working on different aspects of small-molecule endofullerenes—those intriguing chemical systems in which small molecules such as H 2 or H 2 O are encapsulated in tiny carbon cages.

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Predicting the paramagnet-enhanced NMR relaxation of H₂encapsulated in endofullerene nitroxides by density-functional theory calculations

Abstract: One contribution of 13 to a Theo Murphy Meeting Issue 'Nanolaboratories: physics and chemistry of small-molecule endofullerenes' .

Cited by 5 publications

References 46 publications

Probing the C ₆₀ triplet state coupling to nuclear spins inside and out

Probing the C ₆₀ triplet state coupling to nuclear spins inside and out

Interaction of H₂@C₆₀ and Nitroxide through Conformationally Constrained Peptide Bridges

Nanolaboratories: physics and chemistry of small-molecule endofullerenes

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Predicting the paramagnet-enhanced NMR relaxation of H2encapsulated in endofullerene nitroxides by density-functional theory calculations

Abstract: One contribution of 13 to a Theo Murphy Meeting Issue 'Nanolaboratories: physics and chemistry of small-molecule endofullerenes' .

Cited by 5 publications

References 46 publications

Probing the C 60 triplet state coupling to nuclear spins inside and out

Probing the C 60 triplet state coupling to nuclear spins inside and out

Interaction of H2@C60 and Nitroxide through Conformationally Constrained Peptide Bridges

Nanolaboratories: physics and chemistry of small-molecule endofullerenes

Contact Info

Product

Resources

About

Predicting the paramagnet-enhanced NMR relaxation of H₂encapsulated in endofullerene nitroxides by density-functional theory calculations

Probing the C ₆₀ triplet state coupling to nuclear spins inside and out

Probing the C ₆₀ triplet state coupling to nuclear spins inside and out

Interaction of H₂@C₆₀ and Nitroxide through Conformationally Constrained Peptide Bridges