arXiv subjects

Maria Grazia Concilio

Publications and source records attributed to Maria Grazia Concilio.

9 recordsLinked to original sources

arXiv2026

Quantum Sensing with Triplet Pair States: A Theoretical Study

Molecular quantum sensors represent a promising frontier for the detection of nuclear magnetic resonance signals and alternating current magnetic fields at the nanoscale, potentially reaching single-proton sensitivity. Although the triplet states of molecular pentacene provide a viable sensing architecture, the triplet pair states produced by singlet fission of pentacene dimers could enable more flexible quantum manipulations through entanglement. In this work, we model the quantum sensing efficacy of a spin-polarized quintet manifold in a photoexcited pentacene dimer generated via intramolecular singlet fission. Using a Lindblad master equation approach, we simulate the evolution of the triplet pair state under standard dynamical decoupling sequences, including spin echo, XY4, and XY8 and provide a direct performance comparison to the traditional pentacene monomer benchmark. While both architectures exhibit comparable sensitivity for isolated single-spin detection, our findings indicate that the dimer architecture provides a superior interaction cross-section for detecting small ensembles of nuclear spins. Analytical expressions derived for fluorescence modulation demonstrate that sensitivity is optimized in the low-magnetic field regime and scales with the number of pulses in the sensing protocol. This study establishes a theoretical baseline for utilizing high-spin multi-excitonic states as chemically tunable, high-sensitivity quantum probes.

physics.chem-ph↗

arXiv2025

Triplet J-driven DNP, a proposal to increase the sensitivity of solution-state NMR without microwave

Dynamic nuclear polarization (DNP) is an important method to enhance the limited sensitivity of nuclear magnetic resonance (NMR). Using the existing mechanisms such as Overhauser DNP (ODNP) is still difficult to achieve significant enhancement of NMR signals in solutions at a high magnetic field. The recently proposed J-driven DNP (JDNP) condition (when the exchange interaction of two electron spins matches their Lamour frequency) may enable signal enhancement in solution as it requires only dipolar interaction between the biradical polarization agent and the analyte. However, likewise ODNP, the current JDNP strategy still requires the saturation of the electron polarization with high microwave power which has poor penetration and is associated with heating effects in most liquids. The replacement of high-power microwave irradiation is possible if the temporal electron polarization imbalance is created by a different wavelength such as the visible light. Here, we propose a triplet JDNP mechanism which first exploits the light-induced singlet fission process (i.e., a singlet exciton is converted into two triplet excitons). As the JDNP condition is fulfilled, a triplet-to-triplet cross-relaxation process will occur with different rates and consequently lead to the creation of hyperpolarization on the coupled nuclear spin states. This communication discusses the theory behind the triplet JDNP proposal, as well as the polarizing agents and conditions that will enable the new approach to enhance the sensitivity of NMR without the need of microwave irradiation.

physics.chem-ph↗

arXiv2023

Steady state effects introduced by local relaxation modes on J-driven DNP-enhanced NMR

One of solution-state Nuclear Magnetic Resonance (NMR)'s main weaknesses, is its relative insensitivity. J-driven Dynamic Nuclear Polarization (JDNP) was recently proposed for enhancing the sensitivity of solution-state NMR, by bypassing the limitations faced by conventional Overhauser DNP (ODNP), at the high magnetic fields where most analytical research is performed. By relying on biradicals with inter-electron exchange couplings on the order of the electron Larmor frequency, JDNP was predicted to introduce a transient enhancement in the nuclear polarization at high magnetic fields, and for a wide range of rotational correlation times of medium-sized molecules in conventional solvents. This communication revisits the JDNP proposal, including additional effects and conditions that were not considered in the original treatment. These include relaxation mechanisms arising from local vibrational modes that often dominate electron relaxation in organic radicals, as well as the possibility of using biradicals with inter-electron exchange couplings of the order of the nuclear Larmor frequency as potential polarizing agents. The presence of these new relaxation effects lead to variations in the JDNP polarization mechanism originally proposed, and indicate that triplet-to-singlet cross-relaxation processes may lead to a nuclear polarization enhancement that persists even at steady states. The physics and potential limitations of the ensuing theoretical derivations, are briefly discussed.

physics.chem-ph↗

arXiv2023

Microwave-free J-driven DNP (MF-JDNP): A proposal for enhancing the sensitivity of solution-state NMR

J-driven Dynamic Nuclear Polarization (JDNP) was recently proposed for enhancing the sensitivity of solution-state nuclear magnetic resonance (NMR), while bypassing the limitations faced by conventional (Overhauser) DNP at magnetic fields of interest in analytical applications. Like Overhauser DNP, JDNP also requires saturating the electronic polarization using high-frequency microwaves, known to have poor penetration and associated heating effects in most liquids. The present microwave-free JDNP (MF-JDNP) proposal seeks to enhance the sensitivity of the solution state NMR by shuttling the sample between higher and lower magnetic fields, with one of these fields providing an electron Larmor frequency that matches the inter-electron exchange coupling Jex. If spins cross this so-called JDNP condition sufficiently fast, we predict that a sizable nuclear polarization will be created without microwave irradiation. This MF-JDNP proposal requires radicals whose singlet/triplet self-relaxation rates are dominated by dipolar hyperfine relaxation, and shuttling times that can compete with these electron relaxation processes. This communication discusses the theory behind the MF-JDNP, as well as proposals for radicals and conditions that could enable this new approach to NMR sensitivity enhancement.

physics.chem-ph↗

arXiv2021

J-driven Dynamic Nuclear Polarization for sensitizing high field solution state NMR

Dynamic nuclear polarization is widely used to enhance the sensitivity of nuclear magnetic resonance. It is presently the method of choice for enhancing the sensitivity of high-field solid state NMR experiments performed under cryogenic conditions. In liquids, however, its efficiency decays rapidly with magnetic field Bo and with the rotational correlation time, leading to negligible enhancements in mid- and high-field solution-state NMR experiments for all but exceptional cases. This study discusses a potential solution to this fundamental sensitivity problem, that relies on biradical species possessing inter-electron exchange couplings, that are on the order of the electron Larmor frequency.

physics.chem-ph↗

arXiv2021

Heteronuclear transfers from labile protons in biomolecular NMR: Cross Polarization, revisited

INEPT- and HMQC-based pulse sequences are widely used to transfer polarization between heteronuclei, particularly in biomolecular spectroscopy: they are easy to setup and involve low power deposition. Still, these short-pulse polarization transfers schemes are challenged by fast solvent chemical exchange. An alternative to improve these heteronuclear transfers is J-driven cross polarization (J-CP), which transfers polarization by spin-locking the coupled spins under Hartmann-Hahn conditions. J-CP provides certain immunity against chemical exchange and other T2-like relaxation effects, a behavior that is here examined in depth by both Liouville-space numerical and analytical derivations describing the transfer efficiency. While superior to INEPT-based transfers, fast exchange may also slow down these J-CP transfers, hurting their efficiency. This study therefore explores the potential of repeated projective operations to improve 1H->15N and 1H->15N->13C J-CP transfers in the presence of fast solvent chemical exchanges. It is found that while repeating J-CP provides little 1H->15N transfer advantages over a prolonged CP, multiple contacts that keep both the water and the labile protons effectively spin-locked can improve 1H->15N->13C transfers in the presence of chemical exchange. The ensuing Looped, Concatenated Cross Polarization (L-CCP) compensates for single J-CP losses by relying on the 13C longer lifetimes, leading to a kind of algorithmic cooling that can provide high polarization for the 15N as well as carbonyl and alpha 13Cs. This can facilitate certain experiments, as demonstrated with triple resonance experiments on intrinsically disordered proteins involving labile, chemically exchanging protons.

physics.chem-ph↗

arXiv2020

High-field solution state DNP using cross-correlations

At the magnetic fields of common NMR instruments, electron Zeeman frequencies are too high for efficient electron-nuclear dipolar cross-relaxation to occur in solution. The rate of that process fades with the electron Zeeman frequency as omega^{-2} - in the absence of isotropic hyperfine couplings, liquid state dynamic nuclear polarisation (DNP) in high-field magnets is therefore impractical. However, contact coupling and dipolar cross-relaxation are not the only mechanisms that can move electron magnetisation to nuclei in liquids: multiple cross-correlated (CC) relaxation processes also exist, involving various combinations of interaction tensor anisotropies. The rates of some of those processes have more favourable high-field behaviour than dipolar cross-relaxation, but due to the difficulty of their numerical - and particularly analytical - treatment, they remain largely uncharted. In this communication, we report analytical evaluation of every rotationally driven relaxation process in liquid state for 1e1n and 2e1n spin systems, as well as numerical optimisations of the steady-state DNP with respect to spin Hamiltonian parameters. A previously unreported cross-correlation DNP (CCDNP) mechanism was identified for the 2e1n system, involving multiple relaxation interference effects and inter-electron exchange coupling. Using simulations, we found realistic spin Hamiltonian parameters that yield stronger nuclear polarisation at high magnetic fields than dipolar cross-relaxation.

quant-ph↗

arXiv2016

MD and EPR studies of the structure and dynamics of the MTSL spin-labelled activation loop of the Aurora-A kinase

The understanding of kinase structure is mostly based on protein crystallography, which is limited by the requirement to trap molecules within a crystal lattice. Therefore, characterisations of the conformational dynamics of the activation loop in solution are important to enhance the understanding of molecular processes related to diseases and to support the discovery of small molecule kinase inhibitors. In this work, we demonstrated that long molecular dynamics simulations exhaustively sampled all the conformational space of the activation loop of the Aurora-A kinase and of the methane-thiosulfonate spin label, introduced into the activation loop for the electron paramagnetic measurements. MD was used to determine structural fluctuations, order parameters and rotational correlation times of the motion of the activation loop and of the MTSL. Theoretical data obtained were used as input for the calculation of the room temperature 9 GHz continuous wave EPR of the Aurora-A kinase in solution and the comparison between simulated and experimental date revealed that the motion of the protein and spin label occurred on comparable timescales. This work is a starting point for deeper experimental and theoretical studies of the rotational and translational diffusion properties of the Aurora-A kinase protein related to its biological activity.

physics.chem-ph↗

arXiv2016

Density functional theory studies of MTSL nitroxide side chain conformations attached to an activation loop

A quantum-mechanical (QM) method rooted on density functional theory (DFT) has been employed to determine conformations of the methane-thiosulfonate spin label (MTSL) attached to a fragment extracted from the activation loop of Aurora-A kinase. The features of the calculated energy surface revealed low energy barriers between isoenergetic minima and the system could be described in a population of 76 rotamers that can be also considered for other systems since it was found that the X3, X4 and X5 do not depend on the previous two dihedral angles. Conformational states obtained were seen to comparable to those obtained in the α-helix systems studied previously, indicating that the protein backbone does not affect the torsional profiles significantly and suggesting the possibility to use determined conformations for other protein systems for further modelling studies.

physics.chem-ph↗