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1. Electron Paramagnetic Resonance, Electronic Ground State, and Electron Spin Relaxation of Seven Lanthanide Ions Bound to Lanmodulin and the Bioinspired Chelator, 3,4,3‐LI(1,2‐HOPO)

   https://doi.org/10.1002/chem.202303215  

   Larrinaga, Wyatt B.; Cotruvo, Joseph A.; Worrell, Brady T.; Eaton, Sandra S.; Eaton, Gareth R. (December 2023, Chemistry – A European Journal)

   Abstract The electron paramagnetic resonance (EPR) spectra of lanthanide(III) ions besides Gd³⁺, bound to small‐molecule and protein chelators, are uncharacterized. Here, the EPR properties of 7 lanthanide(III) ions bound to the natural lanthanide‐binding protein, lanmodulin (LanM), and the synthetic small‐molecule chelator, 3,4,3‐LI(1,2‐HOPO) (“HOPO”), were systematically investigated. Echo‐detected pulsed EPR spectra reveal intense signals from ions for which the normal continuous‐wave first‐derivative spectra are negligibly different from zero. Spectra of Kramers lanthanide ions Ce³⁺, Nd³⁺, Sm³⁺, Er³⁺, and Yb³⁺, and non‐Kramers Tb³⁺and Tm³⁺, bound to LanM are more similar to the ions in dilute aqueous:ethanol solution than to those coordinated with HOPO. Lanmodulins from two bacteria, with distinct metal‐binding sites, had similar spectra for Tb³⁺but different spectra for Nd³⁺. Spin echo dephasing rates (1/T_m) are faster for lanthanides than for most transition metals and limited detection of echoes to temperatures below ~6 to 12 K. Dephasing rates were environment dependent and decreased in the order water:ethanol>LanM>HOPO, which is attributed to decreasing librational motion. These results demonstrate that the EPR spectra and relaxation times of lanthanide(III) ions are sensitive to coordination environment, motivating wider application of these methods for characterization of both small‐molecule and biomolecule interactions with lanthanides. 

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2. Experimental electron impact ionization cross sections of Fe XXV and Maxwellian-averaged rate coefficients

   https://doi.org/10.1051/0004-6361/202554332  

   Yang, Y; Dipti; Foster, A R; Gall, A C; Brickhouse, N; Szypryt, P; O’Neil, G C; Hosier, A T; Naing, A S; Tan, J N; et al (August 2025, Astronomy & Astrophysics)

   Context. Collisionally ionized plasmas produce X-ray spectra that depend on electron energy and atomic processes, requiring accurate atomic rate coefficients for modeling. While most data are theoretical, experimental measurements – such as those for Fe XXV – are critical for providing important benchmarks and quantifying uncertainties, thereby improving astrophysical spectral analysis, especially with high-resolution observatories like XRISM. Aims. This study aimed to experimentally measure the electron impact ionization (EII) cross section of Fe XXV, a key ion in astrophysical plasma diagnostics, and to evaluate the impact of these measurements on the interpretation of X-ray spectra from high-temperature plasma environments. Methods. The EII cross sections were measured using X-ray spectroscopy with an electron beam ion trap (EBIT) at various electron beam energies. The intensity ratios of thewresonance line in Fe XXV and the Lyα_1,2lines in Fe XXVI were used to derive the cross sections. Level-resolved population calculations were performed using the NOMAD collisional-radiative code to account for processes affecting the emission ratios and ionization balance in the non-Maxwellian EBIT plasma. Results. The measured EII cross sections show good agreement with relativistic convergent close-coupling calculations. The uncertainties in the measurements, ranging from 8% to 12%, are discussed in terms of their impact on the accuracy of temperature diagnostics for astrophysical plasma environments. 

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3. Influence of hydrogen bonds on the electron-phonon coupling strength/marker mode structure and charge separation rates in reaction centers from Rhodobacter sphaeroides

   A. Khmelnitskiy, J C. (January 2019, Journal of physical chemistry)

   Low-temperature persistent and transient hole-burning (HB) spectra are presented for the triple hydrogen-bonded L131LH + M160LH + M197FH mutant of Rhodobacter sphaeroides. These spectra expose the heterogeneous nature of the P-, B-, and H-bands, consistent with a distribution of electron transfer (ET) times and excitation energy transfer (EET) rates. Transient P+Q − holes are observed for A fast (tens of picoseconds or faster) ET times and reveal strong coupling to phonons and marker mode(s), while the persistent holes are bleached in a fraction of reaction centers with long-lived excited states characterized by much weaker electron−phonon coupling. Exposed differences in electron−phonon coupling strength, as well as a different coupling to the marker mode(s), appear to affect the ET times. Both resonantly and nonresonantly burned persistent HB spectra show weak blue- (∼150 cm−1) and large, red-shifted (∼300 cm−1) antiholes of the P band. Slower EET times from the H- and B-bands to the special pair dimer provide new insight on the influence of hydrogen bonds on mutation-induced heterogeneity. 

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4. Beyond the single-site approximation modeling of electron-phonon coupling effects on resonant inelastic X-ray scattering spectra

   https://doi.org/10.21468/SciPostPhys.11.3.062  

   Bieniasz, Krzysztof; Johnston, Steven; Berciu, Mona (January 2021, SciPost Physics)

   null (Ed.)

   Resonant inelastic X-ray scattering (RIXS) is used increasingly for characterizing low-energy collective excitations inmaterials. RIXS is a powerful probe, which often requiressophisticated theoretical descriptions to interpret the data. Inparticular, the need for accurate theories describing the influence of electron-phonon (e-p) coupling on RIXS spectra is becoming timely, as instrument resolution improves and this energy regime is rapidly becoming accessible. To date, only rather exploratory theoretical work has beencarried out for such problems. We begin to bridge this gap byproposing a versatile variational approximation for calculating RIXS spectra in weakly doped materials, for a variety of models with diverse e-p couplings. Here, we illustrate some of its potential by studying the role of electron mobility, which is completely neglected in the widely used local approximation based on Lang-Firsov theory. Assuming that the e-p coupling is of the simplest, Holstein type, we discuss the regimes where the local approximation fails, and demonstrate that its improper use may grossly underestimate the e-p coupling strength. 

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5. Integrating Electron Paramagnetic Resonance Spectroscopy and Computational Modeling to Measure Protein Structure and Dynamics

   https://doi.org/10.1002/cplu.202300506  

   Bogetti, Xiaowei; Saxena, Sunil (January 2024, ChemPlusChem)

   Abstract Electron paramagnetic resonance (EPR) has become a powerful probe of conformational heterogeneity and dynamics of biomolecules. In this Review, we discuss different computational modeling techniques that enrich the interpretation of EPR measurements of dynamics or distance restraints. A variety of spin labels are surveyed to provide a background for the discussion of modeling tools. Molecular dynamics (MD) simulations of models containing spin labels provide dynamical properties of biomolecules and their labels. These simulations can be used to predict EPR spectra, sample stable conformations and sample rotameric preferences of label sidechains. For molecular motions longer than milliseconds, enhanced sampling strategies and de novo prediction software incorporating or validated by EPR measurements are able to efficiently refine or predict protein conformations, respectively. To sample large‐amplitude conformational transition, a coarse‐grained or an atomistic weighted ensemble (WE) strategy can be guided with EPR insights. Looking forward, we anticipate an integrative strategy for efficient sampling of alternate conformations by de novo predictions, followed by validations by systematic EPR measurements and MD simulations. Continuous pathways between alternate states can be further sampled by WE‐MD including all intermediate states. 

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