Daria Ruth Galimberti

We present a new enhanced-sampling scheme for obtaining the underlying conformer starting from a spectrum: the SPectroscopy Informed Configurational Enhanced Sampling (SPICES) method. SPICES is driven by a history-dependent biased molecular dynamics, in which the biases are governed by spectral information rather than by energetic considerations. The performance of SPICES is hence rather insensitive to the target conformer’s relative energy compared to the global minimum structure. Furthermore, it does not require pretraining or prior knowledge of the system. We have critically assessed the performance of SPICES and demonstrated that it can identify the correct conformer of our test system, diphenylalanine (FF), among the 400 stable conformations in 22 spectral calculations (median value). We also show that SPICES is robust to noise in the experimental spectrum and to small discrepancies between theory and experiment.

The suggested detection of sulfur-based biomarkers in the atmosphere of exoplanet K2–18b has triggered intensive discussions about the use of observational data from the James Webb Space Telescope (JWST) to search for life on exoplanets. This methodology, however, requires precise infrared spectroscopic data of biomarker molecules, ideally without the influence of pressure broadening or contaminants. In this work, we use the light of the free-electron laser FELIX to record the infrared spectrum of three sulfur-based biomarkers, dimethyl sulfide (DMS), dimethyl disulfide (DMDS), and dimethyl sulfoxide (DMSO), in the isolated conditions of a molecular beam. The use of FELIX allows the sampling of a wide spectral range, spanning from 650 to 3300 cm^–1, where JWST is most sensitive. In addition, separate spectra of the (DMS)₂, (DMDS)₂ and (DMSO)₂ dimers are recorded, allowing for a clear assessment of the effect of complexation on the infrared spectra of the molecules. Density functional theory calculations and Born–Oppenheimer molecular dynamics simulations are performed to interpret the measured infrared spectra and to estimate absolute cross sections.

We disclose the nature of the 4-DBpFO thermosalient (or "jumping") crystal phase transition 40 cm^-1 (i.e., 1.2 THz) "gateway" mode using computed low-frequency Raman spectra (LFRS) benchmarked to experimental spectra and show that it is a coherent/in-phase collective motion of the inner-outer rings. We explore and reveal the roles of anharmonicity, thermal disorder, and volume fluctuations in determining the THz spectral shape. The anharmonic couplings and cell fluctuations appear to be more than just innocent spectators, and indeed, the intermolecular correlations for this mode involve multiple cells. To obtain this information, we use our Activity Weighted Velocities (AWV) method to integrate classical trajectories with the accuracy of hybrid Density Functional Theory (DFT) Raman activities. We demonstrate that this combination effectively computes accurate LFRS and offers a way to predict the Raman activity of thermally disordered systems and entropically stabilized phases, where current methods (harmonic spectra and DFT-Molecular Dynamics) fail.

Polymeric organic semiconductors play a pivotal role in the development of new organic thermoelectric materials, sensing, and organic optoelectronics. Understanding the relation between their structure and properties is essential for designing the next generation of materials with improved features. Theoretical modelling based on first-principles calculations is a powerful aid for interpreting experimental structural and spectroscopic data of π-conjugated polymers, both in their pristine and doped states. Two approaches are currently available, i.e., oligomeric models and one-dimensional (1D) periodic crystal, each of one with its advantages and disadvantages. The combination of both allows to overcome the limitations of each. However, to do this, it is fundamental to systematically address the differences between these two approaches (molecular models vs. crystals). Here, we present a first systematic comparison between oligomeric and (1D) crystal models for describing the structural and spectroscopic properties of polyconjugated polymers. Using polythiophene (PT) and poly(3-hexylthiophene) (P3HT) as prototypical benchmark systems, we examine the relationship between finite-size oligomers and the corresponding infinite polymer treated as a one-dimensional (1D) crystal under periodic boundary conditions. Density functional theory (DFT) calculations are performed to examine the convergence of geometrical parameters and vibrational features (IR and Raman) as the oligomer length increases. The 1D crystal model is then evaluated as the limiting case of the oligomeric series. Its advantages in simplifying vibrational mode analysis are illustrated. This study establishes a methodological framework connecting molecular and periodic models, with direct relevance to the interpretation of experimental vibrational spectra of conducting polymers.

Zeolites play a pivotal role as catalysts in biomass conversion, and understanding how alcohols interact with these materials is essential for designing next-generation catalysts that reduce dependence on nonrenewable fuels and enable a more sustainable energy landscape. Achieving this understanding requires accurate free-energy calculations. In this study, we present the anharmonic enthalpy, entropy, and vibrational free energy associated with ethanol adsorption on H-ZSM-5, computed at a hybrid DFT level of theory. We critically assess the need to go beyond both GGA functionals and the harmonic approximation to achieve chemically accurate vibrational free energies. The vibrational contributions to the free energy are obtained using a newly implemented strategy that combines the DOS-P method with a QM/QM molecular-dynamics scheme. This approach yields significant improvement in accuracy compared to the commonly used PBE + D2 functional. By combining the anharmonic vibrational free energies computed at the B3LYP + D2 level with electronic energies refined at the CCSD(T) level, we obtain an anharmonic adsorption enthalpy, ΔH, of -101.9 kJ mol^-1, the entropic term, -TΔS, equal to 61.0 kJ mol^-1, and a free energy of adsorption, ΔG, of -40.8 kJ mol^-1 at 313 K. We performed a critical comparison between these values and the experimental data. Notably, the entropic term agrees well with the experimental value of 62.0 kJ mol^-1. We also examine the significance of anharmonicity, finding a correction of approximately 1 kJ mol^-1 for both the vibrational entropy and enthalpy, and about 3.7 kJ mol^-1 for the ZPE.

In interstellar ices, the ice matrix can have a great influence on the chemical reactions. The hydrogen-bonding network in pure water ices facilitates fast energy dissipation that, for example, stabilizes the HOCO complex, a crucial step in the formation of CO₂. To better understand the energy dynamics and its possible influence on the processes in the ice, we investigated a H₂O:CO₂ 1:4 ice mixture exposed to infrared irradiation on-resonance with the CO₂ vibrations. Experimentally, we find changes in the OH stretch of H₂O after irradiating the asymmetric stretch of CO₂ for several minutes with the intense monochromatic light of the FELIX free electron lasers. Using molecular dynamics simulations, we found that an excitation of the asymmetric stretch of CO₂ readily dissipates to other asymmetric stretches in the environment, but only dissipates to the CO₂ libration and H₂O twist modes after roughly 2 ns because of its minimal anharmonicity and coupling with other modes. This is significantly longer than the off-time between laser pulses of 1 ns, suggesting ladder climbing or that the stacking of the excitation boosts the experimentally observed changes. For infrared excitation of the CO₂ bending vibration, the simulations reveal a fast distribution of energy and coupling to the intermolecular interactions that lead to thermal heating of the H₂O vibrational modes. This is not observed on the time scale of the experiments. Still, both simulations and experiments reveal nonthermal annealing of the H₂O component of the mixed ice when exposed to infrared irradiation on-resonance with the CO₂ vibrations.

Zwitterionic polymers are often non-degradable due to their polyolefin backbones. We present an Fe( ii )-catalyzed step-growth polymerization that incorporates N -acyliminophosphoranes into the main chain, enabling tailored pH-responsive degradability.

Surface fouling induced by biomolecules and microorganisms remains a persistent challenge in materials science, particularly in healthcare applications, where biofilm formation on medical devices may lead to infections and antimicrobial resistance. Antifouling strategies typically rely on the formation of either hydration layers or cytotoxic materials for direct antimicrobial effects. Recent advances in zwitterionic polymers derived from ylides offer a promising yet unexplored toolbox for the construction of antifouling and antimicrobial coatings. While N-oxide-based ylides have been extensively studied as building blocks for antifouling materials, sulfur-ylide-based materials, and the precise underlying mechanisms remain underexplored despite their broader chemical versatility. Here, we present a fully water-soluble acrylamide-based poly(sulfur ylide) and compare its properties to those of previously reported hydrophobic polystyrene-derived analogues. Notably, water-soluble poly(sulfur ylides) retain antimicrobial efficacy on surfaces but lose cytotoxicity in solution, unlike its hydrophobic counterpart. Computational studies reveal that the dipole moment of sulfur ylides is environmentally responsive, stabilizing in hydrophobic environments. Genetic analysis confirms outer membrane destabilization for both polymers but suggests that the hydrophobicity of the polystyrene backbone promotes stronger interactions. We suggest that future work should focus on elucidating additional interactions, including supramolecular behaviors of amphiphilic sulfur ylides, to refine their structure-property relationships and optimize their antifouling and antimicrobial properties.

Understanding how alcohol molecules interact with the Brønsted acid sites (BAS) of zeolites is a prerequisite to the design of zeolite catalysts and catalytic processes. Here, we report IR spectra for the adsorption of ethanol on a highly crystalline sample of H-ZSM-5 zeolites exposed to ethanol gas at increasing pressure. We use density functional theory in combination with a FERMI resonance model to assign the measured spectra to a single adsorbed ethanol molecule per BAS. Specifically, we assign the bands at 2450 cm⁻¹ and 1670 cm⁻¹ to a FERMI resonance between the fundamental (Z)O–H stretching band of a single-ethanol-loaded BAS and the first overtone of the (Z)O–H out-of-plane bending. We conclude that adsorbed dimers do not contribute in a noticeable way up to a concentration of almost one ethanol molecule per BAS site. We further show that hybrid functionals (B3LYP) are required to get a close match between the predicted and experimental spectra, whereas commonly used generalized gradient type functionals such as PBE incorrectly describe the potential energy surface. They overestimate the redshift of the OH stretching band on hydrogen bond formation which results in an erroneous assignment of the IR bands.