Physical Chemistry Chemical Physics

doi: 10.1039/d6cp90110gpmid: N/A

doi: 10.1039/d6cp90111epmid: N/A

doi: 10.1039/d6cp90112cpmid: N/A

Zhou, Youbin; Zhang, Xianren

doi: 10.1039/d5cp04894jpmid: 42171224

Bulk nanobubbles exhibit exceptionally long lifetimes in solution, fundamentally contradicting classical thermodynamic predictions, which suggest rapid dissolution due to immense internal pressure. In this review we first discuss the theoretical challenges underlying this contradiction: (i) when system characteristic scales shrink to the nanometer range, traditional thermodynamic quantities like pressure and interfacial tension are no longer well-defined intensive properties because they exhibit a strong dependence on size and curvature; (ii) the interfacial phase of nanobubbles remains essentially a black box, with its microscopic structure and composition either unknown or difficult to measure, rendering prediction of surface tension and internal pressure from the interfacial phase often misleading. Then we discuss the fundamental advantage of chemical potential for nanoscale systems: equality of chemical potential remains valid regardless of changes in system size or interfacial characteristics, providing a more reliable foundation for predicting nanobubble properties from known environmental characteristics.

Oh, Minseok; Park, Jiseong; Kim, Byungjoo; Lim, Hyeok; Lee, Seunghoon

doi: 10.1039/d6cp00700gpmid: 42186991

Orbital-relaxed bath theory (ORBT) provides a practical theoretical framework for describing charge-transfer processes in transition-metal complexes. Insights from the Schmidt decomposition of the full configuration interaction wave function underscore the importance of bath orbital relaxation for achieving a balanced description of electronic states with different charge distributions. Directions and implications for the systematic development of these approaches are discussed.

Yadav, Desh Deepak; Bhandary, Debdip; Paik, Pradip

doi: 10.1039/d6cp00760kpmid: 42187070

Molecular dynamics and umbrella sampling were employed to investigate the translocation of siRNA–NAPA oligomer complexes across a POPC membrane, revealing a high energy barrier (63–95 kcal mol−1) accompanied by significant membrane deformation, underscoring the need for improved carrier design in siRNA therapeutics.

Altenhof, Adam R.; Erickson, Karla A.; Rehn, Daniel A.; Fetrow, Taylor V.; Mattsson, Ann E.; Monreal, Marisa J.; Mason, Harris E.

doi: 10.1039/d5cp03944dpmid: 42065504

Solid-state NMR (SSNMR) spectroscopy is a powerful technique for studying actinide chemistry but has been significantly limited due to the complex paramagnetism, and radiological hazards presented by these materials. Lanthanide and actinide salts often feature magnetic ordering and can be paramagnetic, ferromagnetic, or antiferromagnetic depending on temperature and electronic structure. Paramagnetic interactions can manifest in SSNMR both as secular spectral shifts and/or couplings as well as contributions from non-secular relaxation. Both effects can be directly measured with NMR and used to extrapolate rich chemical information such as coordination environments, bonding characteristics, local molecular dynamics, and correlation times. Typically, these studies are carried out on high-γ and highly abundant NMR-active isotopes (e.g., 1H, 6/7Li, 19F, 23Na, etc.) or on enriched rare isotopes (e.g., 2H and 17O), which can be expensive. Herein, we present a facile methodology to measure the 35/37Cl electric-field gradient (EFG) and paramagnetic shift anisotropy (SA) tensor components using static wideline SSNMR measurements of LaCl3, NdCl3, UCl3, and UCl4. The static powder spectra were measured with both 35Cl and 37Cl SSNMR to increase the fidelity of the extracted tensor parameters. Variable temperature NMR of a select case confirms the Curie–Weiss paramagnetism. Relaxation measurements of both nuclei further corroborate observations owing to the paramagnetic relaxation enhancement and reveal simultaneous quadrupolar relaxation mechanisms. Density functional theory (DFT) calculations using Hubbard U corrections to the uranium valence orbitals show excellent agreement with experimental EFG tensor parameters and help describe the bonding characteristics in these lanthanide and actinide systems.

Arifuzzaman, Md; Carrillo, Jan-Michael; Sumpter, Bobby; Saito, Tomonori; Do, Changwoo

doi: 10.1039/d6cp00433dpmid: 42210817

The dissolution of polyethylene terephthalate (PET) is a critical step for a solvent-based process, yet it typically requires highly corrosive or toxic solvents. Here, we investigate the solubilization and conformational behavior of PET in binary mixtures of hexafluoro-2-propanol (HFIP) and dichloromethane (DCM) as a strategy to reduce HFIP usage while maintaining effective dissolution. Small-angle neutron scattering (SANS) measurements reveal that PET remains molecularly dissolved in HFIP/DCM mixtures up to 50 vol% DCM. Analysis of PET chain conformations shows a transition from Gaussian behavior at low HFIP fractions to more swollen chains at intermediate compositions, accompanied by a counter-intuitive minimum in the radius of gyration at 50% HFIP. Complementary SANS measurements of the binary solvents demonstrate that compositional heterogeneity is maximized at this same solvent composition, suggesting a direct coupling between solvent microstructure and polymer dimensions. Molecular dynamics simulations corroborate the experimental findings, revealing solvent domain formation, preferential solvation of PET by HFIP, and a “caging” effect arising from solvent heterogeneity that leads to polymer coil compaction. Together, these results provide molecular-level insight into polymer behavior in mixed solvent systems and establish HFIP/DCM mixtures as a promising, more sustainable solvent platform for the PET post-process.

Aleshin, Dmitrii; Butbul, Korin; Hahamy, Itai; Abergel, Daniel; Frydman, Lucio

doi: 10.1039/d6cp00956epmid: 42148947

The exceptionally high spin polarizations that result from dissolution dynamic nuclear polarization (d-DNP), can lead to unusual liquid-state nuclear magnetic resonance (NMR) spectral features. This study analyzes such features, when performing d-DNP of hyperpolarized water to dissolve and sensitize the NMR spectra of co-dissolved molecules. Most evident among the collective spin effects that arise in such “HyperW” experiments is the very strong radiation damping (RD) affecting the water resonance. In addition, the presence of such strongly magnetized water signal alters both the amplitude and the phase of resonances emerging from the solutes co-dissolved in the hyperpolarized H2O, for as long as these remain within the RD-broadened line width of water's resonance. These phase- and amplitude RD effects are superimposed on cross-relaxation and chemical exchange effects, which will also affect the phases and amplitudes of all peaks. Demonstrations and derivations of these effects, as well as a discussion of their consequences in HyperW experiments on solute-oriented measurements, are presented.

Peterka, Lukáš; Janoš, Jiří; Slavíček, Petr

doi: 10.1039/d6cp00995fpmid: 42149001

Although bilirubin photochemistry is central to neonatal jaundice phototherapy, the mechanism of bilirubin photooxidation remains unclear. Here, we use a comprehensive computational approach to investigate whether this mechanism might be initiated by photoinduced electron transfer (PET) to molecular oxygen (O2), generating superoxide (O2˙−). For this purpose, we employed a simplified bilirubin model compound—tetramethyldipyrrinone (TMD). We use a combination of multireference, coupled cluster methods, and density functional theory techniques to assess the feasibility of the TMD–O2 complex formation and PET from TMD to O2. Our results support the feasibility of PET in the TMD–O2 complex and suggest that PET could potentially initiate bilirubin photooxidation. Beyond the bilirubin case, this work underscores the need for efficient and accurate protocols to compute binding free energies of weak O2 encounter complexes with organic chromophores in solution, and it highlights the broader challenge of modeling triplet photochemistry with dense manifolds of near-degenerate states, crossings, and strongly state-specific solvent response.