Physical Chemistry Chemical Physics

Chuang, Weipai; Sowa, Keisei; Kitazumi, Yuki; Shirai, Osamu

doi: 10.1039/d5cp02791hpmid: 41404866

I− and I3− usually coexist in nature, and it is well-known that I3− is much more hydrophobic than I−. Both I− and I3− play a crucial role in human physiological activities and can be applied to various medical applications, such as synthesis of medicine, antibiotics, etc. During the measurement of the ion-transport current of KI aqueous solution, I3− is spontaneously generated and causes an increase in ion permeation. However, the mechanism of facilitated ion transport remains unclear. In this study, the influence of I3− on the ion transport across bilayer lipid membranes (BLMs) was elucidated. Physically stabilized BLMs were formed using the track-etched membrane (TM), and the ion-transport current was measured by applying a membrane potential across BLMs. Under asymmetric ionic concentration conditions, the permeability of K+, I−, and I3− was evaluated. The permeability of I− across BLMs was about 8 times higher than that of K+. In the presence of I3−, the permeability of K+ across BLMs drastically increased. The permeability of K+ became 9 times higher than that of I− in the presence of 50 µM I3−. It is considered that I3− facilitated the transport of K+ across BLMs by serving as a carrier of K+ within BLMs.

Tucker, Max R.; Xue, Yuan; Speake, Nathan R.; Nickolson, Eden; Carr, Jeremy M.; Tschumper, Gregory S.

doi: 10.1039/d5cp03769gpmid: 41403352

This work examines various homogeneous and heterogeneous clusters of hydrogen-bonded (HF)x(H2O)y(HCl)z complexes, where x + y + z = 3 or 4. For each unique cyclic structure associated with the xyz permutations, the geometries of the reactant, product, and transition state (TS) for concerted proton transfer (CPT) were fully optimized using second-order Møller-Plesset perturbation theory (MP2) with a mixed basis set consisting of cc-pVTZ for H atoms and aug-cc-pVTZ for O, Cl, and F atoms (denoted haTZ). Harmonic vibrational frequencies were also computed at the same level of theory to verify the nature of the stationary points. Intrinsic reaction coordinate (IRC) calculations confirm that all transition states reported herein connect the two minima associated with the CPT process, and these reaction profiles provide a means to assess the associated barrier width. Single-point energies were computed on the optimized structures using an explicitly correlated coupled cluster method with an analogous quadruple-ζ basis set (CCSD(T)-F12/haQZ-F12) to determine the dissociation energy (De) of each trimer and tetramer minimum, as well as the barrier height (ΔE‡) and energy difference between the reactants and products (ΔE) associated with the CPT process in each cluster. The energetics calculated utilizing this methodology were compared to CCSD(T) benchmark data for the homogeneous clusters (Y. Xue, T. M. Sexton, J. Yang and G. S. Tschumper, Phys. Chem. Chem. Phys., 2024, 26, 12483–12494, DOI: https://doi.org/10.1039/D4CP00422A), and deviations never exceeded 0.1 kcal mol−1. For the heterogeneous trimer systems, (H2O)2(HCl)1 had the smallest ΔE‡ at only 11.9 kcal mol−1, just below the corresponding De of 13.8 kcal mol−1. Among the heterogeneous tetramers, six systems were identified with an even smaller ΔE‡ (7.9 to 11.8 kcal mol−1) and a larger De (19.8 to 30.8 kcal mol−1). Among those, (HF)3(H2O)1 has one of the narrowest barrier widths of any tetramer system, based upon MP2/haTZ IRC profiles.

Hernandez, Renato Olarte; Soldera, Armand; Champagne, Benoît

doi: 10.1039/d5cp03805gpmid: 41490094

The vibronic structure of electronic circular dichroism (ECD) spectra is simulated in silico using a hybrid method that encompasses ab initio time-dependent density functional theory (TD-DFT) calculations and the Doktorov quantum algorithm. Four low-energy electronic excitations of the chiral tryptophan amino acid are characterized and their spectra are simulated with and without considering the Duschinsky rotation effects. The normal mode mixing shows a very small impact on the vibronic structure. Moreover, it demonstrates the versatility of the quantum algorithm to focus on individual normal mode contributions to the vibronic structure of the spectrum.

Ziese, Ferdinand; Dehnen, Stefanie; Sanna, Simone

doi: 10.1039/d5cp03750fpmid: 41328497

In order to explore the effect of the presence of CPh versus SiPh parts on the optical nonlinearities of phenyl-decorated adamantane-type clusters, the second harmonic generation (SHG) spectra of molecular clusters with the general formula [(CPh)x(SiPh)4−xS6] and x = 0,…, 4, are calculated within (hybrid) density functional theory. The stepwise replacement of C atoms with Si at the bridgehead positions leads to the blue-shift of the first SHG peak and to a redistribution of the spectral weights of the different signatures. The electronic transitions related to the SHG peaks are found to occur mainly at the substituents, which are common to all investigated compounds. However, the peak intensity strongly depends on the substitution induced distortion of the cluster core. Thus, although the cluster core is not directly involved in the genesis of the optical nonlinearities, it heavily impacts their intensity. The presented results suggest that reducing the core symmetry provides a pathway to enhance the SHG response of the clusters and yields a theoretical foundation for the design of nonlinear optical materials with tailored properties.

Nekrasov, V. M.; Matveeva, A. G.; Syryamina, V. N.; Agarkin, S. A.; Bowman, M. K.

doi: 10.1039/d5cp04144apmid: 41542978

Non-uniform data acquisition protocols are derived analytically for optimizing the measurement of nanometer distance using pulsed dipolar spectroscopy methods, such as DEER (double electron–electron resonance). The random measurement noise is redistributed by non-uniform averaging of the signal. This optimizes the accuracy and efficiency of the measurement of the first four non-central moments of the distribution of distances within pairs of spin labels attached to nanostructures. With these protocols, the mean distance can typically be measured with the same accuracy in half the time or with 40% greater accuracy in the same time. Different signal averaging schemes are optimal for each of the first four moments, but the optimal scheme for the first moment works well for all moments and for the measurement of the entire distance distribution of distances in the sample. These protocols were tested in silico using three approaches for analysis of the DEER data: the Tikhonov regularization, model-based fitting, and Mellin transform approaches. The non-uniform acquisition protocols produced significantly better results than each of the analysis protocols.

Klushin, Leonid I.; Lukiev, Ivan V.; Mikhailov, Ivan V.; Borisov, Oleg V.; Skvortsov, Aleksander M.

doi: 10.1039/d5cp03222apmid: 41543312

The present study investigates the interpenetration properties of two opposing monodisperse asymmetric polymer brushes under external pressure, utilizing a numerical self-consistent field method. The polymer brushes under consideration were composed of chemically identical units, had the same stiffness values, and differed in the grafting density values σ1,2 and/or in the number of backbone units N1,2. Both brushes were immersed in an athermal solvent. Contrary to our expectations, the interpenetration zone of various asymmetric brushes always had a symmetrical appearance. We propose an analytical scaling theory rationalizing the symmetry of the interpenetration picture and suggesting how the penetration length scales with the four brush parameters (σ1,2; N1,2). Analytical expressions for the interpenetration zone were proposed and verified using numerical SCF calculations. The interpenetration of the two opposing brushes was quantified by two integral parameters: (i) the overlap integral, denoted by Γ, which represents the number of contacts between brushes and (ii) the number of monomer brush units in the foreign half-space, denoted by Σ. We demonstrate that a panoply of curves specifying Σ and Γ as functions of external pressure for different asymmetric brush pairs collapse onto universal master curves once they are rescaled as suggested by the analytical theory.

Scholz, Marek; Moučka, Jan; Pšenčík, Jakub; Hála, Jan; Dědic, Roman

doi: 10.1039/d5cp03884gpmid: 41543341

Riboflavin, a water-soluble vitamin and important nutrient found in many foods, also functions as an effective photosensitiser, with a singlet oxygen quantum yield of 0.54. This makes it relevant not only for photodynamic therapy (PDT) but also as a contributor to light-induced degradation of food and beverages. However, literature reports on its triplet and singlet oxygen dynamics remain inconsistent. We show that in phosphate buffered water, riboflavin exhibits a triplet state lifetime of 3.2 µs and a singlet oxygen lifetime of 3.7 µs, unusually close values that require careful kinetic analysis for a correct interpretation. Contrary to some assumptions, we find that sodium azide efficiently quenches riboflavin triplets (rate constant 4 × 109 M−1 s−1), far exceeding the quenching rate of azide for singlet oxygen. In contrast, we demonstrate that the quenching of singlet oxygen by riboflavin is negligible under typical conditions in H2O. We also report pronounced delayed fluorescence (DF) of riboflavin in air-saturated samples, attributed to the singlet oxygen feedback mechanism. Finally, we discuss how the DF signal can be used to reveal energy transfer efficiency to other sensitisers, such as aluminium phthalocyanine, where we demonstrate a dominant role of the triplet–triplet transfer mechanism.

Rajput, Swati Singh; Razdan, Samarth; Banana, Tejendra; Chandravanshi, Neelam; Alam, Md Mehboob

doi: 10.1039/d5cp03388hpmid: 41552997

To meet increasing energy demand, several molecules have been explored as dyes for dye-sensitized solar-cell (DSSC) applications. However, such designed cells are yet to attain a solar-power conversion efficiency (η) of more than 13%. To achieve this, new molecules should be investigated. In this work, for the first time, an antiaromatic metal-free molecule is explored for DSSC applications. We consider the antiaromatic orangarin core and load it with different donor and acceptor moieties at rationally chosen places that can enhance the absorption of sunlight. In this way, we design ten potential candidates for use as dyes in DSSCs. The photovoltaic properties, including the light-harvesting efficiency (LHE), open-circuit voltage, maximum short-circuit current density, fill factor, and η of all the designed molecules are calculated and analyzed using the state-of-the-art density functional theory and time-dependent density functional theory methods. Our study reveals that the antiaromatic nature of the core indeed increases the absorption strengths of the dyes and hence enhances the LHE and η up to an incredible value of 26%. The present study clearly demonstrates that an antiaromatic core should be explored further for DSSC application.

Wu, Meng; Shao, Ruiqi; Siddique, Amna; Akbarjon, Nishonov; Li, Tianyu; Ma, Tianshuai; Liu, Shouguo; Wang, Wei; Xu, Zhiwei

doi: 10.1039/d5cp04111bpmid: 41553257

Defects generated during the pre-oxidation of polyacrylonitrile (PAN)-based carbon fibers can significantly affect the ultimate quality of the resultant carbon fibers. Introducing irradiation in the pre-oxidation process has emerged as a potential approach to optimize the defect structure of polyacrylonitrile fibers. However, the evolution of defects and molecular transformation under irradiation-heat pre-oxidation remains unclear at the molecular-scale. This study employs molecular dynamics simulations alongside experimental characterization of polyacrylonitrile fibers to investigate the formation and evolution of defects in a crystalline region of a polyacrylonitrile model subjected to irradiation followed by heat treatment. Under constant dose rate conditions, the simulation results revealed that increasing irradiation energy induces the transition from vacancy defects to void defects in polyacrylonitrile crystalline domains. Defects caused by free-volume fluctuations are positively correlated with irradiation energy. The molecular species increased with rising irradiation energy, resulting in more severe morphological damage to the polyacrylonitrile model. Irradiation at 7.5 keV induced maximum chain scission in the crystalline regions of polyacrylonitrile, exerting a detrimental effect on heat treatment outcomes. Conversely, 10 keV irradiation generated the most extensive area of chain cross-linking. The study proposes that irradiation energy around 7.5 keV serves as a critical threshold for inducing maximum defect formation in PAN crystalline molecular models.

Anversa, Jonas; Baierle, Rogério José; Piquini, Paulo César

doi: 10.1039/d5cp03197dpmid: 41556132

First-principles calculations within spin polarized density functional theory (SP-DFT) were used to study the stability, and the electronic and magnetic properties of a vdW heterostructure by stacking an MXene (Ca2C) and silicene, forming the Ca2C/silicene van der Waals (vdW) heterostructure. Our results show that the Ca2C/silicene presents structural integrity without deformations, being a ferromagnetic metal system. The small magnetic moment (0.087µB) in the pristine Ca2C layer, which is mainly localized in the p-planar orbitals of the C atom, increases to 0.64µB in the Ca2C/silicene heterostructure due to the asymmetry in the spin of the π electrons that flow from MXene to silicene. Furthermore, the Curie temperature in the Ca2C/silicene heterostructure is strongly enhanced (TC = 340 K) and calculations of the magnetic anisotropy energy (MAE) show that it is double when the vdW heterostructure forms. Furthermore, the easy magnetization axis changes from the planar (Ca2C monolayer) to the perpendicular direction (vdW heterostructure). The high TC and MAE open a channel for the construction of magnetic devices using light atoms (without the presence of d and/or f electrons). In addition, the electronic and magnetic properties of the vdW heterostructure can be tailored by vertical strain.