Dissociation Process Research Articles

Anterior and posterior thalamic volumes differentially correlate with memory, attention, and motor processes in HIV infection and alcohol use disorder comorbidity

The thalamus, with its reciprocal connections to and from cortical, subcortical, and cerebellar regions, is a central active participant in multiple functional brain networks. Structural MRI studies measuring the entire thalamus without respect to its regional or nuclear divisions report volume shrinkage in diseases including HIV infection, alcohol use disorder (AUD), and their comorbidity (HIV+AUD). Here, we examined relations between thalamic subregions (anterior, ventral, medial, and posterior) and neuropsychological functions (attention/working memory, executive functioning, episodic memory, and motor skills). Volumes of thalamic subregions were derived from automatic segmentations of standard T1 weighted MRIs of 65 individuals with HIV, 189 with AUD, 80 with HIV+AUD comorbidity, and 141 healthy controls (CTRL). Total thalamic volume was smaller and cognitive and motor composite scores were lower in the three diagnostic groups relative to the CTRL group. The AUD and HIV+AUD groups had significantly smaller thalamic subregional volumes than the CTRL group. The HIV+AUD group had smaller anterior thalamic volume than the HIV-only group and smaller ventral thalamic volume than the AUD-only group. In the HIV+AUD group, memory scores correlated with anterior thalamic volumes, attention/working memory scores correlated with posterior and medial thalamic volumes, and motor skill scores correlated with posterior thalamic volumes. Exploratory analyses focused on the HIV+AUD group indicated that within the posterior thalamic region, the pulvinar and medial geniculate nuclei were related to attention/working memory scores, and the pulvinar was related to motor skills scores. This study is novel in locating volume deficits in specific thalamic subregions, in addition to the thalamus as a whole, in HIV, AUD, and their comorbidity and in identifying functional ramifications of these deficits. Taken together, this study highlights the relevance of thalamic subregional volume deficits to dissociable cognitive and motor processes.

Multireference calculations on bond dissociation and biradical polycyclic aromatic hydrocarbons as guidance for fractional occupation number weighted density analysis in DFT calculations

This study explores open-shell biradical and polyradical molecular compounds based on extended multireference (MR) methods (MR-configuration interaction with singles and doubles (CISD) and MR-averaged quadratic coupled cluster (AQCC) approach) using the numbers of unpaired densities NU. These results were used to guide the analysis of the fractional occupation number weighted density (FOD) calculated within the finite temperature (FT) density functional theory (DFT) approach. As critical test examples, the dissociation of carbon–carbon (CC) single, double and triple bonds and a benchmark set of polycyclic aromatic hydrocarbons (PAHs) have been chosen. By examining single, double, and triple bond dissociations, we demonstrate the utility and accuracy but also limitations of the FOD analysis for describing these dissociation processes. In significant extension of previous work (Phys Chem Chem Phys 25: 27380–27393), the assessment of FOD applications for different classes of DFT functionals was performed examining the range-separated functionals ωB97XD, ωB97M-V, CAM-B3LYP, LC-ωPBE, and MN12-SX, the hybrid (M06-2X) functional and the double hybrid (B2P-LYP) functional. In all cases, strong correlations between NFOD and NU values are found. The major task was to develop a new linear regression formula for range-separated functionals allowing a convenient determination of the optimal electronic temperature Tel for the FT-DFT calculation. We also established an optimal temperature for the semiempirical extended tight-binding GFN2-xTB method. These findings significantly broaden the applicability of FOD analysis across various DFT functionals and semiempirical methods.

Distinguishing laser-induced dissociation pathways of O 2 molecule based on alignment-dependent dissociation spectra in intense laser fields

We experimentally investigate the dissociative single ionization process, O 2 → O + + O, of aligned O 2 molecule in intense laser fields. The yield of a vibrational structure in the kinetic energy release spectra is measured as a function of alignment angle. By quantitative comparison of the measured angle-dependent dissociation probability with the simulation of a classical model that considers ionization and thus additional interaction within the laser pulse, we are able to distinguish the dissociation pathway that contribute to the vibrational structure. It is found that for a relative low laser intensity, the vibrational structure are produced from the dissociation pathway of a 4Π u → f 4Π g − 1ω. As the laser intensity increases, the increasing of the population probability of higher vibrational states and the absorbtion probability of more photons makes another two dissociation pathways open and become dominant.

Enhanced Photocatalytic Hydrogen Evolution Activity Driven by the Synergy Between Surface Vacancies and Cocatalysts: Surface Reaction Matters.

The incorporation of defects and cocatalysts is known to be effective in improving photocatalytic activity, yet their coupled contribution to the photocatalytic hydrogen evolution process has not been well-explored. In this study, We demonstrate that the incorporation of S vacancies and NiSe can contribute to the improvement of charge separation efficiency via the formation of a strong electric field within the bulk ZnIn2S4 (ZIS) and on its surface. More importantly, We also demonstrate that the synergy of S vacancies and NiSe benefits the overall hydrogen evolution activity by facilitating the H2O adsorption and dissociation process. This is particularly important for hydrogen evolution taking place under alkaline conditions where the proton concentration is low, allowing ZISv-NiSe (containing abundant S vacancies) to outperform ZIS-NiSe under alkaline conditions. In contrast, under acid conditions, since there are already sufficient amounts of protons available for reaction, the hydrogen evolution activity became governed by the hydrogen adsorption/desorption process rather than the H2O dissociation process. This leads to ZIS-NiSe exhibiting higher activity than ZISv-NiSe due to its more favorable hydrogen adsorption energy. The findings thus provide insights into how defect and cocatalyst modification strategies can be tailor-made to improve hydrogen evolution activity under different pH conditions.

Assessing Solid Catalysts with Ionic Liquid Layers (SCILL) from Molecular Dynamics Simulations: On the Role of Local Charge Polarization.

Recent developments in molecular mechanics modelling of metal catalyst surfaces with interfaces to complex ad-layers or bulk liquids enable the study of 10 nm scale systems by molecular dynamics simulations of up to microseconds. Therein, electronic polarization as otherwise benchmarked by quantum calculations is mimicked via atom-centered partial charges that are adjusted dynamically to account for changes in local environment. Apart from thermal fluctuations, this encompasses molecule association and dissociation processes as well as externally applied voltage. Here, we elaborate the concept of employing the charge equilibration method to the molecular dynamics simulation of solid catalysts, namely metal surfaces and substrate-supported metal nanoparticles. This showcases the association of reactants and their interplay with local charge polarization upon co-adsorption of ionic liquids or application of external voltage - thus paving the way to understanding complex interfaces in (electro-)catalysis from molecular dynamics simulation.

Structural Effects on the Energy Disposal and Atomic Photofragment Alignment for the Photodissociation of Alkyl Iodides at Excitation Wavelengths of 254 and 268 nm.

This work represents a step forward in the understanding of the widely studied photodynamics of alkyl iodides in the first absorption band. Ultraviolet (UV) photodissociation of several alkyl iodides (RI), specifically, a series of linear and ramified molecules with R = CnH2n+1, n = 1-4, at excitation wavelengths of 254 and 268 nm, which correspond to the maximum of the first absorption A-band, has been studied by combining resonance-enhanced multiphoton ionization (REMPI) detection of atomic photofragments I(2P3/2) and I*(2P1/2) and of pulsed slice imaging. Detailed examination of the total translational energy distributions of both atomic photofragments has been combined with stereodynamical information on the process obtained from the anisotropy β and alignment a02(∥) and Re[a12(∥, ⊥)] parameters to provide a description of the role played by the molecular structure of alkyl iodides in adiabatic and, especially, in nonadiabatic photodissociation dynamics through conical intersections or avoided crossings. The present results suggest that the linear structures couple more efficiently with the pure C-I reaction coordinate, whereas for the branched structures, the coupling with additional vibrational (bending) modes gains importance, showing the dissociation process a multidimensional character. In addition, a large degree of cofragment rotational alignment has been found for the small linear CH3I and C2H5I and, unexpectedly, for the branched t-C4H9I (C3v symmetry), whereas the rest of the alkyl iodides show low alignment parameters.

Exploring Ground and Excited States Via Single Reference Coupled-Cluster Theory and Algebraic Geometry.

The exploration of the root structure of coupled cluster (CC) equations holds both foundational and practical significance for computational quantum chemistry. This study provides insight into the intricate root structures of these nonlinear equations at both the CCD and CCSD level of theory. We utilize computational techniques from algebraic geometry, specifically the monodromy and parametric homotopy continuation methods, to calculate the full solution set. We compare the computed CC roots against various established theoretical upper bounds, shedding light on the accuracy and efficiency of these bounds. We hereby focus on the dissociation processes of four-electron systems such as (H2)2 in both D2h and D∞h configurations, H4 symmetrically distorted on a circle, and lithium hydride. We moreover investigate the ability of single-reference CC solutions to approximate excited state energies. We find that multiple CC roots describe energies of excited states with high accuracy. Our investigations reveal that for systems like lithium hydride, CC not only provides high-accuracy approximations to several excited state energies but also to the states themselves.

Strong Electronic Metal-Support Interactions Enable the Increased Spin State of Co-N4 Active Sites and Performance for Acidic Oxygen Reduction Reaction.

Nonprecious metal catalysts, particularly M-N-C catalysts, are widely recognized as promising contenders for the oxygen reduction reaction (ORR). However, a notable performance gap persists between M-N-C catalysts and Pt-based catalysts under acidic conditions. In this study, hybrid catalysts comprising single Co atoms and ultralow concentrations of Pt3Co intermetallic nanoparticles (NPs) are introduced to enhance ORR performance. Under acidic conditions, these hybrid catalysts demonstrate ORR efficiency with a half-wave potential of 0.895 V, negligible decay even after 80 000 cycles, and a high maximum power density of 1.34 W cm-2 in fuel cells. This performance surpasses those of Co-N-C and Pt/Co-N-C catalysts. Both experimental findings and theoretical computations suggest that the heightened ORR activity stems from an increase in the spin density of Co sites induced by noble metal NPs, facilitating the activation of O-O bonds via side-on overlapping and enabling a transition in the reaction pathway from associative to dissociative processes. This research offers a promising avenue for the systematic design of M-N-C cathodes with an enhanced performance for acidic fuel cells.

Photochemical Mechanism of Co-C Bond Activation via Triplet Energy Transfer in Ethyl(aqua)cobaloxime.

The photochemical decomposition of ethyl(aqua)cobaloxime, [EtCoIII(dmgH)2H2O], a vitamin B12 derivative model complex, was investigated to understand the mechanism of the Co-CEt bond scission induced by light. Upon irradiation of [EtCoIII(dmgH)2H2O], the Co-CEt bond undergoes homolytic scission, resulting in Et/Co(II) radical pair (RP) formation in a similar fashion observed in alkylcobalamins. The [EtCoIII(dmgH)2H2O] complex acts as a potent quencher of a wide variety of excited states in the presence of organic molecules such as benzophenone. It has been proposed that the reaction mechanism involves Dexter energy transfer, resulting in the bond dissociation process. Two issues associated with the proposed mechanism have been investigated, namely, (i) how the energy transfer occurs from benzophenone to cobaloxime and (ii) how the Co-CEt bond is activated and cleaved. Both TD-DFT and CASSCF/NEVPT2 methods have been applied to show the feasibility of the energy transfer reaction via the triplet pathway from photocatalyst to substrate.

Alkali Metals Activated High Entropy Double Perovskites for Boosted Hydrogen Evolution Reaction.

An efficient and facile water dissociation process plays a crucial role in enhancing the activity of alkaline hydrogen evolution reaction (HER). Considering the intricate influence between interfacial water and intermediates in typical catalytic systems, meticulously engineered catalysts should be developed by modulating electron configurations and optimizing surface chemical bonds. Here, a high-entropy double perovskite (HEDP) electrocatalyst La2(Co1/6Ni1/6Mg1/6Zn1/6Na1/6Li1/6)RuO6, achieving a reduced overpotential of 40.7mV at 10mA cm-2 and maintaining exemplary stability over 82 h in a 1m KOH electrolyte is reported. Advanced spectral characterization and first-principles calculations elucidate the electron transfer from Ru to Co and Ni positions, facilitated by alkali metal-induced super-exchange interaction in high-entropy crystals. This significantly optimizes hydrogen adsorption energy and lowers the water decomposition barrier. Concurrently, the super-exchange interaction enhances orbital hybridization and narrows the bandgap, thus improving catalytic efficiency and adsorption capacity while mitigating hysteresis-driven proton transfer. The high-entropy framework also ensures structural stability and longevity in alkaline environments. The work provides further insights into the formation mechanisms of HEDP and offers guidelines for discovering advanced, efficient hydrogen evolution catalysts through super-exchange interaction.

Vibrational spectroscopy and structural characterization of neutral and cationic hydroxyacetone

In this study, we utilized the infrared (IR)–vacuum-ultraviolet (VUV) non-resonant ionization and fragmentation detected IR spectroscopy (NRIFD-IR) technique to explore the IR spectra (2700–7200 cm-1) and the structures of both neutral and cationic hydroxyacetone. By comparing the experimentally obtained IR spectra with the anharmonic frequencies calculated at the B2PLYP-D3/cc-pVTZ and B3LYP-D3(BJ)/def2-TZVPP level of theory, we assigned the structures of hydroxyacetone and its cation. Notably, we observed a discrepancy in the neutral spectrum within the CH stretch region, depending on whether the parent or fragment channel was monitored. This observation suggests that the near-threshold dissociative ionization process exhibits mode-selectivity, implying that certain vibrational modes play a crucial role in either facilitating or inhibiting the dissociation event.

The superiority of isomeric, fluorination and curtailed π-conjunction on A–D–A type acceptors for organic photovoltaics

The performance of organic solar cell (OSC) devices has been significantly enhanced by the dramatic evolution of A–D–A type non-fullerene acceptors (NFAs). Nevertheless, the structure–property-performance relationship of NFAs in the OSC device is unclear. Here, the intrinsic design factors of isomeric, fluorination and π-conjunction curtailing on the photophysical properties of benzodi (thienopyran) (BDTP) (named NBDTP-M, NBDTTP-M, NBDTP-Fin, and NBDTP-Fout)-based NFAs are discussed. The results show that fluorination on the terminal group of NBDTP-Fout could effectively decrease the highest occupied orbital (HOMO) energy level and the lowest unoccupied orbital (LUMO) energy level. And the long π-conjugated donor unit for NBDTTP-M could increase the HOMO energy level and bring a small HOMO-LUMO energy bandgap. Meanwhile, the substitution of external oxygen atoms and the fluorine atoms in the terminal group could introduce positive changes to the electrostatic potential of the NBDTP-Fout, favouring the charge separation at the donor/acceptor interface. Moreover, the structural design of external oxygen atom substitution, fluorination on the terminal group and curtailed π-conjugated donor unit could decrease the electron vibration-coupling of exciton diffusion, exciton dissociation and electronic transfer processes. The suppression of the exciton decay and charge recombination in those high-performance NFAs indicate that the investigated molecular designs could be effective for further improvement of OSCs.

Overcoming Chemical Dissociation Processes: Electrochemical Modulation of High‐Affinity Binding Sites for Rapid Uranium Extraction from Seawater

AbstractCurrently reported adsorption (hydroxyl or amidoxime) groups must dissociate hydrogen ions to form ─O− units for the coordination with uranyl ions. However, this process suffers a high energy barrier for bond dissociation, leading to the sluggish uptake speed and low adsorption capacity for uranium extraction from natural seawater. Herein, this study proposes a strategy for electrochemical modulation of adsorption sites, which overcomes the chemical dissociation processes of hydrogen ions. Poly‐2,5‐dihydroxy‐1,4‐benzoquinone containing redox carbonyl groups is intercalated into the channels of a covalent organic framework (COF) through in situ cross‐linking of 2,5‐dihydroxy‐1,4‐benzoquinone. Under electrochemical modulation, the C═O groups are transformed into adjacent phenol–oxygen anions to cooperate with the coordination atoms (O and N) on the COF channel for rapid binding of uranyl ions, which gave an absorption rate of 4.2 mg g−1 d−1 (≈3.3 ppb of uranium in natural seawater). Notably, the COF‐based electrodes delivered an average capacity of ≈20.8 mg‐U per g for uranyl ion adsorption during 5 days of extraction, ≈3000 times larger than that of classical tannin‐based adsorbents. The proposed method for preparing electrochemically modulated binding sites is expected to provide guidance for designing high‐efficiency adsorbents in the future.

Doping dependence of boron–hydrogen dynamics in crystalline silicon

In this contribution, we investigate the formation and dissociation of boron–hydrogen (BH) pairs in crystalline silicon under thermal equilibrium conditions. Our samples span doping concentrations of nearly two orders of magnitude and are passivated with a layer stack consisting of thin aluminum oxide and hydrogen-rich silicon nitride (Al2O3/SiNx:H). This layer stack acts as a hydrogen source during a following rapid thermal annealing. We characterize the samples using low-temperature Fourier-transform infrared spectroscopy and four-point-probe resistivity measurements. Our findings show that the proportion of hydrogen atoms initially bound to boron (BH pairs) rises with increasing boron concentration. Upon isothermal dark annealing at (163 ± 2) °C, hydrogen present in molecular form, H2, dissociates at a rate directly proportional to the concentration of boron atoms, ∝ [B−], leading to the formation of BH pairs. With prolonged annealing, an unknown hydrogen complex is formed at a rate that is inversely proportional to the square of the boron concentration, ∝ 1/[B−]2, resulting in the disappearance of BH pairs. Based on experimental observations, we derive a kinetic model in which we describe the formation of the unknown complex through neutral hydrogen H0 binding to a sink. Additionally, we investigate the temperature dependence of the reaction rates and find that the H2 dissociation process has an activation energy of (1.11 ± 0.05) eV, which is in close agreement with theoretical predictions.

Non-metal doping enhsances oxygen reduction kinetics and CO2 tolerance of SrFeO3-δ perovskite as high-performance cathodes for solid oxide fuel cells

The sluggish of the oxygen reduction reaction (ORR) kinetics and the susceptibility to CO2 interactions are major barriers to the widespread application of solid oxide fuel cells (SOFCs). In this study, a non-metal cation doping strategy was employed to enhance the ORR catalytic activity and CO2 tolerance of SrFeO3-δ cathode. SrFe1-xPxO3-δ (SFPx, x = 0, 0.05, 0.1, 0.15, 0.2) materials were synthesized by substituting phosphorus (P) for Fe in SrFeO3-δ. The doping of P facilitated the formation of oxygen vacancies in SrFeO3-δ, enhancing oxygen adsorption, dissociation, diffusion, and charge transfer processes, leading to a notable increase in ORR catalytic activity. At 800 ℃, the polarization resistance of SFP0.15 was 0.08 Ω cm2, a reduction of 42.86 % compared to undoped SrFeO3-δ. Additionally, SFP0.15 achieved a peak power density of 749.36 mW cm2, representing a 91.99 % enhancement over SrFeO3-δ. These findings suggest that non-metal cation doping is an effective approach to boost the performance of SrFeO3-δ perovskite cathode.

Factors Affecting Cell Viability during the Enzymatic Dissociation of Human Endocrine Tumor Tissues.

The enzymatic dissociation of human solid tissues is a critical process for disaggregating extracellular matrix and the isolation of individual cells for various applications, including the immortalizing primary cells, creating novel cell lines, and performing flow cytometry and its specialized type, FACS, as well as conducting scRNA-seq studies. Tissue dissociation procedures should yield intact, highly viable single cells that preserve morphology and cell surface markers. However, endocrine tissues, such as adrenal gland tumors, thyroid carcinomas, and pituitary neuroendocrine tumors, present unique challenges due to their complex tissue organization and morphological features. Our study conducted a morphological examination of these tissues, highlighting the intricate structures and secondary degenerative changes that complicate the dissociation process. We investigated the effects of various dissociation parameters, including the types of enzymes, incubation duration, and post-dissociation purification procedures, such as debris removal and nontarget blood cell lysis, on the viability of cells derived from different tumor types. The findings emphasize the importance of optimizing tissue digestion protocols to preserve cell viability and integrity, ensuring reliable outcomes for downstream analyses.

Mean field approximation of a surface-reaction growth model with dissociation

We utilize mean field approximation to derive a set of coupled non-linear differential equations for a surface-reaction growth model, incorporating dissociative adsorption processes. These equations account for inaccessible sites caused by the height differences in the growing film, which inhibit dissociative adsorption. Numerical integration of these equations highlights the substantial effect of dissociation rates on growth kinetics, showing excellent agreement with prior kinetic Monte Carlo simulations, offering crucial insights into the interaction between dissociative adsorption and surface growth dynamics.

Study on the Micromorphology and Rheology of Tetrahydrofuran Hydrate during Formation and Dissociation Processes

Study on the Micromorphology and Rheology of Tetrahydrofuran Hydrate during Formation and Dissociation Processes

Enhanced De/hydrogenation Kinetics and Cycle Stability of Mg/MgH2 by the MnOx-Coated Ti2CTx Catalyst with Optimized Ti-H Bond Stability.

MXene based catalysts can significantly enhance hydrogenation and dehydrogenation (de/hydrogenation) kinetics of Mg/MgH2, but they suffer from uncontrollable catalysts-hydrogen bond strength and structural instability. Here, we propose Tx density control of MXene-based catalysts and MnOx coating as a promising solution. The MnOx@Ti2CTx-catalyzed Mg/MgH2 can release 5.97 wt % H2 at 300 °C in 3 min and 5.60 wt % H2 at 240 °C in 15 min with an activation energy of 75.57 kJ·mol-1. In addition, the samples showed excellent de/hydrogenation-cycle stability, and the degradation of hydrogen storage capacity is negligible even after 100 cycles. DFT calculations combined with XPS analysis showed that the Tx defect on the surface of the MnOx@Ti2CTx catalyst could optimize the strength of the Ti-H bond, accelerating both hydrogen dissociation and diffusion processes. The catalyst's surface properties were protected by the MnOx coating, achieving high chemical and catalytic stability. These findings offer a strategy for surface structure optimization and protection of MXene-based catalysts, realizing controllable catalyst-hydrogen bond strength.

Heterogeneous Structure of Ni-Mo Nanoalloys Decorated on MoOx for an Efficient Hydrogen Evolution Reaction Using Hydrogen Spillover.

Herein, a heterogeneous structure of Ni-Mo catalyst comprising Ni4Mo nanoalloys decorated on a MoOx matrix via electrodeposition is introduced. This catalyst exhibits remarkable hydrogen evolution reaction (HER) activity across a range of pH conditions. The heterogeneous Ni-Mo catalyst showed low overpotentials only of 24 and 86, 21 and 60, and 37 and 168mV to produce a current density of 10 and 100mAcm-2 (η10 and η100) in alkaline, acidic, and neutral media, respectively, which represents one of the most active catalysts for the HER. The enhanced activity is attributed to the hydrogen spillover effect, where hydrogen atoms migrate between the Ni4Mo alloys and the MoOx matrix, forming hydrogen molybdenum bronze as additional active sites. Additionally, the Ni4Mo facilitated the water dissociation process, which helps the Volmer step in the alkaline/neutral HER. Through electrochemical analysis, in situ Raman spectroscopy, and density functional theory calculations, the fast HER mechanism is elucidated.