Bond Proton Research Articles

Investigating proton shuttling and electrochemical mechanisms of amines in integrated CO2 capture and utilization

Carbon capture and utilization (CCU) technologies present a promising solution for converting CO2 emissions into valuable products. Here we show how amines, such as monoethanolamine (MEA) and 2-amino-2-methyl-1-propanol (AMP), influence the electrochemical CO2 reduction process in an integrated CCU system. Using in situ spectroscopic techniques, we identify the key roles of carbamate bond strength, proton shuttling, and amine structure in dictating reaction pathways on copper (Cu) and lead (Pb) electrodes. Our findings demonstrate that on Cu electrodes, surface blockage by ammonium species impedes CO₂ reduction, whereas on Pb electrodes, proton shuttling enhances the production of hydrocarbon products. This study provides additional insights into optimizing CCU systems by tailoring the choice of amines and electrode materials, advancing the selective conversion of CO₂ into valuable chemicals.

Hydrogen bonding network in the electrical double layer mediates fast proton skipping to Get Rid of Fenton reaction pH dependence enables highly efficient alkaline water purification

A fundamental scientific quandary in environmental has always been the pH dependence in Fenton reaction, that is, the reaction kinetics decreases by approximately 1–3 orders of magnitude upon transitioning from an acidic to an alkaline state. Here, we discovered that protons significantly contribute to the Fenton reaction through an examination of the reaction's interfacial behavior characteristics. Proton transfer mediated by hydrogen bond network connectivity in the electric double layer is responsible for the pH dependence of Fenton reaction kinetics. On this basis, the surface potential of Fenton reaction catalyst was modified to optimize the distribution of H2O in the electrical double layer, enhancing the connectivity of the interfacial hydrogen bond network and providing a fast channel for rapid proton transfer. The consecutive hydrogen bond network mediates rapid proton hopping, increasing the proton concentration in the Helmholtz layer, and consequently promoting the proton conductivity from 5.38×10−7 S·cm−2 to 4.35×10−6 S·cm−2 in alkaline conditions for Fenton reaction. Meanwhile, the kinetics reaction rate was improved 20 times, and the pH dependence was reduced from 70.9 % to 12.6 %. This discovery clarifies the key role of the interfacial hydrogen bond network and proton transfer in Fenton reaction kinetics pH dependence. It provides new theories and methods for achieving alkaline high Fenton reaction kinetics.

Computer-aided drug design supporting sunscreen research: a showcase study using previously synthesized hybrid UV filter-antioxidant compounds.

Although quantum mechanical calculations have proven effective in accurately predicting UV absorption and assessing the antioxidant potential of compounds, the utilization of computer-aided drug design (CADD) to support sustainable synthesis research of new sunscreen active ingredients remains an area with limited exploration. Furthermore, there are ongoing concerns about the safety and effectiveness of existing sunscreens. Therefore, it remains crucial to investigate photoprotection mechanisms and develop enhanced strategies for mitigating the harmful effects of UVR exposure, improving both the safety and efficacy of sunscreen products. A previous study conducted synthesis research on eight novel hybrid compounds (I-VIII) for use in sunscreen products by molecular hybridization of trans-resveratrol (RESV), avobenzone (AVO), and octinoxate (OMC). Herein, time-dependent density functional theory (TD-DFT) calculations performed in the gas phase on the isolated hybrid compounds (I-VIII) proved to reproduce the experimental UV absorption. Resveratrol-avobenzone structure-based hybrids (I-IV) present absorption maxima in the UVB range with slight differences between them, while resveratrol-OMC structure-based hybrids (V-VIII) showed main absorption in the UVA range. Among RESV-OMC hybrids, compounds V and VI exhibited higher UV absorption intensity, and compound VIII stood out for its broad-spectrum coverage in our simulations. Furthermore, both in silico and in vitro analyses revealed that compounds VII and VIII exhibited the highest antioxidant activity, with compound I emerging as the most reactive antioxidant within RESV-AVO hybrids. The study suggests a preference for the hydrogen atom transfer (HAT) mechanism over single-electron transfer followed by proton transfer (SET-PT) in the gas phase. With a strong focus on sustainability, this approach reduces costs and minimizes effluent production in synthesis research, promoting the eco-friendly development of new sunscreen active ingredients. The SPARTAN'20 program was utilized for the geometry optimization and energy calculations of all compounds. Conformer distribution analysis was performed using the Merck molecular force field 94 (MMFF94), and geometry optimization was carried out using the parametric method 6 (PM6) followed by density functional theory (DFT/B3LYP/6-31G(d)). The antioxidant behavior of the hybrid compounds (I-VIII) was determined using the highest occupied molecular orbital (εHOMO) and the lowest unoccupied molecular orbital (εLUMO) energies, as well as the bond dissociation enthalpy (BDE), ionization potential (IP), and proton dissociation enthalpy (PDE) values, all calculated at the same level of structural optimization. TD-DFT study is carried out to calculate the excitation energy using the B3LYP functional with the 6-31G(d) basis set. The calculated transitions were convoluted with a Gaussian profile using the Gabedit program.

Bridged Pt-OH-Mn Mediator in N-coordinated Mn Single Atoms and Pt Nanoparticles for Electrochemical Biomolecule Oxidation and Discrimination.

The rational design of efficient catalysts for uric acid (UA) electrooxidation, as well as the establishment of structure-activity relationships, remains a critical bottleneck in the field of electrochemical sensing. To address these challenges, herein, a hybrid catalyst that integrates carbon-supported Pt nanoparticles and nitrogen-coordinated Mn single atoms (PtNPs/MnNC) is developed. The metal-metal interaction during annealing affords the construction of metallic-bonded Pt-Mn pairs between PtNPs and Mn single atoms, facilitating the electron transfer from PtNPs to the support and thereby optimizing the electronic structure of catalysts. More importantly, experiments and theoretical calculations provide visual proof for the 'incipient hydrous oxide adatom mediator' mechanism for UA oxidation. The Pt-Mn pairs first adsorb OH* to construct the bridged Pt-OH-Mn mediators to serve as a highly active intermediate for N-H bond dissociation and proton transfer. Benefiting from the unique electronic and geometric structure of the catalytic center and reactive intermediates, PtNPs/MnNC exhibits superior electrooxidation performance. The electrochemical sensor based on PtNPs/MnNC enables sensitive detection and discrimination of UA and dopamine in serum samples. This work offers new insights into the construction of novel electrocatalysts for sensitive sensing platforms.

Bridged Pt−OH−Mn Mediator in N‐coordinated Mn Single Atoms and Pt Nanoparticles for Electrochemical Biomolecule Oxidation and Discrimination

AbstractThe rational design of efficient catalysts for uric acid (UA) electrooxidation, as well as the establishment of structure‐activity relationships, remains a critical bottleneck in the field of electrochemical sensing. To address these challenges, herein, a hybrid catalyst that integrates carbon‐supported Pt nanoparticles and nitrogen‐coordinated Mn single atoms (PtNPs/MnNC) is developed. The metal‐metal interaction during annealing affords the construction of metallic‐bonded Pt−Mn pairs between PtNPs and Mn single atoms, facilitating the electron transfer from PtNPs to the support and thereby optimizing the electronic structure of catalysts. More importantly, experiments and theoretical calculations provide visual proof for the ‘incipient hydrous oxide adatom mediator’ mechanism for UA oxidation. The Pt−Mn pairs first adsorb OH* to construct the bridged Pt−OH−Mn mediators to serve as a highly active intermediate for N−H bond dissociation and proton transfer. Benefiting from the unique electronic and geometric structure of the catalytic center and reactive intermediates, PtNPs/MnNC exhibits superior electrooxidation performance. The electrochemical sensor based on PtNPs/MnNC enables sensitive detection and discrimination of UA and dopamine in serum samples. This work offers new insights into the construction of novel electrocatalysts for sensitive sensing platforms.

Stepwise Protonation of Three-Dimensional Covalent Organic Frameworks for Enhancing Hydrogen Peroxide Photosynthesis.

Three-dimensional covalent organic frameworks (3D COFs), recognized for their tailorable structures and accessible active sites, offer a promising platform for developing advanced photocatalysts. However, the difficulty in the synthesis and functionalization of 3D COFs hinders their further development. In this study, we present a series of 3D-bcu-COFs with 8 connected porphyrin units linked by linear linkers through imine bonds as a versatile platform for photocatalyst design. The photoresponse of 3D-bcu-COFs was initially modulated by functionalizing linear linkers with benzo-thiadiazole or benzo-selenadiazole groups. Furthermore, taking advantage of the well-exposed porphyrin and imine sites in 3D-bcu-COFs, their photocatalytic activity was optimized by stepwise protonation of imine bonds and porphyrin centers. The dual protonated COF with benzo-selenadiazole groups exhibited enhanced charge separation, leading to an increased photocatalytic H2O2 production under visible light. This enhancement demonstrates the combined benefits of linker functionalization and stepwise protonation on photocatalytic efficiency.

Stepwise Protonation of Three‐Dimensional Covalent Organic Frameworks for Enhancing Hydrogen Peroxide Photosynthesis

AbstractThree‐dimensional covalent organic frameworks (3D COFs), recognized for their tailorable structures and accessible active sites, offer a promising platform for developing advanced photocatalysts. However, the difficulty in the synthesis and functionalization of 3D COFs hinders their further development. In this study, we present a series of 3D‐bcu‐COFs with 8 connected porphyrin units linked by linear linkers through imine bonds as a versatile platform for photocatalyst design. The photoresponse of 3D‐bcu‐COFs was initially modulated by functionalizing linear linkers with benzo‐thiadiazole or benzo‐selenadiazole groups. Furthermore, taking advantage of the well‐exposed porphyrin and imine sites in 3D‐bcu‐COFs, their photocatalytic activity was optimized by stepwise protonation of imine bonds and porphyrin centers. The dual protonated COF with benzo‐selenadiazole groups exhibited enhanced charge separation, leading to an increased photocatalytic H2O2 production under visible light. This enhancement demonstrates the combined benefits of linker functionalization and stepwise protonation on photocatalytic efficiency.

Molecular Hydrogen Acts as a Hydrogen Bond Proton Acceptor: From Protonated Betaine Tagging to the Weakest Hydrogen Bond.

In an attempt to gain further insights into the intermolecular interactions implied by Rizzo's group's cautionary tale related to molecular tagging in infrared multiple photon dissociation (IRMPD) spectroscopy with molecular messengers [Masson, A. . J. Chem. Phys. 2015, 143, 104313], in the present study, we provide an in-depth analysis of the noncovalent interaction between the molecular hydrogen and protonated betaine molecule in the gas phase. We aim to shed some new light on the fundamental issues concerning the wide diapason of hydrogen-bonding-type intermolecular interactions, with a wide variety of proton acceptors. We demonstrate that in the course of tagging the protonated betaine with molecular hydrogen from the OH group side, it is the σ bond of molecular hydrogen that plays the role of hydrogen-bonding proton acceptor. The tagging thus induces a small yet significant red shift of the protonated betaine O-H stretching mode. We investigate the performance of a wide range of density functional theory (DFT) functionals for the calculation of anharmonic vibrational frequency shifts of the studied system, which are essential for the correct interpretation of the experimental IRMPD data. For an accurate prediction of the OH stretching frequency shifts, specifically designed functionals such as Handy's group HCTH/407 should be applied. The empirical dispersion correction enhances the systematic overestimation of the anharmonic frequency shift, characteristic of the most widely used DFT functionals. Combining the full-wave function approach with the charge field perturbation and natural bond orbital (NBO) deletion analyses, we demonstrate that the frequency shift in the OH-tagged structure is governed by the σHH → σ*OH intermolecular charge transfer. This interaction stabilizes the OH-tagged dimer as well, in contrast to the dipole-quadrupole electrostatic interaction energy term. Topological analysis of the electron density reveals the presence of an intermolecular bond critical point with a positive value of the density Laplacian very close to the lower limit for hydrogen bonds. NCI analyses demonstrate that the OH···H2 interaction is weaker than the intramolecular CH···O one within the protonated betaine molecule, with the through of reduced density gradient appearing at less negative sign(λ2)·ρ values. Analyzing the O-H stretching vibrational potential with the second-generation absolutely localized molecular orbitals energy decomposition analysis (ALMO-EDA 2) revealed that in the case of betaineH(+) tagged from the OH group side, the permanent electrostatics (ΔEelec), polarization (ΔEpol), and charge-transfer (ΔEct) contributions to the total intermolecular interaction energy contribute favorably to the weak hydrogen bond formation and to the red shift of the fundamental O-H stretching frequency, the ΔEct contribution being the most significant in the last context. The Pauli repulsion term, on the other hand, favors an O-H stretching frequency blue shift as a consequence of the vibrational confinement effects.

Vibrational signatures of dynamic excess proton storage between primary amine and carboxylic acid groups.

Ammonium and carboxylic moieties play a central role in proton-mediated processes of molecular recognition, charge transfer or chemical change in (bio)materials. Whereas both chemical groups constitute acid-base pairs in organic salt-bridge structures, they may as well host excess protons in acidic environments. The binding of excess protons often precedes proton transfer reactions and it is therefore of fundamental interest, though challenging from a quantum chemical perspective. As a benchmark for this process, we investigate proton storage in the amphoteric compound 5-aminovaleric acid (AV), within an intramolecular proton bond shared by its primary amine and carboxylic acid terminal groups. Infrared ion spectroscopy is combined with abinitio Molecular Dynamics (AIMD) calculations to expose and rationalize the spectral signatures of protonated AV and its deuterated isotopologues. The dynamic character of the proton bond confers a fluxional structure to the molecular framework, leading to wide-ranging bands in the vibrational spectrum. These features are reproduced with remarkable accuracy by AIMD computations, which serves to lay out microscopic insights into the excess proton binding scenario.

Imine-Linked 2D Conjugated Porous Organic Polymer Films for Tunable Acid Vapor Sensing.

Two-dimensional (2D) films of conjugated porous organic polymers (C-POPs) can translate the rich in-plane functionalities of conjugated frameworks into diverse optical and electronic applications while addressing the processability issues of their crystalline analogs for adaptable device architectures. However, the lack of facile single-step synthetic routes to obtain large-area high-quality films of 2D-C-POPs has limited their application possibilities so far. Here, we report the synthesis of four mechanically robust imine-linked 2D-C-POP free-standing films using a single-step fast condensation route that is scalable and tunable. The rigid covalently bonded 2D structures of the C-POP films offer high stability for volatile gas sensing in harsh environments while simultaneously enhancing site accessibility for gas molecules due to mesoporosity by structural design. Structurally, all films were composed of exfoliable layers of 2D polymeric nanosheets (NSs) that displayed anisotropy from disordered stacking, evinced by out-of-plane birefringent properties. The tunable in-plane conjugation, different nitrogen centers, and porous structures allow the films to act as ultraresponsive colorimetric sensors for acid sensing via reversible imine bond protonation. All the films could detect hydrogen chloride (HCl) gas down to 0.05 ppm, far exceeding the Occupational Safety and Health Administration's permissible exposure limit of 5 ppm with fast response time and good recyclability. Computational insights elucidated the effect of conjugation and tertiary nitrogen in the structures on the sensitivity and response time of the films. Furthermore, we exploited the exfoliated large 2D NSs and anisotropic optoelectronic properties of the films to adapt them into micro-optical and triboelectric devices to demonstrate their real-time sensing capabilities.

CuI-amidobis(phosphine) catalyzed C(sp3)-C(sp3) direct homo- and hetero-coupling of unactivated alkanes via C(sp3)-H activation.

Herein, we present a CuI-dimer, [CuI{Ph2PC6H4C(O)NC6H4PPh2-o}]2, which catalyzed direct C(sp3)-H homocoupling of benzyl and cycloalkane derivatives with excellent yields and regio-selectivity. The method is very simple and tolerates various functionalities. Synergistic metal-ligand cooperativity was observed in Cu-N bond cleavage and protonation of nitrogen, and facilitates a bifunctional pathway, minimising the free energy corrugation for catalytic intermediates.

Effects of hydroxychromone rings with chalcogen atoms on ESIPT for 3-hydroxy-2-(5-(5-(5-(3-hydroxy-4-oxo-4H-chromen-2-yl)thiophen-2-yl)thiophen-2-yl)thiophen-2-yl)-4H-chromen-4-one derivatives: A theoretical study

Inspired by fascinating photochemical and photophysical characteristics of novel organic molecules with chalcogenide substitution, this study focuses on exploring the effects of atomic electronegativity of chalcogens (O, S, and Se) on hydrogen bond interactions and proton transfer reaction mechanisms for 3-hydroxy-2-(5-(5-(5-(3-hydroxy-4-oxo-4H-chromen-2-yl)thiophen-2-yl)thiophen-2-yl)thiophen-2-yl)-4H-chromen-4-one (FT). By comparing structural changes and infrared (IR) spectra, combined with preliminary detection of hydrogen bond interaction by core-valence bifurcation (CVB) index, we conclude S1-state hydrogen bond is strengthened, which is favorable for occurrence of ESIPT reaction. Charge recombination and constructed potential energy surfaces (PESs) reveal atomic electronegativity has a regulatory effect on ESIPT behavior for FT derivatives.

Effects of substituted chalcogen atoms on excited state reaction for 1-(benzo[d]thiazol-2-yl)-6-substituted-naphthalen-2-ol derivatives

Inspired by the brilliant photophysical properties of novel organic molecules containing chalcogenide substitution, in this work, effects of atomic electronegativity of chalcogen (O, S and Se) on hydrogen bond interactions and proton transfer (PT) reaction are focused. We present the characteristic CN-BTN is the main objective to explore the influence of atomic electronegativity on the hydrogen bond interaction and excited state intramolecular proton transfer (ESIPT) behaviour by photoexcitation. By comparing the structural changes and infrared (IR) vibrational spectra of the CN-BTN derivatives (CN-BTN-O, CN-BTN-S and CN-BTN-Se) fluorophores in S0 and S1 states, combined with the preliminary detection of hydrogen bond interaction by core-valence bifurcation (CVB) index, we can conclude that hydrogen bond is strengthened in S1 state, which is favourable for the occurrence of ESIPT reaction. The charge recombination behaviour of hydrogen bond induced by photoexcitation also further illustrates this point. Via constructing potential energy curves (PECs) based on restrictive optimisation and searching transition state (TS) configuration, we finally clarify the ESIPT mechanism for CN-BTN derivatives. Specially, we confirm change of atomic electronegativity has a regulatory effect on the ESIPT behaviour of CN-BTN derivatives, that is, the lower the atomic electronegativity is more conducive to the ESIPT reaction.

Mitigation mechanism of resveratrol on thermally induced trans-α-linolenic acid of trilinolenin

Investigations in the control of the thermal isomerization of trans fatty acids (TFAs) in edible oils are of great significance in effectively improving the safety of edible oil. The mitigation mechanism of resveratrol (Res) on thermally induced trans-α-linolenic acids (TALAs) of trilinolenin was delved by gas chromatography and density functional theory. The results revealed that the mitigative rate of Res on TALAs in trilinolenin increased with the heating temperature and time, and C18-3:9c,12c,15t (3.82 ∼ 13.90%) > C18-3:9t,12c,15c (3.47 ∼ 11.50%) > C18-3:9c,12t,15c (4.22 ∼ 4.72%). After heating at 180 °C and 200 °C for 4 h and 8 h without oxygen, the mitigation of TALAs by Res was mainly exerted by the hydrogen extraction and proton transfer isomerism mechanism. Both mitigation mechanisms were that Res firstly bound to the Ln allyl position to increase molecular steric hindrance, thereby preventing the bond rotation and proton transfer to inhibit the formation of TALAs; Res was preferentially bound to the di-allyl sites (Ln-11 site > Ln-14 site), followed by the mono-allyl sites (Ln-17 site > Ln-8 site). The study provides a theoretical foundation for the precise control of TALAs in edible oil systems.

A Computational Study on the Reaction Mechanism of Stereocontrolled Synthesis of β-Lactam within [2]Rotaxane.

The macrocycle effect of [2]rotaxane on the highly trans-stereoselective cyclization reaction of N-benzylfumaramide was extensively investigated by various computational methods, including DFT and high-level DLPNO-CCSD(T) methods. Our computational results suggest that the most favorable mechanism of the CsOH-promoted cyclization of the fumaramide into trans-β-lactam within [2]rotaxane initiates with deprotonation of a N-benzyl group of the interlocked fumaramide substrate by CsOH, followed by the trans-selective C-C bond formation and protonation by one amide functional group of the macrocycle. Our distortion/interaction analysis further shows that the uncommon trans-stereoselective cyclization forming β-lactam within the rotaxane may be attributed to a higher distortion energy (mainly from the distortion of the twisted cis-fumaramide conformation enforced by the rotaxane). Our systematic study should give deeper mechanistic insight into the reaction mechanism influenced by a supramolecular host.

Controllable preparation of imine-based nanofilms towards ozone detection and removal

Developing affordable, robust and less cumbersome ozone sensing materials is of pivotal importance for on-site and at real-time ozone monitoring in air, but that remains a challenge. Herein, we report for the first time the highly controllable preparation of a new kind of imine-based nanofilms with commercially available tris(4-aminophenyl) amine (TAPA) and 4,4',4''-((1,3,5-Triazine-2,4,6-triyl)tris(oxy))tribenzaldehyde (TOH-CHO) as the building blocks and their applications in the fast, sensitive detection and efficient removal of the analyte. The nanofilms as prepared are highly flexible and adaptive to substrates of very different properties and morphologies. In addition, the thickness of the nanofilms can be fine-tuned via variation of the precursor concentration. Ozone sensing and removal were realized by cumulative adsorption and decomposition accompanied with color change, where the nanofilms can be fully recovered via ammonia purging. Mechanism studies revealed that the high sensing and removing performance may originate from the protonation of imine bonds within the nanofilms. Further studies demonstrated that the sensing is highly selective and shows an experimental detection limit lower than 0.7 ppm. Moreover, visualized sensing of ozone in real-life scenarios was also realized via utilization of a test strip based on the nanofilms.

Theoretical Investigation on the Mechanistic Pathways of Cp*Cobalt(III)- Catalyzed Transformation of N-Substituted Carbamoyl Indoles to Pyrroloindolone Derivatives

Aim: A theoretical study on the Cp*cobalt(III) catalyzed C-H functionalization transformation of N-substituted carbamoyl indoles with alkyne derivatives to pyrroloindolone derivatives has been performed using DFT method. Background: Indole skeleton is an important part for developing regioselective C-H bond functionalisation reactions. Pyrrolo[1,2-a]indole bearing a 6-5-5 tricyclic skeleton (Scheme-1) is an important structural component found in many biologically active natural products and pharmaceuticals, (such as antitumor mitomycin C, antimalarial flinderole B etc.).Thus C−H activation process has great demand methods for efficiently synthesizing a pyrrolo[1,2-a]indole unit from readily available starting materials. One such attractive report was published by Matsunaga & Kanai et.al., Which shows pyrroloindolone derivatives can be synthesized (Scheme-2) through Cp*Co(III) catalysed C-H alkenylation and annulations from N-substituted carbamoyl indoles. Objective: Our current project deals with the determination of the rate determining step of the reaction, to determine the energetically favourable pathway. Investigation of the actual reason behind the regioselectivity of the products whether it is steric or electronic effects of the substituents. Method: The geometry optimization and energy calculations of all the systems were carried out with the Gaussian 09 software. Construction of trial geometries, monitoring the progress of calculations and visualization of the final output were done by several graphical user interface softwares like Gauss View, Molden etc. Geometry optimization of all species is performed using M06-2X functional in DFT method as a method for performing optimization of structures. 6-31G (d, p) basis set was employed for all non-metal atoms and the LANL2DZ basis set was employed for cobalt. To find out the geometries of several transition structures on the potential energy surface (PES) of the reaction pathway, relaxed scan method was used. Result: DFT study on a reaction of carbamoyl indoles with alkyne derivatives by activate Co(III)Cp* catalytic condition is done here. The target scheme followed the energetics of two possible pathways. The initial step of the reaction is the alkyne insertion step which needs 21.27 kcal mol-1 amount of energy. In the first case the final annulated product has been generated through a carbon-carbon bond formation, proton transfer and demetallation processes in path-a. The global activation barrier has been found to be quite high (30.17 kcal mol-1). However the study of the second pathway, which generated the simple alkenylated product through the proto-demetalation process in path-b, reveals a more reliable activation barrier (21.27 kcal mol-1). Conclusion: Comparison of the energy requirement clearly reveals that the formation of the final product should go through favourable simple alkenylation process that is path-b for dimethyl amine. Due to lower energy barrier the simple alkenylation pathway (i.e Path-b) is more favourable one. Initial alkyne addition step is the rate determining step. The regioselectivity of the alkyne addition is purely governed by the steric crowding around the substrate. Thus the favourable mode of alkyne addition has lower energy barrier due to lesser steric interactions. This theoretical investigation may guide the future researchers for developing some other economical route for generating similar derivatives.

Front Cover Picture: Rhodium(III)‐Catalyzed Divergent C−H Functionalization of N‐Aryl Amidines with Iodonium Ylides: Access to Carbazolones and Zwitterionic Salts (Adv. Synth. Catal. 11/2023)

The cover design shows a Chinese fairy tale “Carp jump over the dragon gate”. There was a Dragon Gate on the Yellow River. Carps could jump over it and turn into dragons, which means that everyone should conquer some difficulty before success. Herein, this design illustrates the Rhodium(III)-catalyzed C−H bond intramolecular annulations and proton transfer strategy. The “dragon gate” represents the energy to be overcome in the catalytic cycle. The “leaping carp” represents the intramolecular annulation and proton transfer progress, indicating that the carp would become a dragon (products) after it crosses the dragon gate (energy). Details can be found in the Research Article by Cui, Wu and co-workers (J. Ren, L. Yang, C. Pi, X. Cui, Y. Wu, Adv. Synth. Catal. 2023, 365, XXXX–XXXX; DOI: 10.1002/adsc.202300039)

A Dynamic Proton Bond: MH+·H2O ⇌ M·H3O+ Interconversion in Loosely Coordinated Environments.

The interaction of organic molecules with oxonium cations within their solvation shell may lead to the emergence of dynamic supramolecular structures with recurrently changing host-guest chemical identity. We illustrate this phenomenon in benchmark proton-bonded complexes of water with polyether macrocyles. Despite the smaller proton affinity of water versus the ether group, water in fact retains the proton in the form of H3O+, with increasing stability as the coordination number increases. Hindrance in many-fold coordination induces dynamic reversible (ether)·H3O+ ⇌ (etherH+)·H2O interconversion. We perform infrared action ion spectroscopy over a broad spectral range to expose the vibrational signatures of the loose proton bonding in these systems. Remarkably, characteristic bands for the two limiting proton bonding configurations are observed in the experimental vibrational spectra, superimposed onto diffuse bands associated with proton delocalization. These features cannot be described by static equilibrium structures but are accurately modeled within the framework of ab initio molecular dynamics.

Antioxidant activity and enzymatic of lichen substances: A study based on cyclic voltammetry and theoretical

The antioxidant activity of nine lichen substances, including methylatrarate (1), methyl haematommate (2), lobaric acid (3), fumarprotocetraric acid (4), sphaerophorin (5), subsphaeric acid (6), diffractaic acid (7), barbatolic acid (8) and salazinic acid (9) has been determined through cyclic voltammetry. The compounds 1–4 presented slopes close to the Nernst constant of 0.059 V, indicating a 2H+/2e− relation between protons and electrons, as long as the compounds 5, 6, 7, 8, and 9 present slopes between 0.037 V and 0.032 V, indicating a 1H+/2e− relation between protons and electrons. These results show a high free radical scavenging activity by means of the release of H+, suggesting an important antioxidant capacity of these molecules. Theoretical calculations of hydrogen bond dissociation enthalpies (BDE), proton affinities (PA), and Proton Transfer (PT) mechanisms, at M06-2x/6-311+G(d,p) level complement the experimental results. Computations support that the best antioxidant activity is obtained for the molecules (3, 4, 5, 6, 7 and 8), that have a carboxylic acid group close to a phenolic hydroxyl group, through hydrogen atomic transfer (HAT) and sequential proton loss electron transfer (SPLET) mechanisms. Additional computations were performed for modelling binding affinity of the lichen substances with CYPs enzymes, mainly CYP1A2, CYP51, and CYP2C9*2 isoforms, showing strong affinity for all the compounds described in this study.