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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 ab initio 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. [ABSTRACT FROM AUTHOR]

Quantum state-to-state nonadiabatic dynamics of the charge transfer reaction H+ + NO(X2Π, vi = 1, 3, ji = 0, 1) → H + NO+(X1Σ+) has been studied based on the recently constructed diabatic potential energy matrix. It was found that the vibrational excitation of reactant NO inhibits the reactivity, while the rotational excitation of reactant NO has little effect on the reaction probability. These attributes were also observed in the semi-classical trajectory calculations employed in the adiabatic representation. Such an inhibitory effect of the vibrational excitation of reactant NO was owing to lower accessibility of the conical intersection and avoided crossing regions, which are located in the wells with respect to the Π diabat, as evidenced by the analysis of the population of the time-independent wave functions. Calculated vibrational state distributions of the product show that the decrease of the reaction mainly leads to the less formation of low vibrational states (vf < 6), and the product vibrational state distributions are more evenly populated for vi = 1 and 3, suggesting a non-statistical behavior. However, the overall shapes of the product rotational distributions remain unchanged, indicating that the redistribution of energy into the rotation of product NO is sufficient in the charge transfer process between H+ and NO. While the reaction is dominated by the forward and backward scattering in differential cross sections (DCSs), consistent with the complex-forming mechanism, a clear forward bias in the DCSs appears, indicating that the occurrence of the reaction is not sufficiently long to undergo the whole phase space of the interaction configurations. [ABSTRACT FROM AUTHOR]

Effective photoinduced charge transfer makes molecular bimetallic assemblies attractive for applications as active light‐induced proton reduction systems. Developing competitive base metal dyads is mandatory for a more sustainable future. However, the electron transfer mechanisms from the photosensitizer to the proton reduction catalyst in base metal dyads remain so far unexplored. A Fe─Co dyad that exhibits photocatalytic H2 production activity is studied using femtosecond X‐ray emission spectroscopy, complemented by ultrafast optical spectroscopy and theoretical time‐dependent DFT calculations, to understand the electronic and structural dynamics after photoexcitation and during the subsequent charge transfer process from the FeII photosensitizer to the cobaloxime catalyst. This novel approach enables the simultaneous measurement of the transient X‐ray emission at the iron and cobalt K‐edges in a two‐color experiment. With this methodology, the excited state dynamics are correlated to the electron transfer processes, and evidence of the Fe→Co electron transfer as an initial step of proton reduction activity is unraveled. [ABSTRACT FROM AUTHOR]

Replacing the slow protonation process of oxygen evolution reaction (OER) with the fast protonation of alcohol electro‐oxidation can decrease the driving potentials, thus improving overall efficiency of electrochemical devices. However, the formation of effective catalytic sites for alcohol oxidation remains challenging in accelerating protonation to inhibit metal leaching and improve catalyst stability. Herein, asymmetric Ni‐O‐Cr sites are constructed by alloying Cr into the NiO matrix to optimize coordination environments, showing significantly enhanced stability during alcohol electro‐oxidation. The asymmetric Ni‐O‐Cr can maintain constant valence states of Cr and Ni during alcohol oxidation, efficiently suppressing metal dissolution even at high oxidation potentials. In situ electrochemical characterizations combined with theoretical calculations indicate that asymmetric Ni‐O‐Cr can improve adsorption and activation of OH* and alcohol molecules compared to pure NiO, thus increasing anodic kinetics. The theoretical results also indicate that the smaller gap of Ni 3d‐O 2p in asymmetric Ni‐O‐Cr strengthens charge transfer, leading to fast protonation of catalytic sites with enhanced stability. This work gives insights into boosting anodic protonation using asymmetric sites‐enriched solid‐solution electrocatalysts. [ABSTRACT FROM AUTHOR]

Motivated by the captivating allure of exquisitely regulated characteristics exhibited by 2‐(2‐hydroxyphenyl)‐benzoxazole and its derivatives in the domains of photochemistry and photophysics, our current endeavor primarily focuses on delving into the intricacies of photo‐induced excited state reactions for derivatives of 2,5‐bis(benzoxazol‐2‐yl)‐thiophene‐3,4‐diol (BTD). Given the profound impact of chalcogen element doping, our primary focus lies in investigating the excited state behaviors of BTD‐O, BTD‐S, and BTD‐Se fluorophores. Through simulations encompassing variations in geometry and vertical excitation charge reorganization, we unveil atomic‐electronegativity‐dependent hydrogen bonding interactions and photoexcitation‐induced charge recombination that can significantly augment the intramolecular double proton transfer (ESDPT) reaction in the excited state for BTD‐O, BTD‐S, and BTD‐Se fluorophores. By constructing potential energy surfaces and identifying transition state forms, we elucidate the ultrafast stepwise ESDPT mechanism facilitated by the low potential barriers. Moreover, we rigorously validate the chalcogen atomic electronegativity‐driven regulation of the stepwise ESDPT mechanism. We sincerely anticipate that manipulating solvent polarity will pave the way for groundbreaking advancements in luminescent materials. [ABSTRACT FROM AUTHOR]

The excited‐state double proton transfer (ESDPT) reaction in the intermolecular hydrogen‐bonded complex 7‐azaindole:piperidin‐2‐one is investigated by quantum chemical calculations with particular emphasis on the H‐bonding interactions within the system. The natural bond orbital (NBO) calculations show that the X─H···Y H‐bonds in the studied complexes, namely, 7‐azaindole:piperidin‐2‐one (N‐form) and 7H‐pyrrolo[2,3‐b]pyridine:3,4,5,6‐tetrahydropyridin‐2‐ol (T‐form, proton transferred tautomer) are aptly described by nY→σ∗(X−H)${n}_{\mathrm{Y}} \to {\sigma }^*({{\mathrm{X}} - {\mathrm{H}}})$ hyperconjugative charge transfer effect (nY${n}_{\mathrm{Y}}$ is non‐bonded lone‐pair on Y‐atom). That the hyperconjugation effect outplays the rehybridization effect is invoked to account for the observed red‐shifting H‐bonds in harmony with the Bent's rule. The differential nature of interactions underlying the origin of X─H···Y H‐bonds in the complexes (N‐form and T‐form) is explored from atoms‐in‐molecules (AIM) calculations. The H‐bonds in the N‐form are found to have a primarily electrostatic origin (closed‐shell interaction) whereas the relatively stronger H‐bonds in the T‐form are assisted by contribution from shared‐shell (covalent) interaction. The nonoccurrence of the double‐proton transfer reaction in the S0 state is argued from the large barrier for the transformation N‐form → T‐form (N‐form constitutes the global minimum on the S0‐PEC), whereas the stability order is reversed together with a marked reduction of the energy barrier in the S1‐PEC accounting for the ESDPT process. [ABSTRACT FROM AUTHOR]

Photochromic 1,3,3-trimethylindolino-β-naphthopyrylospiran (TMI–NPS) and 1,3,3-trimethylindolinonaphthospirooxazine (TMI–NSO) spiropyrans transform into the open merocyanine (MC) form, which exhibits a red-violet color upon reacting with one equivalent of anhydrous FeIIICl3 or FeIIIBr3 in o-dichlorobenzene. Slow mixing with n-hexane precipitates black crystals of the coordination complexes: (TMI–NPS)·FeIIICl3 (1), (TMI–NPS)·FeIIIBr3·2C6H4Cl2 (2) and (TMI–NSO)·FeX3·0.5C6H4Cl2 (where X = Cl for 3 and Br for 4). The oxygen atoms of the MC form of spiropyrans coordinate to FeIII forming short Fe–O bonds of 1.841(2) for 1, 1.839(2) for 2, and 1.888(2) Å length for 4. Complexes manifest intense absorption bands in the visible range, and the spectra are different for the two spiropyrans. Iron(III) ions have high (S = 5/2) spin states in 1 and 2, and complexes 2–4 manifest broad isotropic EPR signals with g = 2.05–2.11. An asymmetric EPR signal with the main component at g = 3.44 (4.2 K) is observed for 1. According to DFT, strong charge transfer from ligands to electron accepting FeIII ions and large dipole moments are evaluated in the complexes. The intense color of the (TMI–NSO)·FeIIIBr3 complex disappears when it reacts with 5,6,11,12,17,18-hexaazatrinaphthylene (HATNA). This decoloration indicates the formation of a colorless closed form of TMI–NPS and (HATNA)·FeIIIX3. Slow mixing with n-hexane precipitates crystals of (C22H19N2O+)(FeIIIBr4−) (5) salt containing nearly planar C22H19N2O+ cations (1,3,3-trimethyl-2-(naphtho[1,2-d]oxazol-2yl-3H-indol-1-ium cations) obtained as a result of the oxidative rearrangement and deprotonation of TMI–NSO. These cations manifest intense bands at 471 and 497 nm. They are diamagnetic and only an isotropic EPR signal with g = 2.15–2.16 is observed from the FeIIIBr4− anions. The properties of the complexes and possible routes to the formation of 5 are discussed based on DFT calculations. [ABSTRACT FROM AUTHOR]

Photochromic 1,3,3-trimethylindolino-β-naphthopyrylospiran (TMI–NPS) and 1,3,3-trimethylindolinonaphthospirooxazine (TMI–NSO) spiropyrans transform into the open merocyanine (MC) form, which exhibits a red-violet color upon reacting with one equivalent of anhydrous FeIIICl3 or FeIIIBr3 in o-dichlorobenzene. Slow mixing with n-hexane precipitates black crystals of the coordination complexes: (TMI–NPS)·FeIIICl3 (1), (TMI–NPS)·FeIIIBr3·2C6H4Cl2 (2) and (TMI–NSO)·FeX3·0.5C6H4Cl2 (where X = Cl for 3 and Br for 4). The oxygen atoms of the MC form of spiropyrans coordinate to FeIII forming short Fe–O bonds of 1.841(2) for 1, 1.839(2) for 2, and 1.888(2) Å length for 4. Complexes manifest intense absorption bands in the visible range, and the spectra are different for the two spiropyrans. Iron(III) ions have high (S = 5/2) spin states in 1 and 2, and complexes 2–4 manifest broad isotropic EPR signals with g = 2.05–2.11. An asymmetric EPR signal with the main component at g = 3.44 (4.2 K) is observed for 1. According to DFT, strong charge transfer from ligands to electron accepting FeIII ions and large dipole moments are evaluated in the complexes. The intense color of the (TMI–NSO)·FeIIIBr3 complex disappears when it reacts with 5,6,11,12,17,18-hexaazatrinaphthylene (HATNA). This decoloration indicates the formation of a colorless closed form of TMI–NPS and (HATNA)·FeIIIX3. Slow mixing with n-hexane precipitates crystals of (C22H19N2O+)(FeIIIBr4−) (5) salt containing nearly planar C22H19N2O+ cations (1,3,3-trimethyl-2-(naphtho[1,2-d]oxazol-2yl-3H-indol-1-ium cations) obtained as a result of the oxidative rearrangement and deprotonation of TMI–NSO. These cations manifest intense bands at 471 and 497 nm. They are diamagnetic and only an isotropic EPR signal with g = 2.15–2.16 is observed from the FeIIIBr4− anions. The properties of the complexes and possible routes to the formation of 5 are discussed based on DFT calculations. [ABSTRACT FROM AUTHOR]

Nature‐inspired supramolecular self‐assemblies are attractive photocatalysts, but their quantum yields are limited by poor charge separation and transportation. A promising strategy for efficient charge transfer is to enhance the built‐in electric field by symmetry breaking. Herein, an unsymmetric protonation, N‐heterocyclic π‐conjugated anthrazoline‐based supramolecular photocatalyst SA‐DADK‐H+ was developed. The unsymmetric protonation breaks the initial structural symmetry of DADK, resulting in ca. 50‐fold increase in the molecular dipole, and facilitates efficient charge separation and transfer within SA‐DADK‐H+. The protonation process also creates numerous active sites for H2O adsorption, and serves as crucial proton relays, significantly improving the photocatalytic efficiency. Remarkably, SA‐DADK‐H+ exhibits an outstanding hydrogen evolution rate of 278.2 mmol g−1 h−1 and a remarkable apparent quantum efficiency of 25.1 % at 450 nm, placing it among the state‐of‐the‐art performances in organic semiconductor photocatalysts. Furthermore, the versatility of the unsymmetric protonation approach has been successfully applied to four other photocatalysts, enhancing their photocatalytic performance by 39 to 533 times. These findings highlight the considerable potential of unsymmetric protonation induced symmetry breaking strategy in tailoring supramolecular photocatalysts for efficient solar‐to‐fuel production. [ABSTRACT FROM AUTHOR]

Aerobic life is powered by membrane-bound redox enzymes that shuttle electrons to oxygen and transfer protons across a biological membrane. Structural studies suggest that these energy-transducing enzymes operate as higher-order supercomplexes, but their functional role remains poorly understood and highly debated. Here we resolve the functional dynamics of the 0.7 MDa III2IV2 obligate supercomplex from Mycobacterium smegmatis, a close relative of M. tuberculosis, the causative agent of tuberculosis. By combining computational, biochemical, and high-resolution (2.3 Å) cryo-electron microscopy experiments, we show how the mycobacterial supercomplex catalyses long-range charge transport from its menaquinol oxidation site to the binuclear active site for oxygen reduction. Our data reveal proton and electron pathways responsible for the charge transfer reactions, mechanistic principles of the quinone catalysis, and how unique molecular adaptations, water molecules, and lipid interactions enable the proton-coupled electron transfer (PCET) reactions. Our combined findings provide a mechanistic blueprint of mycobacterial supercomplexes and a basis for developing drugs against pathogenic bacteria. The obligate supercomplex from M. Tuberculosis has emerged as a promising drug target. Here the authors employ structural experiments, activity assays, and multiscale molecular simulations, to elucidate the mechanism of charge transfer in this enzyme. [ABSTRACT FROM AUTHOR]

Atomically dispersed Fe─N─C catalysts display great potential for efficient CO production in the field of electrochemical CO2 reduction (ECR), but still suffer from unsatisfactory activity limited by the slow proton and electron transfer during the ECR process. Here, a superior Fe─N─C electrocatalyst is designed by anchoring the individual FeN4 sites and Fe nanoparticles onto highly conductive carbon nanotubes. The resultant catalyst displays a commendable CO partial current density of 16.01 mA cm−2 with a turnover frequency of 3519.6 h−1 at −0.65 V in an H‐type cell, and also exhibits CO selectivity > 90% under high current density over 120 mA cm−2 in a flow cell. This remarkable activity exceeds a host of previously reported Fe─N─C catalysts. The findings indicate that the carbon nanotube facilitates CO production due to its strong capability of electron transport and charge transfer. In situ spectroscopic analysis, controlled experiments, and theoretical calculations reveal that Fe nanoparticles effectively promote water dissociation and the subsequent protonation step, accelerate the formation of *COOH intermediate, and thus greatly enhance the ECR activity. [ABSTRACT FROM AUTHOR]

Artificial photosynthesis in carbon dioxide (CO2) conversion into value-added chemicals attracts considerable attention but suffers from the low activity induced by sluggish separation of photogenerated carriers and the kinetic bottleneck-induced unsatisfied selectivity. Herein, we prepare a new-style Bi/TiO2 catalyst formed by pinning bismuth clusters on TiO2 nanowires through being confined by pores, which exhibits high activity and selectivity towards photocatalytic production of CH4 from CO2. Boosted charge transfer from TiO2 through Bi to the reactants is revealed via in situ X-ray photon spectroscopy and time-resolved photoluminescence (PL). Further, in situ Fourier transform infrared results confirm that Bi/TiO2 not only overcomes the multi-electron kinetics challenge of CO2 to CH4 via boosting charge transfer, but also facilitates proton production and transfer as well as the intermediates ⋆CHO and ⋆CH3O generation, ultimately achieving the tandem catalysis towards methanation. Theoretical calculation also underlies that the more favorable reaction step from ⋆CO to ⋆CHO on Bi/TiO2 results in CH4 production with higher selectivity. Our work brings new insights into rational design of photocatalysts with high performance and the formation mechanism of CO2 to CH4 for solar energy storage in future. [ABSTRACT FROM AUTHOR]

Embedding theory is a powerful computational chemistry approach to exploring the electronic structure and dynamics of complex systems, with Quantum Mechanical/Molecular Mechanics (QM/MM) being the prime example. A challenge arises when trying to apply embedding methodology to systems with diffusible particles, e.g., solvents, if some of them must be included in the QM region, for example, in the description of solvent-supported electronic states or reactions involving proton transfer or charge-transfer-to-solvent: without a special treatment, inter-diffusion of QM and MM particles will eventually lead to a loss of QM/MM separation. We have developed a new method called Flexible Boundary Layer using Exchange (FlexiBLE) that solves the problem by adding a biasing potential to the system that closely maintains QM/MM separation. The method rigorously preserves ensemble averages by leveraging their invariance to an exchange of identical particles. With a careful choice of the biasing potential and the use of a tree algorithm to include only important QM and MM exchanges, we find that the method has an MM-forcefield-like computational cost and thus adds negligible overhead to a QM/MM simulation. Furthermore, we show that molecular dynamics with the FlexiBLE bias conserves total energy, and remarkably, sub-diffusional dynamical quantities in the inner QM region are unaffected by the applied bias. FlexiBLE thus widens the range of chemistry that can be studied with embedding theory. [ABSTRACT FROM AUTHOR]

In this manuscript, a photoinduced ligand-to-metal charge transfer (LMCT) approach, employing transition-metal-based photocatalysts, for the efficient alkylation of electron-poor olefin is described. The developed redox-neutral process benefits from mild reaction conditions and involves a wide range of chromone-3-carboxylic acids as well as nucleophiles amenable to selective C–H functionalization leading to the formation of 2-substituted chroman-4-one compounds with potential biological activity. [ABSTRACT FROM AUTHOR]

Photocatalytic CO2 reduction is one of the best solutions to solve the global energy crisis and to realize carbon neutralization. The tetradentate phosphine‐bipyridine (bpy)‐phosphine (PNNP)‐type Ir(III) photocatalyst, Mes‐IrPCY2, was reported with a high HCOOH selectivity but the photocatalytic mechanism remains elusive. Herein, we employ electronic structure methods in combination with radiative, nonradiative, and electron transfer rate calculations, to explore the entire photocatalytic cycle to either HCOOH or CO, based on which a new mechanistic scenario is proposed. The catalytic reduction reaction starts from the generation of the precursor metal‐to‐ligand charge transfer (3MLCT) state. Subsequently, the divergence happens from the 3MLCT state, the single electron transfer (SET) and deprotonation process lead to the formation of one‐electron‐reduced species and Ir(I) species, which initiate the reduction reaction to HCOOH and CO, respectively. Interestingly, the efficient occurrence of proton or electron transfer reduces barriers of critical steps. In addition, nonadiabatic transitions play a nonnegligible role in the cycle. We suggest a lower free‐energy barrier in the reaction‐limiting step and the very efficient SET in 3MLCT are cooperatively responsible for a high HCOOH selectivity. The gained mechanistic insights could help chemists to understand, regulate, and design photocatalytic CO2 reduction reaction of similar function‐integrated molecular photocatalyst. [ABSTRACT FROM AUTHOR]

One electron oxidation of the monometallic alkenylacetylide complexes [Ru{C≡CC(R)=CH2}(dppe)Cp*] (1) and [Ru{C≡CC(R)=CH2}Cl(dppe)2] (2) (R = Ph (a); R = 4-MeS-C6H4 (b)) generates in each case a dinuclear bis(allenylidene) complex [{Ru}2{μ-C=C=C(R)–CH2–H2C–(R)C=C=C}][PF6]2 ({Ru} = Ru(dppe)Cp* ([3a,b][PF6]2); {Ru} = RuCl(dppe)2 ([4a,b][PF6]2), containing an unsaturated ethane bridge between both allenylidene moieties. Deprotonation of this ethane bridge results in the formation of the previously reported octa-3,5-diene-1,7-diyndiyl-bridged bimetallic species [{Ru}2{μ-C≡CC(R)=CH–HC=(R)CC≡C}] ({Ru} = Ru(dppe)Cp* (5a,b); {Ru} = RuCl(dppe)2 (6a,b). The isolation of these complexes illustrates a general synthetic route to these conjugated bimetallic species from monomeric alkenylacetylide precursors. Electrochemical and spectroelectrochemical investigations evince the ready formation of the representative redox series [5a]n+, and TD-DFT calculations performed on optimised structures featuring the simplified {Ru(dmpe)Cp} coordination sphere [{Ru(dmpe)Cp}2{μ-C≡CC(Ph)=HC–CH(Ph)CC≡C}]n+ ([5a†]n+) (n = 0, 1, 2) reveal significant delocalisation of the unpaired charge in the formally mixed-valent species (n = 1), consistent with Class III assignment within the Robin–Day classification scheme. [ABSTRACT FROM AUTHOR]

Decaniobate is a polyoxoniobate considered in photocatalytic studies lacking more detailed electronic transition data. Moreover, its stability in aqueous solution depends on the pH and little is known regarding the protonation of this polyanion. Hence, this electronic structure study based on Density Functional Theory calculations shows that initial protonations occur at specific external oxygen sites situated above and below the equatorial plane of the polyanion [Oe(A)]. Moreover, these Oe(A) protonations cause small perturbations to the inner core structural skeleton constituted by bonds between niobium and internal oxygen atoms via a trans effect. The ultraviolet/visible spectra are slightly affected by these protonations as well, exhibiting a general trend for formation of four main bands in the range from 150 to 250 nm with similar positions and relative intensity profiles. The nature of the lowest energy electronic transitions (231 to 249 nm) indicates that these are charge transfer bands mainly from bridging oxygen to niobium atoms, with an amount of electronic charge received by metal atoms nearly unaltered by the protonations (from 0.32 to 0.38 e). [ABSTRACT FROM AUTHOR]

Carbon dots modified iridium nanowires (Ir NWs/CDs) show high catalytic activity and stability for acidic hydrogen evolution/oxidation reactions, which are attributed to the large compression stress generated in Ir NWs and the fast proton/electron transfer ability and good conductivity of CDs. [Display omitted] • One-dimensional Ir nanowires modified with carbon dots are employed as catalysts for HER/HOR. • The Ir nanowires show a high compressive strain intensity of −0.563%. • CDs act as a bridge connecting hydrogen proton and electron with Ir active sites. • Ir NWs/CDs-15 requires 18 mV to obtain a current density of −10 mA cm−2 for HER. • Ir NWs/CDs-15 shows anti-CO ability which is twice the level of the PtRu/C. The effective harnessing of hydrogen energy relies on the development of bifunctional electrocatalysts that facilitate hydrogen evolution/oxidation reactions (HER/HOR) with high catalytic activity. The design of such electrocatalysts requires the consideration of not only the volcano relationship with hydrogen binding energy (HBE) or hydrogen adsorption Gibbs free energy (ΔG H) but also the regulation of catalytic kinetics such as interfacial proton/electron transfer. In this work, unique one-dimensional iridium nanowires with compressive stress are successfully prepared and combined with carbon dots (Ir NWs/CDs). Acting as an electrocatalyst for HER in 0.5 M H 2 SO 4 , the optimal Ir NWs/CDs only requires an 18 mV overpotential to achieve a current density of −10 mA cm−2. Furthermore, the optimal Ir NWs/CDs shows high HOR performance with a mass activity (@ 50 mV versus RHE) 1.5 times that of 20% Pt/C and excellent anti-CO toxicity ability which is twice the level of the PtRu/C catalyst. Ir NWs/CDs exhibit enhanced HER/HOR activity due to (1) the appropriate modulation of the binding energy to hydrogen intermediate facilitated by the compressive stress applied to the Ir structure and (2) the improved proton/electron transfer kinetics by optimizing the electronic properties and surface structures through tailored CDs. This study delivers a new strategy for designing and synthesizing efficient acidic HER/HOR bifunctional catalysts. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials have driven great interest due to a large specific surface area to volume ratio and adjustable surface behaviors, which show huge potentials for enhancing the activity of energy conversion and property optimization. In order to regulate the physicochemical properties of photocatalyst for water splitting reaction, defect engineering on 2D materials have drawn great attention. Meanwhile, a widely used strategy to improve the H 2 evolution rate kinetics has been achieved. In this paper, we prepared AgBr/g-C 3 N 4 catalyst by chemical precipitation. The obtained photocatalyst shows a unique charge transfer pathway. In addition, a deep understanding of the proton shuttle during H 2 evolution reactions can offer profound opinion into heterostructure construction and property optimization. It is found that the enhanced performance is correlated to the superiority of the S-scheme heterojunction and defect engineering on graphitic carbon nitride 2D materials. This work offers a novel method for improving efficiency in terms of energy conversion and property optimization. [Display omitted] • Surface nitrogen vacancy is instrumental in the chemisorption and activation of H 2 O. • S-scheme band of AgBr/g-C 3 N 4 is conjectured by the experiments and DFT calculations. • The prolonged photocarrier lifetime has increased H 2 production. • The results of XPS are consistent with the mechanism of S-scheme heterojunction. [ABSTRACT FROM AUTHOR]

A large, strained (SE=44.2 kcal/mol) and conformationally flexible mixed cyclophane of pyridine and teropyrene was synthesized using two intramolecular Wurtz coupling reactions and an unprecedented Scholl reaction between the unreactive 2 positions of the pyrene systems in a triply bridged pyrenophane. Protonation of the pyridine unit results in a greatly enhanced preference for nesting in the cavity of the highly bent teropyrene system (θcalc=162.6°) and emergence of a charge transfer absorption band (λmax=592 nm) due to a long range (5.0–5.5 Å), through‐space intramolecular transition between the teropyrene and pyridinium units, which does not exist in the neutral cyclophane. [ABSTRACT FROM AUTHOR]

The geometrical regioselective E→Z isomerization of a conjugated alkene under thermal activation pose a challenge due to microscopic reversibility. Herein we report that such reversibility issues can be circumvented by integrating E→Z isomerization with subsequent cyclization cascade, particularly in the absence of commonly employed light, acids, or metal‐catalysts. Thus, linearly conjugated dienals in a mixture of toluene‐alcohol (2 : 1) solvents or only with alcohol at 60–70 °C can be converted to γ‐alkoxybutenolides in moderate to good yields. The intermediary 2Z,4E‐isomer can be isolated, which includes the first example of isolating the regioselective isomerization product under thermal conditions. Density functional theory (DFT) studies have been employed to shed light on the feasibility of geometrical alkene isomerization and ensuing cascade sequences. It has been observed that the regioselective 2E,4E→2Z,4E isomerization of dienal is a thermodynamically facile (ΔG <0) process. Structural elucidation further reveals that the presence of a certain charge transfer and a non‐covalent interaction may be the primary reasons for the enhanced stability of the 2Z,4E‐isomer. The thermodynamic plausibility of the subsequent cascade reaction from the Z‐isomer to the anticipated product in the presence of a polar protic solvent (here MeOH) is also explicated. Out of the two probable pathways, the "hemiacetal pathway" involving a relay proton transfer is kinetically more feasible due to the diminished activation barrier than the "conjugate addition pathway". [ABSTRACT FROM AUTHOR]

Bimetallic end‐on μ2‐η1:η1‐N2 bridging dinitrogen complexes have served as the platform for photochemical N2 activation, mainly for the N−N cleavage. However, the alternate N−N π‐photoactivation route has remained largely unexplored. This study strengthens the notion of weakening the N−N bond through the population of π* orbital upon electronic excitation from the ground to the first excited state using four prototypical complexes based on Fe (1), Mo (2), and Ru (3,4). The complexes 1–4 possess characteristic N−N π* based LUMO (π*‐π*‐π*) centered on their M−N−N−M core, which was earlier postulated to play a central role in the N2 photoactivation. Vertical electronic excitation of the highest oscillator strength involves transitions to the N−N π*‐based acceptor orbital (π*‐π*‐π*) in complexes 1–4. This induces geometry relaxation of the first excited metal‐to‐nitrogen (π*) charge transfer (1MNCT) state leading to a "zigzag" M−N−N−M core in the equilibrium structure. Obtaining the equilibrium geometry in the first excited state with the full‐sized complexes widens the scope of N−N π‐photoactivation with μ2‐η1:η1‐N2 bridging dinitrogen complexes. Promisingly, the elongated N−N bond and bent ∠MNN angle in the photoexcited S1 state of 1–4 resemble their radical‐ and di‐anion forms, which lead toward thermodynamically feasible N−N protonation in the S1 excited state. [ABSTRACT FROM AUTHOR]

A key challenge in the design of magnetic molecules with intramolecular charge transfer behavior is to obtain reversible magnetic bistability triggered by external stimuli. Here, we show that two dinuclear metal complexes, [(bbp)Fe(CN)3Mn(Py5Me2)]·2.5CH3OH (4) and [(bbp)Fe(CN)3Ni(Py5Me2)]·2.5CH3OH (5) (Py5Me2 = 2,6-bis(1,1-di(pyridine-2-yl)ethyl)pyridine, H2bbp = 2,6-bis(benzimidazole-2-yl)pyridine), were self-assembly synthesized by (Bu4N)2[(bbp)FeIII(CN)3] and [Mn(Py5Me2)(OH2)](ClO4)2 or [Ni(Py5Me2)(OH2)](ClO4)2, respectively. Complexes 4 and 5 exhibited intramolecular metal-to-metal charge transfer with the addition of acids or bases in solution by UV–visible spectrophotometric measurements and electrochemistry studies, and concomitant switching of the {FeIII(μ-CN)MnII/NiII} state to the {FeII(μ-CN)MnIII/NiIII} state. [ABSTRACT FROM AUTHOR]

Selected ion flow tube mass spectrometry (SIFT‐MS) and proton transfer reaction mass spectrometry with switchable reagent ion capability (PTR+SRI‐MS) are analytical techniques for real‐time qualification and quantification of compounds in gas samples with trace level concentrations. In the detection process, neutral compounds—mainly volatile organic compounds—are ionized via chemical ionization with ionic reagents or primary ions. The most common reagent ions are H3O+, NO+ and O2+•. While ionization with H3O+ occurs by means of proton transfer, the ionization via NO+ and O2+• offers a larger variety on ionization pathways, as charge transfer, hydride abstraction and so on are possible. The distribution of the reactant into various reaction channels depends not only on the usage of either NO+ or O2+•, but also on the class of analyte compounds. Furthermore, the choice of the reaction conditions as well as the choice of either SIFT‐MS or PTR+SRI‐MS might have a large impact on the resulting products. Therefore, an overview of both NO+ and O2+• as reagent ions is given, showing differences between SIFT‐MS and PTR+SRI‐MS as used analytical methods revealing the potential how the knowledge obtained with H3O+ for different classes of compounds can be extended with the usage of NO+ and O2+•. [ABSTRACT FROM AUTHOR]

The photoluminescence spectra and luminescence lifetimes of Eu3+-doped oxyhalides, YOX:Eu3+ (X = Cl or Br), and their temperature dependence on different halide species of mixed-anion coordinations were investigated and analyzed. In terms of the ionic and covalent nature of bonding, Eu3+ ions form different coordination polyhedra in the isostructural YOCl and YOBr hosts: a ninefold [Eu3+O4Cl5] and an eightfold [Eu3+O4Br4] polyhedra. The Judd–Ofelt Ω2 parameter for YOCl:Eu3+ takes a very large value (=8.81 × 10−20 cm2) due to the ninefold polyhedron with C4v symmetry. On the other hand, despite the same C4v symmetry, YOBr:Eu3+ shows a very small Ω2 parameter (=2.72 × 10−20 cm2) because of its structural similarity to the square antiprism polyhedron with D4 symmetry. The Ω4 parameters for YOX:Eu3+ are much larger than those for other Eu3+-doped oxides, possibly related to the covalency of halide anions, Cl− and Br−, showing an intense luminescence band (5D0 → 7F4) at around 700 nm. The Eu3+ ions in these YOX hosts were excitable by charge transfer bands in 270–280 nm regions. The relaxation pathways from the charge transfer states to the initial states for luminescence are discussed, using the configuration coordinate diagrams with the spectroscopic characterization. [ABSTRACT FROM AUTHOR]

The non-adiabatic quantum dynamics of the H + H 2 + → H 2 + H+ charge transfer reactions, and some isotopic variants, is studied with an accurate wave packet method. A recently developed 3 × 3 diabatic potential model is used, which is based on very accurate ab initio calculations and includes the long-range interactions for ground and excited states. It is found that for initial H 2 + (v = 0), the quasi-degenerate H2(v′ = 4) non-reactive charge transfer product is enhanced, producing an increase in the reaction probability and cross section. It becomes the dominant channel from collision energies above 0.2 eV, producing a ratio between v′ = 4 and the rest of v's, which that increase up to 1 eV. The H + H 2 + → H 2 + + H exchange reaction channel is nearly negligible, while the reactive and non-reactive charge transfer reaction channels are of the same order, except that corresponding to H2(v′ = 4), and the two charge transfer processes compete below 0.2 eV. This enhancement is expected to play an important vibrational and isotopic effect that needs to be evaluated. For the three proton case, the problem of the permutation symmetry is discussed when using reactant Jacobi coordinates. [ABSTRACT FROM AUTHOR]

Rhodium (Rh) acylnitrene complexes are widely implicated in catalytic C–H amidation reactions but have eluded isolation and structural characterization. To overcome this challenge, we designed a chromophoric octahedral Rh complex with a bidentate dioxazolone ligand, in which photoinduced metal-to-ligand charge transfer initiates catalytic C–H amidation. X-ray photocrystallographic analysis of the Rh-dioxazolone complex allowed structural elucidation of the targeted Rh-acylnitrenoid and provided firm evidence that the singlet nitrenoid species is primarily responsible for acylamino transfer reactions. We also monitored in crystallo reaction of a nucleophile with the in situ–generated Rh-acylnitrenoid, which provided a crystallographically traceable reaction system to capture mechanistic snapshots of nitrenoid transfer. [ABSTRACT FROM AUTHOR]

The hypothetical molecule 4-dimethylaminopyridinium salicylate monohydrate was synthesized and investigated leveraging FT-IR spectra, UV visible, NMR and quantum chemical calculations and also compared with its precursor molecules 4-dimethylamino pyridine and salicylic acid in the present work. To explore the impingement of hydrogen bonding on molecule the geometrical parameters, interaction energies, and vibrational spectra are employed. Natural Bond Orbital analysis indicated the existence of intermolecular hydrogen bonding N–H...O contact, which is mediated by a hyperconjugative interaction between the carbonyl oxygen atom donor and the pyridine ring N–H acceptor. The stretching wavenumber of hydrogen bond donor O–H and hydrogen bond acceptor C–O is red shifted due to elongation in respective bond lengths, according to vibrational analysis. The presence of intermolecular charge transfer from electron-rich pyridine to electron-deficient salicylate is revealed by FMO analysis, and this is corroborated by charge transfer due to excitation. A molecular docking simulation was also executed to better understand the structure-activity relation and further antibacterial tests confirmed that the compound inhibits the bacterial pathogens. [ABSTRACT FROM AUTHOR]

Recently, many novel two-dimensional materials have been identified through data-driven computational methods, whose tribological properties are bound to be further investigated. Here, the first principles calculation and machine learning were combined to predict the maximum sliding potential barrier of elemental two-dimensional materials and the importance of different descriptors were discussed. Due to literature reports and high correlation coefficients, RF and Bagging algorithms are used to present the final prediction results. The prediction results show that R2 is about 0.8, and the root mean square error (RMSE) of ∼0.0027 eV and 0.0029 eV, respectively. Importantly, when considering the interfacial charge transfer as the eigenvalue, the R2 of both models increased (R2 can reach 0.89), and the RMSEs decreased tõ0.0020 eV and 0.0024 eV. This indicates that interfacial charge transfer has a significant impact on the prediction of the maximum sliding energy barrier. That is, adjusting the charge transfer at the interface can improve the tribological properties of the interface. In addition, the geometric structure, such as lattice parameter, and mechanical properties of the material are also important factors affecting its maximum sliding energy barrier. Compared with traditional first principles calculation, machine learning based on statistics may be a promising choice for predicting friction performance, and it is expected to find the influencing factors directly related to friction behavior. [ABSTRACT FROM AUTHOR]

In this work, a new method to extend the light absorption and improve the photocatalytic activity of metal‐organic frameworks (MOFs) with nitrogen‐containing ligand is reported, namely, the protonation of nitrogen. Specifically, a protonated Bi‐based MOF synthesized by a hydrothermal method (Bi‐MMTAA‐H, MMTAA=2‐mercapto‐4‐methyl‐5‐thiazoleacetic acid) displays a wider visible light absorption than Bi‐MMTAA‐R with the same single‐crystal structure, but synthesized by a reflux method. The redshifted light absorption was confirmed to be caused by the protonation of nitrogen in the thiazolyl ring in MMTAA. Moreover, this protonation also facilitates the charge separation and transfer and improves the photocatalytic activity of selective oxidation of α‐terpinene to p‐cymene. Our results provide a new idea for nitrogen‐containing Bi‐based MOFs to extend the light absorption and improve the photocatalytic performance. [ABSTRACT FROM AUTHOR]

Introduction: Enalapril maleate is an antihypertensive ethyl ester pro-drug with two crystalline forms. A network of hydrogen bonds in both polymorphs plays an important role on solid-state stability, charge transfer process and degradation reactions (when exposed to high humidity, temperature and/or pH changes). Computational Procedures: Supramolecular arrangement was proposed by Hirshfeld surface using the CrystalExplorer17 software and quantum theory of atoms in molecules. The electronic structure properties were calculated using the functional hybrid M06-2X with 6–311++G** base function employing diffuse and polarization functions to improve the description of hydrogen atoms on intermolecular interactions. Also, the H+ charge transfer between enalapril and maleate molecules was performed using Car-Parrinello molecular dynamics with the Verlet algorithm. In both simulations, the temperature of the ionic system was maintained around 300 K using the Nosé-Hoover thermostat and the electronic system evolved without the use of the thermostat. Results: This work evaluates the effect of maleate on the structural stability of enalapril maleate solid state. The electronic structural analysis points out a partially covalent character for N1-H∙∙∙O7 interaction; and the molecular dynamic showed a decentralized hydrogen on maleate driving a decomposition by charge transfer process while a centered hydrogen driving the stabilization. The charge transfer process and the mobility of the proton (H+) between enalapril and maleate molecules was demonstrated using supramolecular modeling analyses and molecular dynamics calculations. [ABSTRACT FROM AUTHOR]

We synthesized the luminescent ruthenium(II) polypyridyl complexes of type [Ru(bpy)2(L1)][ClO4]2 (1) (where L1 = 4,4-dicarboxy-2,2-bipyridine); [Ru(bpy)2(L2)][ClO4]2 (2); and [Ru(L2)3][ClO4]2 (3) (where L2 = 4,4-dimethanol-2,2-bipyridine). Photo-physical and electrochemical properties of the Ru(II) complexes were investigated along with the emission vs. pH. This reveals that the carboxylic acids in the 2,2-bipyridine ligand had a more important influence on the photophysical and electrochemical properties of the Ru(II) complexes than alcohol. The crystal structure of the Ru(II) complexes 1–3 is also discussed in this paper. The cyclic voltammetry of 1–3 yields a reversible RuIII/II wave that shifts 1.4–1.2 V. UV/Visible absorbance spectroscopy reveals that Metal-to-Ligand Charge Transfer (MLCT) transitions shift to lower energy upon deprotonation of the complex. [ABSTRACT FROM AUTHOR]

We show how to incorporate the possibility of kinetic control in the conceptual density functional theory formalism. This allow us to prove that the hard/soft acid/base principle will likely fail when the reactions are not thermodynamically-driven. [ABSTRACT FROM AUTHOR]

Dimensionality plays a vital role at the nanoscale in tuning the electronical and photophysical properties and surface features of perovskite nanocrystals. Here, 3D and 1D all-inorganic CsPbBr3 nanocrystals were chosen as model materials to systemically reveal the dimensionality-dependent effect in photocatalytic H2 evolution. In terms of facilitating photoinduced electron–hole pair separation and charge transfer, as well as inducing proton reduction potential with the presence of fewer Br vacancies, 1D CsPbBr3 nanorods gave about a 5-fold improvement for solar H2 evolution. [ABSTRACT FROM AUTHOR]

Inspired by the crucial role of the proton pump of quinone moieties in natural photosynthesis, we demonstrated a novel "donor–acceptor" strategy for boosting the aerobic visible-light photocatalytic C–H oxygenation of unactivated alkanes, through the protonation of anthraquinones by Brønsted acids. As expected, the combination of 2-ethylanthraquinones and HCl efficiently photooxidized cyclohexane to afford the corresponding alcohol and ketone products, with a high cyclohexane conversion of up to 36% and a 3.6-fold enhancement over 2-ethylanthraquinone alone. In comparison, H3PO4 or KH2PO4 as an acid source promotes the process with a higher chemoselectivity towards the ketone (>90%). This increased photooxidation power of protonated anthraquinone was used for the selective photooxygenation of other alkanes in good yields, resulting in altered product distributions. Spectroscopic evidence and photoelectrochemical studies revealed that the hydrogen bond (⋯[H+]⋯) formed between the anthraquinones and Brønsted acids established a proton coupled electron transfer (PCET) pathway for charge transfer with a longer-lived charge separation state, which modulated the reactivity of excited-state organic reactions. Control experiments and computational studies further support the importance of the thermodynamic driving force as well as geometrical reorganization, in which the formation of a hydrogen-bonded anthraquinone decreases the reorganization penalty during the energy transfer event. [ABSTRACT FROM AUTHOR]

Protic ruthenium complexes using the dihydroxybipyridine (dhbp) ligand combined with a spectator ligand (N,N = bpy, phen, dop, Bphen) have been studied for their potential activity vs. cancer cells and their photophysical luminescent properties. These complexes vary in the extent of π expansion and the use of proximal (6,6′-dhbp) or distal (4,4′-dhbp) hydroxy groups. Eight complexes are studied herein as the acidic (OH bearing) form, [(N,N)2Ru(n,n′-dhbp)]Cl2, or as the doubly deprotonated (O− bearing) form. Thus, the presence of these two protonation states gives 16 complexes that have been isolated and studied. Complex 7A, [(dop)2Ru(4,4′-dhbp)]Cl2, has been recently synthesized and characterized spectroscopically and by X-ray crystallography. The deprotonated forms of three complexes are also reported herein for the first time. The other complexes studied have been synthesized previously. Three complexes are light-activated and exhibit photocytotoxicity. The log(Do/w) values of the complexes are used herein to correlate photocytotoxicity with improved cellular uptake. For Ru complexes 1–4 bearing the 6,6′-dhbp ligand, photoluminescence studies (all in deaerated acetonitrile) have revealed that steric strain leads to photodissociation which tends to reduce photoluminescent lifetimes and quantum yields in both protonation states. For Ru complexes 5–8 bearing the 4,4′-dhbp ligand, the deprotonated Ru complexes (5B–8B) have low photoluminescent lifetimes and quantum yields due to quenching that is proposed to involve the 3LLCT excited state and charge transfer from the [O2-bpy]2− ligand to the N,N spectator ligand. The protonated OH bearing 4,4′-dhbp Ru complexes (5A–8A) have long luminescence lifetimes which increase with increasing π expansion on the N,N spectator ligand. The Bphen complex, 8A, has the longest lifetime of the series at 3.45 μs and a photoluminescence quantum yield of 18.7%. This Ru complex also exhibits the best photocytotoxicity of the series. A long luminescence lifetime is correlated with greater singlet oxygen quantum yields because the triplet excited state is presumably long-lived enough to interact with 3O2 to yield 1O2. [ABSTRACT FROM AUTHOR]

Oxide-derived Cu catalysts from Cu2O microcrystals are capable of electro-chemically converting CO2 into various value-added chemicals. However, their structural transformation and associated preferred products remain unclear, requiring further investigation. Herein, Cu2O microcrystals with controllable low- and high-index facets exposure are fabricated to differentiate the effects of initial exposed facets on their structural reconstruction and product selectivity in electrochemical CO2 reduction reaction. Combined in situ characterizations and theoretical investigation reveal the direct correlations of Cu2O reconstruction and product selectivity to its initial facet exposure. The Cu2O low-index facet, being more stable with a high energy barrier on material reduction, tends to partially maintain its original crystalline structure and larger Cu2O particle size throughout the transformation. The derived flatter surface and limited Cu2O/ Cu interfaces result in a favorable selectivity toward 2-electron transfer products. The chemically active Cu2O high-index facet (311) is energetically favorable to be reduced owing to the feasible protonation process, thus experiencing a drastic reconstruction with rich newly formed Cu nanoparticles and evolved fine Cu2O grains; Such a reconstruction creates uncoordinated Cu species and abundant boundaries, benefiting charge transfer and increasing the local pH by confining OH-, thus leading to a high selectivity toward C2+ products. [ABSTRACT FROM AUTHOR]

A new gas inlet port combined with a novel ionization scheme have been developed and coupled to a high-resolution time-of-flight mass spectrometer (TOF MS) for the detection and measurement of atmospheric volatile (VOCs) and intermediate volatility organic compounds (IVOCs). Ions are produced predominantly by charge transfer reactions in a low-temperature plasma ionization source with minimal fragmentation. Enhanced sensitivity is accomplished by incorporating an increased-size inlet capillary in a transverse arrangement to maximize throughput in the ionization source. Additional design aspects of the new mass spectrometer enabling superior transmission include a large acceptance ion funnel and a segmented radio frequency (RF) ion guide with increased space charge storage capacity. An orthogonal TOF analyzer equipped with a two-stage reflectron and tuned to second order is employed for the determination of the mass-to-charge ratio of the ions, with a mass resolving power of >20 k at mass 500 Th. The performance of the instrument was evaluated in tests using VOC standards and in atmospheric chamber experiments to demonstrate the ability to measure a wide range of organic compounds with different functional groups. Linear signal response is demonstrated over a wide range of VOCs used in the calibration processes in the ppb range, while the instrument exhibits linear response in the ppt range as well. Detection limits as low as 1 ppt are accomplished. The potential applications of this new TOF MS instrument were demonstrated in a pilot atmospheric simulation chamber experiment. [ABSTRACT FROM AUTHOR]

Cross sections for charge transfer and ionization in proton–uracil collisions are studied, for collision energies 0.05 < E < 2500 keV, using two computational models. At low energies, below 20 keV, the charge transfer total cross section is calculated employing a semiclassical close-coupling expansion in terms of the electronic functions of the supermolecule (H-uracil) + . At energies above 20 keV, a classical-trajectory Monte Carlo method is employed. The cross sections for charge transfer at low energies have not been previously reported and have high values of the order of 40 Å 2 , and, at the highest energies of the present calculation, they show good agreement with the previous results. The classical-trajectory Monte Carlo calculation provides a charge transfer and electron production cross section in reasonable agreement with the available experiments. The individual molecular orbital contributions to the total electron production and charge transfer cross sections are analyzed in terms of their energies; this permits the extension of the results to other molecular targets, provided the values of the corresponding orbital energies are known. [ABSTRACT FROM AUTHOR]

We present the formalism of analytic gradients and derivative couplings for the spin-flip extended configuration interaction with single excitations (SF-XCIS) method. We report an efficient implementation of the SF-XCIS method in the framework of semiempirical quantum chemistry that allows fast excited-state calculations for large systems. The performance of the SF-XCIS method in combination with semiempirical orthogonalization-corrected models (OMx) is statistically evaluated for vertical singlet excitation energies. The SF-XCIS method treats the ground state and excited states in a fully balanced manner and properly describes conical intersections involving the ground state. It can thus be used in fewest switches surface hopping (FSSH) simulations of nonadiabatic dynamics processes. This is demonstrated in an OM2/SF-XCIS FSSH pilot study of excited-state proton transfer in 7-(2-pyridyl)indole. [ABSTRACT FROM AUTHOR]

Designing the architecture of l-lysine-based polymeric structures is a highly challenging task that requires careful control of the amino acid reactive groups. Conventional processes to obtain branched polylysine need several steps and the addition of specific catalysts. In the present work, to gain a better understanding and control of the formation of l-lysine-based polymers, we have investigated the correlation between the protonation state of l-lysine and the corresponding hydrothermally grown structures. The samples have been characterized by combining optical spectroscopies, such as UV–Vis, fluorescence, and synchrotron radiation circular dichroism with structural analysis by Nuclear Magnetic Resonance, Fourier Transform Infrared spectroscopy, and dynamic light scattering. We have observed that aqueous precursor solutions with alkaline pHs promote the formation of branched structures. In contrast, high pHs favour the reactivity of the ε-amino groups leading to linear structures, as shown by circular dichroism analyses. On the other hand, acidic conditions trigger the branching of the amino acid. Interestingly, the polymeric forms of l-lysine emit in the blue because the increasing number of intermolecular hydrogen bonds promote the intermolecular charge transfer responsible for the emission. Understanding the correlation between the l-lysine charged states and the polymeric structures that could form controlling the protonation–deprotonation states of the amino acid opens the route to a refined design of polypeptide systems based on l-lysine. [ABSTRACT FROM AUTHOR]

Electrical bistability existing in biochemical networks is critical for the proper functionalization of living systems. The development of artificial materials with electrical bistability begun to attract much interest due to their broad application prospects, especially in the field of memristors. Metal–organic frameworks (MOFs) have advantages in regular pores, crystallinity, structural designability and easy functionalization, which can promote the construction of novel MOF-based memristors and facilitate a better understanding of switching mechanisms. Here, we highlight recent advances in electrically bistable MOFs as memristors, and discuss their switching mechanisms, including interfacial reaction, proton-transfer mechanism, metal ion migration, charge trapping/detrapping and other mechanisms. Challenges and future perspectives are also presented. [ABSTRACT FROM AUTHOR]

Current values of the neutron lifetime, determined by two entirely distinct measurement techniques of comparable precision, differ to a statistically significant degree, a result which has become known as the neutron lifetime anomaly. In a previous publication we have shown that the discrepancy can be resolved by taking account of electron transfer charge exchange reactions between residual gases and final state protons stored in a quasi-Penning trap. In this article we analyze unique experimental data obtained during the course of the first published neutron lifetime measurement that used a proton trap. These data employed trapping times greater by a factor of a thousand than became conventional in later experiments. The data show that significant event losses occur, probably due to residual gas other than molecular hydrogen or helium. Additionally, the molecular ion H2+ produced by charge exchange in H2 undergoes secondary molecular reactions, producing the molecular ion H3+ and the ion HeH+ which is also produced by secondary reactions in helium. These ions could result in event losses depending on the energy and time-of-flight acceptance windows. Energy losses are evaluated and ionic compositions are quantitively assessed as functions of trapping time and residual gas density to account for an energy spectrum obtained using a silicon surface barrier detector. The spectrum is strongly influenced by charge exchange, secondary molecular reactions and backscattering in the detector dead layer. [ABSTRACT FROM AUTHOR]

The reaction of HNO3 with hydrated electrons (H2O)n- (n = 35-65) in the gas phase was studied using Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and ab initio molecular dynamics simulations. Kinetic analysis of the experimental data shows that OH−(H2O)m is formed primarily via a reaction of the hydrated electron with HNO3 inside the cluster, while proton transfer is not observed and NO3-(H2O)m is just a secondary product. The reaction enthalpy was determined using nanocalorimetry, revealing a quite exothermic charge transfer with −241 ± 69 kJ mol-1. Ab initio molecular dynamics simulations indicate that proton transfer is an allowed reaction pathway, but the overall thermochemistry favors charge transfer. [ABSTRACT FROM AUTHOR]

[Display omitted] • The interconversion of double proton transfer of DPNAP in S 1 state is a stepwise reaction. • The single fluorescence band of DPNAP is ascribed to overlap of emission spectra of normal structure and proton transfer isomers. • The AIE induced by hydroxyl groups is clarified by increasing molecular planarity and restricted intramolecular charge transfer. The DPNAP is a multifunctional nanoprobe designed for selective illumination of fungi and targeted antimicrobial applications. By introducing hydroxyl groups into the DPNAP, the aggregation-induced emission (AIE) characteristic can be obtained. However, its optical properties and underlying theoretical mechanisms are not fully understood. In this work, we explored the stable DPNAP configurations by constructing the potential energy surfaces and elucidated the mechanism of the proton transfer reaction. Our findings indicate that proton transfer occurs through a stepwise reaction with energy barriers of < 10 kcal/mol , owing to the variation in hydrogen-bonding strength as revealed by hydrogen-bond parameters and infrared vibrational analyses. The theoretical fluorescence peak (λ cal = 541 nm) based on the optimized structures is consistent with the experimental peak (λ exp = 500 nm). The experimental single-fluorescence band is attributed to the overlap of emission spectra of normal structure and single- and double-proton transfer isomers. Moreover, the hydroxyl-induced AIE mechanism is attributed to increased molecular planarity and restricted intramolecular charge transfer in the aggregate state. Understanding of the AIE characteristic and ESIPT mechanism is of fundamental importance in molecular electronics and photonics, and is also beneficial to the development of novel biomedical materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • A chalcone HPPP was synthesized, and structure obtained by X-ray diffraction. • HPPP showed ESIPT in organic solvents except DMF and DMSO. • In DMSO, ESICT predominated over ESIPT in HPPP. • HPPP acts as a turn-off nanomolar sensor for Fe3+. • Paper strips coated with HPPP can detect aqueous Fe3+. The interplay of excited state photophysical phenomena like excited state charge transfer (ESICT) and excited state proton transfer (ESIPT) in tailor made molecular systems has been a fascinating field of research. In the current work, a detailed photophysical dissection of a chalcone (E)-1-(2-hydroxyphenyl)-3-(4-(piperidin-1-yl)phenyl)prop-2-en-1-one (HPPP) is reported. HPPP could probably show both or either of ESIPT and ESICT due to the presence of a piperidinyl ring as a charge donor and six-membered carbonyl-phenolic –OH Hydrogen bonded system (platform for ESIPT), the latter evidenced from the crystal structure. In order to disentangle the photophysical events, detailed spectrodynamic experiments were performed for control compound (E)-1-(2-methoxyphenyl)-3-(4-(piperidin-1-yl)phenyl)prop-2-en-1-one (MePPP), which bears only charge transfer moiety. Careful comparison led to the conclusion that ESICT is fully suppressed and ESIPT is favored for HPPP in organic solvents except DMF and DMSO, where ESICT is dominant over ESIPT. The practical utility of HPPP was explored by fluorimetric nanomolar sensing (limit of detection: 30 nM) of aqueous Fe3+ ion by the mode of emission quenching in DMF medium. Practical utility of HPPP was demonstrated by detection of Fe3+ on paper strips. The current work serves the dual purpose of boosting the understanding of emissive dyes showing coupled photophysical phenomena and construction of efficient fluorogenic sensors for biorelevant ions like Fe3+. [ABSTRACT FROM AUTHOR]

The interaction among relative humidity, current density, and internal polarization plays a crucial role in optimizing the performance of polymer electrolyte membrane fuel cells (PEMFCs). However, achieving swift analysis and feedback on the internal humidity status of PEMFCs through on-vehicle impedance spectroscopy measurements remains a significant challenge. Conducting a series of impedance spectra under operating conditions of 30 %, 50 %, and 80 % relative humidity sheds light on the impact of humidity on performance. Correlations between specific distribution of relaxation times (DRT) peaks and internal polarization are established. Through DRT analysis, four polarization dynamics related to proton transfer at the proton exchange membrane interface, proton transport in the cathode catalyst layer, charge transfer, and the oxygen diffusion process are effectively identified based on characteristic frequencies and peaks. The rate-determining step of the polarization varies under idling, rated, and overload conditions, providing valuable insights. This study contributes analytical models and strategic guidance for tailoring relative humidity conditions to mitigate polarization, thereby enabling real-time control and enhancement of PEMFC performance. [Display omitted] • Unveiled dynamic interactions among humidity and polarization in PEMFCs. • Employe DRT for precise analysis, unveiling four key polarization dynamics. • Reveal characteristic frequencies for on-vehicle DRT analysis at varied operation. [ABSTRACT FROM AUTHOR]

• Gab-CLA interaction: solution investigation and solid isolation. • The Gab-CLA solid products were characterized via physicochemical tools. • Solid products were isolated in 1:1 and 1: 2 (CLA: Gab) mole ratios. • DFT/TDDFT computational study is performed to 1:1 product. • Biological evaluation and molecular docking simulation are followed. The behavior of Gabapentin (Gab) towards Chloranilic acid (CLA) in solution is checked using UV–visible spectroscopy in three different solvents: methanol, ethanol, and acetonitrile. Applying Job's continuous variation method, the reaction is proved to proceed as a 1:1 molar composition in solution. On the other hand, two nanocrystalline solid products are isolated from the reaction of Gabapentin (Gab) with chloranilic acid (CLA), depending on the initial mole ratio (G1CLA and G2CLA). The isolated solid products are characterized by physicochemical tools (UV–vis., FT-IR, 1HNMR), proving the existence of proton transfer interaction. The semi-crystalline G2CLA (1CLA: 2Gab) product was investigated using powder x-ray diffraction, whereas the crystallized G1CLA (1CLA: 1Gab) product was analyzed by SXRD. The determined crystallite sizes for G1CLA and G2CLA were 30.02 nm and 40.17 nm, respectively. G1CLA was optimized in ethanol and gas phase, using DFT computational study, with basis sets B3LYP/6–31+ G (d,p). The calculations showed the occurrence of charge transfer and hydrogen bonding in gas phase whereas proton transfer took place in ethanol. NBO charge calculations, reactivity parameters, and MEP maps indicated that CLA exhibits e-accepting ability, while Gab demonstrates e-donating properties. The main electronic transition states were determined by TD-DFT method. Moreover, the isolated solids were subjected to biological activity study, against six pathogens: two fungi, two gram-positive, and two gram-negative bacteria. Molecular docking simulation of G1CLA was performed on the crystal structure of proteus vulgaris HigA antitoxin (6CF1), revealing a total binding energy of -74.8704 Kcal/mole. [Display omitted] [ABSTRACT FROM AUTHOR]

Protonolysis of [Cp*M] (M=Ga, In, Tl) with [(Me4TACD)H][BAr4Me] (Me4TACD=N,N′,N′′,N′′′‐tetramethyl‐1,4,7,10‐tetraazacyclododecane; [BAr4Me]−=[B{C6H3‐3,5‐(CH3)2}4]−) provided monovalent salts [(Me4TACD)M][BAr4Me], whereas [Cp*Al]4 yielded trivalent [(Me4TACD)AlH][BAr4Me]2. Protonation of [(Me4TACD)Ga][BAr4Me] with [Et3NH][BAr4Me] gave an unusually acidic (pKa(CH3CN)=24.5) gallium(III) hydride dication [(Me4TACD)GaH][BAr4Me]2. Deprotonation with IMe4 (1,3,4,5‐tetramethyl‐imidazol‐ylidene) returned [(Me4TACD)Ga][BAr4Me]. These reversible processes occur with formal two‐electron oxidation and reduction of gallium. DFT calculations suggest that gallium(I) protonation is facilitated by strong coordination of the tetradentate ligand, which raises the HOMO energy. High nuclear charge of [(Me4TACD)GaH]2+ facilitates hydride‐to‐metal charge transfer during deprotonation. Attempts to prepare a gallium(III) dihydride cation resulted in spontaneous dehydrogenation to [(Me4TACD)Ga]+. [ABSTRACT FROM AUTHOR]

Protonolysis of [Cp*M] (M=Ga, In, Tl) with [(Me4TACD)H][BAr4Me] (Me4TACD=N,N′,N′′,N′′′‐tetramethyl‐1,4,7,10‐tetraazacyclododecane; [BAr4Me]−=[B{C6H3‐3,5‐(CH3)2}4]−) provided monovalent salts [(Me4TACD)M][BAr4Me], whereas [Cp*Al]4 yielded trivalent [(Me4TACD)AlH][BAr4Me]2. Protonation of [(Me4TACD)Ga][BAr4Me] with [Et3NH][BAr4Me] gave an unusually acidic (pKa(CH3CN)=24.5) gallium(III) hydride dication [(Me4TACD)GaH][BAr4Me]2. Deprotonation with IMe4 (1,3,4,5‐tetramethyl‐imidazol‐ylidene) returned [(Me4TACD)Ga][BAr4Me]. These reversible processes occur with formal two‐electron oxidation and reduction of gallium. DFT calculations suggest that gallium(I) protonation is facilitated by strong coordination of the tetradentate ligand, which raises the HOMO energy. High nuclear charge of [(Me4TACD)GaH]2+ facilitates hydride‐to‐metal charge transfer during deprotonation. Attempts to prepare a gallium(III) dihydride cation resulted in spontaneous dehydrogenation to [(Me4TACD)Ga]+. [ABSTRACT FROM AUTHOR]