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A double harmonic oscillator model is applied to compute the negative ion photoelectron spectra (NIPES) of the 1- and 2-cyanonaphthalene (CNN) radical anions. The computed Franck–Condon factors utilize optimized structures and harmonic vibrational frequencies obtained using density functional theory with the B3LYP 6-311++G (2d,2p) basis set while considering the mode-mixing Duschinsky effects. To test the accuracy of our model, the NIPES of α and β naphthyl radical anions were computed, and a strong agreement between the slow electron velocity-map ion imaging spectra and the predicted spectra was found. The adiabatic electron affinities (EAs) of the ground singlet states (S0) in 1-CNN and 2-CNN are 0.856 and 0.798 eV, respectively. The origin of the lowest-lying triplet (T1) states in 1-CNN and 2-CNN is found to be 3.226 and 3.266 eV, resulting in singlet–triplet energy splittings (ΔEST) of 2.370 and 2.468 eV, respectively. Both the NIPES for electron detachment to the S0 and T1 states exhibit well-resolved vibrational features, allowing for the assignment of several vibrational fundamental frequencies. Following deprotonation, several isomers are formed, with the most stable deprotonated radical anions in 1-CNN and 2-CNN, corresponding to the removal of the most acidic proton, with EAs of 2.062 and 2.16 eV. The rich spectroscopic and thermochemical data obtained in the current study make the CNN radical anions and their deprotonated species interesting systems for investigation in gas-phase, negative-ion experiments. [ABSTRACT FROM AUTHOR]

In the recently discovered proton-coupled energy transfer (PCEnT) mechanism, the transfer of electronic excitation energy between donor and acceptor chromophores is coupled to a proton transfer reaction. Herein, we develop a general theory for PCEnT and derive an analytical expression for the nonadiabatic PCEnT rate constant. This theory treats the transferring hydrogen nucleus quantum mechanically and describes the PCEnT process in terms of nonadiabatic transitions between reactant and product electron–proton vibronic states. The rate constant is expressed as a summation over these vibronic states, and the contribution of each pair of vibronic states depends on the square of the vibronic coupling as well as the spectral convolution integral, which can be viewed as a generalization of the Förster-type spectral overlap integral for vibronic rather than electronic states. The convolution integral also accounts for the common vibrational modes shared by the donor and acceptor chromophores for intramolecular PCEnT. We apply this theory to model systems to investigate the key features of PCEnT processes. The excited vibronic states can contribute significantly to the total PCEnT rate constant, and the common modes can either slow down or speed up the process. Because the pairs of vibronic states that contribute the most to the PCEnT rate constant may correspond to spectroscopically dark states, PCEnT could occur even when there is no apparent overlap between the donor emission and acceptor absorption spectra. This theory will assist in the interpretation of experimental data and will guide the design of additional PCEnT systems. [ABSTRACT FROM AUTHOR]

8-oxo-7,8-dihydro-2′-dexyoguanine (8-oxo-dG) can be tautomerized to a 6-enolate,8-keto tautomer through nearby-NH deprotonation at elevated pH. In this work, the N3-protonated 8-oxo-dG tautomers in deuterated pH-buffer solutions were studied using steady-state UV/Vis, FTIR, and ultrafast two-dimensional IR spectroscopies. The presence of 6,8-diketo and C6-anionic tautomers at neutral to basic conditions (pD = 7.4–12.0) was revealed by UV/Vis and FTIR results and was further confirmed by 2D IR signals in both diagonal and off-diagonal regions. However, the C6-enol tautomer, which may be an intermediate during the transition from 6,8-diketo to C6-enolate,C8-keto, was not observed appreciably due to its extreme low population. Furthermore, the neutral-to-anionic tautomeric transition of N3H-8-oxo-dG studied in this work occurs under more basic conditions than the N1H-8-oxo-dG reported previously, showing a higher pKa value for N3H than N1H. Finally, vibrational relaxation of the carbonyl stretching mode was found to be both molecular site dependent and pD dependent for 8oxo-dG. Taken together, this work shows that the ultrafast infrared spectroscopic method is effective for examining tautomers and their dynamics in nucleic acids. [ABSTRACT FROM AUTHOR]

We report the development and testing of new integrated cyberinfrastructure for performing free energy simulations with generalized hybrid quantum mechanical/molecular mechanical (QM/MM) and machine learning potentials (MLPs) in Amber. The Sander molecular dynamics program has been extended to leverage fast, density-functional tight-binding models implemented in the DFTB+ and xTB packages, and an interface to the DeePMD-kit software enables the use of MLPs. The software is integrated through application program interfaces that circumvent the need to perform "system calls" and enable the incorporation of long-range Ewald electrostatics into the external software's self-consistent field procedure. The infrastructure provides access to QM/MM models that may serve as the foundation for QM/MM–ΔMLP potentials, which supplement the semiempirical QM/MM model with a MLP correction trained to reproduce ab initio QM/MM energies and forces. Efficient optimization of minimum free energy pathways is enabled through a new surface-accelerated finite-temperature string method implemented in the FE-ToolKit package. Furthermore, we interfaced Sander with the i-PI software by implementing the socket communication protocol used in the i-PI client–server model. The new interface with i-PI allows for the treatment of nuclear quantum effects with semiempirical QM/MM–ΔMLP models. The modular interoperable software is demonstrated on proton transfer reactions in guanine-thymine mispairs in a B-form deoxyribonucleic acid helix. The current work represents a considerable advance in the development of modular software for performing free energy simulations of chemical reactions that are important in a wide range of applications. [ABSTRACT FROM AUTHOR]

This article investigates the relaxation dynamics of the ionized 2a1 state of a water molecule within a water dimer. The study was motivated by findings from two previous pieces of research that focused on the relaxation behaviors of the inner-valence ionized water dimer. The present study discloses an observation indicating that water dimers display specific fragmentation patterns following inner-valence ionization, depending on the position of the vacancy. Vacancies were created in the 2a1 state of the proton-donating water molecule (PDWM) and proton-accepting water molecule (PAWM). Utilizing Born–Oppenheimer molecular dynamics simulations, the propagation of the 2a1 ionized state was carried out for both scenarios. The results revealed proton transfer occurred when the vacancy resided in the PDWM, accompanied by the closing of decay channels for O–H bond distance (RO–H) > 1.187 Å (matching Richter et al.'s findings). Conversely, when vacancy was on PAWM, we observed no closing of decay channels (aligning with Jahnke et al.'s findings). This difference translates to distinct fragmentation pathways. In PDWM cases, 2a1 state ionization leads to H3O+ −OH• formation. In contrast, PAWM vacancies result in decay pathways leading to H2O+–H2O+ products. [ABSTRACT FROM AUTHOR]

Langmuir monolayers of fatty aniline (C16-aniline) were investigated using sum-frequency vibrational spectroscopy at various pH levels and NaCl concentrations. To analyze the sum-frequency generation (SFG) spectra of aniline, a multi-peak Lorentzian model, in accordance with the theory of SFG for a charged interface, was applied. First, SFG spectra of C16-aniline from pH 2 to 6 at a constant ionic strength of 10 mM (where the phase of the complex potential of the dc-induced signal was suppressed to a few degrees) were fitted with the above-mentioned method. The mean-field theory that considers the chemical equilibrium of the aniline headgroup was used to analyze the fitting results to find that the pKa of aniline is 4.4 ± 0.3. The protonation fraction of the aniline headgroup was estimated to be less than 5% at pH 6 and NaCl concentrations were up to 1M. The generalized Poisson–Boltzmann equation in the Gouy–Chapmann model effectively explained the observed SFG spectra in the OH region for fatty aniline at pH as low as 2, even for the systems without addition of any salt. [ABSTRACT FROM AUTHOR]

The photochemical dynamics of the acetic acid and trifluoro-acetic acid dimers in hexane are studied using time-resolved infrared absorption spectroscopy and ab initio electronic structure calculations. The different hydrogen bond strengths of the two systems lead to changes in the character of the accessed excited states and in the timescales of the initial structural rearrangement that define the early time dynamics following UV excitation. The much stronger hydrogen bonding in the acetic acid dimer stabilizes the system against dissociation. Ground state recovery is mediated by a structural buckling around the hydrogen bond itself with no evidence for excited state proton transfer processes that are usually considered to drive ultrafast relaxation processes in hydrogen bonded systems. The buckling of the ring leads to relaxation through two conical intersections and the eventual reformation of the electronic and vibrational ground states on a few picosecond timescale. In trifluoro-acetic acid, the weaker hydrogen bonding interaction means that the dimer dissociates under similar irradiation conditions. The surrounding solvent cage restricts the full separation of the monomer components, meaning that the dimer is reformed and returns to the ground state structure via a similar buckled structure but over a much longer, ∼100 ps, timescale. [ABSTRACT FROM AUTHOR]

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]

Understanding the protonation behavior of metal-oxo water oxidation catalysts is essential to improve catalyst efficiency and long-term performance, as well as to tune their properties for specific applications. In this work, we explore the basicity and protonation effects of the highly active water oxidation catalyst [(Mn4O4) (V4O13) (OAc)3]3− using density functional theory. We computed the relative free energies of protonation in a systematic fashion for all symmetry-inequivalent O atoms, where the presence of multiple oxidation states from Mn 4 IV to Mn 4 III and a rich Jahn–Teller isomerism adds a significant amount of complexity. For high oxidation states, the compound behaves like some other polyoxometalates, showing protonation preferably at the terminal and μ2-bridging O atoms of the vanadate cap. However, upon reduction, eventually, the protonation preference switches to the cubane O atoms, mostly driven by a strong increase in basicity for O atoms located along the Jahn–Teller axes. Our work further evidences that protonation can potentially lead to several chemical transformations, like disproportionation and charge transfer to vanadium, dissociation of ligands, or the opening of the cubane structure. Our simulated UV/Vis absorption spectra additionally provide valuable insights about how the protonation of the catalyst could be tracked experimentally. Overall, our analysis highlights the complexity involved in the protonation of heterometallic polyoxometalate clusters. [ABSTRACT FROM AUTHOR]

The iron(III) complexes [Fe(H2O)n(OH)m]3−m (n + m = 5, 6, m ≤ 3) and corresponding proton transfer reactions are studied with total energy calculations, the nudged elastic band (NEB) method, and molecular dynamics (MD) simulations using ab initio and a modification of reactive force field potentials, the ReaxFF-AQ potentials, based on the implementation according to Böhm et al. [J. Phys. Chem. C 120, 10849–10856 (2016)]. Applying ab initio potentials, the energies for the reactions [Fe(H2O)n(OH)m]3−m + H2O → [Fe(H2O)n−1(OH)m+1]2−m + H3O+ in a gaseous environment are in good agreement with comparable theoretical results. In an aqueous (aq) or alkaline environment, with the aid of NEB computations, respective minimum energy paths with energy barriers of up to 14.6 kcal/mol and a collective transfer of protons are modeled. Within MD simulations at room temperature, a permanent transfer of protons around the iron(III) ion is observed. The information gained concerning the geometrical and energetic properties of water and the [Fe(H2O)n(OH)m]3−m complexes from the ab initio computations has been used as reference data to optimize parameters for the O–H–Fe interaction within the ReaxFF-AQ approach. For the optimized ReaxFF-AQ parameter set, the statistical properties of the basic water model, such as the radial distribution functions and the proton hopping functions, are evaluated. For the [Fe(H2O)n(OH)m]3−m complexes, it was found that while geometrical and energetic properties are in good agreement with the ab initio data for gaseous environment, the statistical properties as obtained from the MD simulations are only partly in accordance with the ab initio results for the iron(III) complexes in aqueous or alkaline environments. [ABSTRACT FROM AUTHOR]

Diffusion of electrons over distances on the order of 100 μm has been observed in crystals of a small tetraheme cytochrome (STC) from Shewanella oneidensis [J. Huang et al. J. Am. Chem. Soc. 142, 10459–10467 (2020)]. Electron transfer between hemes in adjacent subunits of the crystal is slower and more strongly dependent on temperature than had been expected based on semiclassical electron-transfer theory. We here explore explanations for these findings by molecular-dynamics simulations of crystalline and monomeric STC. New procedures are developed for including time-dependent quantum mechanical energy differences in the gap between the energies of the reactant and product states and for evaluating fluctuations of the electronic-interaction matrix element that couples the two hemes. Rate constants for electron transfer are calculated from the time- and temperature-dependent energy gaps, coupling factors, and Franck–Condon-weighted densities of states using an expression with no freely adjustable parameters. Back reactions are considered, as are the effects of various protonation states of the carboxyl groups on the heme side chains. Interactions with water are found to dominate the fluctuations of the energy gap between the reactant and product states. The calculated rate constant for electron transfer from heme IV to heme Ib in a neighboring subunit at 300 K agrees well with the measured value. However, the calculated activation energy of the reaction in the crystal is considerably smaller than observed. We suggest two possible explanations for this discrepancy. The calculated rate constant for transfer from heme I to II within the same subunit of the crystal is about one-third that for monomeric STC in solution. [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]

The pH-dependent change in protonation of ionizable lipids is crucial for the success of lipid-based nanoparticles as mRNA delivery systems. Despite their widespread application in vaccines, the structural changes upon acidification are not well understood. Molecular dynamics simulations support structure prediction but require an a priori knowledge of the lipid packing and protonation degree. The presetting of the protonation degree is a challenging task in the case of ionizable lipids since it depends on pH and on the local lipid environment and often lacks experimental validation. Here, we introduce a methodology of combining all-atom molecular dynamics simulations with experimental total-reflection x-ray fluorescence and scattering measurements for the ionizable lipid Dlin-MC3-DMA (MC3) in POPC monolayers. This joint approach allows us to simultaneously determine the lipid packing and the protonation degree of MC3. The consistent parameterization is expected to be useful for further predictive modeling of the action of MC3-based lipid nanoparticles. [ABSTRACT FROM AUTHOR]

We present a simulation method that allows us to calculate the titration curves for systems undergoing protonation/deprotonation reactions—such as charged colloidal suspensions with acidic/basic surface groups, polyelectrolytes, polyampholytes, and proteins. The new approach allows us to simultaneously obtain titration curves both for systems in contact with salt and acid reservoir (semi-grand canonical ensemble) and for isolated suspensions (canonical ensemble). To treat the electrostatic interactions, we present a new method based on Ewald summation—which accounts for the existence of both Bethe and Donnan potentials within the simulation cell. We show that the Donnan potential dramatically affects the pH of a suspension. Counterintuitively, we find that in suspensions with a large volume fraction of nanoparticles and low ionic strength, the number of deprotonated groups can be 100% larger in an isolated system, compared to a system connected to a reservoir by a semi-permeable membrane—both systems being at exactly the same pH. [ABSTRACT FROM AUTHOR]

Understanding the structure and chemical bonding in water dimers is central to the study of many (photo-)electrochemical oxidation reactions. Two structures of the water dimer radical cation, namely, proton-transfer and hemi-bonded structures, have been suggested using density functional theory (DFT) and coupled cluster singles, doubles, and perturbative triples [CCSD(T)]. Both structures are identified by us as local minima, and their relative stability strongly depends on the level of theory. The exact exchange correlates linearly to the energy difference between both local minima. DFT functionals with less than 20 percent exact exchange predict the hemi-bonded structure to be more stable, while more than 20 percent of the exact exchange stabilizes the proton-transfer structure. The latter structure is also confirmed by CCSD(T) benchmark computations. These computations, furthermore, indicate that the oxidized water dimer consists of a hydronium cation (H3O+) and an HO· radical. These results are reproduced by DFT functionals with more than 50% of exact exchange (BHandH, M06-2X, and M06-HF). The transition barrier for the interconversion from the proton-transfer to the hemi-bonded structure is 0.6 eV, while the reverse reaction has a barrier of 0.1 eV. [ABSTRACT FROM AUTHOR]

The coherent transfer of electron spin polarization to nuclei by means of a microwave pulse sequence is a promising new approach to enhancing the sensitivity of solid-state nuclear magnetic resonance (NMR). The development of pulse sequences for dynamic nuclear polarization (DNP) of bulk nuclei is far from complete, as is the understanding of what makes a good DNP sequence. In this context, we introduce a new sequence, termed Two-Pulse Phase Modulation (TPPM) DNP. We provide a general theoretical description for electron–proton polarization transfer by periodic DNP pulse sequences and find it in excellent agreement with numerical simulations. In experiments at 1.2 T, TPPM DNP generates a higher gain in sensitivity than existing sequences XiX (X-inverse-X) and TOP (Time-Optimized Pulsed) DNP but does so at relatively high nutation frequencies. In contrast, we find that the XiX sequence performs very well at nutation frequencies as low as 7 MHz. A combination of theoretical analysis and experimental investigation makes clear that fast electron–proton polarization transfer, due to a well-preserved dipolar coupling in the effective Hamiltonian, correlates with a short build-up time of the dynamic nuclear polarization of the bulk. Experiments further show that the performances of XiX and TOP DNP are affected differently by the concentration of the polarizing agent. These results constitute important reference points for the development of new and better DNP sequences. [ABSTRACT FROM AUTHOR]

The 2D porous protonated NiSe/g-C 3 N 4 nanosheets are synthesized via a chemical-calcination-etching-acidification-hydrothermal method. The obtained 2D NiSe/g-C 3 N 4 nanosheets (NiSe/HCN-3) exhibit signally enhanced HER (∼1184.74 μmol g−1 h−1)/degradation (∼0.04645 min−1) than the monomer g-C 3 N 4 (∼150/5-folds), including a decent stability (average HER ∼1152.71 μmol g−1 h−1). It mainly attributes to the NiSe/g-C 3 N 4 interface owns appropriate potential gradient can promote the interface carrier driving to optimize efficiency, including increasing carrier transport, extending carrier lifetime, and reducing recombination, as well as the porous nanosheets and surface protonation obtain numerous active sites for decreasing overpotential and promoting electron solid/liquid interfacial diffusion. Additionally, the 2D porous nanosheets can improve the solar efficiency (multiple internal reflections) and shorten the carrier pathway. [Display omitted] • NiSe co-catalyst optimize carrier efficiency by appropriate Fermi level gradient. • Surface protonation increase active sites to promote electron interfacial diffusion. • Porous nanosheets increase active sites/solar efficiency and shorten carrier path. [ABSTRACT FROM AUTHOR]

An unusual example of a potassium capped terminal cobalt–oxido complex has been isolated and crystallographically characterized. The synthesis of [tBu,TolDHP]CoOK proceeds from a previously reported parent compound, [tBu,TolDHP]CoOH, via deprotonation with KOtBu. Structural and electronic characterization suggest a weakly coupled dimer in a distinct seesaw geometry with a Co(III) oxidation state and a non-innocent radical ligand. [ABSTRACT FROM AUTHOR]

In situ formed poly(1,3‐dioxolane) (PDOL) electrolytes are of great interest due to the facile process and the improved interface contact. However, the practical application of in situ PDOL electrolytes is still plagued by fast solidification time (liquid state) and poor high‐voltage stability (solid state). Herein, the slow‐release carriers triglycidyl isocyanurate (TGIC), which play dual roles as initiator sustained‐release and network confinement, can tune DOL curing time and cathode/electrolyte interface chemistry is demonstrated. Specifically, the electronegative C≐O and epoxy groups in TGIC have an affinity with BF3, the decomposition product of lithium bis(oxalate)borate (LiDFOB), delaying BF3 protonation reaction and thus extending DOL solidification time. In addition, the epoxy groups in TGIC serve as crosslinking sites to form in situ crosslinked polymer electrolytes (TPDOL@FEC). The corresponding network structure suppresses the contact reaction between high‐fluidity organic components and cathodes, generating a uniform and thin cathode electrolyte interface layer. As a result, the TPDOL@FEC precursor solution can remain its liquid state even after resting 24 h at room temperature. The assembled LiNi0.6Co0.2Mn0.2O2||TPDOL@FEC||Li cells display an impressive capacity retention of 91.5% after 100 cycles at 4.4 V (0.5 C). This study is expected to be a leap in the pursuit of practically feasible in situ formed PDOL electrolytes. [ABSTRACT FROM AUTHOR]

Although strategies of olefin hydroalkylation continue to emerge rapidly, the precise control of the regio- or chemoselectivity and the expansion of the reaction range are still challenges. Herein, a straightforward route for cobalt-catalyzed anti-Markovnikov hydroalkylation of unactivated olefins with alkyl iodides has been achieved. The developed reaction is compatible with oxa-, aza-, cyclo- and a series of other functional groups as well as the frameworks of some bioactive compounds. Mechanism studies confirm that an alkyl radical is involved and cobalt–alkyl insertion followed by protonation with water are possible pathways in this reaction. [ABSTRACT FROM AUTHOR]

In comparison to the sensing activity, the reactivity of arsenite (AsO2−) is less explored. Herein, we focused on AsO2− reactivity studies based on its pKa and compared the study with other common anions. All three pKa values of arsenite are >9.0, affording a flexible working pH range to design a probe for reactivity studies. We designed and synthesized six pH dependent benzothiazole-based Schiff bases, namely, 1-(((6-nitrobenzo[d]thiazol-2-yl)imino)methyl)naphthalen-2-ol (1), 5-(diethylamino)-2-(((6-nitrobenzo[d]thiazol-2-yl)imino)methyl)phenol (2), 9-(((6-nitrobenzo[d]thiazol-2-yl)imino)methyl)-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-ol (3), 5-methoxy-2-(((6-nitrobenzo[d]thiazol-2-yl)imino)methyl)phenol (4), 4-(((6-nitrobenzo[d]thiazol-2-yl)imino)methyl)benzene-1,3-diol (5), and 2-(((6-nitrobenzo[d]thiazol-2-yl)imino)methyl)phenol (6), as probes for hydrolysis studies containing 5% water in acetonitrile. In spite of the presence of water in the solution, no hydrolysis was observed for all the probes in the absence of a salt. In the presence of selected sodium salts of various anions in solution, intramolecular charge transfer (ICT) was observed after the deprotonation of an aromatic hydroxy group at the ortho position with respect to the imine groups within the probes. Among the studied anions, selective AsO2− induced imine hydrolysis was observed for probes 1 and 4. In the case of 5 with both o- and p-hydroxy groups, no hydrolysis was observed in the presence of AsO2−. Probe 6 with only the o-hydroxy group showed very fast hydrolysis with poor selectivity. The p-hydroxy group in 4-(((6-nitrobenzo[d]thiazol-2-yl)imino)methyl)phenol (7) resulted in poor AsO2− induced hydrolysis. The aldehyde, which was generated after hydrolysis of probe 1, showed selective emission at 450 nm in the presence of AsO2−. The time dependent hydrolysis reaction of probe 1 controls the emission intensity enhancement. [ABSTRACT FROM AUTHOR]

Quinazolines are biologically potent heterocyclic compounds; however, their synthesis poses high challenges. In this present study, we have developed an inexpensive cobalt metal‐catalyzed acceptorless dehydrogenative pathway for the sequential synthesis of alkenylated quinazolines from benzhydrol via dehydrogenation, cyclization, and subsequent dehydrogenative sp3 C−H functionalization. This transformation holds potential owing to its commercially available key starting materials, good functional tolerance, moderate reaction conditions, environmental friendliness, and applicability for gram‐scale synthesis. Furthermore, the synthetic utility of the synthesized derivatives has been explored through various reactions, including reduction, halogenation, methoxylation, Michael addition, and spiro cyclization. Additionally, the photophysical properties indicate that the nitrogen atom of the synthesized derivatives readily undergoes a reversible protonation, leading to significant changes in colour. This characteristic presents an opportunity for the creation of pH sensors with colourimetric capabilities. [ABSTRACT FROM AUTHOR]

This work elucidates the fabrication and electrochemical performance of solid-state symmetric supercapacitors based on polyaniline and polypyrrole films synthesized through electrochemical deposition. The study systematically investigates the impact of electrolyte pH on the performance of these devices, comparing responses in acidic, neutral, and alkaline environments. The polyaniline-based device demonstrates a superior response in acidic electrolyte conditions, which is attributed to the protonation/deprotonation mechanisms inherent in the polymer matrix, a phenomenon that is explored and interpreted in the paper. However, the symmetric supercapacitor employing polypyrrole exhibits superior performance in both acidic and alkaline electrolytes, suggesting the pseudocapacitive nature of polypyrrole even in alkaline conditions. The redox behavior of polypyrrole in alkaline environments primarily relies on the exchange of hydroxide ions, facilitating polypyrrole's superior retention of its redox characteristics compared to polyaniline. The findings contribute to the rational design of solid-state supercapacitors tailored for specific electrolyte conditions, with potential applications in diverse electrochemical energy storage systems. [ABSTRACT FROM AUTHOR]

[Display omitted] Polyaniline (PANI) has been widely used as a cathode in aqueous zinc-ion batteries (AZIBs) because of its attractive conductivity and energy storage capability. However, the extensive application of PANI is limited by spontaneous deprotonation and slow diffusion kinetics. Herein, an 18-crown-6-functionalised PANI pseudorotaxane (18C6@PANI) cathode is successfully developed through a facile template-directed polymerisation reaction. The 18C6@PANI cathode exhibits a high specific capacity of 256 mAh g−1 at 0.2 A/g, excellent rate performance of 134 mAh g−1 at 6 A/g and outstanding cycle stability at a high current density of 3 A/g over 10,000 cycles. Experimental and theoretical analyses demonstrate the formation of the –N–Zn–O– structure. The abundant supramolecular channels in pseudorotaxane, induced by crown ether functional groups, are beneficial for achieving superior cyclability and rate capability. These encouraging results highlight the potential for designing more efficient PANI-based cathodes for high-performance AZIBs. [ABSTRACT FROM AUTHOR]

The proton affinity (PA) and gas phase basicity values of previously reported cyclic allene series are investigated using high-level quantum chemical calculations. Some of the studied structures possessed more than one protonation site. All protonation types were explored for each structure and the compounds with PA value more than ≈1030 kJ mol−1 were considered superbasic structures. Cyclic allene's basicity strength was affected by ring size, adjacent heteroatom's presence and resonance existence in protonated form. [ABSTRACT FROM AUTHOR]

The supramolecular hydrogen‐bonded self‐assembled resorcinarene hexameric capsule promotes the ring closing isomerization of cannabidiol through encapsulation of the intermediate carbocation species formed by protonation with HCl. The confinement effect imparted by the capsule steers product selectivity towards the uncommon products Δ8‐iso‐THC, Δ4(8)‐iso‐THC, together with the hydrated 8‐Hydroxy‐iso‐THC. [ABSTRACT FROM AUTHOR]

Nine potentially bidentate thiosemicarbazone (HLn) ligands and their tricarbonylrhenium(I) complexes, [ReY(HLn)(CO)3] (Y=Cl, Br), were synthesized and their binding affinity towards the alpha and beta receptors were determined using a competitive standard radiometric assay with [3H]‐estradiol. Even in the absence of a base, coordinated thiosemicarbazones can undergo deprotonation causing the release of the coordinated halide forming dimeric species, [Re2(Ln)2(CO)6]. The observation of the formation of the dinuclear complex where the thiosemicarbazone ligand adopts the zwitterionic form, [Re2(HL9)2(CO)6]Br2, motivated the theoretical study of the relative stability of these species. Despite the ease of formation of the dimer complexes, it was possible to optimize a synthetic route to obtain the [2+1] complexes [Re(Ln)(pym)(CO)3] where pym is the monodentate ligand 4‐dimethylamino‐pyridine or 4‐hydroxy ‐pyridine. The inclusion of this additional ligand substantially improves the affinity against the receptors (in some cases against both). [99mTc(Ln)(pym)(CO)3] complexes were also prepared using [99mTc(H2O)(CO)3]+, an excess of HLn ligand and in the presence of pym. The radiochromatograms show the formation of the [2+1] complex but also the presence of species resulting from the substitution of pym by chloride and water. However, the ratio of intensities between the three signals remains constant with the variation of the relative concentration of the three monodentate ligands suggesting an equilibrium between the three complexes. [ABSTRACT FROM AUTHOR]

Atomic Fe sites enabled electrochemical carbon dioxide (CO2) reduction (ECO2R) to carbon monoxide (CO) at low overpotentials. However, the narrow potential ranges for selective CO2 conversion on atomic Fe sites hindered the CO production at high current densities. Therefore, unveiling the CO2 electroreduction processes and clarifying the catalytic mechanisms on different atomic Fe sites are important for better design of atomic Fe catalysts toward efficient ECO2R. Herein, the ECO2R processes on single‐atom, dual‐atom, and cluster Fe sites are systematically investigated, and clarify that the balanced water dissociation and CO2 protonation on dual‐atom Fe sites promote the efficient CO production. The dual‐atom Fe catalyst achieves Faradaic efficiencies of CO (FECO) above 92% over a wide potential range of −0.4–−0.9 V versus reversible hydrogen electrode and maintains FECO of 91% after 153‐h electrolysis in H‐type cell. Benefitting from the favorable CO2 protonation for ECO2R on dual‐atom Fe sites, pH‐universal CO2 electroreduction is achieved in alkali‐/acid‐/bicarbonate‐fed membrane electrode assembly electrolyzer, with FECO exceeds 98% in strongly acidic/alkaline and neutral mediums. The work reveals a water dissociation‐promoted CO2 electroreduction on dual‐atom Fe sites and presents a feasible regulation of atomic Fe sites for highly active/selective ECO2R. [ABSTRACT FROM AUTHOR]

Photoactive N-hydroxysulfonamides photocaged with the (6-bromo-7-hydroxycoumarin-4-yl)methyl chromophore have been successfully synthesized, and the mechanisms of photodecomposition investigated for two of the compounds. Upon irradiation up to 97% of a diagnostic marker for (H)NO release, sulfinate was observed for the trifluoromethanesulfonamide system. In the absence of a species that reacts rapidly with (H)NO, (H)NO instead reacts with the carbocation intermediate to ultimately generate (E)-BHC-oxime and (Z)-BHC-oxime. Alternatively, the carbocation intermediate reacts with solvent water to give a diol. Deprotonation of the N(H) proton is required for HNO generation via concerted C-O/N-S bond cleavage, whereas the protonation state of the O(H) does not affect the observed photoproducts. If the N(H) is protonated, C-O bond cleavage to generate the parent N-hydroxysulfonamide will occur, and/or O-N bond cleavage to generate a sulfonamide. The undesired competing O-N bond cleavage pathway increases when the volume percentage of water in acetonitrile/water solvent mixtures is increased. [ABSTRACT FROM AUTHOR]

One of the key physicochemical parameters of polyelectrolyte microcapsules (PMCs) is their buffer capacity (BC). The BC of the microcapsules allows for an assessment of the change in protonation state across the entire polyelectrolyte system, which directly impacts the buffer barrier of PMCs, as well as the stability and physical properties of their shell. However, the buffer capacity of PMCs and their behavior under changes in ionic strength and temperature can differ depending on the type of core used to form the microcapsules. As part of this study, we revealed the buffer capacity (BC) of polyelectrolyte microcapsules formed on polystyrene cores (PMCPs) and studied the influence of ionic strength and environmental temperature on the BC of these capsules. We found that the buffer capacity of PMCPs differs from the BC of water at a pH above 8; the addition of sodium chloride leads to an increase in buffer capacity in alkaline conditions, and conversely, thermal treatment leads to its decrease at a pH of 9. The results obtained are different from the BC of polyelectrolyte microcapsules formed on CaCO3 cores, which suggests a difference in the physicochemical properties of these types of capsules. The buffer capacity of polyelectrolyte microcapsules depends on the type of template used. [ABSTRACT FROM AUTHOR]

A new variant of Fisher indole synthesis involving Bronsted acid-catalyzed hydrohydrazination of unactivated terminal and internal acetylenes with arylhydrazines is reported. The use of polyphosphoric acid alone either as the reaction medium or in the presence of a co-solvent appears to provide the required balance for activating the C–C triple bond towards the nucleophilic attack of the hydrazine moiety without unrepairable reactivity loss of the latter due to competing amino group protonation. Additionally, the formal hydration of acetylenes to the corresponding ketones occurs under the same conditions, making it an alternative approach for generating carbonyl groups from alkynes. [ABSTRACT FROM AUTHOR]

This document is a contents list for the New Journal of Chemistry, a publication by The Royal Society of Chemistry. It provides information about the journal's editorial, cover image, and articles featured in the current issue. The articles cover a wide range of topics in chemistry, including electrodeposition, supercapacitors, catalysis, and photocatalysis. Some specific papers discussed include the bactericidal effects of zeolitic imidazolate frameworks, the use of nanoparticle-decorated glyceryl monostearate as a targeted drug carrier, and the construction of S@C composites for Mg-S batteries. Other papers explore topics such as metal-organic framework-derived bimetallic oxides as anode materials for lithium-ion batteries, advancements in protection of steel surfaces using polystyrene supported nanoparticles, and the enhancement of vanadium dioxide for supercapacitor applications. The document also includes papers on coordination chemistry, synthetic approaches for coumestan derivatives, and the design of metal complexes for targeting breast cancer. [Extracted from the article]

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]

Mono or bis(tetrazole–thiolato) Pd(II) or Pt(II) complexes were obtained from the reactions of dialkyl Pd(II) or Pt(II) complexes with organic tetrazole–thiones (1-aryl- or 1-alkyl-1H-tetrazole-5-thiones) via deprotonation. In contrast, equimolar reactions of zerovalent Pt(0) or Pd(0) complexes with organic tetrazole–thiones afforded hydrido or bis(tetrazole–thiolato) Pt(II) and Pd(II) complexes, and cyclometallated Pt(II) or Pd(II) complexes bearing a tetrazole–thiolato moiety via oxidative addition, depending on the organic substituents on the tetrazole–thiones. In particular, variable (time and temperature)-dependent 1H-NMR spectra of the hydrido Pt(II) tetrazole–thiolates reveal an upfield shift of the hydride signal, suggesting N,S-coordination behavior of the tetrazole–thiolato ligand. Additionally, the N-CH2 signal corresponds to the six-membered ring of platinacycle or palladacycle exhibiting geminal coupling with multiple protons and PR3 ligands; these coupling values were further determined using 1H{31P} experiments. Finally, treatment of the alkyl Pd(II) tetrazole–thiolate or Pd(II) bis(tetrazole–thiolates) with organic tert-butyl isocyanide, thiophenol, and organic halides caused the selective insertion of the isocyanide into the Pd–C bond or deprotonation to afford a Pd(II) disulfide complex and substitution to afford new organic tetrazolyl sulfides. [ABSTRACT FROM AUTHOR]

The electrocatalytic recycling of waste nitrate (NO3RR) is a promising decentralized route for green ammonia synthesis. Nonetheless, it suffers from the competing hydrogen evolution reaction and the insufficient proton supply in high pH conditions. Herein, iron oxide nanoparticles anchored on ZnO is introduced as a strategy to enhance the water dissociation ability and proton transfer rate, advancing NH4+ production from alkaline NO3RR. Supported by a set of ex situ and in situ characterization, the findings reveal the reduction of iron oxides, along with improvements in charge transfer properties and proton generation from H2O. Theoretical calculations show that iron oxides reduce the kinetic barrier of the rate‐limiting step (*NO2‐to‐*NO2H) and result in a thermodynamically favorable process to hydrogenation steps, which in turn reduce the overall energy barrier of alkaline NO3RR. Optimal catalytic activity is realized with a Fe loading of 0.5 wt.%, delivering a Faradaic efficiency of ≈83% for ammonium with a NH4+ yield rate of 31 nmol s−1 cm−2 at −0.7 V versus RHE. The results pave the way for the utilization of bi‐metal interaction to tune the reaction pathway for achieving sustainable ammonium synthesis in alkaline, contributing to ongoing efforts to achieve a sustainable nitrogen cycle via N‐based electrochemistry. [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]

The article describes for the first time the synthesis of the diaminoacetylene ligand, which is a by-product of the synthesis of [W(CN)6(bpy)]2− involving the thermal decomposition of (bpyH)3(H3O)[W(CN)8]·H2O. The formation of the diaminoacetylene ligand, H2NC≡CNH2, occurs through protonation of cyanido ligands and the formation of a C–C bond between two neighbouring CN− ligands through a reductive coupling mechanism. In this way, three salts of the anion [W(CN)6(C2N2H4)]2− with cations: PPh4+ (1), rubidium (2), and caesium (3) were isolated and then structurally and spectroscopically characterised. The formation of an additional by-product (PPh4)3[W(CN)8]·4.25H2O (4) was also discussed. IR measurements of the reaction mixture indicate that proton transfer from the Hbpy+ cation is accompanied by the formation of the acetylene ligand. NMR spectra indicate strong interactions between the cyanido ligands and the protons of the acetylene ligand. [ABSTRACT FROM AUTHOR]

Reactions of tricyclic 1,4-diphosphinines 1,4 with LiOH, followed by protonation are reported. 1,3-Thiazole-2-thione-derived 1 enabled only observation of the first anionic addition product 2/3. On the other hand, imidazole-2-selone-annelated derivative 4 enabled the identification of the first (5) and second product (6) at low temperature. As water was eliminated upon warming in both cases, DFT calculations were performed to gain more insight into the reaction pathway(s). [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) are promising photocatalysts for H2O2 production from water via oxygen reduction reaction (ORR). The design of COFs for efficient H2O2 production indubitably hinges on an in‐depth understanding of their ORR mechanisms. In this work, taking an imine‐linked COF as an example, we demonstrate that protonation of the functional units such as imine, amine, and triazine, is a highly efficient strategy to upgrade the activity levels for H2O2 synthesis. The protonation not only extends the light absorption of the COF but also provides proton sources that directly participate in H2O2 generation. Notably, the protonation simplifies the reaction pathways of ORR to H2O2, i.e. from an indirect superoxide radical (O2•- ${{O}_{2}^{\bullet -}}$) mediated route to a direct one‐step two‐electron route. Theoretical calculations confirm that the protonation favors H2O2 synthesis due to easy access of protons near the reaction sites that removes the energy barrier for generating *OOH intermediate. These findings not only extend the mechanistic insight into H2O2 photosynthesis but also provide a rational guideline for the design and upgradation of efficient COFs. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Molecular ferroelastics with the natural features of mechanical flexibility and switchable spontaneous strain have attracted widespread attention in the scientific community due to their potential applications in tunable gratings, flexible memorizers, strain sensors, and intelligent actuators. However, most designs of molecular ferroelastics remain in the stage of blind exploration, posing a challenge to achieve a functional ferroelastic more effectively. Herein, we have successfully obtained a molecular ferroelastic, [Me2NH(CH2)2NH3](ReO4)2 (Me2NH(CH2)2NH3 = N,N‐dimethylethylenediammonium), under the guidance of the mono‐/double‐protonation strategy. The double‐protonated [Me2NH(CH2)2NH3](ReO4)2 undergoes a paraelastic‐ferroelastic phase transition with the Aizu notation of 2/mF1¯ at 322 K. Meanwhile, the theoretical calculation and experimental measurement simultaneously show that [Me2NH(CH2)2NH3](ReO4)2 possesses good mechanical flexibility, because its elastic modulus (E) of 8.26 GPa and hardness (H) of 0.45 GPa are smaller than the average values of organic crystals (E of 12.05 GPa and H of 0.5 GPa), which makes it promising to apply in wearable pressure sensors, implantable medical sensors, high‐precision tuners, etc. This work further enriches the molecular ferroelastic family and demonstrates that mono‐/double‐protonation is one of the effective molecular modification strategies for designing ferroelastics. [ABSTRACT FROM AUTHOR]

In this study, the density functional M06‐2X/6‐311++G(3df,3pd) method was employed to investigate the mutual isomerization reaction mechanism of 5‐chlorouracil from diketone to diol under the catalysis of water, methanol, formic acid, and an electric field. Parameters such as reaction enthalpy, activation energy, activation Gibbs free energy, and proton transfer reaction rate were obtained. The computational results show that under the same conditions, formic acid demonstrates the best catalytic effect, while the influence of electric field catalysis on the reaction barrier is minimal. [ABSTRACT FROM AUTHOR]

Developing pragmatic strategies for accessing functional benzofuran‐2‐ones from 3‐([1,1′‐biphenyl]‐2‐yl)benzofuran remains an enduring challenge. Herein, we have achieved a highly discriminating electrochemical oxidative dearomative spiroannulation of 3‐([1,1′‐biphenyl]‐2‐yl)benzofuran, culminating in the synthesis of 2H‐spiro[benzofuran‐3,9′‐fluoren]‐2‐one derivatives. By harnessing the electrophilic intermediates of benzofuryl radical cations supported by DFT calculations, we attain exceptional regioselectivity while eliminating the need for stoichiometric oxidants. Mechanistic investigations reveal a sequence of events involving the benzofuran radical cation, encompassing the capture of H2O, nucleophilic arene attack, and subsequent deprotonation, ultimately yielding the final benzofuran‐2‐ones. [ABSTRACT FROM AUTHOR]

Ion exchange is a promising synthetic method for alleviating severe cation mixing in traditional layered oxide materials for lithium-ion batteries, leading to enhanced structural stability. However, the underlying mechanisms of ion exchange are still not fully understood. Such a fundamental study of the ion-exchange mechanism is needed for achieving the controllable synthesis of layered oxides with a stable structure. Herein, we thoroughly unearth the underlying mechanism that triggers the ion exchange of Ni-rich materials in aqueous solutions by examining time-resolved structural evolution combined with theoretical calculations. Our results reveal that the reaction pathway of ion exchange can be divided into two steps: protonation and lithiation. The proton is the key to achieving charge balance in the ion exchange process, as revealed by X-ray adsorption spectroscopy and inductive coupled plasma analysis. In addition, the intermediate product shows high lattice distortion during ion exchange, but it ends up with a most stable product with high lattice energy. Such apparent discrepancies in lattice energy between materials before and after ion exchange emphasize the importance of synthetic design in structural stability. This work provides new insights into the ion-exchange synthesis of Ni-rich oxide materials, which advances the development of cathode materials for high-performance lithium-ion batteries. [ABSTRACT FROM AUTHOR]

In this study, compounds with phenylethynyl (PE) groups introduced at all of the possible positions of the methylene‐bridged structure of the 1,1′‐bi‐2‐naphthol backbone (3‐PE to 8‐PE) were synthesized. Compounds with four or six phenylethynyl groups (3,6‐PE, 4,6‐PE, 5,6‐PE, 6,7‐PE, and 3,4,6‐PE) were also synthesized. The key reaction for the synthesis of these compounds was the Sonogashira reaction using halogen scaffolds. The new transformation methods include (1) selective bromination of the 5‐position of the binaphthyl skeleton and (2) bromination of the 6‐position and then iodination of the 4‐position, followed by the Sonogashira reaction of iodine at the 4‐position and lithiation and protonation of bromine at the 6‐position. The optical properties of the compounds were evaluated. The extension of the π system greatly differed depending on the position of the phenylethynyl group. 4‐PE, 4,6‐PE, and 3,4,6‐PE, in which the phenylethynyl groups were introduced in the extended direction of the naphthalene linkage axis, showed longer absorption and emission wavelengths and higher fluorescence quantum yields than the other compounds. In circularly polarized luminescence measurements, 7‐PE showed a relatively large glum value, an interesting finding that reverses the sense. [ABSTRACT FROM AUTHOR]

Histidine can be protonated on either or both of the two N atoms of the imidazole moiety. Each of the three possible forms occurs as a result of the stereochemical environment of the histidine side chain. In an atomic model, comparing the possible protonation states in situ, looking at possible hydrogen bonding and metal coordination, it is possible to predict which is most likely to be correct. A more direct method is described that uses quantum‐mechanical methods to calculate, also in situ, the minimum geometry and energy for comparison, and therefore to more accurately identify the most likely protonation state. [ABSTRACT FROM AUTHOR]

Photoisomerization is a key photochemical reaction in microbial and animal rhodopsins. It is well established that such photoisomerization is highly selective; all-trans to 13-cis, and 11-cis to all-trans forms in microbial and animal rhodopsins, respectively. Nevertheless, unusual photoisomerization pathways have been discovered recently in microbial rhodopsins. In an enzymerhodopsin NeoR, the all-trans chromophore is isomerized into the 7-cis form exclusively, which is stable at room temperature. Although, the 7-cis form is produced by illumination of retinal, formation of the 7-cis form was never reported for a protonated Schiff base of all-trans retinal in solution. Present HPLC analysis of retinal oximes prepared by hydroxylamine reaction revealed that all-trans and 7-cis forms cannot be separated from the syn peaks under the standard HPLC conditions, while it is possible by the analysis of the anti-peaks. Consequently, we found formation of the 7-cis form by the photoreaction of all-trans chromophore in solution, regardless of the protonation state of the Schiff base. Upon light absorption of all-trans protonated retinal Schiff base in solution, excited-state relaxation accompanies double-bond isomerization, producing 7-cis, 9-cis, 11-cis, or 13-cis form. In contrast, specific chromophore-protein interaction enforces selective isomerization into the 13-cis form in many microbial rhodopsins, but into 7-cis in NeoR. [ABSTRACT FROM AUTHOR]

Betanin (Bn), a natural dye in the Betalains family, predominantly takes on a cationic form known as Bn+. However, it exists in a neutral state as Bn_C2, Bn_C15, and Bn_C17 by losing an H+ from one of its carboxylic acids. Density functional theory (DFT) and Time‐dependent density functional theory (TD‐DFT) studies evaluate the efficiency of each betanin form and pinpoint the most probable anchoring point to TiO2. The Bn_C17 variant stands out as a highly promising candidate for DSSC cells, demonstrating a distinctive combination of electron injection efficiency, electrochemical performance, hole transport capabilities, and photovoltaic behavior. Considering factors like adsorption energy, binding mode, structural compatibility, electronic properties, and absorption characteristics, Bn_C17@TiO2 emerges as the most favorable dye@TiO2 complex among the studied betanin forms for DSSC applications. Contrastingly, the C2‐COOH anchoring point presents challenges with monodentate binding, a different orientation, and potential load distribution issues. This behavior, resembling that of a p‐type dye, differs from the n‐type behavior exhibited by the C15‐COOH and C17‐COOH forms, making the latter two more suitable as sensitizers. Consequently, C2‐COOH may not be the optimal anchoring point for TiO2 in the investigated betanin forms, especially when compared to the more favorable C17‐COOH anchoring point. [ABSTRACT FROM AUTHOR]

This study developed three microstructured chitosan nanocapsules with immobilized lipase to explore chitosan-lipase interactions at different pH levels. Chitosan undergoes complete protonation or deprotonation based on pH level. Three distinct pH levels were examined: 5.5, where chitosan is fully protonated; 6.5, where chitosan is partially protonated/deprotonated; and 7.5, where chitosan is fully deprotonated. The nanocapsules exhibited nanoscale dimensions and the microstructures showed porous morphology. Immobilized lipase showed improved temperature stability, compared to free enzyme, especially in lipase supports at pH 5.5 and 7.5 due to electrostatic and hydrophobic interactions. The interactions between chitosan and lipase influenced the microenvironment around the active site, resulting in an optimum pH of 8 for all supports. Immobilized lipase at pH 5.5 and 7.5 displayed the best reusability in the hydrolysis of p-nitrophenyl palmitate under reaction conditions of 37 °C and pH 8. During refrigeration storage, all immobilized lipases maintained total activity for 7 days, but lipase immobilized at pH 6.5 maintained more the activity after 28 days. Therefore, this study has developed promising immobilized lipase, standing out not only for industrial application concerning cost-effectiveness, but also for the innovation in investigating the influence of chitosan-lipase interactions during immobilization. [ABSTRACT FROM AUTHOR]

Betanin (Bn), a natural dye in the Betalains family, predominantly takes on a cationic form known as Bn+. However, it exists in a neutral state as Bn_C2, Bn_C15, and Bn_C17 by losing an H+ from one of its carboxylic acids. Density functional theory (DFT) and Time‐dependent density functional theory (TD‐DFT) studies evaluate the efficiency of each betanin form and pinpoint the most probable anchoring point to TiO2. The Bn_C17 variant stands out as a highly promising candidate for DSSC cells, demonstrating a distinctive combination of electron injection efficiency, electrochemical performance, hole transport capabilities, and photovoltaic behavior. Considering factors like adsorption energy, binding mode, structural compatibility, electronic properties, and absorption characteristics, Bn_C17@TiO2 emerges as the most favorable dye@TiO2 complex among the studied betanin forms for DSSC applications. Contrastingly, the C2‐COOH anchoring point presents challenges with monodentate binding, a different orientation, and potential load distribution issues. This behavior, resembling that of a p‐type dye, differs from the n‐type behavior exhibited by the C15‐COOH and C17‐COOH forms, making the latter two more suitable as sensitizers. Consequently, C2‐COOH may not be the optimal anchoring point for TiO2 in the investigated betanin forms, especially when compared to the more favorable C17‐COOH anchoring point. [ABSTRACT FROM AUTHOR]

Volatile organic compounds (VOCs) are secondary metabolites emitted by all living carbon-based organisms. These VOCs are of great importance in the agricultural sector due to their use as biofungicides and biopesticides. In addition, they can also be used as indicators of microbial contamination. The latter has rarely been studied; however, such a role is very relevant because it allows the timely application of corrective treatments that avoid food waste, the development of toxins dangerous to humans, and the design of biosensors. Gas chromatography–mass spectrometry (GC-MS), electronic nose (e-nose), and proton transfer reaction mass spectrometry (PTR-MS) are some of the techniques used to detect VOCs in fruits and vegetables contaminated by microorganisms. Therefore, the objective of this work is to deepen our knowledge of VOCs emitted by microorganisms in terms of their use as an indicator of microbial contamination of fresh agricultural products, as well as the analytical techniques used for their detection. [ABSTRACT FROM AUTHOR]