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Protonation of oxide cathodes triggers surface transition metal dissolution and accelerates the performance degradation of Li-ion batteries. While strategies are developed to improve cathode material surface stability, little is known about the effects of protonation on bulk phase transitions in these cathode materials or their sodium-ion battery counterparts. Here, using NaNiO2 in electrolytes with different proton-generating levels as model systems, a holistic picture of the effect of incorporated protons is presented. Protonation of lattice oxygens stimulate transition metal migration to the alkaline layer and accelerates layered-rock-salt phase transition, which leads to bulk structure disintegration and anisotropic surface reconstruction layers formation. A cathode that undergoes severe protonation reactions attains a porous architecture corresponding to its multifold performance fade. This work reveals that interactions between electrolyte and cathode that result in protonation can dominate the structural reversibility/stability of bulk cathodes, and the insight sheds light for the development of future batteries.

Fluorescing proteins emitting in the near-infrared region are of high importance in various fields of biomedicine and applied life sciences. Promising candidates are phytochromes that can be engineered to a small size and genetically attached to a target system for in vivo monitoring. Here, we have investigated two of these minimal single-domain phytochromes, miRFP670nano3 and miRFP718nano, aiming at a better understanding of the structural parameters that control the fluorescence properties of the covalently bound biliverdin (BV) chromophore. On the basis of resonance Raman and time-resolved fluorescence spectroscopy, it is shown that in both proteins, BV is deprotonated at one of the inner pyrrole rings (B or C). This protonation pattern, which is unusual for tetrapyrroles in proteins, implies an equilibrium between a B- and C-protonated tautomer. The dynamics of the equilibrium are slow compared to the fluorescence lifetime in miRFP670nano3 but much faster in miRFP718nano, both in the ground and excited states. The different rates of proton exchange are most likely due to the different structural dynamics of the more rigid and more flexible chromophore in miRFP670nano3 and miRFP718nano, respectively. We suggest that these structural properties account for the quite different fluorescent quantum yields of both proteins. [ABSTRACT FROM AUTHOR]

Treating the amide acetanilide (N‐phenylacetamide, C8H9NO) with aqueous strong acids allowed the structures of five hemi‐protonated salt forms of acetanilide to be elucidated. N‐(1‐Hydroxyethylidene)anilinium chloride–N‐phenylacetamide (1/1), [(C8H9NO)2H][Cl], and the bromide, [(C8H9NO)2H][Br], triiodide, [(C8H9NO)2H][I3], tetrafluoroborate, [(C8H9NO)2H][BF4], and diiodobromide hemi(diiodine), [(C8H9NO)2H][I2Br]·0.5I2, analogues all feature centrosymmetric dimeric units linked by O—H...O hydrogen bonds that extend into one‐dimensional hydrogen‐bonded chains through N—H...X interactions, where X is the halide atom of the anion. Protonation occurs at the amide O atom and results in systematic lengthening of the C=O bond and a corresponding shortening of the C—N bond. The size of these geometric changes is similar to those found for hemi‐protonated paracetamol structures, but less than those in fully protonated paracetamol structures. The bond angles of the amide fragments are also found to change on protonation, but these angular changes are also influenced by conformation, namely, whether the amide group is coplanar with the phenyl ring or twisted out of plane. [ABSTRACT FROM AUTHOR]

Methoxypolyethylene glycol 1900 and α-bromoisobutanoyl bromide were utilized for alcoholysis reaction to obtain a macromolecular initiator. Then, a simple amphiphilic diblockpolymer (mPEG-PDMAEMA) based on the initiator and dimethylaminoethyl methacrylate was synthesized through the atomic transfer radical polymerization (ATRP) method. The structures of the initiator and diblock polymer were accurately characterized using infrared spectrum and proton nuclear magnetic resonance spectroscopy (1H NMR). Cryo-transmission electron microscopy revealed the self-assembly of mPEG-PDMAEMA into vesicle-like structures in water. Upon injection of CO2 into the solution, the tertiary amine structure within PDMAEMA underwent protonation, resulting in the mPEG-PDMAEMA adopting a hydrophilic structure. Consequently, the vesicles dissociated and dispersed, forming a network-like structure in water. The protonation phenomenon was confirmed by 1H NMR, as evidenced by the shifting of alkyl hydrogen atoms near nitrogen atoms toward downfield positions. [ABSTRACT FROM AUTHOR]

Methoxypolyethylene glycol 1900 and α-bromoisobutanoyl bromide were utilized for alcoholysis reaction to obtain a macromolecular initiator. Then, a simple amphiphilic diblockpolymer (mPEG-PDMAEMA) based on the initiator and dimethylaminoethyl methacrylate was synthesized through the atomic transfer radical polymerization (ATRP) method. The structures of the initiator and diblock polymer were accurately characterized using infrared spectrum and proton nuclear magnetic resonance spectroscopy (1H NMR). Cryo-transmission electron microscopy revealed the self-assembly of mPEG-PDMAEMA into vesicle-like structures in water. Upon injection of CO2 into the solution, the tertiary amine structure within PDMAEMA underwent protonation, resulting in the mPEG-PDMAEMA adopting a hydrophilic structure. Consequently, the vesicles dissociated and dispersed, forming a network-like structure in water. The protonation phenomenon was confirmed by 1H NMR, as evidenced by the shifting of alkyl hydrogen atoms near nitrogen atoms toward downfield positions.

Z-scheme CdS-COF-Ni-AC heterojunction was successfully synthesized by in-situ growth of CdS nanosheets on the obtained COF-Ni component and then protonation in ascorbic acid aqueous solution. Under the synergistic effect of the interfacial interaction and surface protonation treatment, the photocatalytic performance of CdS-COF-Ni-AC towards H 2 evolution has been significantly enhanced. [Display omitted] • A Z-scheme CdS-COF-Ni-AC heterojunction is successfully constructed. • Protonation treatment is used to improve the reaction kinetics for H 2 production. • A built-in electric field is formed to accelerate charge separation and transfer. • Interfacial interaction and protonation show synergistic effect on H 2 production. The low efficiency of photocatalytic hydrogen production from water is mainly suffer from limited light absorption, charge separation and water delivery to the active centers. Herein, an inorganic–organic Z-scheme heterojunction (CdS-COF-Ni) is constructed by in-situ growth of CdS nanosheets on the porphyrin-based covalent organic framework with nickel ions (COF-Ni) in the porphyrin centers. A built-in electric field is formed at the interface, which accelerates the separation and transfer of photogenerated charges. Moreover, through the surface protonation treatment in ascorbic acid (AC) solution, the hydrophilicity of the obtained composite is obviously increased and facilitates the transport of water molecules to the photocatalytic centers. Under the synergistic effect of the interfacial interaction and surface protonation treatment, the photocatalytic hydrogen production rate is optimized to be 18.23 mmol h−1 g−1 without adding any cocatalysts, which is 21 times that of CdS. After a series of photoelectrochemical measurements, in situ X-ray photoelectron spectroscopy (XPS) analysis, and density functional theory (DFT) calculations, it is found that the photocatalytic charge transfer pathway conforms to the Z-scheme mechanism, which not only greatly accelerates the separation and transfer of photogenerated charges, but also retains a high reduction capacity for water splitting. This work offers a good strategy for constructing highly efficient organic–inorganic heterojunctions for water splitting. [ABSTRACT FROM AUTHOR]

Electron-rich heteroaromatics, such as furan, thiophene and pyrrole, as well as their benzo-condensed derivatives, are of great interest as components of natural products and as starting substances for various products including high-tech materials. Although their reactions with Brønsted and Lewis acids play important roles, in particular as the primary step of various transformations, they are often disregarded and mechanistically not understood. The present publication gives a first overview about this chemistry focusing on the parent compounds. It comprises reactions with strong Brønsted acids forming adducts that can undergo intramolecular proton and/or substituent transfer reactions, ring openings or ring transformations into other heterocycles, depending on their structure. Interactions with weak Brønsted acids usually initiate oligomerizations/polymerizations. A similar behaviour is observed in reactions of these heteroaromatics with Lewis acids. Special effects are achieved when the Lewis acids are activated through primary protonation. Deuterated Brønsted acids allow straight forward deuteration of electron-rich heteroaromatics. Mercury salts as extremely weak Lewis acids cause direct metalation in a straight forward way replacing ring H-atoms yielding organomercury heterocycles. This review will provide comprehensive information about the chemistry of adducts of such heterocycles with Brønsted and Lewis acids enabling chemists to understand the mechanisms and the potential of this field and to apply the findings in future syntheses. [ABSTRACT FROM AUTHOR]

The salts bis(2‐amino‐3‐methylpyridinium) fumarate dihydrate, 2C6H9N2+·C4H2O22−·2H2O (I), and 2‐amino‐3‐methylpyridinium 5‐chlorosalicylate, C6H9N2+·C7H4ClO3− (II), were synthesized from 2‐amino‐3‐methylpyridine with fumaric acid and 5‐chlorosalicylic acid, respectively. The crystal structures of these salts were characterized by single‐crystal X‐ray diffraction, revealing protonation in I and II by the transfer of a H atom from the acid to the pyridine base. In the crystals of both I and II, N—H...O interactions form an R22(8) ring motif. Hirshfeld surface analysis distinguishes the interactions present in the crystal structures of I and II, and the two‐dimensional (2D) fingerprint plot analysis shows the percentage contribution of each type of interaction in the crystal packing. The volumes of the crystal voids of I (39.65 Å3) and II (118.10 Å3) have been calculated and reveal that the crystal of I is more mechanically stable than II. Frontier molecular orbital (FMO) analysis predicts that the band gap energy of II (2.6577 eV) is lower compared to I (4.0035 eV). The Quantum Theory of Atoms In Molecules (QTAIM) analysis shows that the pyridinium–carboxylate N—H...O interaction present in I is stronger than the other interactions, whereas in II, the hydroxy–carboxylate O—H...O interaction is stronger than the pyridinium–carboxylate N—H...O interaction; the bond dissociation energies also confirm these results. The positive Laplacian [∇2ρ(r) > 0] of these interactions shows that the interactions are of the closed shell type. An in‐silico ADME (Absorption, Distribution, Metabolism and Excretion) study predicts that both salts will exhibit good pharmacokinetic properties and druglikeness. [ABSTRACT FROM AUTHOR]

Li7La3Zr2O12 garnets are among the most promising materials for solid‐state electrolytes thanks to their high electrochemical stability and ionic conductivity. However, they are unstable in air and easily undergo a Li+/H+ exchange reaction, forming a lithiophobic and poorly Li‐conducting surface layer composed of LiOH and Li2CO3 upon further reaction with CO2. Despite a simple reaction mechanism, protonation of LLZO is a complex phenomenon. The thickness and composition of the secondary phases on the surface depend on many parameters both in the LLZO properties and in the storage atmosphere. Due to this complexity, proposing a universal procedure for removing the secondary phases is not simple. However, understanding the role of different parameters and rational selection of characterization techniques makes it possible to find the optimal conditions for removing the LiOH/Li2CO3 layer and further processing each material. This work compares some of the main approaches for cleaning the LLZO surface and describes their advantages and shortcomings. Additionally, the strengths and limitations of the most common characterization techniques for analyzing the (de)protonation of LLZO (XRD, XPS, Raman, NMR, TGA) are explained to help researchers design their experiments more accurately. [ABSTRACT FROM AUTHOR]

This study investigates the impact of thermal decomposition on the ion mobility spectrum of L-alanine using ion mobility spectrometry (IMS) and computational methods. By employing a post-injection delay system, we examined the evolution of ion peaks corresponding to thermal decomposition products and their interaction with protonated alanine. Experimental results revealed that the observed ion mobility spectra predominantly feature protonated isomers and adduct ions. Computational analysis using Density Functional Theory (DFT) predicted the thermodynamically favored structures and stabilities of these products. Findings indicate that protonation at the nitrogen site in alanine is more stable than at the oxygen site, and observed peaks correspond to protonated isomers and adducts formed with ammonium ions. Further investigations showed that thermal decomposition of alanine generates ammonia, contributing to the formation of new adduct ions. This research provides new insights into the behavior of amino acids under thermal conditions with implications for analytical chemistry and biochemistry.

A novel approach to enhance the utilization of low-cost and sustainable chitosan for wastewater remediation is presented in this investigation. The study centers around the modification of chitosan beads using a deep eutectic solvent composed of choline chloride and urea at a molar ratio of 1:2, followed by treatment with sulfuric acid using an impregnation accessible methodology. The effectiveness of the modified chitosan beads as an adsorbent was evaluated by studying the removal of the azo dye Reactive Black 5 (RB5) from aqueous solutions. Remarkably, the modified chitosan beads demonstrated a substantial increase in adsorption efficiency, achieving excellent removal of RB5 within the concentration range of 25–250 mg/L, ultimately leading to complete elimination. Several key parameters influencing the adsorption process were investigated, including initial RB5 concentration, adsorbent dosage, contact time, temperature, and pH. Quantitative analysis revealed that the pseudo-second-order kinetic model provided the best fit for the experimental data at lower dye concentrations, while the intraparticle diffusion model showed superior performance at higher RB5 concentration ranges (150–250 mg/L). The experimental data were successfully explained by the Langmuir isotherm model, and the maximum adsorption capacities were found to be 116.78 mg/g at 298 K and 379.90 mg/g at 318 K. Desorption studies demonstrated that approximately 41.7% of the dye could be successfully desorbed in a single cycle. Moreover, the regenerated adsorbent exhibited highly efficient RB5 removal (80.0–87.6%) for at least five consecutive uses. The outstanding adsorption properties of the modified chitosan beads can be attributed to the increased porosity, surface area, and swelling behavior resulting from the acidic treatment in combination with the DES modification. These findings establish the modified chitosan beads as a stable, versatile, and reusable eco-friendly adsorbent with high potential for industrial implementation. [ABSTRACT FROM AUTHOR]

An enantioselective addition reaction for the construction of 1,3‐nonadjacent stereogenic centers is developed by means of a chiral strong Brønsted base catalyst. The chiral sodium ureate catalyst efficiently promoted the reaction of α‐thioacetamides as less acidic pronucleophiles with vinyl sulfones having a variety of α‐substituents including aryl, alkyl and halo groups, and α‐phenylacrylates, accomplishing the construction of various 1,3‐nonadjacent stereogenic centers in highly diastereo‐ and enantioselective manners. This is a rare example of the construction of 1,3‐nonadjacent stereogenic centers with less acidic pronucleophiles. In addition, the application of Michael acceptors having various types of α‐substituents in a single catalyst system is achieved for the first time, demonstrating the utility of the present catalyst system for the construction of 1,3‐nonadjacent stereogenic centers. [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.

Proton-coupled oligopeptide transporters (POTs) are of great pharmaceutical interest owing to their promiscuous substrate binding site that has been linked to improved oral bioavailability of several classes of drugs. Members of the POT family are conserved across all phylogenetic kingdoms and function by coupling peptide uptake to the proton electrochemical gradient. Cryo-EM structures and alphafold models have recently provided new insights into different conformational states of two mammalian POTs, SLC15A1, and SLC15A2. Nevertheless, these studies leave open important questions regarding the mechanism of proton and substrate coupling, while simultaneously providing a unique opportunity to investigate these processes using molecular dynamics (MD) simulations. Here, we employ extensive unbiased and enhanced-sampling MD to map out the full SLC15A2 conformational cycle and its thermodynamic driving forces. By computing conformational free energy landscapes in different protonation states and in the absence or presence of peptide substrate, we identify a likely sequence of intermediate protonation steps that drive inward-directed alternating access. These simulations identify key differences in the extracellular gate between mammalian and bacterial POTs, which we validate experimentally in cell-based transport assays. Our results from constant-PH MD and absolute binding free energy (ABFE) calculations also establish a mechanistic link between proton binding and peptide recognition, revealing key details underpining secondary active transport in POTs. This study provides a vital step forward in understanding proton-coupled peptide and drug transport in mammals and pave the way to integrate knowledge of solute carrier structural biology with enhanced drug design to target tissue and organ bioavailability.

Abstract Li7La3Zr2O12 garnets are among the most promising materials for solid‐state electrolytes thanks to their high electrochemical stability and ionic conductivity. However, they are unstable in air and easily undergo a Li+/H+ exchange reaction, forming a lithiophobic and poorly Li‐conducting surface layer composed of LiOH and Li2CO3 upon further reaction with CO2. Despite a simple reaction mechanism, protonation of LLZO is a complex phenomenon. The thickness and composition of the secondary phases on the surface depend on many parameters both in the LLZO properties and in the storage atmosphere. Due to this complexity, proposing a universal procedure for removing the secondary phases is not simple. However, understanding the role of different parameters and rational selection of characterization techniques makes it possible to find the optimal conditions for removing the LiOH/Li2CO3 layer and further processing each material. This work compares some of the main approaches for cleaning the LLZO surface and describes their advantages and shortcomings. Additionally, the strengths and limitations of the most common characterization techniques for analyzing the (de)protonation of LLZO (XRD, XPS, Raman, NMR, TGA) are explained to help researchers design their experiments more accurately.

Fluorescing proteins emitting in the near-infrared region are of high importance in various fields of biomedicine and applied life sciences. Promising candidates are phytochromes that can be engineered to a small size and genetically attached to a target system for in vivo monitoring. Here, we have investigated two of these minimal single-domain phytochromes, miRFP670nano3 and miRFP718nano, aiming at a better understanding of the structural parameters that control the fluorescence properties of the covalently bound biliverdin (BV) chromophore. On the basis of resonance Raman and time-resolved fluorescence spectroscopy, it is shown that in both proteins, BV is deprotonated at one of the inner pyrrole rings (B or C). This protonation pattern, which is unusual for tetrapyrroles in proteins, implies an equilibrium between a B- and C-protonated tautomer. The dynamics of the equilibrium are slow compared to the fluorescence lifetime in miRFP670nano3 but much faster in miRFP718nano, both in the ground and excited states. The different rates of proton exchange are most likely due to the different structural dynamics of the more rigid and more flexible chromophore in miRFP670nano3 and miRFP718nano, respectively. We suggest that these structural properties account for the quite different fluorescent quantum yields of both proteins.

In chordates, energy buffering is achieved in part through phosphocreatine, which requires cellular uptake of creatine by the membrane‐embedded creatine transporter (CRT1/SLC6A8). Mutations in human slc6a8 lead to creatine transporter deficiency syndrome, for which there is only limited treatment. Here, we used a combined homology modeling, molecular dynamics, and experimental approach to generate a structural model of CRT1. Our observations support the following conclusions: contrary to previous proposals, C144, a key residue in the substrate binding site, is not present in a charged state. Similarly, the side chain D458 must be present in a protonated form to maintain the structural integrity of CRT1. Finally, we identified that the interaction chain Y148‐creatine‐Na+ is essential to the process of occlusion, which occurs via a "hold‐and‐pull" mechanism. The model should be useful to study the impact of disease‐associated point mutations on the folding of CRT1 and identify approaches which correct folding‐deficient mutants. [ABSTRACT FROM AUTHOR]

The origin of individual features in the ground state absorption spectra of two protonated corroles differing in the architecture of peripheral substitution (either Cm-aryl or Cb-alkyl) have been studied in detail with the ground state absorption spectroscopy and density functional theory calculations. The geometry optimization, molecular orbitals and absorption spectra calculation have been carried out. It was found that protonation leads to the saddle type macrocycle conformation in contrast with the wave type conformation known for the parent-free base corroles. The mean plane deviation parameter Δ23 for the macrocycle, pyrrole tilting angles and the degree of pyramidalization λ2 of all four pyrrole nitrogens was found to depend on the peripheral substitution architecture. Macrocycle conformation of the protonated forms has distinct asymmetrical features which are reflected by the sets of values of the tilting angles and values of pyramidalization degree. The pair of pyrroles B and C has smaller tilting angles and higher pyramidalization degree values, whereas the opposite trend was found for the pair of pyrroles A and D. Electronic effects and structural differences induced by substitution lead to the pronounced shifts of the molecular orbitals. In the Cb-alkylated corrole, almost-degenerated HOMO and HOMO-1 molecular orbitals lead to enhancement of the configuration interaction. As a result, the Qx transition oscillator strength goes down, becoming comparable to that of the Qy one. A large HOMO-HUMO-1gap in the Cm-aryl corrole minimizes the configuration interaction, giving rise to Qx band domination in the visible range spectrum. [ABSTRACT FROM AUTHOR]

Abstract An enantioselective addition reaction for the construction of 1,3‐nonadjacent stereogenic centers is developed by means of a chiral strong Brønsted base catalyst. The chiral sodium ureate catalyst efficiently promoted the reaction of α‐thioacetamides as less acidic pronucleophiles with vinyl sulfones having a variety of α‐substituents including aryl, alkyl and halo groups, and α‐phenylacrylates, accomplishing the construction of various 1,3‐nonadjacent stereogenic centers in highly diastereo‐ and enantioselective manners. This is a rare example of the construction of 1,3‐nonadjacent stereogenic centers with less acidic pronucleophiles. In addition, the application of Michael acceptors having various types of α‐substituents in a single catalyst system is achieved for the first time, demonstrating the utility of the present catalyst system for the construction of 1,3‐nonadjacent stereogenic centers.

The origin of individual features in the ground state absorption spectra of two protonated corroles differing in the architecture of peripheral substitution (either Cm-aryl or Cb-alkyl) have been studied in detail with the ground state absorption spectroscopy and density functional theory calculations. The geometry optimization, molecular orbitals and absorption spectra calculation have been carried out. It was found that protonation leads to the saddle type macrocycle conformation in contrast with the wave type conformation known for the parent-free base corroles. The mean plane deviation parameter Δ23 for the macrocycle, pyrrole tilting angles and the degree of pyramidalization λ2 of all four pyrrole nitrogens was found to depend on the peripheral substitution architecture. Macrocycle conformation of the protonated forms has distinct asymmetrical features which are reflected by the sets of values of the tilting angles and values of pyramidalization degree. The pair of pyrroles B and C has smaller tilting angles and higher pyramidalization degree values, whereas the opposite trend was found for the pair of pyrroles A and D. Electronic effects and structural differences induced by substitution lead to the pronounced shifts of the molecular orbitals. In the Cb-alkylated corrole, almost-degenerated HOMO and HOMO-1 molecular orbitals lead to enhancement of the configuration interaction. As a result, the Qx transition oscillator strength goes down, becoming comparable to that of the Qy one. A large HOMO-HUMO-1gap in the Cm-aryl corrole minimizes the configuration interaction, giving rise to Qx band domination in the visible range spectrum.

Electron-rich heteroaromatics, such as furan, thiophene and pyrrole, as well as their benzo-condensed derivatives, are of great interest as components of natural products and as starting substances for various products including high-tech materials. Although their reactions with Brønsted and Lewis acids play important roles, in particular as the primary step of various transformations, they are often disregarded and mechanistically not understood. The present publication gives a first overview about this chemistry focusing on the parent compounds. It comprises reactions with strong Brønsted acids forming adducts that can undergo intramolecular proton and/or substituent transfer reactions, ring openings or ring transformations into other heterocycles, depending on their structure. Interactions with weak Brønsted acids usually initiate oligomerizations/polymerizations. A similar behaviour is observed in reactions of these heteroaromatics with Lewis acids. Special effects are achieved when the Lewis acids are activated through primary protonation. Deuterated Brønsted acids allow straight forward deuteration of electron-rich heteroaromatics. Mercury salts as extremely weak Lewis acids cause direct metalation in a straight forward way replacing ring H-atoms yielding organomercury heterocycles. This review will provide comprehensive information about the chemistry of adducts of such heterocycles with Brønsted and Lewis acids enabling chemists to understand the mechanisms and the potential of this field and to apply the findings in future syntheses.

PsbS is one of the key photoprotective proteins, ensuring the tolerance of the photosynthetic apparatus (PSA) of a plant to abrupt changes in irradiance. Being a component of photosystem II, it provides the formation of quenching centers for excited states of chlorophyll in the photosynthetic antenna with an excess of light energy. The signal for "turning on" the photoprotective function of the protein is an excessive decrease in pH in the thylakoid lumen occurring when all the absorbed light energy (stored in the form of transmembrane proton potential) cannot be used for carbon assimilation. Hence, lumen-exposed protonatable amino acid residues that could serve as pH sensors are the essential components of PsbS-dependent photoprotection, and their pKa values are necessary to describe it. Previously, calculations of the lumen-exposed protonatable residue pKa values in PsbS from spinach were described in the literature. However, it has recently become clear that PsbS, although typical of higher plants and charophytes, can also provide photoprotection in green algae. Namely, the stress-induced expression of PsbS was recently shown for two green microalgae species: Chlamydomonas reinhardtii and Lobosphaera incisa. Therefore, we determined the amino acid sequence and modeled the three-dimensional structure of the PsbS from L. incisa, as well as calculated the pKa values of its lumen-exposed protonatable residues. Despite significant differences in amino acid sequence, proteins from L. incisa and Spinacia oleracea have similar three-dimensional structures. Along with the other differences, one of the two pH-sensing glutamates in PsbS from S. oleracea (namely, Glu-173) has no analogue in L. incisa protein. Moreover, there are only four glutamate residues in the lumenal region of the L. incisa protein, while there are eight glutamates in S. oleracea. However, our calculations show that, despite the relative deficiency in protonatable residues, at least two residues of L. incisa PsbS can be considered probable pH sensors: Glu-87 and Lys-196. [ABSTRACT FROM AUTHOR]

The electrochemical and electrophysical properties of basic and protonated potassium titanates in contact with the graphite electrodes were studied using the method of impedance spectroscopy. The characteristics of potassium titanates are given depending on the methods of modification and on the methods of their processing. The activation energies for some compositions were determined.

The removal of the azo dyes Orange II (OII) and Reactive Black 5 (RB5) from aqueous solutions was studied using three types of adsorbents derived from chitosan: unmodified chitosan beads (un-Ch), chitosan beads tuned with a deep eutectic solvent (DES) composed of choline chloride:urea at a 1:2 molar ratio (Ch-DES), along with FeO nanoparticles added to chitosan and modified with DES (Ch-FeO-DES). Both dyes were effectively removed in 3–4 h when Ch-DES beads were used, at a dye concentration range of 25–50 mg/L. The modification with DES improved the removal efficiency to achieve increases of around 32% for OII and 17% for RB5. The adsorbent dosage and the initial dye concentration influenced the adsorption process. Isotherm adsorption models (Langmuir, Freundlich, and Temkin) and kinetic models (pseudo-first-order, pseudo-second-order, intraparticle diffusion, and Elovich models) were applied to identify the adsorption behavior. The process could be characterized by employing the pseudo-second-order kinetic model and fitting it to the monolayer Langmuir isotherm. The adsorption occurred on a monolayer with no interaction among dye molecules when electrostatic forces would determine the attaching of dye molecules on the adsorbent. OII was efficiently desorbed by an alkaline solution, while RB5 was more strongly attached. The adsorbent could be recycled, after regeneration with an acid solution, for at least 5 reuse cycles while still achieving effective OII removal. Reactivation with a diluted EDTA solution allowed the authors to recycle RB5-attached beads, achieving optimum removal in two further uses. [ABSTRACT FROM AUTHOR]

Room-temperature phosphorescence (RTP) of purely organic materials is easily quenched with unexpected purposes because the excited triplet state is extremely susceptible to external stimuli. How to stabilize the RTP property of purely organic luminogens is still challenging and considered as the bottleneck in the further advancement of the bottom-up approach. Here, we describe a gated strategy that can effectively harness RTP by employing complexation/dissociation with proton. Due to the order-disorder transition orientation of intermolecular packing, the RTP of organic molecules 2,4,6-tris(4'-bromo-[1,1'-biphenyl]-4-yl)-1,3,5-triazine (Br-TRZ) will easily vanish upon mechanical force. Impressively, by enhancing its intramolecular charge transfer effect, the protonated Br-TRZ stubbornly possesses an obvious RTP under external grinding, whatever in the ordered or disordered intermolecular arrangement state. Consequently, the "Lock" gate of RTP was achieved in the protonated Br-TRZ molecule. Combined with theoretical calculation analysis, the enhanced charge transfer effect can narrow the singlet-triplet energy gap significantly, and stabilize the RTP property of triazine derivative sequentially. Furthermore, the locked RTP can be tuned via proton and counterions repeatedly and show excellent reversibility. This gated RTP concept provides an effective strategy for stabilizing the RTP emission of purely organic systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • The polyaniline functionalized glass fiber separator (PANI-GF) was synthesized in situ. • PANI-GF as synergistic medium can stabilize the anode and cathode jointly. • PANI hindered dendrites and side reactions on anode by desolvation and the ion-confinement effect. • PANI adjusted pH to inhibit dissolution of the cathode by protonation. • The full cell using PANI-GF exhibited excellent cycling performance. Aqueous zinc-ion batteries (AZIBs) have received increasing attention as a promising energy storage device. However, it was rarely reported that the separators as a synergistic medium stabilize the cathode and anode materials. Herein, a polyaniline functionalized glass fiber separator (PANI-GF) was synthesized in situ. The porous structure of PANI effectively regulated the flux of zinc ions inside the separator and its deposition behavior through ion confinement. The abundant N -containing functional groups can adsorb water molecules and effectively reduce harmful side reactions. Moreover, the PANI-GF separator adjusted pH to inhibit dissolution of the cathode by protonation. Importantly, based on the synergistic separator, the Zn-MnO 2 full cell exhibited more than twice discharge capacity compared to the conventional cell after 1000 cycles at 2 A g−1. This study provided in-depth insight into the design of convenient, reliable, cost-effective, and synergistic separators for AZIBs. [ABSTRACT FROM AUTHOR]

Human MutT homolog 1 (MTH1), also known as Nudix‐type motif 1 (NUDT1), hydrolyzes 8‐oxo‐dGTP and 2‐oxo‐dATP with broad substrate recognition and has attracted attention in anticancer therapeutics. Previous studies on MTH1 have proposed that the exchange of the protonation state between Asp119 and Asp120 is essential for the broad substrate recognition of MTH1. To understand the relationship between protonation states and substrate binding, we determined the crystal structures of MTH1 at pH 7.7–9.7. With increasing pH, MTH1 gradually loses its substrate‐binding ability, indicating that Asp119 is deprotonated at pH 8.0–9.1 in 8‐oxo‐dGTP recognition and Asp120 is deprotonated at pH 8.6–9.7 in 2‐oxo‐dATP recognition. These results confirm that MTH1 recognizes 8‐oxo‐dGTP and 2‐oxo‐dATP by exchanging the protonation state between Asp119 and Asp120 with higher pKa. [ABSTRACT FROM AUTHOR]

The International Society of Cancer Metabolism (ISCaM) meeting on Cancer Metabolic Rewiring, held in Braga Portugal in October 2019, provided an outstanding forum for investigators to present current findings and views, and discuss ideas and future directions on fundamental biology as well as clinical translations. The first session on Cancer pH Dynamics was preceded by the opening keynote presentation from our group entitled Intracellular pH Regulation of Protein Dynamics: From Cancer to Stem Cell Behaviors. In this review we introduce a brief background on intracellular pH (pHi) dynamics, including how it is regulated as well as functional consequences, summarize key findings included in our presentation, and conclude with perspectives on how understanding the role of pHi dynamics in stem cells can be relevant for understanding how pHi dynamics enables cancer progression.

Despite numerous studies investigating histamine and its receptors, the impact of histamine protonation states on binding to the histamine H 1 -receptor (H 1 R) has remained elusive. Therefore, we assessed the influence of different histamine tautomers (τ -tautomer, π -tautomer) and charge states (mono- vs. dicationic) on the interaction with the ternary histamine-H 1 R-Gq complex. In atomistic molecular dynamics simulations, the τ -tautomer formed stable interactions with the receptor, while the π -tautomer induced a rotation of the histamine ring by 180° and formed only weaker hydrogen bonding interactions. This suggests that the τ -tautomer is more relevant for stabilization of the active ternary histamine-H 1 R-Gq complex. In addition to the two monocationic tautomers, the binding of dicationic histamine was investigated, whose interaction with the H 1 R had been observed in a previous experimental study. Our simulations showed that the dication is less compatible with the ternary histamine-H 1 R-Gq complex and rather induces an inactive conformation in the absence of the Gq protein. Our data thus indicate that the charge state of histamine critically affects its interactions with the H 1 R. Ultimately these findings might have implications for the future development of new ligands that stabilize distinct H 1 R activation states. [ABSTRACT FROM AUTHOR]

Synthesis of layered perovskite-like niobates APb2Nb3O10 (A = Rb, Cs), being promising visible light active photocatalysts, has been conducted by the ceramic method under variable conditions to obtain the samples with the highest possible phase purity. The oxides prepared were shown practically not to undergo protonation and hydration of the interlayer space upon keeping in water. Both phases APb2Nb3O10 were used to yield corresponding protonated hydrated forms HxA1 − xPb2Nb3O10∙yH2O via acid treatment. It was found that the propensity of the samples to the substitution of interlayer cations by protons depends clearly on the A+ cation: while the Rb-containing niobate is capable of complete protonation (x = 1) upon a single treatment with 6 M nitric acid, the Cs-containing counterpart gives a high enough protonation degree (x ≥ 0.9) only after several renewals of the acid solution. The protonated niobates obtained were exposed to an additional water treatment under hydrothermal conditions, which allowed producing new hydrated derivatives with the enhanced thermal stability towards interlayer dehydration as compared with the protonated precursors. [ABSTRACT FROM AUTHOR]

Pyrazoloporphyrins (PzPs), which are porphyrin analogues incorporating a pyrazole subunit, are examples of carbaporphyrin-type structures with a carbon atom within the macrocyclic cavity. DFT calculations were used to assess a series of 17 PzP tautomers, nine monoprotonated species and four related diprotonated PzP dications. The geometries of the structures were optimized using M06-2X/6-311++G(d,p), and the relative stabilities computed with the cc-PVTZ functional. Nucleus independent chemical shifts, both NICS(0) and NICS(1)zz, were calculated, and the anisotropy of the induced current density (AICD) plots were generated for all of the species under investigation. The results for free base PzPs show that fully aromatic PzP tautomers are not significantly more stable than weakly aromatic cross-conjugated species. In addition, strongly aromatic structures with internal CH2′s are much less stable, a feature that is also seen for protonated PzPs. The degree of planarity for the individual macrocycles does not significantly correlate with the stability of these structures. The results allow significant aromatic conjugation pathways to be identified in many cases, and provide insights into the aromatic properties of this poorly studied system. These investigations also complement experimental results for PzPs and emphasize the need for further studies in this area. [ABSTRACT FROM AUTHOR]

Chitin is one of the most abundant biopolymers in nature. Herein, we report the successful preparation of chitin nanofibers (ChNFs) from shrimp shell waste using a partial deacetylation process with NaOH and high-speed blending. The effects of the deacetylation reaction with NaOH concentrations (0–40 wt%) on the degree of acetylation (DA), crystallinity, zeta potential, thermal stability, and morphology of the ChNFs were investigated. With the more aggressive deacetylation reaction (higher NaOH concentration), ChNFs had the lower DA, crystallinity degree, and thermal stability, and their widths and lengths became smaller and shorter. The presence of amino groups in the chitin molecule caused by deacetylation generated repulsive forces with aids of acetic acid, efficiently leading to the individualization of ChNFs using high-speed blending. The individualized ChNFs deacetylated with 30 wt% NaOH had an average width of 8.07 ± 1.80 nm and length of less than 500 nm, whereas bundles of aggregated fibers with widths in the range of 30–100 nm and lengths of up to several μm were extracted from chitin without deacetylation. Additionally, the deacetylation with 40 wt% NaOH completely converted chitin to chitosan. The ChNFs could be efficiently used for composites, biomaterials, and packaging applications.

Ionic-liquid-gating- (ILG-) induced proton evolution has emerged as a novel strategy to realize electron doping and manipulate the electronic and magnetic ground states in complex oxides. While the study of a wide range of systems (e.g., SrCoO2.5 , VO2 , WO3 , etc.) has demonstrated important opportunities to incorporate protons through ILG, protonation remains a big challenge for many others. Furthermore, the mechanism of proton intercalation from the ionic liquid/solid interface to whole film has not yet been revealed. Here, with a model system of inverse spinel NiCo2 O4 , an increase in system temperature during ILG forms a single but effective method to efficiently achieve protonation. Moreover, the ILG induces a novel phase transformation in NiCo2 O4 from ferrimagnetic metallic into antiferromagnetic insulating with protonation at elevated temperatures. This study shows that environmental temperature is an efficient tuning knob to manipulate ILG-induced ionic evolution.

Ionic-liquid-gating- (ILG-) induced proton evolution has emerged as a novel strategy to realize electron doping and manipulate the electronic and magnetic ground states in complex oxides. While the study of a wide range of systems (e.g., SrCoO2.5 , VO2 , WO3 , etc.) has demonstrated important opportunities to incorporate protons through ILG, protonation remains a big challenge for many others. Furthermore, the mechanism of proton intercalation from the ionic liquid/solid interface to whole film has not yet been revealed. Here, with a model system of inverse spinel NiCo2 O4 , an increase in system temperature during ILG forms a single but effective method to efficiently achieve protonation. Moreover, the ILG induces a novel phase transformation in NiCo2 O4 from ferrimagnetic metallic into antiferromagnetic insulating with protonation at elevated temperatures. This study shows that environmental temperature is an efficient tuning knob to manipulate ILG-induced ionic evolution.

Chitin is one of the most abundant biopolymers in nature. Herein, we report the successful preparation of chitin nanofibers (ChNFs) from shrimp shell waste using a partial deacetylation process with NaOH and high-speed blending. The effects of the deacetylation reaction with NaOH concentrations (0–40 wt%) on the degree of acetylation (DA), crystallinity, zeta potential, thermal stability, and morphology of the ChNFs were investigated. With the more aggressive deacetylation reaction (higher NaOH concentration), ChNFs had the lower DA, crystallinity degree, and thermal stability, and their widths and lengths became smaller and shorter. The presence of amino groups in the chitin molecule caused by deacetylation generated repulsive forces with aids of acetic acid, efficiently leading to the individualization of ChNFs using high-speed blending. The individualized ChNFs deacetylated with 30 wt% NaOH had an average width of 8.07 ± 1.80 nm and length of less than 500 nm, whereas bundles of aggregated fibers with widths in the range of 30–100 nm and lengths of up to several μm were extracted from chitin without deacetylation. Additionally, the deacetylation with 40 wt% NaOH completely converted chitin to chitosan. The ChNFs could be efficiently used for composites, biomaterials, and packaging applications. [ABSTRACT FROM AUTHOR]

One of the most important methods for modifying semiconductors is defect engineering, but only the right quantity of defects in the right chemical environment can produce desirable results. Heat treatment processes associated with g-C3N4 are occasionally carried out in N2 atmosphere, however, the catalytic performance of g-C3N4 produced by direct condensation of only nitrogen-rich precursors in N2 atmosphere is often unsatisfactory. This is typically attributed to the introduction of numerous defects, but the actual relationship between the formation of defects and the N2 atmosphere is rarely explained, and the resulting quantity of defects is difficult to control. We propose that the melam to melem transition is restricted due to the lack of O2 during the heat treatment of the nitrogen-rich precursor of g-C3N4 in N2 atmosphere, which leads to a substantial quantity of defects in the synthesized g-C3N4. To enhance its photocatalytic property, we propose a method to reduce the quantity of defects due to calcinating in N2 atmosphere by protonating the precursor in a way that increases the polymerization of the product. The test analysis indicated that only a moderate quantity of defects that contribute to electron excitation and enhance the separation efficiency and density of photogenerated carriers were retained, and the hydrogen evolution performance of the prepared catalyst was significantly improved. [ABSTRACT FROM AUTHOR]

A novel, efficient, two-step approach to the synthesis of merocyanine dyes was developed. Initially, N-substituted picolinium salts were formylated with N,N-dimethylformamide dimethyl acetal to produce enamine derivatives. Then a series of merocyanine dyes were obtained by the high-yield reaction between the enamines and various active methylene compounds. The described reactions, carried out in mild conditions, provide access to the synthesis of a wide range of dyes. This innovative method enabled the synthesis of a number of new merocyanine dyes and increased the yields of the known compounds. [ABSTRACT FROM AUTHOR]

The spectral luminescent properties of dipyrromethenates halogenated with bromine on both ends of the long axis and coordinated using boron fluoride, zinc, or cadmium in neutral ethanol and acidified with hydrochloric acid solutions were studied. The constants of the acid–base equilibrium of the complexes in the proton-donor solvents in the ground and excited states was determined. The mechanisms of complex protonation were discussed, depending on the structure of the compounds. The electronic structures of the neutral and protonated compounds were modeled and analyzed based on the quantum-chemical method. The structures and spectral-luminescence properties were calculated using the SMD model of ethanol solvent using the TD-DFT theory with the B3LYP functional and the composite def2-SVP/def2-TZVP/def2-TZVPP_ECP basis sets, depending on the atomic number of the elements. [ABSTRACT FROM AUTHOR]

• The protonation degree of polyaniline is greatly improved. • The -N-Zn-O- bond is formed during the cycles. • The growth of polyaniline nanocones is compact and uniform. • The cell shows excellent reaction kinetics and rate performance. • The cell shows high capacity retention after 10,000 cycles at 10 A g−1. As one of the most important cathode materials for aqueous zinc-ion batteries (AZIBs), polyaniline (PANI) has attracted much attention because of its high electrical conductivity, simple synthesis procedure and excellent redox reversibility. However, the morphology of PANI macromolecules and its spontaneous deprotonation properties lead to low capacity and poor cycle stability, which limits its further application. To address these issues, in this work, PANI is in-situ prepared on the surface of carbon cloth (CC) through chemical oxidation polymerization under the presence of carbonized polymer dots (CPDs). Compared with pure PANI cathode electrodes, the materials with appropriate amount of CPDs (CPDs/PANI@CC-10) show a high specific discharge capacity of 168 mAh g−1 at 0.1 A g−1. Even at a high current density of 10 A g−1, CPDs/PANI@CC-10 still exhibits a capacity of 102 mAh g−1, and maintains 94.3 % of the capacity after 10,000 cycles. The profound mechanism investigation reveals that during the charge/discharge cycles, the percentage of protonated N greatly increases due to the addition of CPDs, and new N Zn O bonds are formed, which is beneficial to more stable cycle and larger amount of Zn2+ storage. This work provides a new route for control the morphology and structure of PANI, which is of significant for its practical application in AZIBs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electro-Fe(II) can significantly promote PI to degrade SMX. • Fe(IV)-oxo and 1O 2 as the main reactive species are generated under the E(Fe/C)/PI system in pH=3 and 6.5, respectively. • Density functional theory (DFT) calculations are employed to reveal the differences of catalytic mechanisms in both pH conditions. • SMX degradation intermediates and toxicities are presented through experimental results and DFT calculations. The ferrous species (Fe(II))-periodate (PI) system employs efficient decontamination by generating ferryl species (Fe(IV)-oxo) under acidic pH conditions. However, the mechanisms by which the Fe(II)/PI system operates across a broad pH range remain elusive. In light of the rapid oxidation and consumption of Fe(II) at neutral pH, we developed an electro-Fe(II) system utilizing an iron plate anode to activate PI (E(Fe/C)/PI). Efficient sulfamethoxazole (SMX) degradation was achieved under the E(Fe/C)/PI system across a range of pH values. Quenching and chemical probe experiments revealed a transition from Fe(IV)-oxo to singlet oxygen (1O 2) as the predominant reactive species from acidic to near-neutral pH, respectively. Density functional theory (DFT) calculations indicated that the differences in one-electron transfer capacity and hydrolysis pathways for various protonated Fe(IV)-oxo species underlie the variations in catalytic mechanisms. This study not only enhances the efficiency of the Fe(II)/PI system but also provides a comprehensive understanding of the activation mechanisms at different pH levels. [ABSTRACT FROM AUTHOR]

PsbS is one of the key photoprotective proteins, ensuring the tolerance of the photosynthetic apparatus (PSA) of a plant to abrupt changes in irradiance. Being a component of photosystem II, it provides the formation of quenching centers for excited states of chlorophyll in the photosynthetic antenna with an excess of light energy. The signal for “turning on” the photoprotective function of the protein is an excessive decrease in pH in the thylakoid lumen occurring when all the absorbed light energy (stored in the form of transmembrane proton potential) cannot be used for carbon assimilation. Hence, lumen-exposed protonatable amino acid residues that could serve as pH sensors are the essential components of PsbS-dependent photoprotection, and their pKa values are necessary to describe it. Previously, calculations of the lumen-exposed protonatable residue pKa values in PsbS from spinach were described in the literature. However, it has recently become clear that PsbS, although typical of higher plants and charophytes, can also provide photoprotection in green algae. Namely, the stress-induced expression of PsbS was recently shown for two green microalgae species: Chlamydomonas reinhardtii and Lobosphaera incisa. Therefore, we determined the amino acid sequence and modeled the three-dimensional structure of the PsbS from L. incisa, as well as calculated the pKa values of its lumen-exposed protonatable residues. Despite significant differences in amino acid sequence, proteins from L. incisa and Spinacia oleracea have similar three-dimensional structures. Along with the other differences, one of the two pH-sensing glutamates in PsbS from S. oleracea (namely, Glu-173) has no analogue in L. incisa protein. Moreover, there are only four glutamate residues in the lumenal region of the L. incisa protein, while there are eight glutamates in S. oleracea. However, our calculations show that, despite the relative deficiency in protonatable residues, at least two residues of L. incisa PsbS can be considered probable pH sensors: Glu-87 and Lys-196.

Objectives. To determine the ion mobility of N-methylimidazole, establish the structure of ions corresponding to characteristic signals, and determine the detection limit of N-methylimidazole on the ion-drift detector Kerber.Methods. Ion mobility spectrometry was used to study the ionization processes. The enthalpies of the reactions of monomer and dimer ions were calculated in the ORCA 4.1.1 software by the B3LYP density functional method with a set of basic functions 6-31G (d, p).Results. The drift time and ion mobility values of N-methylimidazole were determined. A method for mathematical processing of spectra and a program for its implementation was developed. The changing peculiarities of the ion mobility spectrum during measurement at a given time were studied. According to the interpretation of the spectrum signals, the structure of the generated ions was proposed, and the enthalpies of ion formation were determined.Conclusions. The characteristic signal of the N-methylimidazole ion protonated at the nitrogen atom of the pyridine type was revealed. It was found that two signals in the ion mobility spectra of N-methylimidazole correspond to the presence of the monomer and dimer ions. The detection limit of N-methylimidazole on the ion-drift detector Kerber was determined, amounting to 3 pg.

Radioastronomy is a powerful tool for the discovery of molecules in space but it requires molecular species to be polar. The observation of apolar species can be however enabled by protonation, which occurs from reaction with the abundant H3+ ion whenever the proton affinity of the species under consideration is greater than that of H2. This property can be easily investigated by computational chemistry and, in this work, it has been used to asses the potential protonation of simple homo diatomics, such as Cl2, P2, and Si2, as well as apolar species containing two equivalent CN moieties, such as diisocyanogen (CNNC) and (E)-1,2-dicyanoethene. Quantum chemistry has also been exploited to investigate the mechanisms of three protonation reactions of H3+ with Cl2, P2, and CNNC. To support laboratory measurements and astronomical observations of the resulting transient species, their rotational spectroscopic parameters were accurately computed together with fundamental vibrational frequencies. For this purpose, we have employed CCSD(T)-based computational methodologies, which provide equilibrium structures with errors smaller than 0.001 Å and 0.1° for bond distances and angles, respectively. Such an accuracy is expected to lead to rotational constants predicted, in relative terms, with uncertainties better than 0.2%. Instead, the expected accuracy on vibrational frequencies is ∼10 cm−1, thus being well suited to guide band assignments.

Dynamic disorder of the lipid bilayer presents a challenge for establishing structure-function relationships in membranous systems. The resulting structural heterogeneity is especially evident for peripheral and spontaneously inserting membrane proteins, which are not constrained by the well-defined transmembrane topology and exert their action in the context of intimate interaction with lipids. Here, we propose a concerted approach combining depth-dependent fluorescence quenching with Molecular Dynamics simulation to decipher dynamic interactions of membrane proteins with the lipid bilayers. We apply this approach to characterize membrane-mediated action of the diphtheria toxin translocation domain. First, we use a combination of the steady-state and time-resolved fluorescence spectroscopy to characterize bilayer penetration of the NBD probe selectively attached to different sites of the protein into membranes containing lipid-attached nitroxyl quenching groups. The constructed quenching profiles are analyzed with the Distribution Analysis methodology allowing for accurate determination of transverse distribution of the probe. The results obtained for 12 NBD-labeled single-Cys mutants are consistent with the so-called Open-Channel topology model. The experimentally determined quenching profiles for labeling sites corresponding to L350, N373, and P378 were used as initial constraints for positioning TH8-9 hairpin into the lipid bilayer for Molecular Dynamics simulation. Finally, we used alchemical free energy calculations to characterize protonation of E362 in soluble translocation domain and membrane-inserted conformation of its TH8-9 fragment. Our results indicate that membrane partitioning of the neutral E362 is more favorable energetically (by ~ 6 kcal/mol), but causes stronger perturbation of the bilayer, than the charged E362.

In this work, protonated forms of potassium polytitanate were obtained by treating the precursor in HCl solution at pH 2.0, 3.0, 4.0, 5.0, 6.0, or 7.0. The synthesized materials were studied using XRD, FTIR, and XRF. The ion-exchange properties were studied using a LiCl solution with a concentration of C(Li+) = 0.01 mol/L. It was shown that extraction of lithium by potassium polytitanates is dependent on their protonation degree. It has been established that the samples with the highest degree of protonation obtained at pH = 2.0 and 3.0 have the highest efficiency in the ion-exchange extraction of Li+ ions from an aqueous solution. For determination of exchange ion rates and the mechanism of the ion-exchange process, pseudo-first- and pseudo-second-order models as well as the Weber–Morris intraparticle diffusion model, were employed. Experimental data with their participation are in good agreement with the pseudo-second-order kinetic model. The calculated kinetic parameters were qe = 0.47–0.52 mmol/g and k2 = 0.25–0.43, depending on the protonation degree of potassium polytitanate. The obtained experimental and calculated values of the sorption capacity were compared with the cation-exchange capacity of materials studied. According to the kinetics study, the mechanism of lithium adsorption by potassium polytitanates with a higher protonation degree is the ion-exchange chemical reaction. Low-cost protonated potassium polytitanates are promising to extract Li+ ions from aqueous solutions with a low concentration, as confirmed by the analysis of the results. [ABSTRACT FROM AUTHOR]

The introduction of an electron-donating triphenylamine motive into a 2,2′,6′,2′′-terpyridine (terpy) moiety, a cornerstone molecular unit in coordination chemistry, opens new ways for a rational design of photophysical properties of organic and inorganic compounds. A push-pull compound, 4′-(4-(di(4-tert-butylphenyl)amine)phenyl)-2,2′,6′,2′′-terpyridine (tBuTPAterpy), was thoroughly investigated with the use of steady-state and time-resolved spectroscopies and Density Functional Theory (DFT) calculations. Our results demonstrate that solvent parameters have an enormous influence on the optical properties of this molecule, acting as knobs for external control of its photophysics. The Intramolecular Charge Transfer (ICT) process introduces a remarkable solvent polarity effect on the emission spectra without affecting the lowest absorption band, as confirmed by DFT simulations, including solvation effects. The calculations ascribe the lowest absorption transitions to two singlet ICT excited states, S1 and S2, with S1 having several orders of magnitude higher oscillator strength than the "dark" S2 state. Temperature and viscosity investigations suggest the existence of two emitting excited states with different structural conformations. The phosphorescence emission band observed at 77 K is assigned to a localized 3terpy state. Finally, protonation studies show that tBuTPAterpy undergoes a reversible process, making it a promising probe of the pH level in the context of acidity determination. [ABSTRACT FROM AUTHOR]

The direct hydroxylation of benzene is a green and economical-efficient alternative to the existing cumene process for phenol production. However, the undesired phenol selectivity at high benzene conversion hinders its wide application. Here, we develop a one-pot synthesis of protonated g-C3N4 supporting vanadia catalysts (V-pg-C3N4) for the efficient and selective hydroxylation of benzene. Characterizations suggest that protonating g-C3N4 in diluted HCl can boost the generation of amino groups (NH/NH2) without changing the bulk structure. The content of surface amino groups, which determines the dispersion of vanadia, can be easily regulated by the amount of HCl added in the preparation. Increasing the content of surface amino groups benefits the dispersion of vanadia, which eventually leads to improved H2O2 activation and benzene hydroxylation. The optimal catalyst, V-pg-C3N4-0.46, achieves 60% benzene conversion and 99.7% phenol selectivity at 60 oC with H2O2 as the oxidant. [ABSTRACT FROM AUTHOR]

Carbon dots (CDs) have excellent optical properties, low toxicity and easy preparation, which have led to them being widely used in biomedicine, sensing and optical devices. However, although great progress has been made in the preparation of CDs, the detailed exploration of their photoluminescence (PL) mechanism is still under debate due to their complex structures and surface functionalities. Here, we proposed a single change in the pH of the synthesis condition, which had no effect on the CDs intrinsic core states and avoided the mutual influence of multiple PL origins. The m-phenylenediamine (m–PD) served as a carbon source, whose protonation degree determined the surface state of the resulting CDs and the accompanying fluorescence characteristics. The as-obtained CDs materials can be applied in the chemical sensor and anti-counterfeiting fields in a targeted manner. Therefore, our work not only contributes to the explanation of the CDs PL mechanism, but also obtains a series of CDs materials with controllable PL properties. [ABSTRACT FROM AUTHOR]

Today, the development of nanomaterials with sensing properties attracts much scientific interest because of the demand for low-cost nontoxic colloidal nanoprobes with high sensitivity and selectivity for various biomedical and environment-related applications. Carbon dots (CDs) are promising candidates for these applications as they demonstrate unique optical properties with intense emissions, biocompatibility, and ease of fabrication. Herein, we developed synthesis protocols to obtain CDs based on o-phenylenediamine with a variety of optical responses depending on additional precursors and changes in the reaction media. The obtained CDs are N-doped (N,S-doped in case of thiourea addition) less than 10 nm spherical particles with emissions observed in the 300–600 nm spectral region depending on their chemical composition. These CDs may act simultaneously as absorptive/fluorescent sensing probes for solvent polarity with ∆ S / ∆ E N T   up to 85, for ∆ E N T from 0.099 to 1.0 and for pH values in the range of 3.0–8.0, thus opening an opportunity to check the pH in non-pure water or a mixture of solvents. Moreover, CDs preserve their optical properties when embedded in cellulose strips that can be used as sensing probes for fast and easy pH checks. We believe that the resulting dual-purpose sensing nano probes based on CDs will have high demand in various sensing applications. [ABSTRACT FROM AUTHOR]