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.

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.

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.

Salmonella enterica serovar Typhimurium melibiose permease (MelBSt) is a prototype of the major facilitator superfamily (MFS) transporters, which play important roles in human health and diseases. MelBSt catalyzed the symport of galactosides with Na+, Li+, or H+ but prefers the coupling with Na+. Previously, we determined the structures of the inward- and outward-facing conformation of MelBSt and the molecular recognition for galactoside and Na+. However, the molecular mechanisms for H+- and Na+-coupled symport remain poorly understood. In this study, we solved two x-ray crystal structures of MelBSt, the cation-binding site mutants D59C at an unliganded apo-state and D55C at a ligand-bound state, and both structures display the outward-facing conformations virtually identical as published. We determined the energetic contributions of three major Na+-binding residues for the selection of Na+ and H+ by free energy simulations. Transport assays showed that the D55C mutant converted MelBSt to a solely H+-coupled symporter, and together with the free-energy perturbation calculation, Asp59 is affirmed to be the sole protonation site of MelBSt. Unexpectedly, the H+-coupled melibiose transport exhibited poor activities at greater bulky ΔpH and better activities at reversal ΔpH, supporting the novel theory of transmembrane-electrostatically localized protons and the associated membrane potential as the primary driving force for the H+-coupled symport mediated by MelBSt. This integrated study of crystal structure, bioenergetics, and free energy simulations, demonstrated the distinct roles of the major binding residues in the cation-binding pocket of MelBSt.

Vitamins are responsible for providing biological properties to the human body; however, their instability under certain environmental conditions limits their utilization in the food industry. The objective was to conduct a systematic review on the use of biopolymers and lipid bases in microencapsulation processes, assessing their impact on the stability, controlled release, and viability of fortified foods with microencapsulated vitamins. The literature search was conducted between the years 2013-2023, gathering information from databases such as Scopus, PubMed, Web of Science and publishers including Taylor & Francis, Elsevier, Springer and MDPI; a total of 49 articles were compiled The results were classified according to the microencapsulation method, considering the following information: core, coating material, solvent, formulation, process conditions, particle size, efficiency, yield, bioavailability, bioaccessibility, in vitro release, correlation coefficient and references. It has been evidenced that gums are the most frequently employed coatings in the protection of vitamins (14.04%), followed by alginate (10.53%), modified chitosan (9.65%), whey protein (8.77%), lipid bases (8.77%), chitosan (7.89%), modified starch (7.89%), starch (7.02%), gelatin (6.14%), maltodextrin (5.26%), zein (3.51%), pectin (2.63%) and other materials (7.89%). The factors influencing the release of vitamins include pH, modification of the coating material and crosslinking agents; additionally, it was determined that the most fitting mathematical model for release values is Weibull, followed by Zero Order, Higuchi and Korsmeyer-Peppas; finally, foods commonly fortified with microencapsulated vitamins were described, with yogurt, bakery products and gummy candies being notable examples.

Covalent organic frameworks (COFs) are promising photocatalysts for H2O2 production from water via oxygen reduction reactions (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 ([[EQUATION]]) 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.

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.

Heat shock factor 1 (HSF1) primarily regulates various cellular stress responses. Previous studies have shown that low pH within the physiological range directly activates HSF1 function in vitro. However, the detailed molecular mechanisms remain unclear. This study proposes a molecular mechanism based on the trimerization behavior of HSF1 at different pH values. Extensive mutagenesis of human and goldfish HSF1 revealed that the optimal pH for trimerization depended on the identity of residue 103. In particular, when residue 103 was occupied by tyrosine, a significant increase in the optimal pH was observed, regardless of the rest of the sequence. This behavior can be explained by the protonation state of the neighboring histidine residues, His101 and His110. Residue 103 plays a key role in trimerization by forming disulfide or non-covalent bonds with Cys36. If tyrosine resides at residue 103 in an acidic environment, its electrostatic interactions with positively charged histidine residues prevent effective trimerization. His101 and His110 are neutralized at a higher pH, which releases Tyr103 to interact with Cys36 and drives the effective trimerization of HSF1. This study showed that the protonation state of a histidine residue can regulate the intramolecular interactions, which consequently leads to a drastic change in the oligomerization behavior of the entire protein.

Salts of protonated sulfur dioxide were synthesized by recrystallization of [FS(OX)2][SbF6] (X=H, D) in aprotic solvents at low temperatures. Hemiprotonated sulfur dioxide [(SO2)2H][Sb2F11] was obtained from the solvent SO2 and the monoprotonated sulfur dioxide [OSOD][Sb2F11], using 1,1,1,2-tetrafluoroethane as solvent. For both compounds, single crystals were obtained and an X-ray structure analysis was conducted. Furthermore, the salts were characterized by Raman spectroscopy and the results were discussed together with quantum chemical calculations on the M06-2X/aug-cc-pVTZ level of theory.

We report a light-irradiation method to control the synchronous nucleation of a donor-acceptor (D-A) fluorophore for growing highly uniform single-crystalline microrods, which is in sharp contrast to the prevailing methods of restricting spontaneous nucleation and additionally adding seeds. The D-A fluorophore was observed to undergo photoinduced electron transfer to CrCl3, leading to the generation of HCl and the subsequent protonation of the D-A fluorophore. By intensifying photoirradiation or prolonging its duration, the concentration of protonated D-A fluorophores can be rapidly increased to a high supersaturation level. This results in the formation of a controlled number of nuclei in a synchronous manner, which in turn kickstart the epitaxial growth of protonated D-A fluorophores towards uniform single-crystalline microrods of controlled sizes. The light-regulated synchronous nucleation and uniform growth of microrods are a unique phenomenon that can only be achieved by specific Lewis acids, making it a novel probing method for sensitively detecting strong Lewis acids such as chromium chloride.