Journal Description
Chemistry
Chemistry
is a peer-reviewed, open access journal of chemistry, published quarterly online by MDPI.
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Latest Articles
Au Single Metal Atom for Carbon Dioxide Reduction Reaction
Chemistry 2023, 5(2), 1395-1406; https://doi.org/10.3390/chemistry5020095 - 05 Jun 2023
Abstract
CO2 is the gas that contributes the most to the greenhouse effect and, therefore, to global warming. One of the greatest challenges facing humanity is the reduction of the concentration of CO2 in the air. Here, we analyze the possible use
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CO2 is the gas that contributes the most to the greenhouse effect and, therefore, to global warming. One of the greatest challenges facing humanity is the reduction of the concentration of CO2 in the air. Here, we analyze the possible use of Au1@g-C3N4 electrocatalyst to transform CO2 into added-value products. We use density functional theory (DFT) to determine the reaction Gibbs energies for eight electron–proton transfer reaction paths of the electrochemical carbon dioxide reduction reaction (CO2RR) using a single Au atom supported on 2D carbon nitride support. Our simulations classify the Au1@g-C3N4 electrocatalysts as “beyond CO” since their formation is energetically favored, although their strong binding with a Au single atom does not allow the desorption process. DFT calculations revealed that the lowest energy pathway is CO2 (g) → COOH* → CO* → HCO* → HCOH* → CH2OH* → CH2* → CH3* → CH4 (g), where the first hydrogenation of CO to HCO is predicted as the rate-limiting step of the reaction with slightly lower potential than predicted for Cu electrodes, the most effective catalysts for CO2RR. Methane is predicted to be the main reaction product after eight proton–electron transfers (CO2 + 8 H+ + 8e− → CH4 + 2H2O). The generation of formaldehyde is discarded due to the large formation energy of the adsorbed moiety and the production of methanol is slightly less favorable than methane formation. Our computational study helps to identify suitable electrocatalysts for CO2RR by reducing the amount of metal and using stable and low-cost supports.
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(This article belongs to the Special Issue Heterogeneous Catalysis — a Theme Issue in Honor of Prof. Dr. Avelino Corma)
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Reactivity of Rare-Earth Oxides in Anhydrous Imidazolium Acetate Ionic Liquids
Chemistry 2023, 5(2), 1378-1394; https://doi.org/10.3390/chemistry5020094 - 02 Jun 2023
Abstract
Rare-earth metal sesquioxides (RE2O3) are stable compounds that require high activation energies in solid-state reactions or strong acids for dissolution in aqueous media. Alternatively, dissolution and downstream chemistry of RE2O3 have been achieved with ionic
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Rare-earth metal sesquioxides (RE2O3) are stable compounds that require high activation energies in solid-state reactions or strong acids for dissolution in aqueous media. Alternatively, dissolution and downstream chemistry of RE2O3 have been achieved with ionic liquids (ILs), but typically with additional water. In contrast, the anhydrous IL 1-butyl-3-methylimidazolium acetate [BMIm][OAc] dissolves RE2O3 for RE = La–Ho and forms homoleptic dinuclear metal complexes that crystallize as [BMIm]2[RE2(OAc)8] salts. Chloride ions promote the dissolution without being included in the compounds. Since the lattice energy of RE2O3 increases with decreasing size of the RE3+ cation, Ho2O3 dissolves very slowly, while the sesquioxides with even smaller cations appear to be inert under the applied conditions. The Sm and Eu complex salts show blue and red photoluminescence and Van Vleck paramagnetism. The proton source for the dissolution is the imidazolium cation. Abstraction of the acidic proton at the C2-atom yields an N-heterocyclic carbene (imidazole-2-ylidene). The IL can be regenerated by subsequent reaction with acetic acid. In the overall process, RE2O3 is dissolved by anhydrous acetic acid, a reaction that does not proceed directly.
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(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)
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Palladium-Catalyzed sp3 C–H Acetoxylation of α,α-Disubstituted α-Amino Acids
Chemistry 2023, 5(2), 1369-1377; https://doi.org/10.3390/chemistry5020093 - 01 Jun 2023
Abstract
The sp3 C–H acetoxylation at the β-position of α,α-disubstituted α-amino acids proceeds smoothly under palladium catalysis in the presence of PhI(OAc)2. This reaction provides a straightforward synthetic route to non-natural β-acetoxy-α-amino acids. The reaction of α-aminocyclopropanecarboxylic acid takes place via
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The sp3 C–H acetoxylation at the β-position of α,α-disubstituted α-amino acids proceeds smoothly under palladium catalysis in the presence of PhI(OAc)2. This reaction provides a straightforward synthetic route to non-natural β-acetoxy-α-amino acids. The reaction of α-aminocyclopropanecarboxylic acid takes place via ring-opening to selectively afford an acyclic γ-acetoxy-α,β-unsaturated amino acid.
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(This article belongs to the Special Issue Catalytic Organic Synthesis—A Special Issue in Honor of Professor Masahiro Miura)
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Open AccessArticle
The Anion Impact on Dimensionality of Cadmium(II) Complexes with Nicotinamide
Chemistry 2023, 5(2), 1357-1368; https://doi.org/10.3390/chemistry5020092 - 01 Jun 2023
Abstract
Three novel cadmium(II) coordination compounds, the dimeric [Cd(CH3COO)2(nia)2]2 (1), the polymeric {[Cd(nia)4](ClO4)2}n (2), and the monomeric [Cd(H2O)3(nia)3](ClO4)
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Three novel cadmium(II) coordination compounds, the dimeric [Cd(CH3COO)2(nia)2]2 (1), the polymeric {[Cd(nia)4](ClO4)2}n (2), and the monomeric [Cd(H2O)3(nia)3](ClO4)2·nia (3), were prepared in the reactions of the nicotinamide (pyridine-3-carboxamide, nia) with the corresponding cadmium(II) salts. All prepared compounds were characterized by elemental analyses, FT-IR spectroscopy, TGA/DTA, and single crystal X-ray analysis. The impact of anions (acetate, perchlorate) and solvent used on the dimensionality of cadmium(II) complexes and the cadmium(II) coordination environment was investigated. The bridging capabilities of acetate ions enabled the formation of dimers in the crystal structure of 1. It was shown that the dimensionality of perchlorate complexes depends on the solvent used. The coordination polymer 2 is isolated from an ethanol solution, while monomeric compound 3 was obtained by using a water/ethanol mixture as a solvent. The pentagonal-bipyramidal coordination of cadmium(II) was found in the presence of chelating and bridging acetate ions in 1. In the presence of non-coordinating perchlorate anions in 2 and 3, the coordination geometry of cadmium(II) is found to be octahedral. The supramolecular amide-amide homosynthon was preserved in the hydrogen-bonded frameworks of all three compounds.
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(This article belongs to the Special Issue Coordination Chemistry: Current Developments and Future Perspectives — a Themed Issue in Honor of Professor Spyros P. Perlepes on the Occasion of His 70th Birthday)
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Open AccessArticle
Synthesis and Characterization of Abasic β-Diol-C-nucleosides
Chemistry 2023, 5(2), 1343-1356; https://doi.org/10.3390/chemistry5020091 - 31 May 2023
Abstract
Modified nucleobases are potentially useful building blocks when containing catalytically active functionalities and could be introduced in chiral tridimensional molecules such as nucleic acids, which creates the premises for the development of novel catalytic species. Herein, we describe the synthesis of a novel
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Modified nucleobases are potentially useful building blocks when containing catalytically active functionalities and could be introduced in chiral tridimensional molecules such as nucleic acids, which creates the premises for the development of novel catalytic species. Herein, we describe the synthesis of a novel β-C-nucleoside bearing a diol group at anomeric position, amenable as a metal ligand or organocatalyst. An abasic ligand was successfully prepared and inserted into a complementary DNA strand.
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(This article belongs to the Special Issue Organic Chemistry Research in Italy)
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Using Imidazolium in the Construction of Hybrid 2D and 3D Lead Bromide Pseudoperovskites
Chemistry 2023, 5(2), 1329-1342; https://doi.org/10.3390/chemistry5020090 - 26 May 2023
Abstract
The field of hybrid organic–inorganic perovskite materials continues to attract the interest of the scientific community due to their fascinating properties and the plethora of promising applications in photovoltaic and optoelectronic devices. To enhance the efficiency and stability of perovskite-based devices, it is
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The field of hybrid organic–inorganic perovskite materials continues to attract the interest of the scientific community due to their fascinating properties and the plethora of promising applications in photovoltaic and optoelectronic devices. To enhance the efficiency and stability of perovskite-based devices, it is essential to discover novel compounds but also to investigate their various physicochemical, structural, and thermal properties. In this work, we report the synthesis and structural characterization of two novel hybrid lead bromide perovskites, combining the imidazolium cation (IMI) with methylammonium (MA) or formamidinium (FA) cations. The isolated polycrystalline powders were studied with X-ray powder diffraction (XPRD) and were formulated as (IMI)(MA)Pb2Br6, a 3D structure consisting of dimers of face-sharing octahedra linked in corner-sharing mode, and (IMI)(FA)PbBr4, a 2D (110) oriented layer structure with zig-zag corner-sharing octahedra. The thermal stability of (IMI)(MA)Pb2Br6 and (IMI)(FA)PbBr4 was investigated with thermogravimetric (TG) and differential scanning calorimetry (DSC) experiments which showed that both compounds are chemically stable (at least) up to 250 °C. Variable-temperature X-ray diffractometric (VT-XRD) studies of (IMI)(FA)PbBr4 highlighted a structural modification occurring above 100 °C, that is a phase transformation from triclinic to orthorhombic, via an elusive monoclinic phase.
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(This article belongs to the Special Issue Coordination Chemistry: Current Developments and Future Perspectives — a Themed Issue in Honor of Professor Spyros P. Perlepes on the Occasion of His 70th Birthday)
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Multiple Intramolecular Hydrogen Bonding in Large Biomolecules: DFT Calculations and Deuterium Isotope Effects on 13C Chemical Shifts as a Tool in Structural Studies
Chemistry 2023, 5(2), 1317-1328; https://doi.org/10.3390/chemistry5020089 - 23 May 2023
Abstract
Large biomolecules often have multiple intramolecular hydrogen bonds. In the cases where these interact, it requires special tools to disentangle the patterns. Such a tool could be deuterium isotope effects on chemical shifts. The use of theoretical calculations is an indispensable tool in
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Large biomolecules often have multiple intramolecular hydrogen bonds. In the cases where these interact, it requires special tools to disentangle the patterns. Such a tool could be deuterium isotope effects on chemical shifts. The use of theoretical calculations is an indispensable tool in such studies. The present paper illustrates how DFT calculations of chemical shifts and deuterium isotope effects on chemical shifts in combination with measurements of these effects can establish the complex intramolecular hydrogen bond patterns of rifampicin as an example) The structures were calculated using DFT theoretical calculations, performed with the Gaussian 16 software. The geometries were optimized using the B3LYP functional and the Pople basis set 6-31G(d) and the solvent (DMSO) was taken into account in the PCM approach. Besides the 6-31G(d) basis set, the 6-31 G(d,p) and the 6-3111G(d,p) basis sets were also tested. The nuclear shieldings were calculated using the GIAO approach. Deuteriation was simulated by shortening the X-H bond lengths by 0.01 Å.
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(This article belongs to the Section Theoretical Chemistry)
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Fe Doping Enhances the Peroxidase-Like Activity of CuO for Ascorbic Acid Sensing
Chemistry 2023, 5(2), 1302-1316; https://doi.org/10.3390/chemistry5020088 - 23 May 2023
Abstract
Although significant advances have been witnessed in the application of nanozymes in recent years, exploring new strategies to enhance the enzyme-like activity of nanozymes is of urgent importance. Herein, we investigate the feasibility of accelerating the peroxidase-like reaction rate of CuO nanostructures through
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Although significant advances have been witnessed in the application of nanozymes in recent years, exploring new strategies to enhance the enzyme-like activity of nanozymes is of urgent importance. Herein, we investigate the feasibility of accelerating the peroxidase-like reaction rate of CuO nanostructures through Fe doping. The coprecipitation method was used to synthesize Fe-doped CuO (Fe-CuO) nanozymes, and the results indicate that the diversified valence of Fe benefits the redox reaction driven by CuO-based nanozymes. With the improved peroxidase-like activity, the Fe-CuO nanozyme enables the significant chromogenic oxidation reaction of 3,3′,5,5′-tetramethylbenzidine (TMB), facilitating the construction of a visual sensing platform for the sensitive and selective determination of ascorbic acid. Under optimal conditions, the absorbance at 652 nm decreases linearly with the concentration of ascorbic acid in the range of 5–50 μM, with a limit of detection as low as 4.66 μM. This work exemplifies the activity enhancement for peroxidase-mimicking nanozymes with a metal-doping strategy and provides a broad prospect for the design of more high-performance nanozymes for biosensing applications.
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(This article belongs to the Special Issue Functional Biomolecule-Based Composites and Nanostructures: Current Developments and Applications—A Themed Issue in Honor of Prof. Dr. Itamar Willner)
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Open AccessArticle
On the Redox Equilibrium of TPP/TPPO Containing Cu(I) and Cu(II) Complexes
Chemistry 2023, 5(2), 1288-1301; https://doi.org/10.3390/chemistry5020087 - 17 May 2023
Abstract
Copper(II) clusters of the type [CuII4OCl6L4] (L = ligand or solvent) are a well-studied example of inverse coordination compounds. In the past, they have been studied because of their structural, magnetic, and spectroscopic features. They have
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Copper(II) clusters of the type [CuII4OCl6L4] (L = ligand or solvent) are a well-studied example of inverse coordination compounds. In the past, they have been studied because of their structural, magnetic, and spectroscopic features. They have long been believed to be redox-inactive compounds, but recent findings indicate a complex chemical equilibrium with diverse mononuclear as well as multinuclear copper(I) and copper(II) compounds. Furthermore, depending on the ligand system, such cluster compounds have proven to be versatile catalysts, e.g., in the oxidation of cyclohexane to adipic acid. This report covers a systematic study of the formation of [CuII4OCl6(TPP)4] and [CuII4OCl6(TPPO)4] (TPP = triphenylphosphine, PPh3; TPPO = triphenylphosphine oxide, O=PPh3) as well as the redox equilibrium of these compounds with mononuclear copper(I) and copper(II) complexes such as [CuIICl2(TPPO)2], [{CuIICl2}2(TPPO)2], [{CuIICl2}3(TPPO)2], [{CuII4Cl4}(TPP)4], and [CuICl(TPP)n] (n = 1–3).
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(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)
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Improved Synthesis and Coordination Behavior of 1H-1,2,3-Triazole-4,5-dithiolates (tazdt2−) with NiII, PdII, PtII and CoIII
Chemistry 2023, 5(2), 1271-1287; https://doi.org/10.3390/chemistry5020086 - 17 May 2023
Abstract
A new synthetic route to 1H-1,2,3-triazole-4,5-dithiols (tazdtH2) as ligands for the coordination of NiII, PdII, PtII and CoIII via the dithiolate unit is presented. Different N-protective groups were introduced with the corresponding azide
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A new synthetic route to 1H-1,2,3-triazole-4,5-dithiols (tazdtH2) as ligands for the coordination of NiII, PdII, PtII and CoIII via the dithiolate unit is presented. Different N-protective groups were introduced with the corresponding azide via a click-like copper-catalyzed azide-alkyne [3 + 2] cycloaddition (CuAAC) and fully characterized by NMR spectroscopy. Possible isomers were isolated and an alternative synthetic route was investigated and discussed. After removal of the benzyl protective groups on sulfur by in situ-generated sodium naphthalide, complexes at the [(dppe)M] (M = Ni, Pd, Pt), [(PPh3)2Pt] and [(η5-C5H5)Co] moieties were prepared and structurally characterized by XRD analysis. In this process, the by-products 11 and 12 as monothiolate derivatives were isolated and structurally characterized as well. With regioselective coordination via the dithiolate unit, the electronic influence of different metals or protective groups at N was investigated and compared spectroscopically by means of UV/Vis spectroscopy and cyclic voltammetry. Complex [(η5-C5H5)Co(5c)] (10), is subject to a dimerization equilibrium, which was investigated by temperature-dependent NMR and UV/Vis spectroscopy (solution and solid-state). The thermodynamic parameters of the monomer/dimer equilibrium were derived.
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(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)
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Investigation of the Properties of Mo/ZSM-5 Catalysts Based on Zeolites with Microporous and Micro–Mesoporous Structures
Chemistry 2023, 5(2), 1256-1270; https://doi.org/10.3390/chemistry5020085 - 17 May 2023
Abstract
The dehydroaromatization of methane (MDA) is of great interest as a promising process for processing natural and associated petroleum gases, the main component of which is methane. The rapid loss of catalyst activity because of coke formation hinders the introduction of the DHA
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The dehydroaromatization of methane (MDA) is of great interest as a promising process for processing natural and associated petroleum gases, the main component of which is methane. The rapid loss of catalyst activity because of coke formation hinders the introduction of the DHA methane process into the industry. Therefore, the aim of this research was to find ways to improve Mo/ZSM-5 catalysts for MDA. The paper presents the results of the synthesis of high-silica zeolites of the ZSM-5 type with microporous and micro–mesoporous structures, the preparation of Mo/ZSM-5 catalysts based on them, and the study of the physicochemical and catalytic properties of the obtained samples during the non-oxidative conversion of methane into aromatic hydrocarbons. Zeolite catalysts were investigated using IR spectroscopy, X-ray diffraction, TPD-NH3, SEM, HR-TEM, and N2 adsorption. It was found that the addition of carbon black in the stage of the synthesis of zeolite type ZSM-5 did not lead to structural changes, and the obtained samples had a crystallinity degree equal to 100%. The creation of the micro–mesoporous structure in Mo/ZSM-5 catalysts led to an increase in their activity and stability in the process of methane dehydroaromatization. The highest conversion of methane was observed on a 4.0%Mo/ZSM-5 catalyst prepared based on zeolite synthesized using 1.0% carbon black and was 13.0% after 20 min of reaction, while the benzene yield reached 7.0%. It was shown using HR-TEM that a more uniform distribution of the active metal component was observed in a zeolite catalyst with a micro–mesoporous structure than in a microporous zeolite.
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(This article belongs to the Special Issue Catalytic Organic Synthesis—A Special Issue in Honor of Professor Masahiro Miura)
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Modification of the Bridging Unit in Luminescent Pt(II) Complexes Bearing C^N*N and C^N*N^C Ligands
Chemistry 2023, 5(2), 1243-1255; https://doi.org/10.3390/chemistry5020084 - 15 May 2023
Abstract
In this work, we explored the synthesis and characterization of Pt(II) complexes bearing different tri- and tetradentate luminophores acting as C^N*N- and C^N*N^C-chelators. Thus, we investigated diverse substitution patterns in order to improve their processability and assessed the effects of structural variations on
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In this work, we explored the synthesis and characterization of Pt(II) complexes bearing different tri- and tetradentate luminophores acting as C^N*N- and C^N*N^C-chelators. Thus, we investigated diverse substitution patterns in order to improve their processability and assessed the effects of structural variations on their excited state properties. Hence, a detailed analysis of the different synthetic pathways is presented; the photophysical properties were studied by using steady-state and time-resolved photoluminescence spectroscopy. We determined the absorption and emission spectra, the photoluminescence efficiencies, and the excited state lifetimes of the complexes in fluid solutions at room temperature and frozen glassy matrices at 77 K. Finally, a structure–property relationship was established, showing that the decoration of the bridging unit on the tridentate luminophores only marginally affects the excited state properties, whereas the double cyclometallation related to the tetradentate chelator prolongs the excited state lifetime and increases the photoluminescence quantum yield.
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(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)
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Short I⋯O Interactions in the Crystal Structures of Two 2-Iodo-Phenyl Methyl-Amides as Substrates for Radical Translocation Reactions
Chemistry 2023, 5(2), 1233-1242; https://doi.org/10.3390/chemistry5020083 - 12 May 2023
Abstract
Radical translocation reactions are finding various uses in organic synthesis, in particular the stereospecific formation of complex natural products. In this work, the syntheses and single-crystal structures of two substituted 2-iodo-phenyl methyl-amides are reported, namely cyclo-propane carboxylic acid (2-iodo-phenyl)-methyl-amide, C11H
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Radical translocation reactions are finding various uses in organic synthesis, in particular the stereospecific formation of complex natural products. In this work, the syntheses and single-crystal structures of two substituted 2-iodo-phenyl methyl-amides are reported, namely cyclo-propane carboxylic acid (2-iodo-phenyl)-methyl-amide, C11H12INO (1), and cyclo-heptane carboxylic acid (2-iodo-phenyl)-methyl-amide, C15H20INO (2). In each case, the methyl-amide group has a syn conformation, and this grouping is perpendicular to the plane of the benzene ring: these solid-state conformations appear to be well setup to allow an intramolecular hydrogen atom transfer to take place as part of a radical translocation reaction. Short intermolecular I⋯O halogen bonds occur in each crystal structure, leading to [010] chains in 1 [I⋯O = 3.012 (2) Å] and isolated dimers in 2 [I⋯O = 3.024 (4) and 3.057 (4) Å]. The intermolecular interactions are further quantified by Hirshfeld surface analyses.
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(This article belongs to the Section Crystallography)
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Selective Fluorimetric Detection of Pyrimidine Nucleotides in Neutral Aqueous Solution with a Styrylpyridine-Based Cyclophane
Chemistry 2023, 5(2), 1220-1232; https://doi.org/10.3390/chemistry5020082 - 11 May 2023
Abstract
A styrylpyridine-containing cyclophane with diethylenetriamine linkers is presented as a host system whose association with representative nucleotides was examined with photometric and fluorimetric titrations. The spectrometric titrations revealed the formation of 1:1 complexes with log Kb values in the range of 2.3–3.2
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A styrylpyridine-containing cyclophane with diethylenetriamine linkers is presented as a host system whose association with representative nucleotides was examined with photometric and fluorimetric titrations. The spectrometric titrations revealed the formation of 1:1 complexes with log Kb values in the range of 2.3–3.2 for pyrimidine nucleotides TMP (thymidine monophosphate), TTP (thymidine triphosphate) and CMP (cytidine monophosphate) and 3.8–5.0 for purine nucleotides AMP (adenosine monophosphate), ATP (adenosine triphosphate), and dGMP (deoxyguanosine monophosphate). Notably, in a neutral buffer solution, the fluorimetric response to the complex formation depends on the type of nucleotide. Hence, quenching of the already weak fluorescence was observed with the purine bases, whereas the association of the cyclophane with pyrimidine bases TMP, TTP, and CMP resulted in a significant fluorescence light-up effect. Thus, it was demonstrated that the styrylpyridine unit is a useful and complementary fluorophore for the development of selective nucleotide-targeting fluorescent probes based on alkylamine-linked cyclophanes.
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(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)
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A Pathway for Aldol Additions Catalyzed by l-Hydroxyproline-Peptides via a β-Hydroxyketone Hemiaminal Intermediate
Chemistry 2023, 5(2), 1203-1219; https://doi.org/10.3390/chemistry5020081 - 10 May 2023
Abstract
While the use of l-proline-derived peptides has been proven similarly successful with respect to enantioselectivity, the physico-chemical and conformational properties of these organocatalysts are not fully compatible with transition state and intermediate structures previously suggested for l-proline catalysis. l-Proline or
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While the use of l-proline-derived peptides has been proven similarly successful with respect to enantioselectivity, the physico-chemical and conformational properties of these organocatalysts are not fully compatible with transition state and intermediate structures previously suggested for l-proline catalysis. l-Proline or l-4-hydroxyproline catalysis is assumed to involve proton transfers mediated by the carboxylic acid group, whereas a similar mechanism is unlikely for peptides, which lack a proton donor. Herein, we prepared an array of hydroxyproline-based dipeptides through amide coupling of Boc-protected cis- or trans-4-l-hydroxyproline (cis- or trans-4-Hyp) to benzylated glycine (Gly-OBn) and l-valine (l-Val-OBn) and used these dipeptides as catalysts for a model aldol reaction. Despite the lack of a proton donor in the catalytic site, we observed good stereoselectivities for the R-configured aldol product both with dipeptides formed from cis- or trans-4-Hyp at moderate conversions after 24 h. To explain this conundrum, we modeled reaction cycles for aldol additions in the presence of cis-4-Hyp, trans-4-Hyp, and cis- and trans-configured 4-Hyp-peptides as catalysts by calculation of free energies of conformers of intermediates and transition states at the density functional theory level (B3LYP/6-31G(d), DMSO PCM as solvent model). While a catalytic cycle as previously suggested with l-proline is also plausible for cis- or trans-4-Hyp, with the peptides, the energy barrier of the first reaction step would be too high to allow conversions at room temperature. Calculations on modeled transition states suggest an alternative pathway that would explain the experimental results: here, the catalytic cycle is entered by the acetone self-adduct 4-hydroxy-4-methylpentan-2-one, which forms spontaneously to a small extent in the presence of a base, leading to considerably reduced calculated free energy levels of transition states of reaction steps that are considered rate-determining.
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(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)
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Tweaking of Peripheral Moieties in Catalytic Amyloid for Modulating Hydrogel Strength and Hydrolase Activity
Chemistry 2023, 5(2), 1190-1202; https://doi.org/10.3390/chemistry5020080 - 10 May 2023
Abstract
The de novo design and synthesis of peptide-based biocatalysts that can mimic the activity of natural enzymes is an exciting field with unique opportunities and challenges. In a natural enzyme, the active site is composed of an assembly of different amino acid residues,
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The de novo design and synthesis of peptide-based biocatalysts that can mimic the activity of natural enzymes is an exciting field with unique opportunities and challenges. In a natural enzyme, the active site is composed of an assembly of different amino acid residues, often coordinated with a metal ion. A metalloenzyme’s catalytic activity results from the dynamic and concerted interplay of various interactions among the residues and metal ions. Aiming to mimic such enzymes, simple peptide fragments, drawing structural inspiration from natural enzymes, can be utilized as a model. In our effort to mimic a metal-containing hydrolase, we designed peptide amphiphiles (PA) 1 and 2 with a terminal histidine having amide and acid functionalities, respectively, at its C-terminal, imparting differential ability to coordinate with Zn and Cu ions. The PAs demonstrate remarkable self-assembly behavior forming excellent nanofibers. Upon coordination with metal ions, depending on the coordination site the nanofibers become rigidified or weakened. Rheological studies revealed excellent mechanical properties of the hydrogels formed by the PAs and the PA–metal co-assemblies. Using such co-assemblies, we mimic hydrolase activity against a p-nitrophenyl acetate (p-NPA) substrate. Michaelis–Menten’s enzyme kinetic parameters indicated superior catalytic activity of 2 with Zn amongst all the assemblies.
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(This article belongs to the Special Issue Programmable and Stimulus-Responsive Supramolecular Assemblies)
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Platform Chemicals from Ethylene Glycol and Isobutene: Thermodynamics “Pays” for Biomass Valorisation and Acquires “Cashback”
Chemistry 2023, 5(2), 1171-1189; https://doi.org/10.3390/chemistry5020079 - 09 May 2023
Abstract
Ethylene glycol (EG) produced from biomass is a promising candidate for several new applications. In this paper, EG derivatives such as mono- and di-tert-butyl ethers are considered. However, accurate thermodynamic data are essential to optimise the technology of the direct tert-butyl ether EG
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Ethylene glycol (EG) produced from biomass is a promising candidate for several new applications. In this paper, EG derivatives such as mono- and di-tert-butyl ethers are considered. However, accurate thermodynamic data are essential to optimise the technology of the direct tert-butyl ether EG synthesis reaction or reverse process isobutene release. The aim of this work is to measure the vapour pressures and combustion energies for these ethers and determine the vaporisation enthalpies and enthalpies of formation from these measurements. Methods based on the First and Second Law of Thermodynamics were combined to discover the reliable thermodynamics of ether synthesis reactions. The thermochemical data for ethylene glycol tert-butyl ethers were validated using structure–property correlations and quantum chemical calculations. The literature results of the equilibrium study of alkylation of EG with isobutene were evaluated and the thermodynamic functions of ethylene glycol tert-butyl ethers were derived. The energetics of alkylation determined according to the “First Law” and the “Second Law” methods agree very well. Some interesting aspects related to the entropy of ethylene glycol tert-butyl ethers were also revealed and discussed.
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(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)
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Open AccessReview
Liquid Phase Calorimetric Method as a Tool for Acid Strength Measurements and Application to a Variety of Sustainable Catalysts
by
, , , , and
Chemistry 2023, 5(2), 1138-1170; https://doi.org/10.3390/chemistry5020078 - 09 May 2023
Abstract
It has been about 36 years since the first published paper about the calorimetry and adsorption (Cal-Ad) method by Prof. Drago. These separated methods are very old and important characterization tools for different molecules and materials, as recognized in chemistry. The idea of
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It has been about 36 years since the first published paper about the calorimetry and adsorption (Cal-Ad) method by Prof. Drago. These separated methods are very old and important characterization tools for different molecules and materials, as recognized in chemistry. The idea of coupling these two techniques arose from the need to have more information about the thermodynamic parameters of a catalyst. The Cal-Ad method provides a measure of the magnitude (Ki), strength (−∆Hi), and quantity (ni) of sites present in a catalyst. The original idea is based on the application of the donor-acceptor concept using the Electrostatic Covalent Model, ECW in the areas of catalysis and material chemistry. Particularly, enthalpy measurements of acidity are directly related to the activity of various catalysts in a variety of reactions. Currently, more than twenty-five catalysts have been carefully characterized by this method in addition to spectroscopic and other thermal methods. Thus, this review seeks to present the fundamentals of the method and show different applications of the characterized catalysts for a variety of reactions in order to use these data as an alternative to choose a catalyst for an acid-dependent type reaction.
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(This article belongs to the Section Catalysis)
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Activated Carbon from Sugarcane Bagasse: A Low-Cost Approach towards Cr(VI) Removal from Wastewater
by
, , , , , , and
Chemistry 2023, 5(2), 1124-1137; https://doi.org/10.3390/chemistry5020077 - 09 May 2023
Abstract
The potential of pretreated sugarcane bagasse (SCB) as a low-cost and renewable source to yield activated carbon (AC) for chromate CrO42− removal from an aqueous solution has been investigated. Raw sugarcane bagasse was pretreated with H2SO4, H
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The potential of pretreated sugarcane bagasse (SCB) as a low-cost and renewable source to yield activated carbon (AC) for chromate CrO42− removal from an aqueous solution has been investigated. Raw sugarcane bagasse was pretreated with H2SO4, H3PO4, HCl, HNO3, KOH, NaOH, or ZnCl2 before carbonization at 700 °C. Only pretreatments with H2SO4 and KOH yield clean AC powders, while the other powders still contain non-carbonaceous components. The point of zero charge for ACs obtained from SCB pretreated with H2SO4 and KOH is 7.71 and 2.62, respectively. Batch equilibrium studies show that the most effective conditions for chromate removal are a low pH (i.e., below 3) where >96% of the chromate is removed from the aqueous solution.
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(This article belongs to the Special Issue Commemorating 150 Years of Justus von Liebig’s Legacy)
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Open AccessCommunication
Five Bonds to Carbon through Tri-Coordination in
Chemistry 2023, 5(2), 1113-1123; https://doi.org/10.3390/chemistry5020076 - 09 May 2023
Abstract
Here, five bonds to carbon through tri-coordination are theoretically established in the global minimum energy isomers of anion (1a) and neutral (1n) for the first time. Various isomers of
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Here, five bonds to carbon through tri-coordination are theoretically established in the global minimum energy isomers of anion (1a) and neutral (1n) for the first time. Various isomers of are theoretically identified using density functional theory at the PBE0-D3/def2-TZVP level. Chemical bonding features are thoroughly analyzed for these two isomers (1a and 1n) with different bonding and topological quantum chemical tools, such as adaptive natural density partitioning (AdNDP), Wiberg Bond Indices (WBIs), nucleus-independent chemical shifts (NICS), and atoms in molecules (AIM) analyses. The structure of isomer 1a is planar with C2v symmetry, whereas its neutral counterpart 1n is non-planar with C2 symmetry, in which its terminal aluminum atoms are out of the plane. The central allenic carbon atom of isomers 1a and 1n exhibits tri-coordination and thus makes it a case of five bonds to carbon, which is confirmed through their total bond order as observed in WBI. Both the isomers show σ- and π-aromaticity and are predicted with the NICS and AdNDP analyses. Further, the results of ab initio molecular dynamics simulations reveal their kinetic stability at room temperature; thus, they are experimentally viable systems.
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(This article belongs to the Special Issue Hypercoordinate Carbon)
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