Monthly Archives: January 2024

In‐Bridge Stereochemistry: A Determinant of Stapled Peptide Conformation and Activity

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In-Bridge Stereochemistry: A Determinant of Stapled Peptide Conformation and Activity

The significance of in-bridge stereochemistry has been underscored as a decisive factor influencing stapled peptides’ α-helicity, protease resistance, protein-binding affinity, and various other properties. This aspect introduces fresh opportunities for the innovative design and development of novel peptide tools and therapeutics.


Abstract

Peptide side chain stapling has been proven to be an effective strategy for fine-tuning peptide properties. This innovative approach leads to the creation of stapled peptides characterized by stabilized α-helical conformations, enhanced protein-binding affinity, improved cell permeability, superior enzymatic stability, and numerous other advantages. Extensive research has explored the impact of various stapling bridges on the properties of these peptides, with limited investigation into the influence of bridge chirality, until very recently. In this concise review, we provide a brief overview of the current state of knowledge regarding the stereochemistry within the bridges of stapled peptides, offering insights into the potential applications of chiral bridges in the design and development of stapled peptides.

Cinchona‐Based Hydrogen‐Bond Donor Organocatalyst Metal Complexes: Asymmetric Catalysis and Structure Determination

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Cinchona-Based Hydrogen-Bond Donor Organocatalyst Metal Complexes: Asymmetric Catalysis and Structure Determination

Three different cinchona-based organocatalysts containing different hydrogen-bond donor moieties worked together with inorganic transition metal salts to catalyze pharmaceutically relevant asymmetric reactions. They were also studied experimentally and quantum chemically, providing insight into the complex structures of these catalytically active species. In many cases, the application of these catalysts led to significant increases in both yield and enantioselectivity.


Abstract

In this study, we describe the synthesis of cinchona (thio)squaramide and a novel cinchona thiourea organocatalyst. These catalysts were employed in pharmaceutically relevant catalytic asymmetric reactions, such as Michael, Friedel–Crafts, and A3 coupling reactions, in combination with Ag(I), Cu(II), and Ni(II) salts. We identified several organocatalyst-metal salt combinations that led to a significant increase in both yield and enantioselectivity. To gain insight into the active catalyst species, we prepared organocatalyst-metal complexes and characterized them using HRMS, NMR spectroscopy, and quantum chemical calculations (B3LYP-D4/def2-TZVP), which allowed us to establish a structure-activity relationship.

Deciphering Nitroaromatics Reduction: Theoretical Insights into Dioxomolybdenum Catalysis with Biomass‐Derived Pinacol

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Density Functional Theory is used to unravel the mechanism of the nitrobenzene to aniline reduction, catalyzed by dioxomolybdenum (VI) dichloride. The use of pinacol as an oxoaccepting reagent and the production of only acetone and water as byproducts, signals a novel and environmentally friendly way to add value to the oxygen-rich biomass-derived polyols. The reaction proceeds through three consecutive cycles, each one responsible for one of the three reductive steps needed to yield aniline from nitrobenzene, with  nitrosobenzene and hydroxylamine as intermediates. Each cycle regenerates the catalyst and releases one water and two acetone molecules. The mechanism involves  singlet/triplet state crossings, a crucial feature in polyoxomolibdate catalyzed processes. The role of the Mo-coordinated water as the provider of the mysterious protons needed to reduce the nitro group, was revealed. The disclosure of this challenging mechanism and its rate limiting step can contribute to the design of more effective Mo(VI) catalysts.

Surface Modification Engineering Enabling LiMnxFe1−xPO4 Cathode Against Aggressive Cathode Chemistries for Excellent Performance Lithium‐ion batteries

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Surface Modification Engineering Enabling LiMnxFe1−xPO4 Cathode Against Aggressive Cathode Chemistries for Excellent Performance Lithium-ion batteries

The LiMn0.6Fe0.4PO4@C@Al2O3 (LMFP64/CA) compound was synthesized through solvothermal and liquid-phase coating methodologies. The LMFP64/CA composite with the carbon layer and Al2O3 protective layer as cathode materials can obtain excellent cycle performance and rate performance.


Abstract

As an indispensable cathode material for lithium-ion batteries, LiMn x Fe1−x PO4 (LMFP) has garnered significant attention among scholars due to its considerable energy density and remarkable safety characteristics. However, the further advancement of LMFP is hindered by its poor conductivity and limitations in terms of cycle stability. Herein, LiMn0.6Fe0.4PO4@C@Al2O3 (LMFP64/CA) composite materials with core-shell structure were prepared through simple solvothermal and liquid phase coating methods. The carbon layer can further bolster the structural robustness of the active material, increase conductivity, and facilitate ion and electron transfer; while the Al2O3 layer can function as a protective interface, effectively mitigating the detrimental electrochemical side effects arising from hydrofluoric acid (HF) generated during electrolyte decomposition within a wide voltage range. Consequently, the LMFP64/CA electrode exhibits impressive electrochemical performance including notable reversible capacity (125.1 mAh g−1 at 0.5 C), exceptional rate performance (111.2 mAh g−1 at 1 C), and remarkable cycle stability at 5 C (0.021 % decay rate over 500 cycles).

Design of Promising Uranyl(VI) Complexes Thin Films with Potential Applications in Molecular Electronics

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Design of Promising Uranyl(VI) Complexes Thin Films with Potential Applications in Molecular Electronics

Oxo uranyl(VI) complexes were successfully synthesized, characterized and deposited by thermal evaporation and optical and electrical features of films were examined. The bandgap for the films is in the Interval of 2.39 and 2.79 eV and the films present ohmic electrical behavior, with maximum current values of order of 10−3 A. These uranyl films can be used in Molecular Electronics applications.


Abstract

In this work, it is proposed the development of organic semiconductors (OS) based on uranyl(VI) complexes. The above by means of the synthesis and the characterization of the complexes by Infrared spectroscopy, Nuclear magnetic resonance spectroscopy, mass spectrometry, and X-ray diffraction. Films of these complexes were deposited and subsequently, topographic and structural characterization was carried out by Scanning Electron Microscopy, X-ray diffraction, and Atomic Force Microscopy. Additionally, the nanomechanical evaluation was performed to know the stiffness of uranyl films using their modulus of elasticity. Also, the optical characterization took place in the devices and their bandgap value ranges between 2.40 and 2.93 eV being the minor for the film of the uranyl complex with the N on pyridine in position 4 (2 c). Finally, the electrical behavior of the uranyl(VI) films was evaluated, and important differences were obtained: the uranyl complex with the N on pyridine in position 2 (2 a) film is not influenced by changes in lighting and its current density is in the order of 10−3 A/cm2. The film with uranyl complex with the N on pyridine in position 3 (2 b) and 2 c presents a greater current flow under lighting conditions and two orders of magnitude larger than in film 2 a. In these films 2 b and 2 c, ohmic behavior occurs at low voltages, while at high voltages the charge transport changes to space-charge limited current behavior.

Photocatalytic Degradation of Malachite Green by Titanium Dioxide/Covalent Organic Framework Composite: Characterization, Performance and Mechanism

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Photocatalytic Degradation of Malachite Green by Titanium Dioxide/Covalent Organic Framework Composite: Characterization, Performance and Mechanism

In this paper, a titanium dioxide/covalent organic framework (TiO2/COF) composite was prepared and its photocatalytic removal of dye was investigated. Using tetrabutyl titanate as a titanium source, TiO2 nanomaterial was prepared by sol-gel method. In the presence of TiO2, TiO2/COF core-shell composite was prepared by solvothermal synthesis using melamine and 1,4-phthalaldehyde as ligands. The prepared materials are characterized by SEM, TEM, XPS, XRD, TG, FTIR, BET, EPR, PL, and UV-Vis-DRS techniques. Using malachite green (MG) as a model of dye wastewater, the photocatalytic degradation performance of TiO2/COF composites was investigated under the irradiation of ultraviolet light. The results show that the modification of COF significantly improves the photocatalytic efficiency of TiO2, the degradation rate increases from 69.77 % to 93.64 %, and the reaction rate constant of the first-order kinetic equation is increased from 0.0078 min−1 to 0.0192 min−1. Based on the free radical capture experiment, the photocatalytic degradation mechanism of TiO2/COF was discussed, and the feasibility of its photocatalytic degradation of malachite green was theoretically clarified. Accordingly, a simple and practical method for photocatalytic degradation of malachite green was constructed, which has potential application value in the degradation of dye wastewater.


Abstract

In this paper, a titanium dioxide/covalent organic framework (TiO2/COF) composite was prepared and its photocatalytic removal of dye was investigated. Using tetrabutyl titanate as a titanium source, TiO2 nanomaterial was prepared by sol-gel method. In the presence of TiO2, TiO2/COF core-shell composite was prepared by solvothermal synthesis using melamine and 1,4-phthalaldehyde as ligands. The prepared materials are characterized by SEM, TEM, XPS, XRD, TG, FTIR, BET, EPR, PL, and UV-Vis-DRS techniques. Using malachite green as a model of dye wastewater, the photocatalytic degradation performance of TiO2/COF composites was investigated under the irradiation of ultraviolet light. The results show that the modification of COF significantly improves the photocatalytic efficiency of TiO2, the degradation rate increases from 69.77 % to 93.64 %, and the reaction rate constant of the first-order kinetic equation is increased from 0.0078 min−1 to 0.0192 min−1. Based on the free radical capture experiment, the photocatalytic degradation mechanism of TiO2/COF was discussed, and the feasibility of its photocatalytic degradation of malachite green was theoretically clarified. Accordingly, a simple and practical method for photocatalytic degradation of malachite green was constructed, which has potential application value in the degradation of dye wastewater.

Superconducting Quasicrystals

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Superconducting Quasicrystals


Abstract

Dan Shechtman's discovery of quasicrystals in 1982 introduced the scientific world to aperiodic crystals with unique rotational symmetries, redefining traditional crystallography. Although superconductivity in related periodic approximants has since been observed, true bulk superconductivity in quasicrystals was confirmed only in 2018. This recent discovery opens a new horizon not only for the study of correlated quasicrystals but more generally for the study of superconductivity with nontrivial spatial order. The theoretical understanding of superconducting quasicrystals poses challenges due to their lack of periodicity. Notably, they exhibit non-BCS type superconductivity and distinct electromagnetic responses, reminiscent of the so-called FFLO state. In this review, we provide an overview of superconducting quasicrystals, along with some “behind-the-scenes” information.