Explore the vast range of titles available.

The use of macrocyclic compounds to remove organic dyes is fascinating because they have a wide surface area range and can be used for different things. new (14E, 34E)-7-Hydroxy-7, 8, 22, 23, 24, 25, 26, 27-Octahydro-6H, 16H, 33H Tetrabenzo[f,k,u,z][1,5,13,20]Tetraoxacycloheptacosine-16,33-Dione (HOTTD) was obtained by a simple high-dilution method, and characterized by FTIR, .sup.1 H-NMR, FESEM, EDX, and XRD. It worked well in removing organic dyes from aqueous solutions. Contact time, pH, dosage, initial concentration and temperature were studied. The optimum conditions were achieved by using 20 mg/L dye concentration, 50 mg dose of adsorbent and pH 9.0 at room temperature. The adsorption process was remarkably fast and reached equilibrium within 10 min for both Brilliant Green and Malachite Green while 70 min for Safranin. The batch adsorption experiments followed a pseudo 2.sup.nd order and Langmuir model with maximum adsorption capacity 19.26 mg/g, 18.28 mg/g, and 14.35 mg/g for Brilliant Green, Malachite green and Safranin respectively. The process was endothermic and spontaneous in nature. Adsorbent regeneration test provides an excellent value 5 times.

The rise of antibiotic resistance calls for new therapeutics targeting resistance factors such as the New Delhi metallo-β-lactamase 1 (NDM-1), a bacterial enzyme that degrades β-lactam antibiotics. We present structure-guided computational methods for designing peptide macrocycles built from mixtures of L- and D-amino acids that are able to bind to and inhibit targets of therapeutic interest. Our methods explicitly consider the propensity of a peptide to favor a binding-competent conformation, which we found to predict rank order of experimentally observed IC50 values across seven designed NDM-1- inhibiting peptides. We were able to determine X-ray crystal structures of three of the designed inhibitors in complex with NDM-1, and in all three the conformation of the peptide is very close to the computationally designed model. In two of the three structures, the binding mode with NDM-1 is also very similar to the design model, while in the third, we observed an alternative binding mode likely arising from internal symmetry in the shape of the design combined with flexibility of the target. Although challenges remain in robustly predicting target backbone changes, binding mode, and the effects of mutations on binding affinity, our methods for designing ordered, binding-competent macrocycles should have broad applicability to a wide range of therapeutic targets.

The presence of anomalous chirality in a roll of graphitic carbon sheets has been recognized since the discovery of carbon nanotubes, which are becoming available in higher quantities through the isolation of chiral single-wall congeners with high purity. Exploration of the properties arising from cylinder chirality is expected to expand the scope of tubular entities in the future. By studying molecular fragments of helical carbon nanotubes, we herein reveal interesting properties that arise from this chirality. The chirality of nanoscale cylinders resulted in chirality of larger dimensions in the form of a double-helix assembly. Cylinder chirality in solution gave rise to a large dissymmetry factor of metal-free entities in circular polarized luminescence. Theoretical investigations revealed the pivotal role of cylindrical shapes in enhancing magnetic dipole transition moments to yield extreme rotatory strength. Unique effects of cylinder chirality in this study may prompt the development of tubular entities, for instance, toward chiroptical applications.

43,44,47,48‐Tetrathiaoctaphyrin (2.1.1.1.2.1.1.1), obtained in a concise synthesis, is found to adopt a C2‐symmetric figure‐eight conformation in solution and in the solid state. The macrocycle is globally nonaromatic but exhibits strong absorption in the visible and near‐infrared regions. Metalation of the octaphyrin with [RhI(CO)2Cl]2 produced an unprecedented dinuclear complex featuring two octahedral Rh(III) centers and four RhC bonds. The latter species is globally aromatic and has a distinct, quasi‐rectangular shape. Using an in‐depth NMR and computational analysis, the Rh2 complex is found to exhibit an unusual case of isomerism resulting from the combined effect of local helicity, conformationally locked trans‐vinylene bridges, and polar axial ligation. A figure‐eight‐shaped tetrathiaoctaphyrin (left) undergoes reversible redox and conformational switching upon coordination to two Rh(III) centers, yielding a globally aromatic [38]annulene structure (right). The Rh2 complex, formed via fourfold CH metalation, displays rare isomerism driven by local helicity and axial ligand switching.

Organic 2D Materials In article number 2300521, Kim, Oaki, and co‐workers show a new type of organic 2D materials. Conventional organic 2D materials, such as 2D polymers and covalent organic frameworks, consist of the planar π‐conjugated macromolecules linked and extended parallel to the layers. The present work shows 2D materials based on the perpendicularly stacked macrocycles to the lateral direction.

Per(6-O-tert-butyldimethylsilyl)-[alpha]-, [beta]- and [gamma]-cyclodextrin derivatives are well-known as synthetic intermediates that enable the selective mono-, partial, or perfunctionalization of the secondary face of the macrocycles. Although silylation of the primary rim is readily achieved by treatment with tert-butyldimethylsilyl chloride in the presence of pyridine (either alone or mixed with a co-solvent), the reaction typically results in a mixture containing both under- and oversilylated byproducts that are difficult to remove. To address this challenge in preparing a pure product in high yield, we describe an approach that centers on the addition of a controlled excess of silylating agent to avoid the presence of undersilylated species, followed by the removal of oversilylated species by column chromatography elution with carefully designed solvent mixtures. This methodology works well for 6-, 7-, and 8-member rings ([alpha]-, [beta]-, and [gamma]-cyclodextrins, respectively) and has enabled us to repeatedly prepare up to â35 g of [greater than or equal to]98% pure product (as determined by HPLC) in 3 d. We also provide procedures for lower-scale reactions, as well as an example of how the [beta]-cyclodextrin derivative can be used for functionalization of the secondary face of the molecule.

Sulfur-containing macrocycles have attracted substantial interest because they exhibit unique characteristics due to their polygonal ring-shaped skeleton. In this study, a thianthrene-based cyclic tetramer with the sulfur linker, thiacalix[4]-2,8-thianthrene (TC[4]TT), was successfully prepared from a cyclo-p-phenylenesulfide derivative using acid-induced intramolecular condensation. Single crystal X-ray diffraction revealed that TC[4]TT adopts an alternative octagonal form recessed to the inner side. Its internal cavity included small solvents, such as chloroform and carbon disulfide. Due to its polygonal geometry, TC[4]TT laminated in a honeycomb-like pattern with a porous channel. Furthermore, TC[4]TT showed fluorescence and phosphorescence emission in a CH2Cl2 solution at ambient and liquid nitrogen temperatures. Both emission bands were slightly redshifted compared with those of the reference compounds (di(thanthren-2-yl)sulfane (TT2S) and thianthrene (TT)). This work describes a sulfur-containing thiacalixheterocycle-based macrocyclic system with intriguing supramolecular chemistry based on molecular tiling and photophysical properties in solution.

Iron- and nitrogen-doped carbon (Fe-N-C) materials are leading candidates to replace platinum catalysts for the oxygen reduction reaction (ORR) in fuel cells; however, their active site structures remain poorly understood. A leading postulate is that the iron-containing active sites exist primarily in a pyridinic Fe-N 4 ligation environment, yet, molecular model catalysts generally feature pyrrolic coordination. Herein, we report a molecular pyridinic hexaazacyclophane macrocycle, (phen 2 N 2 )Fe, and compare its spectroscopic, electrochemical, and catalytic properties for ORR to a typical Fe-N-C material and prototypical pyrrolic iron macrocycles. N 1s XPS and XAS signatures for (phen 2 N 2 )Fe are remarkably similar to those of Fe-N-C. Electrochemical studies reveal that (phen 2 N 2 )Fe has a relatively high Fe(III/II) potential with a correlated ORR onset potential within 150 mV of Fe-N-C. Unlike the pyrrolic macrocycles, (phen 2 N 2 )Fe displays excellent selectivity for four-electron ORR, comparable to Fe-N-C materials. The aggregate spectroscopic and electrochemical data demonstrate that (phen 2 N 2 )Fe is a more effective model of Fe-N-C active sites relative to the pyrrolic iron macrocycles, thereby establishing a new molecular platform that can aid understanding of this important class of catalytic materials. Iron- and nitrogen-doped carbon materials are effective catalysts for the oxygen reduction reaction whose active sites are poorly understood. Here, the authors establish a new pyridinic iron macrocycle complex as a more effective active site model relative to legacy pyrrolic model complexes.

Ion‐pair recognition has emerged from cation and anion recognition and become a diverse and active field in its own right. The last decade has seen significant advances in receptor design in terms of the types of binding motifs, understanding of cooperativity and increase in complexity from heteroditopic to multitopic receptors. As a result, attention has turned to applying this knowledge to the rational design of ion‐pair receptors for applications in salt solubilisation and extraction, membrane transport and sensing. This Review highlights recent progress and developments in the design and applications of heteroditopic and multitopic receptors for ion‐pair recognition. From Design to Application: In the last decade ion‐pair recognition has evolved from an emerging to an established field. This Review discusses recent developments in the design and applications of heteroditopic and multitopic ion‐pair receptors. Unusual recognition motifs and topologies are highlighted as well as the applications of ion‐pair receptors as salt solubilisation and extraction agents, in membrane transport, sensing and as switchable receptors.

There is an urgent need for new antibiotics against Gram-negative pathogens that are resistant to carbapenem and third-generation cephalosporins, against which antibiotics of last resort have lost most of their efficacy. Here we describe a class of synthetic antibiotics inspired by scaffolds derived from natural products. These chimeric antibiotics contain a β-hairpin peptide macrocycle linked to the macrocycle found in the polymyxin and colistin family of natural products. They are bactericidal and have a mechanism of action that involves binding to both lipopolysaccharide and the main component (BamA) of the β-barrel folding complex (BAM) that is required for the folding and insertion of β-barrel proteins into the outer membrane of Gram-negative bacteria. Extensively optimized derivatives show potent activity against multidrug-resistant pathogens, including all of the Gram-negative members of the ESKAPE pathogens 1 . These derivatives also show favourable drug properties and overcome colistin resistance, both in vitro and in vivo. The lead candidate is currently in preclinical toxicology studies that—if successful—will allow progress into clinical studies that have the potential to address life-threatening infections by the Gram-negative pathogens, and thus to resolve a considerable unmet medical need. A class of chimeric synthetic antibiotics that bind to lipopolysaccharide and BamA shows potent activity against multidrug-resistant Gram-negative bacteria, with the potential to address life-threatening infections.