Transformation of SBUs and Synergy of MOF Host-Guest in Single Crystalline State: Ingenious Strategies for Modulating Third-Order NLO Signals.

Central metal exchange can innovatively open the cavity of metal-organic frameworks (MOFs) by alternating the framework topology. Here, the single-crystal-to-single-crystal (SC-SC) transformation is reported from a Co-based MOF {[Co1.25 (HL)0.5 (Pz-NH2 )0.25 (µ3 -O)0.25 (µ2 -OH)0.25 (H2 O)]·0.125 Co·0.125 L·10.25H2 O}n (Co-MOF, L = 5,5'-(1H-2,3,5-triazole-1,4-diyl)diisophthalic acid) into two novel MOF materials, {[Cu1.75 L0.75 (Pz-NH2 )0.125 (µ3 -O)0.125 (µ2 -OH)0.25 (H2 O)0.375 ]•3CH3 CN}n (Cu-MOF) and {[Zn1.75 L0.625 (Pz-NH2 )0.25 (µ3 -O)0.25 (µ2 -O)0.25 (H2 O)1.25 ]•4CH3 CN}n (Zn-MOF), through exchanging the Co2+ in the MOF into Cu2+ or Zn2+ , respectively. The free Co2+ and L4- in the Co-MOF channels fuse with the skeleton during the Co→Cu and Co→Zn exchange processes, leading to the expansion of the channel space and the transformation of the secondary building units (SBUs) to form an adjustable skeleton. The nonlinear optical response results show that the MOFs generated by the exchange of the central metal exhibit different saturable absorption and the self-focusing effect. In addition, loading polypyrrole (PPy) into the MOFs can not only improve the stability of the MOFs but also further optimize the nonlinear optical behavior. This work suggests that SC-SC central metal exchange and the introduction of polymer molecules can tune the nonlinear optical response, which provides a new perspective for the future study of nonlinear optical materials.

High-Efficiency Pure Blue Circularly Polarized Phosphorescence from Chiral N-Heterocyclic-Carbene-Stabilized Copper(I) Clusters.

Circularly polarized luminescence (CPL) materials have attracted considerable attention for their promising applications in encryption, chiral sensing, and three-dimensional (3D) displays. However, the preparation of high-efficiency, pure blue CPL materials remains challenging. In this study, we reported an enantiomeric pair of triangle copper(I) clusters (R/S-Cu3) rigidified by employing chiral N-heterocyclic carbene (NHC) ligands with two pyridine-functionalized wingtips. These chiral clusters emitted pure blue phosphorescence that overlapped with that of the commercial blue phosphor having Commission Internationale de l'Eclairage (CIE) chromaticity coordinates of (0.14, 0.10), and the films exhibited an unprecedented photoluminescence quantum yield (PLQY) of ∼70.0%. Additionally, the solutions showed very bright circularly polarized phosphorescence (CPP) with a dissymmetry factor of ±2.1 × 10-3. The excellent solubility and photostability endowed these pure-blue-emitting chiral clusters with promising applications as pure blue CPP inks for 3D printing white objects, such as precise-atomic-enlarged models of metal clusters and a lovely white stereoscopic "rabbit". The intricate mechanism underlying blue phosphorescence in this small cluster and across various states is elucidated through a comprehensive approach that integrates thorough analysis of luminescence properties, controlled experiments, and theoretical calculations. For the first time, we propose that the dominant high-energy emission center is constituted by delocalized hybrid orbitals over multiple atomic centers, encompassing both the metal and the coordinated atoms. This challenges stereotypical assumptions that the cluster center solely supports low-energy emissions. This work expands the currently limited range of CPP functional materials and provides a new direction for CPP applications involving NHC-stabilized metal clusters.

A study of impurities in the repurposed COVID-19 drug hydroxychloroquine sulfate using ultra-high-performance liquid chromatography-quadrupole/time-of-flight mass spectrometry and liquid chromatography-solid-phase extraction-nuclear magnetic resonance.

RATIONALE: Hydroxychloroquine sulfate is effective in the treatment of malaria and autoimmune diseases and as an antiviral drug. However, unreported impurities are often detected in this drug, which pose a health risk. In this study, the structures of hydroxychloroquine and six unknown impurities were analyzed using ultra-high-performance liquid chromatography-quadrupole/time-of-flight-tandem mass spectrometry (UHPLC-Q/TOF/MS/MS), and the structures were characterized using liquid chromatography-solid-phase extraction-nuclear magnetic resonance (LC-SPE-NMR) spectroscopy. METHODS: An Agilent InfinityLad Poroshell HPH-C18 column (100 × 4.6 mm, 2.7 µm) was used. For the analysis of hydroxychloroquine and six unknown impurities, the mobile phase was 20 mM ammonium formate aqueous solution and methanol/acetonitrile (80:20, v/v) using gradient elution. Full-scan MS and MS2 were performed to obtain as much structural information as possible. In addition, six unknown impurities were separated by semi-preparative liquid chromatography and characterized using LC-SPE-NMR. RESULTS: The MS2 fragmentation patterns of the impurities were investigated, leading to more structural information and an understanding of the fragmentation pathways of the impurities. The structures of the unknown impurities were confirmed using NMR. In addition, some possible pathways of the formation of the impurities in the drugs were outlined, and these impurities were found to be process impurities. CONCLUSIONS: Based on the identification and characterization of these impurities, this study also describes the cause of the production of the impurities and provides insights for companies to improve their production processes and a scientific basis for the improvement of the related pharmacopoeias.

Confinement inside a Crystalline Sponge Induces Pyrrole To Form N-H⋠⋠⋠π Bonded Tetramers.

Based on the DFT-level-calculated molecular volume (Vmol ) of pyrrole and its liquid density, pyrrole manifests the highest liquid density coefficient LDc (defined as [Vmol ×density ×0.6023]/FW) value of 0.7. Normal liquids have LDc <0.63. This very high LDc is due to the strong N-H⋅⋅⋅π interactions in solution, and hence pyrrole can be considered to be a pseudo-crystalline liquid. When trapped inside the confined space of a crystalline sponge, a reorientation of the N-H⋅⋅⋅π interaction is observed leading to specific cyclic N-H⋅⋅⋅π tetramers and N-H⋅⋅⋅π dimers, as verified by single-crystal X-ray crystallographic and computational methods. These tetramers are of the same size as four pyrrole molecules in the solid-state of pyrrole, yet the cyclic N-H⋅⋅⋅π intermolecular interactions are circularly oriented instead of being in the linear zigzag structure found in the X-ray structure of a solid pyrrole. The confinement thus acts as an external driving force for tetramer formation.

Postsynthetic-Modified PANI/MOF Composites with Tunable Thermoelectric and Photoelectric Properties.

A 3D Co-based metal-organic framework (Co-MOF) with two kinds of large pores filled by free Co2+ ions and ligands was synthesized and characterized. To expand the MOF structure and conductivity, the free Co2+ ions and ligands were exchanged by conductive ionic liquid EtpyBr and photosensitive AgNO3 through single crystal-to-single crystal transformation, which produced structure-changed 3D MOFs Co-MOF-Br and Co-Ag-MOF, which were characterized by single-crystal X-ray diffraction. Incorporating small quantities of doped polyaniline (PANI) with redox activity into the pores could further tune the stability and conductivity of the three MOFs. The PANI/MOFs all show outstanding electrical conductivity (≈10-2  S cm-1 ), and PANI/Co-MOF-Br has the largest p-type Seebeck coefficient of 66.6 µV K-1 . PANI/Co-MOF-Br and PANI/Co-Ag-MOF have 4 and 15 times higher photocurrent density compared with PANI/Co-MOF, respectively. This work sheds light on the design of advanced electrically conductive 3D MOFs.

Bringing a Molecular Plus One: Synergistic Binding Creates Guest-Mediated Three-Component Complexes.

Cethyl-2-methylresorcinarene (A), pyridine (B), and a set of 10 carboxylic acids (Cn) associate to form A·B·Cn ternary assemblies with 1:1:1 stoichiometry, representing a useful class of ternary systems where the guest mediates complex formation between the host and a third component. Although individually weak in solution, the combined strength of the multiple noncovalent interactions organizes the complexes even in a highly hydrogen-bond competing methanol solution, as explored by both experimental and computational methods. The interactions between A·B and Cn are dependent on the pKa values of carboxylic acids. The weak interactions between A and C further reinforce the interactions between A and B, demonstrating positive cooperativity. Our results reveal that the two-component system such as that formed by A and B can form the basis for the development of specific sensors for the molecular recognition of carboxylic acids.

Iodine Clathrated: A Solid-State Analogue of the Iodine-Starch Complex.

Co-crystallizing iodine with a simple dicationic salt (1,8-diammoniumoctane chloride) results in the clathration of the iodine (I2 ) molecules inside trigonal and hexagonal helical channels of the crystal lattice with 72 wt % overall I2 loading. The I2 inside the bigger trigonal channel forms a I-I⋅⋅⋅I-I⋅⋅⋅I-I halogen-bonded infinite helical chain, while the I2 in the smaller hexagonal channel is disordered. In both channels the I2 interaction with the channel wall happens through I-I⋅⋅⋅Cl- halogen bonds. The helical channels in the crystal lattice are constructed via the strong charge-assisted H2 N+ H⋅⋅⋅Cl- hydrogen bonds between the dications and the chloride anions. The structure shows a marked similarity with the well-known starch-I2 system, and thus may provide insight for the yet unresolved structure of the I2 in the helical starch channel.

Halogen Bonding in a Crystalline Sponge.

Host-guest interactions are the key to the supramolecular chemistry and the further application of the receptors to study the structural details of the small guest molecules. Crystalline sponges as a kind of supramolecular receptor need to be investigated in terms of the binding ability with the guests. We found in this work that one guest with σ-hole donors and another with electron-donating species were separately entrapped in two distinct channels of the host framework via the crystalline sponge method. Halogen bonding and weak hydrogen bonding were detected between the host and the two guests, respectively. The ability of the crystalline sponge to absorb and sort guests of different types was unambiguously confirmed by X-ray crystallography.

Cationic Iridium Complexes with 5-Phenyl-1H-1,2,4-triazole Type Cyclometalating Ligands: Toward Blue-Shifted Emission.

Four cationic iridium complexes with 5-phenyl-1H-1,2,4-triazole (phtz) type cyclometalating ligands (C^N) and different ancillary ligands (N^N), namely, [Ir(dphtz)2(bpy)]PF6 (1), [Ir(dphtz)2(pzpy)]PF6 (2), [Ir(Mephtz)2(pzpy)]PF6 (3), and [Ir(Mephtz)2(dma-pzpy)]PF6 (4), have been designed, synthesized, and fully characterized (dphtz = 1-(2,6-dimethylphenyl)-3-methyl-5-phenyl-1H-1,2,4-triazole, Mephtz = 1,3-dimethyl-5-phenyl-1H-1,2,4-triazole; bpy = 2,2'-bipyridine, pzpy = 2-(1H-pyrazol-1-yl)pyridine, dma-pzpy = 4-dimethylamino-2-(1H-pyrazol-1-yl) pyridine). In solution, complex 1 emits efficient yellow light (λmax = 547 nm), which is blue-shifted by nearly 40 nm (or by 1187 cm-1) compared with that from the archetypal complex [Ir(ppy)2(bpy)]PF6 (Hppy = 2-phenylpyridine), owing to the stabilization of the highest occupied molecular orbital by the phtz-type C^N ligand. In the lightly doped rigid films, complex 1 emits green light with a high luminescent efficiency of 0.89. Although complexes 2-4 with electron-rich N^N ligands are weakly emissive or nearly nonemissive in the solution, they emit relatively strong deep-blue light peaked around 435 and 461 nm in the lightly doped films, which is among the bluest reported for cationic iridium complexes. Theoretical calculations reveal that for complex 1, the emission always comes from the charge-transfer (CT) (Ir/C^N → N^N) state; for complexes 2 and 3, the 3CT and C^N-centered 3π-π* states lie close in energy and the emission could originate from either or both of them; for complex 4, the emission comes predominantly from the C^N-centered 3π-π* state. For blue-emitting complexes 2-4, metal-centered states play an active role in the nonradiative deactivation of the emitting triplet states. Solid-state light-emitting electrochemical cells (LECs) based on complexes 1-3 show yellow-green, blue, and blue-green electroluminescence, respectively, with the yellow-green LEC affording a peak current efficiency of 21.5 cd A-1.

A New Benzopyranyl Cadenane Sesquiterpene and Other Antiplasmodial and Cytotoxic Metabolites from Cleistochlamys kirkii.

Phytochemical investigations of ethanol root bark and stem bark extracts of Cleistochlamys kirkii (Benth.) Oliv. (Annonaceae) yielded a new benzopyranyl cadinane-type sesquiterpene (cleistonol, 1) alongside 12 known compounds (2-13). The structures of the isolated compounds were established from NMR spectroscopic and mass spectrometric analyses. Structures of compounds 5 and 10 were further confirmed by single crystal X-ray crystallographic analyses, which also established their absolute stereochemical configuration. The ethanolic crude extract of C. kirkii root bark gave 72% inhibition against the chloroquine-sensitive 3D7-strain malaria parasite Plasmodium falciparum at 0.01 µg/mL. The isolated metabolites dichamanetin, (E)-acetylmelodorinol, and cleistenolide showed IC50 = 9.3, 7.6 and 15.2 µM, respectively, against P. falciparum 3D7. Both the crude extract and the isolated compounds exhibited cytotoxicity against the triple-negative, aggressive breast cancer cell line, MDA-MB-231, with IC50 = 42.0 µg/mL (crude extract) and 9.6-30.7 µM (isolated compounds). Our findings demonstrate the potential applicability of C. kirkii as a source of antimalarial and anticancer agents.

Exploration of a Chiral Cobalt Catalyst for Visible-Light-Induced Enantioselective Radical Conjugate Addition.

Chiral catalysts tolerating photochemical reactions are in great demand for the vast development of visible-light-induced asymmetric synthesis. Now, chiral octahedral complexes based on earth-abundant metal and chiral N4 ligands are reported. One well-defined chiral CoII -complex is shown to be an efficient catalyst in the visible-light-induced conjugated addition of enones by alkyl and acyl radicals, providing synthetically valued chiral ketones and 1,4-dicarbonyls in 47->99 % yields with up to 97:3 e.r.

Discrete π-Stacks from Self-Assembled Perylenediimide Analogues.

The formation of well-defined finite-sized aggregates represents an attractive goal in supramolecular chemistry. In particular, construction of discrete π-stacked dye assemblies remains a challenge. Reported here is the design and synthesis of a novel type of discrete π-stacked aggregate from two comparable perylenediimide (PDI) dyads (PEP and PBP). The criss-cross PEP-PBP dimers in solution and (PBP-PEP)-(PEP-PBP) tetramers in the solid state are well elucidated using single-crystal X-ray diffraction, dynamic light scattering, and diffusion-ordered NMR spectroscopy. Extensive π-π stacking between the PDI units of PEP and PBP as well as repulsive interactions of swallow-tailed alkyl substituents are responsible for the selective formation of discrete dimer and tetramer stacks. Our results reveal a new approach to preparing discrete π stacks that are appealing for making assemblies with well-defined optoelectronic properties.

Halogen bonding and host-guest chemistry between N-alkylammonium resorcinarene halides, diiodoperfluorobutane and neutral guests.

Single crystal X-ray structures of halogen-bonded assemblies formed between host N-hexylammonium resorcinarene bromide (1) or N-cyclohexylammonium resorcinarene chloride (2), and 1,4-diiodooctafluorobutane and accompanying small solvent guests (methanol, acetonitrile and water) are presented. The guests' inclusion affects the geometry of the cavity of the receptors 1 and 2, while the divalent halogen bond donor 1,4-diiodooctafluorobutane determines the overall nature of the halogen bond assembly. The crystal lattice of 1 contains two structurally different dimeric assemblies A and B, formally resulting in the mixture of a capsular dimer and a dimeric pseudo-capsule. 1H and 19F NMR analyses supports the existence of these halogen-bonded complexes and enhanced guest inclusion in solution.

Binding Profiles of Self-Assembled Supramolecular Cages from ESI-MS Based Methodology.

Confined molecular environments have peculiar characteristics that make their properties unique in the field of biological and chemical sciences. In recent years, advances in supramolecular capsule and cage synthesis have presented the possibility to interpret the principles behind their self-assembly and functions, which has led to new molecular systems that display outstanding properties in molecular recognition and catalysis. Herein, we report a rapid method based on ESI-MS to determine the binding profiles for linear saturated dicarboxylic acids in a series of different cages. The cages were obtained by self-assembly of modified tris(pyridylmethyl)amine (TPMA) complexes and diamines chosen to explore variations in their size and flexibility. This methodology has provided information on how small changes in the structures of the host and guest can contribute to recognition events. Moreover, it was possible to study molecular systems that contain paramagnetic metals, which are not suitable for classical binding-constant determination by 1 H NMR spectroscopy.

Effect of quality control on the antiproliferative activity of the extract from Portulaca oleracea L. in Aspergillus flavus.

Similarity evaluation of complicated chromatographic profiles is a potential protocol for the identification and quality control of herbal medicinal products to ensure their biological activity. In this work, a high-performance liquid chromatography method was established for controlling the batch quality of the extract from Portulaca oleracea L. Using this method, the coefficients of correlation of the similarity of 10 batches extract of P. oleracea L. were ≥ 0.97. The 10 batch extracts from P. oleracea L. possessed stable antiproliferative activity in Aspergillus flavus. The antiproliferative activity stability is correlated with the stability quality of the of the extract from P. oleracea L. Therefore, the present study successfully set up a sensitive and efficient method which might be used to guarantee stable biological activity of the extract from P. oleracea L.

A conformationally adaptive macrocycle: conformational complexity and host-guest chemistry of zorb[4]arene.

Large amplitude conformational change is one of the features of biomolecular recognition and is also the basis for allosteric effects and signal transduction in functional biological systems. However, synthetic receptors with controllable conformational changes are rare. In this article, we present a thorough study on the host-guest chemistry of a conformationally adaptive macrocycle, namely per-O-ethoxyzorb[4]arene (ZB4). Similar to per-O-ethoxyoxatub[4]arene, ZB4 is capable of accommodating a wide range of organic cations. However, ZB4 does not show large amplitude conformational responses to the electronic substituents on the guests. Instead of a linear free-energy relationship, ZB4 follows a parabolic free-energy relationship. This is explained by invoking the influence of secondary C-H···O hydrogen bonds on the primary cation···π interactions based on the information obtained from four representative crystal structures. In addition, heat capacity changes (ΔCp) and enthalpy-entropy compensation phenomena both indicate that solvent reorganization is also involved during the binding. This research further deepens our understanding on the binding behavior of ZB4 and lays the basis for the construction of stimuli-responsive materials with ZB4 as a major component.

Electrocrystallization of Monolayer-Protected Gold Clusters: Opening the Door to Quality, Quantity, and New Structures.

Thiolate-protected metal clusters are materials of ever-growing importance in fundamental and applied research. Knowledge of their single-crystal X-ray structures has been instrumental to enable advanced molecular understanding of their intriguing properties. So far, however, a general, reliable, chemically clean approach to prepare single crystals suitable for accurate crystallographic analysis was missing. Here we show that single crystals of thiolate-protected clusters can be grown in large quantity and very high quality by electrocrystallization. This method relies on the fact that charged clusters display a higher solubility in polar solvents than their neutral counterparts. Nucleation of the electrogenerated insoluble clusters directly onto the electrode surface eventually leads to the formation of a dense forest of millimeter-long single crystals. Electrocrystallization of three known Au25(SR)180 clusters is described. A new cluster, Au25(S-nC5H11)18, was also prepared and found to crystallize by forming bundles of millimeter-long Au25 polymers.

Guest-Induced Folding and Self-Assembly of Conformationally Adaptive Macrocycles into Nanosheets and Nanotubes.

A conformationally adaptive macrocycle is presented, namely zorb[4]arene, which exists in multiple conformations in the uncomplexed state. The binding cavity of zorb[4]arene is concealed, either due to a collapsed conformation or by self-inclusion. The zorb[4]arene with long alkyl chains manifests itself with surprisingly low melting point and thus exist as an oil at room temperature. Binding of a guest molecule induces the folding and conformational rigidity of zorb[4]arene and leads to well-defined three-dimensional structures, which can further self-assemble into nanosheets or nanotubes upon solvent evaporation, depending on guest molecules and the conformations they can induce.

Recognition of Viologen Derivatives in Water by N-Alkyl Ammonium Resorcinarene Chlorides.

Three water-soluble N-alkyl ammonium resorcinarene chlorides decorated with terminal hydroxyl groups at the lower rims were synthesized and characterized. The receptors were decorated at the upper rim with either terminal hydroxyl, rigid cyclohexyl, or flexible benzyl groups. The binding affinities of these receptors toward three viologen derivatives, two of which possess an acetylmethyl group attached to one of the pyridine nitrogens, in water were investigated via 1H NMR spectroscopy, fluorescence spectroscopy, and isothermal titration calorimetry (ITC). ITC quantification of the binding process gave association constants of up to 103 M-1. Analyses reveal a spontaneous binding process which are all exothermic and are both enthalpy and entropy driven.

Isoflavones and Rotenoids from the Leaves of Millettia oblata ssp. teitensis.

A new isoflavone, 8-prenylmilldrone (1), and four new rotenoids, oblarotenoids A-D (2-5), along with nine known compounds (6-14), were isolated from the CH2Cl2/CH3OH (1:1) extract of the leaves of Millettia oblata ssp. teitensis by chromatographic separation. The purified compounds were identified by NMR spectroscopic and mass spectrometric analyses, whereas the absolute configurations of the rotenoids were established on the basis of chiroptical data and in some cases by single-crystal X-ray crystallography. Maximaisoflavone J (11) and oblarotenoid C (4) showed weak activity against the human breast cancer cell line MDA-MB-231 with IC50 values of 33.3 and 93.8 µM, respectively.