Prussian Blue Analogue Glasses for Photoinduced CO2 Conversion.

Crystal-to-glass transformation is a powerful approach to modulating the chemical and physical properties of crystals. Here we demonstrate that the glass transformation of cobalt hexacyanoferrate crystals, one of the Prussian blue analogues, increased the concentration of open metal sites and altered the electronic state while maintaining coordination geometries and short-range ordering in the structure. The compositional and structural changes were characterized by X-ray absorption fine structure, energy dispersive X-ray spectroscopy, and X-ray total scattering. The changes contribute to the flat band potential of the glass becoming closer to the redox potential of CO2 reduction. The valence band energy of the glass also shifts, resulting in lower band gap energy. Both the increased open metal sites and the optimal electronic structure upon vitrification enhance photocatalytic activity toward CO2-to-CO conversions (9.9 µmol h-1 CO production) and selectivity (72.4%) in comparison with the crystalline counterpart (3.9 µmol h-1 and 42.8%).

Photoexcited Anhydrous Proton Conductivity in Coordination Polymer Glass.

Optically switchable proton-conductive materials will enable the development of artificial ionic circuits. However, most switchable platforms rely on conformational changes in crystals to alter the connectivity of guest molecules. Guest dependency, low transmittance, and poor processability of polycrystalline materials hinder overall light responsiveness and contrast between on and off states. Here, we optically control anhydrous proton conductivity in a transparent coordination polymer (CP) glass. Photoexcitation of tris(bipyrazine)ruthenium(II) complex in CP glass causes reversible increases in proton conductivity by a factor of 181.9 and a decrease in activation energy barrier from 0.76 eV to 0.30 eV. Modulating light intensity and ambient temperature enables total control of anhydrous protonic conductivity. Spectroscopies and density functional theory studies reveal the relationship between the presence of proton deficiencies and the decreasing activation energy barrier for proton migrations.

Cassane diterpenoids with α-glucosidase inhibitory activity from the fruits of Pterolobium macropterum.

Two new cassane diterpenoids, 14ß-hydroxycassa-11(12),13(15)-dien-12,16-olide (1) and 6'-acetoxypterolobirin B (3), together with a known analogue, identified as 12α,14ß-dihydroxycassa-13(15)-en-12,16-olide (2), were isolated from the fruits of Pterolobium macropterum. Compound 1 is a cassane diterpenoid with a Δ11(12) double bond conjugated with an α,ß-butenolide-type, whereas compound 3 is a dimeric caged cassane diterpenoid with unique 6/6/6/6/6/5/6/6/6 nonacyclic ring system. The structures of 1 and 3 were characterized by extensive spectroscopic analysis combined with computational ECD analyses. The α-glucosidase inhibitory activity of isolated compounds was evaluated, and compounds 1 and 3 showed significant α-glucosidase inhibitory activity with IC50 values of 66 and 44 µM.

Bandgap Modulation in Zr-Based Metal-Organic Frameworks by Mixed-Linker Approach.

Metal-organic frameworks (MOFs) have been a promising material for many applications, e.g., photocatalysis, luminescence-based sensing, optoelectronics, and electrochemical devices, due to their tunable electronic properties through linker functionalization. In this work, we investigate the effect of mixed organic linkers on the bandgap modulation of polymorphic zirconium-based MOFs, UiO-66 and MIL-140A using density functional theory (DFT) calculations. We show that the electronic properties of both MOFs are in contrast to Vegard's law for semiconductors, that is, mixed-linker systems exhibit bandgaps not intermediate within the range of single-linker systems. Calculations of the total and partial density of states revealed the formation of mid-gap states in mixed-linker MOFs, causing the bandgap reduction. Interestingly, although both MOFs have similar composition, the effect is more significant in MIL-140A than in UiO-66. This is due to the presence of π-π stacking interactions in MIL-140A, which does not occur in UiO-66. The simulation results reveal a direct relationship between the strength of π-π interactions and the bandgap. This illustrates that distinct structural features, particularly the orientation of organic linkers can give rise to different consequences in bandgap modulation. Moreover, this computational work highlights the possibility to engineer the electronic properties of MOFs through a mixed-linker approach.

Biotransformation of 1α,11α-dihydroxyisopimara-8(14),15-diene by Cunninghamella echinulata NRRL 1386 and their neuroprotective activity.

The isopimarane diterpene, 1α,11α-dihydroxyisopimara-8(14),15-diene (1), is the major constituents from the rhizomes of Kaempferia marginata (Zingiberaceae), a Thai medicinal plant. The microbial transformation of parent compound 1 by the fungus Cunninghamella echinulata NRRL 1386 gave five new metabolites, 7α,11α-dihydroxy-1-oxoisopimara-8(14),15-diene (2), 3ß,7α,11α-trihydroxy-1-oxoisopimara-8(14),15-diene (3), 7ß,11α-dihydroxy-1-oxoisopimara-8(14),15-diene (4), 7α-hydroxy-1,11-dioxoisopimara-8(14),15-diene (5) and 1α,7ß,11α-trihydroxyisopimara-8(14),15-diene (6), together with three known metabolites, 7-9. The structures of the new metabolites were elucidated by spectroscopic techniques. The known compounds were identified by comparison of the spectroscopic and physical data with those of reported values. The parent compound 1 and the metabolites have been neuroprotective activities evaluated against Aß25-35-induced damage in human neuroblastoma cells (SK-N-SH). Among them, compounds 1-3, 5 and 7-9 had significant neuroprotective activities at a concentration of 2.5 µM. The results demonstrated that these compounds might be worth for further development into therapeutic agents for the treatment of neurodegenerative diseases.

Isopimarane Diterpenoids from the Rhizomes of Kaempferia marginata and Their Potential Anti-inflammatory Activities.

Six new isopimarane diterpenes, marginaols A-F (1-6), along with eight known compounds (7-14), were isolated from the rhizomes of Kaempferia marginata. The structures and absolute configurations of 1-6 were established on the basis of spectroscopic methods and the experimental and calculated ECD data as well as comparison with the literature values. Most of the isolated compounds were tested for their nitric oxide (NO) inhibitory effects in lipopolysaccharide-activated RAW264.7 cells. Among them, marginaol B (2) was found to reduce NO levels in murine macrophage cells with an IC50 value of 28.1 ± 1.7 µM.

A proton transfer mechanism along the PO4 anion chain in the [Zn(HPO4)(H2PO4)]2- coordination polymer.

In this study, we revisit the proton transfer mechanism in [Zn(HPO4)(H2PO4)]2-, a coordination polymer possessing high proton conductivity. In a previous report [N. Phattharasupakun, J. Wutthiprom, S. Kaenket, Th. Maihom, J. Limtrakul, M. Probst, S. S. Nagarkar, S. Horike and M. Sawangphruk, Chem. Commun., 2017, 53, 11786-11789], it was hypothesized that protons could move along the ImH+ chain involving phosphate anions within the polymer structure, with energy barriers >1.3 eV. Adopting M06-2X calculations to examine the reaction pathway, we observe that it is much more favorable for H+ to move along a one-dimensional channel formed by HPO42- and H2PO4- anions. Within a unit cell, the proton hopping process can be divided into three elementary steps. For the forward proton transfer direction, the maximum energy barrier is only 0.04 eV, while that of the backward direction is 0.27 eV. Even though the barriers of the backward direction seem to outreach the barriers of the forward direction, both are still low in comparison with those reported in the literature. Moreover, we also point out the involvement of PO4 rotation during the proton transfer process. Activation energies of 0.37 eV and 0.15 eV are required for single steps of rotation of the phosphate anion. Both H+ translation (hopping) and rotation steps of PO4 anions simultaneously participate in the course of proton transfer in the coordination polymer.

Adsorption-Induced Dye Stability of Cationic Dyes on Clay Nanosheets.

Rhodamine 6G (R6G) was adsorbed on smectite clays, a natural montmorillonite, a synthetic saponite, and synthetic hectorites, and the decolorization of the dyes upon visible light irradiation was examined for aqueous suspensions and cast films. Excellent dye stability was achieved when a natural montmorillonite was used. Apart from R6G, better photostability was also achieved when the tris(2,2'-bipyridine)ruthenium(II) complex was adsorbed on a natural montmorillonite. The excited state of the dye was quenched efficiently by the impurities in the natural montmorillonite. From the relationship between the excited-state quenching (as derived from photoluminescence quantum efficiency and photoluminescence intensity) and the decolorization rate constant, the quenching of the excited state of the dye adsorbed on the natural montmorillonite was proposed as the important mechanism for the stabilization of dyes upon photoirradiation.

Lanthanide Coordination Polymers of Mixed Phthalate/Adipate for Ratiometric Temperature Sensing in the Upper-Intermediate Temperature Range.

Based on the mixed phthalate (phth2-) and adipate (ad2-), [Nd2(ad)(phth)2(H2O)4] (I) and [Ln(ad)0.5(phth)(H2O)2] (Ln = EuIII (II), GdIII (III), TbIII (IV), DyIII (V), ErIII (VI), TmIII (VII), 1EuIII:10TbIII (VIII), 3EuIII:10TbIII (IX), and 5EuIII:10TbIII (X)) were synthesized and characterized. Complexes VIII-X show excellent ratiometric temperature sensing behavior in physiological and higher temperature ranges (303-423 K) rendered by the TbIII-to-EuIII energy transfer process. The efficiency of the process as illustrated through the lifetime measurements depends on both the EuIII:TbIII mole ratio and the temperature. The performance of X in terms of relative sensitivity ( Sr), temperature resolution, and measurement repeatability were determined, revealing the maximum Sr ( Sm) of 1.21%·K-1 at 303 K with reliable temperature resolution and excellent repeatability.

Polymerization of ε-Caprolactone Using Bis(phenoxy)-amine Aluminum Complex: Deactivation by Lactide.

Polymerizations of biodegradable lactide and lactones have been the subjects of intense research during the past decade. They can be polymerized/copolymerized effectively by several catalyst systems. With bis(phenolate)-amine aluminum complex, we have shown for the first time that lactide monomer can deactivate the aluminum complex during the ongoing polymerization of ε-caprolactone to a complete stop. After hours of dormant state, the aluminum complex can be reactivated again by heating at 100 °C without the addition of any external chemicals still giving polymer with narrow dispersity. Studies using NMR, in situ FTIR, and single-crystal X-ray crystallography indicated that the coordination of the carbonyl group in lactyl unit was responsible for the unusual behavior of lactide. In addition, the unusual methyl-migration from methyl lactate ligand to the amine side chain of the aluminum complex was observed through intermolecular nucleophilic-attack mechanism.

Unsaturated Mn(II)-Centered [Mn(BDC)] n Metal-Organic Framework with Strong Water Binding Ability and Its Potential for Dehydration of an Ethanol/Water Mixture.

An unsaturated Mn(II)-centered metal-organic framework was synthesized. The presence of an unsaturated Mn(II) center, together with a guest-responsive structural changing feature, plays a crucial role for strong binding with water, leading to its potential application for water/ethanol separation. In addition, the present framework is thermally stable up to 400 °C, which is beneficial for the regeneration process after adsorption.

Efficient Concentration of Indium(III) from Aqueous Solution Using Layered Silicates.

A synthetic layered alkali silicate, magadiite, and a natural montmorillite were found to concentrate indium(III) ion from aqueous solution by ion exchange reactions. The adsorption was examined by the reaction between silicates and aqueous solution of indium(III) chloride of different concentration at room temperature for 10 min. The adsorption isotherms were H type, indicating strong interactions between the silicates and indium(III) ion. The maximum adsorbed indium(III) amount for magadiite was quite high, ca. 0.70 mmol/g silicate, which corresponded to 96% of the ideal cation exchange capacity of magadiite derived from the chemical formula of Na2Si14O29. In addition, the selectivity of the indium was very high, and efficient adsorption of indium was observed from the sodium chloride solutions and the solutions containing zinc, nickel, and copper. The large adsorption capacity, high selectivity of indium, and short reaction time (10 min at room temperature) make the adsorption on magadiite useful for the concentration of indium(III) ion from aqueous environments.

Size-Controlled Synthesis of Anatase in a Mesoporous Silica, SBA-15.

The preparation of anatase in the cylindrical mesopore of SBA-15 (pore size of 8 nm) was done by the impregnation of tetraisopropyl orthotitanate and its subsequent crystallization. The impregnation was done without a solvent. Hydrolysis and condensation were promoted by the HCl vapor to encapsulate a larger amount of titanium oxo species in the mesopore and to suppress the desorption of the titanium oxo species during crystallization to anatase. After the reaction, the shape of the N2 adsorption isotherm changed significantly, indicating the decrease of the Brunauer-Emmett-Teller surface area from 743 to 283 m2/g and of the pore volume from 1.27 to 0.26 cm3/g, respectively. After the crystallization to anatase, the TiO2 content in the product was estimated to be 62 mass %, filling 30% of the pore volume of SBA-15. The homogeneous distribution of titanium in the SBA-15 sample was confirmed by elemental mapping based on scanning electron microscopy/energy-dispersive X-ray spectrometry. The crystal size of the anatase was determined to be ca. 8.1 nm, which is consistent with the pore size of the used SBA-15 (8.0 nm, derived from the Barrett-Joyner-Halenda analysis of the nitrogen adsorption isotherm). The zeta potential measurements showed the absence of anatase as isolated particles or on the surface of SBA-15 particles. All of these characterizations confirmed the successful size-controlled synthesis of anatase in the mesopore of SBA-15.

Synthesis of Manganese ZIF-8 from [Mn(BH4)2·3THF]·NaBH4.

Cubic and highly porous [Mn(2-methylimidazolate)2] (Mn-ZIF-8) was synthesized from [Mn(BH4)2·3THF]·NaBH4 under an Ar atmosphere. The structure contains rare Mn2+-4N tetrahedral geometry and has larger cell parameters, resulting in 20% larger amounts of gas uptake compared with [Zn(2-methylimidazolate)2]. A kinetically favored reaction using a reactive metal borohydride precursor is key for the construction of new metal-organic framework systems.

Ethane C-H bond activation on the Fe(iv)-oxo species in a Zn-based cluster of metal-organic frameworks: a density functional theory study.

We first investigate the feasibility of designing a Fe-oxo complex for the activation of alkane C-H bonds by (a) incorporating an Fe ion into a Zn-based cluster derived from a metal-organic framework (MOF) and (b) creating the Fe-oxo complex via decomposition of N2O over a Fe2+-substituted Zn-based cluster (Fe-Zn3O(pyrazole)6). From the energy profile, it turns out that both steps should be feasible and that the resulting Fe-oxo complex is stable. In the main step, we then investigate the reactivity of this Fe-oxo cluster for the C-H bond cleavage of ethane by calculating the reaction energy profile and analyzing the electronic structure along the relevant steps. Two mechanisms, namely the σ and π pathways on the triplet and quintet potential energy surfaces, were unraveled for this study of catalytic activity. It is shown that the σ pathway on the quintet surface is kinetically and thermodynamically favorable with an energy barrier of 22.5 kcal mol-1. The π pathway on the quintet and triplet surfaces has activation energies of 26.9 kcal mol-1 and 24.9 kcal mol-1, respectively. An alternative unusual pathway called the δ mechanism on the triplet surface is also observed with an energy barrier of 12.6 kcal mol-1. It is, however, thermodynamically at a disadvantage compared to the σ pathway on the quintet surface. Favorable d-d interaction on the Fe center and less steric hindrance from the equatorial ligands at the transition state are the key factors that cause the σ pathway on the quintet surface to have the lowest activation energy. All our calculations are of the cluster type and have been performed at the B3LYP-D3/def2-TZVP level of theory.

Almost enclosed buckyball joints: synthesis, complex formation, and computational simulations of pentypticene-extended tribenzotriquinacene.

We report the synthesis of a tribenzotriquinacene-based (TBTQ) receptor (3) for C60 fullerene, which is extended by pentiptycene moieties to provide an almost enclosed concave ball bearing. The system serves as a model for a self-assembling molecular rotor with a flexible and adapting stator. Unexpectedly, nuclear magnetic resonance spectroscopic investigations reveal a surprisingly low complex stability constant of K1 =213±37 M(-1) for [C60 ⊂3], seemingly inconsistent with the previously reported TBTQ systems. Molecular dynamics (MD) simulations have been conducted for three different [C60 ⊂TBTQ] complexes to resolve this. Because of the dominating dispersive interactions, the binding energies increase with the contact area between guest and host, however, only for rigid host structures. By means of free-energy calculations with an explicit solvent model it can be shown that the novel flexible TBTQ receptor 3 binds weakly because of hampering entropic contributions.

Valorizing natural-abundant glucose to lactic acid using a MOF-808 catalyst under green hydrothermal conditions.

Highly robust Zr-based MOF-808, featuring Lewis acid Zr sites and coordinate hydroxide ions upon the removal of the monocarboxylate capping reagent, emerges as an efficient catalyst for the hydrothermal conversion of glucose into lactic acid. A remarkable 99% glucose conversion with an impressive 76.6% yield of lactic acid can be achieved. The large pore window of MOF-808 facilitates the diffusion of glucose to the active sites within the framework. The single-site attribute of the catalytic center enables a high selectivity of lactic acid over the competitive product, 5-(hydroxymethyl)furfural, under hydrothermal reaction conditions.

Co-based metal-organic framework for photocatalytic hydrogen generation.

Hydrogen production through an artificial photocatalytic process in the solar light region using a water-stable Co-Tz (Tz = 1,2,4-triazolate) framework was demonstrated. Possessing such a high photostability and highly reactive sites at the tetrahedral cobalt centers, Co-Tz exhibits a great photocatalytic performance converting water into hydrogen of 9.32 mmol g-1 at 4 h in the presence of fluorescein (FI) and triethylamine (TEA) as a photosensitizer and sacrificial agent, respectively. In addition, the framework is reusable without losing its catalytical integrity.

Separation of Etiracetam Enantiomers Using Enantiospecific Cocrystallization with 2-Chloromandelic Acid.

Chirality plays an important role in the pharmaceutical industry since the two enantiomers of a drug molecule usually display significantly different bioactivities, and hence, most products are produced as pure enantiomers. However, many drug precursors are synthesized as racemates, and hence, enantioseparation has become a significant process in the industry. Cocrystallization is one of the attractive crystallization approaches to obtain the desired enantiomer from racemic compounds. In this work, we propose a chiral resolution route for an antiepileptic drug, S-etiracetam (S-ETI), via enantiospecific cocrystallization with S-2-chloro-S-mandelic acid (CLMA) as a coformer. The experiments indicate that the system is highly enantiospecific; S-2CLMA cocrystallizes only with S-ETI but not with R-ETI or RS-ETI. Therefore, the chiral purification of S-ETI can be achieved efficiently with a 69.1% yield and close to 100% enantiopurity from the racemic solution. Additionally, structural simulations of the S-ETI:S-2CLMA cocrystal reveal that the cocrystal structure has higher thermodynamic stability than that of R-ETI:S-2CLMA by about 5.5 kcal/mol (per cocrystal formula unit), which helps to confirm the favorability of the enantiospecification in this system.

Conductive Co-triazole metal-organic framework exploited as an oxygen evolution electrocatalyst.

A Co-triazole metal-organic framework (Co-trz) endowed with electrical conductivity was synthesized effortlessly via a microwave-based method. Providing a high density of catalytic centers with electrically conductive features, as suggested by DFT calculations, the framework exhibited a low overpotential for the oxygen evolution reaction (OER) with good kinetics. A mechanistic reaction pathway was proposed based on monitoring alterations in the oxidation state and local coordination environment of Co centers upon the occurrence of the OER. Due to its performance and its chemical and electrochemical robustness, the framework was highlighted as a promising MOF electrocatalyst for the OER.