In situ monitoring of mechanochemical MOF formation by NMR relaxation time correlation.

In this paper, we present a new approach to monitoring mechanochemical transformations, based on a magnetic resonance (MR) method in which relaxation time correlation maps are used to track the formation of the popular metal-organic framework (MOF) materials Zn-MOF-74 and ZIF-8. The two-dimensional (2D) relaxation correlation measurement employed yields a spectrum which visually and analytically identifies different 1H environments in the sample of interest. The measurement is well-suited to analyzing solid mixtures, and liquids, in complex systems. Application in this work to monitoring MOF formation shows changes in signal amplitudes, and their MR lifetime coordinates, within the 2D plots as the reaction progresses, confirming reaction completion. This new measurement provides a simple way to analyse solid-state reactions without dissolution, and there is a logical pathway to benchtop measurement with a new generation of permanent magnet-based MR instruments. The methodology described permits measurement in an MR compatible milling container, which may be directly transferred from the shaker assembly to the MR magnet for in situ measurement of the entire reaction mixture.

High-yielding synthesis of cyclometallated iridium complexes with hydrogen bond-rich ligands.

A library of cyclometallated iridium(III) complexes with a strong H-bonding motif in their ancillary ligand was synthesized, characterized and their photophysical properties measured. Demonstrated herein is a general synthetic high yield procedure for these compounds. We ascribe these yields to the use of an intermediary primer ligand. This de novo strategy circumnavigates the standard synthetic issues of H-bond rich ligand precursors (self-aggregation and poor solubility in organic solvents).

Elucidation of Charge Contribution in Iridium-Chelated Hydrogen-Bonding Systems.

We present two iridium complexes 1H + and 2H + that contain cationic ligands to extend the knowledge of charge-assisted hydrogen bonding (CAHB), which counts among the strongest non-covalent bonding interactions. Upon protonation, both complexes were converted into new hydrogen-bonding arrays with various selectivity for respective H-bonding partners. This study compares the association strengths of four hydrogen-bonding co-systems, emphasizing the roles of CAHB in supramolecular systems. We determined that the cationic charge in these systems contributed up to 2.7 kJ mol-1 in the H-bonding complexation processes.

Immobilising giant unilamellar vesicles with zirconium metal-organic framework anchors.

Lipid bilayer vesicles have provided a window into the function and fundamental properties of cells. However, as is the case for most living and soft matter, vesicles do not remain still. This necessitates some microscopy experiments to include a preparatory immobilisation step. Here, we describe a straightforward method to immobilise giant unilamellar vesicles (GUVs) using zirconium-based metal-organic frameworks (MOFs) and demonstrate that GUVs bound in this way will stay in position on a timescale of minutes to hours.

Swell and Destroy: A Metal-Organic Framework-Containing Polymer Sponge That Immobilizes and Catalytically Degrades Nerve Agents.

Organophosphorus chemical warfare agents function as potent neurotoxins. Whilst the destruction of nerve agents is most readily achieved by hydrolysis, their storage and transport are hazardous and lethal in milligram doses, with any spillage resulting in fatalities. Furthermore, current decontamination and remediation measures are limited by a need for stoichiometric reagents, solvents, and buffered solutions, complicating the process for the treatment of bulk contaminants. Herein, we report a composite polymer material capable of rendering bulk VX unusable by immobilization within a porous polymer until a metal-organic framework (MOF) catalyst fully hydrolyzes the neurotoxin. This is an all-in-one capability that minimizes the use of multiple reagents, facilitated by a porous high internal phase emulsion-based polystyrene monolith housing an active zirconia MOF catalyst (MOF-808); the porous polymer absorbs and immobilizes the liquid agents, while the MOF enables hydrolysis. The dichotomous hierarchy of porous materials facilitates the containment and rapid hydrolysis of VX (>80% degradation in 8 h) in the presence of excess H2O. This composite can further enable the hydrolysis of neat VX with reliance on ambient humidity (>95% in 11 days). Potentially, 4.5 kg of the composite can absorb, immobilize, and degrade the contents of a standard chemical drum/barrel (208 L, 55 gal) of the chemical warfare agent (CWA). We believe that this composite is the first example of what will be the go-to approach for CWA immobilization and degradation in the future. Furthermore, we believe that this demonstration of a catalytically reusable absorbent sponge provides a signpost for the development of similar materials where immobilization of a substrate in a catalytically active environment is desirable.

A pH-Switchable Triple Hydrogen-Bonding Motif.

A stimuli responsive linear hydrogen bonding motif, capable of in situ protonation and deprotonation, has been investigated. The interactions of the responsive hydrogen bonding motif with complementary partners were examined through a series of 1H NMR experiments, revealing that the recognition preference of the responsive hydrogen bonding motif in a mixture can be switched between two states.

Thiourea and Guanidine Compounds and Their Iridium Complexes in Drug-Resistant Cancer Cell Lines: Structure-Activity Relationships and Direct Luminescent Imaging.

Thiourea and guanidine units are found in nature, medicine, and materials. Their continued exploration in applications as diverse as cancer therapy, sensors, and electronics means that their toxicity is an important consideration. Iridium complexes present new opportunities for drug development and imaging in terms of structure and photoactivity. We have systematically synthesised a set of thiourea and guanidine compounds and iridium complexes thereof, and elucidated structure-activity relationships for cellular toxicity in three ovarian cancer cell lines and their cisplatin-resistant sub-lines. We have been able to use the intrinsic luminescence of iridium complexes to visualise the effect of both structure alteration and cellular resistance mechanisms. These findings provide starting points for the development of new drugs and consideration of safety issues for novel thiourea-, guanidine-, and iridium-based materials.

Structures, Phase Behavior, and Fluorescent Properties of 3-Phenyl-1-(pyridin-2-yl)-1H-pyrazol-5-amine and Its ZnCl2 Complex.

The synthesis of the asymmetric ligand 3-phenyl-1-(pyridin-2-yl)-1H-pyrazol-5-amine (L1) and its single-crystal X-ray structure are reported. L1 displays crystallographic symmetry (orthorhombic, Pccn) higher than its molecular symmetry (point group C1) and also displays supercooling, with a difference in the melting and solidification points of over 100 °C. Upon complexation with ZnCl2, L1 engages in both primary cation and secondary anion coordination via hydrogen bonding, and the complex exhibits a room-to-low-temperature single crystal-to-crystal phase transition. The ZnCl2 complex becomes a birefringent fluid mixed with crystalline domains at high temperatures, as detected by polarized optical microscopy. Examination of the photoluminescence properties showed that the emission intensity increased and a pronounced bathochromic shift was observed in the emission maximum upon going from solution to the solid state, for both the ligand and complex, consistent with aggregation-induced emission behavior.

Influencing the Optoelectronic Properties of a Heteroleptic Iridium Complex by Second-Sphere H-Bonding Interactions.

The use of a new second-sphere coordination methodology for emission color tuning of iridium complexes is presented. We demonstrate that a complementary H-bonding guest molecule binding through contiguous triple H-bonding interactions can induce a shift in the emission of the iridium complex from green to blue without the need to alter the ligand structure around the metal center, while simultaneously increasing the photoluminescence quantum yield in solution. The association constant for this host-guest interaction was determined to be Ka = 4.3 × 103 M-1 in a solution of 2% dimethyl sulfoxide in chloroform by UV-vis titration analysis and the impact of the hydrogen bonding interaction further probed by photoluminescence, electrochemical, and computational methods. Our findings suggest that directed self-assemblies are an effective approach to influencing emission properties of phosphorescent iridium(III) complexes.

Poly High Internal Phase Emulsion for the Immobilization of Chemical Warfare Agents.

We report a facile method for the absorption (characterized by the weight/weight swelling degree, Q) of a variety of chemical warfare agents (CWAs); including sulfur mustard (HD) (Q = 40) and V-series (VM, VX, i-Bu-VX, n-Bu-VX) of nerve agents (Q ≥ 45) and a simulant, methyl benzoate (Q = 55), through the use of a poly(styrene-co-vinyl benzyl chloride-co-divinylbenzene) lightly cross-linked poly high internal phase emulsion (polyHIPE). By varying the vinyl benzyl chloride (VBC) content and the volume of the internal phase of the precursor emulsion it is demonstrated that absorption is facilitated both by the swelling of the polymer and the uptake of liquid in the pores. In particular the sample prepared from a 95% internal emulsion water content showed rapid swelling (<5 min to total absorption) and the ability to swell both from a monolithic state and from a compressed state, making these systems ideal practical candidates for the rapid immobilization of CWAs.

Functional Versatility of a Series of Zr Metal-Organic Frameworks Probed by Solid-State Photoluminescence Spectroscopy.

Many of the desirable properties of metal-organic frameworks (MOFs) can be tuned by chemical functionalization of the organic ligands that connect their metal clusters into multidimensional network solids. When these linker molecules are intrinsically fluorescent, they can pass on this property to the resultant MOF, potentially generating solid-state sensors, as analytes can be bound within their porous interiors. Herein, we report the synthesis of a series of 14 interpenetrated Zr and Hf MOFs linked by functionalized 4,4'-[1,4-phenylene-bis(ethyne-2,1-diyl)]-dibenzoate (peb2-) ligands, and we analyze the effect of functional group incorporation on their structures and properties. Addition of methyl, fluoro, naphthyl, and benzothiadiazolyl units does not affect the underlying topology, but induces subtle structural changes, such as ligand rotation, and mediates host-guest interactions. Further, we demonstrate that solid-state photoluminescence spectroscopy can be used to probe these effects. For instance, introduction of naphthyl and benzothiadiazolyl units yields MOFs that can act as stable fluorescent water sensors, a dimethyl modified MOF exhibits a temperature dependent phase change controlled by steric clashes between interpenetrated nets, and a tetrafluorinated analogue is found to be superhydrophobic despite only partial fluorination of its organic backbone. These subtle changes in ligand structure coupled with the consistent framework topology give rise to a series of MOFs with a remarkable range of physical properties that are not observed with the ligands alone.

ABCB1 as predominant resistance mechanism in cells with acquired SNS-032 resistance.

The CDK inhibitor SNS-032 had previously exerted promising anti-neuroblastoma activity via CDK7 and 9 inhibition. ABCB1 expression was identified as major determinant of SNS-032 resistance. Here, we investigated the role of ABCB1 in acquired SNS-032 resistance. In contrast to ABCB1-expressing UKF-NB-3 sub-lines resistant to other ABCB1 substrates, SNS-032-adapted UKF-NB-3 (UKF-NB-3rSNS- 032300nM) cells remained sensitive to the non-ABCB1 substrate cisplatin and were completely re-sensitized to cytotoxic ABCB1 substrates by ABCB1 inhibition. Moreover, UKF-NB-3rSNS-032300nM cells remained similarly sensitive to CDK7 and 9 inhibition as UKF-NB-3 cells. In contrast, SHEPrSNS-0322000nM, the SNS-032-resistant sub-line of the neuroblastoma cell line SHEP, displayed low level SNS-032 resistance also when ABCB1 was inhibited. This discrepancy may be explained by the higher SNS-032 concentrations that were used to establish SHEPrSNS-0322000nM cells, since SHEP cells intrinsically express ABCB1 and are less sensitive to SNS-032 (IC50 912 nM) than UKF-NB-3 cells (IC50 153 nM). In conclusion, we show that ABCB1 expression represents the primary (sometimes exclusive) resistance mechanism in neuroblastoma cells with acquired resistance to SNS-032. Thus, ABCB1 inhibitors may increase the SNS-032 efficacy in ABCB1-expressing cells and prolong or avoid resistance formation.

Sensitizing Tb(III) and Eu(III) emission with triarylboron functionalized 1,3-diketonato ligands.

Four BMes2Ar (Mes = mesityl, Ar = phenyl or duryl) functionalized 1,3-diketonato ligands have been investigated for use in selective sensitization of Tb(III) and Eu(III) emission. These ligands have the general formula of [R1C(O)CR2C(O)R3](-) (R1 = Ph, R2 = H, R3 = p-Ph-BMes2, L1; R1 = R3 = p-Ph-BMes2, R2 = H, L2; R1 = R3 = Me, R2 = p-Ph-BMes2, L3; R1 = R3 = Me, R2 = p-duryl-BMes2, L4) and belong to class I (L1 and L2) and class II (L3 and L4), respectively. In class I, the boron unit is conjugated with the phenyl linker and the diketone backbone, while in class II, the boron unit, the linker unit, and the diketone unit are nonconjugated with a mutually orthogonal arrangement. To understand the impact of the location of the BMes2Ar unit on the electronic properties of the 1,3-diketone molecules and their ability in activating lanthanide emission, the difluoroboron chelate compounds (1-BF2 to 4-BF2) of ligands L1-L4 were synthesized and examined. The class I ligands were effective in activating Eu(III) emission, while the class II ligands were effective in activating Tb(III) emission. Four Ln(III) complexes, 1Eu, 2Eu, 3Tb, and 4Tb, based on the L1-L4 ligands, respectively, were prepared and examined. The emission quantum efficiency of 1Eu and 2Eu is low (Φ(Eu) ≤ 0.01 in THF, 0.07-0.13 in the solid state), but can be greatly enhanced by the addition of fluoride ions. In contrast, the complex 4Tb has a moderate emission efficiency (Φ(Tb) = 0.14 in THF, 0.47 in the solid state) and experiences a distinct emission quenching upon the addition of fluoride. The selective sensitization of Eu(III) and Tb(III) by L1-L4 and the distinct luminescent response of their Ln(III) complexes toward fluoride ions are caused by the distinct intraligand charge transfer transitions of the two different classes of ligands involving the BMes2 unit.

Toward metal complexes that can directionally walk along tracks: controlled stepping of a molecular biped with a palladium(II) foot.

We report on the design, synthesis, and operation of a bimetallic molecular biped on a three-foothold track. The "walker" features a palladium(II) complex "foot" that can be selectively stepped between 4-dimethylaminopyridine and pyridine ligand sites on the track via reversible protonation while the walker remains attached to the track throughout by means of a kinetically inert platinum(II) complex foot. The substitution pattern of the three ligand binding sites, together with the kinetic stability of the metal-ligand coordination bonds, affords the two positional isomers a high degree of metastability, meaning that altering the chemical state of the track does not automatically instigate stepping in the absence of an additional stimulus (heat in the presence of a coordinating solvent). The use of metastable metal complexes for foot-track interactions offers a promising alternative to dynamic covalent chemistry for the design of small-molecule synthetic molecular walkers.

Triarylboryl-functionalized dibenzoylmethane and its phosphorescent platinum(II) complexes.

An acetylacetonato derivative ligand, dibenzoylmethane (dbm), has been functionalized with a dimesitylboryl group. Phosphorescent N^C-chelate Pt(II) compounds with the new molecule as an ancillary ligand have been achieved and used as effective turn-on phosphorescent sensors for fluoride ions under air.

Luminescent triarylboron-functionalized zinc carboxylate metal-organic framework.

A luminescent triarylboron ligand functionalized with three carboxylic groups has been synthesized and fully characterized. Its use in boron-containing metal-organic frameworks (B-MOFs) has been demonstrated by the synthesis and isolation of a Zn(II)B-MOF compound (B-MOF-1). The crystals of B-MOF-1 belong to the cubic space group F432 with 8-fold interpenetrated networks and ∼21% void space. B-MOF-1 exhibits blue fluorescence and is capable of modest gas sorption of N(2), argon, and CO(2).

Selective activation of lanthanide luminescence with triarylboron-functionalized ligands and visual fluoride indicators.

Two triarylboron-functionalized carboxylate ligands have been found to be highly effective in selective activation of Tb(III) and Eu(III) emission and enable the use of the Tb(III) and Eu(III) complexes as highly effective luminescent indicators for F(-) and CN(-) in solution and on a solid substrate.

Efficient and high yield one-pot synthesis of cyclometalated platinum(II) ß-diketonates at ambient temperature.

Cyclometalated Pt(II) ß-diketonates are widely used as efficient luminescent materials but are typically prepared at high temperatures in low yields using excess reagents. A one-pot synthesis of these complexes is described employing stoichiometric reagents and short reaction times at ambient temperature, giving yields of up to 94%. The method is applicable to a broad range of substrates including N^C, P^C, and C^C chelate Pt(II) complexes and different ß-diketonate ligands.

Triarylboron-functionalized Cu(II) carboxylate paddlewheel complexes.

The assembly of two copper(II)-carboxylate dimer complexes appended with four peripheral triarylborane functionalities has been achieved. Complex stabilities in the presence of fluoride are examined.