Role of Metal-Organic Framework Topology on Thermodynamics of Polyoxometalate Encapsulation.

Polyoxometalates (POMs) are discrete anionic clusters whose rich redox properties, strong BroÌ·nsted acidity, and high availability of active sites make them potent catalysts for oxidation reactions. Metal-organic frameworks (MOFs) have emerged as tunable, porous platforms to immobilize POMs, thus increasing their solution stability and catalytic activity. While POM@MOF composite materials have been widely used for a variety of applications, little is known about the thermodynamics of the encapsulation process. Here, we utilize an up-and-coming technique in the field of heterogeneous materials, isothermal titration calorimetry (ITC), to obtain full thermodynamic profiles (ΔH, ΔS, ΔG, and Ka) of POM binding. Six different 8-connected hexanuclear Zr-MOFs were investigated to determine the impact of MOF topology (csq, scu, and the) on POM encapsulation thermodynamics.

Separation of Aromatic Hydrocarbons in Porous Materials.

Industrial-scale thermal separation processes have contributed greatly to the rise in carbon dioxide emissions. Porous materials, such as metal-organic frameworks (MOFs), can potentially reduce these emissions by achieving nonthermal chemical separations through the physical adsorption of targeted species with high selectivity. Here, we report the synthesis of the channel-based MOFs NU-2000 and NU-2001, which are constructed from three-dimensional (3D) linkers, to separate the industrially relevant xylene isomers under ambient conditions by leveraging sub-Ångstrom differences in the sizes of each isomer. While the rotation of two-dimensional (2D) linkers in MOFs often affords changes in pore apertures and pore sizes that are substantial enough to hinder separation efficiency, increasing the linker dimensionality from 2D to three-dimensional (3D) enables precise control of the MOF pore size and aperture regardless of the linker orientation, establishing this design principle as a broadly applicable strategy.

Leveraging Isothermal Titration Calorimetry to Explore Structure-Property Relationships of Protein Immobilization in Metal-Organic Frameworks.

Proteins immobilized in metal-organic frameworks (MOFs) often show extraordinary stability. However, most efforts to immobilize proteins in MOFs have only been exploratory. Herein, we present the first systematic study on the thermodynamics of protein immobilization in MOFs. Using insulin as a probe, we leveraged isothermal titration calorimetry (ITC) to investigate how topology, pore size, and hydrophobicity of MOFs influence immobilization. ITC data obtained from the encapsulation of insulin in a series of Zr-MOFs reveals that MOFs provide proteins with a hydrophobic stabilizing microenvironment, making the encapsulation entropically driven. In particular, the pyrene-based NU-1000 tightly encapsulates insulin in its ideally sized mesopores and stabilizes insulin through π-π stacking interactions, resulting in the most enthalpically favored encapsulation process among this series. This study reveals critical insights into the structure-property relationships of protein immobilization.

Leveraging Isothermal Titration Calorimetry to Obtain Thermodynamic Insights into the Binding Behavior and Formation of Metal-Organic Frameworks.

Isothermal titration calorimetry (ITC) is a technique which directly measures the thermodynamic parameters of binding events. Although historically it has been used to investigate interactions in biological macromolecules and the kinetics of enzyme-catalyzed reactions, ITC has also been demonstrated to provide relevant thermodynamic information about interactions in synthetic systems, such as those in metal-organic frameworks (MOFs). MOFs are a family of crystalline porous materials that have been widely studied as supports for molecules ranging from gases to biomolecules through physisorption and chemisorption. Herein, we offer a perspective on the current applications of ITC in MOFs, including the mechanism of small molecule adsorption and the formation of MOF-based composite materials through noncovalent interactions. Experimental considerations specific to running ITC experiments in MOF systems are reviewed on the basis of existing reports. We conclude by discussing underexplored, but promising, MOF-related research directions which could be elucidated by ITC.

Absolute Configurations of Topologically Chiral [2]Catenanes and the Acid/Base-Flippable Directions of Their Optical Rotations.

The absolute configurations of the two enantiomers of a topologically chiral [2]catenane were determined unambiguously based on HPLC resolution and X-ray crystal analysis. Although structurally dissimilar to simple amino acids, the optical rotations of these separated [2]catenanes share the Clough-Lutz-Jirgensons behavior of amino acids: the optical rotation flips direction in the presence of acid and base, the first example of such behavior for a mechanically interlocked topologically chiral catenane.

Aspirin inhibits monocyte chemoattractant protein-1 and interleukin-8 expression in TNF-alpha stimulated human umbilical vein endothelial cells.

Atherosclerosis and its complications such as stroke, myocardial infraction and peripheral vascular disease, remain the major causes of morbidity and mortality in the world. Studies have showed that chemokines and adhesion molecules are involved in causing atherosclerosis by promoting directed migration of inflammatory cells. Monocyte chemoattractant protein-1 (MCP-1) is one of the key factors critical for the initiating and developing of atherosclerotic lesions. IL-8, a CXC chemokine, stimulates neutrophil chemotaxis. Aspirin is the most common drug used to prevent the complications of atherosclerosis such as stroke and coronary heart disease. In this study, we found that aspirin inhibited TNF-alpha (10 ng/ml)-induced MCP-1 and IL-8 expression at the RNA and protein levels in human umbilical vein endothelial cells (HUVECs), monocyte adhesion and transmigration, and that its inhibitory effects were not due to decreased HUVEC viability as assessed by MTT test. Aspirin at the dose as low as 10 microg/ml significantly inhibited the release of TNF-stimulated MCP-1 by 29.1% (P = 0.008) and IL-8 by 26.9% (P = 0.0146) as compared to TNF-stimulated release. Antibodies pretreatment were likely to decrease the production of MCP-1 (P < 0.0001) and IL-8 (P < 0.0001). Furthermore, aspirin (10 microg/ml) inhibited U937 cell adhesion by a 13.4% (P = 0.0119) inhibition as compared to TNF-stimulated alone. Finally, at higher concentration, aspirin also inhibited U937 migration to HUVEC by 89.1% (P = 0.0475) as compared to TNF-stimulated alone. These results in our study suggest that aspirin inhibits TNF-alpha stimulated MCP-1 and IL-8 release in HUVECs, for its additional therapeutic effects of aspirin in causing atherosclerosis.