Among the important properties of metal-organic frameworks (MOFs) is stability, which may limit applications, for example, in separations and catalysis. Many MOFs consist of metal oxo cluster nodes connected by carboxylate linkers. Addressing MOF stability, we highlight connections between metal oxo cluster chemistry and MOF node chemistry, including results characterizing Keggin ions and biological clusters. MOF syntheses yield diverse metal oxo cluster node structures, with varying numbers of metal atoms (3-13) and the tendency to form chains. MOF stabilities reflect a balance between the number of node-linker connections and the degree of node hydrolysis. We summarize literature results showing how MOF stability (the temperature of decomposition in air) depends on the degree of hydrolysis/condensation of the node metals, which is correlated to their degree of substitution with linkers. We suggest that this correlation may help guide the discovery of stable new MOFs, and we foresee opportunities for progress in MOF chemistry emerging from progress in metal oxo cluster chemistry.

We analyzed Medical Subject Headings (MeSH) from 21.6 million research articles indexed by PubMed to map this vast space of entities and their relations, providing insights into the origins and future of biomedical convergence. Detailed analysis of MeSH co-occurrence networks identifies three robust knowledge clusters: the vast universe of microscopic biological entities and structures; systems, disease and diagnostics; and emergent biological and social phenomena underlying the complex problems driving the health, behavioral and brain science frontiers. These domains integrated from the 1990s onward by way of technological and informatic capabilities that introduced highly controllable, scalable and permutable research processes and invaluable imaging techniques for illuminating fundamental structure-function-behavior questions. Article-level analysis confirms a positive relationship between team size and topical diversity, and shows convergence to be increasing in prominence but with recent saturation. Together, our results invite additional policy support for cross-disciplinary team assembly to harness transdisciplinary convergence.

We leverage the knowledge network representation of the Medical Subject Heading (MeSH) ontology to infer conceptual distances between roughly 30,000 distinct MeSH keywords — each being prescribed to particular knowledge domains — in order to quantify the origins of cross-domain biomedical convergence. Analysis of MeSH co-occurrence networks based upon 21.6 million research articles indexed by PubMed identifies three robust knowledge clusters: micro-level biological entities and structures; meso-level representations of systems, and diseases and diagnostics; and emergent macro-level biological and social phenomena. Analysis of cross-cluster dynamics shows how these domains integrated from the 1990s onward via technological and informatic capabilities — captured by MeSH belonging to the “Technology, Industry, and Agriculture” (J) and “Information Science” (L) branches — representing highly controllable, scalable and permutable research processes and invaluable imaging techniques for illuminating fundamental yet transformative structure–function–behavior questions. Our results indicate that 8.2% of biomedical research from 2000 to 2018 include MeSH terms from both the J and L MeSH branches, representing a 291% increase from 1980s levels. Article-level MeSH analysis further identifies the increasing prominence of cross-domain integration, and confirms a positive relationship between team size and topical diversity. Journal-level analysis reveals variable trends in topical diversity, suggesting that demand and appreciation for convergence science vary by scholarly community. Altogether, we develop a knowledge network framework that identifies the critical role of techno-informatic inputs as convergence bridges — or catalyzers of integration across distinct knowledge domains — as highlighted by the 1990s genomics revolution, and onward in contemporary brain, behavior and health science initiatives.

Purpose

To assess the feasibility of a new shape configuration involving a partially hollow and porous lower part for dental implants.

Materials and methods

Cylindrical zirconia dental implants coated with bioactive glass were fabricated in the laboratory. Each implant has a solid upper part and a partially hollow lower part. It is open at the bottom with holes through the lower cylindrical walls. This hollow and porous configuration permits bone growth into the lower part of the implant that, over time, forms an interlinked network to lock the implant into the alveolar bone. Biomechanical properties of the new design were evaluated through material testing and experiments with dogs.

Results

Mechanical testing of bending strength, hardness, fracture toughness, and fatigue life indicated that zirconia implants with the proposed partially hollow configuration can be fabricated to have structural properties comparable to or exceeding the usual requirements for implants. Animal testing suggests that there is appreciable improvement in lock-in strength and osteointegration due to the hollow and porous configuration.

Conclusion

The new shape configuration is biomechanically feasible and further research is warranted to improve the design for human use.

Many metal-organic frameworks (MOFs) incorporate nodes that are small metal oxide clusters. Some of these MOFs are stable at high temperatures, offering good prospects as catalysts-prospects that focus attention on their defect sites and reactivities-all part of a broader subject: the surface chemistry of metal oxide clusters, illustrated here for MOF nodes and for polyoxocations and polyoxoanions. Ligands on MOF defect sites form during synthesis and are central to the understanding and control of MOF reactivity. Reactions of alcohols are illustrative probes of Zr₆O₈ node defects in UiO-66, characterized by the interconversions of formate, methoxy, hydroxy, and linker carboxylate ligands and by catalysis of alcohol dehydration reactions. We posit that new reactivities of MOF nodes will emerge from incorporation of a wide range of groups on their surfaces and from targeted substitutions of metals within them.

The initial steps of rhodium cluster formation from zeolite-supported mononuclear Rh(C2H4)2 complexes in H2 at 373 K and 1 bar were investigated by infrared and extended X-ray absorption fine structure spectroscopies and scanning transmission electron microscopy (STEM). The data show that ethylene ligands on the rhodium react with H2 to give supported rhodium hydrides and trigger the formation of rhodium clusters. STEM provided the first images of the smallest rhodium clusters (Rh2) and their further conversion into larger clusters. The samples were investigated in a plug-flow reactor as catalysts for the conversion of ethylene + H2 in a molar ratio of 4:1 at 1 bar and 298 K, with the results showing how the changes in catalyst structure affect the activity and selectivity; the rhodium clusters are more active for hydrogenation of ethylene than the single-site complexes, which are more selective for dimerization of ethylene to give butenes.

MgO-supported osmium dioxo species, described as Os(=O)₂ {-O_support }_1 or 2 (the brackets denote O atoms of the MgO surface), formed from Os₃ (CO)₁₂ via supported Os(CO)₂ , and characterized by spectroscopy, microscopy, and theory, react with ethylene at 298 K to form osmium glycol species or with CO to give osmium mono- and di-carbonyls. Os(=O)₂ {-O_support }_1 or 2 is the precursor of a CO oxidation catalyst characterized by a turnover frequency of 4.0×10^-3 (molecules of CO)/(Os atom×s) at 473 K; the active species are inferred to be osmium monocarbonyls. The structures and frequencies calculated at the level of density functional theory with the B3LYP functional bolster the experimental results and facilitate structural assignments. The lowest-energy structures have various osmium oxidation and spin states. The results demonstrate not only new chemistry of the supported single-site catalysts but also their complexity and the value of complementary techniques used in concert to unravel the chemistry.

Supported rhodium acetate dimers were prepared by the reaction of Rh2(OAc)4 (OAc is acetate) with highly dehydroxylated MgO powder and characterized by extended X-ray absorption fine structure and infrared (IR) spectra, which show that the supported species were well represented as Rh2(OAc)3, with each Rh atom on average bonded to one oxygen atom of the MgO surface. Aberration-corrected scanning transmission electron microscopy gave images of Rh atoms in pairs on the MgO. The supported rhodium dimers were probed with a pulse of CO, and the IR spectra indicate a Rh(II) species with weakly bonded carbonyl ligands; the sharpness of the νCO band indicates highly uniform surface species. Further treatment in CO led to breakup of the rhodium dimers into mononuclear species; such fragmentation took place in other treatment gases as well, with the degree of fragmentation decreasing in the order CO > C2H4 > helium. The fragmentation is inferred on the basis of IR spectra to have proceeded through intermediate Rh2 species without acetate ligands. In contrast, rhodium dimers were reduced and not fragmented in the presence of H2 at 353 K, but at higher temperatures the rhodium aggregated to give larger clusters. The supported species catalyzed ethylene hydrogenation at 298 K and 1 bar at a H2:ethylene molar ratio of 4; after 27 h of catalysis in a once-through flow reactor, acetate ligands were removed from the dimers, and some of them fragmented, as shown by IR spectroscopy. The intermediate dirhodium species without acetate ligands are two or three orders of magnitude more active as catalysts than the supported mononuclear rhodium species or those present predominantly as Rh2(OAc)3, respectively.