Open Sites Research Articles

Laetoli, Tanzania: Extant terrestrial mollusc faunas shed new light on climate and palaeoecology at a Pliocene hominin site.

Laetoli, Tanzania is one of the most important palaeontological and palaeoanthropological localities in Africa. We report on a survey of the extant terrestrial gastropod faunas of the Laetoli-Endulen area, examine their ecological associations and re-examine the utility of Pliocene fossil molluscs in palaeoenvironmental reconstruction. Standardised collecting at 15 sites yielded 7302 individuals representing 58 mollusc species. Significant dissimilarities were found among the faunas of three broad habitat types: forest, woodland/bushland and open (grassland and scattered, xeric shrubland). Overall, more species were recorded in the woodland/bushland sites than in the forest sites. Open sites were less diverse. Environmental factors contributing most strongly to the separation of habitat types were aridity index and elevation. The results are supplemented with new mollusc data from the Mbulu Plateau south of Lake Eyasi, and compared to the list of species cumulatively recorded from the Ngorongoro area. Some regional variation is apparent and historical factors may explain the absence of some fossil taxa from Laetoli today. Differences in seasonality separated upland forest sites on the Mbulu plateau from those at Lemagurut at Laetoli. Indicator species were identified for each habitat. These included several large-bodied species analogous to the Laetoli Pliocene fossil species that were then used for palaeoenvironmental reconstruction. Based on the estimated aridity index, and adopting the widely used United Nations Environment Programme (UNEP) global climate classification, the four stratigraphic subunits of the Upper Laetolil Beds (3.6-3.85 Ma) would be placed in either the UNEP's Dry Sub-humid or Semi-arid climate classes, whereas the Upper Ndolanya Beds (2.66 Ma) and Lower Laetolil Beds (3.85-<4.36 Ma) would be assigned to the Humid and Semi-arid climate classes respectively. Pliocene precipitation at Laetoli is estimated as 847-965 mm per year, refining previous estimates. This is close or slightly higher than the present mean annual precipitation, and is likely to have corresponded to a mosaic of forest, woodland and bushland within a grassland matrix consistent with other reconstructions.

IPr*Thia - wingtip-flexible, sterically hindered, modular, N,C/S,C-chelating thiazole-donor N-heterocyclic carbene ligands.

N-Heterocyclic carbenes (NHCs) represent a pivotal class of ligands in coordination chemistry owing to their unique electronic properties. In particular, hemilabile N-heterocyclic carbenes have garnered significant attention over the past decade due to their capacity to transiently coordinate to metals and open coordination sites. However, hemilabile NHC ligands have been predominantly limited to N, O and P donors, while NHC ligands bearing versatile S-donors have been severely underdeveloped. Herein, we report wingtip-flexible, sterically hindered NHC ligands that feature N,C/S,C-chelating thiazole donors in combination with the powerful IPr* (IPr* = (2,6-bis(diphenylmethyl)-4-methylphenyl)imidazol-2-ylidene) scaffold. These ligands are prepared using a highly modular SNAr arylation of thiazole derivatives. Full structural and electronic characterization is reported. The ligands feature a high barrier to rotation around the N-thiazole axis (10 kcal mol-1). The ligands are evaluated for their steric, electron-donating and π-accepting properties as well as coordination chemistry to Ag(I), Pd(II), Rh(I) and Se. Preliminary studies on Ag, Pd and Rh catalysis are presented. The efficiency of the approach is highlighted by preparing a library of unsymmetrical imidazolium precursors. The mono-IPr* wingtip provides a highly hindered yet sterically flexible environment adjusting to metal centers, while the N-thiazolyl wingtip displays a fluxional behavior that interchanges from the hard/soft N,C to soft/soft S,C coordination. Considering the importance of hemilabile N-heterocyclic carbene ligands in metal stabilization in inorganic and organometallic chemistry, we expect that this class of ligands will be of broad interest.

Click catalysis and DNA conjugation using a nanoscale DNA/silver cluster pair.

DNA-bound silver clusters are most readily recognized by their strong fluorescence that spans the visible and near-infrared regions. From this suite of chromophores, we chose a green-emitting Ag106+ bound to C4AC4TC3GT4 and describe how this DNA/cluster pair is also a catalyst. A DNA-tethered alkyne conjugates with an azide via cycloaddition, an inherently slow reaction that is facilitated through the joint efforts of the cluster and DNA. The Ag106+ structure is the catalytic core in this complex, and it has three distinguishing characteristics. It facilitates cycloaddition while preserving its stoichiometry, charge, and spectra. It also acidifies its nearby alkyne to promote H/D exchange, suggesting a silver-alkyne complex. Finally, it is markedly more efficient when compared with related multinuclear DNA-silver complexes. The Ag106+ is trapped within its C4AC4TC3GT4 host, which governs the catalytic activity in two ways. The DNA has orthogonal functional groups for both the alkyne and cluster, and these can be systematically separated to quench the click reaction. It is also a polydentate ligand that imprints an elongated shape on its cluster adduct. This extended structure suggests that DNA may pry apart the cluster to open coordination sites for the alkyne and azide reactants. These studies indicate that this DNA/silver cluster pair work together with catalysis directly driven by the silver cluster and indirectly guided by the DNA host.

High adsorption selectivity, capacity and rate of fructose using metal–organic frameworks with abundant zirconium open metal sites

MOF-808 with abundant zirconium sites enables high adsorption selectivity (17.8), high capacity (362 mg g−1), and rapid adsorption and separation (18.9 h−1) of fructose from glucose and fructose mixed solutions and has excellent cycling stability.

A Study Over Brain Connectivity Network of Parkinson's Patients, Using Nonparametric Bayesian Model.

Parkinson disease is a neurodegenerative disease that disrupts functional brain networks. Many neurodegenerative disorders are associated with changes in brain communication patterns. Resting-state functional connectivity studies can distinguish the topological structure of Parkinson patients from healthy individuals by analyzing patterns between different regions of the brain. Accordingly, the present study aimed to determine the brain topological features and functional connectivity in patients with Parkinson disease, using a Bayesian approach. The data of this study were downloaded from the open neuro site. These data include resting-state functional magnetic resonance imaging (rs-fMRI) of 11 healthy individuals and 11 Parkinson patients with mean ages of 64.36 and 63.73, respectively. An advanced nonparametric Bayesian model was used to evaluate topological characteristics, including clustering of brain regions and correlation coefficient of the clusters. The significance of functional relationships based on each edge between the two groups was examined through false discovery rate (FDR) and network-based statistics (NBS) methods. Brain connectivity results showed a major difference in terms of the number of regions in each cluster and the correlation coefficient between the patient and healthy groups. The largest clusters in the patient and control groups were 26 and 53 regions, respectively, with clustering correlation values of 0.36 and 0.26. Although there are 15 common areas across the two clusters, the intensity of the functional relationship between these areas was different in the two groups. Moreover, using NBS and FDR methods, no significant difference was observed for each edge between the patient and healthy groups (P>0.05). The results of this study show a different topological configuration of the brain network between the patient and healthy groups, indicating changes in the functional relationship between a set of areas of the brain.

Enhancing CO2/N2 and CH4/N2 separation performance by salt-modified aluminum-based metal-organic frameworks.

The energy-saving separation of CO2/N2 and CH4/N2 in the energy industry facilitates the reduction of greenhouse gas emissions and replenishes energy resources, but is a challenging separation process. The trade-off between adsorption capacity and selectivity of the adsorbents is one of the key bottlenecks in adsorption separation technologies' large-scale application in the above separation task. Herein, we introduced a series of fluoroborate or fluorosilicate salts (Cu(BF4)2, Zn(BF4)2 and ZnSiF6) into the open coordination nitrogen sites of aluminum-based metal-organic frameworks (MOF-253) to create multiple binding sites to simultaneously enhance the adsorption capacity and selectivity for the target gas. By the synergistic adsorption effect of metal ions (Cu2+ or Zn2+) and fluorinated anions (BF4- or (SiF6)2-), the single-component adsorption capacity and selectivity of salt-modified MOF-253 (MOF-253@Cu(BF4)2, MOF-253@Zn(BF4)2 and MOF-253@ZnSiF6) for CO2 and CH4 were effectively improved when compared to pristine MOF-253 at 298 K and 1 bar. In addition, the salt-modified MOF-253 has a moderate adsorption heat (<30 kJ mol-1) which could be rapidly regenerated at low energy by evacuation desorption. As confirmed by the ambient breakthrough experiments of MOF-253 and MOF-253@ZnSiF6, the real separation performance for both CO2/N2 (1/4) and CH4/N2 (1/4) was obviously improved. This work provides a feasible post-modification strategy on uncoordinated sites of the framework to improve adsorption separation performance and promote the development of ideal adsorbents with a view to realizing their application in the energy industry.

Towalink: An open and flexible site networking solution

Towalink: An open and flexible site networking solution

MOF based membranes in gas separation area

Microporous metal organic framework materials are a series of noticeable membrane materials for the separation of gas molecules and liquid molecules. MOFs can be functionalized through tuning pore size through the variation of ligand length, metal nodes and more, or through adjusting adsorption site such as functional sites, linker functional sites, and open metal sites. Membranes can provide higher structure stability for MOFs, however, addressing synthetic, processing, and design challenges is crucial to produce MOF films with excellent mechanical integrity, chemical stability, and high performance under relevant industrial conditions，such as interfacial compatibility issues towards Mixed-Matrix-Membranes (MMMs) and Pure-MOF film issues regarding chemical and thermal robustness, morphology, and orientation. The alkyne/alkene separation, alkane/alkene separation and more gas mixture has been proven can be achieved through the use of MOF-based membranes, moreover, compared to traditional methods, MOF-based membranes possess better performance on separating forementioned gas mixtures with higher selectivity, purity and less harm to the environment.

A steric hindrance-driven amorphization strategy on MOF/COF for boosting CO2 separation in mixed matrix membranes

The amorphous MOF/COF exposed Lewis basic sites and open metal sites in MMMs, improving the CO2/CH4 separation performance.

Impact of climatic factors on air pollution and human health in the Lucknow city of Uttar Pradesh, India

Urban air pollution is a complex and ever-changing blend of gaseous pollutants, particulate matter and land surface temperature. This multifaceted mixture experiences daily and seasonal fluctuations influenced by anthropogenic activities, land-cover transformation, and climatic conditions. This study investigates the impact of climatic factors such as temperature, precipitation, and relative humidity on air pollution and human health in Lucknow city of India. NASA's open data site (Data Access Viewer (DAV) - NASA POWER) was used to gather information on the earth's skin temperature, 2-meter temperature, precipitation, and relative humidity. Data on air pollutants like PM10, SO2, NO2, and the Air Quality Index across seven locations has been collected from the government pollution control board. The present research examines the correlation between these climatic factors and pollutants, such as particulate matter and sulphur dioxide, as well as the relationship between temperature and relative humidity with the incidence of respiratory and cardiovascular diseases in the study area. This research shows a negative correlation between pollutants and precipitation, temperature at 2m, relative humidity and earth skin temperature, respectively. On the other hand, it shows a positive correlation between precipitation and disease. Thus, this paper will provide valuable insights into the potential impacts of climate change on air pollution and human health in Lucknow and similar urban areas.

Emerging investigator series: open dumping and burning: an overlooked source of terrestrial microplastics in underserved communities.

Open dumping and burning of solid waste are widely practiced in underserved communities lacking access to solid waste management facilities; however, the generation of microplastics from these sites has been overlooked. We report elevated concentrations of microplastics (MPs) in soil of three solid waste open dump and burn sites: a single-family site in Tuttle, Oklahoma, USA, and two community-wide sites in Crow Agency and Lodge Grass, Montana, USA. We extracted, quantified, and characterized MPs from two soil depths (0-9 cm and 9-18 cm). The average of abundance of particles found at community-wide sites three sites (18, 460 particles kg-1 soil) equals or exceeds reported concentrations from currently understood sources of MPs including biosolids application and other agricultural practices. Attenuated total reflectance Fourier transformed infrared (ATR-FTIR) identified polyethylene as the dominant polymer across all sites (46.2-84.8%). We also detected rayon (≤11.5%), polystyrene (up to 11.5%), polyethylene terephthalate (≤5.1), polyvinyl chloride (≤4.4%), polyester (≤3.1), and acrylic (≤2.2%). Burned MPs accounted for 76.3 to 96.9% of the MPs found in both community wide dumping sites. These results indicate that solid waste dumping and burning activities are a major source of thermally oxidized MPs for the surrounding terrestrial environment with potential to negatively affect underserved communities.

Size matters: altering the metal-surface coordination in micropores via structural confinement effects

NMR experiments reveal how surface curvature can impact metal coordination. It was observed that under extreme confinement, secondary support–metal interactions are prevented, leading to a dynamic complex with an open coordination site.

Rational design of a cyclohexanone dehydrogenase for enhanced α,β-desaturation and substrate specificity.

The selective α,β-desaturation of cyclic carbonyl compounds, which are found in the core of many steroid and bioactive molecules, using green chemistry is highly desirable. To achieve this task, we have for the first time described and solved the de novo structure of a member of the cyclohexanone dehydrogenase class of enzymes. The breadth of substrate specificity was investigated by assaying the cyclohexanone dehydrogenase, from Alicycliphilus denitrificans, against several cyclic ketones, lactones and lactams. To investigate substrate binding, a catalytic variant, Y195F, was generated and used to obtain a crystallographic complex with the natural substrate, cyclohexanone. This revealed substrate-active site interactions, as well as the proximity of the cofactor, flavin adenine dinucleotide, and enabled us to propose a mechanistic function to key amino acids. We then used molecular dynamic simulations to guide design to add functionality to the cyclohexanone dehydrogenase enzyme. The resulting W113A variant had overall improved enzyme activity and substrate scope, i.e., accepting the bulkier carbonyl compound, dihydrocoumarin. Structural analysis of the W113A variant revealed a broader, more open active site, which helped explain the modified substrate specificity. This work paves the way for future bespoke regioselective α,β-desaturation in the synthesis of important bioactive molecules via rational enzyme engineering.

Construction of a series of pH stable Ca-based MOFs, their CO2 adsorption and catalytic activity.

In this study, three different solvent systems have been employed to investigate the effect of reaction parameters on the synthesis of four alkaline earth metal-based MOFs namely [Ca(0.5 1,4-phenyl diacetic acid)2(H2O)DMF]∞ (Ca-MOF-1), [Ca(1,4-naphthalene dicarboxylate)DMF]∞ (Ca-MOF-2), [Ca2(0.5 1,2,4,5-benzene tetracarboxylate)2(H2O)3DMF]∞ (Ca-MOF-3) and [Ca2(2,6-naphthalene dicarboxylate)2(H2O)6]∞ (Ca-MOF-4). The crystal structures of these four MOFs have been resolved through single crystal X-ray analysis and the bulk phase purity of these MOFs was assessed using PXRD and FT-IR analysis. To check the stability of these MOFs, thermogravimetric analysis (TGA) was carried out. To analyze the robustness of these MOFs, the PXRD of the samples was also collected at different pH levels. These MOFs were further explored as Lewis acid catalysts for the alcoholysis of epoxides and the activity of these catalysts depend on the open metal sites present in the MOFs. The catalytic activity follows the order: Ca-MOF-2 > Ca-MOF-4 > Ca-MOF-1 > Ca-MOF-3. The activity was also checked with various epoxide substrates using Ca-MOF-2. Density functional theory (DFT) calculations also support this trend with the help of the thermodynamic feasibility of epoxide binding, considering model MOF structures. The weak interaction between the epoxide oxygen and the metal centre of the most stable MOF structure has also been clarified by computational studies.

Ionic liquid post-modified carboxylate-rich MOFs for efficient catalytic CO2 cycloaddition under solvent-free conditions.

The synthesis of cyclic carbonates through cycloaddition reactions between epoxides and carbon dioxide (CO2) is an important industrial process. Metal-Organic Frameworks (MOFs) have functional and ordered pore structures, making them attractive catalysts for converting gas molecules into valuable products. One approach to enhance the catalytic activity of MOFs in CO2 cycloaddition reactions is to create open metal sites within MOFs. In this study, the amino-functionalized rare earth Gd-MOF (Gd-TPTC-NH2) and its ionic liquid composite catalysts (Gd-TPTC-NH-[BMIM]Br) were synthesized using 2'-amino-[1,1':4',1''-terphenyl]-3,3'',5,5''-tetracarboxylic acid (H4TPTC-NH2) as the ligand. The catalytic performance of these two catalysts was observed in the cycloaddition reaction of CO2 and epoxides. Under the optimized reaction conditions, Gd-TPTC-NH-[BMIM]Br can effectively catalyze the cycloaddition reaction of a variety of epoxide substrates with good to excellent yields of cyclic carbonate products. Comparatively, epichlorohydrin and epibromohydrin, which possess halogen substituents, promote higher yields of cyclic carbonates due to the electron-withdrawing nature of Cl and Br substituents. Additionally, the Gd-TPTC-NH-[BMIM]Br catalyst demonstrated good recyclability and reproducibility, maintaining its catalytic activity without any changes in its structure or properties after five reuse cycles.

Enabling a bioinspired N,N,N-copper coordination motif through spatial control in UiO-67: synthesis and reactivity.

Metal-organic frameworks (MOFs) featuring zirconium-based clusters are widely used for the development of functionalized materials due to their exceptional stability. In this study, we report the synthesis of a novel N,N,N-ligand compatible with a biphenyl dicarboxylic acid-based MOF. However, the resulting copper(I) complex exhibited unexpected coordination behaviour, lacking the intended trifold coordination motif. Herein, we demonstrate the successful immobilization of a bioinspired ligand within the MOF, which preserved its crystalline and porous nature while generating a well-defined copper site. Comprehensive spectroscopic analyses, including X-ray absorption, UV/Vis, and infrared spectroscopy, were conducted to investigate the copper site and its thermal behaviour. The immobilized ligand exhibited the desired tridentate coordination to copper, providing access to a coordination motif otherwise unattainable. Notably, water molecules were also found to coordinate to copper. Upon heating, the copper centre within the MOF exhibited reversible dehydration, suggesting facile creation of open coordination sites. Furthermore, the copper site displayed reduction at elevated temperatures and subsequent susceptibility to oxidation by molecular oxygen. Lastly, both the molecular complexes and the MOF were evaluated as catalysts for the oxidation of cyclohexane using hydrogen peroxide. This work highlights the successful immobilization of a bioinspired ligand in a zirconium-based MOF, shedding light on the structural features, thermal behaviour, and catalytic potential of the resulting copper sites.

Boosting the degradation of antibiotics via peroxymonosulfate activation with a Cu-based metal–organic framework

A new [Cu3(µ3-O)]4+-based metal–organic framework (MOF) with rich open metal sites (OMSs) exhibits excellent degradation performance towards various types of antibiotics by activation of peroxymonosulfate.

Fabrication of bimetallic MOF-74 derived materials for high-efficiency adsorption of iodine.

Owing to their high porosity, open metal sites, and huge surface area, metal-organic framework (MOF) materials are commonly employed in iodine adsorption processes. Bimetallic MOFs have drawn a lot of attention since mono-metal MOFs have been unable to keep up with the demand. Bimetallic MOF materials still have drawbacks, including limited adsorption capacity, extended adsorption time, poor stability, and poor selectivity, despite their positive performance in radioactive iodine capture. It has been therefore difficult to develop adsorbents with quick iodine adsorption rates and high iodine adsorption efficiency. This study investigated the adsorption properties of a series of bimetallic MOF-74 materials (Mn-Co-MOF-74, Mn-Zn-MOF-74, and Mn-Ni-MOF-74) for radioactive iodine, as well as their design and synthesis utilizing the reflux approach. It was discovered that the adsorption performance of Mn-Ni-MOF-74 for radioiodine was superior to that of the other two bimetallic MOF-74 materials. Using the bimetallic Mn-Ni-MOF-74 as a precursor, a variety of bimetallic MOF-74 derived carbon compounds (Mn-Ni-CX) were prepared by high-temperature pyrolysis. Simultaneously, the structure of the material and the iodine adsorption characteristics have been thoroughly studied.

Defect-enabling zirconium-based metal-organic frameworks for energy and environmental remediation applications.

This comprehensive review explores the diverse applications of defective zirconium-based metal-organic frameworks (Zr-MOFs) in energy and environmental remediation. Zr-MOFs have gained significant attention due to their unique properties, and deliberate introduction of defects further enhances their functionality. The review encompasses several areas where defective Zr-MOFs exhibit promise, including environmental remediation, detoxification of chemical warfare agents, photocatalytic energy conversions, and electrochemical applications. Defects play a pivotal role by creating open sites within the framework, facilitating effective adsorption and remediation of pollutants. They also contribute to the catalytic activity of Zr-MOFs, enabling efficient energy conversion processes such as hydrogen production and CO2 reduction. The review underscores the importance of defect manipulation, including control over their distribution and type, to optimize the performance of Zr-MOFs. Through tailored defect engineering and precise selection of functional groups, researchers can enhance the selectivity and efficiency of Zr-MOFs for specific applications. Additionally, pore size manipulation influences the adsorption capacity and transport properties of Zr-MOFs, further expanding their potential in environmental remediation and energy conversion. Defective Zr-MOFs exhibit remarkable stability and synthetic versatility, making them suitable for diverse environmental conditions and allowing for the introduction of missing linkers, cluster defects, or post-synthetic modifications to precisely tailor their properties. Overall, this review highlights the promising prospects of defective Zr-MOFs in addressing energy and environmental challenges, positioning them as versatile tools for sustainable solutions and paving the way for advancements in various sectors toward a cleaner and more sustainable future.

An unprecedented Cu6 cluster-based bimetallic MOF with multiple open sites for high CO2 capture and efficient CO2 conversion

Through soft-hard acid-base theory, a novel bimetallic MOF (JLU-MOF108) with an unprecedented 12-connected Cu6 cluster SBU was synthesized. LAS and LBS inside JLU-MOF108 exhibited significant CO2 capture and conversion capability.