Catalysts are central to accelerating chemistry in biology and technology. In biochemistry, the relationship between the velocity of an enzymatic reaction and the concentration of chemical substrates is described via the Michaelis-Menten model. The modeling and benchmarking of synthetic molecular electrocatalysts are also well developed. However, such efforts have not been as rigorously extended to photoelectrosynthetic reactions, where, in addition to chemical substrates and charge carriers, light is a required reagent. In this perspective, we draw parallels between concepts involving enzyme catalytic efficiency, the benchmarking of molecular electrocatalysts, and the performance of photoelectrosynthetic assemblies, while highlighting key differences, assumptions, and limitations.
The conversion of CO2 into functional materials under ambient conditions is a major challenge to realize a carbon-neutral society. Metal–organic frameworks (MOFs) have been extensively studied as designable porous materials. Despite the fact that CO2 is an attractive renewable resource, the synthesis of MOFs from CO2 remains unexplored. Chemical inertness of CO2 has hampered its conversion into typical MOF linkers such as carboxylates without high energy reactants and/or harsh conditions. Here, we present a one-pot conversion of CO2 into highly porous crystalline MOFs at ambient temperature and pressure. Cubic [Zn4O(piperazine dicarbamate)3] is synthesized via in situ formation of bridging dicarbamate linkers from piperazines and CO2 and shows high surface areas (∼2366 m2 g–1) and CO2 contents (>30 wt %). Whereas the dicarbamate linkers are thermodynamically unstable by themselves and readily release CO2, the formation of an extended coordination network in the MOF lattices stabilizes the linker enough to demonstrate stable permanent porosity.
A synthetic approach to the modification of the drug “riluzole” with pharmacologically active fragments such as carbazole, tetrahydrocarbazole, phenothiazine, and aminothiophene, based on the copper-catalyzed alkyne-azide 1,3-dipolar cycloaddition of azide-containing pharmacophores with “riluzole” decorated with 5-trifluoromethylhydantoin, has been suggested.
The highly unfavorable thermodynamics of direct aluminum hydrogenation can be overcome by stabilizing alane within a nanoporous bipyridine-functionalized covalent triazine framework (AlH3@CTF-bipyridine). This material and the counterpart AlH3@CTF-biphenyl rapidly desorb H2 between 95 and 154 °C, with desorption complete at 250 °C. Sieverts measurements, 27Al MAS NMR and 27Al1H REDOR experiments, and computational spectroscopy reveal that AlH3@CTF-bipyridine dehydrogenation is reversible at 60 °C under 700 bar hydrogen, >10 times lower pressure than that required to hydrogenate bulk aluminum. DFT calculations and EPR measurements support an unconventional mechanism whereby strong AlH3 binding to bipyridine results in single-electron transfer to form AlH2(AlH3)n clusters. The resulting size-dependent charge redistribution alters the dehydrogenation/rehydrogenation thermochemistry, suggesting a novel strategy to enable reversibility in high-capacity metal hydrides.
Background The World Health Organization has warned that cigarette smoking is an avoidable risk factor for endothelial injury. Myogenin might play a role in muscle metabolism and energy utilization. Electrolytes and minerals are involved in most cellular activities. The objective of this study was to compare myogenin and electrolyte levels between adult male cigarette smokers (CS) and non-smokers (NS). Methods A cross-sectional study was conducted involving 90 subjects, consisting of 55 CS and 35 NS. The sandwich enzyme-linked immunosorbent assay was used to determine myogenin levels while the ion-selective electrode method was used to determine electrolyte levels. The levels of sodium, potassium, and chloride and the body mass index (BMI) were measured. Mann-Whitney and independent t-test were used to analyse the data. Results The BMI of CS was significantly lower than that of NS (p
Despite essentially identical crystallography and equilibrium structuring of water, nanoscopic channels composed of hexagonal boron nitride and graphite exhibit an order-of-magnitude difference in fluid slip. We investigate this difference using molecular dynamics simulations, demonstrating that its origin is in the distinct chemistries of the two materials. In particular, the presence of polar bonds in hexagonal boron nitride, absent in graphite, leads to Coulombic interactions between the polar water molecules and the wall. We demonstrate that this interaction is manifested in a large typical lateral force experienced by a layer of oriented hydrogen atoms in the vicinity of the wall, leading to the enhanced friction in hexagonal boron nitride. The fluid adhesion to the wall is dominated by dispersive forces in both materials, leading to similar wettabilities. Our results rationalize recent observations that the difference in frictional characteristics of graphite and hexagonal boron nitride cannot be explained on the basis of the minor differences in their wettabilities.
The detection of ~20 ppb of phosphine in Venus clouds by observations in the millimetre-wavelength range from JCMT and ALMA is puzzling, because according to our knowledge of Venus, no phosphine should be there. As the most plausible formation paths do not work, the source could be unknown chemical processes—maybe even life?
With a sharp increase in the cases of multi-drug resistant (MDR) bacteria all over the world, there is a huge demand to develop a new generation of antibiotic agents to fight against them. As an alternative to the traditional drug discovery route, we have designed an effective antibacterial agent by modifying an existing commercial antibiotic, kanamycin, conjugated on the surface of gold nanoparticles (AuNPs). In this study, we report a single-step synthesis of kanamycin-capped AuNPs (Kan-AuNPs) utilizing the combined reducing and capping properties of kanamycin. While Kan-AuNPs have increased toxicity to a primate cell line (Vero 76), antibacterial assays showed dose-dependent broad spectrum activity of Kan-AuNPs against both Gram-positive and Gram-negative bacteria including Kanamycin resistant bacteria. Further, a significant reduction in the minimum inhibitory concentration (MIC100) of Kan-AuNPs was observed when compared to free kanamycin against all the bacterial strains tested. Mechanistic studies using transmission electron microscopy and fluorescence microscopy indicated that at least part of Kan-AuNPs increased efficacy may be through disrupting the bacterial envelope, resulting in the leakage of cytoplasmic content and the death of bacterial cells. Results of this study provide critical information about a novel method for the development of antibiotic capped AuNPs as potent next-generation antibacterial agents.
Microporous polymers feature shape-persistent free volume elements (FVEs), which are permeated by small molecules and ions when used as membranes for chemical separations, water purification, fuel cells and batteries1–3. Identifying FVEs that have analyte specificity remains a challenge, owing to difficulties in generating polymers with sufficient diversity to enable screening of their properties. Here we describe a diversity-oriented synthetic strategy for microporous polymer membranes to identify candidates featuring FVEs that serve as solvation cages for lithium ions (Li+). This strategy includes diversification of bis(catechol) monomers by Mannich reactions to introduce Li+-coordinating functionality within FVEs, topology-enforcing polymerizations for networking FVEs into different pore architectures, and several on-polymer reactions for diversifying pore geometries and dielectric properties. The most promising candidate membranes featuring ion solvation cages exhibited both higher ionic conductivity and higher cation transference number than control membranes, in which FVEs were aspecific, indicating that conventional bounds for membrane permeability and selectivity for ion transport can be overcome4. These advantages are associated with enhanced Li+ partitioning from the electrolyte when cages are present, higher diffusion barriers for anions within pores, and network-enforced restrictions on Li+ coordination number compared to the bulk electrolyte, which reduces the effective mass of the working ion. Such membranes show promise as anode-stabilizing interlayers in high-voltage lithium metal batteries.