The development of base metal catalysts for the synthesis of pharmaceutically relevant compounds remains an important goal of chemical research. Here, we report that cobalt nanoparticles encapsulated by a graphitic shell are broadly effective reductive amination catalysts. Their convenient and practical preparation entailed template assembly of cobalt-diamine-dicarboxylic acid metal organic frameworks on carbon and subsequent pyrolysis under inert atmosphere. The resulting stable and reusable catalysts were active for synthesis of primary, secondary, tertiary, and -methylamines (more than 140 examples). The reaction couples easily accessible carbonyl compounds (aldehydes and ketones) with ammonia, amines, or nitro compounds, and molecular hydrogen under industrially viable and scalable conditions, offering cost-effective access to numerous amines, amino acid derivatives, and more complex drug targets.
Materials development for artificial photosynthesis, in particular, CO reduction, has been under extensive efforts, ranging from inorganic semiconductors to molecular complexes. In this report, we demonstrate a metal-organic framework (MOF)-coated nanoparticle photocatalyst with enhanced CO reduction activity and stability, which stems from having two different functional units for activity enhancement and catalytic stability combined together as a single construct. Covalently attaching a CO-to-CO conversion photocatalyst Re(CO)(BPYDC)Cl, BPYDC = 2,2'-bipyridine-5,5'-dicarboxylate, to a zirconium MOF, UiO-67 (Re-MOF), prevents dimerization leading to deactivation. By systematically controlling its density in the framework (n = 0, 1, 2, 3, 5, 11, 16, and 24 complexes per unit cell), the highest photocatalytic activity was found for Re-MOF. Structural analysis of Re-MOFs suggests that a fine balance of proximity between photoactive centers is needed for cooperatively enhanced photocatalytic activity, where an optimum number of Re complexes per unit cell should reach the highest activity. Based on the structure-activity correlation of Re-MOFs, Re-MOF was coated onto Ag nanocubes (Ag⊂Re-MOF), which spatially confined photoactive Re centers to the intensified near-surface electric fields at the surface of Ag nanocubes, resulting in a 7-fold enhancement of CO-to-CO conversion under visible light with long-term stability maintained up to 48 h.
A three-dimensional covalent organic framework (COF-505) constructed from helical organic threads, designed to be mutually weaving at regular intervals, has been synthesized by imine condensation reactions of aldehyde functionalized copper(I)-bisphenanthroline tetrafluoroborate, Cu(PDB)2(BF4), and benzidine (BZ). The copper centers are topologically independent of the weaving within the COF structure and serve as templates for bringing the threads into a woven pattern rather than the more commonly observed parallel arrangement. The copper(I) ions can be reversibly removed and added without loss of the COF structure, for which a tenfold increase in elasticity accompanies its demetalation. The threads in COF-505 have many degrees of freedom for enormous deviations to take place between them, throughout the material, without undoing the weaving of the overall structure.
Two porous, chiral metal-organic frameworks (MOFs), Ca(l-lactate)(acetate)(CHOH)(HO) (MOF-1201) and Ca(l-lactate)(acetate)(HO) (MOF-1203), are constructed from Ca ions and l-lactate [CHCH(OH)COO], where Ca ions are bridged by the carboxylate and hydroxyl groups of lactate and the carboxylate group of acetate to give a three-dimensional arrangement of Ca(-COO, -OH) polyhedra supporting one-dimensional pores with apertures and internal diameters of 7.8 and 9.6 Å (MOF-1201) and 4.6 and 5.6 Å (MOF-1203), respectively. These MOFs represent the first examples of extended porous structures based on Ca and lactate. They show permanent porosity of 430 and 160 m g, respectively, and can encapsulate an agriculturally important fumigant, cis-1,3-dichloropropene. MOF-1201 shows a 100 times lower release rate compared with liquid cis-1,3-dichloropropene under the same test conditions (25 °C, air flow rate of 1 cm min). The hydrolysis of MOF-1201 in water makes it the first example of a degradable porous solid carrier for such fumigants.
C-doped ZnO with a large surface area was prepared via F127-assisted pyrolysis at 500 C and used for visible-light-responsive photocatalytic water purification. The band structure of the C-doped ZnO was investigated using valance band XPS and DFT simulation. The C-doped ZnO possessed enhanced absorption of UV and visible light, though it showed lower visible-light-responsive photocatalytic activity than ZnO because of significant recombination of photogenerated charge carriers arising from overloaded C-dopant and oxygen vacancies.
Aims. To synthesize, characterize, and analyze antimicrobial activity of AgNPs of Escherichia hermannii (SHE), Citrobacter sedlakii (S11P), and Pseudomonas putida (S5). Methods. The synthesized AgNPs were examined using ultraviolet-visible spectroscopy (UV-vis) and, zeta potential, and the size and the morphology obtained from the three different isolates were also confirmed by TEM. Results. Among the three isolates tested, SHE showed the best antimicrobial activity due to the presence of small (4–12 nm) and stable (−22 mV) AgNPs. Stability of AgNPs was also investigated and found to be dependent on the nature of isolates. Conclusion. Produced AgNPs showed particle stability and antimicrobial efficacy up to 90 days of production. Our AgNPs exhibited greater antimicrobial activity compared with gentamicin against P. aeruginosa isolates and vancomycin against S. aureus and MRSA isolates at very low concentration (0.0002 mg per Microliters).
Despite numerous
studies on chemical and thermal stability of metal–organic
frameworks (MOFs), mechanical stability remains largely undeveloped.
To date, no strategy exists to control the mechanical deformation
of MOFs under ultrahigh pressure. Here, we show that the mechanically
unstable MOF-520 can be retrofitted by precise placement of a rigid
4,4′-biphenyldicarboxylate (BPDC) linker as a “girder”
to afford a mechanically robust framework: MOF-520-BPDC. This retrofitting
alters how the structure deforms under ultrahigh pressure and thus
leads to a drastic enhancement of its mechanical robustness. While
in the parent MOF-520 the pressure transmitting medium molecules diffuse
into the pore and expand the structure from the inside upon compression,
the girder in the new retrofitted MOF-520-BPDC prevents the framework
from expansion by linking two adjacent secondary building units together.
As a result, the modified MOF is stable under hydrostatic compression
in a diamond-anvil cell up to 5.5 gigapascal. The increased mechanical
stability of MOF-520-BPDC prohibits the typical amorphization observed
for MOFs in this pressure range. Direct correlation between the orientation
of these girders within the framework and its linear strain was estimated,
providing new insights for the design of MOFs with optimized mechanical
properties.
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