Anderson-type polyoxometalate-based metal-organic framework as an efficient heterogeneous catalyst for selective oxidation of benzylic C-H bonds.

Oxidative transformation of benzylic C-H bonds into functional carbonyl groups under mild conditions represents an efficient method for the synthesis of aromatic carboxylic acids and ketones. Here we report a high-efficiency catalyst system constructed from an Anderson-type polyoxometalate-based metal-Organic framework (POMOF-1) and N-hydroxyphthalimide (NHPI) for selective oxidation of methylarenes and alkylarenes under 1 atm O2 atmosphere. POMOF-1 exerted a synergistic effect originating from the well-aligned Anderson {CrMo6} clusters and Cu centers within the framework, and this entailed good cooperation with NHPI to catalyze the selective oxidation. Accordingly, the reactions exhibit good tolerance and chemical selectivity for a wide range of substrates bearing diverse substituent groups, and the corresponding carboxylic acids and ketones were harvested in good yields under mild conditions. Mechanism study reveals that POMOF-1 worked synergistically with NPHI to activate the benzylic C-H bonds of substrates, which are sequentially oxidized by oxygen and HOO˙ to give rise to the products. This work may pave a way to design high-efficiency catalysts by integration of polyoxometalate-based materials with NPHI for challenging C-H activation.

[Determination of trace genotoxic impurities in nifedipine by ultra high performance liquid chromatography-electrostatic field orbitrap high resolution mass spectrometry].

A method based on ultra high performance liquid chromatography-electrostatic field orbitrap high resolution mass spectrometry (UHPLC-Orbitrap HRMS) was established for the determination of genotoxic impurities 2, 6, and 12 in nifedipine. After extraction with methanol, the sample was injected into the UHPLC-Orbitrap HRMS system for analysis. An ACE EXCELTM 3 C18-AR column (150 mm×4.6 mm, 3 µm) was used for chromatographic separation. The mobile phase was methanol-0.1% formic acid aqueous solution (65∶35, v/v). The flow rate was 0.6 mL/min, while the column temperature and autosampler temperature were set as 35 ℃ and 8 ℃, respectively. The divert valve switching technique was used to protect the mass spectrometer. The six-way valve was set to divert the eluent of 7.5-11.6 min to waste and the rest of the eluent into the mass spectrometer. The Orbitrap mass spectrometer was coupled with the UHPLC system by an electrospray ion (ESI) source. The sheath gas and auxiliary gas flow rates were 60 and 20 arb (arbitrary units), respectively. The spray voltage was 3.5 kV, while the capillary temperature and auxiliary gas heater temperature were set as 350 ℃ and 400 ℃, respectively. The positive ion parallel reaction monitoring (PRM) scanning mode was adopted, and the mass spectral resolution was set to 35000 FWHM. The accurate masses of the [M+H]+ precursor ions of impurities 2, 6, and 12 were m/z 347.1230, 361.1026, and 347.1230, respectively. The accurate masses of the extracted [M+H]+ fragment ions of impurities 2, 6, and 12 were m/z 315.0968, 298.1069, and 315.0968, respectively. The normalized collision energies (NCEs) were optimized to 10%, 42%, and 10% for impurities 2, 6, and 12, respectively. The external standard method was utilized for quantitative analysis. The established method was validated in detail by investigating the specificity, linear range, limit of detection (LOD), limit of quantification (LOQ), recovery, precision, and stability. This method had good specificity, and the solvent did not interfere with the determination of impurities. The peak areas of impurities 2, 6, and 12 as well as their concentrations showed good linear relationships in the ranges of 0.2-100 ng/mL, with all correlation coefficients (r)≥0.9998. The recoveries of impurities 2, 6, and 12 at three levels (low, medium, and high) were in the range of 96.9%-105.0%, while the RSDs were between 1.21% and 5.12%. The LODs were 0.05 ng/mL and the LOQs were 0.2 ng/mL for all three impurities. This analytical method was used to determine impurities 2, 6, and 12 in three batches of nifedipine samples. Impurity 6 was not detected in the three batches, but impurities 2 and 12 were detected in all the three samples, and the detection amount was within the limit. The developed method is sensitive, fast, accurate, and easy to operate. It can provide a reference for the quality control of nifedipine by pharmaceutical companies and extend strong technical support for the supervision by drug regulatory authorities.

Preparation and evaluation of an innovative antibacterial bi-layered composite dressing for skin wound healing.

AIM OF THE STUDY: The aim of the current study was to develop collagen-based bi-layered composite dressings with antibacterial property and evaluate the efficiency for wound healing. MATERIALS AND METHODS: A bi-layered composite wound dressing was fabricated using two marine biomacromolecules (collagen and chitosan or carboxymethyl chitosan). Non-crosslinked and N-Ethyl-N'-(3-dimethylaminopropyl) carbodiimide/N-Hydroxy succinimide (EDC/NHS) cross-linked collagen sponges fabricated by vacuum freeze-drying technology was used as the inner layer. The medical spun-laced nonwoven coated with chitosan and carboxymethyl chitosan was used as the outer layer. The antibacterial activities against E. coli and S. aureus were evaluated by the inhibition zone assay. Deep second-degree scald model was performed to evaluate the efficiency of bi-layered composite dressings for wound healing. RESULTS: In view of comprehensive evaluation of appearance and in vitro antibacterial activity, medical spun-laced nonwoven coated with 3% of chitosan solution was chosen to be used as the optimized preparation conditions to produce the outer layer of composite dressing, which acted as a barrier against microorganisms and provided mechanical support. Furthermore, the results of wound closure and histopathological analysis indicated that EDC/NHS cross-linked collagen-based bi-layered composite dressing was superior to non-crosslinked and commercial products, which stimulated the wound healing process and accomplished deep second-degree scalded skin healing within a time span of 28 days. CONCLUSION: The EDC/NHS cross-linked collagen-based bi-layered composite dressing had immense potential to be applied for an ideal wound dressing for more efficient and faster wound healing. Therefore, the findings provided the essential theoretical basis for great potential of collagen-based composite dressing used in wound healing applications.

Chiral metal-organic frameworks bearing free carboxylic acids for organocatalyst encapsulation.

Two chiral carboxylic acid functionalized micro- and mesoporous metal-organic frameworks (MOFs) are constructed by the stepwise assembly of triple-stranded heptametallic helicates with six carboxylic acid groups. The mesoporous MOF with permanent porosity functions as a host for encapsulation of an enantiopure organic amine catalyst by combining carboxylic acids and chiral amines in situ through acid-base interactions. The organocatalyst-loaded framework is shown to be an efficient and recyclable heterogeneous catalyst for the asymmetric direct aldol reactions with significantly enhanced stereoselectivity in relative to the homogeneous organocatalyst.

Engineering chiral porous metal-organic frameworks for enantioselective adsorption and separation.

The separation of racemic molecules is of substantial significance not only for basic science but also for technical applications, such as fine chemicals and drug development. Here we report two isostructural chiral metal-organic frameworks decorated with chiral dihydroxy or -methoxy auxiliares from enantiopure tetracarboxylate-bridging ligands of 1,1'-biphenol and a manganese carboxylate chain. The framework bearing dihydroxy groups functions as a solid-state host capable of adsorbing and separating mixtures of a range of chiral aromatic and aliphatic amines, with high enantioselectivity. The host material can be readily recycled and reused without any apparent loss of performance. The utility of the present adsorption separation is demonstrated in the large-scale resolution of racemic 1-phenylethylamine. Control experiments and molecular simulations suggest that the chiral recognition and separation are attributed to the different orientations and specific binding energies of the enantiomers in the microenvironment of the framework.

A homochiral porous metal-organic framework for enantioselective adsorption of mandelates and photocyclizaton of tropolone ethers.

A chiral porous metal-organic framework of an axially C2-symmetric 1,1'-biphenol ligand is constructed and can be used as a solid-state host to enanioselectively adsorb mandelates with up to 93.1% ee and to entrap achiral tropolone ethers and induce their asymmetric photocyclization with up to 98.5% ee.