Fast multipoint immobilization of lipase through chiral L-proline on a MOF as a chiral bioreactor.

In this paper, we describe the facile preparation of a chiral catalyst by the combination of the amino acid, l-proline (Pro), and the enzyme, porcine pancreas lipase (PPL), immobilized on a microporous metal-organic framework (PPL-Pro@MOF). The multipoint immobilization of PPL onto the MOF is made possible with the aid of Pro, which also provided a chiral environment for enhanced enantioselectivity. The application of the microporous MOF is pivotal in maintaining the catalytic activity of PPL, wherein it prevented the leaching of Pro during the catalytic reaction, leading to the enhanced activity of PPL. The prepared biocatalyst was applied in asymmetric carbon-carbon bond formation, demonstrating the potential of this simple approach for chemical transformations.

A simple approach to achieve a metastable metal oxide derived from carbonized metal-organic gels.

A strategy for fabricating zirconium oxide doped nanoporous carbons derived from metal-organic gels (MOGs) is reported. For the first time, the achievement of metastable ZrO2-NPCs is demonstrated. The direct pyrolysis of MOGs provided new perspective in developing metal oxide-doped NPCs and circumvented the shortcomings of existing methods in synthesizing metastable ZrO2 doped NPCs.

Monitoring the Effect of Different Metal Centers in Metal-Organic Frameworks and Their Adsorption of Aromatic Molecules using Experimental and Simulation Studies.

In this study, the adsorption behavior of different metal centers in analogous M-1,4-NDC frameworks (1,4-NDC=1,4-naphthalenedicarboxylate) towards guest molecules through simulation studies and experimental studies is reported. Simulation studies showed that the adsorption behavior of analogous M-1,4-NDC is affected by the atomic radius of the metal center, which was found to be in agreement with the experimental studies.

The Cooperativity of Fe3 O4 and Metal-Organic Framework as Multifunctional Nanocomposites for Laser Desorption Ionization Process.

A novel and facile strategy in developing a water stable magnetic metal-organic framework nanocomposite (Fe3 O4 @MOF) is herein reported, in which a Keggin polyoxometalate, phosphotungstic acid (HPW), was encapsulated within the MOF framework via one-pot synthesis method. The combination of HPW-embedded MOF and Fe3 O4 endowed the composite with high surface area, strong UV absorption, good hydrophilicity, and enhanced water stability. With these unique properties, the Fe3 O4 @MOF embedded HPW served as adsorbent as well as matrix for SALDI-MS (surface-assisted laser desorption ionization mass spectrometry) analysis of polar and non-polar compounds. The synergistic effect of Fe3 O4 and MOF showed an interference-free background at low mass region than the pristine MOF or Fe3 O4 counterparts. This simple approach can be used as new platform in developing magnetic MOF composites without the time consuming and labor-intensive preparation.

Nitrogen-doped porous carbon material derived from metal-organic gel for small biomolecular sensing.

A simple preparation method of N-doped PCM via direct carbonization of nitrogen containing metal-organic gel was demonstrated. The resultant N-PCM, with high surface area, mesoporosity, and high UV absorption ability, was used as a matrix to assist small-biomolecule sensing in laser desorption/ionization mass spectrometry.

Enzyme Immobilized on Nanoporous Carbon Derived from Metal-Organic Framework: A New Support for Biodiesel Synthesis.

In this study, nanoporous carbon (NPC) derived from metal-organic framework was used as support for the immobilization of Burkholderia cepacia lipase. The decorated aluminum oxide within the mesoporous NPC improved the enzyme loading efficiency as well as the catalytic ability for the transesterification of soybean oil, thus making it a promising green and sustainable catalytic system for industrial application.

A Simple Approach to Enhance the Water Stability of a Metal-Organic Framework.

A facile method to improve the feasibility of water-unstable metal-organic frameworks in an aqueous environment has been developed that involves imbedding in a polymer monolith. The effect of compartment type during polymerization plays a significant role in maintaining the crystalline structure and thermal stability of the MOFs, which was confirmed by powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA), respectively. The MOF-polymer composite prepared in a narrow compartment (column, ID 0.8 mm) has better thermal and chemical stability than that prepared in a broad compartment (vial, ID 7 mm). The developed MOF-polymer composite was applied as an adsorbent in solid-phase microextraction of nine non-steroidal anti-inflammatory drugs (NSAIDs) and could be used for extraction more than 30 times, demonstrating that the proposed approach has potential for industrial applications.

Metal-Organic Framework-Polymer Composite as a Highly Efficient Sorbent for Sulfonamide Adsorption and Desorption: Effect of Coordinatively Unsaturated Metal Site and Topology.

In this study, we first demonstrated the effect of two types of metal-organic framework-polymer (MOF-polymer) monoliths on in-tube solid-phase microextraction (IT-SPME) of sulfonamides. Sulfonamides were successfully adsorbed onto MIL-101(Cr)-polymer but were difficult to elute due to these sulfonamides could interact via Lewis acid-base interaction with the presence of Cr(III) coordinatively unsaturated metal sites (CUS). Moreover, the cage-type topology of MIL-101(Cr) that could produce multiple pathways thus complicates the desorption of the test analytes from the sorbent. Contrastingly, MIL-53(Al)-polymer provided weaker Al(III) CUS, and its one-dimensional channel pore structure could provide an unhindered pathway for sulfonamides transfer during elution. After optimizing the IT-SPME condition such as MOF content, pH of sample matrix, column length, extraction flow rate, and elution volume, the calculated extraction recovery of sulfonamides in MIL-53(Al)-polymer as analyzed by microemulsion electrokinetic chromatography (MEEKC) were in the range of 40%-90% with relative standard deviations (RSDs) below 5% and a reusability of at least 30 times.

Nanoporous Carbons Derived from Metal-Organic Frameworks as Novel Matrices for Surface-Assisted Laser Desorption/Ionization Mass Spectrometry.

Surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS) represents a powerful tool for the analysis of biomolecules, synthetic polymers, and even small organic compounds; its performances largely depend on the type of matrix materials utilized. Here, for the first time the employment of nanoporous carbons derived from metal-organic frameworks (MOFs) as novel matrices for SALDI-MS is demonstrated. The nanoporous carbons derived from MOFs not only circumvent the shortcomings of existing matrix materials but also demonstrate much higher efficiency of laser desorption/ionization for various compounds than any other nanoporous carbons reported so far. A new perspective for the development of matrix materials for SALDI-MS application is therefore provided.

Determination of imidazole derivatives by micellar electrokinetic chromatography combined with solid-phase microextraction using activated carbon-polymer monolith as adsorbent.

In this study, an effective method for the separation of imidazole derivatives 2-methylimidazole (2-MEI), 4- methylimidazole (4-MEI) and 2-acetyl-4-tetrahydroxybutylimidazole (THI) in caramel colors using cation-selective exhaustive injection and sweeping micellar electrokinetic chromatography (CSEI-sweeping-MEKC) was developed. The limits of detection (LOD) and quantitation (LOQ) for the CSEI-sweeping-MEKC method were in the range of 4.3-80µgL(-1) and 14-270µgL(-1), respectively. Meanwhile, a rapid fabrication activated carbon-polymer (AC-polymer) monolithic column as adsorbent for solid-phase microextraction (SPME) of imidazole colors was developed. Under the optimized SPME condition, the extraction recoveries for intra-day, inter-day and column-to-column were in the range of 84.5-95.1% (<6.3% RSDs), 85.6-96.1% (<4.9% RSDs), and 81.3-96.1% (<7.1% RSDs), respectively. The LODs and LOQs of AC-polymer monolithic column combined with CSEI-sweeping-MEKC method were in the range of 33.4-60.4µgL(-1) and 111.7-201.2µgL(-1), respectively. The use of AC-polymer as SPME adsorbent demonstrated the reduction of matrix effect in food samples such as soft drink and alcoholic beverage thereby benefiting successful determination of trace-level caramel colors residues using CSEI-sweeping-MEKC method. The developed AC-polymer monolithic column can be reused for more than 30 times without any significant loss in the extraction recovery for imidazole derivatives.

Metal-organic frameworks: new matrices for surface-assisted laser desorption-ionization mass spectrometry.

The cage-type MIL-100(Fe) metal-organic frameworks (MOFs) were used as matrices for surface assisted laser desorption-ionization mass spectrometry. The unique 3D cage frameworks and the iron-center feature good reproducibility of MS intensity and a high signal-to-noise ratio compared to organic or other nanoparticle matrices.

Ionic liquids as porogens in the microwave-assisted synthesis of methacrylate monoliths for chromatographic application.

Several imidazolium-based ionic liquids (ILs) with varying cation alkyl chain length (C(4)-C(10)) and anion type (tetrafluoroborate ([BF(4)](-)), hexafluorophosphate ([PF(6)](-)) and bis(trifluoromethylsulfonyl)imide ([Tf(2)N](-))) were used as reaction media in the microwave polymerization of methacrylate-based stationary phases. Scanning electron micrographs and backpressures of poly(butyl methacrylate-ethylene dimethacrylate) (poly(BMA-EDMA)) monoliths synthesized in the presence of these ionic liquids demonstrated that porosity and permeability decreased when cation alkyl chain length and anion hydrophobicity were increased. Performance of these monoliths was assessed for their ability to separate parabens by capillary electrochromatography (CEC). Intra-batch precision (n=3 columns) for retention time and peak area ranged was 0.80-1.13% and 3.71-4.58%, respectively. In addition, a good repeatability of RSD(Retention time)=<0.30% and ~1.0%, RSD(Peak area)=<1.30% and <4.3%, and RSD(Efficiency)=<0.6% and <11.5% for intra-day and inter-day, respectively exemplify monolith performance reliability for poly(BMA-EDMA) fabricated using 1-hexyl-3-methylimidazolium tetrafluoroborate ([C(6)mim][BF(4)]) porogen. This monolith was also tested for its potential in nanoLC to separate protein digests in gradient mode. ILs as porogens also fabricated different alkyl methacrylate (AMA) (C4-C18) monoliths. Furthermore, employing binary IL porogen mixture such as 1-butyl-3-methylimidazolium tetrafluoroborate ([C(4)mim][BF(4)]) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C(4)mim][Tf(2)N]) successfully decreased the denseness of the monolith, than when using [C(4)mim][Tf(2)N] IL alone, enabling a chromatographic run to be performed with 1:1 ratio produced baseline separation for the analytes. The combination of ILs and microwave irradiation made polymer synthesis very fast (~10min), entirely green (organic solvent-free) and energy saving process.

On-line concentration sample stacking coupled with water-in-oil microemulsion electrokinetic chromatography.

This study describes for the first time, the ability of a normal stacking mode (NSM) on-line concentration step coupled with water-in-oil (W/O) microemulsion electrokinetic chromatography (MEEKC), using six common penicillin antibiotics (oxacillin, penicillin V, penicillin G, nafcillin, ampicillin, and amoxicillin) as test analytes. Optimization of penicillin separation in the conventional W/O MEEKC system demonstrated that change in the type and concentration of the oil phase (1-butanol) and column temperature had a pronounced effect on the separation. With the subsequent development of the NSM coupled with W/O MEEKC, improved separation and detection sensitivities were observed when an organic solvent plug (1-propanol; 1.04 cm) was placed between the W/O microemulsion and the sample solutions. This could be attributed to the solution viscosity difference between the aqueous sample zone and the organic solvent plug causing the penicillin to be stacked in this 1-propanol plug. The optimal NSM W/O MEEKC provided about 12-fold increase in detection sensitivity compared with conventional sample injection (50 mbar, 3 s). Finally, this proposed method was successfully applied in the analyses of several food samples (porcine organs) spiked with penicillin.