Metal-organic frameworks for analytical chemistry: from sample collection to chromatographic separation

Development of the affinity materials for phosphorylated proteins/peptides enrichment in phosphoproteomics analysis

Reversible protein phosphorylation is a key event in numerous biological processes. Mass spectrometry (MS) is the most powerful analysis tool in modern phosphoproteomics. However, the direct MS analysis of phosphorylated proteins/peptides is still a big challenge because of the low abundance and insufficient ionization of phosphorylated proteins/peptides as well as the suppression effects of nontargets. Enrichment of phosphorylated proteins/peptides by affinity materials from complex biosamples is the most widely used strategy to enhance the MS detection. The demand of efficiently enriching phosphorylated proteins/peptides has spawned diverse affinity materials based on different enrichment principles (e.g., electronic attraction, chelating). In this review, we summarize the recent development of various affinity materials for phosphorylated proteins/peptides enrichment. We will highlight the design and fabrication of these affinity materials, discuss the enrichment mechanisms involved in different affinity materials, and suggest the future challenges and research directions in this field.

Exploiting Framework Flexibility of a Metal-Organic Framework for Selective Adsorption of Styrene over Ethylbenzene

The separation of styrene and ethylbenzene mixtures is industrially important and is currently performed in highly energy-intensive vacuum distillation columns. The primary objective of our investigation is to offer an energy-efficient alternative for selective adsorption of styrene by a flexible metal-organic framework, DynaMOF-100. The structural transformation of DynaMOF-100 is specifically triggered on inclusion of styrene within the framework; this structural transformation is reversible. The styrene/ethylbenzene adsorption selectivity, originated as an outcome of the framework flexibility, is found to be much superior to the only two MOFs yet reported, serving styrene/ethylbenzene separation purpose.

Exploiting parameter space in MOFs: a 20-fold enhancement of phosphate-ester hydrolysis with UiO-66-NH2

The hydrolysis of nerve agents is of primary concern due to the severe toxicity of these agents. Using a MOF-based catalyst (UiO-66), we have previously demonstrated that the hydrolysis can occur with relatively fast half-lives of 50 minutes. However, these rates are still prohibitively slow to be efficiently utilized for some practical applications (e.g., decontamination wipes used to clean exposed clothing/skin/vehicles). We thus turned our attention to derivatives of UiO-66 in order to probe the importance of functional groups on the hydrolysis rate. Three UiO-66 derivatives were explored; UiO-66-NO2 and UiO-66-(OH)2 showed little to no change in hydrolysis rate. However, UiO-66-NH2 showed a 20 fold increase in hydrolysis rate over the parent UiO-66 MOF. Half-lives of 1 minute were observed with this MOF. In order to probe the role of the amino moiety, we turned our attention to UiO-67, UiO-67-NMe2 and UiO-67-NH2. In these MOFs, the amino moiety is in close proximity to the zirconium node. We observed that UiO-67-NH2 is a faster catalyst than UiO-67 and UiO-67-NMe2. We conclude that the role of the amino moiety is to act as a proton-transfer agent during the catalytic cycle and not to hydrogen bond or to form a phosphorane intermediate.

Selective recognition of 6-mercaptopurine based on luminescent metal-organic frameworks Fe-MIL-88NH₂

A novel and rapid spectrofluorometry method for the recognition of 6-mercaptopurine (6-MP) has been developed based on luminescent metal-organic frameworks Fe-MIL-88NH2 as fluorescent probe. The strong fluorescence of Fe-MIL-88NH2 at 430 nm could be quenched by 6-MP directly, and the Fe-MIL-88NH2 shows high selectivity for 6-MP compared to other thiol-containing amino acids such as homocysteine (Hcy), cysteine (Cys), glutathione (GSH), etc. Under optimal conditions, the relative fluorescence intensity was linearly proportional to the concentration of 6-MP in the range of 5-600 μM with the detection limit at 1.17 μM (S/N=3). Furthermore, the present approach has been successfully applied to the determination of 6-MP in human serum samples. The possible fluorescence quenching mechanism has also been investigated, where it is revealed that the quenching was attributed to competition of absorption of the light source energy as well as electron transfer between Fe-MIL-88NH2 and 6-MP.

An in situ growth approach to the fabrication of zeolite imidazolate framework-90 bonded capillary column for gas chromatography separation

The unique properties of metal-organic frameworks, such as diversity in structures and pore sizes, high surface area, shape selectivity and available to functionality make them as potential materials of the stationary phase for gas chromatography. Here we show an in situ growth approach to the fabrication of zeolite imidazolate framework-90 (ZIF-90) bonded capillary column for gas chromatography separation. ZIF-90 was directly grown onto the inner wall of the carboxyl modified capillary via the coordination between Zn(II) and carboxyl group. The fabricated ZIF-90 bonded capillary column acted as a weak polar stationary phase. It not only exhibits high capacity in the separation of linear molecules, but also offers excellent features for the separation of 2- and 3-substituted ketones.

Dispersive micro-solid-phase extraction of herbicides in vegetable oil with metal-organic framework MIL-101

Dispersive microsolid-phase extraction based on metal-organic framework has been developed and applied to the extraction of triazine and phenylurea herbicides in vegetable oils in this work. The herbicides were directly extracted with MIL-101 from diluted vegetables oils without any further cleanup. The separation and determination of herbicides were carried out on high performance liquid chromatography. The effects of experimental parameters, including volume ratio of n-hexane to oil sample, mass of MIL-101, extraction time, centrifugation time, eluting solvent, and elution time were investigated. The Student's t test was applied to evaluate the selected experimental conditions. The limits of detection for the herbicides ranged from 0.585 to 1.04 μg/L. The recoveries of the herbicides ranged from 87.3 to 107%. Our results showed that the present method is rapid, simple, and effective for extracting herbicides in vegetable oils.

Synthesis of a metal-organic framework confined in periodic mesoporous silica with enhanced hydrostability as a novel fiber coating for solid-phase microextraction

A metal-organic framework/periodic mesoporous silica (MOF-5@SBA-15) hybrid material has been prepared by using SBA-15 as a matrix. The prepared MOF-5@SBA-15 hybrid material was then deposited on a stainless-steel wire to obtain the fiber for the solid-phase microextraction of phenolic compounds. Modifications in the metal-organic framework structure have proven to improve the extraction performance of MOF/SBA-15 hybrid materials, compared to pure MOF-5 and SBA-15. Optimum conditions include an extraction temperature of 75°C, a desorption temperature of 260°C, and a salt concentration of 20% w/v. The dynamic linear range and limit of detection range from 0.1-500 and from 0.01-3.12 ng/mL, respectively. The repeatability for one fiber (n = 3), expressed as relative standard deviation, is between 4.3 and 9.6%. The method offers the advantage of being simple to use, rapid, and low cost, the thermal stability of the fiber, and high relative recovery (compared to conventional methods) represent additional attractive features.

Tuning fluorocarbon adsorption in new isoreticular porous coordination frameworks for heat transformation applications

We report adsorption behaviors of a typical fluorocarbon R22 (CHClF₂) in a new series of isoreticular porous coordination frameworks [Zn₄O(bpz)₂(ldc)].

Adsorption heat transformation is one of the most energy-efficient technologies, which relies much on the type and performance of the adsorbent–adsorbate pair. Here, we report adsorption behaviors of a typical fluorocarbon R22 (CHClF₂) in a new series of isoreticular porous coordination polymers [Zn₄O(bpz)₂(ldc)], in which the typical Zn₄O clusters are connected by hydrophobic 3,3′,5,5′-tetramethyl-4,4′-bipyrazolate (bpz^2–) and different linear dicarboxylates (ldc^2–) to form non-interpenetrated pcu networks with variable pore sizes, shapes, and volumes. Fluorocarbon sorption measurements of these materials revealed high R22 uptakes of 0.73–0.97 g g^–1 (0.62–0.65 g cm^–3) at 298 K and 1 bar and working capacities of 0.41–0.72 g g^–1 (0.35–0.47 g cm^–3) between 273 and 313 K at about 0.13, 0.11 and 0.52 bar, respectively, as well as very large diffusion coefficients of 5.1–7.3 × 10^–7 cm² s^–1. Noteworthily, the R22 sorption performance can be dramatically improved by subtle modification of the pore size and shape, demonstrating porous coordination polymer–fluorocarbon as a promising adsorbent–adsorbate pair for heat transformation applications.

Synthesis of magnetic framework composites for the discrimination of Escherichia coli at the strain level

Rapid and efficient characterization and identification of pathogens at the strain level is of key importance for epidemiologic investigations, which still remains a challenge. In this work, solvothermically Fe3O4-COOH@MIL-101 composites were fabricated by in situ crystallization approach. The composites combine the excellent properties of both chromium (III) terephthalate (MIL-101) and carboxylic-functionalized magnetite (Fe3O4-COOH) particles and possess the efficient peptides/proteins enrichment properties and magnetic responsiveness. Fe3O4-COOH@MIL-101 composites as magnetic solid phase extraction materials were used to increase the discriminatory power of MALDI-TOF MS profiles. BSA tryptic peptides at a low concentration of 0.25 fmol μL(-1) could be detected by MALDI-TOF MS. In addition, Fe3O4-COOH@MIL-101 composites were successfully applied in the selective enrichment of the protein biomarkers from bacterial cell lysates and discrimination of Escherichia coli at the strain level. This work provides the possibility for wide applications of magnetic MOFs to discriminate pathogens below the species level.

A sensor for formaldehyde detection: luminescent metal–organic framework [Zn2(H2L)(2,2′-bpy)2(H2O)]n

The comparison between the two systems shows that the encapsulation of formaldehyde can affect the luminescence behavior of [Zn₂(H₂L)(2,2′-bpy)₂(H₂O)]_n.

Automated growth of metal–organic framework coatings on flow-through functional supports

Metal–organic framework coatings on flow-through functional supports were prepared using automated flow-based techniques.

In situ synthesis of metal–organic frameworks in a porous polymer monolith as the stationary phase for capillary liquid chromatography

In this study, HKUST-1 was synthesized in situ on the porous polymer monolith as the stationary phase for capillary liquid chromatography (cLC).

Facile synthesis of hydrophilic magnetic graphene@metal–organic framework for highly selective enrichment of phosphopeptides

A hydrophilic magnetic graphene@metal–organic framework (MOF) was designed and synthesized for highly selective enrichment of phosphopeptides.

Syntheses, characterization and properties of nine novel Zn(ii) coordination polymers based on 4,4′-(phenylazanediyl)dibenzoic acid and various N-donor ligands

An 2D sheet consists of two kind of 1D helical chains. The corresponding helical chains in adjoining layers exhibit the opposite handedness.

Water-mediated promotion of direct oxidation of benzene over the metal–organic framework HKUST-1

Pretreatment of a HKUST-1 catalyst with water significantly accelerated the catalytic oxidation of benzene to phenol and hydroquinone with hydrogen peroxide as an oxidant.

Fabrication of hybrid magnetic HKUST-1 and its highly efficient adsorption performance for Congo red dye

A hybrid magnetic metal–organic framework HKUST-1 synthesized via chemical bonding approach possesses efficient and recyclable adsorption performance for Congo red.

Dispersive micro-solid-phase extraction of dopamine, epinephrine and norepinephrine from biological samples based on green deep eutectic solvents and Fe3O4@MIL-100 (Fe) core–shell nanoparticles grafted with pyrocatechol

DA, EP and NE were determined without interference of ascorbic acid using grafted Fe₃O₄@MIL-100 (Fe) NPs and a green solvent.

Three new luminescent Cd(ii)-MOFs by regulating the tetracarboxylate and auxiliary co-ligands, displaying high sensitivity for Fe3+ in aqueous solution

Three new luminescent Cd(ii)-MOFs have been synthesized by regulating the steric effect of tetracarboxylate and auxiliary co-ligands. Notably, 3 displayed high sensitivity for Fe³⁺ in aqueous solution with mixed ions.

Dual amplifying fluorescence anisotropy for detection of respiratory syncytial virus DNA fragments with size-control synthesized metal–organic framework MIL-101

Nanosized MIL-101 with negligible scattered light, synthesized by the addition of glycerol, was used to amplify FA for the detection of DNA with a dual amplification effect.

Optical recognition of alkyl nitrile by a homochiral iron(ii) spin crossover host

In this work, a chiral mononuclear spin crossover host1·MeCN was found to have the ability to optically recognize lactonitrile (LN) and methylglutaronitrile (MGN).

Reverse-phase high performance liquid chromatography separation of positional isomers on a MIL-53(Fe) packed column

The application of the metal–organic framework (MOF) MIL-53(Fe) as a novel stationary phase for reverse-phase high performance liquid chromatography (HPLC) separation of positional isomers is described for the first time.

Zeolitic imidazolate framework dispersions for the fast and highly efficient extraction of organic micropollutants

Porous crystal dispersions in solvent mixtures as a fast and efficient approach for the extraction of organic pollutants from water.

A sensitive and selective sensor for biothiols based on the turn-on fluorescence of the Fe-MIL-88 metal–organic frameworks–hydrogen peroxide system

A novel and simple spectrofluorometry method for the recognition of biothiols using metal–organic frameworks Fe-MIL-88 and H₂O₂ is developed.

Rational synthesis of novel recyclable Fe3O4@MOF nanocomposites for enzymatic digestion

Magnetic MOFs were synthesized for enzyme immobilization. The magnetic MOF–trypsin exhibited significantly improved digestion performance for different kinds of enzymes.

Separation of polar compounds using a flexible metal–organic framework

A flexible metal–organic framework, TetZB, shows remarkable affinity and separation capability of polar compounds (propanol isomers).

Selective gas adsorption in microporous metal–organic frameworks incorporating urotropine basic sites: an experimental and theoretical study

Urotropine-based porous coordination polymers with free N-donors demonstrate selective adsorption towards acidic gas substrates (C₂H₂ or CO₂) as confirmed by isotherm measurements and ab initio DFT calculations.

Postsynthetic ligand exchange for the synthesis of benzotriazole-containing zeolitic imidazolate framework

A postsynthetic ligand exchange strategy is used for introducing benzotriazole to ZIF-7 without changing its framework, high stability and morphology.

Methodologies for evaluation of metal–organic frameworks in separation applications

The separation performance of fixed-bed adsorbers is governed by a number of factors that include (a) adsorption selectivity, (b) uptake capacity, and (c) intra-crystalline diffusion limitations.