Barbara Gil

A new Al-MOF based on a unique column-shaped inorganic building unit exhibiting strongly hydrophilic sorption behaviour

The new Al-based metal-organic framework [Al(13)(OH)(27)(H(2)O)(6)(BDC-NH(2))(3)Cl(6)(C(3)H(7)OH)(6)] denoted CAU-6 (CAU = Christian-Albrechts-Universität) was solvothermally synthesized in 2-propanol and was thoroughly characterized. The framework structure exhibits a unique column-shaped inorganic building unit, which is based on stacked, corner-sharing Al(13)-clusters. The compound exhibits unprecedented hydrophilicity for metal-organic frameworks.

Thermal post-synthetic modification of Al-MIL-53–COOH: systematic investigation of the decarboxylation and condensation reaction

Aluminium trimellitate [Al(OH)(BDC–COOH)]·0.9H2O (1), the Al-MIL-53–COOH derivative, was discovered under solvothermal conditions using a high-throughput set-up suitable for microwave (MW)-assisted heating. The compound shows high structural flexibility. The large-pore (lp) form of the framework is obtained under large excess of H2O or after solvothermal treatment with N,N-dimethylformamide upon which [Al(OH)(BDC–COOH)]·0.7DMF (2) is obtained. Exposure of the water rich lp form of 1 to ambient conditions leads to the transformation to the narrow-pore (np) form. Thermal activation of both compounds results in the formation of the empty lp form and the activation of 1 was studied in detail by in situ IR-spectroscopy. Depending on the activation temperature and time two post-synthetic modification (PSM) processes are observed: the partial decarboxylation and the formation of acid anhydride groups. Thus at high temperatures and long activation times [Al(OH)(BDC–OCOCO–BDC)x/2(BDC)y] (x + y = 1) is formed. Upon cooling in air the anhydride functionality still remains intact, but the np form is obtained in air due to the adsorption of H2O molecules. Sorption measurements of 1 confirm a preference for polar gases like H2O and CO2 in comparison to N2, H2, and CH4. The N2 capacity depends strongly on the degree of decarboxylation.

An in situ IR study of the NOx adsorption/reduction mechanism on modified Y zeolites

The surface species formed during adsorption of NO, NO + O2 and NO2 on sodium and barium exchanged Y zeolites have been investigated by in situ IR spectroscopy. Ionically bound nitrates and nitrites on the exchanged metal cation sites are the main species formed during adsorption of NO and NO2. Extra framework alumina was identified as additional sorption site forming small concentrations of bridging, chelating and monodentate nitrates. N2O4 and NO+ were found to be reaction intermediates during the NOx adsorption process. The direct oxidation of NO2 with reactive oxygen from the zeolite surface is facilitated by the formation of nitrates via the disproportionation reaction of N2O4 to NO+ and NO3−. NO+ was found to act as precursor for the creation of nitrites. Decomposition of the nitrate species occurs between 150 and 450 °C. During the temperature increase less stable nitrite/nitrate species are transformed into Ba-nitrates showing the highest thermal stability. The stability of surface nitrates/nitrites was found to be lower, if NO instead of NO2 is present in the feed during temperature increase. For the interaction of surface NOx species with propene two pathways are proposed. At low temperatures, NO+ was identified as the active NOx surface species reacting with propene to nitriles. At higher temperatures the reduction of surface nitrates/nitrites occurred via organic nitro/nitrito species, carboxylic species and isocyanates.

Metal-organic frameworks: mechanisms of antibacterial action and potential applications.

The growing resistance of pathogens to conventional antibiotics has become a public health problem and raises the need to seek new effective solutions. Metal-organic frameworks (MOFs) are porous, hybrid materials comprising metal ions linked by organic binding ligands. The possibility of using a variety of chemical building components in MOFs enables the formation of structures with desired properties. They can act as a reservoir of metal ions, providing their gradual release and resulting in a sustained antibacterial action analogous to that proposed for metal/metal oxide nanoparticles (NPs) but different to that of antibiotics. These features make MOFs promising candidates for pharmaceutical and biomedical applications, as illustrated by examples discussed in this review.

The interaction of CO, N2 and NO with Cu cations in ZSM-5: quantum chemical description and IR study

In this paper we study the properties of Cu ions and their interactions with diatomic molecules in Cu-exchanged ZSM-5. We present DFT quantum chemical calculations for models composed of the Cu site and a diatomic molecule accompanied by IR investigations for various forms of CuZSM-5. Two series of calculations with density functional theory have been undertaken in order to investigate the influence of zeolitic framework on properties of exchanged cations: (i) for small models built of free mono- and divalent copper cation interacting with CO, N2 and NO and (ii) 5- or 6-member ring models of ZSM-5 hosting the cation and a diatomic molecule. Comparison of calculated and experimental IR X–Y frequencies supports our model and brings some insight into the activation mechanism.

Metal–organic frameworks as potential multi-carriers of drugs

The metal–organic framework CPO-27-Ni is presented as a proof-of-concept model for the incorporation and release of two non-conventional anticancer drugs: [Ru(p-cymene)Cl2(pta)] (RAPTA-C) and NO.

FTIR study of hydration of dodecatungstosilicic acid

The dehydration of H4SiW12 O40·15.6 H2O was studied in situ in the IR chamber. On evacuation at room temperature the departure of most loosely bonded water characterized by bands at 3550 and 1616 cm−1 was observed. In the remaining hexahydrate the band at 3445 cm−1 was ascribed to the hydrogen bond between the Od oxygen atom of the Keggin unit and dioxonium H5O2+ ion, the presence of which is manifested by the 1710 and 1100 cm−1 vibrations. All these bands vanish in the case of anhydrous H4SiW12O40, in which the band at 3106 cm−1 ascribed to the hydrogen bond between neighbouring HPA anions Od−H+−Oc is still present. The dehydration of hexahydrate is accompanied by splitting of the W=Od band into 987 and 1010 cm−1 reflecting the change of the kind of hydrogen bond in which the Od oxygen atom is involved. Based on the above results it was concluded that protons forming oxonium ions in hydrated solid heteropoly acid are more strongly bonded than those in anhydrous one which are forming hydrogen bonds between neighbouring Keggin units.

T–O–T skeletal vibration in CuZSM-5 zeolite: IR study and quantum chemical modeling

The location of Cu cations in CuZSM-5, properties of cationic sites and their interaction with guest molecules have been studied by quantum chemical (DFT) modeling and IR spectroscopy based on the frequency shift of antisymmetric T–O–T vibration of oxygen rings. The shift has been found sensitive both to the framework interaction with cations and to the interaction with adsorbed molecules. It has been measured and estimated theoretically from parameters characterising framework distorsion by Cu+ and Cu2+, with MgZSM-5 and NaZSM-5 used as ‘‘reference samples’’. It was found that the ordering of the cation perturbing effect was: Na+<Cu+<Mg2+<Cu2+. NO interaction with Cu cations was much stronger than that of CO and N2 . Divalent copper showed polarized 2-electron covalent bonding with NO strengthening its bond while moderate bonding ability of monovalent copper led to NO bond activation, in accordance with high catalytic activity of Cu+ZSM-5.

Multirate delivery of multiple therapeutic agents from metal-organic frameworks

The highly porous nature of metal-organic frameworks (MOFs) offers great potential for the delivery of therapeutic agents. Here, we show that highly porous metal-organic frameworks can be used to deliver multiple therapeutic agents—a biologically active gas, an antibiotic drug molecule, and an active metal ion—simultaneously but at different rates. The possibilities offered by delivery of multiple agents with different mechanisms of action and, in particular, variable timescales may allow new therapy approaches. Here, we show that the loaded MOFs are highly active against various strains of bacteria.

Heterogeneity of hydroxyl groups in zeolites studied by IR spectroscopy

Abstract A hypothesis has been proposed that homogeneous hydroxyl groups would be present in zeolites in which all the hydroxyls have the same number of Al atoms in the close vicinity and also have the same bridge geometry (the same SiO and AlO bond distances and the same SiOHAl bridge angle). However, heterogeneous hydroxyl groups would appear in zeolites in which there are hydroxyls with various Al numbers or with various geometries. Heterogeneity of hydroxyl groups was expected in NaHA and NaHX zeolites (the same bridge geometry and the same number of Al atoms). However, heterogeneity was expected in NaHY zeolite (the same geometry but various number of Al atoms), in NaHZSM-5 and NaH-ferrisilicate (the same Al or Fe number but various geometries) and also in NaH-mordenites (various Al numbers and various geometries). The heterogeneity of hydroxyl groups was studied by analysis of the IR band of hydroxyls hydrogen-bonded to aromatic hydrocarbons, their derivatives and to ethene. Principal component analysis evidenced that the splitting of the IR band of hydrogen-bonded hydroxyl groups is due to the heterogeneity of the hydroxyls and not to Fermi resonance. The results of our IR studies concerning the properties of hydroxyl groups were compared with the results of quantum-chemical calculations (MNDO method) and also the results of 29 Si MAS NMR studies of properties of framework Si atoms.