A green approach to encapsulate proteins and enzymes within crystalline lanthanide-based Tb and Gd MOFs

In this work, bovine serum albumin (BSA) and Aspergillus sp. laccase (LC) were encapsulated in situ within two lanthanide-based MOFs (TbBTC and GdBTC) through a green one-pot synthesis (almost neutral aqueous solution, T = 25 °C, and atmospheric pressure) in about 1 h. Pristine MOFs and protein-encapsulated MOFs were characterized through wide angle X-ray scattering, scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared and Raman spectroscopies. The location of immobilized BSA molecules, used as a model protein, was investigated through small angle X-ray scattering. BSA occurs both on the inner and on the outer surface of the MOFs. LC@TbBTC, and LC@GdBTC samples were also characterized in terms of specific activity, kinetic parameters, and storage stability both in water and acetate buffer. The specific activity of LC@TbBTC was almost twice that of LC@GdBTC (10.8 μmol min-1 mg-1vs. 6.6 μmol min-1 mg-1). Both biocatalysts showed similar storage stabilities retaining ∼60% of their initial activity after 7 days and ∼20% after 21 days. LC@TbBTC dispersed in acetate buffer exhibited a higher storage stability than LC@GdBTC. Additionally, terbium-based MOFs showed interesting luminescent properties. Together, these findings suggest that TbBTC and GdBTC are promising supports for the in situ immobilization of proteins and enzymes.

The Structure and Optical Properties of Luminescent Europium Terephthalate Antenna Metal-Organic Frameworks Doped by Yttrium, Gadolinium, and Lanthanum Ions

New heterometallic antenna terephthalate MOFs, namely, (EuxM1-x)2bdc3·4H2O (M = Y, La, Gd) (x = 0.001-1), were synthesized by a one-step method from aqueous solutions. The resulting compounds are isomorphic to each other; the crystalline phase corresponds to Ln2bdc3∙4H2O. Upon 300 nm excitation to the singlet excited state of terephthalate ions, all compounds exhibit a bright red emission corresponding to the of 5D0-7FJ (J = 0-4) f-f transitions of Eu3+ ions. The Eu(III) concentration dependence of the photophysical properties was carefully studied. We revealed that Gd-doping results in photoluminescence enhancement due to the heavy atom effect. To quantitatively compare the antenna effect among different compounds, we proposed the new approach, where the quantum yield of the 5D0 formation is used to characterize the efficiency of energy transfer from the ligand antenna to the Eu3+ emitter.

Structure-Property Relationships in Photoluminescent Bismuth Halide Organic Hybrid Materials

Seven novel bismuth(III)-halide phases, Bi₂Cl₆(terpy)₂·0.5(H₂O) (1), Bi₂Cl₄(terpy)₂(k₂-TC)₂(2) (TC = 2-thiophene monocarboxylate), BiCl(terpy)(k₂-TC)₂ (3A-Cl), BiBr(terpy)(k₂-TC)₂ (3A-Br), BiCl(terpy)(k₂-TC)₂ (3B-Cl), [BiCl(terpy)(k₂-TC)₂][Bi(terpy)(k₂-TC)₃]·0.55(TCA) (4), [BiBr₃(terpy)(MeOH)] (5), and [BiBr₂(terpy)(k₂-TC)][BiBr_1.16(terpy)(k₂-TC)_1.84] (6), were prepared under mild synthetic conditions from methanolic/aqueous solutions containing BiX₃ (X = Cl, Br) and 2,2':6',2″-terpyridine (terpy) and/or 2-thiophene monocarboxylic acid (TCA). A heterometallic series, 3A-Bi_1-xEu_xCl, with the general formula Bi_1-xEu_xCl(terpy)(k₂-TC)₂ (x = 0.001, 0.005, 0.01, 0.05) was also prepared through trace Eu doping of the 3A-Cl phase. The structures were determined through single-crystal X-ray diffraction and are built from a range of molecular units including monomeric and dimeric complexes. The solid-state photoluminescent properties of the compounds were examined through steady-state and time-resolved methods. While the homometallic phases exhibited broad green to yellow emission, the heterometallic phases displayed yellow, orange, and red emission that can be attributed to the simultaneous ligand/Bi-halide and Eu centered emissions. Photoluminescent color tuning was achieved by controlling the relative intensities of these concurrent emissions through compositional modifications including the Eu doping percentage. Notably, all emissive homo- and heterometallic phases exhibited rare visible excitation pathways that based on theoretical quantum mechanical calculations are attributed to halide-metal to ligand charge transfer (XMLCT). Through a combined experimental and computational approach, fundamental insight into the structure-property relationships within these Bi halide organic hybrid materials is provided.

Dual vis-NIR emissive bimetallic naphthoates of Eu-Yb-Gd: a new approach toward Yb luminescence intensity increase through Eu → Yb energy transfer

Homo- and heteroligand mono-, bi-, and trimetallic lanthanide naphtoates Eu_xYb_yGd_1-x-y(naph)₃(Phen)_n (n = 0, 1) were obtained and thoroughly investigated. Homoligand naphthoates of the new phase were obtained as anhydrous powders from water. The photophysical properties of the obtained compounds were studied in detail. The first example of Eu-to-Yb energy transfer was found in these systems. Careful selection of the metal ratio allowed a dual vis-NIR emissive complex with a ytterbium quantum yield of 1.5% to be obtained.

Single-step approach to sensitized luminescence through bulk-embedded organics in crystalline fluorides

Luminescent materials enable warm white LEDs, molecular tagging, enhanced optoelectronics and can improve energy harvesting. With the recent development of multi-step processes like down- and upconversion and the difficulty in sensitizing these, it is clear that optimizing all properties simultaneously is not possible within a single material class. In this work, we have utilized the layer-by-layer approach of atomic layer deposition to combine broad absorption from an aromatic molecule with the high emission yields of crystalline multi-layer lanthanide fluorides in a single-step nanocomposite process. This approach results in complete energy transfer from the organic molecule while providing inorganic fluoride-like lanthanide luminescence. Sm³⁺ is easily quenched by organic sensitizers, but in our case we obtain strong fluoride-like Sm³⁺ emission sensitized by strong UV absorption of terephthalic acid. This design allows combinations of otherwise incompatible species, both with respect to normally incompatible synthesis requirements and in controlling energy transfer and quenching routes.

Ln-CPs constructed from unsymmetrical tetracarboxylic acid ligand: Tunable white-light emission and highly sensitive detection of CrO42-, Cr2O72-, MnO4- in water

A series of isostructural lanthanide coordination polymers (Ln-CPs), [Ln(Hbptc)(H₂O)₄]·H₂O [Ln = Er (1), Pr (2), Dy (3), Sm (4), Gd (5), Nd (6) and Tb(7); H₄bptc = 2,3,3',4'-biphenyl tetracarboxylic acid] have been isolated based on an unsymmetrical tetracarboxylic acid. Single-crystal X-ray diffraction analysis reveals that all CPs featured a two dimensional (2D) layer with (6, 6, 6)-connected 6³ topology. Luminescent spectra demonstrate that CPs 1-7 exhibit impressive UV-visible luminescence in the solid state at room temperature. More significantly, a single-component white-light material with International Commission on Illumination (CIE) coordinates of (0.335, 0.334) for 4 (Sm-CP), very closing to the pure white-light of (0.333, 0.333) was obtained by finely tuning of the excitation wavelength. In addition, the luminescent detection for anions of 7 is investigated. Fluorescence measurements show that 7 can detect oxoanion pollutants Cr₂O₇^2-, CrO₄^2-, and MnO₄^- anions in aqueous solutions with high selectivity and sensitivity, which suggests that the Tb-CP is a promising functional luminescence probe for toxic oxoanions. The possible mechanisms of the quenching effect were also discussed in detail.

Design and properties of multiple-emitter luminescent metal–organic frameworks

This feature article reviews the design strategies by which multiple different emission sources could be combined for creating multi-emitter luminescent metal–organic frameworks (LMOFs).

Mixed-metal metal–organic frameworks

Mixed-metal MOFs contain at least 2 different metal ions presenting promising potential in heterogeneous catalysis, gas sorption/separation, luminescence and sensing.

Highly emissive host–guest based on nanoclay intercalated with an Eu3+ complex bearing a new Ru2+ organometallic ligand

An optical nanomaterial of bentonite clay with efficient red pure luminescence from a new europium(iii) complex based on an organometallic ruthenium(ii) cationic ligand.