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Highly Active Anti-Diabetic Metal-Organic Framework David Briones, Belen Fernandez, Antonio J. Calahorro, David Fairen-Jimenez, Raúl Sanz, Fernando Martínez, Gisela Orcajo, Eider San Sebastian, Jose M. Seco, Cristina Sánchez González, Juan Llopis, and Antonio Rodriguez-Dieguez Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.5b01274 • Publication Date (Web): 28 Dec 2015 Downloaded from http://pubs.acs.org on December 28, 2015
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Highly Active Anti-Diabetic Metal-Organic Framework David Briones,¥ Belén Fernández,†,* Antonio J. Calahorro,† David Fairen-Jimenez,§ Raúl Sanz,¥ Fernando Martínez,¥ Gisela Orcajo,¥ Eider San Sebastián,‡ José M. Seco,‡ Cristina Sánchez González,ζ,* Juan Llopisζ and Antonio Rodríguez-Diéguez.†,* ¥ Chemical and Energy Technology Department, Chemical and Environmental Technology, Mechanical Techno-logy and Analytical Chemistry, Universidad Rey Juan Carlos, CalleTulipán s/n, 28933 Móstoles, Spain. † Departamento de Química Inorgánica, Universidad de Granada, Avda Fuentenueva s/n, 18071, Granada, Spain. email:
[email protected] ,
[email protected] § Dept. of Chemical Engineering & Biotechnology, University of Cambridge, Pembroke St., Cambridge CB2 3RA, United Kingdom. ‡ Departamento de Química Aplicada, Facultad de Químicas de San Sebastián, Universidad del País Vasco/EuskalHerrikoUnibertsitatea, UPV/EHU. Paseo Manuel de Lardizabal 3, 20018, San Sebastián, Spain. ζ Instituto de Nutrición y Tecnología de los Alimentos y Departamento de Fisiología, Campus Cartuja, Universidad de Granada, 18071, Granada, Spain. email:
[email protected] ABSTRACT: We have synthesized a novel zinc metal-organicframework (MOF) under mild hydrothermal routes using 5aminotetrazole and methyl-2-amino-4-isonicotinate anionic ligands. The MOF exhibits a three-dimensional structure with intense blue-greenish photoluminescence emission at room temperature in the solid state. The luminescence, porosity and adsorption capacity for CO2 and H2 of the Zn-based MOF has been fully determined using a combination of computational methods and experimental techniques. The synthesized Zn-based compound in this study exhibited a remarkable in vivo antidiabetic activity and low in vitro cell toxicity.
In the last two decades, metal-organic frameworks (MOFs) have attracted much attention due to their exceptional properties.1,2 MOFs are built up from metal ions or clusters connected through organic linkers giving rise to a large diversity of multidimensional structures. The large variety of organic molecules that may act as linkers make possible the rational design of novel MOF structures, tailoring both the chemical and physical properties of the framework. Nowadays, MOFs have evolved enormously3,4 in areas such as luminescence,5,6 gas adsorption,7 drug delivery,8,9 sensing and optical storage.10,11 In the last years, we have designed and synthesized novel Zn-based MOFs with different nitrogen derivative ligands with interesting luminescent properties, such as, tetrazolate and pyrimidine linkers.12 Methyl-2amino-4-isonicotinic acid was selected in this work as a potential linker due to its different coordination modes to form new MOF structures. To the best of our knowledge, five compounds comprised by only two isostructural MOF materials based on different metals ions such as cadmium, cobalt and zinc have been described in literature using this ligand.13,14 Following these works, we report here the synthesis, structure, luminescence, stability and adsorption of a novel zinc MOF based on 5-aminotetrazole (Hatz) and 2-amino-4-isonicotinic (Hain) ligands [Zn(ain)(atz)]n (1). We demonstrate the potential of the ain-1 anionic linker and the secondary nitrogen ligand atz-1 to construct novel MOFs. Thanks to its extended aromaticity and to the presence of poly-
heterosubstituted penta- and hexa-atomic rings, these linkers are good candidates to show enhanced emissive properties, which may be tunable by coordination to different metals with different chemical environments. The synthesized compound 1 has a potential interest in the treatment of diabetes, a pathology where Zn-containing compounds have shown promising hypoglycemic properties.15-18 Hyperglycaemia, is a common effect of uncontrolled diabetes and over time leads to serious damage of the body system.16 Zinc has shown insulin-like effects by supporting the signal transduction of insulin and by reducing the production of cytokines, which lead to beta-cell death during the inflammatory process in the pancreas in the course of the disease. Genetic polymorphisms in the gene of zinc transporter and in metallothionein (MT)-encoding genes could be related to type 2 diabetes mellitus. Antibodies against this zinc trans-porter have been detected in type 1 diabetic patients.17 It has been demonstrated that Zn compounds inhibit the protein-tyrosine phosphatase 1B (PTP1B), enzyme that plays a major role in modulating both insulin sensitivity and fuel metabolism.18 The synthesis of this new three dimensional Zn carrier structure 1 could be an excellent tool to improve the distribution of Zn and therefore its effectiveness as oral antidiabetic agent in the treatment of diabetes mellitus, becoming an alternative -or synergistic agent- to traditional parenteral insulin therapy. The treatment of diabetic rats with this Zn-based MOF synthesized in this study is pioneer and opens a new line of research in the field of healthcare applications of MOFs and the pharmacological treatment of diabetes. Soft hydrothermal reaction of zinc acetate (0.2 mmol) with 5-aminotetrazole (0.2 mmol) and methyl-2-amino-4-isonicotinic acid (0.2 mmol) in water/methanol (10 ml) at 150ºC for 12 h followed by cooling to room temperature over 3 h produced prismatic colorless crystals of 1 in 65% yield (ESI). The crystal structure was determined using single crystal X-ray diffraction.19 The asymmetric unit consists on one zinc atom, one ain-1 ligand and one atz-1 linker. Zn ion exhibits distorted tetrahedral ZnN3O geometry (Figure 1) with N1B and N4B nitrogen atoms belonging to tetrazolate group, one oxygen atom pertaining to a carboxylate
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group and a N1A atom from pyridine ring of the anionic ain-1 ligand.
Figure 1. A view of the metal environment and coordination modes of the ligands for 1. Color code: N = blue, O = red, C = grey, Zn = yellow.
Each ain-1 and atz-1 connects two zinc ions through O2A and N1A (for ain-1), resulting in the formation of a 3D-MOF (Figure 2), in which each tetrazolate moiety also coordinates in a bidentate fashion (N1B-N4B) to zinc atoms. Zn-N distances are in the range of 2.002(4)-2.019(3) Å, whereas Zn-O distance has a value of 1.929(3) Å, for O2A. Cis bond angles of metal environment are in the range of 93.01(14)-118.11(14)º and ZnII•••ZnII distances through ain-1 and atz-1 bridge ligands are 8.892 and 5.980 Å, respectively. The crystalline structure of this 3D-MOF generates two types of channel along b axis with different groups oriented toward the center of the pores (Figure S1). In the A pore, there are carboxylate and amino groups from ain-1 and atz-1, respectively, while in B pore there are amino and tetrazolate groups pertaining to ain-1 and atz-1, respectively. Due to the existence of these pores in the structure, porosity and adsorption capacity for CO2 and H2 of the Zn-based MOF has been fully determined without finding significant results (ESI).
Figure 3. Calculated normalized emission spectrum of model 1, upon application of a Gaussian filter to theoretical data (ESI, Figure S8). The three maxima observed in the original spectrum are indicated as red circles.
In order to understand the origin of the observed emission, TD-DFT theoretical calculations were performed. Studies revealed that the band observed in the emission spectrum of compound 1 arises from the interligand charge transfer22,23 between the two pairs of π stacked 2-amino-isonicotinic ligands. In this respect, model 1 shows a smoothed emission band with a maximum at 466 nm (Table 1 and Figure 3), as a consequence of LUMO→HOMO (376 nm), LUMO+1→HOMO-1 (489 nm) and LUMO+1→HOMO-2 (513 nm) electron relaxation processes (Figure S9). The mentioned molecular orbitals are delocalized over the entire 2-amino-isonicotinic moieties (Table 1 and Figure 3). Table 1. Calculated emission bands and involved electronic transitions in model 1. Figure 2. View down the b axis of the structure in the three-dimensional network. Hydrogen atoms have been omitted for clarity. Color code: N = blue, O = red, C = grey, Zn = yellow.
Max. λ (nm)
Calc. Transitions
Osc. Strength
376
L → H(88%)
0.0010
The extended aromaticity of the anionic ligands and th use of d10 metal ions in 1, suggests the existence of enhanced emissive properties in this MOF. Figure S7 shows the emission spectrum of compound 1 in solid state at room temperature upon excitation at 322 nm. This compound exhibits a broad intense emission band centered at 420 nm. The emission in compound 1 can be tentatively as-signed to the metal to ligand charge transfer (MLCT) and/or to the ligand to ligand charge transfer (LLCT). The emission of 1 is significantly red-shifted compared to that of the isolated ligand. This bathochromism may be due to Zn ions show higher d* energy levels, which is consistent with similar bathochromic shifts that have been observed in other compounds.20,21
489
L+1→H-2 (95%);
0.0010
513
L+1→H-1 (96%)
0.0010
Emission
With the aim of using this MOF in healthcare applica-tions, we determined the effect of compound 1 on HEK293 cell viability by using MTS assays (Figures S10 and S11). We found that in the presence of the highest concentration of tested compound 1 (100 µM), cell proliferation of HEK293 was decreased to 80-75%, and 70% in 48 and 72 h, respectively, compared with the control cells (P < 0.05). In 24 h, we did not find any significant variation on the cell viability measurements. Importantly, we demonstrated that compound 1 had a significantly low cytotoxicity, thereby
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providing a rationale clinical use of compound 1 as a promising antidiabetic agent. In vivo experiments were carried out using male Wistar rats. Results showed that compound 1 had no effect on body weight after the experimental period (10 days). However, it showed a significant reduction of food and water intake, thus alleviating the hiperphagia and polydipsia that accompanies diabetes. Fasting glycaemia levels also significantly decreased in the group of rats treated with the compound 1 in comparison with the untreated diabetic group of rats (Table 2).
In order to confirm compound 1 localization within the cells, confocal microscopy studies were performed (Figures 5, S12, S13 and S14). Results show that 1 is rapidly (2h) internalized by HEK293 cells, and remains in the cytosol at least for 48 h without undergoing chemical degradation or disruption of fluorescent properties. These results were corroborated by flow cytometry assays (Figure S14) that revealed a shift to higher density values for those cells incubated with 1 in the first 10 min to 48 h compared to control.
Table 2. Data are presented as mean ± SD. a control vs diabetic, b control vs diabetic treated, and c diabetic vs diabetic treated. P
