Metal-organic frameworks (MOFs) are hybrid (organic/inorganic) crystalline porous solids intensively studied for their potential applications in different domains related to energy, environment or health [1]. Diffraction-based techniques are one of the major methods for the crystal structure determination of MOFs, providing a better understanding of their unique properties. However, the information obtained is the averaged periodic structure, while in some cases - such as adsorption and catalysis - the local structural features (ie., crystal surfaces, interfaces, the presence of guest molecules or defects) are key elements, which can be visualized using high-resolution TEM methods. However, MOFs are among the most beam-sensitive materials and can be easily damaged after exposure to a few electrons/Ų. Therefore, only few successful studies of HRTEM imaging were reported, so far, focusing on just a handful of MOFs [2]. These recent studies have demonstrated that using a direct detection electron counting camera (DDEC) allows performing HRTEM imaging of MOFs with extremely low dose rates (as low as 4 e^-/Ų.s). Thus, individual inorganic clusters could be visualised, while in some cases, the organic linkers could be also resolved [3].

The prediction of the electron-beam stability of a MOF nanocrystal is a difficult task since many structural, morphological or instrumental parameters might be taken into account and could have interconnected effects (Figure 1a). This work aims at identifying the most prominent parameters and assessing their influence on the stability of these objects when exposed to the beam and under given operating conditions. Several known MOFs were imaged by low-dose HRTEM (Figure 1b) enabling the investigation of the effect of the voltage, the particle size and orientation, the presence of guest molecules, as well as the nature and the geometry of the organic and the inorganic moieties. The threshold cumulative electron dose that a MOF can withstand before being completely damaged is determined by monitoring the fading of the spots on the fast Fourier transform images calculated after different exposure times. It has been found that the size of the particle does not have as much impact on the stability as its orientation and its degree of crystallinity, while the presence of guest species encapsulated in the pores has been found to significantly improve the stability. The comparison of the lowest and highest threshold electron doses measured for particles oriented along random off-zone axes of a series of aluminium-based and titanium-based MOFs (Al-MOFs and Ti-MOFs) is given in Figure 1b. The obtained results and the influence of the different features and parameters (ie., linker connectivity, nuclearity of the inorganic building unit, the oxidation state of the metal ions, etc.) on the electron beam stability of these MOFs will be presented. Besides, low-dose HRTEM imaging realised on new in-house MOFs and its use for structure resolution will be also highlighted.

A novel lectin was isolated, purified and characterized from seeds of Entada rheedii using ammonium sulphate precipitation followed by lactose affinity chromatography. On SDS-PAGE, the purified Entadin lectin appeared as a single band (monomer in nature) with a molecular mass of approx. 20 kDa both in reducing as well as in non-reducing conditions. Mass spectroscopic analysis confirms the molecular weight of Entadin lectin as 19333 Da. Entadin lectin showed highest titer value in agglutination against human blood group-B RBC and its Hemagglutination activity was inhibited by lactose, cellobiose, and galactose only. Periodic Acid Schiff’s (PAS) stain confirmed the glycoprotein nature of Entadin lectin with an approx. 5 % of carbohydrate content. The lectin is highly stable even after incubation at a wide range of temperatures (30 to 60 °C) and pH (6 to 10). Antiproliferative effect of Entadin lectin against lung cancer cells A549 and cervical cancer cells HeLa showed IC₅₀ value of 38 µg/mL and 34 µg/mL and no anti-proliferative activity against normal cells. Cell morphological studies revealed that Entadin lectin induced apoptosis both in A549 and HeLa cancer cells which was confirmed by (AO/EB) and Hoechst (33258) nuclear counter staining. Further, Lectin was crystallized using the hanging-drop vapour-diffusion method with 30% PEG 8000 as precipitating agent, 0.2 M ammonium sulphate and 0.1 M sodium cacodylate pH 6.5.

Ternary coordination compounds of copper with amino acids / amino acid derivatives and heterocyclic bases are important in studies related to the biological activity and structural properties. They have potential application in biomedicine and crystal engineering [1,2]. Ternary coordination compounds with amino acids and heterocyclic bases as ligands possess many hydrogen bond acceptors and donors and form diverse but somehow predictable supramolecular motifs based on covalent bonds or noncovalent interactions (porous structures, coordination polymers or other arhitectures) [3,4].

As a part of our ongoing investigation of copper–amino acidato systems, we report 5 new crystal structures of ternary coordination compounds of copper(II) with 1,10-phenanthroline (Phen) and L-threonine (Thr) and sarcosine (Sar): [Cu(Sar)(H₂O)(Phen)][Cu(SO₄)(Sar)(Phen)]·Py·2H₂O (1), [Cu(Sar)(H₂O)(Phen)][Cu(SO₄)(Sar)(Phen)]·7H₂O (2), [Cu(Sar)(H₂O)₂(Phen)][Cu(Sar)(H₂O)(Phen)]SO₄·8H₂O (3), {[Cu(m-Thr)(Phen)]₂SO₄·3.5H₂O}_n (4), [Cu(Thr)(H₂O)(Phen)] [Cu(Thr)(Py)(Phen)]SO₄·2H₂O (5); (Py = pyridine). Except for one complex cation in compound 3 as well as in the coordination polymer 4, the copper(II) ion is pentacoordinated by N, O-donating Thr or Sar ligand and N, N’-donating Phen ligand in the basal plane, and apically coordinated by a solvent molecule (water or pyridine) or sulphate anion. In one of complex cation in 3 the copper(II) ion is octahedrally coordinated with Sar and Phen ligands in the equatorial positions and two water molecules in the axial positions. Compound 4 is a coordination polymer with the copper(II) ion pentacoordinated by didentate Thr and Phen ligands while the axial position is occupied by a carboxylate oxygen atom from the neighbouring complex unit. In all crystal structures infinite double chains are formed through π-interactions of the neighbouring Phen rings, which are interconnected by extensive network of O–H∙∙∙O, N–H∙∙∙O and/or O–H∙∙∙N hydrogen bonds. Except for compound 5, solvents molecules of crystallization are located in 1D channels (Figure 1.a). In 5 the water molecules of crystallization are located in pockets between double chains, and with sulphate ions serve as hydrogen bond bridges between adjacent chains through O–H∙∙∙O and N–H∙∙∙O hydrogen bonds (Figure 1.b).

The cytotoxicity of coordination compounds was investigated on cultured HepG2 (human liver cancer) and THP-1 (human leukemia monocytic) cell lines. The compounds showed prominent cytotoxicity towards both cell lines.

a)

b)

Figure 1. a) 1D channels of solvent molecules in 1, b) pockets of water molecules in 5.

[1] Lakshmipraba, J. et al. (2011) European Journal of Medicinal Chemistry, 46, 3013–3021.

[2] Zhang, S. &. Zhou J. (2008) Journal of Coordination Chemistry 61(15), 2488–2498.

[3] Vušak, D. et al. (2017) Cryst. Growth Des. 17, 6049–6061.

[4] Maji, T. K. (2007) Pure Appl. Chem. 79(12), 2155–2177.

Zeolites are crystalline microporous materials of great interest not only from an academic point of view but also from an industrial point of view due to their properties and multiple applications. These properties largely depend on its chemical composition but also on its structure. At present, the International Zeolite Association (IZA) has accepted 242 different structures [1], each with specific characteristics and a particular crystal structure. Obtaining one or the other structure is highly influenced by the organic structure directing agents (OSDAs) used during the synthesis.

Although the most typical OSDAs consist of alkylammonium cations, molecules containing phosphorous or sulfur atoms instead of nitrogen have also been described in recent years. Recently, our group also described the use of alkylarsonium cations, where nitrogen is replaced by an arsenic atom, which effectively lead to the formation of a zeolitic structure [2].

The use of As in ADE provides some additional benefits, since it allows the incorporation of heavy atoms that can act as a probe for different studies of the materials obtained. Its high electron density, compared to that of nitrogen, allows its easy location even using laboratory X-ray powder diffraction equipment; to date, the location of alkylammonium cations often requires the use of single crystal techniques or the use of complex methods. Furthermore, this substitution of N for As allows the use of other advanced characterization techniques, such as nuclear magnetic resonance MAS-NMR of ⁷⁵As in the solid sample, or X-ray absorption spectroscopy (XAS) at the K border of As, to analyze the location and properties of the molecule within the zeolitic network and its evolution under non-standard conditions.

[1] http://www.iza-structure.org/databases/

[2] Sáez ‐ Ferre S., Lopes Ch.W., Simancas J., Vidal ‐ Moya A., Blasco T., Agostini G., Mínguez Espallargas G., Jordá JL, Rey F. and Oña ‐ Burgos P. (2019) Use of Alkylarsonium Directing Agents for the Synthesis and Study of Zeolites. Chemistry - A European Journal 25, 16390-16396

Keywords: zeolite; alkylarsonium; diffraction; XAS; NMR

The authors acknowledge the funding of the Severo Ochoa SEV-2016-0683 and Maria de Maeztu MDM-2015-0538 programs. S.S-F thanks the MEC for its Severo Ochoa Scholarship SPV-2013-067884. P.O.-B. and G.M.E. They thank the MEC for their Ramón y Cajal contracts (RYC-2014-16620 and RYC-2013-14386). The authors are grateful for the financial support of the Government of Spain (RTI2018-096399-A-I00, RTI2018-101784-B-I00 and CTQ2017-89528-P) and Generalitat Valenciana (PROMETEO / 2017/066). The UPV's Electronic Microscopy Service is thanked for its help in the characterization of samples. We thank the synchrotron ESRF for assigning the beam time (proposal CH-5193), the Italian CRG beamline in ESRF (LISA-BM08) and Alessandro Puri for help and technical support during our experiment. C.W.L. thanks CAPES for a predoctoral fellowship (Science without Frontiers - 13191 / 13-6).

Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) are two highly representative per- and polyfluoroalkyl substances (PFAS) recognized as environmental persistent organic contaminants [1-2]. Adsorption on zeolites is a reliable alternative to eliminate these compounds from water and wastewaters because of their framework flexibility, high organic contaminant selectivity, high specific capacity, rapid kinetics, excellent resistance to chemical, biological, mechanical or thermal stress [3-4]. Ag-exchanged zeolites show unique physical, chemical, and antibacterial properties along with strong absorption property and good stability thus working synergistically in removal of PFAS from water. Consequently, a deep investigation of these materials with exceptional performances must be explored beside their effectiveness for PFAS removal. In this work, the interactions between PFOA and PFOS and Y zeolites (FAU-topology) with different SiO₂/AlO₂ (SAR) were systematically investigated for the first time, in order to evaluate the role of hydrophobic and electrostatic forces in the interaction between polyfluoroalkyl substances and the adsorbents. A careful characterization of Y zeolites (with SAR= 30, 60 and 500, respectively) loaded with PFOA and PFOS, respectively, was carried out before and after silver functionalization in order to: i) investigate the effectiveness of synthetic Y and Ag-Y zeolites with a different SAR ratio towards PFAS, ii) characterize their structure; iii) localize the host species in the zeolites channel system, iv) investigate the thermal stability and their crystallinity degree, v) probe the interaction between PFAS molecules, water molecules, Ag ions and framework oxygen atoms. X-ray powder diffraction patterns (XRD) of the as-synthesized and Ag-loaded Y samples before and after PFAS adsorption, were collected at room temperature by using Bruker D8 Advance Diffractometer with a Sol-X detector, Cu Kα1, α2 radiation. Rietveld structure refinements were performed using the GSAS package with EXPGUI graphical interface in the Fd-3m space group. The zeolites crystallite sizes were achieved by both the Scherrer and Williamson-Hall approaches. TG and DTA measurements of all samples were performed in constant air flux conditions from room temperature up to 1400 °C using an STA 409 PC LUXX® - Netzsch (10 °C/min heating rate). After PFOS and PFOA adsorption, the selected materials maintain a high crystallinity degree. PFASs adsorption on Y and AgY samples was evidenced by differences in both the positions and intensities of the powders diffraction peaks, which are indicative of structural variations in terms of nature and concentration of the extraframework species, unit cell dimensions and framework geometry. The PFOA and PFOS adsorption was accompanied by deformations of the framework, evidenced by the value of the crystallographic free area of the zeolites channel systems. In all samples, PFOA and PFOS molecules were localized at the centre of Y-supercage, thus assuming six different orientations. The bond distances indicated strong interactions mediated via water molecules between zeolite framework and PFASs reactive carboxylic and sulfonyl functional groups. The structure refinements gave an extraframework content corresponding to ~26.0 and 22.0% wt. of PFOA and PFOS, respectively, in good agreement with the weight loss given by the thermogravimetric analyses. Our results highlighted that Ag-exchanged zeolites with high SAR were the most efficient adsorbents thus representing selective tools for PFOS and PFOA abatement as environmentally friendly, bactericidal and low-cost materials.

[1] Sinclair, G.M., Long, S.M., Jones, O.A.H. (2020). What are the effects of PFAS exposure at environmentally relevant concentrations? Chemosphere, 258, 127-340[2] Pan, C., Liu, Y., and Ying, G. (2016). Perfluoroalkyl substances (PFASs) in wastewater treatment plants and drinking water treatment plants: removal efficiency and exposure risk. Water Research. 106, 562-570.[3] Gagliano, E., Sgroi, M., Falciglia, P.P., Vagliasindi, F.G.A., Roccaro, P. (2020). Removal of poly- and perfluoroalkyl substances (PFAS) from water by adsorption: Role of PFAS chain length, effect of organic matter and challenges in adsorbent regeneration. Water Res. 171, 115-381.[4] Mingshu, L., Yujie, R., Ji, W., Yuanhui, W., Jieyu, C., Xinrong, L. and Xiaoyan, Z. (2020). Effect of cations on the structure, physico-chemical properties and photocatalytic behaviors of silver-doped zeolite Y. Microporous and Mesoporous Materials, 293, 109-800.

Identification of agrochemical degradation metabolites occurring in soil, water, and crops, and assessment of their toxicity are of great importance in view of food safety. A common approach to identify the structures of unknown metabolites is to synthesize their canditdates as reference standards based on the structures estimated from chemical information obtained from nuclear magnetic resonance (NMR) and mass spectrometric (MS) analyses, and to compare the unknown metabolites with the reference standards.

However, agrochemical degradation metabolites are usually obtained in only very small amounts, and a multitude of structures can occur in the environment and crops. Therefore, synthesizing all such potential metabolites and similar candidate compounds involves extremely time- and money-consuming efforts. If the molecular structures of a wide range of metabolites with very small amount can directly be determined by single crystal X-ray (SCX) analysis, the time and economic costs will dramatically be reduced.

The crystalline sponge (CS) method is a novel technique for sample preparation of SCX developed by Prof. Fujita.[1] The CS method utilizes a crystal of metal-oraganic framework (MOF) as a crystalline molecular container that can incorporate a wide variety of small molecules within the pores and arrange the molecules in a regular pattern according to the periodicity of the host crystal. As a result, the host-guest complex as a whole can be regarded as a single crystal.

The CS method is very advantageous for structure determination of the agrochemical degradation metabolites. Crystal preparation using one crystal of MOF enables trace analysis with a sub-microgram scale. As no other approach is able to produce accurate structural determinations with just micrograms of unidentified sample purified by preparative HPLC, based on degradation/metabolism experiments on a laboratory scale, SCX analysis combined with the CS method thus offers the potential of dramatically changing the conventional modality of degradation metabolite analysis.

In this presentation, we will show the initial examples of the structure identification of agrochemical metabolites (Fig. 1).

Metal-organic frameworks (MOFs) have attracted widespread attention for their porosity and potential applications in separation chemistry, catalysis, molecular sensing and gas storage. [1] This class of materials are coordination polymers and may be 1-periodic, 2-periodic or 3-periodic. Firstly, we report a partially-fluorinated, 2-periodic MOF, [Zn(hfipbb)(bpt)]_n·n(C₃H₇NO)₂·n(H₂O) where H₂hfipbb = 4,4′-(hexafluoroisopropylidene)bis(benzoic acid) and bpt = 4-amino-3,5-bis(4-pyridyl)-1,2,4-triazole. This framework undergoes single-crystal-to-single-crystal in solvent exchange with ethanol, dichloromethane and N,N’-dimethylacetamide, respectively. The solvent-induced ‘breathing’ of the 2-periodic frameworks results in potential void spaces varying from 15.2-35.4%.[2] In addition, we report the synthesis of a pair of isoreticular mixed-ligand MOFs, [Zn(μ₂-ia)(μ₂-bpe)]_n·nDMF and [Zn(μ₂-mia)(μ₂-bpe)]_n·n(C₃H₇NO), where ia = isophthalate, mia = 5-methoxyisophthalate and bpe = 1,2-bis(4-pyridyl)ethane.[3] Both structures consist of doubly interpenetrated 2-periodic frameworks. Despite a lower void space, one of the activated MOFs exhibits significantly higher sorption of carbon dioxide at 195 K, illustrating that small changes in functional groups, even in structurally similar MOFs, may have a large effect on sorption properties.

[1] Zhou, H.; Long, J. R.; Yaghi, O. M. Introduction to Metal-Organic Frameworks. Chem. Rev. 2012, 112, 673-674.

[2] Chatterjee, N. and Oliver, C.L., Cryst. Growth Des. 2018, 18, 7570−7578.

[3] Gcwensa, N., Chatterjee, N., Oliver, C.L., Inorg. Chem. 2019, 58, 2080−2088.