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Bisphosphonate drugs constitute the primary treatment for bone diseases such as Paget’s disease and osteoporosis. Despite their effectiveness, they also exhibit severe drawbacks, such as rapid excretion and limited oral bioavailability. High doses are usually administered to counterbalance these drawbacks. Subsequently, side effects are triggered, such as osteonecrosis of the lower jaw and esophageal cancer. Controlled drug release systems may be viable candidates to overcome those issues. Herein, we present novel functionalized silica-based hydrogels loaded with the osteoporosis drug etidronate (1,1-hydroxyethylidene-diphosphonate) used to control the release profile of the drug. Various methodologies were evaluated to control the initial release rate and the final released concentration of the drug. These included the gel density, by systematically increasing the initial concentration of silicate used to prepare the hydrogels, the presence of metal cations (Ca2+ and Cu2+), and the internal surface functionalization of the gel with silane-based grafting agents (with anionic, cationic, and neutral groups). This study also contributes to our continuous effort to develop new a priori programmable drug-loaded gels for the controlled release of osteoporosis drugs.

A series of 11 compounds, including alkali (Li, Na, K, Rb, Cs) and alkaline-earth (Mg, Ca, Sr, Ba) coordination polymers, transition-metal (Cu, Cd) complexes, and the ammonium salt of 3,5-dimethylp...

The fully deprotonated anion of 1,3,5-benzene-triphosphonic acid 1,3,5-C6H3[PO32−]3 gives rise to deceptively simple 1H and 31P NMR spectra due to a corresponding [AX]3 spin system. The 13C{1H} NMR...

Structural data: full structural data are available from iucrdata.iucr.org, Crystallographic Information File (CIF) https://doi.org/10.1107/S2414314622002474/tk4074sup1.cif Contains datablock I, Structure factor file (CIF format) https://doi.org/10.1107/S2414314622002474/tk4074Isup2.hkl Contains datablock I, MDL mol file https://doi.org/10.1107/S2414314622002474/tk4074Isup3.mol Supplementary material, Chemdraw file https://doi.org/10.1107/S2414314622002474/tk4074Isup4.cdx Supplementary material, The crystal structure of the anionic zinc–[amino­(iminio)meth­yl]phospho­nate one-dimensional coordination polymer, Zn-AIMP, is reported; the negative charge is balanced by an oxidanium cation (H3O+) to give the composition {(H3O)[Zn(CH4N2PO3)3]}n. The building unit of the coordination polymer comprises a divalent Zn2+ cation (site symmetry \overline3..) and three [amino(iminio)meth­yl]phospho­nate mono-anionic ligands (point group symmetry m). The AIMP ligand exists in a zwitterionic form with a total charge −1 as the phospho­nate is fully deprotonated (–PO32−), while the amino­(iminio)methyl moiety is protonated (H2N—C—NH2+)., Research project ‘Innovative Materials and Applications’ (INNOVAMAT, KA 10694) by the Special Account for Research Grants

Crystallographic Information File (CIF) https://doi.org/10.1107/S2414314622001894/tx4001sup1.cif Contains datablock I, Structure factor file (CIF format) https://doi.org/10.1107/S2414314622001894/tx4001Isup4.hkl Contains datablock I, MDL mol file https://doi.org/10.1107/S2414314622001894/tx4001Isup5.mol Supplementary material, Chemical Markup Language (CML) file https://doi.org/10.1107/S2414314622001894/tx4001Isup4.cml Supplementary material, The new triazole-functionalized phospho­nic acid 5-phenyl-3-(2-phosphono­eth­yl)-1,2,3-triazol-1-ium chloride, C10H13N3O3P+·Cl− (PTEPHCl), was synthesized by the `click' reaction of the alkyl azide diethyl-(2-azido­eth­yl)phospho­nate with phenyl­acetyl­ene to give the dieth­yl[2-(4-phenyl-1H-1,2,3-triazol-1-yl)eth­yl]phospho­nate ester, which was then hydrolyzed under acidic conditions (HCl) to give the `free' phospho­nic acid. The use of HCl for the hydrolysis caused protonation of the triazole ring, rendering the compound cationic, charged-balanced by a Cl− anion. There are extensive hydrogen-bonding inter­actions in the structure of PTEPHCl, involving the phospho­nic acid (–PO3H2) group, the triazolium ring and the Cl− anion., Research project ‘Innovative Materials and Applications’ (INNOVAMAT, KA 10694) by the Special Account for Research Grants

The research work at UoC was supported by the Hellenic Foundation for Research and Innovation (HFRI) under the HFRI PhD Fellowship grant (Fellowship Number: 258) to M.V.D. Ch.-L. acknowledges funding by project no. PGC2018-102047-B-I00 (MCIU/AEI/FEDER, UE)., Bisphosphonates (BPs) constitute a class of drugs used for the treatment of calcium-and bone-related disorders, including osteoporosis, Paget’s disease, etc. The presence of the anionic phosphonate groups endows them with the ability to act as ligands to metal ions. As a result, the synthesis of complexes or coordination polymers of various structural motifs can be accomplished. In this work, the 3rd generation BP drug risedronate (RIS) was combined with biologically acceptable alkaline earth metal ions (e.g., Ca2+ and Sr2+) in an effort to synthesize new materials. These metal– RIS compounds can operate as controlled delivery systems (CDSs) when exposed to appropriate experimental conditions, such as the low pH of the human stomach. CDS networks containing Ca2+ or Sr2+ and RIS were physicochemically and structurally characterized and were evaluated for their ability to release the free RIS drug during an acid-driven hydrolysis process. Due to the low solubility of RIS at low pH, cationic additives (linear polyethyleneimine and amine-terminated polyaminoamide dendrimer) were utilized as drug solubilizers. Based on the drug release results of this study, there was an attempt to correlate the drug release efficiency with the structural features of these CDSs., Hellenic Foundation for Research and Innovation 258, PGC2018-102047-B-I00

Synthesis redesign and derivatisation of Fe(ii)-hydroxyphosphonoacetate, incorporating different ammonia loads and M(ii) isomorphic substitutions (M = Mn, Co and Zn), have been implemented. The NH3 adsorption led to materials with enhanced proton conductivity, up to ∼10-3 S cm-1, although it caused a progressive amorphization. The Pair Distribution Function (PDF) analysis for this material confirmed the loss of crystallinity but the local order appeared to be maintained. The parent compound was shown to be an efficient photocatalyst for phenol, 4-chlorophenol and methylene blue even under mild conditions, with TOC removal of 75-90% at 50-150 min of reaction. The M(ii)-substituted derivatives displayed similar behaviour in properties, and therefore their multifunctional character, as the parent compound, although with slightly reduced capabilities.

Metal phosphonates containing acidic groups exhibit a wide range of proton conduction properties, which may enhance the performance of membrane electrode assemblies (MEAs). In this work, focus is placed on proton conduction properties of coordination polymers derived from the combination of lanthanide ions with a phosphonate derivative of taurine (2-[bis(phosphonomethyl)amino]ethanesulfonic acid, HSP). High-throughput hydrothermal screening (140 °C) was used to reach optimal synthesis conditions and access pure crystalline phases. Seven compounds with the composition Ln[H(OPCH)-NH-(CH)-SO]·2HO were isolated and characterized, which crystallize in two different structures, monoclinic m-LaHSP and orthorhombic o-LnHSP (Ln = Pr, Nd, Sm, Eu, Gd, and Tb), with unit cell volumes of ∼1200 and ∼2500 Å, respectively. Their crystal structures, solved ab initio from X-ray powder diffraction data, correspond to different layered frameworks depending on the Ln cation size. In the orthorhombic series, o-LnHSP, the sulfonate group is noncoordinated and points toward the interlayer space, while for m-LaHSP, both phosphonate and sulfonate groups coordinate to the Ln centers. As a consequence, different H-bonding networks and proton transfer pathways are generated. Proton conductivity measurements have been carried out between 25 and 80 °C at 70-95% relative humidity. The Sm derivative exhibits a conductivity of ∼1 × 10 S·cm and activation energy characteristic of a Grotthuss-type mechanism for proton transfer. Preliminary MEA assays indicate that these layered lanthanide sulfophosphonates assist in maintaining the proton conductivity of Nafion membranes at least up to 90 °C and perform satisfactorily in single proton-exchange membrane fuel cells., The work at UMA was funded by MAT2016-77648-R research grant (Spain) and by Junta de Andalucía through the P12- FQM-1656 research project. M.B.-G. thanks UMA Research Plan for financial support. The work at CSIC-Madrid was funded by PROTONCELL ENE2017-86711-C3-1-R and REPICOMES ENE2017-90932-REDT and MAT2016-81001- P. The work at UoC was supported by grants from the Research Committee of the University of Crete, ELKE (grant no. KA 10329).

The interactions of six homologous diphosphonate additives, methylamine-N,N-bis(methylenephosphonate) (MBMP, C1-D), ethylamine-N,N-bis(methylenephosphonate) (EBMP, C2-D), butylamine-N,N-bis(methylenephosphonate) (BBMP, C4-D), hexylamine-N,N-bis(methylenephosphonate) (HBMP, C6-D), octylamine-N,N-bis(methylenephosphonate) (OBMP, C8-D), dodecylamine-N,N-bis(methylenephosphonate) (DBMP, C12-D), with carbon steel surfaces are studied by XPS at pH = 3.0. Structurally, all additives possess two methylenephosphonate moieties connected to a single N atom. The third substituent on N is a non-polar, variable-length alkyl chain, –(CH2)xCH3, where x = 0 (C1-D), 1 (C2-D), 3 (C4-D), 5 (C6-D), 7 (C8-D), and 11 (C12-D). XPS studies (on pristine solid diphosphonate samples and also on carbon steel specimens, immersed in aqueous solutions), indicate significant deprotonation of the diphosphonic acid molecules upon interaction with the metallic surface. They also prove that this surface interaction results in adsorption on the surface via the deprotonated phosphonic acid moieties. The adsorption of inhibitors on the metal surface was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy. The changes detected in the charge transfer resistance (Rct) and constant phase element (CPE) independently confirm inhibitor adsorption on metal surface. Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy and Scanning Electron Microscopy was used to investigate the nature of deposited film. Small alkyl chain diphosphonates (C1-D, C2-D and C4-D) exhibited lower corrosion resistance due to the thin, porous and/or incomplete layer formed on carbon steel surface. Longer alkyl chain molecules (C6-D, C8-D and C12-D) were found to adsorb more efficiently and form a more organized and thicker layer. The best results were obtained in the case of C8-D (lower corrosion current, higher Rct and surface coverage). In the presence of C8-D the corrosion rate was reduced by a factor of 6.

Scale inhibition is of crucial importance in harvesting geothermal energy, an attractive, renewable and sustainable energy source. The majority of the geothermal reservoir waters around the world contain a variety of anions and cations, which are prone to precipitation when subjected to vast transformations of both temperature and pressure, causing failures to many parts of the plants. Our goal is to prevent the formation, precipitation and deposition of such scales by stabilizing their respective components. Our working brines are designed based on the saturated conditions of geothermal well waters. Common inorganic scales tested include amorphous silica, magnesium silicate, aluminum silicate, iron (III) silicate, zinc sulfide, lead sulfide, iron (II) sulfide, and calcium carbonate. Against these scales, four interrelated methacrylate-structured polymers were tested as inhibitors, grafted either with polyethylene glycol (PEG), or phosphonic acid (PHOS) side-chains, or both. Based on several results obtained the inhibitor PEGPHOS-LOW (containing 34 PEG grafts and 14 phosphonate grafts) was selected as the most efficient, and was subsequently tested in artificial geothermal brines of variable stress, containing all the scales together.

Phase transformation dynamics and proton conduction properties are reported for cationic layer-featured coordination polymers derived from the combination of lanthanide ions (Ln3+) with nitrilo-tris(methylenephosphonic acid) (H6NMP) in the presence of sulfate ions. Two families of materials are isolated and structurally characterized, i.e., [Ln2(H4NMP)2(H2O)4](HSO4)2·nH2O (Ln = Pr, Nd, Sm, Eu, Gd, Tb, Er, Yb; n = 4-5, Series I) and [Ln(H5NMP)]SO4·2H2O (Ln = Pr, Nd, Eu, Gd, Tb; Series II). Eu/Tb bimetallic solid solutions are also prepared for photoluminescence studies. Members of families I and II display high proton conductivity (10-3 and 10-2 S·cm-1 at 80 °C and 95% relative humidity) and are studied as fillers for Nafion-based composite membranes in PEMFCs, under operating conditions. Composite membranes exhibit higher power and current densities than the pristine Nafion membrane working in the range of 70-90 °C and 100% relative humidity and with similar proton conductivity., Financial support through the following projects is acknowl- edged: UMA authors for MAT2016-77648-R (MICINN/ FEDER); PID2019-110249RB-I00 (MICINN/FEDER) and Junta de Andalucía (FQM113); UoC authors for The Special Account of Research, Program INNOVAMAT KA 10694; D.C.L. for PGC2018-102047-B-I00 (MICINN/FEDER); M.L.G. for PGC2018-095364-B-I00 (MICINN/FEDER); C.R. for ENE2017-86711-C3-1-R and ENE2017-90932- REDT (MICINN/FEDER). A.D.F. for the Russian Science Foundation (Grant No. 19-79-10241)

Scale inhibition is of crucial importance in harvesting geothermal energy, an attractive, renewable and sustainable energy source. The majority of the geothermal reservoir waters around the world contain a variety of anions and cations, which are prone to inorganic precipitation when subjected to drastic changes in both temperature and pressure, causing failures and unwanted shut-downs. Our goal is to prevent the formation, precipitation and deposition of such scales by stabilizing their respective components. Herein, the ability of a methacrylate-structured, grafted co-polymer, coined PEGPHOS-LOW (with polyethylene glycol and phosphonate grafts), to control inorganic precipitation is evaluated for four artificial geothermal brines of variable scaling propensity towards common geothermal scales, such as amorphous silica, magnesium, aluminum and iron silicates, zinc, lead and iron sulfides and calcium carbonate. Inhibitor selection was based on previous results obtained with four, similar inhibitor grafted co-polymers (one containing only polyethylene glycol, PEG, one with only phosphonate grafts, and two containing variable ratios of both grafts) against individual scales. The working brines were designed based on the saturated conditions of geothermal well fluids. PEGPHOS-LOW is a polymer that contains 34 PEG20 grafts, and 14 phosphonate grafts. It is a dual scale control additive, as it can function both as a scale inhibitor (keeping the scaling species soluble) and as a dispersant (keeping the scale particles formed in a suspended form). It displays a dosage-dependent scale inhibition and dispersion behavior, however, very high concentrations are necessary for satisfactory effectiveness, due to the high scaling propensity of the brines.

(Poly)phosphonic acids constitute an exciting family of phosphorus compounds. One of the attractive attributes of these molecules is the rich chemistry of the phosphonate moiety, and, in particular, its high affinity for metal ions and mineral surfaces. Whether the phosphonate group belongs to a “small” molecule or to a polymeric matrix, phosphonate-containing compounds have found a phalanx of real-life applications. Herein, we address a special category of phosphorus compounds called bisphosphonates (BPs, a.k.a. “-dronates”) and also phosphonate containing polymers. The success of BPs in mitigating osteoporosis notwithstanding, these “-dronate” drugs present a number of challenges. Nevertheless, the main drawback of BPs is their limited oral bioavailability. It is, therefore, imperative to design and fabricate “smart” systems that allow controlled delivery of the active BP agent. Here, easy-to-prepare drug delivery systems are presented based on silica gels. These have been synthesized, characterized, and studied as hosts in the control release of several BP drugs. They exhibit variable release rates and final % release, depending on the nature of bisphosphonate (side-chain length, hydro-philicity/-phobicity, water-solubility), cations present, pH and temperature. These gels are robust, injectable, re-loadable and re-usable. Furthermore, alternative drug delivery systems are presented that are based on metal-organic frameworks (MOFs). In these biologically acceptable inorganic metal ions have been incorporated, together with BPs as the organic portion. These materials have been synthesized, characterized, and studied for the self-sacrificial release (by pH-driven dissolution) of the BP active ingredient. Several such materials were prepared with a variety of bisphosphonate drugs. They exhibit variable release rates and final % release, depending on the actual structure of the metal-bisphosphonate material. Lastly, we will present the use of phosphonate-grafted polymers as scale inhibitors for water treatment applications.

We study the interaction of six systematically varied tetraphosphonate molecules with carbon steel surfaces by XPS at pH 3. All tetraphosphonates [EDTMP (C2), TDTMP (C4), HDTMP (C6), ODTMP (C8) and DDTMP (C12)] belong to the aminomethylene-phosphonate family, and they possess systematically elongated backbone (from two to twelve methylene groups separating the N atoms). XPS studies were performed on powdered samples and also on immersed carbon steel specimens in aqueous solutions. The XPS results also suggest that the tetraphosphonic acid molecules become significantly deprotonated upon interaction with the carbon steel surface and that the surface interaction of the tetraphosphonic acid family leads to additive adsorption on the steel surface via the phosphonate groups. The mode of corrosion inhibition was studied by potentiodynamic polarization and electrochemical impedance spectroscopy. The changes observed in the impedance parameters, like charge transfer resistance (Rct) and constant phase element (CPE) confirm the strong adsorption on the metal surface. The nature of the protective layer formed on the carbon steel surface was examined by Attenuated Total Reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and optical microscopy.

The formation, precipitation, and deposition of so-called “magnesium silicate” in geothermal waters have been subjects of intense interest. Such scaling poses a severe threat to the smooth process ...

The synthesis, structural characterization, topological analysis, proton conductivity, and catalytic properties are reported of two Cu(II)-based compounds, namely a dinuclear Cu(II) complex [Cu2(μ-VPA)2(phen)2(H2O)2]·8H2O (1) (H2VPA = vinylphosphonic acid, phen = 1,10-phenanthroline) and a 1D coordination polymer [Cu(μ-SO4)(phen)(H2O)2]∞ (2). Their structural features and H-bonding interactions were investigated in detail, showing that the metal–organic structures of 1 and 2 are extended by multiple hydrogen bonds to more complex 2D or 1D H-bonded architectures with the kgd [Shubnikov plane net (3.6.3.6)/dual] and SP 1-periodic net (4,4)(0,2) topology, respectively. These nets are primarily driven by the H-bonding interactions involving water ligands and H2O molecules of crystallization; besides, the (H2O)4/(H2O)5 clusters were identified in 1. Both 1 and 2 are moderate proton conductors, with proton conductivity values, σ = 3.65 × 10–6 and 3.94 × 10–6 S·cm–1, respectively (measured at 80 °C and 95% relat...

Geology presents a well-defined family of minerals in the case of crystalline magnesium silicates. However, in industrial water processes deposits that contain both “Mg” and “Si” are usually referred to as “magnesium silicate” scales. In this paper we attempt to delineate the true nature of such Mg- and Si-containing precipitates formed under the severe stresses simulating geothermal-like conditions. The purpose of this work is to deliberately form precipitates in the presence of Mg 2+ ions and soluble silica (silicic acid) and study these with a variety of analytical techniques, to reveal morphology, texture, structure and composition. Such precipitates are better described as “magnesium-containing amorphous silica”.

In our effort to develop new synthetic strategies for isolation of new phosphonate frameworks, we exploited the possibility to simultaneously utilize benzene-1,3,5-triphosphonic acid (H6btp) and di-2-pyridyl ketone (py2CO) which is a major player in the field of polynuclear metal complexes. This ligand blend in the Cu(II) chemistry afforded a two-dimensional framework comprising tetranuclear, [CuII4], secondary building units. The thorough investigation of the CuII / di-2-pyridyl ketone / benzene-1,3,5-triphosphonic acid reaction system also afforded a hydrogen bonded framework. The structure of the latter comprises the cationic [Cu{py2C(OH)2}2]2+ complex [py2C(OH)2 is the hydrate of py2CO], the dianion of benzene-1,3,5-triphosphonic acid (H4btp2-) and water solvates. The magnetic properties of the layered material were rationalized on the basis of magnetically isolated [CuII4] units dominated by antiferromagnetic interactions.

Recalcitrant barium sulfate (BaSO4) scale deposits are commonly encountered in industrial applications. They are hard to remove because of the pH-independence of their solubility. The formation of BaSO4 from supersaturated solutions was studied in two series of experiments: (a) the first series was performed under conditions of high supersaturation to determine the domain of stability of the system and (b) the second at low supersaturations, under conditions in which the supersaturated solutions were stable (seeded growth experiments). From the first series, the stability diagram of the system was determined. Through the second series of precipitation experiments, the effect of two types of triphosphonic acid additives on BaSO4 formation was assessed: the rigid aromatic 1,3,5-benzenetriphosphonic acid (BTP) and the flexible aliphatic amino-tris(methylenephosphonic) acid (AMP). Initially, the pH of the solutions was adjusted at 9.5 so that all phosphonate groups were deprotonated. For both additives, the rate of crystal growth of BaSO4 was inhibited. At low pH (3.60) a decrease of the rate of crystal growth with increasing additive concentrations was found. At pH 9.50 however, an irregular trend was observed showing a relative increase of the rates of crystal growth with increasing inhibitor concentration. These inconsistencies were attributed to changes of the solubility of BaSO4 in the presence of additives. The solubility changes in the presence of each test additive were quantified by measuring the apparent solubility of BaSO4 seed crystals. The measurements showed that the changes were negligible at pH 3.60. Kinetics measurements in the presence of the test additives suggested that their adsorption on the BaSO4 seed crystals was responsible for the inhibition. Modelling the adsorption according to the Freundlich isotherm gave a satisfactory fit of the kinetics data in the presence of BTP and AMP at pH 9.50. The presence of the test additives at both pH values did not affect the morphology of the growing BaSO4 crystals.

Organophosphonates are well-known to strongly interact with the surfaces of various minerals, such as brucite, gypsum, and barite. In this work, we study the influence of six systematically varied organophosphonate molecules (tetraphosphonates and diphosphonates) on the dissolution process of the (10.4) surface of calcite. In order to pursue a systematic study, we have selected organophosphonates that exhibit similar structural features, but also systematic architectural differences. The effect of this class of additives on the dissolution process of the calcite (10.4) surface is evaluated using in situ dynamic atomic force microscopy. For all of the six organophosphonate derivatives, we observe a pronounced restructuring of the (10.4) cleavage plane of calcite, demonstrated by the formation of characteristically shaped etch pits. To elucidate their specific influence on the dissolution process of calcite (10.4), we vary systematically the number of functional end groups (two for the tetraphosphonates and...

Synthesis redesign and derivatisation of Fe(ii)-hydroxyphosphonoacetate, incorporating different ammonia loads and M(ii) isomorphic substitutions (M = Mn, Co and Zn), have been implemented. The NH

This chapter focuses on chemical methods for scaling control. We attempt to effectively present all available methods for chemical scale control, placing certain emphasis on selected case studies. Focus is given to small molecule scale inhibitors (mainly polyphosphonic acids for mineral scale inhibition), anionic polymers (mainly derivatives of polyacrylic acid and the likes for mineral scale inhibition) and neutral and cationic polymers (for silica/silicates scale inhibition). Underlying scale inhibition mechanisms, as well as various problems occurring during and due to the scale inhibition, are presented and discussed. The chapter is a concise overview of the chemical control strategies for scaling/fouling, rather than an exhaustive review of the literature. However, appropriate references are given that direct the reader to additional information, as needed.

In this paper we report drug delivery systems that are based on phosphonate MOFs. These employ biologically-acceptable metal ions (e.g. Ca and Mg) and several anti-osteoporosis bisphosphonate drugs (etidronate, pamidronate, alendronate and neridronate), as the organic linkers. These materials have been synthesized, structurally characterized, and studied for the self-sacrificial release (by pH-driven dissolution) of the bisphosphonate active ingredient. They exhibit variable release rates and final % release, depending on the actual structure of the metal-bisphosphonate material. Their cytotoxicity profiles match those of the active ingredients., KDD thanks the Hellenic Foundation for Research and Innovation (HFRI) under the HFRI PhD Fellowship (to MV, Fellowship Number 258). KEP gratefully acknowledges the financial support of the Ministry of Science and Higher Education of the Russian Federation in the framework of Increase Competitiveness Program of NUST {MISiSc (No. K4-2019-017), implemented by a governmental decree dated 16th of March 2013, N 211. Finally, we thank Professors D. Ghanotakis and G. Tsiotis (Department of Chemistry, University of Crete) for supporting the cell viability experiments with the necessary equipment.

The reaction of MoO42- with a number of phosphonic acids [bis(phosphonomethyl)glycine, R,S-hydroxyphosphonoacetic acid, 1-hydroxyethane-1,1-diphosphonic acid, phenylphosphonic acid, aminotris(methylene phosphonic acid), and 1,2-ethylenediphosphonic acid] under oxidizing (H2O2) hydrothermal conditions at low pH leads to rupture of the P-C bond, release of orthophosphate ions, and generation of the octanuclear, phosphate-bridged, polyoxometalate molybdenum cluster (NH4)5[Mo8(OH)2O24(μ8-PO4)](H2O)2 (POMPhos). This cluster has been fully characterized and its structure determined. It was studied as a proton conductor, giving moderate values of σ = 2.13 × 10-5 S·cm-1 (25 °C) and 1.17 × 10-4 S·cm-1 (80 °C) at 95% relative humidity, with Ea = 0.27 eV. The POMPhos cluster was then thermally treated at 310 °C, yielding (NH4)2.6(H3O)0.4(PO4Mo12O36) together with an amorphous impurity containing phosphate and molybdenum oxide. This product was also studied for its proton conductivity properties, giving rise to an impressively high value of σ = 2.43 × 10-3 S·cm-1 (25 °C) and 6.67 × 10-3 S·cm-1 (80 °C) at 95% relative humidity, 2 orders of magnitude higher than those corresponding to the "as-synthesized" solid. The utilization of POMPhos in catalytic reduction of different sulfoxides was also evaluated. POMPhos acts as an efficient homogeneous catalyst for the reduction of diphenyl sulfoxide to diphenyl sulfide, as a model reaction. Pinacol was used as a low-cost, environmentally friendly, and highly efficient reducing agent. The effects of different reaction parameters were investigated, namely the type of solvent and reducing agent, presence of acid promoter, reaction time and temperature, loading of catalyst and pinacol, allowing to achieve up to 84-99% yields of sulfide products under optimized conditions. Substrate scope was tested on the examples of diaryl, alkylaryl, dibenzyl, and dialkyl sulfoxides and excellent product yields were obtained.

M.T is supported by funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 663830. In September 2018, the First European Workshop on Metal Phosphonates Chemistry brought together some prominent researchers in the field of metal phosphonates and phosphinates with the aim of discussing past and current research efforts and identifying future directions. The scope of this perspective article is to provide a critical overview of the topics discussed during the workshop, which are divided into two main areas: synthesis and characterisation, and applications. In terms of synthetic methods, there has been a push towards cleaner and more efficient approaches. This has led to the introduction of high-throughput synthesis and mechanochemical synthesis. The recent success of metal–organic frameworks has also promoted renewed interest in the synthesis of porous metal phosphonates and phosphinates. Regarding characterisation, the main advances are the development of electron diffraction as a tool for crystal structure determination and the deployment of in situ characterisation techniques, which have allowed for a better understanding of reaction pathways. In terms of applications, metal phosphonates have been found to be suitable materials for several purposes: they have been employed as heterogeneous catalysts for the synthesis of fine chemicals, as solid sorbents for gas separation, notably CO2 capture, as materials for electrochemical devices, such as fuel cells and rechargeable batteries, and as matrices for drug delivery. Publisher PDF

The interest in the usage of geothermal energy has increased exponentially during the past few decades and researchers internationally are currently focusing on improving the harvesting methods and promoting it due to its many benefits, compared to traditional energy sources. Corrosion and scaling are two of the most severe problems occurring when harvesting geothermal energy. Scaling takes place due to the variety of anions and cations that the majority of the geothermal reservoir waters contain, and are prone to both precipitation and deposition when subjected to dramatic changes in temperature and pressure, causing failures to several parts of the plant. One of the most commonly occurring scales in such systems is aluminum silicate, a persistent deposit whose structure, as it is formed in geothermal waters, differs completely from its geological counterparts. In this work we focus on revealing the true nature of the so-called “aluminum silicate”, performing a series of synthesis experiments under various conditions that take into account aluminum and silicate concentrations, solution pH and temperature. Complete physicochemical characterization of the aluminum and silicate precipitates reveals that it is a precipitate that shares several characteristics with amorphous silica.

The structural variability of two series of Mg2+- and Zn2+- 2-hydroxyphosphonoacetates have been studied in the range of 25–80°C and 95% relative humidity in order to correlate the structure with the proton conductivity properties. In addition to selected previously reported 1D, 2D and 3D materials, a new compound, KZn6(OOCCH(OH)PO3)4(OH)·5H2O (KZn6-HPAA-3D), has been prepared and thoroughly characterized. The crystal structure of this solid, solved ab initio from synchrotron X-ray powder diffraction data, consists of a negatively charged 3D framework with K+ ions, as compensating counterions. It also contains water molecules filling the cavities in contrast to the potassium-free 3D anhydrous NH4Zn(OOCCH(OH)PO3) (NH4Zn-HPAA-3D). In the range of temperature studied, the 1D materials exhibit a 1D→2D solid-state transition. At 80°C and 95% RH, the 2D solids show moderate proton conductivities, between 2.1×10−5 S·cm−1 and 6.7×10−5 S·cm−1. The proton conductivity is slightly increased by ammonia adsorption up to 2.6×10−4 S·cm−1, although no ammonia intercalation was observed. As synthesized KZn6-HPAA-3D exhibits a low proton conductivity, 1.6×10−6 S·cm−1, attributed to the basic character of the framework and a low mobility of water molecules. However, this solid transforms to the 2D phase, Zn(OOCCH(OH)PO3H)·2H2O, upon exposure to dry HCl(g), which enhances the proton conductivity with respect to the as-synthesized 2D material (4.5×10−4 S·cm−1). On the other hand, NH4Zn-HPAA-3D exhibited a higher proton conductivity, 1.4×10−4 S·cm−1, than the K+ analog.

Silica-mineralizing organisms such as diatoms manage several aspects of silica chemistry when polymerizing monomeric silicic acid into amorphous silica. Silicic acid is undersaturated in the diatoms’ habitats and mechanisms of enrichment and prevention of uncontrolled mineralization are not well understood. Diatom-biosilica is associated with organic compounds, including polycationic, post-translationally modified peptides termed silaffins, which induce the condensation of silicic acid under supersaturated conditions. Here, we report the pleiotropic action of the designed silaffin-like peptide P5S3, which (i) stabilizes 4–8x silicic acid (in supersaturated conditions of 8.3 mm), (ii) decelerates silica hydrolysis in non-saturated conditions (1 mm) and (iii) enhances silica precipitation at 15–30x supersaturation (30 mm), forming a composite precipitate. Abundant cationic amino acids in P5S3 can interact with silica, though blocking experiments with selected anions also indicate a role of non-electrostatic (e. g. amide-silica) interactions. This shows how silaffin-like peptides could potentially contribute to both keeping silica soluble, and forming peptide-silica precipitates.

Silicic acid polycondensation leads to the formation of amorphous silica. This process is of great importance to the survival of certain living organisms, such as diatoms and sponges, but presents a significant problem in various production facilities that use water for heating or cooling. In the latter, amorphous silica can be a recalcitrant deposit that can hamper proper system operation. Hence, inhibition of silicic acid polycondensation by chemical inhibitors is an intensely sought strategy by water system operators. In this manuscript, we report the inhibitory effect of zwitterionic phosphonated analogs (PPEI’s) of the cationic polymeric chemical additive polyethyleneimine (PEI) in mildly supersaturated silica solutions (500 ppm/8.3 mM “Si”) at pH=7. The inhibition efficiency of PPEI’s depends on a variety of parameters, such as concentration and degree of phosphonomethylation of the parent PEI polymer.

In this paper the effect of two synthetic, pH-responsive co-polymers, U-PVPyPEGMA-H and Q-PVPyPEGMA-H, with pyridine and polyethylene glycol grafts, on silicic acid polymerization is presented. The scope of this work was to evaluate the impact of several experimental parameters, such as working pH, polymer MW, polymer concentration, state of the pyridine ring (non-protonated, protonated, quaternized) on the anticipated inhibitory and/or enhancement activity with regards to silicic acid autocondensation to produce amorphous silica. It was found that pH substantially influences the silicification reaction, either in the absence or presence of the polymers. pH also affects the protonation state of the pyridine N atom. For example, pH switching from 5.0 to 7.0 transforms U-PVPyPEGMA-H from a silica formation catalyst (pH = 5.0) to a silicic acid stabilizer (pH = 7.0). Concentration enhances the role of the polymers, either as silicic acid stabilizers or catalysts. Polymer MW appears to have no effect on their activity either as stabilizers or catalysts. Polymer entrapment in the precipitated amorphous silica matrix occurs under these experimental conditions, affecting particle size, morphology and tendency for aggregation. The state of the N atom on the pyridine ring (non-protonated, protonated, quaternized) exhibits a profound effect on silicic acid autocondensation to produce amorphous silica. Based on our results, a “free” (non-protonated) pyridine ring induces silica inhibition, whereas protonation or quaternization enhances silica formation.

Phosphonate ligands demonstrate strong affinity for metal ions. However, there are several cases where the phosphonate is found non-coordinated to the metal ion. Such compounds could be characterized as salts, since the interactions involved are ionic and hydrogen bonding. In this paper we explore a number of such examples, using divalent metal ions (Mg2+, Ca2+, Sr2+ and Ni2+) and the phosphonic acids: p-aminobenzylphosphonic acid (H2PABPA), tetramethylenediamine-tetrakis(methylenephosphonic acid) (H8TDTMP), and 1,2-ethylenediphosphonic acid (H4EDPA). The compounds isolated and structurally characterized are [Mg(H2O)6]&middot, [HPABPA]2&middot, 6H2O, [Ca(H2O)8]&middot, [HPABPA]2, [Sr(H2O)8]&middot, [HPABPA]2, [Mg(H2O)6]&middot, [H6TDTMP], and [Ni(H2O)6]&middot, [H2EDPA]&middot, H2O. Also, the coordination polymer {[Ni(4,4&rsquo, bpy)(H2O)4]&middot, H2O}n was synthesized and characterized, which contains a bridging 4,4&rsquo, bipyridine (4,4&rsquo, bpy) ligand forming an infinite chain with the Ni2+ cations. All these compounds contain the phosphonate anion as the counterion to charge balance the cationic charge originating from the metal cation.

Novel pillared-layered framework materials were synthesized by high-throughput or microwave-assisted methodology that contain Mg2+ and the zwitterionic linker HDTMP (hexamethylenediamine-N,N,N&prime, N&prime, tetrakis(methylenephosphonic acid)). Three compounds were structurally characterized by X-ray powder diffraction. In the compound {Mg[(HO3PCH2)2N(CH2)6N(CH2PO3H2)2]&middot, (H2O)}n(1), obtained at 140 &deg, C by hydrothermal or microwave-assisted reaction, the layers are built by isolated Mg2+ octahedra coordinated by oxygen atoms from six different zwitterionic HDTMP ligands. Each amino-bis(methylenephosphonate) moiety links three Mg2+ ions, bridging two of them through one phosphonate group and connecting the third polyhedron in a monodentate fashion. In Compound 2, {Mg[(HO3PCH2)2N(CH2)6N(CH2PO3H2)2]}n, hydrothermally synthesized at 180 &deg, C, the layers are composed of bidentate amino-bis(methylenephosphonate) moieties connected to three Mg2+ ions, with one of the phosphonate groups acting as a bridging ligand. Various subtle structural changes are noted for the other two compounds. Thermodiffraction of 1 reveals that a crystalline-to-crystalline phase transformation occurs concomitantly with its dehydration, leading to a new anhydrous phase, namely, {Mg[(HO3PCH2)2N(CH2)6N(CH2PO3H2)2]}n(1deh). This process is fully reversible upon equilibrating the solid at room temperature. The reported compounds can adsorb ammonia and CO2. Compound 1 exhibits a moderate proton conductivity, ~1.5 &times, 10&minus, 5 S&middot, cm&minus, 1 at 80 &deg, C and 95% RH, that increases a half order of magnitude after experiencing a complete dehydration/rehydration process, 1&rarr, 1deh&rarr, 1.

The aim of this study was the efficient removal of dark cement crusts from selenite (mineral gypsum) surfaces using lasers. The conservation challenge is to remove a hard, insoluble, and often significantly thick encrustation without affecting the particularly sensitive mineral substrate gypsum, which is susceptible to chemical transformation. Preliminary studies were focused on the determination of removal thresholds for the cement bulk and the establishment of efficient laser cleaning operative parameters. Concurrently, analytical investigations were focused on the irradiated surfaces in order to ensure that the recommended laser operating parameters would safeguard the surface, colour, and composition of gypsum. Analytical techniques (Raman spectroscopy, X-ray powder diffraction, scanning electron microscopy with energy-dispersive X-ray analysis) were used to verify that no discolouration or chemical alteration occurred to the fragile gypsum substrate due to the dehydration of pristine gypsum (...