Konstantinos D. Demadis

Metal phosphonate chemistry : from synthesis to applications

Overview and Historical Perspectives Synthesis Supramolecular Chemistry and Metal Organic Frameworks Applications of Metal Phosphonates Lanthanide and Actinide Phosphonates

Modern Views on Desilicification: Biosilica and Abiotic Silica Dissolution in Natural and Artificial Environments

Institute of Bioanalytical Chemistry, Dresden University of Technology, D-01069 Dresden, Germany, Crystal Engineering, Growth and Design Laboratory, Department of Chemistry, University of Crete, Voutes Campus, GR-71003 Heraklion, Crete, Greece, Laboratory of Mechanisms and Transfer in Geology, Observatory Midi-Pyrenees (OMP), UMR 5563, CNRS, 14 Avenue Edouard Belin, 31400 Toulouse, France, and FORTH-ICEHT and Laboratory of Inorganic and Analytical Chemistry, Department of Chemical Engineering, University of Patras, GR-265 04 Patras, Greece[007f]

METAL-PHOSPHONATE CHEMISTRY: SYNTHESIS, CRYSTAL STRUCTURE OF CALCIUM-AMINO- TRIS-(METHYLENE PHOSPHONATE) AND INHIBITION OF CaCO3 CRYSTAL GROWTH

Organic (poly)phosphonates are additives in water treatment that find broad use as mineral scale and corrosion inhibitors for a plethora of industrial applications. The phenomenon of precipitation of scale inhibitors has been studied intensively. This study reports the synthesis, characterization, and crystal structure of a Ca salt of AMP (AMP = Amino-tris-Methylene Phosphonate). Ca-AMP crystals are monoclinic, space group P 2 1 n with unit cell dimensions, a = 11.3382(5) Å, b = 8.4555(4) Å, c = 15.5254(7) Å, β = 90.6551 o , V = 1488.33(12) Å 3 and Z = 4. The structure is polymeric due to chelation of multiple Ca ions by AMP. The Ca 2 + center is slightly distorted octahedral and is surrounded by five phosphonate oxygens and a water molecule. CaO(P) bond lengths range from 2.2924(14) to 2.3356(14) Å. The CaO(H 2 O) bond distance is 2.3693(17). Each phosphonate group is monodeprotonated, and the nitrogen atom is protonated. CaCO 3 inhibition and crystal modification by AMP are also reported, together with synergistic effects with polyacrylate-based terpolymers.

Principles of demineralization: modern strategies for the isolation of organic frameworks. Part I. Common definitions and history.

In contrast to biomineralization phenomena, that are among the most widely studied topics in modern material and earth science and biomedicine, much less is systematized on modern view of demineralization. Biomineralized structures and tissues are composites, containing a biologically produced organic matrix and nano- or microscale amorphous or crystalline minerals. Demineralization is the process of removing the inorganic part, or the biominerals, that takes place in nature via either physiological or pathological pathways in organisms. In vitro demineralization processes, used to obtain mechanistic information, consist in the isolation of the mineral phase of the composite biomaterials from the organic matrix. Physiological and pathological demineralization include, for example, bone resorption mediated by osteoclasts. Bioerosion, a more general term for the process of deterioration of the composite biomaterials represents chemical deterioration of the organic and mineral phase followed by biological attack of the composite by microorganisms and enzymes. Bioerosional organisms are represented by endolithic cyanobacteria, fungi, algae, plants, sponges, phoronids and polychaetes, mollusks, fish and echinoids. In the history of demineralization studies, the driving force was based on problems of human health, mostly dental caries. In this paper we summarize and integrate a number of events, discoveries, milestone papers and books on different aspect of demineralization during the last 400 years. Overall, demineralization is a rapidly growing and challenging aspect of various scientific disciplines such as astrobiology, paleoclimatology, geomedicine, archaeology, geobiology, dentistry, histology, biotechnology, and others to mention just a few.

Principles of demineralization: modern strategies for the isolation of organic frameworks. Part II. Decalcification.

This is the second paper on principles of demineralization. The initial paper is dedicated to the common definitions and the history of demineralization. In present work we review the principles and mechanisms of decalcification, i.e., removing the mineral Ca-containing compounds (phosphates and carbonates) from the organic matrix in its two main aspects: natural and artificial. Natural chemical erosion of biominerals (cavitation of biogenic calcareous substrata by bacteria, fungi, algae, foraminifera, sponges, polychaetes, and mollusks) is driven by production of mineral and organic acids, acidic polysaccharides, and enzymes (cabonic anhydrase, alkaline and phosphoprotein phosphataes, and H(+)-ATPase). Examples of artifical decalcification includes demineralization of bone, dentin and enamel, and skeletal formations of corals and crustacean. The mechanism and kinetics of Ca-containing biomineral dissolution is analyzed within the framework of (i) diffusion-reaction theory; (ii) surface-reaction controlled, morphology-based theories, and (iii) phenomenological surface coordination models. The application of surface complexation model for describing and predicting the effect of organic ligands on calcium and magnesium dissolution kinetics is also described. Use of the electron microscopy-based methods for observation and visualization of the decalcification phenomenon is discussed.

Inhibitory effects of multicomponent, phosphonate-grafted, zwitterionic chitosan biomacromolecules on silicic acid condensation.

This article reports the inhibitory effects of phosphonated chitosan (PCH, synthesized from chitosan (CHS) by a Mannich-type reaction) on the in vitro silicic acid condensation. In particular, the ability of PCH to retard silicic acid condensation in aqueous supersaturated solutions at circumneutral pH is studied. Furthermore, the effect of anionic carboxymethyl inulin (CMI) polyelectrolyte on the inhibitory activity of PCH is systematically studied. It was discovered that when PCH is added in dosages up to 150 ppm, it can inhibit silicic acid condensation, thereby maintaining soluble silicic acid up to 300 ppm (for 8 h, from a 500 ppm initial stock solution). The addition of CMI to working solutions that already contain PCH can further enhance the inhibitory action of PCH. A combination of 150 ppm PCH and 100 ppm CMI maintains 400 ppm soluble silicic acid for 8 h. PCH and CMI combinations also affect colloidal silica particle morphology.

“Breathing” in Adsorbate-Responsive Metal Tetraphosphonate Hybrid Materials

The structures of various layered calcium tetraphosphonates (CaH6DTMP; H8DTMP=hexamethylenediamine tetrakis(methylenephosphonic acid)), have been determined. Starting from CaH6DTMP.2H2O, thermal treatment and subsequent exposure to NH3 and/or H2O vapors led to four new compounds that showed high storage capacity of guest species between the layers (up to ten H2O/NH3 molecules) and a maximum volume increase of 55 %. The basic building block for these phosphonates consists of an eight-membered ring chelating Ca2+ through two phoshonate groups, and the organic ligand is located within the layers, which are held together by hydrogen bonds. The structural analysis revealed that the uptake/removal of guest species (H2O and NH3) induces significant changes in the framework not only by changing the interlayer distances but also through important conformational changes of the organic ligand. An anisotropic breathing motion could be quantified by the changes of the unit-cell dimensions and ligand arrangements in four crystalline derivatives. Complete characterization revealed the existence of interconversion reactions between the different phases upon gas uptake and release. The observed behavior represents, to the best of our knowledge, the first example of a breathing-like mechanism in metal phosphonates that possess a 2D topology.

Bioinspired control of colloidal silica in vitro by dual polymeric assemblies of zwitterionic phosphomethylated chitosan and polycations or polyanions

This paper focuses on the effects of biological and synthetic polymers on the formation of amorphous silica. A concise review of relevant literature related to biosilicification is presented. The importance of synergies between polyelectrolytes on the inhibition of silicic acid condensation is discussed. A specific example of a zwitterionic polymer phosphonomethylated chitosan (PCH) is further analyzed for its inhibitory activity. Specifically, the ability of PCH to retard silicic acid condensation at circumneutral pH in aqueous supersaturated solutions is explored. It was discovered that in short-term studies (0-8 h) the inhibitory activity is PCH dosage-independent, but for longer condensation times (>24 h) there is a clear increase in inhibition upon PCH dosage increase. Soluble silicic acid levels reach 300 ppm after 24 h in the presence of 160 ppm PCH. Furthermore, the effects of either purely cationic (polyethyleneimine, PEI) or purely anionic (carboxymethylinulin, CMI) polyelectrolytes on the inhibitory activity of PCH is systematically studied. It was found that the action of inhibitor blends is not cumulative. PCH/PEI blends stabilize the same level of silicic acid as PCH alone in both short-term (8 h) and long-term (72 h) experiments. PCH/CMI combinations on the other hand can only achieve short-term inhibition of silicic acid polymerization, but fail to extend this over the first 8 h. PCH and its combinations with PEI or CMI affect silica particle morphology, studied by SEM. Spherical particles and their aggregates, irregularly shaped particles and porous structures are obtained depending on additive or additive blend. It was demonstrated by FT-IR that PCH is trapped in the colloidal silica matrix.

Bioinspired insights into silicic acid stabilization mechanisms: the dominant role of polyethylene glycol-induced hydrogen bonding.

Mono- and disilicic acids were stabilized by uncharged polyethylene glycols (PEGs) in silica-supersaturated solutions (the starting solution contained 500 ppm/8.3 mM sodium orthosilicate, Na2SiO3·5H2O, expressed as SiO2) at pH = 7, most likely by hydrogen bonding between the silanol groups and -CH2-CH2-O-ether moieties. The stabilization was monitored by measuring molybdate-reactive silica and also by a combination of liquid- and solid-state (29)Si NMR spectroscopy. It depends on PEG concentration (20-100 ppm) and molecular weight (1550-20,000 Da). Two narrow (29)Si NMR signals characteristic for monosilicic acid (Q(0)) and disilicic acid (Q(1)) can be observed in (29)Si NMR spectra of solutions containing PEG 10000 with intensities distinctly higher than the control, that is, in the absence of PEG. Silica-containing precipitates are observed in the presence of PEG, in contrast to the gel formed in the absence of PEG. These precipitates exhibit similar degrees of silica polycondensation as found in the gel as can be seen from the (29)Si MAS NMR spectra. However, the (2)D HETCOR spectra show different (1)H NMR signal shifts: The signal due to H-bonded SiOH/H2O, which is found at 6 ppm in the control, is shifted to ~7 ppm in the PEG-containing precipitate. This indicates the formation of slightly stronger H-bonds than in the control sample, most likely between PEG and the silica species. The presence of PEG in these precipitates is unequivocally proven by (13)C CP MAS NMR spectroscopy. The (13)C signal of PEG significantly shifts and is much narrower in the precipitates as compared to the pristine PEG, indicating that PEG is embedded into the silica or at least bound to its surface (or both), and not phase separated. FT-IR spectra corroborate the above arguments. The H-bonding between silanol and ethereal O perturbs the band positions attributed to vibrations involving the O atom. This work may invoke an alternative way to envision silica species stabilization (prior to biosilica formation) in diatoms by investigating possible scenarios of uncharged biomacromolecules playing a role in biosilica synthesis.

Metal tetraphosphonate "wires" and their corrosion inhibiting passive films.

Herein, we describe the preparation and characterization of five new divalent metal tetraphosphonates, M-HDTMP [M = Mg(2+), Ca(2+), Sr(2+), Ba(2+), and Cu(2+); HDTMP = hexamethylenediaminetetrakis(methylenephosphonate) dianion]. Materials {Sr[(HDTMP)(H(2)O)(6)] x 2 H(2)O}(n) (1), {Ba[(HDTMP)(H(2)O)(6)] x 2 H(2)O}(n) (2), and {Cu[(HDTMP)(H(2)O)(4)] x 6 H(2)O}(n) (3), as well as (en)(HDTMP) x 2 H(2)O (en = ethylenediammonium cation) have been structurally characterized. Structures depend on the coordination requirements of the M(2+) center and waters of crystallization content. The formation and characterization of effective anticorrosion passive films of M-HDTMP (M = Sr(2+) and Ba(2+)) are also reported.