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Kostas Demadis

University of Crete, Chemistry, Faculty Member

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Phone: +30 2810 545051
Address: Department of Chemistry
University of Crete
Heraklion, Crete.
GR-71003 Greece
http://www.chemistry.uoc.gr/demadis

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Papers by Kostas Demadis

New evidence about the use of serpentinite in the Minoan architecture. A μ- Raman based study of the "House of the High Priest" drain in Knossos

Journal of Archaeological Science: Reports, 2017

Serpentinites have been widely used as a raw material in a huge repertoire of shapes during the M... more Serpentinites have been widely used as a raw material in a huge repertoire of shapes during the Minoan period, for the construction of artifacts both for domestic use as well as for religious purposes. However, the utilization of serpentinites is extremely limited in the Minoan palatial architecture. In all the cases where the use of ser-pentinite is documented, it has been for the construction of column bases. The aim of this study is the investigation of the material used for the construction of the drain located under the stair leading to the adyton (sanctuary) of the "House of the High Priest" one of the peripheral monuments of the Palace of Knossos. Despite the fact that Sir A. Evans documented the stone drain and described the raw material as stone, no further comments were made regarding the exact type of stone used by the Minoans. Furthermore, the fact that a rather unusual material was used for the construction of a drain instead of a more typical material such as...

Calcium-Phosphonate Interactions: Solution Behavior and Ca 2+ Binding by 2-Hydroxyethylimino-bis(methylenephosphonate) Studied by Multinuclear NMR Spectroscopy

The tetra-acid 2-hydroxyethylimino-bis(methylenephosphonic acid) (HEIBPH, 1) and its ring condens... more The tetra-acid 2-hydroxyethylimino-bis(methylenephosphonic acid) (HEIBPH, 1) and its ring condensation product, the triacid 2-hydroxy-2-oxo-4-phosphonemethyl-1,4,2-oxazaphosphorinane (2), were investigated for determination of protonation constants using 31 P, 1 H, and 13 C NMR spectroscopy in a wide pH range. As for other R-amino-phosphonic acids, the first protonation of 1 is straightforward and occurs at the nitrogen, while for 2 the first protonation occurs simultaneously at the exo phosphonate group, allowing estimation of the microscopic protonation constants. The complexation of Ca 2+ with 1 in a 1:1 molar ratio in aqueous solutions and in the presence of a 5-fold excess Na + is rationalized by the products LCaH 2 , LCaH, LCaNaH, LCa, and LCa 2 (L) 1). Only the phosphonate groups are involved in Ca 2+ binding at pH > 3, while the phosphonate, hydroxyl, and amine functionalities coordinate to Ca 2+ at pH > 6-7, as soon as the proton at N is lost. Probable conformation states of ions of 1 and 2 are estimated by means of the dependence of vicinal coupling constants 3 J HH and 3 J PC from dihedral angles.

Three-component 1D and 2D metal phosphonates: structural variability, topological analysis and catalytic hydrocarboxylation of alkanes

Herein, we report the use of diphosphonate building blocks and chelating auxiliary N,N-ligands to... more Herein, we report the use of diphosphonate building blocks and chelating auxiliary N,N-ligands to generate novel polymeric architectures. Specifically, we report new 1D and 2D coordination polymers incorporating three components: transition metal ions (Co2+, Cu2+, Mn2+ or Zn2+), diphosphonate ligands (methane-diphosphonate, MDPA, or 1,2-ethanediphosphonate, EDPA) and N,N-heterocyclic chelators (1,10-phenanthroline, phen, or 2,2′-bipyridine, bpy). Six compounds were isolated under mild synthesis (ambient temperature) conditions: [Cu2(phen)2(EDPA)2(H2O)4]∞ (1), [Co(phen)(EDPA)(H2O)2]∞ (1a), {[Cu(phen)(MDPA)]·H2O]}∞ (2), [Mn(bpy)(EDPA)(H2O)2]∞ (3), [Zn(bpy)(EDPA)]∞ (4), and, lastly, a discrete Ni2+ molecular derivative [Ni(phen)(H2O)4](EDPA) (5). Synthetic details, crystal structures, and intermolecular interactions (π–π stacking and hydrogen bonding) in 1–5 are discussed. Topological analyses and classification of the underlying metal–organic networks in 1–4 were performed, revealing the uninodal 1D chains with the 2C1 topology in 1–3 and the binodal 2D layers with the 3,4L13 topology in 4. In 1–3 and 5, multiple hydrogen bonds lead to the extension of the structures to give 3D H-bonded nets with the seh-4,6-C2/c topology in 1 and 3, 2D H-bonded layers with the 3,5L52 topology in 2, and a 3D H-bonded net with the 6,6T1 topology in 5. The catalytic activity of compounds 1 and 1a was evaluated in a single-step hydrocarboxylation of cyclic and linear C5–C8 alkanes to furnish the carboxylic acids with one more carbon atom. These reactions proceed in the presence of CO, K2S2O8, and H2O at 60 °C in MeCN/H2O medium. Compound 1 showed higher activity than 1a and was studied in detail. Substrate scope was investigated, revealing that cyclohexane and n-pentane are the most reactive among the cyclic and linear C5–C8 alkanes, and resulting in the total yields of carboxylic acids (based on substrate) of up to 43 and 36%, respectively. In the case of cycloalkane substrates, only one cycloalkanecarboxylic acid is produced, whereas a series of isomeric monocarboxylic acids is generated when using linear alkanes; an increased regioselectivity at the C(2) position of the hydrocarbon chain was also observed.

Pleiotropic Role of Recombinant Silaffin-Like Cationic Polypeptide P5S3: Peptide-Induced Silicic Acid Stabilization, Silica Formation and Inhibition of Silica Dissolution

by Kostas Demadis, Iro Sp, and Stephan Hobe

Silica-mineralizing organisms such as diatoms manage several aspects of silica chemistry when pol... more 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.

Linking 31 P Magnetic Shielding Tensors to Crystal Structures: Experimental and Theoretical Studies on Metal(II) Aminotris(methylenephosphonates)

by Nikos Daskalakis and Kostas Demadis

Inorganic Chemistry, 2012

The (31)P chemical shift tensor of the phosphonate group [RC-PO(2)(OH)](-) is investigated with r... more The (31)P chemical shift tensor of the phosphonate group [RC-PO(2)(OH)](-) is investigated with respect to its principal axis values and its orientation in a local coordinate system (LCS) defined from the P atom and the directly coordinated atoms. For this purpose, six crystalline metal aminotris(methylenephosphonates), MAMP·xH(2)O with M = Zn, Mg, Ca, Sr, Ba, and (2Na) and x = 3, 3, 4.5, 0, 0, and 1.5, respectively, were synthesized and identified by diffraction methods. The crystal structure of water-free BaAMP is described here for the first time. The principal components of the (31)P shift tensor were determined from powders by magic-angle-spinning NMR. Peak assignments and orientations of the chemical shift tensors were established by quantum-chemical calculations from first principles using the extended embedded ion method. Structure optimizations of the H-atom positions were necessary to obtain the chemical shift tensors reliably. We show that the (31)P tensor orientation can be predicted within certain error limits from a well-chosen LCS, which reflects the pseudosymmetry of the phosphonate environment.

Mapping the supramolecular chemistry of pyrazole-4-sulfonate: layered inorganic–organic networks with Zn2+, Cd2+, Ag+, Na+ and NH4+, and their use in copper anticorrosion protective films

by Nikos Daskalakis and Kostas Demadis

CrystEngComm, 2012

Five compounds based on the versatile pyrazole-4-sulfonate anion (4-SO 3-pzH= L−) were synthesize... more

Layered inorganic-organic networks of pyrazole-4-sulfonate metal complexes and their use in copper anticorrosion protective films

by Nikos Daskalakis and Kostas Demadis

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

by Kostas Demadis and PETROS KOUTSOUKOS

Chemical Reviews, 2010

The Effect of Citrate and Phosphocitrate On Struvite Spontaneous Precipitation

by Kostas Demadis and PETROS KOUTSOUKOS

Crystal Growth & Design, 2007

Cation effect on the inorganic–organic layered structure of pyrazole-4-sulfonate networks and inhibitory effects on copper corrosion

by Kostas Demadis and Nikos Daskalakis

The present study demonstrates that the pyrazole-4-sulfonate anion (4-SO 3 -pzH = L À ) is a vers... more The present study demonstrates that the pyrazole-4-sulfonate anion (4-SO 3 -pzH = L À ) is a versatile ligand for the preparation of layered, 3-D solid state lattices. The ligand itself can coordinate to metals with both its sulfonate group and aromatic N-atom, as well as participate in hydrogen bonding both as donor and acceptor, and form various extended p-p networks. Five new complexes with Rb + , Cs + , Mg 2+ , Sr 2+ and Cu 2+ have been prepared and characterized including single crystal X-ray diffraction: RbL, tetragonal I4 1 /a, a = 9.7332(4) Å , b = 9.7332(4) Å , Å , c = 8.6389(9) Å , a = 72.572(2)1, b = 74.370(2)1, g = 76.045(2)1, V = 426.22(8) Å , Z = 1; SrL 2 , triclinic P 1, a = 6.027(2) Å , b = 7.243(3) Å , c = 14.186(5) Å , a = 92.491(8)1, b = 101.383(7)1, g = 97.471(7)1, V = 426.22(8) Å , Z = 2;

A Novel Strategy for the Preparation of Naturally Occurring Phosphocitrate and Its Partially Esterified Derivatives

by Jouko Vepsäläinen, Sirpa Peräniemi, Petri Turhanen, and Kostas Demadis

The Journal of Organic Chemistry, 2007

A novel method for the synthesis of phosphocitrate (1, PC) starting from triethyl ester of citric... more A novel method for the synthesis of phosphocitrate (1, PC) starting from triethyl ester of citric acid and MeOPCl 2 is described. The method is based on selective stepwise hydrolysis of ester moieties from the intermediate Me-O-P(O)(Cl)(Z) (Z ) triethylcitrate), 4a, which also allows one to prepare partially esterified derivatives of PC with good yield and purity without chromatographic purifications.

An Unusual Michael-Induced Skeletal Rearrangement of a Bicyclo[3.3.1]nonane Framework of Phloroglucinols to a Novel Bioactive Bicyclo[3.3.0]octane

A novel skeletal rearrangement of bicyclo[3.3.1]nonane-2,4,9-trione (16) to an unprecedented high... more A novel skeletal rearrangement of bicyclo[3.3.1]nonane-2,4,9-trione (16) to an unprecedented highly functionalized bicyclo[3.3.0]octane system (17), induced by an intramolecular Michael addition, is presented. This novel framework was found to be similarly active to hyperforin (1), against PC-3 cell lines. A mechanistic study was examined in detail, proposing a number of cascade transformations. Also, reactivity of the Δ 7,10-double bond was examined under several conditions to explain the above results.

Guest Molecule-Responsive Functional Calcium Phosphonate Frameworks for Tuned Proton Conductivity

We report the synthesis, structural characterization, and functionality (framework interconversio... more We report the synthesis, structural characterization, and functionality (framework interconversions together with proton conductivity) of an open-framework hybrid that combines Ca 2+ ions and the rigid polyfunctional ligand 5-(dihydroxyphosphoryl)isophthalic acid (PiPhtA). Ca 2 [(HO 3 PC 6 H 3 COOH) 2 ] 2 [(HO 3 PC 6 H 3 (COO) 2 H)(H 2 O) 2 ]•5H 2 O (Ca-PiPh-tA-I) is obtained by slow crystallization at ambient conditions from acidic (pH ≈ 3) aqueous solutions. It possesses a high water content (both Ca coordinated and in the lattice), and importantly, it exhibits water-filled 1D channels. At 75°C, Ca-PiPhtA-I is partially dehydrated and exhibits a crystalline diffraction pattern that can be indexed in a monoclinic cell with parameters close to the pristine phase. Rietveld refinement was carried out for the sample heated at 75°C, Ca-PiPhtA-II, using synchrotron powder X-ray diffraction data, which revealed the molecular formula Ca 2 [(HO 3 PC 6 H 3 COOH) 2 ] 2 [(HO 3 PC 6 H 3 (COO) 2 H)(H 2 O) 2 ]. All connectivity modes of the "parent" Ca-PiPhtA-I framework are retained in Ca-PiPhtA-II. Upon Ca-PiPhtA-I exposure to ammonia vapors (28% aqueous NH 3) a new derivative is obtained (Ca-PiPhtA-NH 3) containing 7 NH 3 and 16 H 2 O molecules according to elemental and thermal analyses. Ca-PiPhtA-NH 3 exhibits a complex X-ray diffraction pattern with peaks at 15.3 and 13.0 Å that suggest partial breaking and transformation of the parent pillared structure. Although detailed structural identification of Ca-PiPhtA-NH 3 was not possible, due in part to nonequilibrium adsorption conditions and the lack of crystallinity, FT-IR spectra and DTA-TG analysis indicate profound structural changes compared to the pristine Ca-PiPhtA-I. At 98% RH and T = 24°C, proton conductivity, σ, for Ca-PiPhtA-I is 5.7 × 10 −4 S•cm −1. It increases to 1.3 × 10 −3 S•cm −1 upon activation by preheating the sample at 40°C for 2 h followed by water equilibration at room temperature under controlled conditions. Ca-PiPhtA-NH 3 exhibits the highest proton conductivity, 6.6 × 10 −3 S•cm −1 , measured at 98% RH and T = 24°C. Activation energies (E a) for proton transfer in the above-mentioned frameworks range between 0.23 and 0.4 eV, typical of a Grothuss mechanism of proton conduction. These results underline the importance of internal H-bonding networks that, in turn, determine conductivity properties of hybrid materials. It is highlighted that new proton transfer pathways may be created by means of cavity "derivatization" with selected guest molecules resulting in improved proton conductivity.

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-super... more 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, Na 2 SiO 3 •5H 2 O, expressed as SiO 2) at pH = 7, most likely by hydrogen bonding between the silanol groups and −CH 2 −CH 2 −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/H 2 O, 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.

Cationic polymeric chemical inhibitors and multifunctional blends for the control of silica scale in process waters

Water is used globally for cooling purposes in industry. During its re-use, scaling and depositio... more Water is used globally for cooling purposes in industry. During its re-use, scaling and deposition can develop due to the high content of dissolved species. Among the toughest to combat is silica scale, or amorphous silicon dioxide. In this paper, we present how certain chemical interventions in the water chemistry can be beneficial for inhibiting silica polycondensation. Specifically, we have used chemical additives known as dendrimers. These are dendrimeric molecules based on polyaminoamide backbones that possess amine moieties as surface groups. These become protonated at circumneutral pH, hence charging the dendrimer molecules cationically. Their blends with anionic polymers such as polyvinylphosphonic acid are also studied for their silica scale inhibition efficiency.

The Localized-to-Delocalized Transition in Mixed-Valence Chemistry.

Vibrational and Structural Mapping of [Os(bpy)3]3+/2+ and [Os(phen)3]3+/2+.

Structural changes between [Os II L 3 ] 2+ and [Os III L 3 ] 3+ (L: 2,2 0 -bipyridine; 1,10-phena... more Structural changes between [Os II L 3 ] 2+ and [Os III L 3 ] 3+ (L: 2,2 0 -bipyridine; 1,10-phenanthroline) and molecular and electronic structures of the Os III complexes [Os III (bpy) 3 ] 3+ and [Os III (phen) 3 ] 3+ are discussed in this paper. Mid-infrared spectra in the m(bpy) and m(phen) ring stretching region for [Os II (bpy) 3 ](PF 6 ) 2 , [Os III (bpy) 3 ](PF 6 ) 3 , [Os II (phen) 3 ](PF 6 ) 2 , and [Os III (phen) 3 ](PF 6 ) 3 are compared, as are X-ray crystal structures. Absorption spectra in the UV region for [Os III (bpy) 3 ](PF 6 ) 3 and [Os III (phen) 3 ](PF 6 ) 3 are dominated by very intense absorptions (e = 40 000-50 000 M À1 cm À1 ) due to bpy and phen intra-ligand p ! p * transitions. In the visible region, relatively narrow bands with vibronic progressions of $1500 cm À1 appear, and have been assigned to bpy or phen-based, spin-orbit coupling enhanced, 1 p ! 3 p * electronic transitions. Also present in the visible region are ligand-to-metal charge transfer bands (LMCT) arising from p(bpy) ! t 2g (Os III ) or p(phen) ! t 2g (Os III ) transitions. In the near infrared, two broad absorption features appear for oxidized forms [Os III (bpy) 3 ](PF 6 ) 3 and [Os III (phen) 3 ](PF 6 ) 3 arising from dp-dp interconfigurational bands characteristic of dp 5 Os III . They are observed at 4580 and 5090 cm À1 for [Os III (bpy) 3 ](PF 6 ) 3 and at 4400 and 4990 cm À1 for [Os III (phen) 3 ](PF 6 ) 3 . The bpy and phen infrared vibrational bands shift to higher energy upon oxidation of Os(II) to Os(III). In the cation structure in [Os III (bpy) 3 ](PF 6 ) 3 , the Os III atom resides at a distorted octahedral site, as judged by \N-Os-N, which varies from 78.78(22)°to 96.61(22)°. Os-N bond lengths are also in general longer for [Os III (bpy) 3 ](PF 6 ) 3 compared to [Os II (bpy) 3 ](PF 6 ) 2 (0.010 Å ), and for [Os III (phen) 3 ](PF 6 ) 3 compared to [Os II (phen) 3 ](PF 6 ) 2 (0.014 Å ). Structural changes in the ligands between oxidation states are discussed as originating from a combination of dp(Os II ) ! p * (bpy or phen) backbonding and charge redistribution on the ligands as calculated by natural population analysis.

A Short Biomimetic Approach to the Fully Functionalized Bicyclic Framework of Type A Acylphloroglucinols.

A biomimetic approach toward type A polyprenylated acylphloroglucinols (PPAPs) is described. The ... more A biomimetic approach toward type A polyprenylated acylphloroglucinols (PPAPs) is described. The method is based on a C-alkylation-cation cyclization reaction sequence, leading to a convenient buildup of molecular complexity, employing the simple and readily available deoxycohumulone and an appropriately functionalized hydroxy halide. Thus, a versatile construction of the fully functionalized bicyclic framework of type A PPAPs (5) was achieved.

Metal Phosphonate Chemistry: From Synthesis to Applications.

Metal phosphonate chemistry is a highly interdisciplinary field, as it encompasses several other ... more Metal phosphonate chemistry is a highly interdisciplinary field, as it encompasses several other areas, such as materials chemistry, gas storage, pharmaceutics, corrosion control, classical chemical synthesis, X-ray crystallography, powder diffraction, etc. It has also acquired additional significance due to "Metal-Organic Frameworks", as evidenced by the hundreds of papers published each year.

Water Treatment Processes.