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Some structural properties of a magnesium salt of 12-tungstophosphoric acid, MgHPW12O40.nH(2)O (MgHVvTA-n), are reported. The influence of the Mg2+ ion on the structure, dynamics of the protonic species, and dielectric and conductive characteristics of the salt have been studied. The interaction of protonic species with Keggin anion was discussed. Preliminary results of the crystal structure indicate that the structure is composed of Keggin anions and Mg(OH2)(6) aqua-complexes. Some comparisons are made with other alkaline-earth and alkaline salts of WPA. The results of thermal analysis (TGA and DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), infrared spectroscopy (IR), conductivity and permittivity measurements of MgHWPA-n are reported and discussed.

A study of decorated Neolithic pottery samples from the excavation site Plocnik, Serbia, was performed using X-ray powder diffraction (XRPD), Fourier transform infrared (FTIR) and X-ray fluorescence (XRF) spectroscopy. The investigated samples belong to the era of the Vinca culture that existed in the central Balkan region from the mid VI until the first half of the V millennium BCE. The mineralogical composition of the pottery samples and comparison of the investigated pottery with thermally treated local clay indicated firing temperatures in the range from 600 to 800 degrees C. Two different types of white pigments were identified in white incrusted decorations: calcium carbonate and bone white (composed of crushed bones). This is the first evidence of the use of bones for decorations in pottery of the Vinca culture from the excavation site Plocnik. In addition to this, it was revealed that the potters used the iron reduction technique for obtaining black decorations.

In this paper local processes and structural phase transformations of the copper salt of 12-tungstophosphoric acid are investigated. The structural phase transformations were followed through bands, characteristic for the host lattice, in the IR and Raman spectra. The results of these investigations, as well as those of XRPD analysis and impedance measurements as a function of temperature show that some local processes provoke the change in the secondary structure of the Keggin anions., U ovom radu ispitivani su lokalni procesi i strukturne fazne transformacije soli bakra 12-volframfosforne kiseline. Strukturne fazne transformacije praćene su preko traka karakterističnih za kristalnu rešetku u infracrvenim i ramanskim spektrima. Rezultati ovih ispitivanja, kao i oni dobiveni rendgeno-strukturnom analizom i iz impedansnih merenja, odnosno provodljivost u funkciji temperature, pokazuju da je fazna transformacija vezana za promene lokalne strukture, tj. sekundarne strukture Keginovih anjona. PR Projekat Ministarstva nauke Republike Srbije.

In this paper the latest results of our continuing investigation of heteropoly acids and their salts are reported. Specially attention was paid to the influence of cations on the dynamic equilibrium of protonic species, as well as on the structure of the host lattice itself, i.e., the Keggin anions. The investigations were done by IR and Raman spectroscopy within the range of 1200-40 cm-1., U ovom radu saopšteni su poslednji rezultati naših sistematskih ispitivanja heteropolikiselina i njihovih soli. Posebna pažnja posvećena je uticaju katjona na dinamičku ravnotežu protonskih vrsta, kao i na strukturu kristalne rešetke, odnosno Keginovih anjona. Ispitivanja su vršena metodama infracrvene i ramanske spektroskopije u oblasti 1200-40 cm-1. Dobijeni rezultati su važni za objašnjenje mehanizma provodljivosti, kao i za rešavanje problema praktične primene ovih jedinjenja kao čvrstih elektrolita. PR Projekat Ministarstva nauke Republike Srbije.

This contribution presents the results of the investigation of Mg2+ and Ca2+ 12-tungstophosphoric acid (WPA) salts as superionic proton conductors. We have identified protonic species as charge carriers in several hydration degrees of these salts by IR spectroscopy at low, room and high temperatures. In the IR spectra we have found the characteristic frequencies for H3O+, OH-, H2O, H5O2+. Also, we have investigated the dynamic equilibrium between protonic entities in the function of temperature, as well as the nature and the strength of hydrogen bonds in those compounds. During the process of calcination, these salts undergo a few phase transformations. The temperatures of interest for the further investigations were taken from data of thermal analysis.

Heteropoly acids arc well known as supcrionic protonic conductors at room temperature. The conductivity depends upon the temperature and relative humidity of the surrounding. Recent results show that the conductivity is very much affected by monovalent exchange counter-ions. In this work the effect of monovalent ions (Li + , Na + , K + and Cs + ) on the nature and structure of hydrogen bonds, the presence of different protonic species as charge carriers, and the dynamic equilibrium of proton species as a function of temperature and ion characteristics were investigated.

The influence of the Li and Na salts of 12-tungstophosphoric acid H3P W12O40(WPA) was tested for in vitro effects on blood coagulation. It was found that only Li3WPA shows anticoagulant effects, but compared with WPA activity, the activity of Li salt is diminished. IR spectroscopy was used to define the reaction between these salts, and coagulation proteins. The appearance of bands characteristic of oxonium ion (H3O+) in the IR spectra indicates blocking of the active center of the protein through a very strong hydrogen bond.

A multianalytical study of two Serbian icons, The Virgin and Child and St. Petka, painted on canvas by unknown authors was performed in order to identify the materials used as pigments, binders and the ground layer. The investigated icons belong to the Museum of the Serbian Orthodox Church in Belgrade. Samples, collected from different parts of the icons, were analysed by: optical microscopy (OM), energy dispersive X-Ray fluorescence (EDXRF), Fourier transform infrared (FTIR) and micro-Raman spectroscopy. The obtained results revealed the presence of the following pigments: Prussian Blue, ultramarine, Green Earth, iron oxides, Lead White and Zinc White. Linseed oil was used as the binder. The materials used for the ground layers were gypsum, calcite, baryte and Lead White. The gilded surface of the icon The Virgin and Child was made of gold. The gilded surface on the frame of this icon was made of imitation of gold, i.e., Schlagmetal, since EDXRF spectroscopy showed the presence of copper and zinc, while gold was not detected. Based on the style and the consideration of an art historian, as well as on the obtained results for the corresponding pigments and binder, both icons were most probably made at the end of 19th or the beginning of the 20th century.

Potassium salts of 12-tungstophosphoric acid with varying amounts of cation, KxH3 - xPW12O40(x = 1, 2, 3) have been prepared and their characteristics investigated by thermal analyses. FT-IR and micro-Raman spectroscopy and SEM-EDS analysis. It was found that the number of replaced protons by potassium ions in the 12-tungstophosphoric acid structure has influence on the presence of different protonic species, their dynamic equilibrium and on the conductivity of salts. The results reported in this study have been applied to improve the structural model of insoluble acidic salts. It is shown that an acidic potassium salt presents a mixture of neutral salt and unreacted acid. The nature of this mixture depends on the number of replaced protons-oxonium ions by cations. Preliminary measurements with synthesized compounds as solid electrolytes in fuel cells have been done, too. (C) 2010 Elsevier Ltd. All rights reserved.

The X-ray structure of ammonium decavanadate hexahydrate was redetermined at a low temperature (100 K) in order to locate the hydrogen sites and to study the hydrogen bonds. The hydrogen atoms were assigned to the appropriate atomic group, NH4+ cations, and water molecules, missing to the best of our knowledge in the literature. A kappa refinement was performed to estimate the experimental atomic charges. These charges were used to generale the electrostatic potential on the molecular surfaces of decavanadate polyanions isolated from the influence of the crystal lattice. Comparisons with previous theoretical (ab initio) calculations were made and are also discussed.

In this study, we have developed a sensitive, rapid and simple procedure for the energy dispersive X-ray fluorescence (EDXRF) spectrometry measurement of tungsten in tobacco plant parts. Only 0.1 g of dried plant material is needed instead of the usual I g. EDXRF spectrometry is used for quantitative measurement, after the foliar application of solutions of tungstophosphoric acid (WPA), its magnesium salt and compounds with glycine (Gly) and alanine (Ala), in exact quantities. After that, the leaves, trunks and summits were collected and prepared separately. Tungsten is determined directly in raw dried material, and the overlap of the tungsten peak with zinc's that is present is avoided by the spectral deconvolution to obtain quantitative results. The prepared dry tablets weighed 100 mg, and measurement time was 2000 s. The radioisotope excitation source used was Cd-109 and tungsten was identified and quantified at the L-alpha 1 and L-alpha 2 lines at the energies of 8397.6eV and 8335.2eV, respectively. EDXRF spectrometry was applied in a wide range of concentrations (up to 2000 mg/kg), with an estimated detection concentration limit of 15 mg/kg, calculated on dried material. Quantitative analysis of different parts of the treated plant plus the washings gave 94.47% recovery of the applied tungsten in different compound forms. After the foliar application of investigated WPA compounds, there were noticed both vertical and horizontal distributions of tungsten through out the tobacco plants, according to the EDXRF spectrometry results. This conclusion is also in agreement with the positive effects of WPA on Tobacco mosaic tobamovirus (TMV) infection of Nicotiana tabacum (Solanaceae).

Compounds of phosphotungstic acid (WPA) containing the amino acids alanine (WPA-Ala) or glycine (WPA-Gly) as counter cations were synthesized and characterized by elemental analysis, thermal analysis, and IR spectroscopy. Cellular toxicity was assessed by the trypan blue exclusion method, and the antiviral activity of WPA and the modified WPA compounds was tested against herpes simplex viruses (HSV) type 1 and type 2. Biological assays indicate that the newly synthesized compounds exhibit no evident cytotoxic effects on Vero cells and negligible antiviral activity against HSV-1 and HSV-2.

In this study, we have developed a sensitive, rapid and simple procedure for the energy dispersive X-ray fluorescence (EDXRF) spectrometry measurement of tungsten in tobacco plant parts. Only 0.1 g of dried plant material is needed instead of the usual I g. EDXRF spectrometry is used for quantitative measurement, after the foliar application of solutions of tungstophosphoric acid (WPA), its magnesium salt and compounds with glycine (Gly) and alanine (Ala), in exact quantities. After that, the leaves, trunks and summits were collected and prepared separately. Tungsten is determined directly in raw dried material, and the overlap of the tungsten peak with zincs that is present is avoided by the spectral deconvolution to obtain quantitative results. The prepared dry tablets weighed 100 mg, and measurement time was 2000 s. The radioisotope excitation source used was Cd-109 and tungsten was identified and quantified at the L-alpha 1 and L-alpha 2 lines at the energies of 8397.6eV and 8335.2eV, respectively. EDXRF spectrometry was applied in a wide range of concentrations (up to 2000 mg/kg), with an estimated detection concentration limit of 15 mg/kg, calculated on dried material. Quantitative analysis of different parts of the treated plant plus the washings gave 94.47% recovery of the applied tungsten in different compound forms. After the foliar application of investigated WPA compounds, there were noticed both vertical and horizontal distributions of tungsten through out the tobacco plants, according to the EDXRF spectrometry results. This conclusion is also in agreement with the positive effects of WPA on Tobacco mosaic tobamovirus (TMV) infection of Nicotiana tabacum (Solanaceae). (c) 2006 Elsevier B.V. All rights reserved.

It is known that various polyoxovanadates interact specifically with enzymes, which is the main way of their biochemical activity. Therefore we have synthesized ammonium decavanadate, (NH4)(6)V(10)O(28)(.)6H(2)O. The novel compound was characterized by elemental and thermal analysis, X-ray powder and single crystal diffraction and IR and Raman spectroscopy. Its conductive properties have been studied, too. The spectroscopic analysis has shown the presence of hydrogen bonds of different strengths. In order to improve the biochemical activity of this compound and having in mind the presence of strong hydrogen bonds, we essayed the synthesis of complex of polyoxovanadate with alanine. The obtained product was characterized by the mentioned methods.

In our previous work we investigated the conductivity and dielectric relaxation phenomena in heteropoly acids and their salts. In this work, we have studied the conductivity of grains and grain boundaries in compressed powders of 12-tungstophosphoric acid (WPA) salts with univalent and bivalent ions. The method of impedance spectroscopy has been employed in the frequency range from 5 Hz to 500 kHz. We obtained grains and grain boundaries conductivities as well as corresponding activation energies. Grain conductivity in all investigated salts is always higher than the grain boundary conductivity.

Aluminum-pillared montmorillonite (PILC MM) was doped with 12-tungstophosphoric acid hexahydrate (WPA-6) by the Solgel method. Using broad band dielectric relaxation spectroscopy (DRS), electrical properties of the obtained material were investigated. Thermally stimulated depolarization current technique was also used due to its high sensitivity and high resolving power. It has been established that pillared montmorillonite doped with WPA-6 (H3PW12O40 center dot 6H(2)O) shows conductivity higher than that of the pure components. Phase transition, which in WPA-6 takes place above 50 degrees C, in doped montmorillonite occurs above 70 degrees C. The conductivity activation energy is 0.27 eV. (c) 2005 Elsevier B.V. All rights reserved.

The effect of monovalent and bivalent cations on some electrical properties of 12-tungstophosphoric acid (WPA) salts were studied. The charge carriers in this acid are protonic entities such as H+, OH- and various forms of hydrated proton H(H2O)(n)(+). Conductivity, dielectric relaxations and activation energies of WPA were investigated. Permittivity measurements were performed on pressed polycrystalline pellets at lower frequencies (5 Hz-500 kHz) and in the X-band microwave range (8-12 GHz); the temperature interval was from room temperature to 360 K. In the microwave region, WPA hexahydrate (WPA-6) and some IATA salts exhibit one, two or three relaxations of the Debye type. Their relaxation times of the order of 10(-11) s are attributed to the fast reorientation of water molecules and/or fast reorientation of oxonium ions (H3O+). In the lower frequency interval, dielectric relaxations of WPA-6 and some IATA salts with longer relaxation times of the order of 10(-7)-10(-5) s were registered and assigned to ion (H+ and/or H3O+) and cation jumps. (c) 2005 Elsevier B.V. All rights reserved.

Heteropoly compounds (HPCs) have been a matter of interest in basic and applied science for more than a century. From their first synthesis, many advances have been made to promote the use of HPCs in different ways in science and technology. The aim of this article is to review the main structural characteristics of heteropoly compounds of the Keggin type (12-tungstophosphoric, 12-molybdophosphoric, 12-tungstosilicic acids; alkaline and alkaline earth salts of 12-tungstophosphoric acid and gels doped with HPCs) to understand and explain their different activities, such as high proton conductivity, and catalytic, biochemical and biomedical activities. (c) 2005 Elsevier B.V. All rights reserved.

Ultrasonic spray pyrolysis has been used to obtain fine spherical powders of WPA bronzes from a 29-tungstenphosphoric acid (WPA-29) feed solution. The average grain size of the obtained powder particles is ca. 1000 nm; these consist of subparticles in the 30-80 run range. The experimentally determined average WPA bronze particle size values are compared with theoretically calculated ones; fairly good agreement between them is found. It is also shown that the average grain size and grain size distribution of the structure and substructure of the obtained powder are predictable. (c) 2005 Elsevier B.V. All rights reserved.

The antitumour action of three polyoxometallate compounds of Keggin's type: 12-molibdophosphoric acid (MoPA), 12-tungstophosphoric acid (WPA) and Mg salt of WPA (MgHWPA) was studied in vitro. For human cervix carcinoma (HeLa) cells survival, as well as for nonstimulated and stimulated peripheral blood mononuclear cells (PBMC), MTT test was applied and IC50 values of POMs were determinated. Index selectivity for WPA and MgHWPA are 1.9 and 1.8, calculated for nonstimulated, as well as 2.5 and 2.0, calculated for stimulated PBMS. Combination of studied POMs do not contribute to their lower IC50 values. Apoptosis detection implies mild cytotoxic effect of WPA and more cytostatical effect of MgHWPA. Combination of each of the studied POMs with caffeine decreases HeLa survival in dose dependent way. None of the studied POMs in the used concentrations (up to 100 mmol/L) damages blood cells and/or decreases their number., Ispitivano je in vitro antitumorsko dejstvo tri jedinjenja iz grupe polioksometalata (POM-a) Keginovog tipa: 12-fosformolibdenska kiselina (MoPA), 12-fosforvolframova kiselina (WPA) i Mg so 12-fosforvolframove kiseline (MgHWPA). Primenom MTT testa na ćelije karcinoma cerviksa (HeLa ćelije), kao i na nestimulisane i stimulisane mononuklearne ćelije iz periferne krvi (PBMC), određene su IC50 vrednosti ispitivanih POM-a. Indeksi selektivnosti za WPA i MgHWPA su 1,9 i 1,8 računati za nestimulisane, odnosno 2,5 i 2,0 za stimulisane PBMC. Kombinacijom ispitivanih POMa ne postiže se smanjenje njihovih IC50 vrednosti. Detekcijom apoptoze utvrđeno je da WPA pokazuje blagi citotoksični efekat, dok MgHWPA ima blagi citotostatski efekat. U kombinaciji sa kofeinom, POM jedinjenja još više smanjuju preživljavanje HeLa ćelija. U ispitivanim koncentracijama (do 100 mmol/L), nijedno od POM jedinjenja ne utiče na broj i izgled krvnih ćelija pune krvi zdravih davalaca.

Bentonite a natural raw material from the Sipovo mining deposits (Republic of Srpska), which contains a high percentage of montmorillonite, was treated to obtain montmorillonite clay ready for further investigations. Al-pillared montmorillonite was doped with 12-tungstophosphoric acid (WPA) by the sol-gel method. Substantial increase in proton conductivity of this new material was achieved. Different physicochemical methods were used to characterize new materials such as X-ray powder diffraction (XRD), thermogravimetric (TG) analysis, porosity measurements, scanning electron microscopy (SEM), and infrared measurements (IR). Impedance spectroscopy technique was applied in order to study the proton conductivity and its dependence on the frequency and tungstophosphoric acid concentration.

The X-ray structure of ammonium decavanadate hexahydrate, (NH4)6V10O28·6H2O, was redetermined at low temperature (100 K) in order to locate the hydrogen sites. A kappa refinement was performed to estimate the experimental atomic charges. Comparisons with previous theoretical calculation results were discussed.

The electrical and dielectric properties of the copper salt of 12-tungstophosphoric acid (WPA) hydrate have been investigated by broadband dielectric relaxation spectroscopy (DRS). This work is a continuation of our previous investigations on the influence of monovalent and bivalent cations on the dielectric properties of WPA hydrates salts. Measurements were made in the frequency range 10 mHz-1 MHz in order to explore the long-range dynamics, following recent microwave measurements aiming at the local dynamics properties. Experiments were done in the temperature interval 293-350 K. Data treatment included complex permittivity epsilon*, complex electric modulus M* and complex impedance Z* formalism, Arrhenius diagram and Cole-Cole diagrams. The results are discussed in terms of conductivity relaxation and conductivity current relaxation. Rather long conductivity relaxation times measured seem to correspond to ion jumping processes. A phase transition was observed at 323 K. (C) 2003 Elsevier B.V. All rights reserved.