Samples of nacrite, dickite, kaolinite, and halloysite were investigated using X-band electron paramagnetic resonance (EPR) and Mössbauer spectroscopy. Fe3+ gave rise to EPR signals at g ≃ 4 which differed with the individual polytype. Only nacrite had no resonance in this region of the spectrum, but it had one at g ≃ 2. Dickite had a quadruple line, kaolinite a triple line, and halloysite a single line in this region. The EPR spectra of these minerals are apparently dependent also on the orientation of adjacent layers in the structures. Other resonances were attributed to (1) clusters of ferric ions giving rise to broad resonance near g ≃ 2, (2) trapped holes, and (3) free radicals linked with organic matter. The Mössbauer spectroscopic results suggest that iron occurs in the ferric state (except in nacrite where Fe2+ is present also) as an ionic substitution (IS) in octahedral layers. This suggestion follows from the difference is the IS values between octahedral and tetrahedral symmetry sites occupied by Fe3+ equal to ∼0.4 mm/sec. Linewidths depend mainly on the way the layers stack; for monoclinic modifications represented by nacrite and dickite, the linewidths are narrow (Γ = 0.45 mm/sec and 0.56 mm/sec, respectively); pseudomonoclinic halloysites also gave narrow linewidths (Γ = 0.39 mm/sec and 0.48 mm/sec). The widest line was observed for triclinic kaolinite (Γ = 0.62 mm/sec and 0.71 mm/sec).

Intercalates of Georgia well-crystallized kaolinite with formamide, N-methylformamide (NMF), and dimethylsulfoxide (DMSO) were prepared at room temperature by dispersing the clay in the organic liquid. Several physical and chemical properties of the intercalated organic molecules and the clay, while intercalated and after de-intercalation, were examined using nuclear magnetic resonance (NMR), infrared (IR), and electron paramagnetic resonance spectroscopy (EPR), and specific heat (Cp) measurements. The chemical bonding between the inner-surface hydroxyls and the organic molecules, as indicated by IR, was strongest for DMSO and weakest for formamide. The distortion of the kaolinite layer, as shown by EPR, also was greatest for DMSO and least for formamide. NMR T1 measurements indicated a relatively strong DMSO-kaolinite surface interaction that slowed down the methyl group reorientation comparable to that in bulk solid DMSO. T1 measurements indicated a weaker interaction for NMF. De-intercalation by mild heating did not return the kaolinite to its original structural state as shown by EPR and Cp. The greatest disorder was found for the DMSO de-intercalate and the least for the formamide de-intercalate. These experiments show that for sufficiently strong bonding between the clay inner surface and the intercalating molecule, the structure of the clay is capable of distortion, which is partly temporary and partly permanent. The permanent changes probably involve the introduction of stacking faults.

The reaction of benzene with exchangeable Cu(II) and Fe(III) in hectorite clay films was studied by electron paramagnetic resonance (EPR). The reaction when carried out in a sealed tube between 60° and 100°C produced a variety of organic radical products. The nature of these products depended on the concentration of water in the reaction medium and the reaction time. The free radicals were accompanied by a reduction in the oxidation state of the metal ions; this process had a zero-order dependence on the metal ion concentration. The activation energies determined from the zero-order rate constants are 67 ± 11 kJ/mole (Cu(II)) and 46 ± 6 kJ/mole (Fe(III)). The free radicals initially formed under anhydrous conditions appeared to populate sites in the interlayer region; the activation energies determined for this first order process are 57 ± 9 kJ/mole (Cu(II)) and 42 ± 3 kJ/mole (Fe(III)). These activation energies are within experimental error of those determined from the metal ion kinetics. The EPR signal due to organic radicals showed little temperature dependence; thus, exchange processes involving organic free radicals were probably not important in determining EPR lineshapes.

Point defect centers in hydrothermal kaolinite have been investigated using electron paramagnetic resonance (EPR). Kaolinite was sampled in petrographically well-defined materials coming from uranium-rich hydrothermally altered volcanic tuffs (Nopal I uranium deposit, Chihuahua, Mexico), which show extensive kaolinization and an intense redistribution of uranium. Several kaolinite parageneses were defined according to their origin (fissure fillings and feldspar pseudomorphs); their location relative to the U6+ mineralization at the scale of the deposit (mineralized breccia pipe vs. barren surrounding rhyolitic tuffs), and at the scale of mineral assemblages; and their crystal chemistry.

Two types of centers of axial symmetry were identified (A- and A′-centers) and represent positive holes trapped on apical oxygens (Si-O−-centers). A-centers were stable to 400°C, whereas A′-centers annealed at 350°C. A relation between defect-center concentration and U content demonstrates that natural irradiation was responsible for these centers. On the other hand, defect-center concentration was not directly linked to the origin (fissural or feldspar pseudomorph) or the crystal chemistry (structural order and substitutional Fe3+ content) of the kaolinite. According to petrographic data, and with respect to the relative thermal stability of A- and A′-centers, two successive irradiations of kaolinite were evidenced: (1) originally during crystallization of kaolinite from radioactive hydrothermal solutions, and (2) permanently when kaolinite was in contact with secondary U-silicates, which led to the formation of A′-centers.

Because of the short half-life of U, these two radiation-induced centers were created by short-lived elements of the U-decay series. As a consequence, variations of defect-center concentration possibly reflect variations in radioactive disequilibrium during the history of the alteration system. This provides a unique tool for tracing the dynamics of the transfer of radionuclides in the geosphere: kaolinite may be used as a sensitive in situ dosimeter, which may be useful in the fields of weathering petrology and nuclear waste management.

A suite of Georgia kaolinites, ranging from well-ordered to very poorly ordered samples, were studied to explore correlations between degree of structural disorder, geological environment, Fe3+ content, Fe3+ electron paramagnetic resonance (EPR) spectrum, and infrared (IR) hydroxyl-stretching band frequencies and bandwidths. Samples from different localities showed a wide range of disorder which appears to be related to differences in their geological environments. High iron content correlated strongly with low degree of order. The areas of both the I and E components of the EPR spectrum and the fractional I area correlated inversely with degree of order. Fourier-transform IR studies of kaolinites and dickites showed that (1) interlayer hydrogen bonding is weaker in dickite than in kaolinite; (2) frequency of the ν11 stretching band of the inner-surface hydroxyls increases sequentially from well-ordered kaolinite through the disordered structures to well-ordered dickite, which is consistent with a model for disorder based on vacancy displacement; and (3) the character and temperature dependence of the inner hydroxyl-stretching band is not compatible with the crystal structures of kaolinite and dickite as refined by Suitch and Young.

A combined application of electron paramagnetic resonance (EPR) and Fourier-transform infrared (FTIR) spectroscopies with thermal methods was used to determine the chemical form of V(IV) in a Georgia kaolinite (KGa-I). Precise values of the EPR spectroscopic g-values and hyperfine coupling constants were obtained for an untreated sample (g∥ = 1.940, A∦ = 18.71 mT; g⊥ = 1.966, A⊥ = 7.63 mT). Heating the sample to 1000°C in steps while monitoring phase changes with EPR and FTIR spectra led to the following structural interpretations: 1) Vanadium (IV) occurs almost entirely as an isomorphically substituted species in the octahedral sheet of KGa-1 kaolinite; 2) during the dehydroxylation of kaolinite at about 500°C and the subsequent formation of metakaolinite, V(IV)-substituted octahedral sites are readily converted into truncated octahedra exhibiting fourfold coordination; and 3) in these highly distorted four-coordinated sites, V(IV) is metastable, being completely oxidized at about 800°C.

A method is proposed to measure the absolute concentration of paramagnetic Fe3+ ions in kaolinite from various geochemical environments using powder X-band electron paramagnetic resonance (EPR) data. An Fe3+-doped corundum sample is used as a concentration standard. The Fe3+ signal is calibrated by calculating the powder EPR spectra of Fe3+ ions in corundum and low-defect kaolinite. The paramagnetic Fe3+ concentration in other samples is obtained by an extrapolation procedure. This study provides a direct assessment of the iron distribution between isolated structural Fe3+ ions and other iron species, such as Fe3+ concentrated phases and Fe2+ ions. The concentration of isolated structural Fe3+ ranges between 200–3000 ppm and represents less than half of the total iron within kaolinite crystals.

Electron paramagnetic resonance (EPR) and Fourier transform infrared (FTIR) spectroscopy in combination with X-ray diffractometry and thermal methods were used to determine the coordination of residual exchangeable Mn(II) in an untreated sample of Wyoming montmorillonite. At room temperature, Mn(II) in a single-layer-hydrate interlayer was proposed to be coordinated directly with oxygen ions of the siloxane surface on one layer and to form water bridges to the oxygens on the siloxane surface of the opposite layer. Dehydration and collapse of the interlayer entrapped and thereby stabilized the partially solvated Mn(II) up to 600°C. A change to Mn(II) in highly symmetric coordination occurred during dehydroxylation of the montmorillonite structure between 600°C and 700°C. Manganese(II) remained coordinated at the surface but positioned in a bicapped trigonal antiprism formed by oxygens of the silicate structure. This coordination was metastable at 800°C when the structural decomposition of the clay mineral began.

Ba3−xSrxTb3−xCexO9 (x = 1 and 1.5) ceramics (BSTC) with a relative density of 93% and a grain size distribution of 0.2–3 µm were prepared by the mixed-oxides reaction route. The crystalline structures, microstructures, valence states, and electrical properties of two ceramics were analyzed using X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and electrical measurements. Rietveld analyses of XRPD patterns show that BSTC1 is indexed as a trigonal structure with the space group R-3c, and BSTC3/2 is indexed as an orthorhombic perovskite structure with the space group Pmcn. The EPR, XPS, and electrical conductivity results confirm that Ce and Tb ions in BSTC exist as Ce4+ and mixed-valence states of Tb4+/Tb3+, respectively. At room temperature, the two BSTC ceramics exhibit a similar semiconducting behavior. The relationships between electrical conductivity and temperature/frequency are provided. The defect chemistry is discussed.

Melatonin-rich and 1,8-cineole-rich extracts have been successfully obtained from yellow mustard (YM) and small cardamom (SC) seeds, respectively, employing green technology of supercritical CO2 (SC-CO2) extraction. Chemical profiling confirmed the presence of melatonin and 1,8-cineole and co-extractants in the respective extracts. Electron paramagnetic resonance spectroscopy attested strong antioxidant activities of the extracts foregoing pan-assay interference compounds involved in spectroscopic analysis. These extracts also exhibited synergistic efficacies greater than unity confirming antioxidant synergy among the co-extracted bioactives therein. To ascertain hypocholesterolaemic efficacies, these extracts were co-administered orally with Triton X (at the pre-optimised dose of 175 mg/kg body weight (BW)) to Wistar albino rats at doses of 550, 175 and 55 mg/kg BW. Serum total cholesterol levels in the rats were monitored on days 3, 7, 15 and 21. On day 21, total cholesterol level reduced appreciably by 49·44 % in rats treated with YM seed extract and by 48·95 % in rats treated with SC seed extract, comparable with atorvastatin-administered rats (51·09 %). Either extract demonstrated inhibitory effects on hepatic 3-hydroxy-3-methyl-glutaryl-CoA (HMG-CoA) reductase activity. A molecular docking exercise identified specific compounds in the extracts which possessed binding affinities comparable with therapeutically used HMG-CoA reductase inhibitors. In silico and in vivo studies concertedly concluded that the consortium of bioactive components in the extracts cannot be considered as invalid metabolic panaceas and therefore these ‘green’ extracts could be safely subjected to clinical studies as preventive biotherapeutics for hypercholesterolaemia. These extracts could be consumed per se as hypocholesterolaemic supplements or could be ingredients of new spice-based therapeutic foods.

Soil kaolins from Indonesia and Western Australia and a range of reference kaolins were studied using Mössbauer spectroscopy, electron paramagnetic resonance (EPR) spectroscopy and SQUID magnetometry. Mössbauer spectra indicate that the Fe within the kaolins is in the highspin Fe3+ oxidation state and that a large fraction of the Fe is present as dispersed atoms residing within the octahedral sites of the kaolinite crystal structure. The EPR spectra are typical for soil kaolins except for the absence of radiation-induced defects for the Indonesian kaolins. The Fe(I) spectra are dominant with a strong symmetric peak at g= 4.3, the presence of Fe(II) spectra is shown by a shoulder on this peak at g= 4.9 and a small phase up peak at g= 9.2.

Low-temperature (5 K) magnetization (M) measurements over large field (H) sweeps (±70 kOe) yielded M(H) curves which are fitted well with Brillouin functions indicating the paramagnetic nature of the kaolins at temperatures down to 5 K. A very small remanent magnetization was detectable in the kaolins. Remanent magnetization to saturation magnetization ratios ranged from 10–4 to 10–3 for the Indonesian kaolins and were all ∼10–3 for the Western Australian kaolins, indicating that at high fields the vast majority of the magnetization of the kaolins is due to paramagnetic ions.

Zero-field-cooled and field-cooled magnetization measurements in small fields (500 Oe) indicate that the Indonesian kaolins are generally free from magnetically-blocked material down to a temperature of 5 K. The magnetic susceptibility of the Indonesian kaolins shows Curie Law behaviour indicating paramagnetic behaviour over all temperatures down to 5 K. Measurements on the Western Australian kaolins indicated the presence of some magnetic material that is magnetically blocked at temperatures below ∼200 ­ 250 K. As a consequence, the magnetic susceptibility showed large deviations from Curie Law behaviour.

Samples of agate and quartz incrustations from different parent volcanic rocks of certain world-wide localities were investigated by EPR, CL and trace element analysis. In all agate samples the following paramagnetic centres were detected:, E′1, [AlO4]0 [FeO4/M+]0 and [GeO4/M+]0. Centres of the type [TiO4/Li+]0 and [TiO4/H+]0, which were detected in quartz of the parent volcanics, are absent in agate. Generally, the abundance of centres (silicon vacancy) and E′1 centres (oxygen vacancy) in agate is remarkably higher than in quartz. The high defect density in agates points to rapid growth of silica from a strongly supersaturated solution probably with a noncrystalline precursor.

CL microscopy reveals internal structures and zoning in agates and quartz incrustations which clearly differ from those discernible by conventional polarizing microscopy. The CL spectra of agates differ from those of quartz from crystalline rocks. At least three broad emission bands were detected in the CL spectra: a blue band of low intensity, a yellow band at about 580 nm, and an intense red band at 650 nm. The CL emission at 650 nm shows some relations to the hydroxyl or alkali content and the abundance of centres and E′1 centres. The emission intensity increases during electron bombardement due to the conversion of different precursors (e.g. ≡Si-O-H, ≡Si-O-Na groups) into hole centres. Another conspicuous feature in the CL spectra of agates is the existence of a yellow emission band centred at around 580 nm. The predominance of the yellow CL emission band and the high concentration of E′1 centres are typical for agates of acidic volcanics and are indicative of a close relationship between the two.