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Structural Water (structural + water)
Selected AbstractsRaman and infrared studies of synthetic Maya pigments as a function of heating time and dye concentrationJOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2007F. S. Manciu Abstract Maya Blue is a famous indigo-based pigment produced by the ancient Mayas. The organic/inorganic complexes inspired by Maya Blue have led to a new class of surface compounds that have novel applications to pigment industries. Materials analyzed in the present work are made by a synthetic route, and demonstrate chemical stability similar to that of the ancient Maya Blue samples. However, we have learned that stable complexes can be synthesized at much higher dye concentrations than used by the Mayas. Analysis by FT-Raman and FT-IR spectroscopy demonstrates the partial elimination of the selection rules for the centrosymmetric indigo, indicating distortion of the molecule. This distortion accounts for the observed color changes, as the molecular orbital structure is modified, allowing the complex to stabilize. The spectroscopic data also shows the disappearance of the indigo NH bonding, as the organic molecules incorporate into palygorskite material. A structural change of indigo to dehydroindigo during heating is suggested by this result. Infrared data confirm the loss of zeolitic water and a partial removal of structural water after the heating process. Evidence of bonding between cationic aluminum and dehydroindigo through oxygen and nitrogen is revealed by FT-Raman measurements at higher dye concentrations. Copyright © 2007 John Wiley & Sons, Ltd. [source] A solid-state NMR investigation of the structure of nanocrystalline hydroxyapatiteMAGNETIC RESONANCE IN CHEMISTRY, Issue 6 2006Christian Jäger Abstract Nanocrystalline hydroxyapatite (HAp) prepared by a precipitation route was investigated. The X-ray diffraction (XRD) powder patterns of the elongated nanocrystals with a typical diameter of about 10 nm and length of 30,50 nm (by transmission electron microscopy (TEM)) revealed the presence of HAp with significantly broadened XRD reflections. However, Ca deficiency was found, as the Ca/P ratio was 1.5 only (so-called calcium-deficient hydroxyapatite (CDHA)), and not 1.67. This Ca deficiency of nanocrystalline HAp is explained using NMR. It is shown unambiguously that (i) the nanocrystals consist of a crystalline core and a (disordered) surface region with a relative phosphate content of about 1:1, (ii) the crystalline core is HAp, and (iii) the surface region is dominated by hydrogen phosphate anions (with no hydroxyapatite-like structural motif) and structural water (hydrate). From the relative phosphate content and taking into account the crystal shape, the thickness of the surface layer along the main crystal axis could be estimated to be about 1 nm, and the average chemical composition of the surface layer has been determined. Finally, a Ca/P ratio of 1.52 was estimated from the NMR data that compares well with the value of 1.51 from chemical analysis. The important consequences are that the surface of nanocrystalline HAp has nothing in common with the bulk composition and that the chemistry of such materials (e.g. the binding of protein molecules to phosphate surfaces) must be reconsidered. Copyright © 2006 John Wiley & Sons, Ltd. [source] Comparison of loss on ignition and thermal analysis stepwise methods for determination of sedimentary organic matterAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue 1 2009Gretel Frangipane Abstract 1.Loss on ignition (LOI) is a widely used method to estimate organic matter (OM) in the sediment of marine and freshwater ecosystems. Thermogravimetric-differential thermal analysis (TG-DTA) of organic species provides information on thermal reactions, the amount and properties of clay structural water, organic species and carbonates. 2.The accuracy of LOI compared with that of TG-DTA was evaluated in 33 sediment samples from the Lagoon of Venice (Italy). 3.In all tests conducted with TG-DTA the mass loss of OM and the loss of clay structural water (LCSW) from oxidized samples were measured. The mass loss of OM at 350°C (TG-DTA 350 OM) and the total extraction of organic matter at 567°C (TEOM) calculated from the difference between natural state samples and oxidized samples highlight the presence of both thermally labile and thermally stable substances. 4.The grain size data of sediment samples from the Lagoon shows a variable distribution between slightly muddy sand and mud. Loss of clay structural water at 350°C (LCSW 350) and total extraction of clay structural water at 567°C (TECSW) both estimated by TG-DTA on oxidized samples, were found to correspond approximately to 6% and 10%, respectively of the clay fraction (<4 µm). This percentage may be used to correct LOI measurements of OM in sediments with high clay content. 5.LOI 350 (loss on ignition at 350°C) and LOI 550 (loss on ignition at 550°C) proved to be ,80% and ,200%, respectively, of total extraction of mass loss at 350°C (TG-DTA 350 tot) and at 567°C (TEML) estimated by TG-DTA on natural samples, meaning that the LOI 550 value represents a significant overestimate. The difference between the LOI 550 and TEML values indicates that the mass loss excess (MLE) may be accounted for by losses due to breakdown of carbonates. Copyright © 2008 John Wiley & Sons, Ltd. [source] Starch phosphorylation,Maltosidic restrains upon 3,- and 6,-phosphorylation investigated by chemical synthesis, molecular dynamics and NMR spectroscopyBIOPOLYMERS, Issue 3 2009Peter I. Hansen Abstract Phosphorylation is the only known in vivo substitution of starch, yet no structural evidence has been provided to explain its implications of the amylosidic backbone and its stimulating effects on starch degradation in plants. In this study, we provide evidence for a major influence on the glucosidic bond in starch specifically induced by the 3-O-phosphate. Two phosphorylated maltose model compounds were synthesized and subjected to combined molecular dynamics (MD) studies and 950 MHz NMR studies. The two phosphorylated disaccharides represent the two possible phosphorylation sites observed in natural starches, namely maltose phosphorylated at the 3,- and 6,-position (maltose-3,-O-phosphate and maltose-6,-O-phosphate). When compared with maltose, both of the maltose-phosphates exhibit a restricted conformational space of the ,(1,4) glycosidic linkage. When maltose is phosphorylated in the 3,-position, MD and NMR show that the glucosidic space is seriously restricted to one narrow potential energy well which is strongly offset from the global potential energy well of maltose and almost 50°degrees from the , angle of the ,-maltose crystal structure. The driving force is primarily steric, but the configuration of the structural waters is also significantly altered. Both the favored conformation of the maltose-3,-phosphate and the maltose-6,-phosphate align well into the 6-fold double helical structure of amylopectin when the effects on the glucosidic bond are not taken into account. However, the restrained geometry of the glucosidic linkage of maltose-3,-phosphate cannot be accommodated in the helical structure, suggesting a major local disturbing effect, if present in the starch granule semi-crystalline lattice. © 2008 Wiley Periodicals, Inc. Biopolymers 91: 179,193, 2009. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] | ||||||||||