Gene/Protein Disease Symptom Drug Enzyme Compound
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Density functional theory (DFT) calculations of EPR parameters and their structure sensitivity for selected surface paramagnetic species involved in oxidative dehydrogenation of methanol over silica grafted molybdenum catalyst were investigated. Two surface complexes, Mo(4c)/SiO2 and {O(-)-Mo(4c)}/SiO2, as well as *CH2OH radical trapped on the SiO2 matrix were taken as the examples. The spin-restricted zeroth order regular approximation (ZORA) implemented in the Amsterdam Density Functional suite was used to calculate the electronic g tensor for those species. The predicted values were in satisfactory agreement with experimental EPR results. Five different coordination modes of the *CH2OH radical on the silica surface were considered and the isotropic 13C, 17O, and 1H hyperfine coupling constants (HFCC) of the resultant surface complexes were calculated. Structure sensitivity of the HFCC values was discussed in terms of the angular deformations caused by hydrogen bonding with the silica surface.
Spectrochim Acta A Mol Biomol Spectrosc 2006 Mar 13
PMID:DFT calculations of magnetic parameters for molybdenum complexes and hydroxymethyl intermediates trapped on silica surface. 1648 60

Raman spectroscopy has been used to study the molecular structure of a series of selected uranyl silicate minerals, including weeksite K2[(UO2)2(Si5O13)].H2O, soddyite [(UO2)2SiO4.2H2O] and haiweeite Ca[(UO2)2(Si5O12(OH)2](H2O)3 with UO2(2+)/SiO2 molar ratio 2:1 or 2:5. Raman spectra clearly show well resolved bands in the 750-800 cm-1 region and in the 950-1000 cm-1 region assigned to the nu1 modes of the (UO2)2+ units and to the (SiO4)4- tetrahedra. For example, soddyite is characterized by Raman bands at 828.0, 808.6 and 801.8 cm-1 (UO2)2+ (nu1), 909.6 and 898.0 cm-1 (UO2)2+ (nu3), 268.2, 257.8 and 246.9 cm-1 are assigned to the nu2 (delta) (UO2)2+. Coincidences of the nu1 (UO2)2+ and the nu1 (SiO4)4- is expected. Bands at 1082.2, 1071.2, 1036.3, 995.1 and 966.3 cm-1 are attributed to the nu3 (SiO4)4-. Sets of Raman bands in the 200-300 cm-1 region are assigned to nu2 (delta) (UO2)2+ and UO ligand vibrations. Multiple bands indicate the non-equivalence of the UO bonds and the lifting of the degeneracy of nu2 (delta) (UO2)2+ vibrations. The (SiO4)4- tetrahedral are characterized by bands in the 470-550 cm-1 and in the 390-420 cm-1 region. These bands are attributed to the nu4 and nu2 (SiO4)4- bending modes. The minerals show characteristic OH stretching bands in the 2900-3500 cm-1 and 3600-3700 cm-1.
Spectrochim Acta A Mol Biomol Spectrosc 2006 May 15
PMID:A Raman and infrared spectroscopic study of the uranyl silicates--weeksite, soddyite and haiweeite. 1668 40

The technique of Raman spectroscopy was used to examine the composition of ancient African domestic clay pottery of South African origin. One sample from each of four archaeological sites including Rooiwal, Lydenburg, Makahane and Graskop was studied. Normal dispersive Raman spectroscopy was found to be the most effective analytical technique in this study. XRF, XRD and FT-IR spectroscopy were used as complementary techniques. All representative samples contained common features, which were characterised by kaolin (Al2Si2O5(OH)5), illite (KAl4(Si7AlO20)(OH)4), feldspar (K- and NaAlSi3O8), quartz (alpha-SiO2), hematite (alpha-Fe2O3), montmorillonite (Mg3(Si,Al)4(OH)2 x 4.5 5H(2)O[Mg]0.35), and calcium silicate (CaSiO3). Gypsum (CaSO4 x 2H2O) and calcium carbonates (most likely calcite, CaCO3) were detected by Raman spectroscopy in Lydenburg, Makahane and Graskop shards. Amorphous carbon (with accompanying phosphates) was observed in the Raman spectra of Lydenburg, Rooiwal and Makahane shards, while rutile (TiO(2)) appeared only in Makahane shard. The Raman spectra of Lydenburg and Rooiwal shards further showed the presence of anhydrite (CaSO4). The results showed that South African potters used a mixture of clays as raw materials. The firing temperature for most samples did not exceed 800 degrees C, which suggests the use of open fire. The reddish brown and grayish black colours were likely due to hematite and amorphous carbon, respectively.
Spectrochim Acta A Mol Biomol Spectrosc 2007 Jan
PMID:Raman spectroscopic study of ancient South African domestic clay pottery. 1683 5

The polymer electrolytes composing of the blend of polyvinyl chloride-polymethyl methacrylate (PVC/PMMA) with lithium triflate (LiCF3SO3) as salt, ethylene carbonate (EC) and dibutyl phthalate (DBP) as plasticizers and silica (SiO2) as the composite filler were prepared. FTIR studies confirm the complexation between PVC/PMMA blends. The CCl stretching mode at 834 cm-1 for pure PVC is shifted to 847 cm-1 in PVC-PMMA-LiCF3SO3 system. This suggests that there is interaction between Cl in PVC with Li+ ion from LiCF3SO3. The band due to OCH3 at 1150 cm-1 for PVC-PMMA blend is shifted to 1168 cm-1 in PVC-PMMA-LiCF3SO3 system. This shift is expected to be due to the interaction between Li+ ion and the oxygen atom in PMMA. The symmetric vibration band and the asymmetric vibration band of LiCF3SO3 at 1033 and 1256 cm-1 shifted to 1075 and 1286 cm-1 in the DBP-EC plasticized PVC-PMMA-LiCF3SO3 complexes. The interaction between Li+ ions and SiO2 will lead to an increase in the number of free plasticizers (which does not interact with Li+ ions). When the silica content increases from 2% to 5%, the intensity of the peak at 896 cm-1 (due to the ring breathing vibration of free EC) increases in PVC-PMMA-LiCF3SO3-DBP-EC system.
Spectrochim Acta A Mol Biomol Spectrosc 2007 Apr
PMID:FTIR studies of PVC/PMMA blend based polymer electrolytes. 1691 98

In this report, we investigate the cooperative energy transfer frequency upconversion in Tb3+/Yb3+-codoped SiO2-Al(2)O(3)-Na2O-ZnF(2) oxyfluoride glasses under 980 nm diode laser excitation. The influence of both Tb3+ and Yb3+ concentration on the emission bands were investigated. With a lower Tb3+ concentration, the emission bands around 381, 416 and 438 nm, and 489, 545, 587 and 623 nm associated with (5)D(3), (5)G(6)-->(7)F(J) (J=6, 5, 4) and (5)D(4)-->(7)F(J) (J=6, 5, 4, 3) transitions were observed. However, only (5)D(4)-->(7)F(J) (J=6, 5, 4, 3) transitions appear in a higher Tb3+ concentration. The integrated upconversion luminescence intensity was examined when the temperature of sample was varied from 40 to 450 K. The dependence of the upconversion emission intensity upon the excitation power was also examined, and the upconversion mechanisms were discussed.
Spectrochim Acta A Mol Biomol Spectrosc 2007 Jul
PMID:Cooperative energy transfer frequency upconversion in Tb3+/Yb3+-codoped oxyfluoride glasses. 1727 22

The Grand Canonical Monte Carlo method was used to analyse the phenomenon of adsorption of aromatic compounds (i.e. phenol, toluene, benzoic acid and salicylic acid) on the surface of the titania-silica (TiO2/SiO2) catalyst. We found that different types of interactions play important roles in the adsorption of molecules having polar and non-polar groups. Moreover, we found that the interactions between sorbate molecules are strong, and are the cause of multilayer adsorption occurring in the investigated temperature and pressure range.
J Mol Model 2007 Jul
PMID:Modeling the adsorption of aromatic compounds on the TiO2/SiO2 catalyst. 1734 Jan 10

The various spatial arrangements of frontier orbitals that may lead to facile reductive splitting of the H2 molecule at mono- or binuclear catalysts containing s, p, d or f-block metals, and on surfaces of solids are briefly reviewed. The postulation is also made that binuclear divalent titanium (Ti(II)) and mononuclear silicon (Si(II)) species might serve as active sites for the H2 attachment reaction for hydridoalanates doped with Ti salts and hydridoborates doped with SiO2, respectively.
J Mol Model 2007 Jul
PMID:Orbital landscapes for reductive 2e- activation of dihydrogen molecule. 1738 Mar 53

Thermal decomposition studies of the free polyhedral oligomeric silsesquioxane, POSSh, and when this compound has been impregnated with Cp2ZrCl2 (Cp = eta5-C5H5) or immobilized on SiO2 were conducted using infrared emission spectroscopy (IES) over a 100-1000 degrees C temperature range and by thermogravimetric analysis (TGA). The organic groups in POSS(h) apparently decompose thermally into Si-CH3, Si-H and other fragments. Upon impregnation with Cp2ZrCl2, however, a different thermal decomposition pathway was followed and new infrared emission bands appeared in the 1000-900 cm(-1) region suggesting the formation of Si-O-Zr moieties. When immobilized on SiO2 and subjected to thermal decomposition, the POSSh compound lost its organic groups and the inorganic structure remaining was incorporated into the SiO2 framework.
Spectrochim Acta A Mol Biomol Spectrosc 2008 Nov 01
PMID:Thermal decomposition studies of the polyhedral oligomeric silsesquioxane, POSSh, and when it is impregnated with the metallocene bis(eta5-cyclopentadienyl)zirconium (IV) dichloride or immobilized on silica. 1822 11

A micro-Raman spectroscopy study of a multi-coloured (yellow, blue, white, redish-brown and brown-black) tile shard from the Citadel of Algiers was undertaken. XRD and EDX were used as complementary techniques. The study shows that the heterogeneous three-shade yellow pigment on the tile is composed largely of the ancient ternary (Pb-Sn-Sb) pyrochlore oxide with a dominant Pb-O vibration at 127 cm(-1) consistent with the Pb2SnSbO6.5 structure as verified by XRD. The literature assignment of this band at 132 cm(-1) probably comes from a mixture of pigments. The redish-brown and the brown-black pigments are found to be Naples yellow (Pb2Sb2O7) and lead(II) stannate (Pb2SnO4), respectively, while cobalt blue (CoAl2O4) gives the blue colour and cassiterite (SnO2) is the origin of the white colour. The bulk of the tile body is composed mainly of hematite (alpha-Fe2O3), maghemite (gamma-Fe2O3), magnetite (Fe3O4) and Quartz (alpha-SiO2) with traces of calcite (CaCO3) and amorphous carbon. Micro-Raman spectroscopy proved to be very useful in the characterization of pigments as well as the tile body. These results further establish Raman spectroscopy as a technique of choice for the analysis of pigments on archaeological artifacts. The results obtained here could be used in the restoration and preservation programme of the Citadel itself which stands today as a symbol of pre-colonial Algerian heritage.
Spectrochim Acta A Mol Biomol Spectrosc 2008 Dec 15
PMID:Raman analysis of ancient pigments on a tile from the Citadel of Algiers. 1860 62

The upconversion luminescence properties of Ho3+/Yb3+-codoped SiO2-BaF2-ZnF2 glasses were investigated upon excitation with 980 nm diode laser. The visible emission bands centered at 546 and 661 nm correspond to 5F4, 5S2-->5I8 and 5F5-->5I8 transitions were observed. The effect of composition and temperature on the upconversion emission intensity was examined. It was found that the upconversion emission signals decrease with increasing ZnF2 content and temperature. The dependence of the upconversion emission intensity upon the excitation power was also examined, and the upconversion mechanisms were discussed.
Spectrochim Acta A Mol Biomol Spectrosc 2009 Jul
PMID:Compositional and thermal effect on upconversion luminescence of Ho3+/Yb3+-codoped oxyfluoride glasses. 1923 11


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