Quantification of chlorpheniramine maleate enantiomers by ultraviolet spectroscopy and chemometric methods

Chlorpheniramine maleate (CLOR) enantiomers were quantified by ultraviolet spectroscopy and partial least squares regression. The CLOR enantiomers were prepared as inclusion complexes with beta-cyclodextrin and 1-butanol with mole fractions in the range from 50 to 100%. For the multivariate calibration the outliers were detected and excluded and variable selection was performed by interval partial least squares and a genetic algorithm. Figures of merit showed results for accuracy of 3.63 and 2.83% (S)-CLOR for root mean square errors of calibration and prediction, respectively. The ellipse confidence region included the point for the intercept and the slope of 1 and 0, respectively. Precision and analytical sensitivity were 0.57 and 0.50% (S)-CLOR, respectively. The sensitivity, selectivity, adjustment, and signal-to-noise ratio were also determined. The model was validated by a paired t test with the results obtained by high-performance liquid chromatography proposed by the European pharmacopoeia and circular dichroism spectroscopy. The results showed there was no significant difference between the methods at the 95% confidence level, indicating that the proposed method can be used as an alternative to standard procedures for chiral analysis.

The solution structure of a copper(II) compound of a new cyclic octapeptide by EPR spectroscopy and force field calculations

A new cyclic octapeptide, cyclo(Ile-Ser-(Gly)Thz-Ile-Thr-(Gly)Thz) (PatN), related to patellamide A, has been synthesized and reacted with copper(II) and base to form mono- and dinuclear complexes. The coordination environments around copper(TI) have been characterized by EPR spectroscopy. The solution structure of the thermodynamically most stable product, a purple dicopper(TI) compound, has been examined by simulating weakly dipole-dipole coupled EPR spectra based upon structural parameters obtained from force field (MM and MD) calculations. The MM-EPR method produces a saddle-shaped structure for [Cu-2(PatN)(OH2)(6)] that is similar to the known solution structure of patellamide A and the known solid-state structure of [Cu-2(AscidH(2))CO3(OH2)(2)]. Compared with the latter, [Cu-2(PatN)] has no carbonate bridge and a significantly flatter topology. The MM-EPR approach to solution-structure determination for paramagnetic metallopeptides may find wide applications to other metallopeptides and metalloproteins.

The relationship between radiation-induced chemical processes and transverse relaxation times in polymer gel dosimeters

The effects of ionizing radiation in different compositions of polymer gel dosimeters are investigated using FT-Raman spectroscopy and NMR T-2 relaxation times. The dosimeters are manufactured from different concentrations of comonomers (acrylamide and N,N'-methylene-bis-acrylamide) dispersed in different concentrations of an aqueous gelatin matrix. Results are analysed using a model of fast exchange of magnetization between three proton pools. The fraction of protons in each pool is determined using the known chemical composition of the dosimeter and FT-Raman spectroscopy. Based on these results, the physical and chemical processes in interplay in the dosimeters are examined in view of their effect on the changes in T-2 The precipitation of growing macroradicals and the scavenging of free radicals by gelatin are used to explain the rate of polymerization. The model describes the changes in T-2 as a function of the absorbed dose up to 50 Gy for the different compositions. This is expected to aid the theoretical design of new, more efficient dosimeters, since it was demonstrated that the optimum dosimeter (i.e, with the lowest dose resolution) must have a range of relaxation times which match the range of T-2 values which can be determined with the lowest uncertainty using an MRI scanner.

Thermal analysis, nuclear magnetic resonance spectroscopy, and impedance spectroscopy of N,N-dimethyl-pyrrolidinium iodide: An ionic solid exhibiting rotator phases

N,N-dimethyl-pyrrolidinium iodide has been investigated using differential scanning calorimetry, nuclear magnetic resonance (NMR) spectroscopy, second moment calculations, and impedance spectroscopy. This pyrrolidinium salt exhibits two solid-solid phase transitions, one at 373 K having an entropy change, Delta S, of 38 J mol(-1) K-1 and one at 478 K having Delta S of 5.7 J mol(-1) K-1. The second moment calculations relate the lower temperature transition to a homogenization of the sample in terms of the mobility of the cations, while the high temperature phase transition is within the temperature region of isotropic tumbling of the cations. At higher temperatures a further decrease in the H-1 NMR linewidth is observed which is suggested to be due to diffusion of the cations. (C) 2005 American Institute of Physics.

Influence of BisGMA, TEGDMA, and BisEMA contents on viscosity, conversion, and flexural strength of experimental resins and composites

Different monomer structures lead to different physical and mechanical properties for both the monomers and the polymers. The objective of this study was to determine the influence of the bisphenylglycidyl dimethacrylate (BisGMA) concentration (33, 50 or 66 mol%) and the co-monomer content [triethylene glycol dimethacrylate (TEGDMA), ethoxylated bisphenol-A dimethacrylate (BisEMA), or both in equal parts] on viscosity (eta), degree of conversion (DC), and flexural strength (FS). eta was measured using a viscometer, DC was obtained by Fourier transfer Raman (FT-Raman) spectroscopy, and FS was determined by three-point bending. At 50 and 66% BisGMA, increases in eta were observed following the partial and total substitution of TEGDMA by BisEMA. For 33% BisGMA, eta increased significantly only when no TEGDMA was present. The DC was influenced by BisGMA content and co-monomer type. Mixtures containing 66% BisGMA showed a lower DC compared with mixtures containing other concentrations of BisGMA. The BisEMA mixtures had a lower DC compared with the TEGDMA mixtures. The FS was influenced by co-monomer content only. BisEMA mixtures presented a statistically lower FS, followed by TEGDMA + BisEMA mixtures, and then by TEGDMA mixtures. Partial or total replacement of TEGDMA by BisEMA increased eta, which was associated with the observed decreases in DC and FS. Although the BisGMA content influenced the DC, it did not affect the FS results.

Ligand K-edge X-ray absorption spectroscopy and DFT calculations on [Fe3S4]0,+ clusters: delocalization, redox, and effect of the protein environment

Ligand K-edge XAS of an [Fe3S4]0 model complex is reported. The pre-edge can be resolved into contributions from the í2Ssulfide, í3Ssulfide, and Sthiolate ligands. The average ligand-metal bond covalencies obtained from these pre-edges are further distributed between Fe3+ and Fe2.5+ components using DFT calculations. The bridging ligand covalency in the [Fe2S2]+ subsite of the [Fe3S4]0 cluster is found to be significantly lower than its value in a reduced [Fe2S2] cluster (38% vs 61%, respectively). This lowered bridging ligand covalency reduces the superexchange coupling parameter J relative to its value in a reduced [Fe2S2]+ site (-146 cm-1 vs -360 cm-1, respectively). This decrease in J, along with estimates of the double exchange parameter B and vibronic coupling parameter ì2/k-, leads to an S ) 2 delocalized ground state in the [Fe3S4]0 cluster. The S K-edge XAS of the protein ferredoxin II (Fd II) from the D. gigas active site shows a decrease in covalency compared to the model complex, in the same oxidation state, which correlates with the number of H-bonding interactions to specific sulfur ligands present in the active site. The changes in ligand-metal bond covalencies upon redox compared with DFT calculations indicate that the redox reaction involves a two-electron change (one-electron ionization plus a spin change of a second electron) with significant electronic relaxation. The presence of the redox inactive Fe3+ center is found to decrease the barrier of the redox process in the [Fe3S4] cluster due to its strong antiferromagnetic coupling with the redox active Fe2S2 subsite.

Structural, optical and magnetic properties of pulsed laser deposited Co-doped ZnO films

Zn1−xCoxO films with different Co concentrations (with x=0.00, 0.10, 0.15, and 0.30) were grown by pulsed laser deposition (PLD) technique. The structural and optical properties of the films were investigated by grazing incidence X-ray diffraction (GIXRD), Raman spectroscopy and photoluminescence (PL). The magnetic properties were measured by conventional magnetometry using a SQUID and simulated by ab-initio calculations using Korring–Khon–Rostoker (KKR) method combined with coherent potential approximation (CPA). The effect of Co-doping on the GIXRD and Raman peaks positions, shape and intensity is discussed. PL studies demonstrate that Co-doping induces a decrease of the bandgap energy and quenching of the UV emission. They also suggest the presence of Zn interstitials when x≥0.15. The 10% Co-doped ZnO film shows ferromagnetism at 390 K with a spontaneous magnetic moment ≈4×10−5 emu and coercive field ≈0.17 kOe. The origin of ferromagnetism is explained based on the calculations using KKR method.

Production and characterization of ZrCN-Ag coatings deposited by mganetron sputtering

Tese de Doutoramento (Programa doutoral em Engenharia de Materiais)

Pigments and plasters discovered in the House of Diana (Cosa, Grosseto, Italy): An integrated study between art history, archaeology and scientific analyses

The pigments and the plasters of the Roman frescoes discovered at the House of Diana (Cosa, Grosseto, Italy) were analysed using non-destructive and destructive mineralogical and chemical techniques. The characterization of both pigments and plasters was performed through optical microscopy, scanning electron microscopy and electron microprobe analysis. The pigments were identified by Raman spectroscopy and submitted to stable isotope analysis. The results were integrated with the archaeological data in order to determine and reconstruct the provenance, trade patterns and the employment of the raw materials used for the elaboration of the frescoes.

Use of NIR spectroscopy and multivariate process spectra calibration methodology for pharmaceutical solid samples analysis

Accomplish high quality of final products in pharmaceutical industry is a challenge that requires the control and supervision of all the manufacturing steps. This request created the necessity of developing fast and accurate analytical methods. Near infrared spectroscopy together with chemometrics, fulfill this growing demand. The high speed providing relevant information and the versatility of its application to different types of samples lead these combined techniques as one of the most appropriated. This study is focused on the development of a calibration model able to determine amounts of API from industrial granulates using NIR, chemometrics and process spectra methodology.

Design and construction of precision heat fluxmeters

InAlAs/InGaAs/InP based high electron mobility transistor devices have been structurally and electrically characterized, using transmission electron microscopy and Raman spectroscopy and measuring Hall mobilities. The InGaAs lattice matched channels, with an In molar fraction of 53%, grown at temperatures lower than 530¿°C exhibit alloy decomposition driving an anisotropic InGaAs surface roughness oriented along [1math0]. Conversely, lattice mismatched channels with an In molar fraction of 75% do not present this lateral decomposition but a strain induced roughness, with higher strength as the channel growth temperature increases beyond 490¿°C. In both cases the presence of the roughness implies low and anisotropic Hall mobilities of the two dimensional electron gas.

Effect of the nanoparticles on the structure and crystallization of amorphous silicon thin films produced by rf glow discharge

Thin films of nanostructured silicon (ns-Si:H) were deposited by plasma-enhanced chemical vapor deposition in the presence of silicon nanoparticles at 100 C substrate temperature using silane and hydrogen gas mixture under continuous wave (cw) plasma conditions. The nanostructure of the films has been demonstrated by diverse ways: transmission electron microscopy, Raman spectroscopy and x-ray diffraction, which have shown the presence of ordered silicon clusters (1!=2 nm) embedded in an amorphous silicon matrix. Due to the presence of these ordered domains, the films crystallize faster than standard hydrogenated amorphous silicon samples, as evidenced by electrical measurements during the thermal annealing.

Nucleation of diamond on silicon, SiAlON, and graphite substrates coated with an a-C:H layer

We investigated the influence of a hydrogenated disordered carbon (a-C:H) layer on the nucleation of diamond. Substrates c-Si<100>, SiAlON, and highly oriented pyrolytic graphite {0001} were used in this study. The substrate surfaces were characterized with Auger electron spectroscopy (AES) while diamond growth was followed with Raman spectroscopy and scanning electron microscopy (SEM). It was found that on silicon and SiAlON substrates the presence of the a-C:H layer enabled diamond to grow readily without any polishing treatment. Moreover, more continuous diamond films could be grown when the substrate was polished with diamond powder prior to the deposition of the a-C:H layer. This important result suggests that the nucleation of diamond occurs readily on disordered carbon surfaces, and that the formation of this type of layer is indeed one step in the diamond nucleation mechanism. Altogether, the data refute the argument that silicon defects play a direct role in the nucleation process. Auger spectra revealed that for short deposition times and untreated silicon surfaces, the deposited layer corresponds to an amorphous carbon layer. In these cases, the subsequent diamond nucleation was found to be limited. However, when the diamond nucleation density was found to be high; i.e., after lengthy deposits of a¿C:H or after diamond polishing, the Auger spectra suggested diamondlike carbon layers.