Ultrafast fiber laser mode-locked by graphene based saturable absorber

A Graphene-based saturable absorber is fabricated using wet chemistry techniques. We use it to passively mode-lock an Erbium doped fiber laser. ~500fs pulses are produced at 1560nm with a 5.2nm spectrum bandwidth. © 2010 Optical Society of America.

Synthesis, characterization and electrical properties of solid state electrolyte materials La2-xCaxMo1.7W0.3O9-delta (0 <= x <= 0.2)

The new compounds La2-xCaxMo1.7W0.3O9-delta (0 <= x <= 0.2) in which La3+ substituted with Ca2+ were synthesized by dry-chemistry techniques based on the oxygen Ionic conductor La2Mo1.7W0.3O9. The new series were characterized by X-ray Diffraction (XRD), Raman and X-ray Photoelectron Spectroscopy (XPS) and the electrical conductivity of samples were investigated by AC impedance spectroscopy. The lattice parameters were reduced due to the smaller atomic radius of the Ca2+ compared with that of the La3+. Furthermore, Additional oxygen vacancies were introduced into La2Mo1.7W0.3O9 lattice by substitution, and then the oxygen ionic conductivity was increased. At 550 degrees C, the conductivity increased 89.9%, that is, from 0.79 x 10(-4) S center dot cm(-1) (x=0) to 1.5 X 10(-4)S center dot cm(-1) (x=0.16, 0.2).

Synthesis, characterization and electrical properties of the new solid electrolyte materials Ce6-xErxMoO15-delta (0.0 < x < 1.5)

A new series of oxides, Ce6-xErxMoO15-delta (0.0 less than or equal to x less than or equal to 1.5), was synthesized using wet-chemistry techniques. The precursors and resultant oxide powders were characterized by differential thermal analysis/thermogravimetry, x-ray diffraction, and IR, Raman and x-ray photoelectron spectroscopy. The formation temperature of the powders was found to be as low as 350degreesC. Ce6-xErxMoO15-delta crystallized to a fluorite-related cubic structure. The electrical conductivity of the samples was investigated by using ac impedance spectroscopy. This showed that the presence of Er was related to the oxygen-ion conductivity, and that the highest oxygen-ion conductivity was found in Ce6-xErxMoO15-delta (x = 0.4), ranging from 5.9 x 10(-5) S cm(-1) at 300degreesC to 1.26 x 10(-2) S cm(-1) at 700degreesC, respectively. This kind of material shows a potential application in intermediate-temperature solid oxide fuel cells.

Protecting group and switchable pore-discriminating adsorption properties of a hydrophilic-hydrophobic metal-organic framework

Formed by linking metals or metal clusters through organic linkers, metal-organic frameworks are a class of solids with structural and chemical properties that mark them out as candidates for many emerging gas storage, separation, catalysis and biomedical applications. Important features of these materials include their high porosity and their flexibility in response to chemical or physical stimuli. Here, a copper-based metal-organic framework has been prepared in which the starting linker (benzene-1,3,5-tricarboxylic acid) undergoes selective monoesterification during synthesis to produce a solid with two different channel systems, lined by hydrophilic and hydrophobic surfaces, respectively. The material reacts differently to gases or vapours of dissimilar chemistry, some stimulating subtle framework flexibility or showing kinetic adsorption effects. Adsorption can be switched between the two channels by judicious choice of the conditions. The monoesterified linker is recoverable in quantitative yield, demonstrating possible uses of metal-organic frameworks in molecular synthetic chemistry as 'protecting groups' to accomplish selective transformations that are difficult using standard chemistry techniques.

Theoretical Investigation of NH3-SCR Processes over Zeolites: A Review

The selective catalytic reduction (SCR) of NOx compounds with NH3 is a hot topic in recent years. Among various catalysts, zeolites are proved to be efficient and promising for NH3-SCR, yet the whole processes and intrinsic mechanism are still not well understood due to the structural complexity of zeolites. With the improvement of theoretical chemistry techniques, quantum-chemical calculations are now capable of modeling the structure, acidity, adsorption, and ultimately reaction pathways over zeolites to some extent. In this review, a brief summary of relevant concepts of NH3-SCR is presented. Cluster approaches, embedded techniques, and periodic treatments are described as three main methods. Details of quantum-chemical investigations toward the key issues such as, the structure of active sites, the adsorption of small molecules, and the reaction mechanism of NH3-SCR over zeolites are discussed. Finally, a perspective for future theoretical research is given. 

Synthesis and NMR spectroscopic analysis of 3-nitro-pyranoside, 3-nitro-septanoside and 4-nitro-septanoside derivatives by condensation of the anion of nitromethane with glycoside

The utility of the nitroaldol reaction for accessing 3-nitro-pyranoside, 3-nitro-septanoside or 4-nitro-septanoside derivatives, by reaction of the anion of nitromethane with glycoside dialdehydes is demonstrated. Initially, the feasibility of using unprotected glucoside dialdehydes was probed for the synthesis of the septanoside products, but this affoided pyranoside rather than septanoside targets. Subsequent studies utilised protected glycoside dialdehydes within the methodology, which allowed entry into a range of 3-nitro or 4-nitro-septanosides in good yield NMR spectroscopic analysis allowed determination of the stereochemistry of each of the products thus afforded.

Tyrosinase activated melanoma prodrugs

Metastatic malignant melanoma remains a highly aggressive form of skin cancer for which no reliable methods for treatment exist. Given the increasing incidence of this cancer, considerable attention has focused on the development of new and improved methods for tackling this disease. Within this article, methods for treating melanoma are reviewed and discussed with particular attention focusing on prodrugs that are activated by the tyrosinase enzyme. This enzyme is up-regulated and is of elevated activity within malignant melanomas compared with healthy melanocytes, providing an ideal in-situ tool for the activation of melanoma prodrugs. By way of background to the prodrug strategies discussed within this review, the causes of melanoma, the enzymology of tyrosinase, and the chemistry of the biosynthetic pathways associated with melanogenesis are presented. Aspects of the design, mode of action, and biological profiles of key prodrugs that are activated by tyrosinase, and that show potential for the treatment of melanoma, are then presented and compared.

Stability-indicating methods for the enantioselective determination of dihydropyridines by high performance liquid chromatography and capillary electrophoresis

This paper presents simple, rapid, precise and accurate stability-indicating HPLC and CE methods, which were developed and validated for the determination of nitrendipine, nimodipine and nisoldipine. These drugs are calcium channel antagonists of the 1,4-dihydropyridine type which are used in the treatment of cardiovascular diseases. Experimental results showed a good linear correlation between the area and the concentration of drugs covering a relatively large domain of concentration in all cases. The linearity of the analytical procedures was in the range of 2.0-120.0 mu g mL-1 for nitrendipine, 1.0-100.0 mu g mL(-1) for nimodipine and 100.0-600.0 mu g mL(-1) for nisoldipine, the regression determination coefficient being higher than 0.99 in all cases. The proposed methods were found to have good precision and accuracy. The chemical stability of these drugs was determined under various conditions and the methods have shown adequate separation for their enantiomers and degradation products. In addition, degradation products produced as a result of stress studies did not interfere with the detection of the drugs' enantiomers and the assays can thus be considered stability-indicating.

Determination of anticonvulsants in human plasma using SPME in a heated interface coupled online to liquid chromatography (SPME-LC)

A simple and sensitive method using solid phase microextraction (SPME) and liquid chromatography (LC) with heated online desorption (SPME-LC) was developed and validated to analyze anticonvulsants (AEDs) in human plasma samples. A heated lab-made interface chamber was used in the desorption procedure, which allowed the transference of the whole extracted sample. The SPME conditions were optimized by applying an experimental design. Important factors are discussed such as fiber coating types, pH, extraction time and desorption conditions. The drugs were analyzed by LC, using a C18 column (150 mm x 4.6 mm x 5 mm); and 50 mmol L-1, pH 5.50 ammonium acetate buffer : acetonitrile : methanol (55 : 22 : 23 v/v) as the mobile phase with a flow rate of 0.8 mL min(-1). The suggested method presented precision (intra-assay and inter-assay), linearity and limit of quantification (LOQ) all adequate for the therapeutic drug monitoring (TDM) of AEDs in plasma.

Multivariate analyses of UV-Vis absorption spectral data from cachaca wood extracts: a model to classify aged Brazilian cachacas according to the wood species used

Multivariate analyses of UV-Vis spectral data from cachaca wood extracts provide a simple and robust model to classify aged Brazilian cachacas according to the wood species used in the maturation barrels. The model is based on inspection of 93 extracts of oak and different Brazilian wood species by a non-aged cachaca used as an extraction solvent. Application of PCA (Principal Components Analysis) and HCA (Hierarchical Cluster Analysis) leads to identification of 6 clusters of cachaca wood extracts (amburana, amendoim, balsamo, castanheira, jatoba, and oak). LDA (Linear Discriminant Analysis) affords classification of 10 different wood species used in the cachaca extracts (amburana, amendoim, balsamo, cabreuva-parda, canela-sassafras, castanheira, jatoba, jequitiba-rosa, louro-canela, and oak) with an accuracy ranging from 80% (amendoim and castanheira) to 100% (balsamo and jequitiba-rosa). The methodology provides a low-cost alternative to methods based on liquid chromatography and mass spectrometry to classify cachacas aged in barrels that are composed of different wood species.

Comparação do perfil químico entre cachaças de um mesmo vinho destiladas em alambiques e em colunas

Six wines were distilled in two different distillation apparatus (alembic and column) producing 24 distillates (6 for each alembic fraction - head, heart and tail; 6 column distillates). The chemical composition of distillates from the same wine was determined using chromatographic techniques. Analytical data were subjected to Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) allowing discrimination of four clusters according to chemical profiles. Both distillation processes influenced the sugarcane spirits chemical quality since two types of distillates with different quantitative chemical profiles were produced after the elimination of fermentation step influence.

Exploring synonymous codon usage preferences of disulfide-bonded and non-disulfide bonded cysteines in the E-coli genome

High-quality data about protein structures and their gene sequences are essential to the understanding of the relationship between protein folding and protein coding sequences. Firstly we constructed the EcoPDB database, which is a high-quality database of Escherichia coli genes and their corresponding PDB structures. Based on EcoPDB, we presented a novel approach based on information theory to investigate the correlation between cysteine synonymous codon usages and local amino acids flanking cysteines, the correlation between cysteine synonymous codon usages and synonymous codon usages of local amino acids flanking cysteines, as well as the correlation between cysteine synonymous codon usages and the disulfide bonding states of cysteines in the E. coli genome. The results indicate that the nearest neighboring residues and their synonymous codons of the C-terminus have the greatest influence on the usages of the synonymous codons of cysteines and the usage of the synonymous codons has a specific correlation with the disulfide bond formation of cysteines in proteins. The correlations may result from the regulation mechanism of protein structures at gene sequence level and reflect the biological function restriction that cysteines pair to form disulfide bonds. The results may also be helpful in identifying residues that are important for synonymous codon selection of cysteines to introduce disulfide bridges in protein engineering and molecular biology. The approach presented in this paper can also be utilized as a complementary computational method and be applicable to analyse the synonymous codon usages in other model organisms. (c) 2005 Elsevier Ltd. All rights reserved.

Predicting residue-wise contact orders in proteins by support vector regression

Background: The residue-wise contact order (RWCO) describes the sequence separations between the residues of interest and its contacting residues in a protein sequence. It is a new kind of one-dimensional protein structure that represents the extent of long-range contacts and is considered as a generalization of contact order. Together with secondary structure, accessible surface area, the B factor, and contact number, RWCO provides comprehensive and indispensable important information to reconstructing the protein three-dimensional structure from a set of one-dimensional structural properties. Accurately predicting RWCO values could have many important applications in protein three-dimensional structure prediction and protein folding rate prediction, and give deep insights into protein sequence-structure relationships. Results: We developed a novel approach to predict residue-wise contact order values in proteins based on support vector regression (SVR), starting from primary amino acid sequences. We explored seven different sequence encoding schemes to examine their effects on the prediction performance, including local sequence in the form of PSI-BLAST profiles, local sequence plus amino acid composition, local sequence plus molecular weight, local sequence plus secondary structure predicted by PSIPRED, local sequence plus molecular weight and amino acid composition, local sequence plus molecular weight and predicted secondary structure, and local sequence plus molecular weight, amino acid composition and predicted secondary structure. When using local sequences with multiple sequence alignments in the form of PSI-BLAST profiles, we could predict the RWCO distribution with a Pearson correlation coefficient (CC) between the predicted and observed RWCO values of 0.55, and root mean square error (RMSE) of 0.82, based on a well-defined dataset with 680 protein sequences. Moreover, by incorporating global features such as molecular weight and amino acid composition we could further improve the prediction performance with the CC to 0.57 and an RMSE of 0.79. In addition, combining the predicted secondary structure by PSIPRED was found to significantly improve the prediction performance and could yield the best prediction accuracy with a CC of 0.60 and RMSE of 0.78, which provided at least comparable performance compared with the other existing methods. Conclusion: The SVR method shows a prediction performance competitive with or at least comparable to the previously developed linear regression-based methods for predicting RWCO values. In contrast to support vector classification (SVC), SVR is very good at estimating the raw value profiles of the samples. The successful application of the SVR approach in this study reinforces the fact that support vector regression is a powerful tool in extracting the protein sequence-structure relationship and in estimating the protein structural profiles from amino acid sequences.

Cellular interactions with hydrogels

An efficient means of evaluating potential biomaterials is to use the in vitro fibroblast cell culture model. However, the chemistry which influences cell adhesion on polymer substrates is poorly understood. The work in this thesis aims to rationalise several theories of current opinion and introduce new chemical techniques that may predict cellular behaviour. The keratoprosthesis is a typical example of the need to be able to manipulate cell adhesion of materials since both adhesive and non adhesive sections are needed for proper integration and optical function. Calcein AM/ethidium homodimer-1 and DAPI assays were carried out using 3T3 and EKl.BR cells. Poly(HEMA) was found to be the most cell adhesive hydrogel tested. The reactivity of monomers and the resulting sequence distribution were found to affect surface properties and this may explain the poor levels of cell adhesion seen on NVP/MMA copolymers. Surface free energy is shown to be dependent on the polar and non polar groups present along the backbone chain of the polymers. Dehydrated and hydrated contact angle measurements show the effect of rotation of surface groups around the backbone chain. This effect is most apparent on hydrogels containing methacrylic acid. Dynamic contact angle measurements confirm sequence distribution irregularities and demonstrate the mobility of surface groups. Incorporation of NVI or DEAEMA into the hydrogels does not affect the mobility of the surface groups despite their bulkiness. Foetal calf serum was used for the first time as a test solution in an attempt to mimic a biological environment during surface experiments. A Vroman effect may be present, and may involve different surface proteins for each material tested. This interdisciplinary study combines surface characterisation and biological testing to further the knowledge of the biomaterial/host interface. Surface chemistry techniques appear to be insufficiently sensitive to predict cellular behaviour. The degree of ionisation of hydrogels containing ionic groups depends on the nature of the functional groups as well as the concentration and this is an important parameter to consider when comparing charged materials.