Search

In recent decades, highly alloyed low-density steels are being developed to reduce the weight of different automotive parts. Dilatometry can be a very useful experimental technique to understand phase transformations during heating or cooling of new low-density steel alloys. When performing dilatometry measurements some assumptions are made such as the homogeneity of the sample material tested during the experiment. In this study, dilatometry tests were performed for two different low-density steels, and the variations of the composition between the surface and the inner part of the sample were analyzed. The migration of manganese by diffusion from the interior of the samples and finally its evaporation on the surface under vacuum were observed. This compositional gradient generated in the samples may influence the veracity and interpretation of the results obtained in dilatometry when working with high manganese steel alloys. The detachment of surface grains created by this compositional change near the surface of the samples is also investigated. This research was funded by the Basque Government under its ELKARTEK Research Program, KK-2016/00029-ABADE project and KK-2018/00016-COFADEN project

In this work, four low carbon steels with different contents of Mn and Ni were heat treated by quenching and partitioning (Q&P) cycles where high partitioning temperatures, in the range of 550 °C-650 °C, were applied. In order to elucidate the effect of applying these high partitioning temperatures with respect to more common Q&P cycles, the materials were also heat treated considering a partitioning temperature of 400 °C. The microstructure evolution during the Q&P cycles was studied by means of dilatometry tests. The microstructural characterization of the treated materials revealed that austenite retention strongly depended on the alloy content and partitioning conditions. It was shown that the occurrence of austenite reverse transformation (ART) in the partitioning stage in some of the alloys and conditions was a very effective mechanism to increase the austenite content in the final microstructure. However, the enhancement of tensile properties achieved by the application of high partitioning temperature cycles was not significant. This research was carried out in the framework of the HIGHQP project, which has received funding from the Research Fund for Coal and Steel under grant agreement no. 709855. This study reflects only the author’s views and the European Commission is not responsible for any use that may be made of the information contained therein.

This paper reports a portable fluorescent sensor platform containing multiple excitation light illumination for quantification and differentiation of multiple analytes. The fluorescent sensor platform utilizes: (i) three different wavelengths of light emitting diodes (LEDs) for selectively stimulating target analytes; (ii) a sensitive photodetector for corresponding fluorescence measurements; (iii) a custom-built electronic system for data measurement and storage; and (iv) a compact three-dimensional printed housing for the developed sensor platform. Based on the fluorescent emission pattern obtained from each target analyte, multivariate analytical methods were applied to differentiate one analyte from the other in a mixture of multiple analytes. The fluorescent sensor platform was tested to selectively detect two target phytoplankton species: Chlorella vulgaris and Spirulina. Fluorescent emission of phytoplankton is caused by stimulation of photosynthetic pigments and is widely utilized to quantify and classify phytoplankton groups. Biomass estimation was therefore conducted by measuring chlorophyll a fluorescence emission for green algae (Chlorella vulgaris) using blue LED excitation and phycocyanin fluorescence emission for cyanobacteria (Spirulina) using amber LED excitation. The results demonstrated the viability of the developed device as a portable generic fluorescence sensor platform for simultaneously detecting various biochemical analytes.

Portable fluorescence sensors have been developed for biochemical detection, water quality monitoring, biomedical sensing, and many other applications. With help of advancement in modern electronics, conventional fluorescence-based instrumentations are now integrated into portable sensing devices for remote and resource-limited settings. In this work, fluorescence sensing technology is introduced and different applications of portable fluorescence sensors and their characteristics are reviewed. Current issues, technological challenges, and future direction of the portable fluorescence sensor development are discussed. The goal is to provide a comprehensive survey on the recent advancements in optics, semiconductors, smartphones, and many other manufacturing technologies that increased the portability, miniaturization, and sensitivity of portable fluorescence sensor devices.

This work reports the development of a field-deployable and fully handheld fluorometer for environmental water monitoring. Our developed fluorimeter can detect both green algae and cyanobacteria (blue-green algae) while simultaneously differentiating and measuring two different species by selectively measuring chlorophyll a fluorescence from green algae and phycocyanin fluorescence from blue-green algae. As a demonstration, chlorophyll a and phycocyanin photopigments were estimated and differentiated. The system was also tested with an environmental water sample collected from a lake to validate the system functionality. The presented results suggest that our developed fluorimeter could be used as a portable water quality monitoring system for detection of different photopigment of algae.

The sulfate release from solidified/stabilized fluorogypsum was measured to develop the effective diffusion coefficients (De) as a parameter to assess the dissolution potential in aquatic a...

Tin(IV) sulfide (SnS2), as a mid-band-gap semiconductor shows good potential as an excellent photocatalyst due to its low cost, wide light spectrum response and environment-friendly nature. However, to meet the demands of large-scale water treatment, a SnS2 photocatalyst with a red-shifted band gap, increased surface area and accelerated molecule and ion diffusion is required. Doping is a facile method to manipulate the optical and chemical properties of semiconductor materials simultaneously. In this work, SnS2 photocatalysts with varied Ag doping content are synthesized through a facile one-step hydrothermal method. The product is characterized by XRD, SEM, TEM and UV-Vis spectrometry. The photocatalytic activity of the as-prepared Sn1−xAgxS2 is studied by the degradation of methylene blue (MB) dye under solar light irradiation. It is found that increasing the Ag dopant concentration can effectively increase the solar light adsorption efficiency of the photocatalyst and accelerate heterogeneous photocatalysis. The optimal concentration of Ag dopant is found to be 5% with the highest rate constant being 1.8251 hour−1. This study demonstrates that an optimal amount of Ag doping can effectively increase the photocatalytic performance of SnS2 and will promote the commercialization of such photocatalysts in the photocatalytic degradation of organic compounds.

In the present work, we report enhanced photocatalytic degradation of methylene blue dye in aqueous solution by using ultra-thin anatase TiO2 nanosheets (NSs) combined with graphene oxide (GO) as a photocatalyst. The two-dimensional ultra-thin anatase TiO2 NSs are fabricated via chemical exfoliation. By completely delaminating a lepidocrocite-type layered protonic titanate HxTi2� x/4□x/4O4 � H2 O( x ¼0.7, □: vacancy) into individual layers through ion exchange with tetrabutylammonium (TBA þ ) cations, well-dispersed ultrathin colloidal Ti0.91O2 NSs with a lateral size up to a few micrometers are obtained. Subsequent acid treatment induces colloidal Ti0.91O2 to reassemble and precipitate into a gelation form, followed by thermal annealing to convert the Ti0.91O2 gelation into anatase TiO2 nanosheets as photocatalyst for methylene blue degradation. TiO2 NSs show a high photocatalytic degradation efficiency of 53.2% due to the ultra-thin thickness for facile electron transfering and large surface area for methylene blue absorption. Moreover, photocatalytic effect can be further improved by simply adding GO suspension to achieve colloidal self-assembly of GO and TiO2 NSs. An optimal GO content of 3 wt% further increases the photocatalytic degradation efficiency to 91.2% due to faster electron–hole seperation and improved surface area provided by GO. This work provides a simple but effective approach by combing graphene oxide with TiO2 nanosheets synthesized via the exfoliation method for methylene blue degradation.

A model of the denitrification on a polyhydroxyalkanoate (PHA) based reactor for recirculating aquaculture was developed. PHA is a family of non-water soluble bioplastics produced by bacteria. The PHA formulation used in this work was polyhydroxybutyrate (PHB). The model considered nitrate concentration, dissolved oxygen, organic carbon and biomass concentration as the most significant variables. The developed model represents adequately the nitrate reduction with the medium used, for nitrate under 100 ppm NO 3 − -N. In the conditions tested, an average ratio of 2.92 g PHA to 1 g NO 3 − -N reduced was found. The model results showed a denitrification rate of 2.97 kg m −3 d −1 for ranges from 10 to 50 mg NO 3 − -N L −1 . Using this model as a management tool, the required size of denitrification units and PHA recharging time can be predicted based on the expected nitrate loading and the time between PHA recharges desired. The unit sizing should be done for the maximum load expected. The slow rate and the energy required for PHA hydrolysis, make it unavailable as electron donor after the nitrate is consumed, so it will not promote the formation of sulfides. The model can be modified for other biodegradable non-water soluble medium by changing the hydrolysis constant, which must be determined experimentally.

The presence of bulk water and the resistant cell walls significantly limit the efficiency of lipid extraction from microalgal biomass paste. Current methods to rupture the cell walls (i.e. grinding after freeze-drying, osmotic shock, sonication) are energy intensive and time consuming. Due to their high surface energy concentration and high surface to volume ratio, silver nanoparticles can enhanced the cell wall rupture to increase the extraction efficiency of cell components. In this study, silver nanofibers were added as enhancers for the Folch’s extraction method and microwave assisted extraction of lipids from wet biomass paste (water content of 80.9%). Nanofibers concentrations of 0–1000 μg g−1 were tested. Two solvent:biomass ratios were tested in the Folch’s extraction method. Two temperatures (70 and 90 °C) and three treatment times (2, 5 and 10 min) were compared in the microwave assisted extraction. The results showed that the extraction efficiency increased with increased concentration of the nanofibers in the range tested. At concentrations of 1000 μg g−1 silver nanofibers (w/w based on the solvent and biomass solution) the efficiency of lipid extraction increased by ∼30% and 50% for the Folch’s and microwave assisted lipid extraction respectively. Treatment with AgNO3 in the same concentration as the nanofibers did not improve the extraction compared with no silver or nanofibers addition. The extraction method affected the lipid fatty acids profile. The Folch’s extraction with no silver nanofibers resulted in proportionally higher short chain saturated fatty acids, but lower lipid extraction. The microwave assisted lipid extraction provides the best results considering fatty acid profile, treatment time, solvent use and lipid extraction efficiency.

Recent interest in the use of microalgae for the production of biofuels and bioproducts has stimulated an interest in methods to enhance the growth rate of microalgae. This review examines past work involving the stimulation of Chlorella sp. growth and metabolite production by plant growth substances as well as by mixed cultures of Chlorella sp. with bacteria. Plant growth substances known to regulate Chlorella sp. growth and metabolite production include auxins, cytokinins, abscisic acid, polyamines, brassinosteroids, jasmonic acid, salicylic acid, and combinations of two or three of the aforementioned substances. Mixed cultures of bacteria are examined, including both natural bacteria–algae consortia and artificially induced symbioses. For natural consortia, commonly occurring bacterial species, including the genera Brevundimonas and Sphingomonas, are discussed. For artificially induced symbioses, the use of the nitrogen-fixing bacterium Azospirillum is examined in detail. In particular, a variety of studies have involved the coimmobilization of Chlorella sp. with Azospirillum sp. in alginate beads, with the goal of using the mixed culture to treat wastewater. In summary, the use of plant growth substances and mixed cultures provides two methods to increase the growth of Chlorella sp., whether for the production of lipids for biofuels, the production of bioproducts, the treatment of wastewater, or a variety of other reasons.

The effect of salinity, dissolved oxygen and NO3-N concentration on the denitrification of recirculating aquaculture water using polyhydroxybutyrate (PHB) was evaluated. Four PHB media with different molecular weights and configurations were tested. The results show that at higher nitrate concentrations in the influent water, the consumed PHB:NO3-N ratio decreased. An average of 2.9 g of PHB:1 g NO3-N removed at temperatures of 20.8 ± 1.1 °C was measured. Although the molecular weight showed an apparent correlation with the denitrification rates, the correlation was not statistically significant. A moderately biofouled granular media displays a heterogeneity of microenvironments that allow some denitrification to occur in the presence of bulk dissolved oxygen levels approaching 5 mg L−1. As a practical approach, the inhibitory effects of oxygen can be mitigated either by design of the denitrification media bed and/or by control or reduction of the influent dissolved oxygen levels. The high plastic consumption needed for oxygen removal indicates that the second approach is more cost efficient. At a flux of 60 m3 m−2 d−1 the denitrification rate decreases at a constant rate in the first 30 cm of the PHB bed. Below this depth, the denitrification rate decreases very slowly and stays above 1 kg-NO3-N m−3 d−1. In a pragmatic sense, denitrification abilities can be expected to be similar in all salinities. Volumetric nitrate removal rates in the order of 2.5 kg-NO3-N m−3 media d−1 should be broadly obtained in fresh and marine water systems. In the range of up to 250 mg NO3-N L−1, the PHB can be used as a base for a passive denitrification unit that requires little management. The availability of an economic source of PHB such as production waste and the development of the bioplastic industry is determinant for the adoption of this material as a carbon source for denitrification processes.

Aims: To design a primer set enabling the identification through PCR of high-quality DNA for routine and high-throughput genomic screening of a diverse range of cyanobacteria. Methods and Results: A codon-equivalent multiple alignment of the phycocyanin alpha-subunit coding sequence (cpcA) of 22 cyanobacteria was generated and analysed to produce a single degeneracy primer set with virtually uniform product size. Also, an 18S ribosomal RNA detection set is proposed for rejecting false positives. The primer sets were tested against five diverse cyanobacteria, Chlorella vulgaris, Saccharomyces cerevisiae, and Escherichia coli. All five cyanobacteria showed positive amplification of cpcA product with homogeneous fragment length, and no products were observed for any other organism. Additionally, the only product formation observed for the 18S rRNA set was in C. vulgaris and S. cerevisiae. Conclusions: The newly proposed primer set served as effective check primers for cyanobacteria. Cyanobacteria gDNA had a positive, homogenous result, while other bacteria, eukaryotes and alga tested were negative. Significance and Impact of the Study: These novel, broad-spectrum primers will greatly increase the utility of PCR on newly discovered cyanobacterial species.

Mass transport of chlorinated benzenes as found at the Petro-Processors of Louisiana, Inc. (PPI) Superfund site was characterized for a range of flow rates in small streams. At this site hazardous waste was historically disposed of in unengineered pits. Hexachlorobenzene and lesser chlorinated degradation products were found among other compounds. As waste was being disposed into unengineered pits, it seeped to lagoons and sediments of Baton Rouge Bayou (BRB), which flows through and nearby the former disposal areas. Characterization of the transport and fate of chlorobenzenes at PPI is an integral part of the Monitored Natural Attenuation (MNA) remedy currently underway. Laboratory experimental results and mathematical model predictions of the flux of 1,3-dichlorobenzene (1,3-DCB) from sediments into water are presented. 1,3-DCB was studied as individually and as part of a mixture of four contaminants with 1,2-DCB, chlorobenzene (MCB) and trichlorobenzene (TCB). Surficial sediments were collected, spiked with contaminants and leached to determine flux over time. Two advection–dispersion models were tested and the effect of low, cycling and fast stream flow on the contaminant flux was assessed. Model results suggest that tortuosity and effective diffusivity are related effective system predictors and descriptors. Statistical analysis supports the models’ predictive capabilities.

Microalgal biomass produced in indoor photobioreactors can be used as inoculum for large-scale outdoor cultures or directly for the production of high-value bioproducts due to the higher control of these cultures compared with outdoor systems. One of the main costs of indoor microalgal cultures is the illumination. This work can be used as a basis for the optimization of the light source for indoor microalgal biomass production, based on the light source type, irradiance, productivity, growth rate, attenuation coefficients, and contaminant growth on the reactor's side-walls. Four commercially available near 400-W artificial light sources for microalgal cultures (metal halide (MH), high-pressure sodium (HPS), Son Agro®, and fluorescent) were compared. The light elevation and the surface scalar irradiance were shown to have a linear relationship. The attenuation coefficient in air (ka) was highest with Son Agro®. A linear partition of the attenuation coefficient between the water and biomass and an exponential relationship between average scalar irradiance and depth were found. An empirical overall scalar attenuation coefficient for each light source was obtained. The lowest maximum observed growth rate was obtained with fluorescent light (0.98 d−1) and the highest with Son Agro® (2.39 d−1). The highest growth on the reactor's wall was obtained with Son Agro®. Further studies resulted in a higher maximum specific growth rate and optimum irradiance for HPS (2.37 d−1 and 460 μmol s−1 m−2) compared with those observed with MH (1.73 d−1 and 391 μmol s−1 m−2).

Aerobic biodegradation of polyhydroxybutyrate (PHB) was investigated. Mass loss experiments were performed to determine degradation kinetics. Tributyl citrate was blended with some test samples to determine the impact of a natural plasticizer on biodegradation. Effects of biodegradation in the physical, chemical, thermal, and mechanical properties of the materials tested were determined. Plates of different thicknesses (0.24, 1.2, 3.5, and 5.0 mm) were degraded to determine the effect of initial mass:initial surface area ratio on degradation rates. The mass:initial surface area is proportional to the plate thickness. PHB biodegradation rates obtained are dependent on the mass:surface area ratio. Temperature affects the relation of degradation rate to initial mass:initial surface area. PHB in plates up to a thickness of 3.5 mm can degrade completely in compost. Plates with an initial mass:initial surface area ratio of

Anaerobic biodegradation in sewage sludge of polyhydroxybutyrate (PHB) was investigated. Evolved gaseous carbon was measured to assess biodegradability according to ASTM D5210. Mass-loss experiments were performed to determine degradation kinetics. Changes in the polymer properties were investigated. The impact of a natural plasticizer [tributyl citrate (TBC)] on biodegradation was determined. Polylactic acid was also biodegraded for comparison. Melt-pressed plates of PHB (with thicknesses of 0.24, 0.5, 1.2, 3.5, and 5.0 mm) were biodegraded to investigate the relationship between initial mass:initial surface area ratios and decay rates. Scanning electron microscopy micrographs of degraded specimens were recorded for visual illustration of the degradation process. A relationship between initial mass:initial surface area and degradation rates indicates that the thickness and surface area of the material affect its degradation. The degradation rates were impacted by the sewage sludge activity. TBC additive hindered PHB's rate of degradation. Thermal properties, molecular bonding, and molecular weight measured by differential scanning calorimetry, Fourier transform infrared, and size exclusion chromatography, respectively, were only slightly affected by biodegradation, indicating that recycling PHB will not affect its performance.

Synthesis and evaluation of a chemical library of inhibitors of the mycothiol biosynthesis enzyme GlcNAc-Ins deacetylase (MshB) and the mycothiol-dependent detoxification enzyme mycothiol- S-conjugate amidase (MCA) from Mycobacterium tuberculosis are reported. The library was biased to include structural features of a group of natural products previously shown to competitively inhibit MCA. Molecular docking studies that reproducibly placed the inhibitors in the active site of the enzyme MshB reveal the mode of binding and are consistent with observed biological activity.

Bioassay guided isolation of an antitubercular extract of the aerial parts of Thalia multiflora led to the isolation of nine stigmast-5-ene and stigmasta-5,22-dien steroids, four isorhamnetin and quercetin flavonoid glycosides, two ceramides, an indole alkaloid and two simple phenolic compounds. Stigmast-5-en-3beta-ol-7-one (2), stigmast-4-ene-6beta-ol-3-one (3), stigmast-5,22-dien-3beta-ol-7-one (7) and stigmast-4,22-dien-6beta-ol-3-one (8) were found to be the most active compounds with MIC values of 1.98 +/- 0.02, 4.2 +/- 0.17, 1.0 +/- 0.06 and 2.2 +/- 0.3 microg/mL, respectively. Compounds 2, 3, 7 and 8 were not cytotoxic to Vero cells at 102 microg/mL. This investigation constitutes the first report of a chemical study of a species of the genus Thalia.

Chemical investigation of the aerial parts of Anadenanthera colubrina led to the isolation of a new flavonoid named anadanthoflavone ( 1), along with 11 known compounds: alnusenol, lupenone, lupeol, betulinic acid, alpha-amyrin, beta-amyrin, beta-sitosterol, stigmasterol, apigenin, 4-hydroxybenzoic acid and cinnamic acid. The isolated compounds were evaluated for their inhibitory activity on human platelet 12-lipoxygenase (12-hLO), human reticulocyte 15-lipoxygenase (15-hLO) and soybean lipoxygenase-1 (15-sLO). Compound 1 was found to be active against 12-hLO and 15-hLO with IC50 values of 13 +/- 3 microM and 17 +/- 3 microM, respectively. Apigenin selectively inhibited the activity of 15-hLO (IC50 : 4.0 +/- 1 microM), while lupenone, lupeol and alpha-amyrin were found active against 15-sLO (IC50 : 22 +/- 3 microM, 35 +/- 9 microM and 15 +/- 3 microM, respectively).

The cysteinyl transferase mycothiol ligase, or MshC, catalyzes the fourth step in the biosynthesis of the small molecular weight thiol mycothiol. MshC is essential for growth of Mycobacterium tuberculosis. Two groups of known aminoacyl tRNA synthetase inhibitors were evaluated for inhibition of M. tuberculosis MshC including aminoacyl adenosine analogs and natural products. Using enzyme assays, isothermal titration calorimetry and NMR, we show that MshC is selectively inhibited by cysteinyl sulfamoyl adenosine, and that discrimination occurs at the amino acid moiety.

Mycothiol ligase (MshC) is a key enzyme in the biosynthesis of mycothiol, a small molecular weight thiol that is unique to actinomycetes and whose primary role is to maintain intracellular redox balance and remove toxins. MshC catalyzes the adenosine triphosphate (ATP)-dependent condensation of cysteine and glucosamine-inositol (GI) to produce cysteine-glucosamine-inositol (CGI). MshC is essential to Mycobacterium tuberculosis and therefore represents an attractive target for chemotherapeutic intervention. A screening protocol was developed to identify MshC inhibitors based on quantification of residual ATP using a coupled luminescent assay. The protocol was used to screen a library of 3100 compounds in a 384-well plate format (Z'>or=0.65). Fifteen hits (0.48%) were identified from the screen, and 2 hits were confirmed in a secondary assay that measures production of CGI. The structures of both hits contain N-substituted quinolinium moieties, and the more potent of the 2-namely, dequalinium chloride-inhibits MshC with an IC50 value of 24+/-1 microM. Further studies showed dequalinium to be an ATP-competitive inhibitor of MshC, to bind MshC with a KD of 0.22 microM, and to inhibit the growth of M. tuberculosis under aerobic and anaerobic conditions with minimum inhibitory and anaerobic bactericidal concentrations of 1.2 and 0.3 microg/mL, respectively. The screening protocol described is robust and has enabled the identification of new MshC inhibitors.

The impact of natural products on the well being of mankind has been enormous, and their study continues to influence research in the fields of chemistry, biology, and ecology. Historically, the majority of our medicines originate from natural products and their synthetic derivatives, many of which have taught us valuable lessons about biology. While advances in synthetic and combinatorial chemistry have given rise to notable successes in the development of new drugs, the perceived value of natural products has not waned when it comes to treating infectious diseases. In this Miniperspective, we review the role natural products have played in the treatment of tuberculosis (TBa), their value and limitations as chemical probes, the challenges associated with TB drug development, and the current status of natural product and synthetic small molecules as new TB drug leads.

The impact of natural products on the well being of mankind has been enormous, and their study continues to influence research in the fields of chemistry, biology, and ecology. Historically, the majority of our medicines originate from natural products and their synthetic derivatives, many of which have taught us valuable lessons about biology. While advances in synthetic and combinatorial chemistry have given rise to notable successes in the development of new drugs, the perceived value of natural products has not waned when it comes to treating infectious diseases. In this Miniperspective, we review the role natural products have played in the treatment of tuberculosis (TBa), their value and limitations as chemical probes, the challenges associated with TB drug development, and the current status of natural product and synthetic small molecules as new TB drug leads.

Polyhydroxybutyrates (PHB; a bacterially produced biodegradable plastic) was used as a carbon source for biological denitrification of water. The use of a solid, nonwater soluble bioplastic in the denitrification process reduces the need for monitoring and dosing of the carbon source. Denitrification rates at four different salt concentrations (0, 5, 15 and 30 ppt) using synthetic salt water were determined. The mean denitrification rates varied from 2.4 to 3.2 kg-NO3N/m 3 -day, with the highest rate in water with a salinity of 15 ppt. While differences in denitrification rates were observed, they were not statistically significant. Additionally, denitrification rates were higher at higher nitrate concentrations. The denitrification rates had no significant differences with PHA of different molecular weights. Hydrogen sulfide production was not observed in any of the studies, even 45 days after the depletion of nitrates. The mean bioplastic consumption was 2.92 ± 2.70 mg/mg of NO3-N reduced.

Mycothiol ligase (MshC) is a key enzyme in the biosynthesis of mycothiol, a small molecular weight thiol found in Mycobacteria spp. and other actinomycetes. Mycothiol plays a fundamental role in these organisms by helping to provide protection from the effects of reactive oxygen species and electrophiles, including many antibiotics. It has recently been demonstrated that the MshC gene and more generally the production of mycothiol are essential to Mycobacterium tuberculosis, indicating that MshC may represent a novel target for new classes of antituberculars. Because MshC cannot be expressed heterologously in Escherichia coli and isolation from Mycobacterium smegmatis is impractical, we have optimized the E. coli-M. smegmatis shuttle vector pACE for cloning and recombinant expression of MshC (under control of an acetamidase-inducible promoter). To improve expression levels and simplify purification, we further constructed three N-terminal-MshC fusion proteins where N-terminal tags included the B1 domain of streptococcal protein G (to give GB1-MshC), glutathione-S-transferase (to give GST-MshC) and maltose binding protein (to give MBP-MshC), for expression in M. smegmatis. By expressing all three fusion proteins in a mutant strain of M. smegmatis mc(2)155, namely I64 L205P MshC M. smegmatis which lacks mycothiol ligase activity, we demonstrate in vivo mycothiol ligase activity for each construct. Recombinant GST-MshC and MBP-MshC were isolated in one step by affinity chromatography in a yield of 0.7 and 1.2 mg fusion protein/L and exhibited specific activities of 9 nmolmin(-1)mg(-1) and 25 nmolmin(-1)mg(-1), respectively.

Four novel compounds consisting of two new pimaranes, lecheronol A (1) and lecheronol B (2), an acylated cycloartane, 3-O-beta-lauroyl-cycloart-(23E)-en-25-ol (10), and a highly oxygenated novel chalconoid, alpha,beta,3,4,5,2',4',6'-octahydroxydihydrochalcone (12), were isolated along with seven known triterpene derivatives and three flavonol glucosides from Mycobacterium tuberculosis growth-inhibiting fractions of the CH(2)Cl(2)/MeOH (1:1) extract of the aerial parts of Sapium haematospermum. Compounds 1, 3 (3 alpha-hydroxyolean-12-ene), 8 [3 alpha-hydroxylup-20(29)-en], and 9 (cycloartanol) were found most active, with MIC values of 4, 12.2, 13.4, and 8 microg/mL, respectively. Cytotoxicity tests in Vero cells for compounds 1, 3, 8, and 9 gave IC(50) values of 104.8, 127.2, 127.2, and 102.4 microg/mL, respectively.

Three new cycloartane-type triterpenes, 16 alpha-hydroxymollic (1), 15 alpha-hydroxymollic (2), and 7 beta,16 beta-dihydroxy-1,23-dideoxyjessic acids (3), were isolated from the aerial parts of Acalypha communis. The structures of the novel triterpenes were determined by spectroscopic methods as well as chemical derivatization. These compounds were tested for their antimicrobial activity against Gram-positive and -negative bacteria. Compounds 1-3 exhibited moderate antimicrobial activity (MIC 8, 32, 8 microg/mL, respectively) against vancomycin-resistant enterococci. In addition, compound 1 was found to be active against methicillin-resistant staphylococci. In contrast, compounds 1-3 were poorly active against Gram-negative bacteria. Compound 3 was tested in an in vivo model; it did not provide protection to mice infected with Staphylococcus aureus.

Different coalescence processes on 1D silver nanostructures synthesized by a PVP assisted reaction in ethylene glycol at 160 °C were studied experimentally and theoretically. Analysis by TEM and HRTEM shows different defects found on the body of these materials, suggesting that they were induced by previous coalescence processes in the synthesis stage. TEM observations showed that irradiation with the electron beam eliminates the boundaries formed near the edges of the structures, suggesting that this process can be carried out by the application of other means of energy (i.e. thermal). These results were also confirmed by theoretical calculations by Monte Carlo simulations using a Sutton-Chen potential. A theoretical study by molecular dynamics simulation of the different coalescence processes on 1D silver nanostructures is presented, showing a surface energy driven sequence followed to form the final coalesced structure. Calculations were made at 1000-1300 K, which is near the melting temperature of silver (1234 K). Based on these results, it is proposed that 1D nanostructures can grow through a secondary mechanism based on coalescence, without losing their dimensionality.