Gly311 residue triggers the enantioselectivity of Staphylococcus xylosus lipase: a monolayer study

Using emulsified triacylglycerols, we have shown recently [Mosbah et al., 2007, submitted for publication] that amino acid residue G311 of Staphylococcus xylosus lipase (SXL) is critically involved in substrate selectivity, pH and temperature dependency. Using the monomolecular film technique, we show in the present study that the four single mutants of this residue (G311L, G311W, G311D, and G311K), interact efficiently with egg-phosphatidyl choline (egg-PC) monomolecular films, comparably to the wild-type (G311). A critical surface pressure (pi(c)) of about 25 mN/m was obtained with the SXL wild-type (SXL-WT) and its mutants. These results support our conclusion that the G311 residue is not involved in the interfacial adsorption step of SXL. A kinetic study on the surface pressure dependency, stereoselectivity, and regioselectivity of SXL-WT and its G311 mutants was also performed using optically pure enantiomers of diacylglycerols (1,2-sn-dicaprin and 2,3-sn-dicaprin) and a prochiral isomer (1,3-sn-dicaprin) spread as monomolecular films at the air-water interface. Our results indicated that the mutation of one single residue at position 311 affects critically the catalytic activity, the stereo- and the regioselectivity of SXL. As previously observed with emulsified substrates [Mosbah et al., 2007, submitted for publication] we observed that an increase in the size of the 311 amino acid side chain residue was accompanied by a decrease of lipase activity measured on dicaprin monolayer. We also noticed that the substitution of G311 by a basic or acidic residue (G311K and G311D), induces a significant shift of the pH optimum from 8 to 9.5 or from 8 to 6.5, respectively.     

Synthesis and structure elucidation of 3,4‐dihydroxy‐2‐quinolin‐2‐ylpyrido[3,2,1‐jk]carbazol‐6‐ones

3,4‐Dihydroxy‐2‐quinolin‐2‐ylpyrido[3,2,1‐jk]carbazol‐6‐ones 6 were obtained by cyclocondensation of carbazole 1 with malonates 2 in the presence of quinoline. The assignment of the structures of 6 was performed by NMR experiments such as 1D ¹H, ¹³C and DEPT, as well as 2D COSY, HSQC, HMBC and 1,1‐ADEQUATE spectra.     

A Novel Thermostable and Alkaline Protease Produced from Bacillus stearothermophilus Isolated from Olive Oil Mill Sols Suitable to Industrial Biotechnology

This study was conducted to identify a new alkaline and thermophilic protease (Ba.St.Pr) produced from Bacillus stearothermophilus isolated from olive oil mill sols and to evaluate its culture conditions, including temperature, pH, carbon and nitrogen sources, and incubation time. The optimum culture conditions for cell growth (10 g/L) and protease production (5050 U/mL) were as follows: temperature 55 °C, pH 10, inoculation density 8 × 10⁸ CFU/mL, and incubation time 24 h. The use of 3% yeast extract as the nitrogen sources and galactose (7.5 g/L) as the carbon sources enhanced both cell growth and protease production. Using reversed-phase analytical HPLC on C-8 column, the new protease was purified with a molecular mass of approximately 28 kDa. The N-terminal sequence of Ba.St.Pr exhibited a high level of identity of approximately 95% with those of Bacillus strains. Characterization under extreme conditions revealed a novel thermostable and alkaline protease with a half-life time of 187 min when incubated with combined Ca²⁺/mannitol. Ba.St.Pr demonstrated a higher stability in the presence of surfactant, solvent, and Ca²⁺ ions. Consequently, all the evaluated activity parameters highlighted the promising properties of this bacterium for industrial and biotechnological applications.     

A magnetic multifunctional dendrimeric coating on a steel fiber for solid phase microextraction of chlorophenols

Microchimica Acta - A polyamidoamine dendrimer was synthesized, placed on magnetite nanoparticles, and the resulting material was then employed as a fiber coating for use in solid phase...     

Electrochemical deposition of cadmium selenide films and their properties: a review

This review gives brief information of experimental conditions employed by different researchers for deposition of cadmium selenide (CdSe) thin films. For the films synthesized at room temperature, films should be annealed and etched to increase the solar cell efficiency. A photoelectrochemical study revealed that values of fill factor and efficiency of CdSe thin films deposited on fluorine-doped tin oxide-coated glass substrates exhibited maximum value compared to the film deposited on titanium and stainless steel substrates. This review will be helpful to researchers entering in field to understand basics about the electrodeposition of CdSe and its development towards next-generation photovoltaics.     

Using partial correlation to enhance structural equation modeling of functional MRI data

In functional magnetic resonance imaging (fMRI) data analysis, effective connectivity investigates the influence that brain regions exert on one another. Structural equation modeling (SEM) has been the main approach to examine effective connectivity. In this paper, we propose a method that, given a set of regions, performs partial correlation analysis. This method provides an approach to effective connectivity that is data driven, in the sense that it does not require any prior information regarding the anatomical or functional connections. To demonstrate the practical relevance of partial correlation analysis for effective connectivity investigation, we reanalyzed data previously published [Bullmore, Horwitz, Honey, Brammer, Williams, Sharma, 2000. How good is good enough in path analysis of fMRI data? NeuroImage 11, 289–301]. Specifically, we show that partial correlation analysis can serve several purposes. In a pre-processing step, it can hint at which effective connections are structuring the interactions and which have little influence on the pattern of connectivity. As a post-processing step, it can be used both as a simple and visual way to check the validity of SEM optimization algorithms and to show which assumptions made by the model are valid, and which ones should be further modified to better fit the data.     

Polybutylene terephthalate-nickel oxide nanocomposite as a fiber coating

A highly efficient polybutylene terephthalate (PBT)-based nanocomposite containing nickel oxide nanoparticles was synthesized by electrospinning technique and used as a fiber coating for solid phase microextraction. The influential morphological parameters and capability of the prepared nanocomposite including the NiO content, the coating time, the PBT concentration and applied voltage were considered for optimization. The applicability of the synthesized fiber coating was examined by headspace solid phase micro extraction and gas chromatography mass spectrometry detection of some volatile organic compounds in aqueous samples. Among the synthesized nanocomposites and pristine PBT nanofibers, the fiber coating with 14% of NiO nanoparticles doping level exhibited the highest extraction efficiency. In addition, important parameters influencing the extraction/desorption process were investigated and optimized. The detection limits were less than 5 ng L⁻¹ using the selected ion monitoring mode. The inter-day and intra-day precisions of the developed method under optimized conditions were below 11%. The method showed a linearity in the range of 10–1000 ng L⁻¹ with the correlation coefficient greater than 0.9987. The optimized method was applied to the sampling of some volatile organic compounds from real water samples. The developed method is convenient, rapid, simple, easy and inexpensive and offers high sensitivity and sufficient reproducibility.     

Sol–gel-based silver nanoparticles-doped silica – Polydiphenylamine nanocomposite for micro-solid-phase extraction

A nanocomposite of silica-polydiphenylamine doped with silver nanoparticles (Ag–SiO₂-PDPA) was successfully synthesized by the sol–gel process. For its preparation, PDPA was mixed with butanethiol capped Ag nanoparticles (NPs) and added to the silica sol solution. The Ag NPs were stabilized as a result of their adsorption on the SiO₂ spheres. The surface characteristic of nanocomposite was investigated using scanning electron microscopy (SEM). In this work the Ag–SiO₂-PDPA nanocomposite was employed as an efficient sorbent for micro-solid-phase extraction (μ-SPE) of some selected pesticides. An amount of 15 mg of the prepared sorbent was used to extract and determine the representatives from organophosphorous, organochlorine and aryloxyphenoxy propionic acids from aqueous samples. After the implementation of extraction process, the analytes were desorbed by methanol and determined using gas chromatography–mass spectrometry (GC–MS). Important parameters influencing the extraction and desorption processes such as pH of sample solution, salting out effect, type and volume of the desorption solvent, the sample loading and eluting flow rates along with the sample volume were experimentally optimized. Limits of detection (LODs) and the limits of quantification (LOQs) were in the range of 0.02–0.05 μg L⁻¹ and 0.1–0.2 μg L⁻¹, respectively, using time scheduled selected ion monitoring (SIM) mode. The relative standard deviation percent (RSD %) with four replicates was in the range of 6–10%. The applicability of the developed method was examined by analyzing different environmental water samples and the relative recovery (RR %) values for the spiked water samples were found to be in the range of 86–103%.     

Turbulent free convection in a vertical converging channel

This paper presents the results of experimental and numerical investigations of the problem of turbulent natural convection in a converging-plate vertical channel. The channel has two isothermally heated inclined walls and two adiabatic vertical side walls. The parameters involved in this study are the channel geometry represented by the channel width at exit, the inclination of the heated walls and the temperature difference between the heated walls and the ambient. The investigation covered modified Rayleigh numbers up to 10⁸ in the computational study and up to 9.3 × 10⁶ in the experimental work. The experimental measurements focused on the velocity field and were carried out using a PIV system and included measurements of the mean velocity profiles as well as the root-mean-square velocity and shear stress profiles. The experiments were conducted for an inclination angle of 30°, a gap width of 10 mm and two temperature differences (∆T=25.4°C and 49.8°C). The velocity profiles in the lower part of the channel indicated the presence of two distinct layers. The first layer is adjacent to the heated plate and driven by buoyancy forces while the second layer extends from the point of maximum velocity to the channel center plane and driven mainly by shear forces. The velocity profile at the upper portion of the channel has shown the merging of the two boundary layers growing over the two heated walls. The measured values of the Reynolds shear stress and root mean square of the horizontal and vertical velocity fluctuation components have reached their maximum near the wall while having smaller values in the core region. The computational results have shown that the average Nusselt number increases approximately linearly with the increase of the modified Rayleigh number when plotted on log–log scale. The variation of the local Nusselt number indicated infinite values at the channel inlet (leading edge effect) and high values at the channel exit (trailing edge effect). For a fixed value of the top channel opening, the increase of the inclination angle tended to reduce flow velocity at the inlet section while changing the flow structure near the heated plates in such a way to create boundary-layer type flow. The maximum value of the average Nusselt number occurs when θ = 0 and decreases with the increase of the inclination angle. On the other hand, the increase of the channel width at exit for the same inclination angle caused a monotonic increase in the flow velocity at the channel inlet.     

Parametric estimation of a bivariate stable Lévy process

We propose a parametric model for a bivariate stable Lévy process based on a Lévy copula as a dependence model. We estimate the parameters of the full bivariate model by maximum likelihood estimation. As an observation scheme we assume that we observe all jumps larger than some ε>0 and base our statistical analysis on the resulting compound Poisson process. We derive the Fisher information matrix and prove asymptotic normality of all estimates when the truncation point ε→0. A simulation study investigates the loss of efficiency because of the truncation.