Chemical Composition and Antibacterial Activity of Lippia multiflora Moldenke Essential Oil from Different Regions of Angola

The purpose of the study was to determine the chemical composition and antibacterial activity of Lippia multiflora Moldenke essential oils (EOs) collected in different regions of Angola. Antibacterial activity was evaluated using the agar wells technique and vapour phase test. Analysis of the oils by GC/MS identified thirty-five components representing 67.5 to 100% of the total oils. Monoterpene hydrocarbons were the most prevalent compounds, followed by oxygenated monoterpenes. The content of the compounds varied according to the samples. The main components were Limonene, Piperitenone, Neral, Citral, Elemol, p-cymene, Transtagetone, and Artemisia ketone. Only one of the eleven samples contained Verbenone as the majority compound. In the vapour phase test, a single oil was the most effective against all the pathogens studied. The principal component analysis (PCA) and hierarchical cluster analysis (HCA) of components of the selected EOs and inhibition zone diameter values of agar wells technique allowed us to identify a variability between the plants from the two provinces, but also intraspecific variability between sub-groups within a population. Each group of essential oils constituted a chemotype responsible for their bacterial inhibition capacity. The results presented here suggest that Angolan Lippia multiflora Moldenke has antibacterial properties and could be a potential source of antimicrobial agents for the pharmaceutical and food industry.     

Multiscale expansions in discrete world

In this paper, we show the attainability of KdV equation from some types of nonlinear Schrödinger equation by using multiscale expansions discretely. The power of this manageable method is confirmed by applying it to two selected nonlinear Schrödinger evolution equations. This approach can also be applied to other nonlinear discrete evolution equations. All the computations have been made with Maple computer packet program.     

Multivariate optimization of a GC-MS method for determination of sixteen priority polycyclic aromatic hydrocarbons in environmental samples

This paper describes the development and optimization, by using multivariate analysis, of a GC-MS-SIM method for evaluation of the 16 polyaromatic hydrocarbons considered as priority pollutants in atmospheric particulate material by the US EPA. In order to assure an adequate separation in the shortest analysis time, a multivariate design was used to set the conditions of the oven temperature program. The optimization process was carried out using factorial fractional design and Box-Behnken design. The following factors were evaluated: initial temperature, temperature rate #1, intermediary temperature, temperature rate #2, and final temperature. The optimized conditions were set at: 70 degrees C (2 min) --> 200 degrees C (30 degrees C/min, 5 min) --> 300 degrees C (5 degrees C/min, 1.67 min). Moreover, we have also optimized the injector temperature as 310 degrees C and sampling time as 0.8 min. The total analysis time was 33 min. Validation of GC-MS-SIM yielded satisfactory results for repetitivity of the detector response and retention times, and linearity of calibration curves. LOD were established as 0.13-0.34 ng/mL (peak area) and 0.18-0.72 ng/mL (peak height). The method has been shown to be appropriate for the analysis of samples of atmospheric particulate material and/or other environmental matrices.     

Connectivity and design of planar global attractors of Sturm type. II: Connection graphs

Based on a Morse-Smale structure we study planar global attractors Af of the scalar reaction-advection-diffusion equation ut=uxx+f(x,u,ux) in one space dimension. We assume Neumann boundary conditions on the unit interval, dissipativeness of f, and hyperbolicity of equilibria. We call Af Sturm attractor because our results strongly rely on nonlinear nodal properties of Sturm type.The planar Sturm attractor consists of equilibria of Morse index 0, 1, or 2, and their heteroclinic connecting orbits. The unique heteroclinic orbits between adjacent Morse levels define a plane graph Cf which we call the connection graph. Its 1-skeleton consists of the unstable manifolds (separatrices) of the index-1 Morse saddles.We present two results which completely characterize the connection graphs Cf and their 1-skeletons in purely graph theoretical terms. Connection graphs are characterized by the existence of pairs of Hamiltonian paths with certain chiral restrictions on face passages. Their 1-skeletons are characterized by the existence of cycle-free orientations with certain restrictions on their criticality. Such orientations are called bipolar in [H. de Fraysseix, P.O. de Mendez, P. Rosenstiehl, Bipolar orientations revisited, Discrete Appl. Math. 56 (1995) 157-179].In [B. Fiedler, C. Rocha, Connectivity and design of planar global attractors of Sturm type. I: Orientations and Hamiltonian paths, Crelle J. Reine Angew. Math. (2007), in press] we have shown the equivalence of the two characterizations. Moreover we have established that connection graphs of Sturm attractors indeed satisfy the required properties. In the present paper we show, conversely, how to design a planar Sturm attractor with prescribed plane connection graph or 1-skeleton of the required properties. In [B. Fiedler, C. Rocha, Connectivity and design of planar global attractors of Sturm type. III: Small and Platonic examples, 2007, submitted for publication] we describe all planar Sturm attractors with up to 11 equilibria. We also design planar Sturm attractors with prescribed Platonic 1-skeletons.     

Solvent-solute interactions in hydrofluoroalkane propellants

Understanding solvation in hydrofluoroalkane (HFA) propellants is of great importance for the development of novel pressurized metered-dose inhaler (pMDI) formulations. HFA-based pMDIs are not only the most widely used inhalation therapy devices for delivering small drug molecules to the respiratory tract, but they also hold promise as vehicles for the delivery of therapeutic biomolecules to and through the lungs. In this work we use binding energy calculations to determine the degree of interaction between HFA propellants and candidate HFA-philes, including a methyl-based tail (isohexane, ISO), and fragments of poly(ethylene oxide) (EO), poly(propylene oxide) (PO), and poly(lactide) (LA). The distinct nature of solvation forces of the two HFA propellants approved by the FDA for use in pMDIs, 1,1,1,2-tetrafluoroethane (HFA134a) and 1,1,1,2,3,3,3-heptafluoropropane (HFA227), is also studied. Binding energy (Ebst) calculations demonstrated that an increase in tail polarity through the addition of oxygen atoms in the fragment backbone provides for sites capable of interacting with the HFA propellant molecules, thus enhancing the stabilization energy of the complexes. The interaction energy between HFA227 and LA (EbHFA227-LA = -24.7 kJ.mol(-1)) is significantly more favorable than that between HFA227 and its hydrocarbon analog (EbHFA227-ISO = -10.0 kJ.mol(-1)). However, it was shown that not only the fragment polarity is of relevance in stabilizing the complexes. The accessibility of the oxygen atoms in the fragments of interest is also relevant. Cluster studies indicate that although both oxygen atoms in the LA fragment are available to form H-bonds with the propellant molecules, the ether oxygen in PO is accessible to only one propellant molecule, thus decreasing significantly the stabilization energy of the cluster. The results shown here serve as a guide for the design of novel HFA-philes for HFA-based pMDIs.     

金的化学状态对Au／CoCeOx催化剂CO氧化性能的影响

以CoCeOx复合氧化物为载体,采用沉积沉淀法制备了负载型的金催化剂,并通过不同温度的预处理控制Au的化学状态. 使用粉末X射线衍射、高分辨透射电子显微镜、程序升温还原和X射线光电子能谱对催化剂进行了表征,考察了在室温条件下该系列催化剂的一氧化碳氧化性能. 结果表明, Au/CoCeOx催化剂的CO氧化性能与催化剂表面Au 的含量成正比, Au 可能是反应的主要活性物种. 添加水汽对反应有一定的促进作用,但由于Au 不能稳定存在,特别是当催化剂表面Au 的含量过高时,在水汽的作用下Au 迅速发生歧化反应,使得催化剂的性能下降.     

Host-guest Assembly Based on γ-Cyclodextrin-functionalized Multiwalled Carbon Nanotubes for Rutin Electrochemical Sensing

Here, we report multiwalled carbon nanotubes (MWCNTs) functionalized with γ-cyclodextrins (γCD) as a novel electrochemical strategy for Rutin determination, showing superior performance than β-cyclodextrins (βCD) modified MWCNTs, suggesting an adequate environment for host-guest interactions. Under optimized conditions, the sensor showed a linear range of 39–975 nmol L⁻¹ and a limit of detection of 7 nmol L⁻¹. When tested with quercetin, catechin, and caffeine, the platform presented high selectivity with an interference response <10 %. The method was employed to quantify Rutin in spiked pharmaceutical and herbal extracts, providing recovery of 93–98.4 %. Also, HPLC-PDA confirmed the method‘s accuracy.