New bioactive labdane diterpenoids from Marrubium aschersonii

A phytochemical investigation of the ethanol extract of Marrubium aschersonii Magnus (Lamiaceae) collected from Tunisia led to the isolation and identification of two new labdane diterpenoids, marrubaschs A (1) and B (2), along with two known compounds (3 and 4). Their structures were elucidated by spectroscopic methods including HRESIMS and NMR techniques. All compounds were evaluated for their inhibitory effects on the nitric oxide (NO) production induced by lipopolysaccharide in RAW 264.7 macrophage cells. Compound 2 exhibited weak inhibition of NO production with an IC₅₀ value of 35 ± 1.0 μM.     

A new biosynthesis of CuCo2S4 nanoparticles as a high-performance supercapacitor electrode and excellent non-enzymatic hydrazine sensor

In this work, we report the biosynthesis of CuCo₂S₄ nanoparticles (Bio-NPs) via hydrothermal method. The synthetized Bio-NPs-CuCo₂S₄ was studied as an active material of working electrode for electrochemical supercapacitor and non-enzymatic hydrazine sensor. The Bio.NPs-CuCo₂S₄/ITO electrode has a specific capacitance of 264 F/g at a current density of 1 A/g. Meanwhile, the electrode exhibits excellent electrochemical performances, such as an energy density of 33 Wh/Kg and a power density of 900 W/Kg. The Bio.NPs-CuCo₂S₄/ITO electrode for non-enzymatic hydrazine sensor exhibits a very high sensitivity of 2400 μA.mM⁻¹.cm⁻², a wide linear range from 0.001 to 1.400 mM and shows an excellent selectivity.     

A novel iridoid glycoside from the aerial parts of the Tunisian Prasium majus

Repeated fractionation of the acetylated methanol extract of Prasium majus afforded acetylated derivatives of a new iridoid glycoside hamighriprasin (1), myoporoside (2), beta-D-glycopyranose (3) and saccharose (4). The structures of 1 and 2 were established by interpretation of 1D and 2D NMR data of their corresponding acetylated derivatives and by comparison with the literature.     

New stability criteria for stochastic perturbed singular systems in mean square

In this study, a generalized equal-peak principle is established to suppress the multimodal vibration of a multiple-degree-of-freedom (M-DOF) nonlinear system. Based on the proposed generalized principle, the design procedure of the multiple time-delayed vibration absorbers (TDVAs) is carried out. By four conditions in the proposed generalized principle, the objective of suppressing all the resonance peaks around multiple modes to the equal minimum values is realized. For the existence of nonlinearity, the necessary and sufficient conditions in the design procedure can guarantee that the two resonance peaks around each mode are simultaneously equal. Moreover, the two equal resonance peaks are suppressed to minimum values with the minimum peak condition. Two case studies verify the efficiency of the TDVAs designed by the generalized equal-peak principle for multimodal vibration suppression. Due to the multimodal vibration suppression capacity of the proposed TDVAs designed by the generalized equal-peak principle, significant broad frequency band vibration suppression effects are achieved. Thus, TDVAs and the proposed equal-peak principle have potential applications in the fields of high-DOF vibration systems, such as civil engineering, precision machining and aerospace.

     

Global Convergence of a Control System by Means of an Observer

In this paper, we propose some sufficient conditions for the global stabilization of a class of nonlinear dynamic systems by using an estimated state feedback law given by an observer design.     

Combined experimental and theoretical investigation of the CO2 adsorption on LaMnO3+y perovskite oxide

The surface interaction of CO₂ with the perovskite-type oxide LaMnO_3+y has been investigated by means of density functional theory calculations and experimental measurements of adsorption isotherms in the temperature range 298-473 K. A (1 0 0) oriented slab of the cubic structure was used for modeling CO₂ adsorption. The reference unit cell contains alternating LaO⁺ layers and layers; one slab is LaO⁺-terminated and the opposite surface is terminated. A Freundlich isotherm fitted the experimental data satisfactorily. Analysis of the isosteric heat revealed an energetically heterogeneous character for the lanthanum manganite oxide surface, mainly due to the degree of heterogeneity of the adsorption center and due to the adsorbate-adsorbate lateral interactions. Considering theoretical calculations and thermodynamical approaches, two types of active sites were found to be responsible for irreversible and reversible adsorption of CO₂ as a function of surface coverage and O₂ treatment. Strong adsorption takes place on the surface containing La cations. The strongest adsorption is associated with surface oxygen vacancies, center. The next strongest adsorption, a flat adaptation of CO₂ molecules with respect to the surface sites, with a strong binding to a surface oxygen, leads to chemisorbed carbonate species. These adsorption modes are chiefly indicative of a high basic character of the lanthanum manganite oxide surface. Several cationic sites formed by lanthanum and manganese cations are able to weakly adsorb CO₂ molecules in perpendicular or bridged forms. The latter adsorption modes suggest a weak acidic character of the manganite adsorbent.     

On the chemistry of 5‐aryl‐2‐hydrazino‐benzo[6,7]cyclohepta[1,2‐b]pyrido[2,3‐e] pyrimidin‐4‐one

Several pyrido[2,3‐e]pyrimidine fused with other rings have been prepared by intramolecular cyclization of 5‐(4‐chlorophenyl)‐2‐hydrazino‐benzo [6,7]cyclohepta‐[1,2‐b]pyrido[2,3‐e]pyrimidine‐4‐one ( 1 ) with acids, carbon disulfide to form triazole derivatives ( 2,4 ), halo‐ketones to give triazine derivative ( 5 ), β‐ketoesters, β‐cyanoesters, and β‐diketones to yield 2‐(1‐pyrazolyl) derivatives ( 7,9,10 ), and aldehydes to form arylhydrazone derivatives ( 11a,b ) which cyclized to form triazoles ( 12a,b ). Also, acyclic N‐nucleosides are prepared by heating under reflux 2‐hydrazino‐benzo[6,7]cyclohepta[1,2‐b]pyrido[2,3‐e] pyrimidin‐4‐one ( 1 ) with xylose and glucose to give the corresponding acyclic N‐nucleosides ( 13a,b ) which are cyclized to afford the corresponding protected tetra and penta–O‐acetate C‐nucleosides ( 14a,b ). Deacetylating of the latter nucleosides afforded the free acyclic C‐nucleosides ( 15a,b ). © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:34–43, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20248