Chemical Composition and Phytotoxic,Antibacterial and Antibiofilm Activity of the Essential Oils of Eucalyptus occidentalis,E. striaticalyx and E. stricklandii

The Eucalyptus genus (Myrtaceae) is characterized by a richness in essential oils (EO) with multiple biological activities. This study reports the chemical composition and the phytotoxic and antimicrobial activities of the EOs from Tunisian E. occidentalis, E. striaticalyx and E. stricklandii. The EOs were analyzed using GC/MS and their phytotoxicities were assessed against the germination and seedling growth of Sinapis arvensis, Trifolium campestre and Lolium rigidum. Antimicrobial activity was investigated against both Gram-negative (Pseudomonas aeruginosa, Escherichia coli and Acinetobacter baumannii) and Gram-positive (Staphylococcus aureus and Listeria monocytogenes) bacteria. The inhibition of biofilm formation and its metabolism was determined at different times. All EOs were rich in oxygenated monoterpenes (36.3–84.8%); the EO of E. occidentalis was rich in sesquiterpenes, both oxygenated and hydrocarbon (40.0% and 15.0%, respectively). Eucalyptol was the main constituent in all samples. The EOs showed phytotoxic activity on seed germination and seedling growth, depending both on chemical composition and weed. The EOs show a remarkable antibacterial potential resulting in a significant inhibition of the formation of bacterial biofilm and its metabolism, depending on the EO and the strain, with activity on the mature biofilm as well. Therefore, these Eucalyptus EOs could have potential applications both in the food and health fields.     

Preparation of Mixed Bis-N-Heterocyclic Carbene Rhodium(I) Complexes

A series of mixed bis-NHC rhodium(I) complexes of type RhCl(η²-olefin)(NHC)(NHC’) have been synthesized by a stepwise reaction of [Rh(μ-Cl)(η²-olefin)₂]₂ with two different NHCs (NHC = N-heterocyclic carbene), in which the steric hindrance of both NHC ligands and the η²-olefin is critical. Similarly, new mixed coumarin-functionalized bis-NHC rhodium complexes have been prepared by a reaction of mono NHC complexes of type RhCl(NHC-coumarin)(η²,η²-cod) with the corresponding azolium salt in the presence of an external base. Both synthetic procedures proceed selectively and allow the preparation of mixed bis-NHC rhodium complexes in good yields.     

Formation and stability of mixed complexes of copper(II) ion ando-phenylenediamine with some mono-, bi-, and tridentate ligands in aqueous solution

Summary The formation and the stability in aqueous solution of copper(II) mixed complexes witho-phenylenediamine and mono-, bi-, or tridentate carboxylic ligands were studied at 25° and I = 0.1 mol dm^–3 [NaClO₄].The effect of the chelating rings, the donor atoms involved, and the type of coordination on the stability constants for the formation of these ternary complexes was evaluated.Attention has been paid an the numerical and statistical analysis of the titration data, which were obtained over a wide concentration range using different experimental equipment and standards in order to avoid systematic errors.     

Nonempirical analysis of unusual chemical bonds. II. AlH2BH4 and AlH2C3H5

Ab initio computations have been performed on the compounds AlH₂BH₄ and AlH₂C₃H₅ in order to achieve a better understanding of the peculiar characteristics of the metal to ligand bond. Our results suggest a bidentate coordination for the tetrahydroborate complex and an η³ coordination for the allyl complex. Due to the nonrigidity of the BH and allyl complexes, possible interconversion paths between different coordination modes have also been analyzed.     

Omnidirectional bandgap in Cantor dielectric multilayers

Analysis of the transmission spectrum of Cantor dielectric multilayers for obliquely incident plane wave shows that the main bandgap shifts towards higher frequencies, substantially retaining its shape, as the incidence angle increases for both s- and p-polarization of the impinging wave. For suitable refractive index values of the two constituent materials a range of frequencies can be found where transmission of the incident wave is almost completely forbidden at any angle of incidence. This omnidirectional bandgap can be found also for lossy media. In this case the stop-band widens as the tangent loss increases, while the depth of the stop-band does not change significantly. Comparison with the periodic quarter-wave stack shows that the Cantor multilayer exhibits a narrower omnidirectional bandgap with transmissivity values that are about one order of magnitude lower.     

New nanohybrids of poly(ε‐caprolactone) and a modified Mg/Al hydrotalcite: Mechanical and thermal properties

Novel composites based on poly(ε‐caprolactone) (PCL) and an organically modified layer double hydroxide (LDH) obtained using the melt‐extrusion technique have been characterized through structural, thermal, and mechanical analyses. Although exfoliation has not been achieved and despite the very low content of filler (from 1 to 3% by weight), significant enhancements are obtained in the physical and mechanical properties of the composites with respect to neat PCL. As a consequence, LDHs can substitute other nanofillers, in particular, cationic clays for polymeric matrices. They can be modified by a large number of organic anions, generally more numerous than the cationic ones, and can be mixed in very simple ways with polymers. This makes such nanofillers suitable to obtain new hybrid materials for a series of applications, from active food packaging to intelligent materials for biomedical device, for example, controlled drug release. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 945–954, 2007     

Lithium hydroxide phase transition under high pressure: an ab initio molecular dynamics study.

The high-pressure phase transition in the deuterated lithium hydroxide crystalline state has been studied by Car-Parrinello molecular dynamics simulations, in the constant-pressure, constant-temperature ensemble. The recently developed metadynamics approach has been applied to encourage the system to transform into different phases in an affordable simulation time. A previously not completely characterized high-pressure phase has been obtained. The structural and spectroscopic properties have been studied and compared with the neutron scattering, infrared and Raman measurements. It has been found that the calculated structure differs slightly from the experimental hypothesis, and that the presence of strong hydrogen bonds is the source of the red shift and of the characteristic features of the OD-stretching bands in both IR and Raman spectra.     

Structural investigation of electrochemically synthesized ZnCuTe thin films

pZnCuTe thin films were prepared by electrochemical synthesis in aqueous solution. Cyclic voltammetric analysis allowed us to single out the potential region where deposition of the species occurs. Upon annealing at 400 °C, formation of cubic ZnCuTe was confirmed by X-ray diffraction. The patterns were modelled using a MarqX algorithm which allows direct refinement of lattice parameters over the entire pattern instead of single-peak profile analysis. Electronic Publication