Thermal stability of the essential oils isolated from Tunisian Thymus capitatus Hoff. et Link.: Effect on the chemical composition and the antioxidant and antibacterial activities

The chemical composition, the antioxidant and the antibacterial activities of essential oils, isolated from the aerial parts of Tunisian Thymus capitatus during the flowering phase, and stored in the dark during 37 days in the oven, at 60 degrees C were evaluated. Samples taken periodically were used to evaluate the chemical composition, the antioxidant and the antibacterial activities. With some fluctuations, carvacrol (68-74%) was the major component of the oil independent of the storage period. alpha-Terpinene and gamma-terpinene decreased over time, whereas p-cymene increased in the same period. Despite the thirty-seven days of storage at 60 degrees C, T. capitatus essential oil still showed high antioxidant and stable antimicrobial activity

Intelligence Territoriale et Écologie

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Pore size distribution in porous glass: fractal dimension obtained by calorimetry

By differential Scanning Calorimetry (DSC), at low heating rate and using a technique of fractionation, we have measured the equilibrium DSC signal (heat flow) $J_q^0$ of two families of porous glass saturated with water. The shape of the DSC peak obtained by these techniques is dependent on the sizes distribution of the pores. For porous glass with large pore size distribution, obtained by sol-gel technology, we show that in the domain of ice melting, the heat flow Jq is related to the melting temperature depression of the solvent, $\Delta T_{\rm m}$ , by the scaling law: $J_q^0\sim \Delta T_{\rm m}^{-(1+D)}$. We suggest that the exponent D is of the order of the fractal dimension of the backbone of the pore network and we discuss the influence of the variation of the melting enthalpy with the temperature on the value of this exponent. Similar D values were obtained from small angle neutron scattering and electronic energy transfer measurements on similar porous glass. The proposed scaling law is explained if one assumes that the pore size distribution is self similar. In porous glass obtained from mesomorphic copolymers, the pore size distribution is very sharp and therefore this law is not observed. One concludes that DSC, at low heating rate ($q\leq 2 ^\circ$C/min) is the most rapid and less expensive method for determining the pore distribution and the fractal exponent of a porous material

Multiplication de l'espèce : aspects fondamentaux et appliqués

Le tégument des graines d'A. raddiana a une structure anatomique typique des légumineuses qui induit une forte inhibition de la germination. Cela implique qu'une scarification naturelle (chocs, feu) ou artificielle (traitement mécanique ou chimique) du tégument est nécessaire pour permettre l'imbibition et la germination des graines. Cette forte inhibition tégumentaire explique aussi que les graines restent intactes après passage dans le tractus digestif des animaux sauvages ou domestiques qui les consomment.Les semences d'A. raddiana peuvent conserver leur viabilité pendant plusieurs années, in situ ou en collections. Elles ont un comportement orthodoxe. La germination est optimale à une température comprise entre 20 et 35 °C, elle est peu perturbée par des contraintes hydriques ou salines fortes. Les graines d'A. raddiana semblent donc bien adaptées aux conditions d'aridité dans lesquelles l'espèce se développe.La présente synthèse montre enfin que la maîtrise de la technologie des semences d'A. raddiana est suffisante pour envisager l'utilisation de cette espèce en reboisement.The seed tegument of A. raddiana has a typical anatomic structure of legumes which induces a high germination inhibition. This implies that a natural (shocks, fire) or artificial (mechanical or chemical processing) scarification of the tegument is required to allow soaking and germination of the seeds. This tegumental high inhibition accounts for the fact that seeds remain undamaged after passing through the digestive tract of wild or domestic animals which consume them. A. raddiana seeds may preserve their viability for several years, in situ or collectively. They have an orthodox behaviour. Optimum germination takes place at a temperature between 20 and 35 °C, and it is little affected by high water and saline stress. Therefore A. raddiana seeds seem to be well adapted to the arid conditions where the species develops.Finally, the current synthesis shows that the control over seeding technology for A. raddiana is enough to envisage the use of the species for reforestation

Melting of ice in porous glass: why water and solvents confined in small pores do not crystallize?

The melting of ice in porous glass having different distribution of pores sizes is analyzed in details. One shows that confined water crystallizes only partially and that an interface layer, between the ice crystallites and the surface of the pore, remains liquid. Properties of this non crystalline interface at low temperature is studied by NMR and DSC. Both methods lead to an interface thickness h of the order of 0.5 nm, this explains why water do not crystallize when the dimension of confinement is less than a critical length $d^{\ast }\sim 1$ nm. The variation of the melting enthalpy per gram of total amount of water with the confinement length is explained taking into account two effects: a) the presence of this layer of water at the interface and b) the linear variation of the melting enthalpy $\Delta H_{m}$ with the melting temperature Tm. From the data of the literature one draws the same conclusions concerning other solvents in similar porous materials. Also one points out the important role of the glass temperature Tg in preventing the crystallization of the liquids confined in small pores and/or between the crystallites and the surface of the pores

Freezing, melting and dynamics of supercooled water confined in porous glass

International audienceThe freezing, melting and dynamics of supercooled water at different hydration of controlled porous glass (CPG) with mean pore sizes 10 nm, 30 nm, 50 nm and 70 nm are studied using differential scanning calorimetry (DSC) and deuteruim nuclear magnetic resonance (2 H-NMR). For saturated samples, the melting tempertaure follows the Gibbs-Thomson relation despite a clear linear decrease of the melting enthalpy when the transition is shifted due to confinement. For partially filled porous glasses the crystalization and melting temperatures as well as enthalpy are lower than for the saturated samples. 2 H-NMR confirms the existence of a non-crystallizable part of water adsorbed on the surface of pores. At room temperature, spin-lattice relaxation rate (1/T1) is proportional to the inverse of the mean pore size indicating that the relaxation is governed by a surface limited process. At low tempertaure relaxation rate follows the Vogel-Fulcher-Tammann (VFT) relation