Bruno Marongiu

Thermodynamics of binary mixtures containing oxaalkanes. Part 3. Monoethers, polyethers, acetals, orthoesters and cyclic monoethers + n-alkanes or cyclohexane

Abstract The data available in the literature for the excess Gibbs energies G E , excess enthalpies H E , activity coefficients γ ∞ i , and partial molar excess enthalpies h E,∞ i at infinite dilution, and excess heat capacities C E P of noncyclic monoethers, polyethers, acetals and orthoesters and of cyclic monoethers + n-alkanes or + cyclohexane are examined on the basis of the DISQUAC group contribution model. The interaction parameters, quasichemical and dispersive, depend on the intramolecular environment of the O atom. There is clear evidence for a steric effect exerted by the alkyl groups adjacent to the O atom, for OCO proximity effect (in acetals and orthoesters), and for a ring strain effect (in cyclic ethers). The steric effect results in a regular decrease of the quasi-chemical interaction parameters; the dispersive parameters remain constant. The proximity effect of O atoms produces a regular decrease, and the ring strain a regular increase, in both the quasi-chemical and the dispersive interaction parameters.

A comparative study of thermodynamic properties and molecular interactions in mono- and polychloroalkane + n-alkane or + cyclohexane mixtures

Abstract The data available in the literature on the excess Gibbs energies, G E , activity coefficients at infinite dilution, γ ∞ i , excess enthalpies, H E , and excess heat capacities, C E p , for 10 classes of mono- or polychloroalkanes + n-alkanes or + cyclohexane are examined on the basis of the DISQUAC group-contribution model. The non-polar CCl 4 -containing mixtures can be treated in the zeroth approximation of the model. The dispersive interaction parameters for CCl 4 + n-alkanes, C dis ad, l , or + cyclohexane, C dis bd, l , are used to describe the dispersive term for polar chloroalkanes + alkanes. The quasichemical parameters for polar chloroalkanes of the series CH 3 (CH 2 ) m −2 CCl u H 3− u are the same for n-alkane and cyclohexane mixtures, C quac ad, l = C quac bd, l , and decrease regularly with increasing u . For any given u , C quac ad, l = C quac bd, l for symmetrical chloroalkanes of the series CCl u H 3− u (CH 2 ) m −2 CCl u H 3− u decreases regularly with decreasing m (proximity effect). The model describes consistently the excess functions G E , H E , and γ ∞ i for the investigated mixtures. Literature data are critically evaluated. The parameters provided may serve to accurately predict missing quantities. Systematic discrepancies between theory and experiment are noted in mixtures containing long-chain molecules, particularly for H E and γ ∞ i . The calculated C E p curves differ considerably from experimental data. Possible sources of disagreement and ways of refining the model are discussed.

Chemical characterization and biological activity of essential oils from Daucus carota L. subsp. carota growing wild on the Mediterranean coast and on the Atlantic coast

The essential oils and supercritical CO(2) extracts of wild Daucus carota L. subsp. carota growing spontaneously in Sardinia and in Portugal were investigated. The main components in the Sardinian essential oil of flowering and mature umbels with seeds are beta-bisabolene (17.6-51.0%) and 11-alpha-(H)-himachal-4-en-1-beta-ol (9.0-21.6%); instead, the oils from Portuguese samples are predominantly composed of geranyl acetate (5.2-65.0%) and alpha-pinene (3.5-37.9%). Supercritical extracts contain lower amounts of monoterpenes and higher amounts of sesquiterpene hydrocarbons. Antifungal activities of the Sardinian oils were the highest, particularly for dermatophytes and Cryptococcus neoformans, with MIC values of 0.16-0.64 microL mL(-1).

Thermodynamics of binary mixtures containing linear or cyclic alkanones + n-alkanes or + cycloalkanes☆

Abstract Marongiu, B., Pittau, B., Porcedda, S., and Tine, M.R., 1994. Thermodynamics of binary mixtures containing linear or cyclic alkenes + n -alkanes or cyclohexane. Fluid Phase Equilibria 93; 249-276. A head-space technique has been used to determine vapor-phase equilibria for binary mixtures of linear or cyclic mono- and polyalkenes + n-alkanes or + cyclohexane. Excess molar Gibbs energies GE for the mixtures investigated were obtained by a least-squares treatment of the equilibrium results. These data the previously measured excess enthalpies HE and the data available in the literature on GE HE activity coefficients at infinite dilution γi∞ and molar excess enthalpies at infinite dilution hiE,∞ are examined on the basis of the DISQUAC group contribution model. The model provides a fairly consistent description of the phase equilibria and the related excess functions using a unique set of structure-dependent dispersive parameters.

Isolation of eucalyptus oil by supercritical fluid extraction

Eucalyptus volatile oil was isolated by supercritical CO2 extraction with a fractional separation technique. GC–MS analysis of the various fractions obtained at different extraction and fractionation conditions allowed the identification of the best operating conditions to isolate the volatile oil. A good extraction performance was obtained by operating at 90 bar and 50°C for 510 min. The optimum fractionation was achieved by operating at 90 bar and −10°C in the first separator and at 15 bar and 15°C in the second one. The influence of the extraction pressure and of the extraction time on the oil composition were also evaluated. A comparison with the hydrodistilled oil is also given. Copyright

Evaluation of the Antimicrobial Properties of the Essential Oil of Myrtus communis L. against Clinical Strains of Mycobacterium spp.

Mycobacterium tuberculosis is the etiological agent of tuberculosis. The World Health Organization has estimated that 8 million of people develop active TB every year and the situation is complicated by an increase of Mycobacterium tuberculosis strains resistant to drugs used in antitubercular therapy: MDR and XDR-TB. Myrtle leaf extracts, used as an antiseptic in Sardinian traditional medicine, have strong antibacterial activity as several investigations showed. In this study we investigated the antimicrobial properties of the essential oil of Myrtus communis against clinical strains of M. tuberculosis and M. paratuberculosis.

Thermodynamic properties of aqueous non-electrolyte mixtures. Alkanols + + water systems.

Abstract The molar excess enthalpies, H E , at 298.15 K, and the liquid-liquid equilibrium, LLE, of aqueous mixtures of alkanols have been measured. The results are interpreted qualitatively in terms of intercomponent molecular interactions and hydrophobic stabilization of the water structure by the alkanol molecules. The results obtained indicate that the geometry, the number of alkyl groups in the aliphatic chain and the relative position of the functional group -OH have an important action on these two effects.

Chemical and biological comparisons on supercritical extracts of Tanacetum cinerariifolium (Trevir) Sch. Bip. with three related species of chrysanthemums of Sardinia (Italy)

In this manuscript, the authors compare the chemical composition and the biological effects of extracts of some Sardinian plant species: Glebionis coronaria (L.) Spach [=Chrysanthemum coronarium L.], locally known as ‘caragantzu’, Glebionis segetum (L.) Fourr. [=Chrysanthemum segetum L.], known as ‘caragantzu masedu’, and Sardinian endemic species Plagius flosculosus (L.) Alavi and Heywood [=Chrysanthemum flosculosus L.], known as ‘caragantzu burdu’. In addition, the authors compare the pyrethrins contained in these species with an extract of Tanacetum cinerariifolium (Trevir.) Sch. Bip. [=Chrysanthemum cinerariifolium (Trevir.) Vis.], a commercial species rich in pyrethrins. The volatile fractions from chrysanthemum flowers were obtained by supercritical fluid extraction (SFE) with CO2 at 90 bar and 50°C and by hydrodistillation. Pyrethrins were extracted, together with other high molecular mass compounds, by SFE at high pressure, 300 bar and 40°C. The composition of the volatile oils is determined by GC–MS analysis and the amount of pyrethrins by HPLC analysis. Moreover, the antibacterial and antimycotic activities of volatile fractions were investigated in order to compare to their traditional uses.

The effect of the molecular shape on the enthalpic behaviour of liquid mixtures : cyclic hydrocarbons in heptane and tetrachloromethane

Excess enthalpies HE at 298.15 K have been determined by flow microcalorimetry for binary mixtures of heptane or tetrachloromethane + a cyclic hydrocarbon (cycloheptane, cyclooctane, cyclodecane, 1,2,3,4-tetrahydronaphthalene, cis-decahydronaphthalene, trans-decahydronaphthalene, bicyclohexyl). With the exception of tetrahydronaphthalene + tetrachloromethane and of trans-decahydronaphtalene + heptane, all mixtures examined exhibit positive deviations. HEs have been analysed in terms of the DISQUAC model. Partial molar excess enthalpies at infinite dilution as well as standard enthalpies of solvation, ΔHo, have been evaluated for cycloalkanes in the two solvents and compared with those of linear and branched alkanes. The effect of cyclization upon ΔHo has been discussed and the contributions to ΔHo of the cavity and of the interaction terms have been estimated through the scaled particle theory.

Thermodynamic properties of binary mixtures containing chloroalkanes. I. Analysis of the excess enthalpies and excess gibbs energies of 1-chloroalkane + + cyclohexane mixtures in terms of an extended quasichemical group contribution model (DISQUAC)☆

Abstract The data available in the literature for the excess enthalpies of ethanal, propanal, butanal, or pentanal + cyclohexane and for the liquid—vapour equilibria of propanal + cyclohexane are examined on the basis of DISQUAC, a very simple extension of the quasi-chemical group contribution theory applied in Parts I and II to correlate and predict excess enthalpies and excess Gibbs energies of n-alkanal + n-alkane mixtures. Using the same four alkyl group increments as in Part II, to account for intramolecular effects in the n-alkanals, and adjusted values for the Gibbs energy and enthalpy of interchange of the formyl(CHO)-cyclohexane contact, the model provides a fairly consistent description of the excess enthalpies as functions of composition and n-alkanal chain length. Molar excess Gibbs energies are estimated for several n-alkanal + cyclohexane mixtures. The (CHO)-cyclohexane interchange parameters are slightly larger than the (CHO)-normal alkane parameters. Ketones (CO group) and esters (COO group) behave similarly.