Plateforme d'Enseignement à Distance de l'Université Oran 1 Ahmed Ben Bella

Feynman–Hibbs corrections in molecular dynamics computer calculations of solid C60 are implemented within the classical effective pair potential approach. The potential model chosen for the site–site interactions is of the Buckingham exp-6 type (Rigby 1986 The Forces Between Molecules (New York: Oxford University Press)), fitted to the Cheng and Klein or the Kitaïgorodsky potential. Structural and thermodynamic properties of the C60 crystal lattice are investigated over a wide range of pressures and temperatures, and data obtained are compared to experimental results and those obtained from a classical approach (Baameur et al 2000 Phys. Status Solidi 220 821). It will be demonstrated that 'quantum corrections' applied in a simple quasi-classical simulations have a great influence upon most calculated properties and increase their accuracy when compared to classical approaches. The observed transition pressure with the distorted lattice and cell contraction compares favourably well with experimental data and equation of state calculations. All measured properties are reported together with the phonon density of states at different pressures.

The local anaesthetic Tetracain has previously been found to block, induce or potentiate Ca2+ release from

the sarcoplasmic reticulum of skeletal muscle. Cyclodextrins (CD) are complexing agents that have been

successfully used as pharmaceutical drug carriers, to improve the bioavailability of medicines. The aim of this work

is to investigate the inclusion process of the local anesthetic Tetracain with the beta-cyclodextrin at the Hartree–Focklevel

of theory calculations with a 6-31G (d) basis set, and to evaluate stabilization upon the formation of the inclusion

compounds for 1:1 association. The inclusion process pathways are described and the most stable structures

of the different complexes are sought through a global potential energy scan. The data suggest that the most

stable structure for the 1:1 stoichiometry between the Tetracain and the β-CD is obtained when the inclusion

complex formed by Tetracain from the tertiary amine group, entering into the cavity of β-CD from its narrow side

(i.e. the primary 6-CH2OH hydroxyl group). Structure–activity relationship is discussed in terms of different

molecular descriptors and experimental Raman spectroscopy measurements at different mole fraction for

the inclusion complexes analyzed and compared with our theoretical constructed Raman spectra.

 

To date, the Wittig reaction remains the most commonly used method in organic chemistry. The synthesis approach yields to a possible functionalization of the olefin product through the transformation of the carbonyl function (ketones or aldehydes) with a phosphoniumylide. In the present work, the two approaches are used to describe the mechanism of the Wittig reaction. Static quantum calculations at the DFT level of theory with a B3LYP functional and 6–31 g(d, p) basis set are carried out and correlated to metadynamics calculations, exploring the free energy landscape of the reaction. The free energy barriers are calculated along the trajectory path, and the mechanism is discussed with the main features observed in the MTD calculations when compared to static quantum investigations. The latter do not allow for the identification of all points that may occur along the reaction path. Static quantum calculation converges to limited geometry states, while the metadynamics converges to several metastable and stable geometries and configurations. Moreover, the strong dependence of the reaction dynamics upon the functional and pseudopotential used highlights the importance of the dispersion forces along the reaction path. A complete description of the reaction mechanism from both the free energy standpoint and the structural configurations of the molecular species is discussed in detail. The differences in the free energy profile are discussed in terms of the limited account of the dispersion interactions within the DFT approach and the standard local XC functionals, confirming the strong non-covalent interactions and molecular rearrangement of charged species that take place all along the reaction path.