Showing papers by "Francisco Torrens published in 1997"

Theoretical characterization of iron and manganese porphyrins for catalyzed saturated alkane hydroxylations

Abstract: The theoretical characterization of porphin (H2Por), iron and manganese porphyrins MIII(Por) and their chlorine derivatives MIII(Por)Cl has been carried out. This work represents a first step for modelling catalyzed saturated alkane hydroxylations. The chlorine atom is responsible for the existence of a dipole moment of 1.2–2.0 D in the MIII(Por)Cl molecules and for a negative value of the mean quadrupole moment (−16–(−14)DA). The charge of the metal atom (1.8–2.2 e) is rather varied (to 2.1–2.6 e) and the effective polarizability (2.8–2.9 A3) is increased (to 3.5–3.6 A3) by the addition of the chlorine atom. Starting from the porphin molecule, the presence of the metal atom decreases the molecular volume, molecular surface area and solvent accessible surface area. The addition of the chlorine atom increases these geometrical descriptors. The fractal dimension for the metal atom solvent accessible surface takes a very high value of 6.1–6.2 when compared with the molecular value averaged for non-buried atoms (D′ = 1.44). This means that the irregularity of the molecular surface is maximal at the metal atom solvent accessible surface. The n-octanol—water partition coefficient is minimal for the metal free porphin (log P = 5.48) and maximal for the non-charged chlorine porphyrin derivative (log P = 6.19).