Cembradienes from the Caribbean sea whip Eunicea sp.

A new cembradiene diterpenoid 1, together with the known antiplasmodial cembradiene 2, was isolated from the sea whip Eunicea sp. collected from Santa Marta Bay on the Colombian Caribbean sea. The structures and absolute stereochemistry of 1-2 were determined by extensive spectroscopic analysis, chemical transformation of 2 to the new diterpenoid 3, and by using modified Mosher’s method. This is the first known report regarding the determination of the absolute configuration of 2.     

Effective anisotropy field variation of magnetite nanoparticles with size reduction

Size effect on the internal magnetic structure has been investigated on weakly interacting magnetite (Fe₃O₄) nanoparticles by ferromagnetic resonance experiments at 9.5 GHz as a function of temperature (4–300 K). A set of three samples with mean particle size of 2.5 nm, 5.0 nm and 13.0 nm, respectively, were prepared by chemical route with narrow size distribution (σ < 0.27). To minimize the dipolar interaction, the particles were dispersed in a liquid and a solid polymer matrix at ∼0.6% in mass. By freezing the liquid suspension with an applied external field, a textured was obtained. Thus, both random and textured suspensions were studied and compared. The ferromagnetic resonance experiments in zero-field-cooled and field-cooled conditions were carried out to study the size effect on the effective anisotropy field. The dc magnetization measurements clearly show that the internal magnetic structure was strongly affected by the particle size.