Structural Studies of β-Diketones and Their Implications on Biological Effects

The paper briefly summarizes methods to determine the structure of β-diketones with emphasis on NMR methods. Density functional calculations are also briefly treated. Emphasis is on the tautomeric equilibria of β-diketones in relation to biological effects. Relevant physical parameters such as acidity and solubility are treated. A series of biologically active molecules are treated with respect to structure (tautomerism). Characteristic molecules or groups of molecules are usnic acids, tetramic and tetronic acids, o-hydroxydibenzoylmethanes, curcumines, lupulones, and hyperforines.

Green Afterglow of Undoped SrAl2O4

Undoped SrAl2O4 nanocrystals were obtained via solution combustion using urea as fuel. The afterglow properties of undoped SrAl2O4 were investigated. Green afterglow from undoped SrAl2O4 is visible to the human eye when the 325 nm irradiation of a helium–cadmium laser (13 mW) is ceased. The afterglow spectrum of undoped SrAl2O4 is peaked at about 520 nm. From the peak temperature (321 K) of the broad thermoluminescence glow curve, the trap depth of trap levels in undoped SrAl2O4 is estimated to be 0.642 eV using Urbach’s formula. Based on first-principles density functional calculations, the bandstructures and densities of states are derived for oxygen-deficient SrAl2O4 and strontium-deficient SrAl2O4, respectively. Our results demonstrate that the green afterglow of undoped SrAl2O4 originates from the midgap states introduced by oxygen and strontium vacancies. The observation of green afterglow from undoped SrAl2O4 helps in gaining new insight in exploring the afterglow mechanisms of SrAl2O4-based afterglow materials.