A Preorganized Metalloreceptor for Alkaline Earth Ions Showing Calcium Versus Magnesium Selectivity in Water: Biological Activity of Selected Metal Complexes

The N,N'-bis[(3-hydroxy-4-pyron-2-yl) methyl]-N, N'-dimethylethylendiamine (Malten = L) forms the highly stable [CuH-2L] species in water, in which the converging maltol oxygen atoms form an electron-rich area able to host hard metal ions. When considering the alkaline earth series (AE), the [Cu(H-2L)] species binds all metal ions, with the exception of Mg2+, exhibiting the relevant property to discriminate Ca2+ versus Mg2+ at physiological pH 7.4; the binding of the AE metal is visible to the naked eye. The stability constant values of the trinuclear [AE{Cu(H-2L)}(2)](2+) species formed reach the maximum for Ca2+ (log K = 7.7). Ca2+ also forms a tetranuclear [Ca{Cu(H-2L)}](2)(4+) species at a high Ca2+ concentration. Tri-and tetranuclear calcium complexes show blue-and pink-colored crystals, respectively. [Cu(H-2L)] is the most active species in inducing DNA alterations. The DNA damages are compatible with its hydrolytic cleavages