Fibrous nanosilica (KCC-1) oxynitrides are promising solid-base catalysts. Paradoxically, when their nitrogen content increases, their catalytic activity decreases. This counterintuitive observation is explained here for the first time using 15 N-solid-state NMR spectroscopy enhanced by dynamic nuclear polarization.

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2-Hydroxyisoquinoline-1,3(2H,4H)-dione was recently discovered as a scaffold for the inhibition of HIV-1 integrase and the ribonuclease H function of HIV-1 reverse transcriptase. First, we investigate its interaction with Mg(2+) and Mn(2+) using different spectroscopic techniques and report that 2-hydroxyisoquinoline-1,3(2H,4H)-dione forms a 1:1 complex with Mg(2+) but a 1:2 complex with Mn(2+). The complex formation requires enolization of the ligand. ESR spectroscopy shows a redox reaction between the ligand and Mn(2+) producing superoxide anions. Second, 2-hydroxyisoquinoline-1,3(2H,4H)-dione, its magnesium complex, and its 4-methyl and 2-hydroxy-4-methoxycarbonylisoquinoline-1,3(2H,4H)-diones were tested as inhibitors of HIV-1 integrase, reverse transcriptase ribonuclease H, and DNA polymerase functions. Their antiviral activities were evaluated and 2-hydroxy-4-methoxycarbonyl-isoquinoline-1,3(2H,4H)-dione was found to inhibit the viral replication of HIV-1 in MT-4 cells. Cross-resistance was measured for this compound on three different viral strains. Experimental data suggest that the antiviral activity of 2-hydroxy-4-methoxycarbonylisoquinoline-1,3(2H,4H)-dione is probably due to the RNase H inhibition.