An amine-modified pteridine; selectively inhibits T. gondii DHFR (IC50 = 0.033 µM) over DHFR from P. carinii and rat liver (IC50s = 0.2 and 1.1 µM, respectively); reduces T. gondii replication in T. gondii-infected MDBK cells (MSI = 1 µM); inhibits the uptake of para-aminobenzoic acid by P. carinii (IC50 = 16.2 µM); increases survival in V. cholera-infected mice at 500 mg/kg; reduces energy loss and increases thermal stability and power conversion efficiency, as well as improves interfacial contacts, when applied to the fullerene/cathode interface in inverted perovskite solar cells