The infrared spectra of twenty Co(III) carbonato complexes have been measured in a range between 4000 and 300 cm—1. Normal coordinate treatments were made with a model based on the unidentate and bidentate forms of the 1:1 (metal/ligand) complex. The theoretical band assignments and force constants obtained by these calculations confirm the validity of the previous qualitative conclusions based on the differences of symmetry and the frequency shifts of the unidentate and bidentate complexes. The Co(III)-O stretching bands were located at 440∼380 (antisymmetric) and at 400∼350 (symmetric) for the bidentate complexes, and at 360∼340 cm—1 for the unidentate complexes.
The infrared spectra of 10 oxalato complexes have been obtained in the frequency range 4000 to 300 cm—1. A normal coordinate treatment made on the 1:1, metal:ligand model of the chelate ring of tris-(oxalato)-Cr(III) resulted in the assignment of metal-oxygen stretching bands in the range between 600 and 300 cm—1 for various oxalato complexes. The force constants and the band assignments obtained are compared with those of the previous normal coordinate analysis based on the free oxalato ion. Relationships between the metal-oxygen and the carbon-oxygen stretching frequencies are discussed.
In the effort to combat antibiotic resistance, inhibitors of the essential bacterial protein FtsZ have emerged as a promising new class of compounds with clinical potential. One such FtsZ inhibitor (TXA707) is associated with potent activity against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) that are resistant to current standard-of-care antibiotics. However, mutations in S. aureus FtsZ (SaFtsZ) that confer resistance to TXA707 have been observed, with mutations in the Gly196 and Gly193 residues being among the most prevalent. Here, we describe structural studies of an FtsZ inhibitor, TXA6101, which retains activity against MRSA that express either G196S or G193D mutant FtsZ. We present the crystal structures of TXA6101 in complex with both wildtype SaFtsZ and G196S mutant SaFtsZ, as well the crystal structure of TXA707 in complex with wildtype SaFtsZ. Comparison of the three structures reveals a molecular basis for the differential targeting abilities of TXA6101 and TXA707. The greater structural flexibility of TXA6101 relative to TXA707 enables TXA6101 to avoid steric clash with Ser196 and Asp193. Our structures also demonstrate that the binding of TXA6101 induces previously unobserved conformational rearrangements of SaFtsZ residues in the binding pocket. In the aggregate, the structures reported in this work reveal key factors for overcoming drug resistance mutations in SaFtsZ, and offer a structural basis for the design of FtsZ inhibitors with enhanced antibacterial potency and a reduced susceptibility to mutational resistance.
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