During the intraerythrocytic stage of malaria, the parasite digests hemoglobin and aggregates the released heme as an insoluble crystalline material called hemozoin. This detoxification step is an excellent drug target for developing new antimalarials, which can bind to hemozoin surface to inhibit further growth. Although the bulk crystalline properties of hemozoin are well-known, the surface properties remain poorly defined. Here, we use a combination of spectroscopic and adsorption techniques to study the surface of synthetic hemozoin, hematin anhydride, produced by two different methods. We show that the two synthetic methods produce crystals with major differences, such as the amount of water adsorbed on the surface and surface carboxylate groups. These results imply that the methodology to produce hematin anhydride affects its surface reactivity; this information needs to be considered whenever hematin anhydride is used as a model to study host immune response or to design new antimalarials.
Soluble nitrosoguanidine- and N-methylnitrosoguanidine-based
metallotriazole complexes of ruthenium(II) monocarbonyls have been
prepared and characterized. Both nitrosoguanidines prove to be strong
chelates with the formally π-accepting nitroso nitrogen binding cis to carbon monoxide and a π-donating amide trans to the CO. The resulting ensemble consists of ruthenium
examples of 1-metallo-2,3,5-triazoles. The ruthenium coordination
sphere is completed by anions, either H–, Cl–, or Ph–, trans to
the nitroso group as well as two mutually trans PPh3 groups. The π-donating amide group is formally sp2 hybridized with a planar nitrogen to give a strongly bound
five-membered chelating anion. Together, these results illustrate
the remarkable potential for the nitrosoguanidinates as a family of
new metal chelates.
The preparation of
stable hypervalent metal complexes containing
Ag(III) has historically been challenging due to their propensity
for reduction under ambient conditions. This work explores the preparation
of a tripotassium silver bisperiodate complex as a tetrahydrate via
chemical oxidation of the central silver atom and orthoperiodate chelation.
The isolation of the chelate complex in high yield and purity was
achieved via acidimetric titration. The comprehensive physiochemical
characterization of the tribasic silver bisperiodate included single
crystal X-ray diffraction, thermogravimetric and differential scanning
calorimetry, and infrared and ultraviolet–visible spectroscopy.
Infrared and UV–visible absorption spectra (λmax 255 and 365 nm) were in good agreement with historically prepared
pentabasic diperiodatoargentate chelate complexes. The C2/c monoclinic distorted square planar structure
of the bis-chelate complex affords a mutually supportive framework
to both Ag(III) and I(VII), conferring stability under both thermal
and long-term ambient conditions. Thermal analysis of the tribasic
silver bisperiodate complex identified an endothermic mass loss, ΔH = +278.35 kJ/mol, observed at 139.0 °C corresponding
to a solid-state reduction of silver from Ag(III) to Ag(I). Under
ambient conditions, no significant degradation was observed over a
12 month period (P = 0.30) for the silver bisperiodate
complex in a solid state, with an observed half-life of τ1/2 = 147 days in a pH-neutral aqueous solution.
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