Modulation of Calcium Oxalate Crystallization by Colloidal Selenium Nanoparticles–Polyphenol Complex

The nanoSe0-polyphenol complexes with a 3:1 polyphenol/nanoSe0 molar ratio were prepared by colloidal selenium nanoparticles (nanoSe0) modified with gallic acid (GA), propyl gallate (PG), and pyrogallic acid (PA), which were spherical with average diameter about 38–77 nm. On this basis, we studied the effect of nanoSe0-polyphenol on the CaC2O4 crystallization and also elaborated the modulation mechanism, which were compared with those for each polyphenol individually. NanoSe0-GA and nanoSe0-PA were easy to induce the formation of calcium oxalate dihydrate (COD) crystals, while nanoSe0-PG induced the formation of quasi-rectangular calcium oxalate monohydrate (COM), multilayered calcium oxalate trihydrate (COT) crystals, and an amount of COD crystals in a dose-dependent fashion by nanoSe0-PG. The strong effect of nanoSe0-polyphenol on the formation of COD and COT crystals could be attributed to electrostatic interaction between nanoSe0-polyphenol and CaC2O4 crystals. The results obtained in the polyphenol system were similar to, as well as different from, nanoSe0-polyphenol because the effect of the polyphenol on the CaC2O4 crystallization could result from not only electrostatic interaction between polyphenols and Ca2+ ions, but also hydrogen bonding interaction between the polyphenols and C2O42– groups. All the obtained COD crystals were thermostable even at 70 °C, while COT crystals were temperature dependent.