Publication details
Raman spectroscopy of calcium oxalate dihydrate (COD) and trihydrate (COT)
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| Year of publication | 2026 |
| Type | Appeared in Conference without Proceedings |
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| Description | Calcium oxalate hydrates (CaC2O4 · nH2O) are common biominerals found in lichens, fungi, plants, and also in sedimentary rocks or on monument surfaces; they are common due to their strong affinity for divalent cations and interaction with weak organic acids (Izatulina et al. 2018). In nature, Ca-oxalates are represented by three hydrated forms: whewellite (CaC2O4 · H2O; COM), weddellite (CaC2O4 · 2H2O; COD), and caoxite (CaC2O4 · 3H2O; COT). The most common biomineral is COM, while COD and COT are considered to be metastable phases; however, COT is expected to be precursor of COD crystal formation (Conti et al. 2015) and may play an important role in calcium oxalate nucleation dynamics. Since COD and COT have very similar Raman spectra, their identification requires careful calibration and measurement, and high-quality reference spectra. In order to obtain monocrystals of COD and COT for oriented Raman spectra measurements, we used syntheses according to Ouyang et al. (2006), Horáková (2022) and Echigo et al. (2005). Crystals of COD and COT were examined using single-crystal X-ray diffraction and their oriented Raman spectra were subsequently collected using the Horiba LabRamHR microspectrometer with Si-based Peltier-cooled CCD detector. Our results show orientation-dependent variations in band intensities and positions in both COD and COT. They improve the high potential of Raman spectroscopy in studies of calcium oxalate nucleation and growth in organisms. |