Raman spectra and Vibrational Assignments of Calcium Oxalate Polyhydrates

ESTEFANÍA COLOMBO; BELLETTI, G.; PAOLA QUAINO; FREDERIK TIELENS

Santa Fe

Conferencia; VI San Luis conference; 2018

INTEC

Fourier Transform (FT)-Raman and FT-Infrared spectroscopies constitute signifcant tools for bio-medical diagnoses1. Raman spectroscopy is not routinely used at the hospital for microcrystallinepathologies, mainly because it has some disadvantages compare to IR spectroscopy (the laser usedas the probe can modify the chemistry of the deposit and the tissue may display a signifcantbackground signal). However, Raman shows major advantages compare to IR spectroscopy.Compositional mapping of samples simply deposited on supports used routinely at the hospital, i.e.glass, can be easily obtained with a submicron resolution. Measurements thought glass cover slipfor air sensitive samples are also possible. In addition, in Raman the 50 cm -1 to 400 cm-1 spectralrange is accessible (10 cm-1 with enhanced fltering of the laser line), providing precise(unambiguous) chemical signature of the sample under scrutiny.The use of Raman spectroscopy, together with IR, as diagnostic tools at the hospital ideallypresupposes a complete understanding of the origin of the diferent bands of pathological deposits.This is achievable through computational calculation Raman spectra of the diferent constitutingcompounds.In this work, the vibrational spectra of the calcium oxalate polyhydrates are investigated usingDFT-D3, and theoretical Raman spectra are obtained following the method of Fonari and Staufer 2.The most important calcium oxalate compounds present in more than 70% of the kidney stones areanalyzed: whewellite (monohydrate: COM), weddellite (dihydrate: COD), and caoxite (trihydrate:COT).The theoretical Raman vibrational spectra of the polyhydrates of the calcium oxalates werecomputed and completely resolved. Most bands were assigned and the theoretical predictions werecompared with experimental data. Then, we provide data that can be used to quantify the diferentpolyhydrates in natural mixtures such as in biological calcifcations or kidney stones.Such an approach allowed a more accurate analysis of vibrational spectra helping in thecompletion of the assignments of the vibrational bands of the three calcium oxalate polyhydrates.Particular attention has been paid to the low Raman frequencies and the presence of oxalic acid innatural calcium oxalate polyhydrates. The obtained results are expected to be supportive in thedetection of the diferent polyhydrates in natural samples.