Crystalline structures of l-cysteine and l-cystine: a combined theoretical and experimental characterization

It is assumed that genetic diseases affecting the metabolism of cysteine and the kidney function lead to two different kinds of pathologies, namely cystinuria and cystinosis whereby generate l-cystine crystals. Recently, the presence of l-cysteine crystal has been underlined in the case of cystinosis. Interestingly, it can be strikingly seen that cystine ([–S–CH₂–CH–(NH₂)–COOH]₂) consists of two cysteine (C₃H₇NO₂S) molecules connected by a disulfide (S–S) bond. Therefore, the study of cystine and cysteine is important for providing a better understanding of cystinuria and cystinosis. In this paper, we elucidate the discrepancy between l-cystine and l-cysteine by investigating the theoretical and experimental infrared spectra (IR), X-ray diffraction (XRD) as well as Raman spectra aiming to obtain a better characterization of abnormal deposits related to these two genetic pathologies.