Bis-Citrullinato Copper(II) Complex: Synthesis, Crystal Structure, and Non-Covalent Interactions

Citrulline (C6H13N3O3) is a non-protein amino acid found in watermelon. In physiological conditions, it is almost entirely present as a zwitterion, so its carboxylic and amine groups can act as Lewis donors, chelating metallic cations. In addition, Citrulline possesses a terminal ureide group of the aliphatic chain, which appears to be non-innocent. Although Citrulline is similar to other classical amino acids, only one coordination complex has been reported in the Cambridge Crystallographic Database. As part of our search for Casiopeina (R) analogs, we synthesized and characterized the copper bis-citrullinato complex, [Cu(Citr)(2)](n). The compound was described using UV-Vis, Infrared, and Raman spectroscopy, together with single-crystal X-ray diffraction. Computational tools were also used. The optimized structure, MEP map, IR and Raman spectra, and H-1 and C-13 chemical shifts were obtained with functional mPW1PW91 using 6-31G(d) basis set for N, O, C, and H atoms, and LANL2DZ basis set and ECP=LANL2DZ for the Cu atom. TD-mPW1PW91 calculations generated the UV-Vis spectrum. Finally, AIM and Hirshfeld surface analysis were used to examine noncovalent interactions. Previous investigations suggest Casiopeina (R)-like complexes can interact with DNA/RNA, creating potential anticancer chemicals. The [Cu(Citr)(2)](n) complex's polymeric nature and insolubility make it difficult for such purposes. However, the facile synthesis of D-Citrulline could be a novel way to find new applications for this interesting amino acid.

Automated summary

Citrulline is a non-protein amino acid found in watermelon. Researchers synthesized and characterized a copper bis-citrullinato complex and found its polymeric nature and insolubility make it unsuitable for potential anticancer chemicals. However, the facile synthesis of D-Citrulline could open up new applications for this interesting amino acid.