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^® 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 ¹H and ¹³C 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 non-covalent interactions. Previous investigations suggest Casiopeina^®-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.

COVID-19 has caused over seven million deaths globally due to its high transmission rate. The virus responsible for the disease requires a transmembrane protease serine type II (TMPRSS2-7MEQ) to infiltrate host cells and has been linked to several cancers, particularly prostate cancer. To investigate COVID-19 potential therapies, a series of Casiopeina-like copper complexes containing 1,10-Phenanthroline and amino acids were investigated as TMPRSS2 inhibitors. The molecular structures of twelve Phenanthroline copper complexes were calculated, and their global reactivity indices were analyzed using DFT and conceptual DFT methods. Three molecular docking algorithms were employed to identify the most effective inhibitors by examining their interactions with amino acid residues in the target protein’s catalytic activity triad (Asp345, His296, and Ser441). All complexes are docked above the catalytic site, blocking the interaction with substrates. The Phenanthroline complexes showed better interactions than the Bipyridine complexes, likely due to increased hydrophobic contacts. Analogs’ cationic nature and amino acids’ basic side chains bring them near the active site by interacting with Asp435. The top complexes in this study contain Ornithine, Lysine, and Arginine, making them promising alternatives for researching new drugs for COVID-19 and cancers like prostate cancer.

Citrulline is a non-protein amino acid that acts as a metabolic intermediate in the urea cycle and arginine synthesis. It is present in some foods, although its name derives from watermelon (Citrullus vulgaris), from which it was first identified. Under normal conditions, Citrulline exists as a zwitterion in aqueous solutions since its carboxylic and amine groups can act as Lewis donors to chelate metal cations. In addition, Citrulline possesses in the aliphatic chain a terminal ureide group, which could also coordinate. Although Citrulline is comparable to other classical amino acids, its coordination chemistry has yet to be explored. Only two metal complexes have been reported, and the copper complex is a polymeric and insoluble material. As part of our search for active Casiopeina^® analogs, we created a more soluble complex by combining 2,2′-Bipyridine into a new mixed material, resulting in the mononuclear complex [Cu(Bipy)(Citr)(H₂O)(NO₃)]·H₂O. Single-crystal X-ray diffraction, spectroscopic methods (FT-IR, UV-Vis, Raman), and mass spectrometry characterized the material. Interestingly, both isomers of Citrulline, R(D), and S(L) are present in the same crystal. In addition, the molecular structure and electronic properties of the complex were calculated using density functional theory (DFT). Non-covalent interactions were characterized using the atoms-in-molecules (AIM) approach and Hirshfeld surface (HS) analysis. This ternary complex containing Citrulline and 2,2′-Bipyridine will be used for docking calculations and preliminary biological studies using calf thymus DNA (CT-DNA) and plasmid pUC19 as a first approximation to cytotoxic activity against cancer cell lines.

Citrulline (C₆H₁₃N₃O₃) is an amino acid found in the body as a zwitterion. This means its carboxylic and amine groups can act as Lewis donors to chelate metal cations. In addition, citrulline possesses a terminal ureido group on its aliphatic chain, which also appears to coordinate. Here, two new mixed complexes of citrulline were made with 1,10-phenanthroline and 2,2′-bipyridine. These compounds, once dissolved in water, gave aquo-complexes that were subject to DFT studies and in vitro toxicity studies on cancer cell lines (HeLa, MDA-MB-231, HCT 15, and MCF7) showed promising results. Docking studies with DNA were also conducted, indicating potential anticancer properties.

The title compound, (C₄H₁₂N₅)₄(C₂H₇N₄O)₂[V₁₀O₂₈]·4H₂O, is a by-product obtained by reacting ammonium metavanadate(V), metformin hydrochloride and acetic acid in the presence of sodium hypochlorite, at pH = 5. The crystal structure comprises a decavanadate(V) anion (V₁₀O₂₈)^6– lying on an inversion centre in space group P\overline{1}, while cations and solvent water molecules are placed in general positions, surrounding the anion, and forming numerous N—H...O and O—H...O hydrogen bonds. Metforminium (C₄H₁₂N₅)⁺ and guanylurea (C₂H₇N₄O)⁺ cations display the expected shape. Interestingly, in physiology the latter cation is known to be the main metabolite of the former one. The reported structure thus supports the role of sodium hypochlorite as an oxidizing reagent being able to degrade metformin hydrochloride to form guanylurea.