3-Hydroxy-4-Pyridinone as Potential Chelating Agent for the Remediation of Ecotoxic Metals from Environmental Matrices

In the last years the increase of pollution and its impact on diseases onset, led the scientific community to a great interest towards the study of the effect of contaminants, including metals, organic and inorganic compounds, on the environment and humans [1]. It is known that the biological and chemical activity of these substances should be attributed to some of the chemical forms in which they are present in the natural fluids. To better understand their mechanism of action, it is necessary to know either their analytical concentration, or their “speciation”, i.e. a term indicating the distribution of the physical and chemical forms in which a component is present in a system [2]. Since these forms could have various effects towards environment and humans, the study of speciation becomes essential to gain information about their environmental impact, toxicity and bioavailability. Aluminium is a naturally occurring metal in various environmental matrices. In soils it is present in the form of aluminosilicates and oxides. Acidic rains can provoke soil acidification (pH ≤ 5.5), promoting the mobility of Al3+ which may hinder plants growth and cause a significant reduction of the concentration of nutrients like Ca2+ and Mg2+ in leaves, roots and shoots [3]. On the other hand, iron is one of the most abundant metals found in the environment [4]. In plants it is mainly present in ferric (Fe3+) form and plays fundamental roles in the photosynthesis, for nitrogen fixation and for plants growth. Iron can become an ecotoxic element for soils and plants when it is accumulated at significant concentration levels. In these matrices, Fenton reaction can produce reactive oxygen species (ROS), like -OH radicals, able to damage DNA, lipids and proteins [5]. The metal ecotoxicity symptoms might be soils bronzing and leaves stippling. The reason of change of colour in leaves could be, for example, the plants synthesis of enzymes aimed to control the effects of free radicals. In addition, Fe3+ can also compete with Zn2+ and Cu2+ in its uptake and transport within plant cells [4]. On this light, the present contribution is focused on the results of a speciation study performed to evaluate if a compound (L2, Figure 1), belonging to the class of 3-hydroxy-4-pyridinones, could be an efficient chelating agent for the remediation of potentially ecotoxic metals such as Al3+ [6] and Fe3+ from soils and plants. In addition, another relevant issue appeared to be worth of investigating to ascertain if, from the thermodynamic point of view, along with the Al3+ and/or Fe3+-sequestration by L2, there could be a possible significant competition with essential metals such as Ca2+, Mg2+ [3], Zn2+ [7] and Cu2+, despite their different charge density, acid-base behaviour [8] and ionic radius. References [1] A. Kot, J. Namiesnik, Trends in Analytical Chemistry, 19 (2000) 69-79. [2] D. M. Templeton, F. Ariese, R. Cornelis L. G. Danielsson, H. Muntau, H. P. Van Leeuwen, R. Łobinsky, Pure and Applied Chemistry, 72 (2000), 1453-1470. [3] A. Irto, P. Cardiano, K. Chand, R. M. Cigala, F. Crea, C. De Stefano, G. Gattuso, S. Sammartano, M. A. Santos, Journal of Molecular Liquids, 319 (2020) 114349. [4] S. Rai, P. K. Singh, S. Mankotia, J. Swain, S. B. Satbhai, Plant Stress 1 (2021) 100008. [5] Elements and their Compounds in the Environment, E. Merian, M. Anke, M. Ihnat, M. Stoeppler, 2nd Edition. 2004. [6] A. Irto, P. Cardiano, K. Chand, R. M. Cigala, F. Crea, C. De Stefano, L. Gano, S. Sammartano, M. A. Santos, Journal of Inorganic Biochemistry 186 (2018) 116-129. [7] A. Irto, P. Cardiano, S. Cataldo, K. Chand, R. M. Cigala, F. Crea, C. De Stefano, G. Gattuso, N. Muratore, A. Pettignano, S. Sammartano, M. A. Santos, Molecules 24 (2019) 4084. [8] The Hydrolysis of Cations, C. F. Baes, R. S. Mesmer, John Wiley & Sons: New York, 1976; 81, 245-246.