What are the essential metals for human health? Are these metals also found in plants we eat? How are they transported from the gut, or soil, into our blood, or plant? Let’s start with a review by Maria Antonietta Zoroddu and her fellow scientists from Italy and Norway. These scientists identified nine. Selenium is not technically a metal, but we’ll add it to their list. A column has been added to the table if it is in this Centrum multivitamin.
| Metal | Centrum | Charge | curcumin | tannic acid | quercetin family | p-coumaric acid | e- transfer |
| Na, | +1 | +1 | no | ||||
| K | 2% | +1 | +1 | no | |||
| Mg | 24% | +2 | +2 | +2 | +2 | no | |
| Ca | 16% | +2 | +2 | +2 | no | ||
| Fe | 33% | +2, +3 | +2, +3 | +2, +3 | +2, +3 | yes [2] | |
| Mn | 100% | +2, +4, +7 | +2 | +2 | +2 | yes [2] | |
| Co | +2, +3 | +2 | +2 | +2 | +2 | yes [2] | |
| Cu | 100% | +1, +2 | +2 | +2 | +2 | +2 | yes [2] |
| Zn | 100% | +2 | +2 | +2 | +2 | no | |
| Mo | 111% | +4, +6 | +2 | +6 | yes [2] | ||
| Se | 182% | -2, +4 | yes [3] |
A review by Fedenko and coauthors provides an excellent analysis of plant polyphenolics that can bind metals and metalloids. [4] This table provides some of the phenolics that readers might be familiar and the oxidation state of the metal, metalloid bound.
These are some screen shots from the Fedenko 2022 review [4] Figure 1. The reader of this post is invited to consult this public access review to toxic metal binding properties of plant polyphenols. The Fedenko review contains a massive amount of peer reviewed data. It is interesting to note that no review mentioned Cu(I) binding. It is not know if this is because Cu(I) was not tested or if it was not considered toxic in the first place. Certainly Fe(II) and Fe(III) was tested in many of the polyphenols referenced by Fedenko and coauthors. [4]
These are some structures of polyphenols from PubChem mentioned in this post. Oxygens are red and carry a partial, if not an outright, negative charge for binding cations. Judging from table 1 of the Fedenko review, the tendency is to bind di- and tri- valent cations.
The philosophical twist
Metal ions may perform structural as well as catalytic roles in proteins of our bodies. [3] Often the catalytic roles involve the well coordinated transfer of electrons from one place to another. Metals may become toxic if they transfer that electron to O2 to form reactive oxygen species. Plant polyphenols have a way of binding metals that are used for legitimate purposes in enzymes as well as environmental contaminates such as cadmium Cd(II) and lead Pb(II). Plants are being considered agents of bioremediation to clean up environmental contaminates.
Perhaps the original goal of this post was to claim that plants contain only Cu(I). This claim could not be made with a quick review of the literature. We can conclude that plants “consider” di and trivalent cations worthy of chelation by small molecules. Do plants consider excess multivalent cations toxic? Since our bodies are not packed with polyphenols, Cu(I) versus Cu(II) is a consideration.
References
- Zoroddu MA, Aaseth J, Crisponi G, Medici S, Peana M, Nurchi VM. The essential metals for humans: a brief overview. J Inorg Biochem. 2019 Jun;195:120-129.
- Jomova K, Makova M, Alomar SY, Alwasel SH, Nepovimova E, Kuca K, Rhodes CJ, Valko M. Essential metals in health and disease. Chem Biol Interact. 2022 Nov 1;367:110173. PMC free article
- Lothrop AP, Snider GW, Ruggles EL, Patel AS, Lees WJ, Hondal RJ. Selenium as an electron acceptor during the catalytic mechanism of thioredoxin reductase. Biochemistry. 2014 Feb 4;53(4):654-63.
- Fedenko VS, Landi M, Shemet SA. Metallophenolomics: A Novel Integrated Approach to Study Complexation of Plant Phenolics with Metal/Metalloid Ions. Int J Mol Sci. 2022 Sep 26;23(19):11370. PMC free article
Cuprous niacin 