The Personal Care Product Council’s online ingredient dictionary, the wINCI, defines chelating agents or sequestrants1 as “ingredients that complex with and inactivate metallic ions to prevent their adverse effects on the stability or appearance of cosmetic products.”2 Metallic impurities can come from many different sources, primarily from either the ingredients themselves—specifically those that are naturally derived, the water system, or minute extractions from metallic equipment and storage containers. If not deactivated, these metallic ions can deteriorate cosmetic products by reducing clarity, compromising fragrance integrity and causing rancidity/oxidation.
The mechanism for chelation, described as a chelate complex, is based on multiple bonding (polydentate ligand) around a single central atom. Common chelating agents include ethylenediaminetetraacetic acid (EDTA) and its derivatives, etidronic acid and its derivatives, galactaric acid, sodium metasilicate and phosphate derivatives. Disodium EDTA and tetrasodium EDTA are two popular chelators used in the US personal care industry. Chelators are used in almost
Chelators are used in almost every personal care formulation type to increase effectiveness and improve stability, thereby improving consumer acceptance. In addition, they have demonstrated the ability to boost preservative activity. Chelators are used in liquid soap and body wash to prevent fragrance and color degradation and for their synergistic effect with antimicrobials. They are also incorporated into bar soap to prevent rancidity, softening, brown-spotting, cracking and discoloration due to metal ions, as well as to enhance foaming and rinsability.
In creams and lotions, again they are used to prevent rancidity, the discoloration particularly of organic dyes, off-odors and the degradation of active ingredients, in addition to improving the shelf life and efficacy of vitamins, essential oils and fatty acids. In wipes, chelators prevent fragrance degradation and provide preservation protection. In deodorants and antiperspirants, they prevent fragrance degradation and provide antioxidant protection, particularly when formulated with botanical actives and vitamins.
Finally, in shampoos and conditioners, chelators prevent fragrance and color degradation, haze formation and precipitation, and again, they provide a synergistic effect with antimicrobials; in coloring shampoos, they preserve formulation stability in addition to stabilizing tint and color intensity by stabilizing the redox system. Another potential use is for the neutralization of reactive oxygen species (ROS) that are generated by iron or other metal catalysts upon exposure to ultraviolet (UV) radiation, which can induce cutaneous pathologies such as skin cancer, photosensitization and photoaging.3
Key Components of Chelating Agents
When working with chelating agents, the formulator should first determine how the ingredient will function in the formula—as an actual chelator, or as an antioxidant or pH stabilizer. Therefore, it is important to know whether it will be used to prevent discoloration, rancidity/off-odors or to improve shelf stability. In addition, the formulator should consider whether one chelator is better than another for the determined purpose, and if the chelating agent should be added early in the formulation process to prevent any degradation from occurring before it has a chance to optimize the shelf stability of the product.
The oxidizing nature and pH of the formula—not the pH of the chelator—will determine the optimum efficacy of the chelating system since they can affect its stability.4 For each metal complex, there is an optimum pH and an active pH range in which the metal complex is stable. In addition, the quantity of chelating agent required is dependent upon the concentration of the metal ion to be chelated and the type of chelating agent used. Generally, sodium-type EDTA chelating agents form a complex with a metal ion on an equimolecular basis, meaning the higher the molecular weight of the chelating agent, the higher the quantity of chelating agent required to chelate the metal ion. Further, order of addition is important; when added at the appropriate time in the formulation process, the chelating agent can provide long-term stability and even boost antimicrobial activity.5
Featured Ingredient: EDTA
EDTA, shown in Figure 1, is a colorless, water-soluble solid that is considered a poly-aminocarboxylic acid. As a hexadentate ligand, it is able to sequester metal ions such as calcium and iron to diminish their availability. Today, EDTA is mainly synthesized from ethylenediamine (1,2-diaminoethane), formaldehyde and sodium cyanide. This route yields the sodium salt, which can be converted with a subsequent step into the acid form. EDTA can adopt more complex structures due to the formation of an additional bond to water, i.e. seven-coordinate complexes, or the displacement of one carboxylate arm by water.6 This and other chelating agents are listed in the sidebar (see Chelating Agents).
Recent Chelating Agent Patents
Recent patents related to chelating agents include applications for bleaching hair, preservation and fading bruises, which are described here.
Oxidation catalyst for bleaching: This patent describes an oxidation catalyst for bleaching, e.g. keratin of hair, comprised of a chelating agent and/or an anion caused by a chelating agent with ≤ coordination position 5, a copper and/or manganese compound, a binder compound, and a hydrogen peroxide-based compound that dissolves in water and generates hydrogen peroxide. The bleaching composition contains a granulated product or a molded product in which at least the copper/manganese compound and the binder are granulated or molded together.7
According to the invention, an oxidation catalyst and/or bleaching composition containing the oxidation catalyst can be utilized that promotes the oxidation effect of hydrogen peroxide-based compounds with a trace amount of the composition, and that suppresses the decomposition of hydrogen peroxide-based compounds and coloration of the catalyst itself. The inventors also noted disinfecting and sterilizing effects of the catalyst against a wide variety of germs.
Preservative substitute: Disclosed in this patent is a preservative composition incorporating alternative molecular compounds that are suitable for partially or totally replacing conventional preservatives in skin care emulsions and heavy duty hand cleansers.8 The described composition includes 0.01–90.0% w/w fatty acid and/or fatty acid ester, 0.01–60.0% w/w of one or more alcohols, and 0.01–20.0% w/w chelating agent, whereby the chelating agent boosts preservative efficacy.
Composition for fading bruises: In the present patent, a composition for oral or topical administration is disclosed comprising a chelating agent, at least one protease, and Arnica montana extract.9 The topical composition is utilized to reduce the time required for hemosiderin to be removed from bruises, causing them to fade. It also reduces inflammation and pain resulting from surgery or skin injury.
During injury or surgery, the skin experiences a shock that breaks small blood vessels. When blood leaves a ruptured blood vessel, the red blood cells die and the hemoglobin is released from them into the extracellular space. White blood cells called macrophages engulf the hemoglobin to degrade it, producing hemosiderin and porphyrin; it is this hemosiderin accumulated under the skin that causes the black, blue and reddish appearance of a bruise. According to the patent, there is thus a need for an anti-inflammatory, pain-reducing composition and method for the easy removal of hemosiderin to shorten the duration of the bruise.
In one embodiment of the invention, the chelating agent is phytic acid and the protease is bromelain. Phytic acid is a phosphorylated alcohol, also known as inositol hexaphosphate or inositol-1, 2,3,4,5,6,-hexakisphosphate (IP6); it is found in whole grains, soybeans, seeds and nuts.
Recent Commercial Product Launches
It is difficult to choose specific commercial personal care product launches to provide examples of chelating agents because most contain a chelating agent. The first example described here was chosen due to the physiological activity claim of the chelating agents. The second example demonstrates the classical use of chelating agents in surfactant systems.
Dr. Dennis Gross Skincare Powerful Sun Protection SPF 30 Towelettes: These towelettes, pictured in Figure 2, are said to offer anti-aging and ozone protection as well as SPF 30 UVA/UVB broad-spectrum protection. The oil-free formulation, shown in Formula 1, contains antioxidants and a chelating technology to protect against free radicals, and vitamin C and green tea for ozone protection, i.e., smog and environmental damage.
Joico K-Pak Chelating Shampoo: The triple-action chelating shampoo shown in Figure 3 is a clarifying formula that cleanses the hair and removes mineral deposits, chlorine and styling product buildup while moisturizing. Pentasodium penetate is used as the chelating agent to prevent heavy metal impurities from discoloring the formula and to boost the effectiveness of the preservative system and antioxidant ingredients. Otherwise, it is a relatively classic shampoo (see Formula 2). This product is pH neutral.
Formulator Beware
As previously mentioned, chelating agents have a number of properties and performance benefits, so it is important for the formulator to understand why they are being used and to choose the proper chelator for the formulating task. It is easy to take 0.1% disodium EDTA and add it to the aqueous phase, just “to be on the safe side.” While in this author’s opinion there is nothing wrong with this approach, why add more ingredients to a formula than are necessary—especially when consumers are looking at the formula to assess whether all the ingredients in it meet their standards?
As an example, one often sees chelating agents used in antiperspirant products and years ago, they may have been necessary in aqueous systems due to potential metallic contamination in the water or in raw materials. However, this is no longer the case and they therefore are probably unnecessary. If the product meets stability requirements, i.e., produces no odor or color development upon elevated temperature stability, then chelating agents are probably not necessary in the formula.
In general, it is this author’s belief that a small amount of chelating agent, 0.05–0.10%, should be added to the water phase of an emulsion and surfactant-based formulas, especially those containing a fragrance, color or botanical extract. And as formulators learn more about the ability of natural chelators to boost preservation effectiveness or minimize ROS activity on the skin surface, these materials could also be used to provide added benefits to further enhance their salient value in personal care products.
References
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1. AD McNaught and A Wilkinson, IUPAC Compendium of Chemical Terminology—the Gold Book, 2nd ed, Blackwell Scientific Publications, Oxford, UK (1997), https://goldbook.iupac.org/terms/view/C01012 (Accessed Apr 18, 2011)
2. Chelating Agents, wINCI Web-based International Cosmetic Ingredient Dictionary and Handbook, Personal Care Products Council, http://webdictionary.personalcarecouncil.org/jsp/Home.jsp (Accessed Apr 18, 2011)
3. A Juzeniene, P Juzenas, V Iani and J Moan, Topical applications of iron chelators in photosensitization, Photochem Photobiol Sci 6 1268–1274 (2007)
4. Dissolvine, AkzoNobel, http://www.akzonobel.com/dissolvine/products/dissolvine/ (Accessed Apr 18, 2011)
5. JJ Kabara, Cosmetic and Drug Preservation, Cosmetic Science and Technology Series: Principles and Practice, Vol. I, CRC Press: Boca Raton, FL USA (1984)
6. JR Hart, Ethylenediaminetetraacetic acid and related chelating agents, in Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany (2005)
7. US Patent Application 20100267602, Oxidation catalyst for bleaching, and bleaching composition using the same, T Kubozono et al, assigned to Lion Corp. (Oct 21, 2010)
8. US Patent Application 20100041774, Chemical compositions for skin care emulsions and heavy duty hand cleansers, PB Grascha and M Battut (Feb 18, 2010)
9. US Patent Application 20100124549, Composition and method for treatment of bruising, J Studin (May 10, 2010)
