Speciation of the Chromium(III)-Salicylic Acid System Studied in 1.5 mol · dm -3 KCl at 25 °C Alberto Feijo ´o, † Mary Lorena Araujo, † Felipe Brito, † Giuseppe Lubes, ‡ Mildred Rodrı ´guez, ‡ and Vito Lubes* ,‡ Centro de Equilibrios en Solucio ´n, Escuela de Quı ´mica, Facultad de Ciencias, Universidad Central de Venezuela (UCV), Caracas, Venezuela, and Departamento de Quı ´mica, Universidad Simo ´ n Bolı ´var (USB), Apartado 89000, Caracas 1080 A, Venezuela The complex species formed between chromium(III) and salicylic acid (H 2 sal) were studied in aqueous solution by means of electromotive force (emf(H)) measurements at 25 °C and in 1.5 mol · dm -3 KCl as the ionic medium. The complexes were studied by the aging solution method, which consists of the preparation of different ligand/metal molar ratios at different pH values; the solutions were maintained at room temperature [(25 ( 1) °C] for 45 days; then potentiometric measurements were done, and the data were analyzed by means of the least-squares computational program LETAGROP, from which the respective stability constants and the stoichiometric coefficients of the complexes formed in aqueous solution were obtained. The results obtained indicate the formation of Cr(sal) + , Cr(sal)(OH), and Cr(sal)(OH) 2 - . 1. Introduction In 1959 chromium was identified as the active component of the “Glucose Tolerance Factor” (GTF). In fact, the symptoms of glucose intolerance are characterized by high glucose and insulin levels, which are considered as a sign of chromium deficiency. A chromium supplement plays a nutritional role and can prevent or reduce clinical symptoms. Supplements of organic chromium(III) complexes exist that are recommended for use in the treatment of diabetes and in patients with high cholesterol levels. In 1980, the National Research Council and the National Academy of Sciences recommended a (50 to 200) µg daily consumption of chromium(III). 1 The trispicolinatechromium(III) complex, Cr(pic) 3 , is a known bioavailable source of chromium(III), which provides (2 to 5) % of the absorbable bioelement, where the picolinate acts as a Cr(III) transporter. 2,3 However, its safety has recently been questioned, especially with regard to its ability to act as a clastogen. At physiologically relevant concentrations, Cr(pic) 3 is reduced by biological reductants, including ascorbate and thiols, to Cr(II)-containing species. These species are susceptible to air oxidation, resulting in the catalytic generation of the potent DNA-damaging hydroxyl radical. In the absence of reductants, H 2 O 2 can interact with Cr(pic) 3 to produce hydroxyl radicals by a second, less efficient mechanism. Cr(pic) 3 is extremely stable, which allows the complex to be readily absorbed but also to potentially be incorporated into cells intact. In this form, Cr(pic) 3 is primed by its redox potential to enter into reactions leading to the generation of hydroxyl radicals. 4 Salicylic acid (H 2 sal), also known as 2-hydroxybenzoic acid, is a weak organic acid which has two acidic functional groups, a carboxylic acid and a phenol. These two acidic groups are in the ortho position, which is important because depending on the pH this compound can act as a monodentate or bidentate ligand by (COO - ,O - ) coordination. Salicylic acid is known for its ability to ease aches and pains and reduce fevers. These medicinal properties, particularly fever relief, have been known since ancient times, and it has been used as an anti-inflammatory drug. In modern medicine, salicylic acid and its derivatives are used as constituents of some rubefacient products. For example, methyl salicylate is used as a liniment to soothe joint and muscle pain, and choline salicylate is used topically to relieve the pain of aphthous ulcers. As with other -hydroxy acids, salicylic acid is a key ingredient in many skin-care products for the treatment of acne, psoriasis, calluses, corns, keratosis pilaris, and warts. It works as both a keratolytic and comedolytic agent by causing the cells of the epidermis to shed more readily, opening clogged pores, and neutralizing bacteria within, preventing pores from clogging up again by constricting pore diameter, and allowing room for new cell growth. Because of its effect on skin cells, salicylic acid is used in several shampoos used to treat dandruff. Bismuth subsalicylate, a salt of bismuth and salicyclic acid, is the active ingredient in stomach relief aids such as Pepto-Bismol. Bismuth subsalicylate helps control nausea, heartburn, indiges- tion, upset stomach, and diarrhea. It is also a very mild antibiotic. Taking into account all of the salicylic acid properties we decided to investigate the reaction of the complex formation between the chromium(III) ion and the salicylic acid in aqueous solution. Because of the inertness of the chromium(III) ion, 5 complex formation reactions are slow, and options to overcome this problem are either increasing the temperature 6 or aging the solution at a certain temperature. 7 In this paper we report the binary complexes formed between the chromium(III) and the salicylic acid, preparing mixtures of metal and ligand at differents molar ratios and aging the solution at room temperature [(25 ( 1) °C] for 45 days, after which the pH of the solutions were measured. 8 These experiments were done as a contribution to the speciation of the chromium(III) salicylic acid system in aqueous solution. 2. Experimental Section 2.1. Chemicals. The salicylic acid was from Merck (analyti- cal grade) and was used as received. A salicylic acid stock solution was prepared at a 25 mM (mM ) mmol · dm -3 ) concentration, and a 10 mM CrCl 3 stock solution was prepared by dissolution of CrCl 3 · 6H 2 O in 100 mM HCl to prevent the * Corresponding author. E-mail address: lubesv@usb.ve. † Universidad Central de Venezuela. ‡ Universidad Simo ´n Bolı ´var. J. Chem. Eng. Data 2010, 55, 4062–4065 4062 10.1021/je1001889  2010 American Chemical Society Published on Web 06/08/2010