Phase behavior of beta hydroxy-acids with laureth 4

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Abstract

The colloidal structures of beta carboxylic acid topical vesicle formulations were determined and the changes during evaporation after applications were estimated from phase diagrams. The results showed significant difference during evaporation between salicylic acid on one hand and three water soluble acids; malic, tartaric, and citric acid, on the other. The water soluble acids showed an increase in the acid concentration in the aqueous solution to levels that must be considered harmful, while salicylic acid showed no increase in concentration in the individual phases even after 99% evaporation of water.

Section snippets

INTRODUCTION

Beta hydroxyl-acids (BHAs) are carboxylic acids with a hydroxyl group attached to the second (beta) carbon.1 They are weak acids, a group of naturally occurring substances, derived from fruit, also called fruit acids.1., 2., 3. Important members of the group are found in natural foods, such as; Malic acid (apple), Citric acid (citrus fruits), and Tartaric acid (grapes),1,4 they might be also considered as alpha and beta acids because of their structure. They have found only limited application

Materials

The following chemicals were used without further purification, Polyoxyethylene-4-laurylether, Laureth 4(Brij® 30) was from Fluka Company, England. Water was deionized and triple distillated. DL-Malic acid (2-hydroxy butanedioic acid) was from E.Merk, Darmstadt.F.R, Germany. L-Tartaric acid (99.5%) (1,2,3-Dihydroxybutanedioic Acid or (1,2,3 dihyroxysuccininc Acid) was from BDH Chemical Ltd., Poole, England. Citric acid (98%) (2-hydroxy-1, 2, 3 propanetricarboxylic acid) was from Gainland

RESULTS

The results will be introduced in the following order. The diagram of the tartaric acid will be first presented, because the acid is the most hydrophilic of all the compounds. The diagrams of the remaining acids will be given in order of increasing hydrophobicity: malic, citric, and salicylic acid.

The diagram of tartaric acid, Figure 1, has four one-phase areas. Of these only the lamellar liquid crystal and the tartaric acid solid solution show some solubility of more than one component. The

DISCUSSION

As mentioned in the introduction part of this article, its focus is the use of the phase diagrams to estimate the importance of the molecular structure of the β-acids for the conditions encountered after their topical application.

It is easily realized that the action on the skin is not as dependent on the initial structure of the formulation, as on the remains after partial or full evaporation of the water and volatile organic solvents. The evaporation of water is a faster process than

CONCLUSIONS

The research provided a fundamental foundation to the well-known preference for salicylic acid as the choice of beta acids for skin treatment. The salicylic acid with no water solubility did not show any concentration variation in the different phases during evaporation, hence, no change in the chemical potential and no danger of irritation due to concentration changes in the process. This behavior is in stark contrast to the case of the three water soluble acids for which the increase of acid

Acknowledgements

The authors thank; Ms. Mervat Sammor, Ms. Ruba Al-Tawalbeh, Ms. Eveen Al-Shalabbi, Ms. Ayat Bozeya, Mr. Anas Al-Jada, and Dr. Ahmad Al-Ajlouni for their valuable help in this research project.

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