Progress in Organic Coatings 58 (2007) 209–216 Interactions of an antimicrobial peptide (Ac-RRWWRF-NH 2 ) and surfactants: Towards antimicrobial peptide additives for coatings applications Alicyn M. Rhoades a , Douglas A. Wicks a,∗ , Bruhaspathy Miriyala b , John Williamson c a School of Polymers and High Performance Materials, The University of Southern Mississippi, 118 College Drive #10076, Hattiesburg, MS 39406, USA b Fluorous Technologies Inc., 970 William Pitt Way, Pittsburgh, PA 15238, USA c Department of Medicinal Chemistry, The University of Mississippi, School of Pharmacy, 417 Faser Hall, Oxford, MS 38677, USA Received 13 June 2006; accepted 20 September 2006 Abstract Waterborne coatings are complex formulations containing a number of components to aid stabilization and eventual coalescence of the polymer particles. Almost all systems contain a number of small molecule functional additives to improve different aspects of system performance. How the performance of these additives depends on interaction with other components of the formulation is relatively unexplored from a fundamental basis. A specific objective of this study is to provide a foundation for continued development of antimicrobial peptides as active polymer coatings components. This work addresses the impact of formulation variables, specifically surfactant structure, on the behavior of a model antimicrobial. Antimicrobials are used because a number of microbes are able to flourish within the water phase of the latexes resulting in a loss of properties commonly known as ‘spoilage’. The model antimicrobial used in this study is a small oligopeptide (known as Combi1) identified as a powerful antimicrobial and has been extensively studied in the areas of pharmaceutics and medicinal chemistry. Monitoring of antimicrobial strength was done through the use of both conventional microbiology methods and high throughput absorbance and fluorescence measurements. © 2006 Published by Elsevier B.V. Keywords: Coatings; Antimicrobials; Latex; Polyurethane dispersion; Surfactants 1. Introduction One of the least understood aspects of waterborne coatings is the impact of the interaction of the different components of a formulation. Waterborne coating systems are complex mixtures of polymers, pigments and functional additives. The simplest formulations for a latex coating consist of more than a dozen components in addition to the polymeric binder resins. These additives are used to improve different appearance or perfor- mance characteristics of the final coating. Unexpected synergies or undermining of performance may arise when certain compo- nents are included. The performance additives can be broadly grouped into three major types based on what characteristic is being modified— chemical, physical and biological: ∗ Corresponding author. E-mail address: douglas.wicks@yahoo.com (D.A. Wicks). • chemical—antioxidants, UV absorbers, thermal stabilizers; • physical—flow aids, rheology modifiers, de-foamers, disper- sants; • biological—antimicrobials, antifungals, algaecides. The ability of all of these additives to fulfill their roles is greatly impacted by the environment in which they operate. If the additive sees specific chemical or hydrophobic interactions or partitions into a discontinuous phase it may not be available to perform its role. Antimicrobials are one class of additive that is very dependant on what else is in the system formulation. Organic solvents and residual monomer contents of water- based coating systems have been eliminated in modern formulations. As a result, waterborne coating systems have become attractive targets for microbial attack. Microbes pro- duce cellulase and other enzymes that attack components in the wet state, resulting in a loss of system properties commonly recognized as ‘spoilage’ [1]. These cellulase enzymes have a noticeable negative impact at concentrations as low as 10 -5 0300-9440/$ – see front matter © 2006 Published by Elsevier B.V. doi:10.1016/j.porgcoat.2006.09.034