Lifecycle of the Antibacterial Triclosan

Abstract

With the rise of liquid soaps, and consumers becoming more environmentally conscious
manufacturers have two duties of care; one being to ensure adequate bug inhibition and the other
to ensure that an excessive burden is not placed on the environment by any benefit agent.[1,2]
Recently there have been concerns about the excessive use of certain benefit agents.[3]
It is key to
deliver the right amount of Triclosan (TC) to the right place at the right time so that at least the Minimum
Inhibitory Concentration is delivered but not to over deliver which causes waste. The antibacterial
TC has been studied as a model active ingredient in surfactant systems and on its own to contribute
to the understanding of the lifecycle of active ingredients when used in soap formulations.
The effect of TC in sodium dodecyl sulphate (SDS) and sodium laurate (SL) systems has been
investigated using a range of physical chemistry techniques including UV-Vis and NMR to determine
the increased solubility of TC in surfactant micelles. The effect of TC on the size and shape of SDS
micelles has been examined using small angle neutron scattering. The surface tension of TC/
surfactant mixtures was studied to find the effects of TC on the critical micelle concentration (CMC)
of the surfactant solutions: TC decreases the CMC of SDS and the effect is pH dependant.
The partitioning of the poorly water soluble TC is dependent on pH as well as the concentration of
surfactant. It is important to understand the partitioning in these soap system to understand factors
such as bioavailability and deposition. I have proposed a model for partitioning between free TC and
TC in micelles, and between anionic and neutral forms based on an NMR study. The phenol form of
TC partitions much more strongly into micelles than the phenolate: when there is 1% SDS, there is
700 times more phenol in the micelles than in the bulk, whereas the proportion of phenolate in bulk
and micelles is nearly the same.
The partitioning of TC into supported lipid bilayers as models for cell membranes has been
investigated by Total Internal Reflection Raman spectroscopy. In these experiments, TC was inserted
into the bilayer at high pH and rinsed with low pH buffer. In these conditions TC is very resistant to
rinsing from the bilayer. When bilayers with mixtures of lipids close to those found in bacterial cells
were treated with TC, the bilayers were removed from the surface.
The work described in this thesis has contributed to the investigation of surfactant systems in
combination with TC and can be applied to other active ingredients in similar formulations as part of
product development. I have investigated the state of the active ingredient TC in surfactant
formulations through dilution and to delivery to one of the sites of action using appropriate physical
chemistry techniques for each stage of the investigation.

(1) FDA. Safety and Effectiveness of Consumer Antiseptics; Topical Antimicrobial Drug Products
for Over-the-Counter Human Use; Proposed Amendment of the Tentative Final Monograph;
Reopening of Administrative Record
https://www.federalregister.gov/articles/2013/12/17/2013-29814/safety-and-effectivenessof-consumer-antiseptics-topical-antimicrobial-drug-products-for
(accessed Dec 17, 2013).
(2) Unilever Sustainability Plan; 2012.
(3) Shaw, C. House Passes Triclosan Retail Ban
http://www.house.leg.state.mn.us/SessionDaily/SDView.aspx?StoryID=5284 (accessed Sep
15, 2014).