Detergents, Eye Rinses, and Other Products with an On/Off Switch

Newswise — Researchers in Australia have developed a "switchable" detergent with a wide range of potential applications — from a laundry detergent that hardly needs a rinse cycle to a non-irritating eye rinse to increasing the amount of oil that companies can extract from a well.

The unusual product, described here today at the 234th national meeting of the American Chemical Society, is a biological detergent or surfactant, called a Pepfactant ® because it is made from peptides, the building blocks of proteins.

"One of the possible applications that we are aware of is a surfactant that would switch between the wash cycle and rinse cycle during clothes washing, which would mean you could remove visible suds without having to use as large a quantity of water," said biochemist Annette Dexter, Ph.D., of the Australian Institute for Bioengineering and Nanotechnology at The University of Queensland. Dexter is a co-inventor of pepfactants, along with Queensland colleague Anton Middelberg, a chemical engineer.

The unique aspect of the pepfactant is that it can be "switched on" or "switched off" depending on its intended application. For example, in laundry detergents there is a built-in pH change that occurs between the wash and rinse cycles. Pepfactants that are designed to respond to that pH change could be added to the detergent to reduce the rinse time, Dexter noted.

During the wash cycle, the pepfactant would be in the "on" position, allowing the detergent to clean soiled clothes. During the rinse cycle when the pH changes, the pepfactant switches "off," allowing the suds to be removed with much less water than conventional detergents. Similarly, the pepfactants can be used to help separate oil from water and increase the number of barrels of oil that can be extracted from a well. "Currently, as little as one-third of the oil present underground is actually extracted from a well," Dexter said.

Compared to conventional surfactants, which cost about $10 per kilogram (2.2 pounds), biologically synthesized pepfactants are expensive, according to Dexter, about $500 per kilogram. But, she added, "We are trying to bring that down by an order of magnitude."

Despite the cost, the enormous potential that pepfactants offer has prompted inquiries from industry. There has been some commercial interest from detergent manufacturers, Dexter said, but she feels the more near-term application could be in the personal care area such as a shampoo, conditioner, skin cream or hand wash. There also could be potential applications for eye drops, she added.

"Chemical surfactants generally are very irritating to biological tissue. We could use our peptide surfactants in that context because they are extremely mild, so they could be used directly as a cleaning application."

"They also could be used in drug delivery," Dexter said. "Some companies have products in clinical trials that could deliver antibiotics to the eye, which are not water soluble. They are delivering those as an emulsion. So there's something we could do with pepfactants, with the additional angle that we could then have that emulsion respond to the pH of the eye so that it would spread across the eye and not be washed away by the tears."

The potential applications of pepfactants are so broad that it's difficult to say which application might be the first to reach the market, according to Dexter. There has been some commercial interest, she said, and hopes that something in the personal care area might be available within the next 18 months.

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The paper on this research, COLL 384, will be presented at 3:25 p.m., Tuesday, Aug. 21, at the Boston Convention & Exhibition Center, Room 153B, during the symposium, "Surfactants and Polymers for Personal, Home and Health Care."

Annette F. Dexter, Ph.D., is a researcher with the Interfacial Bioengineering Group at the Centre for Biomolecular Engineering, Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, St. Lucia, Australia.

Professor Anton P.J. Middelberg is an ARC Federation Fellow and Professor of Chemical and Biomolecular Engineering at the Centre for Biomolecular Engineering, Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, St. Lucia, Australia.

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ALL PAPERS ARE EMBARGOED UNTIL DATE AND TIME OF PRESENTATION, UNLESS OTHERWISE NOTED

The paper on this research, COLL 384, will be presented at 3:25 PM, Tuesday, 21 August 2007, during the symposium, "Surfactants and Polymers for Personal, Home and Health Care."

COLL 384Mixed systems based on a designed surfactant peptide

Program Selection: Division of Colloid & Surface ChemistryTopic Selection: Surfactants and Polymers for Personal, Home and Health Care: Surfactants and their Interactions with Membranes

Abstract

We have recently developed a novel class of surfactant peptides based on an amphipathic helical motif. The peptides form a mechanically strong, non-covalently cross-linked film at fluid interfaces. The film can be switched by changing the bulk solution composition, leading to rapid collapse of peptide-containing foams or emulsions. We here report mixed colloids based on a designed peptide surfactant in combination with conventional polymers and surfactants. The 21-residue cationic peptide was combined with an anionic polyelectrolyte (Eudragit S-100) or an anionic surfactant (sodium dodecyl sulfate) to give novel stimuli-responsive colloidal complexes. The stability of the colloidal complexes can be modified by reversible cross-linking with transition metal ions, leading to changes in foamability. Self-assembly of the mixed complexes has been studied in bulk solution and at the air-water interface using light scattering, neutron reflectometry, dynamic interfacial tension and two-dimensional mechanical testing.

Researcher Provided Non-Technical Summary

Briefly explain in lay language what you have done, why it is significant and what are its implications (particularly to the general public)

We have developed new biological detergents, termed Pepfactants®, that can be "switched on" or "switched off" by adding simple chemicals to water. Switching off the Pepfactants® allows oil to be quickly separated from water, or suds to be removed without rinsing. Pepfactants® are made up of protein components, and do not need to be prepared from petrochemicals, unlike most detergents. They are expected to have low human toxicity and high environmental biodegradability.

Using Pepfactants® in practical applications requires a knowledge of their interactions with other detergents and polymers of the kind used for cleaning, conditioning, and other everyday uses. We have shown that mixing small amounts of Pepfactants® with another detergent or polymer allow the switching properties of the Pepfactants® to be transferred to the whole mixture, giving products with new properties, such as the production of a stable or unstable foam depending on conditions.

How new is this work and how does it differ from that of others who may be doing similar research?

Pepfactants® are a completely new and unique class of detergents, which act by forming a solid-like "skin" around oil droplets or gas bubbles. The skin can then be dissolved away by adding a simple chemical to a water solution. No other class of detergents is switched using this mechanism, and no other class of detergent can be used to achieve rapid and complete separation of oil/water or gas/water mixtures the way Pepfactants® have been shown to do.