A new designer nanomaterial, created by MIT researchers and described in the April 2 online edition of the Proceedings of the National Academy of Sciences , acts like the main ingredient in soaps, shampoos and detergents.
This biological substance may represent a big improvement over chemicals commonly used in the multibillion dollar detergent industry. The research also may lead to novel carriers for dispensing drugs in the body, and may shed light on protein-to-protein interaction and possibly even the origins of life.
Surfactants are oil-based substances that, when dissolved in liquids, reduce surface tension and allow water to wash away dirt. The researchers have created tiny surfactant-like peptides made of amino acids, the building blocks of proteins.
"We are interested in broadening the diversity of the building blocks of self-assembling peptides for scaffolds and biological materials," wrote authors Shuguang Zhang, associate director of MIT's Center for Biomedical Engineering ; postdoctoral associate Sylvain Vauthey; and biology graduate student Steve Santoso. Authors also include Haiyan Gong at Boston University's School of Medicine and Nicki Watson of the Whitehead Institute .
"It is anticipated that self-assemblies and fine-tuning of the surfactant peptide building blocks will lead to construction of a wide range of nanostructures, fostering innovative avenues for the development of scaffold and biologically inspired materials," said Zhang. "This is another example of basic research that can result in unexpected applications in nanobiotechnology and broad applications, such as high-density scaffolds that incorporate inorganic conducting and nonconducting nanomaterials. They also may be able to encapsulate biological substances such as proteins and DNA, as well as create water-insoluble drugs for delivery to human tissues."
Zhang and other scientists have recently discovered that the 80,000-plus kinds of proteins in our body, when in fragments called peptides, can be tweaked into forming completely new natural materials that may be able to perform a variety of useful functions inside and outside the body.
Peptides can form nonprotein-like structures such as fibers, tubules, sheets and thin layers. They can respond to changes in acidity, mechanical forces, temperature, pressure, electrical and magnetic fields and light. They are stable at temperatures up to 350 C and can be produced up to a ton at a time at affordable cost. They can be programmed to biodegrade, which may be crucial to the environmentally conscious detergent industry. One kind of peptide scaffold has proved to be a good base for regenerating nerve cells.
"The emerging perception is that self-assembling peptides form a new class of materials set to become commercially viable," Zhang said.
Like biological phospholipids, surfactant peptides have a hydrophobic (water-repelling) tail and hydrophilic (water-absorbing) head. The peptides interact with one another to form rings, which in turn stack into tubes.
Each three nanotubes connect with each other, mimicking lipid microtubule structures. But unlike lipids, the lengths and water-repellency of these surfactant-like peptides can be fine-tuned into well-organized, unique structures.
In addition to improving existing cleaning products, these nanostructures may have other chemical engineering uses for materials where traditional surfactants are used. Unlike lipids, it's possible to modify these kinds of molecules so that it is easy for them to directly couple with inorganic nanocrystals, opening up a variety of possible applications in molecular electronics for interfacing organic, biological and inorganic materials.
HOW LIFE BEGAN
Another advantage of studying glycine-based surfactant peptides is that glycine, aspartic acid and alanine are of particular interest to researchers studying early chemical and molecular life forms. These substances were thought to be present in the prebiotic environment of early Earth and in intergalactic dust.
Glycine is the simplest of the 20 naturally occurring amino acids and most likely to be the predominant amino acid several billion years ago. These amino acids or their derivatives can form polypeptides when subjected to repeated hydration-dehydration cycles, mimicking the conditions of early life on the planet. These simple biochemical building blocks could produce complex life forms over eons of natural selection and evolution.
If peptides consisting of any combination of these amino acids can self-assemble into nanotubes or vesicles, they would have the potential to provide a primitive enclosure for the earliest RNA-based or peptide enzymes. This would facilitate prebiotic molecular evolution by sequestering the rudimentary enzymes in an enclosed or semi-isolated environment.
This work is supported in part by grants from the United States Army Research Office , the Defense Advanced Research Project Agency/Naval Research Laboratories and the National Institutes of Health .
A version of this article appeared in MIT Tech Talk on April 3, 2002.