Neutrons answer shampoo formulation puzzle

A research team at the Institut Laue-Langevin, the flagship centre for neutron science, has demonstrated quantitatively the science behind an anomaly in the surface tension of polyelectrolyte/surfactant mixtures. Their findings show that the dramatic increase in surface tension that affects the production of various pharmaceutical and cosmetic formulations is caused by the comprehensive aggregation of active ingredients. They have outlined a way to reload interfaces with functional components simply by tuning the way the materials are handled.

Surface tension is a property of liquids resulting from the cohesion of their molecules that helps them resist an external force. It is responsible for the shape of liquid droplets and the reason why insects can run on the surface of ponds.

Surfactants are substances that lower the surface tension of a liquid and can capture other substances, such as oil or grease in cleaning products. They are often combined with polyelectrolytes, made of long charged molecules, to improve the efficiency of detergents, wetting agents, emulsifiers, foaming agents, and dispersants in paints, shampoos and conditioners, and are used throughout the food industry. Also, the strong attractive interactions of surfactants with natural polyelectrolytes, such as proteins or DNA, play an important role in many biological processes, as well as in medical applications, such as drug and gene delivery.

The commercial production and performance of polyelectrolyte/surfactant mixtures, however, is affected by a peculiar phenomenon, first investigated in depth a decade ago. Whilst adding a surfactant to a polyelectrolyte solution initially causes the surface tension to decrease, as further surfactant is added the surface tension dramatically increases again. This feature, known as a ‘cliff edge peak’, is accompanied by a change in the appearance of the mixture, with the eventual loss of the cloudiness that is present as soon as the materials first interact.

From an industrial production point of view, this rise in surface tension reduces the performance of the additive, often requiring the introduction of further surfactant at extra cost. As a result, there is a lot of interest in understanding the interactions between these mixtures at the atomic level both in solutions and at surfaces. Of particular interest are the primary causes of the cliff edge peak and ways to prevent, lessen or delay its effects that could lead to more efficient formulations and reduce the effects of many pollutants in our environment.

To investigate this problem, Dr Richard Campbell (Institut Laue-Langevin), Dr Imre Varga (Eötvös-Loránd University, Hungary) and their co-workers looked at a system studied widely in the literature – an oppositely charged poly (diallyldimethylammonium chloride)/sodium dodecyl sulfate (Pdadmac/SDS) system.

The international research team, which also includes members from the UK and Sweden, used neutron reflectometry, a reflection technique used for measuring the composition and structure of thin films, to monitor the surface properties with respect to the slow generation of the cliff edge peak. The instrument used was the brand new FIGARO reflectometer (Fluid Interfaces Grazing Angles ReflectOmeter) at the Institut Laue-Langevin, which was constructed during the Institute’s innovative Millennium Programme. The researchers showed quantitatively for the first time that this striking feature in the surface tension results from the slow precipitation of particles into sediment from the aqueous solution. The precipitation depletes the solution and consequently the surface of its active ingredients, and also accounts for the loss of cloudiness observed.

As well as uncovering the reasons behind the rise in surface tension, the team were also keen to investigate methods to prevent its impact, which could directly benefit commercial applications. In the literature, researchers have suggested that the way these mixtures are handled could affect the nature of the material in the solution - a phenomenon called “non-equilibrium effects”.

To test whether the re-dispersion of surface-active material could actually switch off the cliff edge peak effect, the team carefully agitated a series of mixtures after the settling process had finished. A small mechanical stress provided just enough energy to re-disperse some of the sedimented particles and re-supplied the air/liquid interface with enough material to lower the surface tension once again.

“By approaching the problem in a different way, we have shown that the way you handle polyelectrolyte/surfactant systems can produce a variety of tuneable surface properties,” says Dr. Richard Campbell. “We hope that our findings will allow future industrial chemists across the pharmaceutical, detergency and cosmetic industries to generate better product output from their raw materials by learning to handle them in a smarter way, and create optimum surface properties on demand, rather than simply buying in more material to improve performance.”

There is hope also that this work can lead on to novel drug or gene delivery applications where one could apply an external stimulus to a stable biomacromolecule system in order to trigger the delivery of proteins or DNA to a given target.

More information: Re.:J. Phys. Chem. B, Article ASAP, DOI: 10.1021/jp2088803

Provided by Institut Laue-Langevin

Researchers use neutrons to spy on the elusive hydronium ion

A Los Alamos National Laboratory research team has harnessed neutrons to view for the first time the critical role that an elusive molecule plays in certain biological reactions. The effort could aid in treatment of peptic ulcers or acid reflux disease, or allow for more efficient conversion of woody waste into transportation fuels.

In a paper appearing this week in Angewandte Chemie International Edition, Los Alamos researchers join an international team in describing the role played by the elusive hydronium ion in the transfer of protons during enzyme-catalyzed reactions.

Prior to this research, no one has ever directly witnessed the role of the hydronium ion, a water molecule bound to an additional hydrogen ion, in macromolecular catalysts—the catalytic mechanisms of enzymes.

Researchers took an interest in an enzyme that has the potential to allow conversion of sugars in woody biomass into alcohol, a potential alternative fuel, because the enzyme loses its effectiveness when the pH value of the milieu is lowered—a common occurrence in the interior of industrial yeast cells fermenting alcohol. As it turns out, this biochemical reaction also has ramifications for the activation of proton pumps in the stomach, which produces excess acid in those afflicted by gastric diseases.

The scientists sought to figure out the mechanism behind these reactions. Neutrons from the Los Alamos Neutron Science Center provided a possible tool for unveiling the secret agent at the heart of the chemistry.

Hydronium ions had not been seen before by researchers who attempted to use X-rays to understand the chemical mechanism of enzymes. This is because tiny hydrogen atoms are essentially invisible under X-rays. To help make things visible, the researchers substituted hydrogen in their enzyme samples with deuterium, an isotope of hydrogen that behaves chemically identical to its nonisotopic counterpart. Deuterium yields a clear signal when bombarded with neutrons. Therefore, neutrons provided a perfect method for uncloaking the elusive hydronium ions, which appeared as a pyramid-shaped mass in the enzyme's active site where the chemical reaction occurs.

The researchers discovered a crucial change as the system they were studying fell into the acidic range of the pH scale (below 6). The hydronium ion that could be seen facilitating the binding of a metal ion cofactor crucial to the conversion of the sugar molecule into its fermentable form suddenly became dehydrated—think of water, H2O, being removed from hydronium, H3O+. The space occupied by the relatively large hydronium ion collapsed into a tiny volume occupied by the remaining proton (a positively charged hydrogen ion, H+). This spatial change in the molecular structure prevented the sugar from being attacked by the enzyme.

The observed phenomenon provided an answer about why pH plays such an important role in the process and renders the enzyme inactive under acidic conditions. More important, it definitively illustrated that the hydronium ion plays a key role in the transport of protons in these types of biochemical systems.

"This is something that has never been seen before," said Los Alamos researcher Andrey Kovalevsky, principal author of the paper. "This proves that hydronium is the active chemical agent in our studies of the catalytic mechanism of enzymes."

The research has broad implications for the possible role of hydronium ions in other biological systems. In addition to acid reflux disease, the research may help provide a better understanding of metabolic transfer of energy in living cells or living organisms.

More information: Angewandte Chemie International Edition Volume 50, Issue 33, pages 7520–7523, August 8, 2011 DOI: 10.1002/anie.201101753

Provided by DOE/Los Alamos National Laboratory

Researchers use neutrons to spy on the elusive hydronium ion: Unprecedented proof of ion's role in enzymatic process

A Los Alamos National Laboratory research team has harnessed neutrons to view for the first time the critical role that an elusive molecule plays in certain biological reactions. The effort could aid in treatment of peptic ulcers or acid reflux disease, or allow for more efficient conversion of woody waste into transportation fuels.

In a paper appearing in Angewandte Chemie International Edition, Los Alamos researchers join an international team in describing the role played by the elusive hydronium ion in the transfer of protons during enzyme-catalyzed reactions.

Prior to this research, no one has ever directly witnessed the role of the hydronium ion, a water molecule bound to an additional hydrogen ion, in macromolecular catalysts -- the catalytic mechanisms of enzymes.

Researchers took an interest in an enzyme that has the potential to allow conversion of sugars in woody biomass into alcohol, a potential alternative fuel, because the enzyme loses its effectiveness when the pH value of the milieu is lowered -- a common occurrence in the interior of industrial yeast cells fermenting alcohol. As it turns out, this biochemical reaction also has ramifications for the activation of proton pumps in the stomach, which produces excess acid in those afflicted by gastric diseases.

The scientists sought to figure out the mechanism behind these reactions. Neutrons from the Los Alamos Neutron Science Center provided a possible tool for unveiling the secret agent at the heart of the chemistry.

Hydronium ions had not been seen before by researchers who attempted to use X-rays to understand the chemical mechanism of enzymes. This is because tiny hydrogen atoms are essentially invisible under X-rays. To help make things visible, the researchers substituted hydrogen in their enzyme samples with deuterium, an isotope of hydrogen that behaves chemically identical to its nonisotopic counterpart. Deuterium yields a clear signal when bombarded with neutrons. Therefore, neutrons provided a perfect method for uncloaking the elusive hydronium ions, which appeared as a pyramid-shaped mass in the enzyme's active site where the chemical reaction occurs.

The researchers discovered a crucial change as the system they were studying fell into the acidic range of the pH scale (below 6). The hydronium ion that could be seen facilitating the binding of a metal ion cofactor crucial to the conversion of the sugar molecule into its fermentable form suddenly became dehydrated -- think of water, H2O, being removed from hydronium, H3O+. The space occupied by the relatively large hydronium ion collapsed into a tiny volume occupied by the remaining proton (a positively charged hydrogen ion, H+). This spatial change in the molecular structure prevented the sugar from being attacked by the enzyme.

The observed phenomenon provided an answer about why pH plays such an important role in the process and renders the enzyme inactive under acidic conditions. More important, it definitively illustrated that the hydronium ion plays a key role in the transport of protons in these types of biochemical systems.

"This is something that has never been seen before," said Los Alamos researcher Andrey Kovalevsky, principal author of the paper. "This proves that hydronium is the active chemical agent in our studies of the catalytic mechanism of enzymes."

The research has broad implications for the possible role of hydronium ions in other biological systems. In addition to acid reflux disease, the research may help provide a better understanding of metabolic transfer of energy in living cells or living organisms.

Other members of the Los Alamos research team include Suzanne Fisher, Marat Mustyakimov, Thomas Yoshida, and Paul Langan (currently at Oak Ridge National Laboratory).

Other institutions involved in the effort are the University of Toledo, Ohio; the Institut Laue Langevin, Grenoble, France; Keele University, Staffordshire, England; and the ISIS facility Oxfordshire, England.

Los Alamos funding for the research came, in part, from the Laboratory's Directed Research and Development Program (LDRD) and the U.S. Department of Energy's Office of Biological and Environmental Research (DOE-OBER). Funding was also provided through the National Institutes of Health.

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by DOE/Los Alamos National Laboratory.

Journal Reference:

Andrey Y. Kovalevsky, B. L. Hanson, S. A. Mason, T. Yoshida, S. Z. Fisher, M. Mustyakimov, V. T. Forsyth, M. P. Blakeley, D. A. Keen, Paul Langan. Identification of the Elusive Hydronium Ion Exchanging Roles with a Proton in an Enzyme at Lower pH Values. Angewandte Chemie International Edition, 2011; 50 (33): 7520 DOI: 10.1002/anie.201101753