Sunday, June 12, 2011

Microcantilevers are masters of measurement

Devices that look like tiny diving boards are a launching platform for research that could improve detergents and advance understanding of disease.

Rice University researcher Sibani Lisa Biswal and Kai-Wei Liu, a graduate student in Biswal's lab who recently earned her doctorate at Rice, used microcantilevers as ultrasensitive measuring devices to study how lipid bilayers interact with surfactants.

Their results were reported online this month in the American Chemical Society journal Analytical Chemistry.

Lipid bilayers are membranes that surround the cells of every . Along with specific , they act as gatekeepers that allow ions, proteins and other essential to pass into the cell. Individual lipid molecules in the bilayer have a hydrophilic head and two hydrophobic tails. They naturally aggregate into two-layered sheets, with the heads pointed out and the water-avoiding tails pointed inward.

Liu and Biswal, an assistant professor in chemical and biomolecular engineering, described in a previous paper how to attach lipid bilayers to microcantilevers, which have traditionally been used as analytical . A protective coating on the thin gold layer makes the top of the "diving board" inert, so the membranes attach themselves to and spread out over the bottom. The exchange of energy as the meets the solid platform changes the surface tension and bends the cantilever enough to be measured by a laser sensor. Any change to the membrane will alter the bend, which can be measured with nanometer resolution, Biswal said.

In the new work, the researchers introduced varying concentrations of lysolipids to the supported lipid bilayers. Lysolipids are surfactants, compounds that lower the surface tension of liquids and can act as detergents, among other things. Like the molecules that make up lipid bilayers, lysolipid molecules have a hydrophilic head but only one hydrophobic tail.

Liu and Biswal found that in low concentrations, lysolipid molecules wedged themselves into the bilayer as their water-hating tails cozied up to the membrane's hydrophobic inner ring; this changed the on the cantilever.

All of these forces can be measured, Biswal said. "The cantilever naturally wants to bend with whatever force the membrane puts on it," she said.

In high concentrations, lysolipid monomers form micelles, rings of molecules that interact with the membranes and disrupt the hydrophobic interactions that keep them together.

Depending on their strength (determined by the chemical makeup of their hydrophobic tails), the micelles can either weaken the membranes by pulling away or destroy the membranes completely.

That is precisely what you want a detergent to do to a stain, and the new technique would be very useful for fine-tuning cleaning agents, Biswal said.

"A vast amount of research has gone into detergency," she said. "There are a lot of detergencies based on enzymes, the biomolecules that cleave peptide bonds. A lot of stains are organic molecules. If you can cleave them, you can clean surfaces much better."

Biswal sees other potential for the technique. "We're interested in using this as a general platform for looking at small molecules," she said.

Liu is pursuing one such path. She is studying how hepatitis C peptides behave in the presence of a microcantilever-mounted membrane. "This could be a way to probe how viruses are able to enter cell membranes or disrupt proteins on their surfaces," she said.

Biswal suggested that carbon-60 atoms -- the buckyballs discovered at Rice in 1985 -- might also be a good subject. "We don't know enough about how nanomaterials interact with cell membranes, and since buckyballs are naturally hydrophobic, they might be interesting to investigate."

Provided by Rice University (news : web)

Chemists shed light on sun's role mixing up molecules

University of Sydney scientists have discovered a startling new mechanism where sunlight can rearrange the atoms of molecules to form new chemical substances.

The research, by Professor Scott Kable, Dr. Meredith Jordan and collaborators at the School of Chemistry, is published in a recent issue of Nature Chemistry. It has implications for the extent that pollutants are dispersed across the Earth's surface, and how quickly they are removed.

Until now, chemical models of the atmosphere assumed a molecule emitted into the atmosphere stays fixed as that molecule, until it is either photolysed (broken up) by sunlight, or attacked by other molecules.

Professor Kable and Dr. Jordan have now overturned this theory using a common, small pollutant molecule, , in a lab-based experiment that substituted a for the sun.

"We chose a special variant of the acetaldehyde compound, where three of the four were replaced with 'heavy hydrogen' (called deuterium)," Professor Kable explains.

"While not changing any of the chemical or photochemical properties to any significant extent, this subtle chemical change did allow us to follow the photochemical reactions with much more detail."

Professor Kable says conventional atmospheric models predicted that acetaldehyde should simply break in half when it absorbs light.

"Our experiments showed that the atoms in the molecules were instead extensively scrambling - specifically the hydrogen and deuterium atoms were scrambling - before the acetaldehyde broke apart."

Acetaldehyde is converted into various other during the scrambling process. The most important of these is an alcohol (vinyl alcohol) which has very different photochemical properties to acetaldehyde and is removed from the atmosphere by different processes.

"Our research shows that compounds such as acetaldehyde, when emitted to the atmosphere, will transform into other substances before the sun has a chance to destroy them," Professor Kable says.

"If are being transformed by sunlight, then the chemistry of the atmosphere is much more complicated than we have considered up until now."

Although this work changes scientific understanding of how pollutants are dispersed through the atmosphere, Professor Kable is careful to note it won't change global warming models. "Nearly all carbon-based compounds in the atmosphere end up as CO2 eventually. It won't change models of CO2 loading in the atmosphere," he says.

More information: The article 'Near-threshold H/D exchange in CD3CHO photodissociation', by Meredith Jordan and Scott H Kable et al, is published in Nature Chemistry, 23 May 2011.

Provided by University of Sydney

A honey of a natural sunblock for UV-protective clothing: Honeysuckle extract

With those months of blazing summer sunshine head, scientists are reporting that an extract of the honeysuckle plant could make a highly-effective natural coating for clothing designed to protect people from exposure to potentially harmful ultraviolet (UV) rays from the sun. Their report appears in ACS' journal Industrial & Engineering Chemistry Research.

Ren-Cheng Tang and Sha-Sha Sun note the growing trend among consumers -- concerned about the risk of skin cancer and premature aging of the skin — toward relying on for protection from the sun ultra-violet rays. Natural UV-protection coatings can have advantages, including production in a more sustainable fashion with less environmental impact. They note that honeysuckle has been used for centuries in traditional Chinese medicine to treat colds and fever. An ingredient in honeysuckle is used to preserve food and as additive in cosmetics to keep the skin looking younger. In their new study, the scientists wanted to see whether honeysuckle extract could boost wool's ability to block UV rays.

They found that wool coated with honeysuckle extract blocked UV rays much more effectively than untreated wool, giving the fabric a high UV protection factor. The extract was durable and remained active on wool, even after a long exposure to sunlight and laundering. The researchers conclude that honeysuckle extract shows significant potential as a natural UV-blocking agent for clothing.

More information: “Adsorption and UV Protection Properties of the Extract from Honeysuckle onto Wool”, Ind. Eng. Chem. Res., 2011, 50 (8), pp 4217–4224. DOI: 10.1021/ie101505q

The adsorption and UV-protection properties of water-extract from honeysuckle whose main ingredient is chlorogenic acid onto wool were studied. The effect of initial pH on the adsorption was investigated, and the extent of adsorption was found to increase with decreasing pH in the range 2-7. Four kinetic equations, namely pseudo-first-order, pseudo-second-order, Elvoich, and intraparticle diffusion equations were employed to investigate the adsorption rates. The pseudo-second-order model provided the best fit to the experimental data and was indicated with the activation energy of 47.91 kJ mol-1. The equilibrium adsorption data were fitted by Freundlich, Langmuir, Redlich-Peterson, and Langmuir-Nernst isotherm models. The adsorption behavior accorded with Redlich-Peterson and Langmuir-Nernst models well. The honeysuckle extract showed good build-up properties, and the UV transmittance in the range of UVA and UVB of wool treated with honeysuckle extract decreased obviously while the ultraviolet protection factors increased. The extract of honeysuckle may be developed as a natural UV-absorbing agent applied to wool finishing.

Provided by American Chemical Society (news : web)

Blueberry's effects on cholesterol examined in lab animal study

Laboratory hamsters that were fed rations spiked with blueberry peels and other blueberry-juice-processing leftovers had better cholesterol health than hamsters whose rations weren't enhanced with blueberries. That's according to a study led by U.S. Department of Agriculture (USDA) chemist Wallace H. Yokoyama.

Yokoyama pointed out that further research is needed to confirm whether the effects observed in hold true for humans. He works at the Western Regional Research Center operated in Albany Calif., by the Agricultural Research Service (ARS), the principal scientific research agency of USDA.

In the investigation, hamsters were fed high-fat rations. For some animals, those rations were supplemented with one of three different kinds of juice byproducts: blueberry skins-that is, peels leftover when berries are pressed to make juice; fiber extracted from the peels; or known as polyphenols, also extracted from the peels. Blueberry polyphenols give the fruit its purple, blue, and red coloration.

In an article published in the in 2010, Yokoyama and his coinvestigators reported that all the hamsters that were fed blueberry-enhanced rations had from 22 to 27 percent lower total than hamsters fed rations that didn't contain blueberry juice byproducts.

Levels of VLDL (very low density lipoprotein-a form of "bad" cholesterol) were about 44 percent lower in the blueberry-fed hamsters.

Yokoyama and his coinvestigators used a procedure known as real-time reverse transcription , or RT-PCR, to learn about the genes responsible for these effects. This approach allowed the scientists to pinpoint differences in the level of activity of certain liver genes.

In hamsters-and in humans-the liver both makes cholesterol and helps get rid of excessive levels of it. Results suggest that activity of some liver genes that either produce or use cholesterol resulted in the lower blood cholesterol levels.

The study is apparently the first published account of cholesterol-lowering effects in laboratory hamsters fed blueberry peels or fiber or polyphenols extracted from those peels.

Of course, some pieces of the cholesterol puzzle are not yet in place. For example, the researchers don't know which berry compound or compounds activated the liver genes, or which parts of the berry have the highest levels of these compounds.

More information: More details about this study are available in the May/June 2011 issue of Agricultural Research magazine: http://www.ars.usd … ruit0511.htm

Provided by United States Department of Agriculture