Chemists devise better way to prepare workhorse molecules

In chemistry, so-called aromatic molecules compose a large and versatile family of chemical compounds that are the stuff of pharmaceuticals, electronic materials and consumer products ranging from sunscreen to plastic soda bottles.

Writing in the current online issue (June 9) of the journal Science, a team led by University of Wisconsin-Madison chemistry Professor Shannon Stahl reports a new, environmentally friendly way to make substituted aromatic molecules that can be customized for different industrial needs.

As college chemistry students know, aromatic molecules have a special stability conferred by a ring of six carbon atoms with alternating single and double bonds. "The ultimate utility of these molecules depends on the chemical groups attached at the corners of this hexagonal platform," explains Stahl. "Interest in preparing substituted aromatic molecules traces back to the dawn of organic chemistry."

In fact, the 2010 Nobel Prize in Chemistry was awarded for catalytic chemical reactions that allow the introduction of specific groups to the periphery of aromatic molecules. These methods, and older traditional methods, rely on modifying an existing aromatic molecule, Stahl explains. But the stability of aromatic molecules can make such approaches difficult, and existing methods also have many limitations in the types and patterns of chemical groups that can be installed.

The method devised by Stahl and Wisconsin colleagues Yusuke Izawa and Doris Pun owes its success to the discovery of a new palladium catalyst. The catalyst gives chemists a way to peel off hydrogen from cyclic molecules to form aromatic products with the desired substitution patterns already in place. The hydrogen removed by the palladium catalyst is combined with oxygen, and water is formed as the only byproduct.

The Wisconsin team demonstrated the utility and efficiency of the new process on phenols, aromatic compounds that are produced on a large scale as precursors to many kinds of industrial materials and pharmaceutical agents. While the new catalytic method can be used to make a broad spectrum of aromatic molecules of interest to science and industry, the new work will be of most immediate practical use to drug companies, according to Stahl. For example, an anticancer agent that was difficult to make using previously known methods was efficiently produced using the strategy devised by the team.

Stahl notes that the work published today in Science will require more development before it is suitable for large-scale industrial production, but he emphasizes that concepts introduced by the new work will have broad utility. "Many new catalysts, reaction conditions and target molecules can be envisioned. Overall, this route to substituted aromatic molecules has a lot of potential," he says.

Provided by University of Wisconsin-Madison (news : web)

Poplar tree leaf bud extract could fight skin aging

Antioxidants are popular anti-aging ingredients in skin creams, and now scientists are reporting a new source of these healthful substances — leaf buds of poplar trees. Their study appears in the ACS' Journal of Agricultural and Food Chemistry.

Xavier Vitrac and colleagues note that there's a long history of using poplar buds to treat various health problems, such as colds, sinusitis, sunburn and arthritis. A substance found in beehives that is made from poplar buds (called propolis) also appears to have similar disease-fighting benefits. Propolis' effects seem to be due to poplar bud compounds, but very little is known about these substances. To see whether poplar buds are a good source of antioxidants for skin creams, the researchers decided to test an extract from the buds.

The group found that poplar bud extract had moderate antioxidant activity, and it demonstrated anti-aging effects on cells in the laboratory. "The collective antioxidant properties and transcriptional effect of this extract suggest potential anti-aging properties which could be utilized in cosmetic and nutraceutical formulations," the scientists say.

More information: “Phenolic Composition and Antioxidant Properties of Poplar Bud (Populus nigra) Extract: Individual Antioxidant Contribution of Phenolics and Transcriptional Effect on Skin Aging” J. Agric. Food Chem., 2011, 59 (9), pp 4527–4536 DOI: 10.1021/jf104791t

Abstract
The Populus species possess great potential for therapeutical applications, especially for their known anti-inflammatory properties. The antioxidant properties of propolis, a hive product collected by honey bees mainly from poplar bud exudates, suggest that poplar buds also possess antioxidant properties. Here is reported the characterization of the antioxidant properties of an aqueous poplar bud (Populus nigra) extract. It presented a high total phenolic content, and moderate antioxidant properties as determined by ORAC assay. The main phenolic compounds identified were phenolic acids and flavonoid aglycons. These phenolic compounds were analyzed by ORAC assay for their individual antioxidant activity, in order to determine the major contributors to the total antioxidant activity of the extract. Thanks to their high antioxidant activity, caffeic and p-coumaric acids were identified as the major antioxidant components. Representing only 3.5% of its dry weight, these compounds represented together about 50% of the total antioxidant activity of the extract. The antioxidant properties of poplar bud extract and the phenolic compounds identified were also analyzed by cellular antioxidant activity assay (CAA), which was weakly correlated with ORAC assay. The transcriptional effect of poplar bud extract on skin aging was evaluated in vitro on a replicative senescence model of normal human dermal fibroblasts, using a customized DNA macroarray specifically designed to investigate skin aging markers. Among the detected genes, poplar bud extract significantly regulated genes involved in antioxidant defenses, inflammatory response and cell renewal. The collective antioxidant properties and transcriptional effect of this extract suggest potential antiaging properties which could be utilized in cosmetic and nutraceutical formulations.

Provided by American Chemical Society (news : web)

Microbe efficiencies could make better fuel cells

Like mutual back-scratching, two common bacteria involved in what was thought to be only a marginally important relationship actually help each other thrive when grown together in bioreactors, Cornell scientists have discovered.

Understanding this symbiotic relationship could lead to, for example, more efficient microbiology-based fuel cells or better methods for preventing such natural processes as rust corrosion.

The research was led by Largus Angenent, associate professor of biological and environmental engineering, and was published online June 2 by Energy and Environmental Science, a publication of the Royal Society of Chemistry.

To study the bacterial interactions, the scientists fed glucose into a bioelectrochemical reactor, which is a reactor in which bacteria on electrodes convert organic material into electricity.

The glucose fed the bacterium Enterobacter aerogenes, which, in turn, produced the product 2,3-butanediol. This became a food source for another bacterium, Pseudomonas aeruginosa.

In the meantime, the researchers discovered, Pseudomonas activity was upregulated, which in turn increased the presence and activity of Enterobacter. The result was a 14-fold increase in the electric current production from Enterobacter and Pseudomonas combined in the bioelectrochemical reactor, than by either microbe by itself.

The fermentation product 2,3-butanediol was the key stimulator for the mutually beneficial interactions between the two bacteria within a closed system bioelectrochemical reactor.

The work could lead to increased efficiency of microbial fuel cells by better understanding of microbial communities. The two bacteria studied also have wide-reaching implications. For example, Pseudomonas is a well-known human pathogen that resides in the lungs. Knowing that this pathogen does better when Enterobacter is present could lead to better therapies or preventative measures against bacterial illnesses, for example.

The paper's first author was graduate student Arvind Venkataraman, who was involved in hypothesis development and designed and conducted the experiments.

Provided by Cornell University (news : web)

How wet is water's surface? Some water molecules split the difference between gas and liquid

 Air and water meet over most of the earth's surface, but exactly where one ends and the other begins turns out to be a surprisingly subtle question.

A new study in Nature narrows the boundary to just one quarter of water molecules in the uppermost layer – those that happen to have one hydrogen atom in water and the other vibrating freely above.

Such molecules straddle gas and liquid phases, according to senior author Alexander Benderskii of the University of Southern California: The free hydrogen behaves like an atom in gas phase, while its twin below acts much like the other atoms that make up "bulk" water.

The finding matters for theoretical reasons and for practical studies of reactions at the water's surface, including the processes that maintain a vital supply of nitrogen, oxygen and carbon dioxide in the atmosphere.

"The air-water interface is about 70 percent of the earth's surface," Benderskii said. "A lot of chemical reactions that are responsible for our atmospheric balance, as well as many processes important in environmental chemistry, happen at the air-water interface."

He added that the study provided a new way for chemists and biologists to study other interfaces, such as the boundary between water and biomembranes that marks the edge of every living cell.

"Water interfaces in general are important," Benderskii said, calling the study "an open door that now we can walk through and broaden the range of our investigations to other, perhaps more complex, acqueous interfaces."

In their study, Benderskii and his colleagues used techniques they invented to test the strength of hydrogen bonds linking water molecules (from the hydrogen of one molecule to the oxygen of another). These are the bonds that keep water a liquid at room temperature.

Specifically, the researchers inferred the bond strength by measuring the hydrogen-oxygen vibration frequency. The bond gets stronger as the frequency decreases, similar to the pull one feels when slowing down a child on a swing.

In the case of straddling molecules with one hydrogen in water, when compared to bonds below the surface, "the hydrogen bond is surprisingly only slightly weaker," according to Benderskii.

Likewise, the bond for the hydrogen atom sticking out of the water is similar in strength to bonds in the gas phase.

The researchers concluded that the change between air and water happens in the space of a single water molecule.

"You recover the bulk phase of water extremely quickly," Benderskii said.

While the transition happens in the uppermost layer of water molecules, the molecules involved change constantly. Even when they rise to the top layer, molecules for the most part are wholly submerged, spending only a quarter of their time straddling air and water.

The study raises the question of how exactly to define the air-water boundary.

If the straddling molecules constitute the boundary, it would be analogous to a wood fence where three of every four boards are missing – except that since water molecules always are moving between submerged and straddling positions, the location of the fourth board would change millions of times per second.

If the boundary were the entire top layer of water molecules, the analogy would be a fence where one in four boards is sticking out at any one time.

Provided by University of Southern California (news : web)