Monday, July 25, 2011

From oil spill to toxic waste: The polymer solution

 Last October, a containment dam belonging to a Hungarian alumina manufacturer collapsed after heavy rains, releasing 200 million gallons of caustic sludge. Eight people died in the flood of lye-like red mud, which overwhelmed nearby towns and created an environmental catastrophe.

In the aftermath, authorities followed standard practice, neutralizing the with acetic acid. Gerard Caneba, a professor of chemical engineering at Michigan Technological University, believes an unlikely chemical may work even better--and might transform into a valuable raw material.

Vinyl acetate polymers that are being developed in Caneba's lab have a near-neutral pH when they are dissolved in water, but something intriguing happens if you mix the solution in an alkaline substance like red mud, which has as high as 13. "When you put it in a base environment, poly(vinyl acetate) converts to poly(vinyl alcohol), and it also kicks out acetic acid within a minute," he said.

Thus, while it is neutralizing the red mud, the poly(vinyl acetate) is also creating a valuable product. A resulting solid material has potential uses in landscaping, insulation and construction. "We did tests and got really nice performance values on simulated alumina tailings," Caneba said. And there's no shortage of potential sites: "They have about 20 repositories in Hungary and could use this method to clean up any contaminated places. Other sources are found in Texas and Louisiana and wherever aluminum is being manufactured from bauxite ore."

This puts a smile on his face. "I like this mechanism," he says. "We're not just cleaning the stuff up with acetic acid. We can neutralize and turn it into something benign and useful."

Caneba has been working with the Hungarian Academy of Sciences to further test the process. Promising preliminary results are included in his new book, which details his research on vinyl acetate polymer solutions. He is also working with mining giant Rio Tinto, which is providing him with actual red mud samples.

Caneba is also developing next-generation chemicals from vinyl acetate polymers that could be used to clean up oil spills and disperse spilled oil. With researchers from Gulf Coast universities, he has been working to obtain funds to investigate this family of polymer surfactants.

In particular, the new surfactants could address deep oil plumes like those from last summer's disastrous spill in the Gulf of Mexico. Deep underwater, these eruptions of hot petroleum exploding from beneath the earth are quickly compressed and chilled in the ocean depths. "It's no surprise that you can have lingering plumes, and that they are particularly difficult to break up," said Caneba. "We think our formula will be able to help break down the oil better, so microbes can eat it up."

Lab tests have been promising, yielding emulsions that look "like cream," he said. The surfactants are also relatively benign from an environmental standpoint, which could give them an advantage over present-day oil dispersants.

"We're all really excited about this," said Caneba. Lab work to develop the vinyl acetate-based dispersants will probably begin this fall. And hopefully, those tests will yield new tools for cleaning up and remediating the next big oil spill.

Provided by Michigan Technological University (news : web)

PSA test for men could get a second life for breast cancer in women

The widely known PSA blood test for prostate cancer in men may get a second life as a much-needed new test for breast cancer, the most common form of cancer in women worldwide, scientists are reporting in a new study in the ACS journal Analytical Chemistry.

Chien Chou and colleagues say that the prostate-specific antigen (PSA) measured in the test also is a potential biomarker of breast cancer in women. However, levels of PSA in healthy women are usually so small that only ultrasensitive tests can measure them.

To improve PSA detection in women, the researchers built a tiny fiber-optic biosensor using and PSA antibodies to detect and report PSA levels via a fluorescent signal. The biosensor's sensitivity (its ability to detect elevated PSA levels in cases of breast cancer) and its specificity (how well it avoids false predictions of breast cancer) are comparable to those found in using PSA as a biomarker for prostate cancer. "Furthermore, these values may compare favorably with the sensitivity and specificity of the current screening methods for breast cancer such as clinical examination… and mammogram," the scientists report.

More information: “Discrimination of breast cancer by measuring prostate-specific antigen levels in women serum” Anal. Chem., 2011, 83 (13), pp 5324–5328. DOI: 10.1021/ac200754x

Prostate-specific antigen (PSA) has been reported to be a potential biomarker of breast cancer. Serum PSA of normal women is around 1 pg/mL, which is usually undetectable by current assay methods; thus an ultrasensitive measurement of PSA expression in women's serum is necessary to distinguish normal from malignant breast diseases. To enhance the sensitivity of conventional immunoassay technology for the detection of PSA in sera, we adopted a localized surface plasmon coupled fluorescence fiber-optic biosensor, which combines a sandwich immunoassay with the localized surface plasmon technique. The concentration of total PSA (t-PSA) (from 0.1 to 1000 pg/mL) in phosphate-buffered saline solution and the normalized fluorescence signal exhibit a linear relationship where the correlation coefficient is 0.9574. In addition, the concentration of additional t-PSA in 10-fold-diluted healthly women's serum across a similar range was measured. The correlation coefficient for this measurement is 0.9142. In clinical serum samples, moreover, the experimental results of t-PSA detection show that both the mean value and median of normalized fluorescence signals in the breast cancer group (155.2 and 145.7, respectively) are higher than those in the noncancer group (46.6 and 37.1, respectively). We also examined the receiver operating characteristic curve for t-PSA, and the area under the curve (AUC) is estimated to be 0.9063, the AUC being used to measure the performance of a test to correctly identify diseased and nondiseased subjects.

Provided by American Chemical Society (news : web)

New way of synthesizing organic chemicals mimics nature

Organic chemists have found a new way of synthesizing multiple complex organic molecules that until now have needed to be synthesized using time-consuming methods. The new strategy, which mimics natural biosynthesis methods, could provide a way to speed up the synthesis of chemicals for use in the laboratory and for testing for possible therapeutic effects.

Chemists can synthesize almost any complex organic chemical in small quantities in the laboratory, but the process can be extremely time consuming and expensive, and difficult or impossible to translate to large-scale production. It is also difficult to synthesize families or related molecules using traditional methods because each has to be synthesized individually.

The new method was developed by researchers from the Center for Catalysis at Princeton University in the U.S., led by organic chemist David MacMillan. The strategy combines two techniques that mimic methods used by living systems to synthesize organic molecules (those based on chains of or ): organocascade catalysis and collective . Combining these two techniques for the first time allowed MacMillan and colleagues to considerably speed up the synthesis of a group of six related .

The alkaloids the team manufactured were akuammicine, aspidospermidine, kopsanone, kopsinine, strychnine, and vincadifformine.

The new strategy, which the team calls “collective total synthesis,” makes it possible to synthesize useful amounts of related, complex molecules from a “common molecular scaffold,” and is much less time-consuming. The synthesis of strychnine, for example took place in only 12 stages, which is the shortest ever reported.

Traditional methods of synthesizing such chemicals have involved using chemical reactions to produce each individual intermediate and then isolating it and using the intermediate in the next reaction, and repeating this process until the target molecule is finally produced.

MacMillan said the new method represents a new way of thinking for organic chemists. Reducing the number of steps required to synthesize molecules reduces the time required and can also reduce the cost and wastage. Their approach can also produce a number of related molecules at the same time, which could reduce the time and cost of producing and testing chemicals to find the most bioactive drug candidates.

MacMillan and the team suggest the collective total synthesis strategy could be used to manufacture other families of molecules that until now have had to be synthesized individually. They say the approach of combining the two techniques of organocascade and collective synthesis could be applicable for many other groups of molecules besides alkaloids.

The paper, the first to be published describing this approach to synthesis, is published in Nature.


The unsolved mystery of kava toxicity

 A major new review of scientific knowledge on kava — a plant used to make dietary supplements and a trendy drink with calming effects — has left unsolved the mystery of why Pacific Island people can consume it safely, while people in the United States, Europe, and other Western cultures sometimes experience toxic effects. The article appears in ACS' journal Chemical Research in Toxicology.

Line Olsen and colleagues point out that for centuries, people of the Pacific Islands have safely consumed a beverage made from crushed kava roots. Kava'scalming effects made it popular in Western cultures in the 1990s, when people also began to use a herbal supplement for the treatment of anxiety, emotional stress and sleep problems. But in 2001, reports of liver damage among Westerners who took kava supplements gained widespread attention. Many Western countries, including the United States, the United Kingdom, and Canada, ban or regulate the sale of kava products. To determine why kava is toxic to some people but not to others, the researchers sifted through the scientific studies published on the topic.

Their review of 85 scientific studies on kava found no consensus on kava toxicity, despite several theories that have emerged over the years. Culprits include methods for preparing kava, the particular species of kava used, the possible toxicity of substances produced by the body when is digested and genetic differences among consumers. "To date, there remains no indisputable reason for the increased prevalence of kava-induced hepatotoxicity in Western countries," the researchers say.

More information: “Constituents in Kava Extracts Potentially Involved in Hepatotoxicity – A Review” Chem. Res. Toxicol., Article ASAP DOI: 10.1021/tx100412m

Aqueous kava root preparations have been consumed in the South Pacific as an apparently safe ceremonial and cultural drink for centuries. However, several reports of hepatotoxicity have been linked to the consumption of kava extracts in Western countries, where mainly ethanolic or acetonic extracts are used. The mechanism of toxicity has not been established, although several theories have been put forward. The composition of the major constituents, the kava lactones, varies according to preparation method and species of kava plant, and thus, the toxicity of the individual lactones has been tested in order to establish whether a single lactone or a certain composition of lactones may be responsible for the increased prevalence of kava-induced hepatotoxicity in Western countries. However, no such conclusion has been made on the basis of current data. Inhibition or induction of the major metabolizing enzymes, which might result in drug interactions, has also gained attention, but ambiguous results have been reported. On the basis of the chemical structures of kava constituents, the formation of reactive metabolites has also been suggested as an explanation of toxicity. Furthermore, skin rash is a side effect in kava consumers, which may be indicative of the formation of reactive metabolites and covalent binding to skin proteins leading to immune-mediated responses. Reactive metabolites of kava lactones have been identified in vitro as glutathione (GSH) conjugates and in vivo as mercapturates excreted in urine. Addition of GSH to kava extracts has been shown to reduce cytotoxicity in vitro, which suggests the presence of inherently reactive constituents. Only a few studies have investigated the toxicity of the minor constituents present in kava extract, such as pipermethystine and the flavokavains, where some have been shown to display higher in vitro cytotoxicity than the lactones. To date, there remains no indisputable reason for the increased prevalence of kava-induced hepatotoxicity in Western countries.

Provided by American Chemical Society (news : web)

Polymer scientist is laying groundwork for next-generation flexible photovoltaics

University of Massachusetts Amherst polymer scientist Ryan Hayward recently received a five-year, $750,000 grant from the U.S. Department of Energy to improve understanding of the fundamentals for the next generation of lightweight and flexible electricity-conducting polymers. They are in limited use now in thin solar panels on messenger bags that can recharge a cell phone battery, for example.

Hayward and colleagues will study the physics of how crystallize and how they can be used to build solar-power-collecting with the optimal combination of p-type/n-type (P-N) junctions for efficient light harvesting. This is expected to lead to a new crop of more cost-effective that are more efficient at conducting electrons than current technology.

When sunlight hits a , electrons become excited and move to P-N junctions, then out of the device as electric power. One problem at present is that the motion of charges through polymer-based often is slowed to a crawl, a flow rate more like the stop-and-go of local traffic than a smooth expressway. One goal of Hayward and colleagues’ new research will be figuring out how to allow electrons to flow faster, enhancing the efficiency and cost effectiveness of charge transport in photovoltaics.

"As electronic materials, polymers have promise in terms of low cost and ease of processing," he says. "These materials are light and flexible, so they can be dissolved into a solution and sprayed onto a surface. There are now small available that are so flexible you can role them up like a map." But such applications are still rather expensive and not as efficient as they could be at producing electric power.

The UMass Amherst research group will conduct basic experiments to understand mechanisms involved in controlling structure and improving conjugated polymer performance. They will study self assembly of these materials across multiple length scales and develop new methods for preparing P-N junctions capable of efficient charge transport.

"For polymer-based electronics it’s important to understand the structure of P-N junctions both on the length-scale of 10 nanometers, which is important for harvesting light, and on the scale of Angstroms, which is important for charge transport. We’ll be trying to assemble new materials where we can control both the crystalline or molecular scale ordering and the nanoscale organization," Hayward points out.

As experts in polymer self-assembly, Hayward and colleagues will work with fellow UMass Amherst polymer scientist Todd Emrick and his research group, who synthesize a number of semi-conducting polymer materials.

"These are really interesting problems in fundamental science," Hayward notes. "We anticipate that the lessons we learn will be useful for many other areas in addition to photovoltaics, such as for polymer-based LEDs and transistors and other types of polymer-based electronics."

Provided by University of Massachusetts Amherst (news : web)