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NEWS FROM ANALYTICAL SCIENCE NETWORK '97
Analytical Science in the U.K.
A look at amyloid David Bradley reports from Manchester, U.K.plaques A showcase is one way to drrve home the message that analytical science is a worthwhile subject for students and young researchers to pursue. Highlighting new and exciting research would boost the results of various scientists from medical researchers to metallurgists by way of chemists. .n the United Kingdom, where funding bodies seem to see the diversity of analytical science as an excuse to pass responsibility for funding to another division, one such showcase held last November at the University of Manchester Institute of Science and Technology (UMIST) demonstrated the breadth of studies being undertaken. Papers discussed current research results ideas and objectives for future work and future collaborations which according to organizer Bernard Treves Brown of the Analytical Science Network covers just about everyone So there was no excuse not to get involved
Liquid crystal separation liquid crystals are more commonly associated with display technology than analytical science. According to Paul Nicholas and James Hay of the School of Metallurgy and Materials at the University of Birmingham (U.K.), however, membranes based on cyanobiphenyl liquid crystals can be used to separate organic mixtures. The fact that liquid crystals can be controlled electrically endows their membranes with smart separation possibilities. The team has extended the application of liquid crystal membranes to boost the performance of poorly selective gas sensors. The researchers say that many sensors are inadequate when it comes to measuring certain volatiles in the presence of others. Inlet membranes are used to reduce interference in industrial and environmental mass spectrometers because they are cheap and simple to use. However, for particularly "difficult" mixtures, chlorinated solvents for instance, more effective preconditioning of the sample is usually needed, and this involves adding a gas or liquid chromatograph to the separation process. More time and effort are needed for the analysis, and costsrise."Even relatively sophisticated analyzers such as 96 A
Alexis Holden and Edmund Lane of the University of Central Lancashire, working with Robert Coward of the Royal Preston Hospital, described the use of circular dichroism (CD) to study the interaction of an amyloid peptide with inorganic elements such as aluminum. "We look at the absorption of polarized light, which depends on the structure of the protein, with a, (3, and random proteins giving different spectra," explains Holden. The presence of plaques composed of (3-amyloid peptide in the brains of Alzheimer's disease patients is actually part of the definition of the disease. Controversy reigns over whether the deposits are a cause or an effect: U.S. researchers tend to favor amyloid as a cause, whereas U.K. and other European scientists concentrate on other aspects of the disease. Amyloidosis is also, however, seen in diseases such as chronic kidney failure. One of the mechanisms hypothesized for the deposition of this short intractable peptide is the presence of a trigger factor such as aluminum The Lancashire team has used CD to detect changes in the secondary structure of proteins on addition of The structure
environmental mass spectrometers cannot distinguish between carbon dioxide and nitrogen, which both have principal peaks at mass 28," points out Nicholas. Ideally, a cheap membrane with the power of GC is needed. The Birmingham team has devised such a membrane. "The level of enhancement is very dependent on the molecules you are trying to distinguish between, the liquid crystals you are using, the operational temperature, and the selectivity of the sensor itself," Nicholas explained to Analytical Chemistry. However, the team has found very promising separations. "In lab experiments," says Nicholas, "thefluxesof ben-
Analytical Chemistry News & Features, February 1, 1998
aluminum, silicon, and other metals to P-amyloid. They have found that as the aluminum concentration increases there is a marked disruption of the a-helical protein secondary structure. At high concentrations of Al:!' (400 uM), however, this trend reverses. They have also found that adding silicon first reverses the effect of aluminum. Silicon is not, of course, involved in brain chemistry. "It may be possible to use silicon to 'mop up' the aluminum." says Holden. The researchers indicate that silicon may have a protective role, perhaps forming aluminum silicate, which precludes the binding of aluminum to the peptide. They point out that aluminum colocalized with silicon as the silicate has been found in senile plaques of Alzheimer's disease patients. They are currently studying the addition of other metals, such as copper and zinc, to see what changes in secondary structure might be induced.
of ^-amyloid peptide.
zene and toluene were altered by a factor of 3.5 and 3.0, respectively, by the appllcatton of a voltage across the [liquid crystal] membrane. In the case of chloroform and carbon tetrachloride the factors by which analyte flux increased were 3.5 and 4.5." Nicholas explains that the liquid crystal membranes work by a steric mechanism— the way molecules diffuse through depends on their size and shape and on the structure of the membrane. By orienting the liquid crystal membrane with a low voltage, its structure is profoundly altered and the diffusion pathways change from a circuitous path through the randomly oriented liquid crystal molecules to a more
