Thursday, September 23, 2010

EDIBLE NANOSTRUCTURES

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Sugar, salt, alcohol and a little serendipity led a Northwestern University research team to discover a new class of nanostructures that could be used for gas storage and food and medical technologies. And the compounds are edible.

The porous crystals are the first known all-natural metal-organic frameworks (MOFs) that are simple to make. Most other MOFs are made from petroleum-based ingredients, but the Northwestern MOFs you can pop into your mouth and eat, and the researchers have.

“They taste kind of bitter, like a Saltine cracker, starchy and bland,” said Ronald A. Smaldone, a postdoctoral fellow at Northwestern. “But the beauty is that all the starting materials are nontoxic, biorenewable and widely available, offering a green approach to storing hydrogen to power vehicles.”

Smaldone is co-first author of a paper about the edible MOFs published by Angewandte Chemie. The study is slated to appear on the cover of one of the journal’s November issues.

“With our accidental discovery, chemistry in the kitchen has taken on a whole new meaning,” said Sir Fraser Stoddart, Board of Trustees Professor of Chemistry in the Weinberg College of Arts and Sciences at Northwestern. The implications of what Sir Fraser refers to as “Bob’s your uncle chemistry” go all the way from cleaner air to healthier living, and it all comes from a product that can be washed down the sink.

Stoddart led the research group that included a trio of postdoctoral fellows in chemistry at Northwestern and colleagues from the University of California, Los Angeles (UCLA) and the University of St. Andrews in the U.K.

Metal-organic frameworks are well-ordered, lattice-like crystals. The nodes of the lattices are metals (such as copper, zinc, nickel or cobalt), and organic molecules connect the nodes. Within their very roomy pores, MOFs can effectively store gases such as hydrogen or carbon dioxide, making the nanostructures of special interest to engineers as well as scientists.

“Using natural products as building blocks provides a new direction for an old technology,” said Jeremiah J. Gassensmith, a postdoctoral fellow in Stoddart’s lab and an author of the paper.

“The metal-organic framework technology has been around since 1999 and relies on chemicals that come from crude oil,” explained Ross S. Forgan, also a postdoctoral fellow in Stoddart’s lab and co-first author of the paper. “Our main constituent is a starch molecule that is a leftover from corn production.”

For their edible MOFs, the researchers use not ordinary table sugar but gamma-cyclodextrin, an eight-membered sugar ring produced from biorenewable cornstarch. The salts can be potassium chloride, a common salt substitute, or potassium benzoate, a commercial food preservative, and the alcohol is the grain spirit Everclear.

With these ingredients in hand, the researchers actually had set out to make new molecular architectures based on gamma-cyclodextrin. Their work produced crystals. Upon examining the crystals’ structures using X-rays, the researchers were surprised to discover they had created metal-organic frameworks -- not an easy feat using natural products.

“Symmetry is very important in metal-organic frameworks,” Stoddart said. “The problem is that natural building blocks are generally not symmetrical, which seems to prevent them from crystallizing as highly ordered, porous frameworks.”

It turns out gamma-cyclodextrin solves the problem: it comprises eight asymmetrical glucose residues arranged in a ring, which is itself symmetrical. The gamma-cyclodextrin and potassium salt are dissolved in water and then crystallized by vapor diffusion with alcohol.

The resulting arrangement -- crystals consisting of cubes made from six gamma-cyclodextrin molecules linked in three-dimensions by potassium ions -- was previously unknown. The research team believes this strategy of marrying symmetry with asymmetry will carry over to other materials.

The cubes form a porous framework with easily accessible pores, perfect for capturing gases and small molecules. The pore volume encompasses 54 percent of the solid body.

“We achieved this level of porosity quickly and using simple ingredients,” Smaldone said. “Creating metal-organic frameworks using petroleum-based materials, on the other hand, can be expensive and very time consuming.”

Stoddart added, “It is both uplifting and humbling to come to terms with the fact that a piece of serendipity could have far-reaching consequences for energy storage and environmental remediation on the one hand and food quality control and health care on the other.”

Northwestern University

WHAT CAN A NEW ZEALAND REPTILE TELL US ABOUT FALSE TEETH?

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Using a moving 3D computer model based on the skull and teeth of a New Zealand reptile called tuatara, a BBSRC-funded team from the University of Hull, University College London and the Hull York Medical School has revealed how damage to dental implants and jaw joints may be prevented by sophisticated interplay between our jaws, muscles and brain. This research will appear in a future edition of the Journal of Biomechanics.

The tuatara is a lizard-like reptile that has iconic status in its homeland of New Zealand because its ancestors were widespread at the time of the dinosaurs. Unlike mammals and crocodiles which have teeth held in sockets by a flexible ligament, tuatara have teeth that are fused to their jaw bone - they have no ligament, much like modern dental implants.

BBSRC postdoctoral fellow Dr Neil Curtis from the University of Hull said "Humans and many other animals prevent damage to their teeth and jaws when eating because the ligament that holds each tooth in place also feeds back to the brain to warn against biting too hard."

Dr Marc Jones from UCL, also a BBSRC postdoctoral fellow, added "In the sugar-rich western world many people end up losing their teeth and have to live with dentures or dental implants instead. They've also lost the periodontal ligament that would attach their teeth so we wanted to know how their brains can tell what's going on when they are eating."

The team has created a 3-D computer model of the skull of the tuatara to investigate the feedback that occurs between the jaw joints and muscles in a creature that lacks periodontal ligaments.

"Tuataras live happily for over 60 years in the wild without replacing their teeth because they have the ability to unconsciously measure the forces in their jaw joint and adjust the strength of the jaw muscle contractions accordingly", said Dr Curtis.

Although this explains why tuatara and people with false teeth manage not to break their teeth and don't end up with jaw joint disorders, it is still clear that having a periodontal ligament is very useful, in particular for fine tuning chewing movements. This may explain why it has evolved independently in the ancestors of mammals, crocodiles, dinosaurs, and even some fish.

There is anecdotal evidence to suggest that people with implants and dentures may make food choices related to their lack of periodontal ligament. However, the tuatara pursues a broad diet on the islands where they live including beetles, spiders, snails, frogs and occasionally young seabirds.

Professor Douglas Kell, BBSRC Chief Executive said "To support the extension of health and wellbeing into old age, it is vital that we appreciate how we as human beings have developed our extraordinary ability to adapt to adverse situations. This work allows us to understand some of the complexities of the feedback and responses occurring in healthy human bodies and brains. It is impossible in evolution to predict future innovations such as dental implants and yet this research indicates a level of redundancy in our biology that opens opportunities to support long term health and wellbeing."

Biotechnology and Biological Sciences Research Council (BBSRC)

NEW STUDY STRENGTHENS LINK BETWEEN EVERYDAY STRESS AND OBESITY

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Stress can take a daily toll on us that has broad physical and psychological implications. Science has long documented the effect of extreme stress, such as war, injury or traumatic grief on humans. Typically, such situations cause victims to decrease their food intake and body weight. Recent studies, however, tend to suggest that social stress--public speaking, tests, job and relationship pressures--may have the opposite effect--over-eating and weight gain. With the rise of obesity rates, science has increasingly focused on its causes and effects--including stress.

A recent study conducted by the Departments of Psychiatry and Biomedical Engineering at the University of Cincinnati College of Medicine, examined the effects of stress on the meal patterns and food intake of animals exposed to the equivalent of everyday stress on humans. The results suggest that, not only does stress have an impact on us in the short term, it can cause metabolic changes in the longer term that contribute to obesity. The study was conducted by Susan J. Melhorn, Eric G. Krause, Karen A. Scott, Marie Mooney, Jeffrey D. Johnson, Stephen C. Woods and Randall R. Sakai at the University of Cincinnati College of Medicine, Cincinnati, OH. Their study was published in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology.

Previous studies have found that meal patterns (number, duration and size of meals) can affect metabolism. Studies of both humans and animals have shown that taking fewer and larger meals promotes the gain of fat mass and can increase triglycerides, lipids and cholesterol independent of total caloric intake. Conversely, weight gain--even while overeating--can be prevented by consuming smaller, more frequent meals. Whether social stress alters the microstructure of food intake, however, was unclear.

The current study used the visible burrow system (VBS), an animal model of chronic social stress, which has been shown to produce stress-associated behavioral, endocrine, physiological and neurochemical changes in animals. Long-Evans rats (90 days old) were individually housed for three weeks prior to the experiment. During this habituation time, they were briefly anesthetized and implanted with a unique subcutaneous microchip just behind their ears which allowed for identification and monitoring of feeding behavior. Meal pattern characteristics were measured for seven days during habituation. Data were calculated for each animal for each day and then averaged together to provide an overall habituation measure as a baseline for all of the conditions.

For the experiment, rats were formed into colonies, composed of four males and two females, and matched with a control group. Within a few days, all colonies formed a hierarchy which established the dominance of one male and the subordination of the other three males. Each colony had equal hours of light and darkness. Meal pattern characteristics were calculated for each animal on a daily basis. As documented by behavioral video analysis and microchip data, both subordinate and dominant rats reduced their initial food intake and body weight compared to the habituation period and as compared to the control group. After the hierarchy was stable, however, the dominant rats recovered their food intake relative to the control animals, while the subordinate rats continued to eat less by reducing their number of meals. Furthermore, although rats are nocturnal animals, the subordinate rats ate primarily during lighted periods, indicating a shift in circadian behavior.

After two weeks, the male rats were individually housed for a three-week recovery period and allowed to eat freely. Compared to the control group, both dominant and subordinate rats over- ate during the recovery period, but the dominant animals ate more frequently, while the subordinate animals ate larger meals, but less frequently. The dominant rats gained weight and lean mass, but only as comparable to the control group, while the subordinate rats gained significant fat in the visceral (belly) region. Throughout the recovery period, subordinate rats continued to overeat, eat longer meals and gain fat, suggesting long-term, deleterious metabolic changes.

Interestingly, the study results suggest that the signals controlling ingestive behavior become impaired or are overridden during social stress. Hypothalamic neuropeptide Y (NPY) is a well-known chemical messenger within the hypothalamus that stimulates food intake in times of negative energy balance, possibly by increasing meal size. In this case, NPY did not mediate the consumption patterns of the animals during the VBS period.

This is the first study of its kind to examine meal patterns in real-time during exposure to chronic social stress and during a subsequent recovery period, as well as to begin to evaluate the neuroendocrine and neurochemical underpinnings of the altered ingestive patterns observed. Stress and recovery induced changes in animals’ body weight and composition and the alterations in meal patterns observed may have contributed to these physiological changes.

Stress is experienced by animals and humans on a daily basis and many individuals experience cycles of stress and recovery throughout the day. If, following stress, we consume larger and less frequent meals, the conditions are favorable for weight gain--especially in the abdomen. We know that belly fat, as well as stress, contributes to the development of cardiovascular disease, immune dysfunction and other metabolic disorders. Further studies using the VBS model will help us understand the relationship between stress and obesity and help us treat and prevent the development of these diseases.

(Photo: APS)

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