Posted on 01/13/2010 4:49:33 PM PST by neverdem
Usually, you'd expect two compounds with the same composition, atom-to-atom connectivity and symmetry to be chemically identical too. But scientists investigating metal-organic frameworks have discovered a surprising exception to this rule by identifying two isomers with the same symmetry and bonding but different gas storage properties.
A team led by Shengqian Ma at the Argonne National Laboratory, Illinois, US, investigated a rod-like tetracarboxylate molecule (ebdc) which can bind to a metal atom from any one of four binding points, one at each corner of a rectangle. When it was heated with a copper salt at 75 °C, a crystal phase formed (the 
-phase) and at 65 °C a phase with different properties (the 
-phase) formed. So far, so normal. But when Ma carried out crystal analysis on these two compounds, he found that they had the same composition, the same atom-to-atom connectivity and the same symmetry. 'This type of symmetry-preserving isomerism has never been observed before in metal-organic frameworks,' says Ma.
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The isomers have the same symmetry but different properties
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The key to what's happening lies in the ligand, Ma explains. In the -phase, the ligands bind end-on to each copper unit, whereas in the -phase they bind side-on. This makes the ring larger in the -phase than in the -phase. So, although the same chemical units are joined together with the same sort of bonds and the same overall symmetry, the properties are different. In particular, the area available for hydrogen absorption is significantly higher in the -isomer: 'This means that it might be possible to improve gas storage capacities by looking for new isomers of known structures,' says Ma. Paul Forster, a materials chemist at the University of Nevada, Las Vegas, US, is intrigued by what he calls a 'very unusual' form of isomerism. 'Structures that are identical in composition and connectivity, but differ in pore geometry, offer unique and important opportunities to address questions related to the kinetics and thermodynamics of hybrid materials synthesis,' he says.
An unusual case of symmetry-preserving isomerism
Daofeng Sun, Shengqian Ma, Jason M. Simmons, Jian-Rong Li, Daqiang Yuan and Hong-Cai Zhou, Chem. Commun., 2010
DOI: 10.1039/b920995f
Metal organic frameworks do the twist
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Wow — the implications of different binding properties of the same materials by changing the environment are MASSIVE.
The more we discover the more we discover that there is more to discover!
r/binding/bonding/
*doh!*
“The more we discover the more we discover that there is more to discover!”
Ditto: and also
parts of me think I should have put that in a copyrighted piece, years ago when I first used it (and before I used it many time here at FreeRep), then I could charge “plagarism” every time I saw it used. /humor
And, for a few decades, at least since the 1980s, I have been amazed at what’s being discovered frequently in materials science, happy to become aware of just how important it is, to so many things, and unhappy that public awareness of that importance seems to always trail many other scientific and technological developments.
An expert is someone who learns more and more about less and less until he knows almost everything about almost nothing.
>>An expert is someone who learns more and more about less and less until he knows almost everything about almost nothing.<<
And a manager is someone who can make good decisions with little information and thus make perfect decisions with zero information.
:)
And removing salt from many products can be complicated. Salt plays many roles in food, enhancing flavor, preventing spoilage and improving shelf life. It helps bread to rise and brown. (Baking soda is sodium bicarbonate.)
Thyme oil can inhibit COX2 and suppress inflammation (Carvacrol)
The last thread mentioned Mobic, an older NSAID that worked for the poster. So I checked an old thread of mine:
Doctors, Too, Ask: Is This Drug Right?
In undertaking its drug review, Veterans Affairs also re-examined the value of a lesser-known pain reliever, etodolac, and began using it more. The drug was first sold in 1991 as Lodine by a company that is now part of GlaxoSmithKline. Like many older medications, however, it was not extensively tested.
A study based on a review of V.A. patient records that was published last month in a medical journal, Gastroenterology, found that the rate of stomach bleeding caused by etodolac was substantially lower than that caused by naproxen and comparable to that of Vioxx.
Byron Cryer, a researcher at the University of Texas Southwestern Medical School in Dallas who led the study, said his group was reviewing those same patient records in effort to determine whether etodolac increased heart risks. Dr. Cryer said that analysis should be completed in about a month.
I couldn't fing anything at PubMed when I checked etodolac and coronary artery disease. When I checked aspirin and coronary artery disease, I got 2265 hits. Folks who have had coronary artery bypass graft surgery, aspirin allergy or during late pregnancy should not take etodolac according to the Monthly Prescribing Reference.
I don't think they realized etodolac was a COX-2 inhibiter when it first came on the market.
Generic Anti-inflammatory Causes Fewer Gastrointestinal Complications
Etodolac is a non-steroidal anti-inflammatory drug (NSAID) in the same class as Celebrex.
--snip--
Further, the decrease in ulcer complications with etodolac was as great as or greater than those seen in earlier studies with Celebrex or Vioxx.
Scientists link plastics chemical to health risks (BPA)
Three Approved GMO Crops Linked to Organ Damage, New Study Shows
FReepmail me if you want on or off my health and science ping list.
(Sound of grey_whiskers purring.)
Cheers!
That was my observation on graduation day at UCSD. I earned the degree and left with a specific set of knowledge. The valuable part of the knowledge was knowing how to acquire more and refresh it constantly. Many of the specifics have long since been eclipsed by new discoveries. The entire body of knowledge was/is a fraction of what possible/available.
Interesting. But surprise? Phase changes in molecules is nothing new. Maybe I’m missing something.
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