From Molecular Movements To Nanoconstruction Tools

UniSci.com ^ | 07-May-2002

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From Molecular Movements To Nanoconstruction Tools Molecular movements that could evolve into some of the first useful tools at future nanoconstruction sites, where proteins might be shuttled from place to place in tiny chemical wheelbarrows or built upon molecular scaffolding, were seen recently. The viewers were researchers at Sandia National Laboratories. Their insights might also help create cell-sized ambulances that could travel to and selectively repair or destroy diseased cells in a human patient's body. Using improved observational methods, the Sandia team watched as huddled receptor -- or grabber -- molecules on a man-made cell membrane rapidly dispersed across the membrane when they latched onto free-floating ligands (chemical particles), then rehuddled when the ligands were removed. The behavior mimics biological reactions at the cell level, such as immune system response to viral particles, says Darryl Sasaki of Sandia. The work is based on previous research at Sandia to create metal-detecting sensors based on chemical recognition events (see this URL.) "When they bind to the ligand, they each race away from their nearest neighbor," says Sasaki. "When the ligands are removed, they race back to where they were." The team's observations are published as the cover story in the May issue of the chemical and biophysics journal Langmuir. Portions of the work were funded by the U.S. Department of Energy's Office of Basic Energy Sciences and through discretionary Sandia research funds. The researchers created an artificial cell membrane made of "phospholipid bilayers" -- rows of long molecules that, like empty soda bottles bobbing on water, self-organize into an orderly heads-up/tails-down formation. They implanted this lipid film with lipids carrying tall receptor headgroups -- pincher- or lasso-shaped structures that chemically grab onto free-floating ligands. Then they watched as the receptors reacted to the addition of metal ions. At rest, the receptor-lipids pooled into aggregate zones between islands of shorter receptor-less lipids. But when metal ions (lead or copper) were added to the solution, the headgroups latched onto the ions, and ZIP!, the receptor-lipids dispersed across the membrane surface as their newly-acquired electrostatic charges caused them to become mutually repulsed. When the metal ions were removed, the wayward receptor-lipids retraced their steps and regrouped into the same aggregated pools. The process was performed repeatedly on the same membranes with the same result -- reversible reorganization. Sasaki believes the trails the receptor-lipids follow and the pools they return to correspond, quite literally, to the paths of least resistance on the membrane's surface -- areas where the lipid film is more liquid than solid, allowing the traveling lipids to flow like water. Although producing such chemical recognition events on an artificial membrane is not an achievement in itself, examining them with such fidelity is, says Sasaki. The Sandia team used novel microscopy and spectroscopic techniques to make the first documented observations of receptor-lipids dispersing and regrouping. Fluorescent pyrene tags were attached to the tails of the receptor-lipids to aid in tracking their travels on the membrane. When the receptors were aggregated -- as seen using fluorescence spectroscopy -- the huddles appeared bright. When the receptors were dispersed, their fluorescent signals were dim. In addition, the team used an atomic force microscope to map the topography of the lipid membrane, identifying locations of the tall receptor headgroups that towered 8 angstroms (about one billionth of a meter) higher than the tops of the membrane lipids. These observations provided unprecedented clarity about the locations of the receptors in both the dispersed and aggregated states, Sasaki says. "We've been able to characterize films as they change their properties at both the macroscale and nanoscale," he says. "It's the first time such a dynamic molecular system has been imaged this way." The observations will provide scientists with a better understanding of chemical recognition on cell-like membrane systems. Perhaps more tantalizing, he says, are the possibilities the new understandings might bring to the nanotechnology community's growing toolbox. "The idea of using chemical recognition to form specific structures in the membrane may be a potent tool to aid in the development of controllable nanoscale architectures," says Sasaki. If receptor headgroups propelled to and fro by chemical recognition events can be enlisted to hoist molecules and proteins and deposit them in planned locations, he says, designing and building nanosized structures, such as single-molecule-wide wires, might be possible. And the receptor-lipids' tendencies to follow preferred pathways offers promise for engineered construction of nano-railroad tracks along which a variety of molecular cargos could be recurringly moved, perhaps aboard motor-protein railcars, he says. If researchers can learn to control these routes, two- or three-dimensional lipid scaffolds might be designed upon which proteins could be laid down to build nanoscale electronic or photonic circuits. Nano-switching structures might be designed that self-construct and self-destruct based on chemical recognition events. And researchers have long sought to build cell-like pods that, when injected into a person's blood stream, would recognize diseased cells and release a drug to destroy those cells selectively. "By harnessing even a fraction of the capability of cellular membrane recognition systems, it may be possible to build unique sensor systems that are not only rapid and specific in response but also are innately biocompatible," adds Sasaki. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin company, for the U.S. Department of Energy. With main facilities in Albuquerque, N.M., and Livermore, Calif., Sandia has major R&D responsibilities in national security, energy and environmental technologies, and economic competitiveness. - By John German Related website: Sandia National Laboratories [Contact: Darryl Sasaki, John German] 07-May-2002

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[ImaGraftedBranch]

I believe he is referring to ionic bonding of electrons, versus covalent bonding.

[VadeRetro]

I believe he is referring to ionic bonding of electrons, versus covalent bonding.

So was I. I remain unaware of ionic chemistry or any other chemistry in the solution/precipitation of sugars. IIRC, unlike, say, table salt, sugars are covalent-bonded compounds that are not ionized in solution.

When you drop a sugar cube in water, collisions with the freely-moving and energetic water molecules overcome the adhesion of the sugars with each other. The sugars are unaffected chemically. They're still sugar. By comparision, a crystal of sodium chloride becomes little Na⁺ and Cl^- ions which are free to recombine with anything else in the solution.

It's just another trivial tangent, of course.

[VadeRetro]

Actually, an excellent point, I should have used "spontaneous"(whatever that means).

Yes, the second law can be interpreted to mean that certain things will not happen "spontaneously." Heat will not spontaneously flow from cold temperature regions to high-temperature regions. "Spontaneously" here means "with release of stored internal energy." "Non-spontaneously" would be "by application of external energy."

There's nothing about order in any of this, or the need for intelligent direction, or the need for design. No basic law of physics makes reference to intelligent direction or design, because the laws of physics are the same in all cases. "There's nothing you can do that can't be done." -- Lennon/McCartney

[Nebullis]

sugars are covalent-bonded compounds

Hmm. Sugar crystals are molecular structures held together by Van der Waal's forces and hydrogen bonds. Covalent is reserved for crystals like diamonds.

[VadeRetro]

I'm out of my depth here, but your characterization of "hydrogen bond" versus "covalent" doesn't quite jive with what I can find out there. The simplest covalent bonds are your ordinary diatomic gasses, H₂, etc. Sugars seem to be included in the covalent category, as they involve electron sharing. "Hydrogen bonds," strictly speaking, seem with some exceptions to be weak intermolecular attractions.

For one example of sugars considered as covalent compounds, Are Ionic Bonds Stronger Than Covalent?

A page on Covalent Bonding. A more detailed treatment.

A page on hydrogen bonds. Another one.

The hydrogen bond is approximately 30 times weaker than a normal covalent bond, because only one of the contributing atoms is supplying electrons to it; the two electrons stay mainly concentrated near the oxygen. Because the hydrogen bond is so weak, it is easily broken. At room temperature, thermal energy is enough to break hydrogen bonds. In liquid water the whole network of hydrogen bonds ``flickers,'' each bond making and breaking again in a millionth of a microsecond. It is this network of flickering hydrogen bonds that gives liquid water its unique properties.

Finally, this page on the types of bonds.

Hydrogen bonding differs from other uses of the word "bond" since it is a force of attraction between a hydrogen atom in one molecule and a small atom of high electronegativity in another molecule. That is, it is an intermolecular force, not an intramolecular force as in the common use of the word bond.

[VadeRetro]

Another link on covalents.

Result: a covalent bond (depicted as C:H or C-H)

[Nebullis]

I don't have time to follow all of your links right now, but sugar crystals are molecular crystals made up of weak interactive forces such as van der Waals and hydrogen. Covalent bonds are much stronger and are involved in the individuals molecules of sugar, not the crystals.

[Nebullis]

You were talking about crystals, right? I see my selective quote talks about sugars alone. I may have jumped the gun. (Bad, bad!) You are correct if you are talking about sugar molecules. But I thought the conversation was about spontaneous crystalization.

Of course, this is just a trivial diversion.

[AndrewC]

For one example of sugars considered as covalent compounds,

You are both right. The confusion here is to what bonding we are talking about. Covalent bonding does not occur between molecules. It occurs within a molecule. It comes about because the wave function for the paired electrons involves multiple centers. The bonding being described in the article and in the dissolving of sugars is bonding between molecules. These are typically much weaker than covalent and true ionic bonds. A diamond is thus one huge molecule, graphite is also composed of sheets of molecules, and bucky balls are typically a 60 carbon molecule.

Molecule of the Month

Diamond

Each of those are covalently bonded within the "molecule". Sucrose on the other hand is constructed of covalent bonds, but a sugar crystal is held together by weaker hydrogen bonding(and others). This is evident in that sugar dissolves in polar solvents, like water but not in non-polar sovents like hexane. Diamond doesn't dissolve.

[VadeRetro]

You were talking about crystals, right? I see my selective quote talks about sugars alone.

All I was really going for was that sugar doesn't dissociate in dissolving/crystallizing. It's a basically mechanical process.

[VadeRetro]

I don't have time to follow all of your links right now, but sugar crystals are molecular crystals made up of weak interactive forces such as van der Waals and hydrogen. Covalent bonds are much stronger and are involved in the individuals molecules of sugar, not the crystals.

Right. We were talking past each other totally, per usual.

[techcor]

Transmutin' elements is a nuclear reaction thing.

So have your nanotech induce electron-capture. Turn your Oxygen 16 into Nitrogen 16 . Then, if your Nitrogen 16 emitts two Neutrons, they would decay to become Hydrogen. Voila`. Humanity takes over the Universe.

[VadeRetro]

So have your nanotech induce electron-capture.

K-capture does happen (it's how potassium₄₀ becomes argon₄₀). But I doubt we know a neat trick for inducing it.

[Nebullis]

We were talking past each other totally, per usual.

That reminds me. A woman is driving on a windy mountain road and as she comes around a bend she almost hits a wild pig. A little later she sees an oncoming car and rolls down the window to warn the driver. "Pig!" she yells and points. The stunned driver rolls down his window and yells "Bitch!"

[Nebullis]

winding road...

[VadeRetro]

"Pig!" she yells and points.

LOL! Utterly off-topic but:

A salesman is driving along a country road when he sees a pig crossing in front of him. The pig is missing its hind legs but has little wagon wheels strapped under it and is thus able to motor right along.

Intrigued, the man stops at the farmhouse where the farmer is sitting on the porch.

"I couldn't help but notice a most unusual pig. What's the story there?"

The farmer was happy to explain.

"Let me tell you about that pig. My boy was playin' by the stream an' he fell in. 'Bout drowned but that pig heard his screams, jumped in, and pulled him out. Smart as any dog, that pig!"

"That's amazing!" said the salesman.

"Then we had a fire one night. That pig come in the house an' woke us all up. Saved us all."

"That's amazing too!," the salesman said. "But what about his hind legs?"

"Well," the farmer said. "You wouldn' wanna eat a pig like that all at once, wouldja?"

[AndrewC]

The stunned driver rolls down his window and yells "Bitch!"

Yes, but then just a little further on she just avoids running over Lassie.

[Nebullis]

Utterly off-topic but:

Ha!

Trying to get the thread LOCKED are ya?

[VadeRetro]

Lassie

I've heard that every Lassie there ever was was male. Worse than Mary Martin playing Peter Pan.

[Junior]

The researchers created an artificial cell membrane made of "phospholipid bilayers" -- rows of long molecules that, like empty soda bottles bobbing on water, self-organize into an orderly heads-up/tails-down formation.