*Minuscule cubes get into a twist*

Magnetism is just one of the forces acting on the nanoparticles.

By JUDY SIEGEL-ITZKOVICH
A scientist looks through a microscope (photo credit: INGIMAGE)
A scientist looks through a microscope
(photo credit: INGIMAGE)
Nanocubes are not some children’s game, but nano-sized cube-shaped particles. Organic chemistry researchers at Rehovot’s Weizmann Institute of Science who used them to create surprisingly yarn-like strands showed that given the right conditions, they are able to align themselves into winding, helical structures. Their results, which reveal how nanomaterials can self-assemble into unexpectedly beautiful and complex structures, were recently published in Science.
Dr. Rafal Klajn and postdoctoral fellow Dr. Gurvinder Singh used nanocubes of an iron oxide material called magnetite. As the name implies, this material is naturally magnetic, and it is found all over the place, including inside bacteria, that use it to sense the Earth’s magnetic field.
Magnetism is just one of the forces acting on the nanoparticles. Together with the research group of Prof. Petr Král of the University of Illinois in Chicago, Klajn and Singh developed theoretical models to understand how the various forces could push and pull the tiny bits of magnetite into different formations.
“Different types of forces compel the nanoparticles to align in different ways,” said Klajn. “These can compete with one another, so the idea is to find the balance of competing forces that can induce the self-assembly of the particles into novel materials.”
The models suggested that the shape of the nanoparticles is important – only cubes would provide a proper balance of forces required for pulling together into helical formations.
The researchers found that the two main competing forces are magnetism and a phenomenon called the van der Waals force. Magnetism causes the magnetic particles to both attract and repel one another, prompting the cubic particles to align at their corners. Van der Waals forces, on the other hand, pull the sides of the cubes closer together, coaxing them to line up in a row. When these forces act together on the tiny cubes, the result is the step-like alignment that produces helical structures.
In their experiments, the scientists exposed relatively high concentrations of magnetite nanocubes placed in a solution to a magnetic field. The long, rope-like helical chains they obtained after the solution was evaporated were surprisingly uniform. They repeated the experiment with nanoparticles of other shapes but, as predicted, only cubes had just the right structure to align in a helix. Klajn and Singh also found that they could get chiral strands – all wound in the same direction – with very high particle concentrations in which a number of strands assembled closely together. Apparently the competing forces can “take into consideration” the most efficient way to pack the strands into the space, said Klajn.
Although the nanocube strands look nice enough to knit with, it is too soon to begin thinking of commercial applications. The immediate value of the work, he added, is that it has proven a fundamental principle of nanoscale self-assembly.
“Although magnetite has been well studied, also its nanoparticle form, for many decades, no one has observed these structures before. Only once we understand how the various physical forces act on nanoparticles can we begin to apply the insights to such goals as the fabrication of previously unknown, self-assembled materials.”
PIG CHEMICAL STOPS DOG BARKING
A dog’s bark is a way of protecting itself and its owner – but it can really get on your nerves if it’s incessant. Now a professor at Texas Tech University has discovered that a pig pheromone (hormone that triggers a social response in members of the same species) named androstenone can stop dogs from barking and jumping.
Animal-behavior scientist John McGlone was just like any other pet owner a few years ago – he simply wanted to keep his Cairn terrier from barking incessantly. As part of his work, he just happened to have a product called Boar Mate on hand at his house from a previous research study, an odorous concoction that helps farmers with swine breeding. So he gave one little spritz to his dog, Toto, and immediately the dog stopped barking.
“One of the most difficult problems is that dogs bark a lot, and it’s one of the top reasons they are given back to shelters or pounds,” he said.
Suddenly, an idea was born. After extensive testing and publishing of the results and with funding help from Sergeant’s pet care products, “Stop That” was developed and hit the stores. It has met with tremendous success among pet owners who were on their last legs in trying to curtail bad behavior in dogs.
The pheromone is produced by pigs in their saliva and fat, secreted by males and picked up by females in heat. It is foul-smelling to humans.
McGlone conducted double-blind, controlled studies and found that the synthesized phernomone stopped 100 percent of dogs from barking. He also found that the androstenone had no effect on the dogs’ heart rates either before or after being sprayed. But, McGlone warns, it’s not an end-all, beat-all to stopping dogs from barking, as the effects last just about a minute.
“If you continue to spray the dog again it will stop,” McGlone said. “If you show the can, they will stop. It’s best used as a training tool rather than a circus act to stop animals from doing what they’re doing.”