Changing the shape of water molecules
Chemical reactions depend on catalysts to speed up reactions, make chemical processes more efficient, and control the products being made. But it’s not always clear why a catalyst works the way it does.
Researchers have uncovered part of the catalysis mystery by looking at nanometre-sized crystals called zeolites, which can change the shape and behaviour of water molecules.
Zeolites are compounds made mostly from aluminium, silicon and oxygen. They get a lot of use in chemistry as moleculesized sieves or sponges. This is because of the physical structure of zeolite crystals: they’re filled with tiny holes.
These pores are a nanometre or less in size, which makes them about a thousand times too small for a bacterium to pass through, but just the right size for molecules.
Researchers based at the University of Illinois at Urbanachampaign, US, used a few spectroscopic techniques to examine the water in several different zeolites, with pores ranging from 0.3 nanometres (nm) to 1.3 nm in diameter.
They found that when the pores were smaller than 0.65 nanometres, the water molecules behaved oddly, forming single-file chains. These onedimensional chains had different chemical properties to regular, “bulk” water.
They also behaved differently when the zeolites were used to catalyse a chemical reaction called “epoxidation”: turning a type of chemical called an alkene into an epoxide.
The researchers say this information will help them to design better catalysts – both zeolite and non-zeolite – in the future.
Zeolites can dramatically alter the shape of water.
You’d be forgiven for thinking that the mystery object in Issue 92 was an antique nautical spyglass. One of our readers,
Gabriel, followed this line of thinking to guess it was a kaleidoscope, while Matthew Hunt from Brisbane gets bonus points for declaring it the world’s “first ‘tik tok’ device”: a two-tone instrument that, when tapped on either end, makes a tick-tock sound. The cylindrical object is in fact related to sound, and it is an instrument – just not the musical kind. It’s one of the first stethoscopes, developed by physician René Laennec in 19th-century Paris to avoid the embarrassment of putting his ear against a female patient’s chest. Crafted from wood and brass, it consists of a single hollow tube, in contrast to the familiar modern stethoscope with rubber tubing going to both ears. Laennec pioneered the use of these instruments in diagnosing diseases of the heart and lungs. Ironically, he died of tuberculosis.