Given how prevalent water is here on earth, you might think scientists would have the substance all figured out. But it seems that at the molecular level, water still has some surprises in store. In a report published today in the journal Nature, researchers reveal new insight into the behavior of individual water molecules in close quarters.
The scientists designed a virtual carbon nanotubea miniature straw composed of carbon atomswith a diameter of a mere 8.1 angstroms. Using computer simulations, they investigated the effects of placing the tube in a pool of water. Because the carbon pipe is strongly hydrophobic, or water-fearing, the investigators did not expect water to enter the tube. Yet they observed spontaneous and continuous filling of the tube by an ordered chain of water molecules. The researchers report that, on average, 17 water molecules pass through the tube every nanosecond and that the watery chain is rarely broken. The impetus for this surprising behavior, they suggest, comes from a tight hydrogen-bonding network inside the tube, which allows density fluctuations in the surrounding solution to push the molecular water chain through the tube in bursts.
"We conclude that, counter to intuition, hydrophobic channels can have significant water occupancy despite a reduction in the number of hydrogen bonds compared to the bulk fluid," the authors write. According to study co-author Jayendran Rasaiah of the University of Maine, the findings have important implications for understanding the mechanism of water conduction through biological channels and membranes. The simulation, he says, provides dynamic information that goes beyond the static pictures of conventional structural biology.