Printer Friendly

Electron Mix Binds Water Molecules.

Life owes its existence to a relatively weak connection called the hydrogen bond, which joins molecules or regions within a molecule. Without it, liquid water would be scarce on Earth and biological machinery involving DNA and proteins would halt. Despite intense scrutiny, the bond has remained mysterious in many ways (SN: 7/20/96, p. 37).

A new study of ice now shows experimentally that the frail hydrogen bond between water molecules taps into a molecule's internal covalent bonds, formed when atoms share electrons. The late Nobel laureate Linus Pauling first suggested this might be the case in 1935.

Although scientists have long assumed that hydrogen bonds are partly covalent, the experimental proof ranks as a major milestone, some hydrogen-bond experts say. Demonstrated in water, the findings apply to all hydrogen bonds, they add. The results may help investigators better understand properties of the bonds, such as why they are strongest in a certain direction, and improve models of their behavior.

A report on the experiment in the Jan. 18 Physical Review Letters is "certainly a very, very important new paper," comments Jose Teixeira of the Saclay research center of France's Atomic Energy Commission.

In water, hydrogen bonds forge links between hydrogen and oxygen atoms in adjacent molecules. Such a bond's character derives mostly from attraction between unlike electric charges that the two types of atoms acquire.

However, the new findings show that an electron contributing to that charge separation spends roughly 10 percent of its time mingling with an electron covalently binding the hydrogen and oxygen atoms within the adjacent molecule. "That's what Pauling said, and it's consistent with our data," says Eric D. Isaacs, the leader of the new study and one of three scientists at Lucent Technologies' Bell Labs in Murray Hill, N.J., who took part in the work. The specific 10 percent estimate has not yet been published, he says.

In the new experiment, Isaacs' team, which also included scientists at Northeastern University in Boston, the European Synchrotron Radiation Facility in Grenoble, France, and the Canadian National Research Council in Ottawa, Ontario, shone X rays at millimeter-thick crystals of ultrapure ice. X rays lose some energy and change direction as they strike electrons in the crystal. Their transformations reveal the spatial distribution of the ice's electrons--considered waves, according to quantum mechanics. By studying X rays bounced off various planes in the crystal with different numbers of hydrogen bonds, the team highlighted features of the bonds.

In the portrait of the electron waves that emerged, the team found fluctuations like those observed when overlapping light waves interfere with each other--their crests and troughs adding and canceling. The researchers deduce that the electron wave in each hydrogen bond is interfering with the wave in an adjacent covalent bond. Consequently, the electrons in both bonds must overlap to some degree, indicating that the electron in the hydrogen bond is circulating around two linked atoms--the hallmark of covalency.
COPYRIGHT 1999 Science Service, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1999, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:hydrogen bonding
Author:Weiss, Peter Ulrich
Publication:Science News
Article Type:Brief Article
Geographic Code:1USA
Date:Jan 23, 1999
Words:489
Previous Article:New radio map of Milky Way's center.
Next Article:Multiplied immune cells combat HIV.
Topics:


Related Articles
Going for a molecular spin.
Split hydrogen bond allows water to flow.
Lock styles of the rich and famous.
Laser reaction control in hot sodium vapor.
Signs of altered bonds in squeezed ice.
Solid hydrogen resists becoming metal.
Light goes on for antimatter-rich [H.sub.2]O.
Vibrations flit along water's fast lane.
Bilirubin: both villain and hero? (Biomedicine).
Surface reaction recorded in real time. (Physics: from Seattle, at the American Physical Society's annual March meeting).

Terms of use | Privacy policy | Copyright © 2020 Farlex, Inc. | Feedback | For webmasters