Hydrogen Bonds

Chapter Two of Biochemistry (Mathews, van Holde, and Ahern) has a section devoted to hydrogen bonds. Some of the main points:

* Hydrogen covalently bonds to an atom called the hydrogen bond donor.
* A nonbonded electron pair forms with an atom called the hydrogen bond acceptor.
* Oxygen and nitrogen are electronegative atoms and common hydrogen bond donors.
* Hydrogen bonds explain unique properties of water.
* Hydrogen bonds facilitate solutions of polar compounds in water.
* Hydrogen bonds are biologically significant. Large polymers like DNA and proteins are stabilized by hydrogen bonding.

Strange Polymer Behavior

Polymers strut their stuff under the spotlight is a Chemical Science article telling of how polymer films, having azobenzine groups, simulate an inchworm walk when exposed to alternating visible and ultraviolet light. The discovery was made by Japanese chemists who have shown that this polymer contracts in response to exposure to visible light and expands under UV light.

The reason for the strange behavior is attributed to N=N double bonds. These bonds have a cis conformation when the polymer bends but upon flattening is associated with bonds being trans.