Zhang, Chen, Yuan, Ji, Cheng, and Qui
Mine is not a science blog and it is not my intent that it should become one, but I could not help but follow up on a post I made a bit ago the focus of which was the Anthropic Principle and which relied heavily on discussion of the significance of the hydrogen bond to life on Earth. In that post I described hydrogen bonds as weak interactions which occur between a hydrogen atom attached to an electronegative atom, such as oxygen, and an electronegative atom of another molecule. Imagine my surprise when I received an email from a colleague the other day which included a link to an article entitled Real-Space Identification of Intermolecular Bonding with Atomic Force Microscopy. The piece described a technique which allows for the visualization of hydrogen bonds forming between molecules of 8-hydroxyquinoline. How, you may well ask, were these folks able to visualize an electrical interaction? The authors, whose names comprise the title of this post, had tweaked their microscope and their computers in such a way that they were able to measure and to then visualize the electron densities about interacting atoms. The image below shows a molecule of 8-hydroxyquinoline: white balls are hydrogen atoms, black ones are carbon, red are oxygen, and blue is nitrogen.
The image below, left, is a micrograph of hydrogen bonds. The figure on the right shows the hydrogen bonds (dotted lines) which form between four adjacent molecules of 8-hydroxyquinoline. Do you see how bonds form between hydrogen and oxygen (four instances) and between hydrogen and nitrogen (three instances)? Now look to the left at the micrograph and at these same interactions. Look more closely and you will see the same seven hydrogen bonds we just enumerated! Fascinating, truly, and really, really impressive. For reference, the frame size of each of the images below is approximately 2 nanometers, or 20 ångströms; a nanometer is one billionth of a meter while an ångström is one ten-billionth of a meter. Totally crazy … but I do love this stuff.