Since Anton van Leeuwenhoek invented the microscope in the 17th century, technology has allowed scientists to delve deeper and deeper into the microscopic world. First, it broke the barriers of the cellular level and quickly moved onto the molecular level. Now, a team of Chinese researchers have reported “seeing” a hydrogen bond for the first time using an atomic force microscope (AFM).
What is atomic force microscopy?
Atomic force microscopy can be performed by two different approaches: either using a contact or non-contact system. With a contact system, a silicon nitride tip gently touches the sample to be analysed and the deflection caused by the repulsive force is transformed into an image of the surface. In the non-contact system, the tip oscillates at a certain frequency over the sample to be imaged. Again the impact on this frequency is converted to an image.
Hydrogen bonds are essential for life. They are involved in keeping our DNA together and many reactions depend on creating or dissolving these bonds to progress. Despite their importance, the debate about the true nature of this type of chemical bond still continues. Chemical text books define it as an electrostatic bond, but recent x-ray diffraction studies have started to question this statement.
Promising preliminary results
The team, led by Xiaohui Qiu, decided to analyse 8-hydroxyquinoline (C9H7NO). The main reason was due to a flat structure with a hydrogen bond sticking out, making it easier to spot. So far, the preliminary results are promising but only show this new technique can be used to identify hydrogen bonds. They don’t add anything new to the debate about the nature of hydrogen bonds, but the authors are confident the next study will. At first sight, this observation is consistent with a positive hydrogen atom between two negative atoms, but now researchers can go further to understand what is causing and regulating this attraction.
Standard analytical procedure?
Mass spectrometry and NMR have become standard analytical procedures, and the authors of this study believe AFM will one day reach the same status. However, many improvements need to be done because, as it stands, sample preparation is a complex and time consuming process. In addition, it requires highly skilled staff, which may make it inaccessible to most research groups. Nevertheless, the need to find out more about chemical bonds and how they manipulate molecules will be the drive to achieve an easier and cheaper system.