Suhm group    
People Teaching Research Publications Links
Martin Suhm Ba Chemistry Summary Group publications Institute
Members Ma Chemistry Equipment Suhm publications HBOND2017
Students Ba/Ma Education SPP 1807 Zeuch publications UniVZ
Been here Dipl. Chem. Complex Systems Miscellanies Seminars
Thomas Zeuch PChem Advisor Popular Science Mol. Sociology Miscellaneous
ga-logo_small.gif (4 KB)

In spring 2015, the DFG started a new Priority Program - SPP 1807 - on

Control of London dispersion interactions in molecular chemistry

Speaker: Peter Schreiner
First funding period: 2015 - 2018
Website: www.spp1807.de

The idea is that theory, spectroscopy and synthesis activities in Germany and beyond are brought together to develop rational design principles which utilize dispersion interactions in the construction of new (supra)molecular structures. To support networking, this page provides some background on our research in this field. Where can we contribute? What can we offer? Where do we need support from other groups? Which are our overarching goals?

Feel free to contact us (msuhm@gwdg.de) in order to discuss possible connections with your own running or planned project.

Selection of our previous publications in the field

(see http://www.hbond.net/suhmpubs.htm for a full list, to which the numbers are linked):

[104] π-π attraction can break hydrogen bonds depending on relative molecular chirality - as shown in this multiexperimental approach towards understanding the interaction between methyl mandelate molecules.

[122] Quantifying dispersion ideally means that we know the binding energy of a complex accurately from experiment and may compare it to theory - this is achieved for formic acid dimer at the 1% level, enough to identify subtle dispersion contributions.

[124] The longitudinal acoustic mode of gas phase n-alkanes is used to show that beyond about 17 carbon atoms, a three-fold chirality synchronization leads to hairpin structures which are actually more stable than a stretched out alkane - a consequence of London dispersion attraction.

[125] In simple peptide models based on protected alanine, the relative chirality of two aggregating units can decide between β-sheet- and α-helix-like aggregation preferences.

[126] The first combination of size-selective IR-UV, FTIR and spontaneous Raman spectroscopy in supersonic jets reveals the subtle interplay between London dispersion and hydrogen bonding in molecular pairs of a chiral aromatic alcohol.

[128] This review summarizes our FTIR capabilities for the aggregation of volatile compounds - our main technical challenge in this SPP is to extend these capabilities to less volatile compounds and therefore to more dispersion-driven aggregation.

[130] For covalently bound fluorine, dispersion interactions are only part of a fascinating electrostatic, steric and polarization interplay - this is one of many systematic studies which are needed to unravel its role, focussing on the effect of progressive fluorination in weak OH...FC contacts.

[133] A systematic comparison between σ-σ, σ-π and π-π dispersion interactions in competition with classical hydrogen bonding, as revealed in the FTIR-spectra of expansion-cooled tailored alcohol dimers.

[135] A detailed description of the London dispersion-driven folding of n-alkanes into hairpins beyond about 17 carbon atoms, revealed by several features in the spontaneous Raman spectra of supersonic jet expansions.

[137] If we want to judge dispersion-driven cohesion, we need reliable reference points which minimize it, such as methanol dimer, scrutinized in this work.

[138] The search for global minimum structures for a given sum formula can reveal surprising winners, often controlled by dispersion interaction.

[141] OH-π hydrogen bonds are strongly dispersion driven and IR spectroscopy reveals associated molecular recognition phenomena.

Where can we contribute?

We have developed vibrational spectroscopy tools which allow for the characterization of flexible molecule conformations, molecular dimers and small oligomers in terms of intermolecular forces. This is typically achieved by supersonic jet cooling, a non-equilibrium method which can stabilize these systems at low effective temperatures in vacuum isolation. By tailoring the side groups, one can learn about their contributions to molecular cohesion, with implications for chirality recognition, tunneling dynamics, conformational preferences, binding energies and other molecular aspects. Solvent molecules can be added step-by-step.

What can we offer?

Linear spectroscopic studies (IR, Raman) of molecular aggregation and conformation for compounds which can be held for some time at temperatures which generate about 1 mbar of vapor pressure. They must show sufficiently large spectral changes as a function of cluster size and conformation.

Where do we need support from other groups?

In cases of spectral overlap, it is helpful to have strictly size-resolved and conformationally selective techniques, which usually need a suitable UV chromophore. To assign our spectra, we often need help from quantum chemistry groups, in particular for large systems, anharmonic effects and very high accuracy. As our experimental methods typically consume gram-scale quantities of the investigated compounds, we have to rely on commercial affordability or support from chemical synthesis groups.

Which are our overarching goals?

To bridge theory and application by experimentally studying benchmark systems which are amenable to high level quantum chemical and dynamical treatment. In this way, we hope to elucidate and quantify the contribution of London dispersion forces to molecular aggregation and shape changing processes.

Who is currently working on this in our group?

Jonas Altnöder is currently completing his PhD on FTIR jet spectroscopy of non-volatile compounds, Anja Poblotzki is starting a PhD thesis on dispersion control, Robert Medel studies alkane-alcohol interactions and conformations. Matthias Heger is applying high level theory and large scale supersonic jet spectroscopy to volatile compounds undergoing weak and medium-strength hydrogen bonding.

Important foundations of our work on London dispersion interactions were laid in GRK 782, a Göttingen research training group funded by the DFG between 2002 and 2012.


Suhm group homepage


Revised 2017-01-27