Institute of Physical and Theoretical Chemistry

Working group of Prof. Gauglitz

Calorimetry

Calorimetry is the science of measuring the heat of chemical reactions or physical changes. The output of an isothermal calorimeter is the heat power generated over time. This allows for calculating the enthalpy of a reaction. The only prerequisite for a reaction to be monitored with calorimetry is that sufficient heat is generated or consumed. Any type reaction, whether it is molecular interactions [1], chemical or enzymatic reactions [2], bacterial metabolism [3] or phase transitions, can be monitored without the need of labeling or surface modifications. Besides thermodynamic characterization of reactions, several different types of information can be obtained depending on the assay design. There are two types of calorimeters employed in the research group Gauglitz, which are an Isothermal Titration Calorimetry (ITC) setup as well as a Chip Calorimeter.

Isothermal Titration Calorimetry

For characterization of molecular interactions, including determination of affinity constants, a titration setup is typically used. The heat generated after each injection is used as a relative measure to quantify the number of reactions taking place. As the system comes closer to saturation, fewer interactions occur and the signals therefore are lowered. By applying the law of mass action, affinity constants can be derived from such data. ITC is particularly powerful when investigating low affinity interactions. These features enable ITC for:

  • Biomolecular interaction studies with low affinity binding (e.g. viral attachment to cellular structures [1])
  • Sorption characteristics of polymeric materials (e.g. PDMS, with and without recognition structures embedded [4], MIPs)

Besides determination of affinity constants, enzymatic reactions or the metabolic rate of living microorganisms can be studied. The heat is detected in a time-resolved manner, so even the kinetics of slow interactions can be studied.

Chip calorimetry

In collaboration with Dr. Lerchner from the TU Freiberg, the research group Gauglitz received a chip calorimeter that operates in isothermal mode. The innovative design of the device combines different features of ITC and the label-free optical sensor technologies established in Tübingen. On the one hand, it uses thermal read-out to monitor reactions taking place in homogeneous or heterogeneous phase, without any disturbances originating from surface coupling or labelling. On the other hand, the reactions take place in a flow cell, which allows for much faster and easier sample handling as well as assay designs similar to the ones established for the optical systems. The miniaturised setup has much smaller time constants and is therefore suitable for kinetic measurements. Chip calorimetry is particularly powerful when studying microbial growth and resistance to antibiotics as well as enzyme kinetics in solution, suspension, or even in solid films.

Literature

  1. Neu et al., PNAS 2008, 105(13), 5219-5224
  2. Lerchner et al., Thermochim. Acta 2006, 445(2), 144-150
  3. Buchholz et al., Antimicrob. Agents Ch. 2009, 54(1), 312-319
  4. Wöllner et al., Anal. Bioanal. Chem. 2007, 389(7-8), 1879-1887