Thermochemistry and preferential interaction of serotonin with unilamellar DMPC liposomes

Nicolaj Cruys-Bagger

Studenteropgave: Semesterprojekt


The present work were conducted to provide experimental evidence for the American physicist Professor Robert Cantor’s hypothesis that neurotransmitters can act as the bodies “endogenous” anaesthetics. The hypothesis relies, to some extent, that neurotransmitters have the ability to change the physical condition of membranes. The system investigated here was serotonin and the model unilamelar di-myristoylphosphatidylcholine membrane because of disagreement in the literature on this system. This work has tried to elucidate the disagreement by correlating experimental data from different techniques with main focus on thermodynamic parameters. Differential scanning calorimetry showed that serotonin has a small effect on the melting point temperature and from a thermodynamic model of general anaesthesia this suggests that some serotonin molecules is located within the membrane. Isotermal titration calorimetry partition experiments confirmed this in from of a negative standard Gibbs free energy. A large positive heat capacity change for the process suggested that the partition is not hydrophobic driven and this was confirmed in form of vapour pressure measurements that showed that serotonin is slightly hydrophilic. The isotermal titration calorimetry data was not found reproducible and when comparing with partition coefficients found by other experimental methods the result from this technique is not found reliable. The insufficient is likely to be cause by either not proper precaution when working with the light reactive serotonin or that the experimental protocol applied is unsuitable to use for this system. It speculated that the lowering of the melting temperature is caused by absorption of 5HT into the head group of the lipid do to electrostatic attractive forces. On basis of the experimental results presented it’s not found plausible that serotonin should have the ability to induce anaesthesia in biological membranes.

UddannelserKemi, (Bachelor/kandidatuddannelse) Bachelor el. kandidat
Udgivelsesdato23 jun. 2009
VejlederePeter Westh


  • Serotonin
  • Calorimetry
  • DMPC