Towards More Specific Microcalorimetric Studies With Special Emphasis on Biological Systems

Sammanfattning: A new approach in isothermal heat conduction microcalorimetric studies of chemical and biological processes is explored. The general (non-specific) method of calorimetry is combined with more specific analytical methods of analysis to "multi-functional microcalorimetric process monitors". A microcalorimeter with specific analytical sensors placed in the reaction vessel for studies of processes in solutions is described. The vessel incorporates pH/pO2 electrodes and a fibre optic spectrophotometer for absorbance measurements. Dynamic properties of the calorimeter was investigated in electrical calibration experiments. The instrument was tested with different systems: (a) Titration measurements with a weak base. The experiment as a model for titrations in ligand-binding studies is discussed. (b) The performance of the system in biological experiments is tested with growth of bacteria. Studies of growing cells where the dependence of the calorimetric signal on pH, oxygen concentration and turbidity is studied. Exemplified with E.coli in a complex medium under oxygen-limiting conditions. (c) Thermodynamic and kinetic studies of the hydrolysis of acetyl salicylic acid in basic buffer. Pseudo first order rate constants calculated from calorimetric and absorbance data are compared. (d) Studies of the oxidation of L-ascorbic acid with consecutive hydrolysis of the oxidation product. Overlapping reactions are deconvoluted and characterised kinetically and thermodynamically. A microcalorimetric gas perfusion system with a calorimetric CO2 analyser connected on-line is described. The instrument is mainly intended for studies of plant energetics and general metabolism in the dark. The system was tested in metabolic experiments of freshly cut potato tuber slices (Solanum tuberosum). The perfusion system was further developed to incorporate light-guides for the study of radiant energy uptake by photobiological / photochemical processes. A green leaf (Spinacia oleracea) was used as a test sample for the instruments. The conservation of light energy and CO2 in the tissue is measured and the energy / CO2 budget discussed.