Laser-induced optoacoustic calorimetry of primary processes in cells of Rhodospirillum rubrum

Mutational control of bioenergetics of bacterial reaction center probed by delayed fluorescence

The free energy gap between the metastable charge separated state P(+)QA(-) and the excited bacteriochlorophyll dimer P* was measured by delayed fluorescence of the dimer in mutant reaction center proteins of the photosynthetic bacterium Rhodobacter sphaeroides. The mutations were engineered both at the donor (L131L, M160L, M197F and M202H) and acceptor (M265I and M234E) sides. While the donor side mutations changed systematically the number of H-bonds to P, the acceptor side mutations modified the energetics of QA by altering the van-der-Waals and electronic interactions (M265IT) and H-bond network to the acidic cluster around QB (M234EH, M234EL, M234EA and M234ER). All mutants decreased the free energy gap of the wild type RC (~890meV), i.e. destabilized the P(+)QA(-) charge pair by 60-110meV at pH8. Multiple modifications in the hydrogen bonding pattern to P resulted in systematic changes of the free energy gap. The destabilization showed no pH-dependence (M234 mutants) or slight increase (WT, donor-side mutants and M265IT above pH8) with average slope of 10-15meV/pH unit over the 6-10.5pH range. In wild type and donor-side mutants, the free energy change of the charge separation consisted of mainly enthalpic term but the acceptor side mutants showed increased entropic (even above that of enthalpic) contributions. This could include softening the structure of the iron ligand (M234EH) and the QA binding pocket (M265IT) and/or increase of the multiplicity of the electron transfer of charge separation in the acceptor side upon mutation.

New laser induced photoacoustic signal measurement method. Example of application: Identification of the uranium(IV)-dioxalato complex in solution

A new laser induced photoacoustic signal measurement method was developed to optimise the parameters of photoacoustic detection: to obtain synchronous measurement, to avoid laser energy fluctuation, to get reproductibility and repeatability. The aim is to apply the technique to solution chemistry, and particularly to studies of the actinides. The initial validation of the new method was done using neodymium(III) and uranium(IV) solutions in acidic media. It was found that the sensitivity of detection of these ions by photoacoustic measurements is improved in comparison with absorption spectrophotometry. This advantage in radiochemistry is the possibility to study actinides at low concentration (<10-4M) to understand their behaviour in solution: speciation, precipitation, kinetics. An example is described and concerns the identification of the uranium(IV)-dioxalato complex in solution by proposing a new mechanism for the precipitation of U(C2O4)2·6H2O.In this work, a measurement device is proposed for rough pressure wave acquisition. It allows sensor definition, local phenomena observation and alternative LIPAS measurement.