Dear Visitor,
Welcome to my website at the Chair for BioMolecular Optics at the Ludwig-Maximilians-Universität München.
My reaserch deals with important reactions taking place in the photosynthetic cycle of purple bacteria at room temperature.
In particular, our study is focused on reaction centers from Rhodobacter sphaeroides where the primary conversion from light into chemical energy occurs.
Current research projects
A. Ultrafast VIS/NIR pump-probe spectroscopy
Using titanium sapphire laser systems it is possible to measure photo-induced reactions in chemical and biological molecules in subpicosecond (1ps = 10 -9 s) time scales.
Modern experimets allow to measure transmission changes ΔT / T ~ 10 -6 .
Figure 1: Schematic representation of our Pump-Probe setup
Nonlinear frequency conversion techniques, in this case non-collinear optical parametric amplification (NOPA),
facilitate the generation of stable and intense pulses for pump-probe experiments.
Figure 2: a) Different types of Probe-Continuum. b) Measured Pulse-Stability over 2000 pulses.
B. Primary reactions in photosynthetic reaction centers from Rhodobacter sphaeroides
The conversion from light into chemical energy in every photosynthetic system takes place in a specialized protein unit called reaction center.
In this particular system, an electron is tranfered from the originally excited spacial pair (P) via a bacteriocholophyll (B) and bacteriopheophitine (H)
towards an ubiquinone (Q) with a transport yield > 97%.
Figure 3: Electron transfer reaction scheme described by a sequential model with four intermediate states.
In order to describe this huge transfer efficiencies it is important to measure the intermediate short-lived states.
In the 1990ies, a simple stepwise reaction model (see Figure 3) based on non-adiabatic Marcus-type electron transfer (ET),
was proposed to explain the molecular processes and to understand optimization of photosynthesis. Recent measurements performed with modern laser systems supported this model [1].
[1] Dominguez et al., Chemical Physics Letters 601 (2014), pp. 103-109
C. Data analysis: Singular value decomposition
The purpose of every data analysis algorithm is to identify the relevant physical information which is present in the measurement.
In particular, using the singular value decomposition (SVD) of the data matrix it is possible to extract its main kinetic components.
To avoid the introduction of systematic errors when dealing with an insuficient amount of SV, many different algorithms were proposed
in order to identify the number of significant SV [1-3].
Figure 4: Singular Value Decomposition of the data matrix.
[2] Shrager et al., Analytical Chemistry 54 (1982), pp. 1147-1152.
[3] Malinowski, Journal of Chemometrics 23 (2009), pp. 1-6.
D. Sample exchange in a closed cuvette
One main assumption of every pump-probe measurements is that every molecule in the excitation volume is in a well defined state, in our case the ground state.
Over the past 20 years, many different exchange systems have been developed to provide fresh molecules after every excitation pulse. One common setup involves
open cell systems, which pumps the molecules through the cuvette at high velocities. However, if the amount of sample available for each experiment is not
enough to fill the pumping circuit, closed cell systems may be used. In our group we developed a device which combines two essential exchange mechanisms:
rapid transverse translational motion and magnetic stirring [4].
Figure 4: Sample exchange system with rotation device and stirrer.
[4] Dominguez et al., Review of scientific Instruments 86, 033101 (2015)
