Physical Chemistry II - Laser spectroscopy and Biophotonics

High resolution spectroscopy with modern laser techniques

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How fast is the proton transfer in double hydrogen bonds?

Ultracold molecules near absolute zero (at 0.37 K!)

Laser spectroscopy in superfluid helium nano-droplets - supported by the SP1116 program Quantum Solvent: Phys. Rev. Lett. 95, 215301 (2005) Supported by DFG Research Group FOR 618 (press release)

Interfacial chemistry

The study of interfaces in condensed phase has attracted a great deal of attention within the last year. Modern experimental and theoretical methods have made it possible to envision a microscopic understanding of this important question in chemistry. Our goal is to use new laser spectroscopic tools to obtain a microscopic understanding of the structure and dynamics at interfaces. Recently, we have investigated biomolecule interfaces including solute-solvent, protein-water interfaces and self assembled monolayers. New experimental tools have been developed to access the fingerprint region for intra- and intermolecular vibrations: The IR and THz spectral range.

1. Biomolecule large amplitude motion and solvation dynamics as probed by THz laser spectroscopy

Whereas much knowledge has been gained in recent years on the structure of biomolecules and proteins it has becomes evident that a full understanding of biomolecular function will require a better description of dynamics. Whereas in small molecules molecular chemistry is governed by intramolecular motions the relevant motions for protein dynamics are though to be large amplitude motions such as skeleton motions and breathing modes. These motions influence, and in turn are influenced by, the solvation environment around the molecule. Terahertz spectroscopy directly probes these large amplitude motions of biomolecules, as well as collective solvent dynamics surrounding biomolecules.

However, the THz spectral region, covering the region between microwave technology and diode laser technology has been known for its lack of available high power laser sources and was characterized as the "THz gap". The study of proteins in solutions is also facilitated by the high absorption of water in this spectral region which makes it difficult to penetrate solutions. We have developed a high power THz germanium laser spectrometer which is able to measure precise THz absorptions in the region between 1-4 THz (New p-Ge THz spectrometer for the study of solutions: THz absorption spectroscopy of water, Rev. Sci. Instr. 76, 063110 (2005)). This enables us to study biomolecules in their natural environment and directly observe solvation and collective motions on the (0.3-1 nm) length scale (current publications: Solute induced retardation of water dynamics probed directly by THz spectroscopy, PNAS 103, 12301 (2006) and D.M. Leitner, M. Havenith, M. Gruebele, Biomolecule large amplitude motion and solvation dynamics: Modeling and probes from THz to X-rays, Int. Rev. Phys. Chem. 25(4), 553-582 (2006).

• News: 02/2008 - Press release - Protein Folding Modifies the Water in the Environment - New Knowledge Gained From Terahertz Spectroscopy - RUB Chemistry Observes “THz Dance“ Changes
• Press release - The terahertz dance of water with proteins - PNAS reports: Disco becomes a minuet - Protein influence has a previously unsuspected long reach
• Press release (in German: PDF): The secret of sugar water - Ancient mystery solved - Water is active: RUB chemists end speculations.
• Archive: Bunsen Discussion Meeting 2007: Exploring THz Spectroscopy. Post-conference information.

This study which is carried out in cooperation with Martin Gruebele and David Leitner and was supported by the Human Frontier Science Program (press release and find more information on THz projects on our webpages).

2. Scanning near field infrared microscopy (SNIM)

The chemical and structural analysis of the molecular composition and orientation of sample surfaces is important in many research fields such as material science, microelectronics or bioengineering. Many of these techniques require special conditions such as vacuum or special sample preparation such as metallic coating. An experimental approach for the mapping of the chemical surface composition with an easy and label-free characterization of functional surface groups on a nanometer scale would be of fundamental importance for a variety of problems in surface science.  Previously, we have report the extension of scanning near field infrared microscopy (SNIM) as a label free method for the characterization of surfaces and subsurface structure in the chemically important O-H and C-H stretching (fingerprint region) on a nm scale (Set-up of a SNIM: Imaging of sub-surface nano-structures, PCCP 8, 753 (2006)). Infrared (IR) spectroscopy is a well-established sensitive technique for detection and characterization of tissues. The lateral resolution is nm, the sensitivity allows the spectral characterization of monolayers. Our recent results demonstrate the high sensitivity of SNIM for label free characterization of functional groups in thin films of 10-20 liter: Chemical Imaging of Microstructured Self-Assembled Monolayers with Nanometer Resolution, J. Phys. Chem. C 111, 8166 (2007). Cover article (see image):  SNIM-Scanning near-field infrared microscopy, Annu. Rep. Prog. Chem., Sect. C: Phys. Chem., 104, 235-255 (2008).

This work is supported by the Deutsche Forschungsgemeinschaft by grant HA2394/12 and by an EU Marie-Curie Early Stage Research Training school INTCHEM: Non colvalent interactions in chemistry and biochemistry. Further details see RUBIN issue autumn 2007: Die Molekulare Zaubertafel (article in German PDF).

Press release (in German): One million Euro for microscopy with infrared and terahertz radiation funded by BMBF (Federal Ministry of Education and Research).

WINTER COLLEGE ON MICRO AND NANO PHOTONICS FOR LIFE SCIENCES, Conference Organizer(s): Directors: Mario Bertolotti (Univ. of Rome, Italy), Martina Havenith (Ruhr Univ., Bochum, Germany) and Oscar. E. Martinez (Univ. of Buenos Aires, Argentina); ICTP Local Organizer: J. J. Niemela, Trieste - Italy, 11 - 22 February 2008.

Press release (in German): Inventor price 2007 for Prof. Dr. Martina Havenith-Newen and Dr. Erik Bründermann.

3. Biophotonics and medical applications

We have developed a label free technique to monitor intracellular water in single cells. Oxidative stress, addition of hormones and substances like insulin and glutamine can alter the water concentration in cells. It has been shown that this is directly connected with a change of proteolysis or signal transduction (D. Häussinger, Biochem. J. 313, 697 (1996)). We have developed spectroscopic methods to monitor the water concentration in single cells in real time. Using a near field diode laser the water content can be directly determined by measuring the absorption on the overtone transition of water at 1400 nm.

As a first example we have measured the changes in the water concentration in hepatocytes of rats. When diluting the buffer HBSS (Hank's balanced salt solution) we could observe a swelling of the cells which is accompanied by changes in their water concentration. For further details on infrared microscopy of living cells see also the press release and more information on our webpages.

These projects are part of the University Center of Medical Technology (Section 2 - Imaging) in Bochum.

The formation of snow crystals, the stability of soap bubbles, and formation of water droplets; the fact that geckos are able to walk upside-down: all these are consequences of intermolecular interactions. Intermolecular interaction determines transport properties of real gases and plays an important role for the structure of liquids and for aggregation.

Hydrogen bonding has an exceptional position among intermolecular interactions. It affects the special properties of liquid water and the crystallisation of snow flakes as much as the structure of proteins and the DNA. Hydrogen bonds are weaker than chemical bonds, but stronger than van-der-Waals interactions and are strongly directional. The strength is in a range where the bond cannot be broken by thermal fluctuation, but it can dissociate with little energy. This allows changes in otherwise rigid configurations and facilitates e.g. the replication of the genetic code. The famous Watson-Crick double-helix structure of DNA is stabilized by double and triple hydrogen bonds.

Our goal is to use high resolution laser spectroscopy to provide a detailed understanding of important prototype systems.