THz sources and THz applications – an overview
M. Havenith
Physical Chemistry II, Ruhr University Bochum, NC 7/74, 44780 Bochum, Germany
martina.havenith@rub.de
In recent years the THz range has been closed. Within the last decades new sources have been
developed in the opitcal community. These involved photonic sources as well as electronic table top
sources. More recently THz FEL has been made available to researches.
In the first part of the lecture I will talk about the main principles over the variety of THz systems in
this previously difficult frequency range over available THz sources. I will also give an overview
about distinct applications ranging from THz imaging to the detection of counterfeit drugs .
Observing the rattling modes of ions in the THz Range
M. Havenith
Ruhr-Universität Bochum
The details of ion hydration still raise fundamental questions relevant to a large variety of
problems in chemistry and biology. The concept of water "structure breaking" and "structure
making" by ions in aqueous solutions has been invoked to explain the Hofmeister series
introduced over 100 years ago, which still provides the basis for the interpretation of
experimental observations, in particular the stabilization/destabilization of biomolecules.
Recent studies, using state-of-the-art experiments and molecular dynamics simulations, either
challenge or support some key points of the structure maker/breaker concept, e.g. regarding
long ranged ordering/disordering effects. Here, we focus on how systematic terahertz
absorption spectroscopy and molecular dynamics simulation study of a series of aqueous
solutions of salts, adds a new piece to the puzzle. Concentration dependent THz absorption
studies of solvates ions allow to determine the dynamical hydration shell of anions as well as
cations. Exmples of monovalent, divalent as well as trivalent salts will be presented. When
dissecting the spectrum of trivalent salts we see the influence on cation due to counter anions
ranges from self-confinement of both ions to solvent shared ion-pairing, with increasing salt
concentration.
Reference: S. Funkner, G. Niehues, D.A. Schmidt, M. Heyden, G. Schwaab,
K.M. Callahan, D.J. Tobias, M. Havenith Watching the low frequency motions in
aqueous salt solutions – the terahertz vibrational signatures of hydrated ions
JACS 134, 1030-1035 (2012).
Some like it cool –
THz absorption studies of as a tool to study biomolecular hydration
Martina Havenith
Ruhr-Universität Bochum
The details of hydration still raise fundamental questions relevant to a large variety of
problems in chemistry and biology. We have shown the THz spectroscopy in combination
with MD simulations is a powerful took to study the sub-nsec hydration.
THz spectroscopy is also able to reveal the important role of hydration on biomolecular
function: Antifreeze proteins (AFPs) are specific proteins which are able to lower the freezing
point of aqueous solutions relative to the melting point. They are preferential docking to ice
nano ice crystals thereby preventing further growth of these. Whereas the antifreeze acitivity
for several of these AFP has been characterized so far, the molecular mechanism is still a
matter of controversial discussion:
By a combination of THz absorption spectroscopy and MD simulations we could show that
the activity of AFPs can be attributed to two distinct molecular mechanisms: a) short range
direct interaction of the protein surface with the growing ice face and b) long range interaction
via protein-induced water dynamics extending up to 20 Å from the protein surface. We
propose a long range retardation of the H-bond dynamics with a gradient towards the ice
binding site. A similar gradient in the H-bond dynamics was found by us for enzymes near the
catalytic site. We will discuss the underlying molecular mechanism supporting the docking at
specific sites.
References:
M. Heyden, E. Bründermann, U. Heugen, G. Niehues, D.M. Leitner, M. Havenith, Long range
influence of carbohydrates on the solvation dynamics of water – Answers from THz absorption
measurements and molecular modeling simulations, J. Am. Chem. Soc. 130, 5773-5779 (2008)
M. Grossmann, B. Born, M. Heyden, D. Tworowski, G.B. Fields, I. Sagi, M. Havenith, Correlated
structural kinetics and retarded solvent dynamics at the metalloprotease active site, Nature
Structural & Molecular Biology 18, 1102-1108 (2011).
S. Funkner, G. Niehues, D.A. Schmidt, M. Heyden, G. Schwaab, K.M. Callahan, D.J. Tobias,
M. Havenith, Watching the low frequency motions in aqueous salt solutions – the terahertz
vibrational signatures of hydrated ions, JACS, 134, 1030-1035 (2012).
K. Meister, S. Ebbinghaus, Y. Xu, J.G. Duman, A. DeVries, M. Gruebele, D.M. Leitner,
M. Havenith, Long-range protein-water dynamics in hyperactive insect antifreeze proteins, Proc.
Natl. Acad. Sci. USA 110(5) 1617-1622 (2013).
Watching the dance of water in the hydration shell of ions and biomolecules
in the THz frequency range
M. Havenith
Physical Chemistry II, Ruhr University Bochum, NC 7/74, 44780 Bochum, Germany
martina.havenith@rub.de
In recent years a new frequency window has been opened: The THz range. In pioneering studies it
could be shown that THz absorption spectroscopy is a new tool to study the solvation dyncamics of
biomolecules [1]. THz spectroscopy probes sensitively the fast (sub-psec) collective network
dynamics of bulk water. Accompanying ab initio MD simulation unravel the underlying molecular
motions: In contrast to the mid infrared regime -where the absorption peaks can be assigned to
intramolecular motions- in the frequency regime below 1000 cm-1 intermolecular motions with
concerted particle motions dictate the spectrum [2]. Precise measurements of absorption coefficients
of solvated solutes in the THz regime allow now a precise view on changes in hydration dynamics of
solutes during biological function [3,4,5].
[1] S. Ebbinghaus, S.J. Kim, M. Heyden, X. Yu, U. Heugen, M. Gruebele, D.M. Leitner, M. Havenith, "An extended dynamical solvation
shell around proteins," Proc. Natl. Acad. Sci. USA, 104, 20749 (2007).
[2] M. Heyden, J. Sun, S. Funkner, G. Mathias, H. Forbert, M. Havenith, D. Marx Dissecting the THz spectrum of liquid water from first
principles via correlations in time and space. Proc. Natl. Acad. Sci. USA, 107, 12068 (2010).
[3] D.A. Schmidt, Ö. Birer, S. Funkner, B. Born, R. Gnanasekaran, G. Schwaab, D.M. Leitner, M. Havenith, Rattling in the cage: Ions as
probes of sub-ps water network dynamics, J. Am. Chem. Soc., 131(51), 18512-18517 (2009)
[4] S.J. Kim, B. Born, M. Havenith, M. Gruebele, Real-time detection of protein-water dynamics upon protein folding by terahertz
absorption, Angewandte Chemie Intl. Edition 47 (34), 6486-6489 (2008).
[5] M. Grossmann, B. Niehues, M. Heyden, D. Tworowski, G.B. Fields, I. Sagi, M. Havenith (2010), Correlated structural kinetics and
retarded solvent dynamics at the metalloprotease active site, Nature Structural & Molecular Biology, published online 18.9.2011;
doi:1038/nsbm.2120