Project

Back to overview

Time-resolved vibrational circular dichroism and vibrational rotary dispersion spectroscopy

English title Time-resolved vibrational circular dichroism and vibrational rotary dispersion spectroscopy
Applicant Helbing Jan
Number 129938
Funding scheme Project funding
Research institution Institut für Physikalische Chemie Universität Zürich
Institution of higher education University of Zurich - ZH
Main discipline Physical Chemistry
Start/End 01.12.2010 - 30.11.2012
Approved amount 125'561.00
Show all

Keywords (7)

femtosecond vibrational spectroscopy; vibrational circular dichroism; condensed phase dynamics; chirality; Vibrational Optical Activity; Ultrafast Chemical Reactions; Molecular Structure

Lay Summary (English)

Lead
Lay summary
Probing vibrational optical activity with ultrashort infrared laser pulses is a new spectroscopic method, promising detailed structural information on fast chemical and biochemical processes. It is currently being developed in Zürich and only a few other specialized laboratories around the world. Proteins, DNA and many other biologically important molecules are chiral, which means that like our hands they cannot be superimposed with their mirror image. We can detect the "handedness" of chiral molecules because they interact differently with left and right circular polarized light, a phenomenon known as optical activity. The difference in absorption of left and right circular polarized light is called circular dichroism, which is today routinely used to analyze secondary structure content of proteins (such as alpha helices and beta-sheets) and to characterize chiral drugs. More detailed information can be obtained when we study the interaction of chiral molecules with infrared light that can excite vibrations, since these are often localized in specific regions of a molecule. Measured vibrational circular dichroism (VCD) spectra can be compared to reliable quantum chemistry calculations, leading to precise knowledge of the configurations of atoms. The goal of this research project is to advance current technology in order to measure not only the vibrational circular dichroism of molecules in equilibrium, but to detect extremely small VCD changes during fast chemical reactions or during the rearrangement of biomolecules. In order to observe molecular motion on the timescale of picoseconds (this is a thousand times faster than a single operation in a 1GHz computer) we use very short laser pulses both to initiate a reaction or conformational change and to record spectra after a certain time delay (pump-probe technique). This method is already well established for measuring ordinary absorption changes in very fast chemical, physical and biological processes. Our unique capability to probe vibrational optical activity with short infrared laser pulses will also enable us to detect variations in chirality. From this development, new insights into the mechanism of a number of chemical and biochemical reactions can be expected. In addition to answering questions of fundamental research, we hope to stimulate the improvement of conventional vibrational optical activity measurements, which are of increasing commercial importance.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Angle determination and scattering suppression in polarization-enhanced two-dimensional infrared spectroscopy in the pump-probe geometry
Réhault Julien, Helbing Jan (2012), Angle determination and scattering suppression in polarization-enhanced two-dimensional infrared spectroscopy in the pump-probe geometry, in Optics Express, 20(19), 21665-21677.
Linear dichroism amplification: Adapting a long-known technique for ultrasensitive femtosecond IR spectroscopy
Réhault Julien, Zanirato Vinicio, Olivucci Massimo, Helbing Jan (2011), Linear dichroism amplification: Adapting a long-known technique for ultrasensitive femtosecond IR spectroscopy, in Journal of Chemical Physics, 134(12), 124516-1-124516-10.

Collaboration

Group / person Country
Types of collaboration
Prof. Massimo Olivucci, Universität Siena und Bowling Green, Ohio, USA Italy (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
Prof. Kazuto Takaishi, Seikei University, Tokio, Japan Japan (Asia)
- in-depth/constructive exchanges on approaches, methods or results

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
CECAM workshop -Vibrational Optical Activity: Interplay of Theory and Experiment Talk given at a conference Dreams and Reality in Time-Resolved Vibrational Optical Activity Measurements 23.09.2012 Pisa, Italy, Italy Helbing Jan;
XVIII International Conference on Ultrafast Phenomena Poster Exploring the polarization degrees of freedom in collinear two-dimensional infrared spectroscopy 08.07.2012 Lausanne, Switzerland, Switzerland Helbing Jan;
Kolloquium der Physikalischen und Theoretischen Chemie Individual talk Optical Activity and Linear Dichroism in Time-Resolved IR-Spectroscopy - New Methods and Challenges 15.05.2012 Würzburg, Germany, Germany Helbing Jan;
Seminar der Chemischen Institute der Universität Zürich Individual talk Vibrational Circular Dichroism as an Analytic Tool for the Chemisty Institutes in Zürich - An Introduction 24.04.2012 Zürich, Switzerland Helbing Jan;
International Workshop on Ultrafast Chemical Physics & Physical Chemistry UCP 2011 Talk given at a conference Structure-Sensitive Probing of Chemical Reactions in the Mid-Infrared: Common Principles for Improving Transient IR, 2D-IR and Vibrational Circular Dichroism Spectroscopy 14.12.2011 Glasgow, UK, Great Britain and Northern Ireland Helbing Jan;
Kolloquium der Physikalischen und Theoretischen Chemie Individual talk Structure-Sensitive Probing of Chemical Reactions in the Mid-Infrared: Common Principles for Improving Transient IR, 2D-IR and Vibrational Circular Dichroism Spectroscopy 14.11.2011 Frankfurt, Germany, Germany Helbing Jan;


Communication with the public

Communication Title Media Place Year
Media relations: print media, online media Spectroscopics explained Interanational Innovation International 2012

Associated projects

Number Title Start Funding scheme
119814 Development of Ultrafast Time-Resolved Vibrational Circular Dichroism Spectroscopy 01.06.2008 Project funding
119814 Development of Ultrafast Time-Resolved Vibrational Circular Dichroism Spectroscopy 01.06.2008 Project funding
143487 Time-resolved vibrational circular dichroism and vibrational rotary dispersion spectroscopy 01.12.2012 Project funding

Abstract

We have shown in first proof of principle experiments that ultrafast transient vibrational circular dichroism spectroscopy (VCD) is experimentally possible, but it has not yet become a routine measurement. Crossed polarizer arrangements, which have already been used with some success in electronic transient chiral spectroscopy, promise to provide the necessary gain in signal-to-noise necessary for a wider application of the technique. They also make it possible to record vibrational optical rotary dispersion (VORD) spectra. With this proposal wee seek financial support for a new PhD student as well as for further technical developments, in order to continue our pioneering efforts of the past three years. An already developed crossed-polarizer VORD/VCD setup will be upgraded with better polarizers and an automated rotation stage for more precise alignment. Elimination of these uncertainties should help us to overcome current difficulties to implement broad band detection. At the same time, an independent set-up will be built, which combines a new concept, recently demonstrated by a Korean research group, with noise-reduction techniques known from non-linear vibrational spectroscopy. We also seek a ‘calibration standard’ for chiral transient vibrational spectroscopy, i.e. molecules with two equally accessible enantiomeric forms that exhibit large VCD and VORD changes of opposite sign upon photoexcitation and are photostable. Like terpenes in static VCD or helical transition metal complexes in transient electronic CD spectroscopy, they are needed to test the performance of the experimental setup prior to measurements on more precious samples.The final goal of the project is to be able to resolve, in real time, inherently chiral processes, such as the unidirectional motion of molecular motors as well as conformational changes in biomolecules.
-