Method and Device for Measuring Optical Activity Spectra
Data di pubblicazione
Data di priorità
Politecnico di Milano
DIPARTIMENTO DI FISICA
Fabrizio Preda, Julien Réhault, Jan Helbing, Dario Polli, Giulio Cerullo
Our innovative device (#1) enables one to measure Circular Dichroism (CD), Optical Rotatory Dispersion (ORD), linear birefringence (LB) and linear dichroism (LD) spectra over a broad bandwidth in any spectral region (comprising the UV, visible, near-infrared and infrared). The CD and ORD spectra are retrieved by means of a Fourier transform of the interference signal between the chiral signal and a local oscillator, whose relative delay is scanned by changing the insertion of a birefringent wedge. This device requires a light source (i.e. a lamp or a laser), one or two polarizers, two birefringent wedges, one birefringent plate and one detector.
A modified device based on the very same principle of measurement (#2) allows one to measure also the Stimulated Raman Optical Activity (Stimulated ROA).
Campo di applicazione
Our device #1 will be mostly considered and exploited in biological and pharmaceutical areas, where CD and ORD measurements in the UV spectral region are performed regularly in order to retrieve crucial information on the structural conformation of macromolecules, molecules, DNA/RNA and proteins, to study and characterize, e.g. their structure, stability (under heat, stress, denaturation), folding, kinetics and interactions.
The device #2 can significantly enhance the sensitivity and shorten the acquisition time of ROA spectra. In combination with density functional theory calculations, ROA spectra allow one to reliably determine the absolute configuration of molecules in solution (i.e. without the need for crystallization), as required by drug regulation authorities.
With respect to standard commercial spectropolarimeters:
• It does not require a PEM (photoelastic modulator) or a lock-in amplifier, thus it is much less expensive
• It does not require a monochromator, thus it is much more compact
• It automatically measures CD and ORD signals simultaneously
• Commercial spectropolarimeters measure the spectra wavelength by wavelength, so that the measurement time increases with increasing spectral coverage required. Our device illuminates the sample with all the light colors simultaneously, so that it measures the entire spectrum at once [multiplex advantage].