Raman optical activity (ROA) is a vibrational spectroscopic technique that is reliant on the difference in intensity of Raman scattered right and left circularly polarised light due to molecular chirality.
History of Raman optical activity
The field began with the doctoral work of Laurence D. Barron with Peter Atkins at the University of Oxford and was later further developed by Barron with David Buckingham at the University of Cambridge.
More developments, including important contributions to the development of practical Raman optical activity instruments, were made by Werner Hug of the University of Fribourg, and Lutz Hecht with Laurence Barron at the University of Glasgow.
Theory of Raman optical activity
The basic principle of Raman optical activity is that there is interference between light waves scattered by the polarizability and optical activity tensors of a chiral molecule, which leads to a difference between the intensities of the right- and left-handed circularly polarised scattered beams. The spectrum of intensity differences recorded over a range of wavenumbers reveals information about chiral centres in the sample molecule.
Raman optical activity can be observed in a number of forms, depending on the polarization of the incident and the scattered light. For instance, in the scattered circular polarization (SCP) experiment, the incident light is linearly polarized and differences in circular polarization of the scattered light are measured. In the dual circular polarization (DCP), both the incident and the scattered light are circularly polarized, either in phase (DCPI ) or out of phase (DCPII ).
Biological Raman optical activity spectroscopy
Due to its sensitivity to chirality, Raman optical activity is a useful probe of biomolecular structure and behaviour in aqueous solution. It has been used to study protein, nucleic acid, carbohydrate and virus structures. Though the method does not reveal information to the atomic resolution of crystallographic approaches, it is able to examine structure and behaviour in biologically more realistic conditions (compare the dynamic solution structure examined by Raman optical activity to the static crystal structure).
Related spectroscopic methods
Raman optical activity spectroscopy is related to Raman spectroscopy and circular dichroism. Recent studies have shown how by using optical vortex light beams, a distinct type of Raman optical activity that is sensitive to the orbital angular momentum of the incident light is manifest [1].
Raman optical activity instruments
Much of the existing work in the field has utilised custom-made instruments, though commercial instruments are now available.
The thinnest chirality assessed by ROA
The symmetry of the neopentane molecule can be broken if some hydrogen atoms are replaced by deuterium atoms. In particular, if each methyl group has a different number of substituted atoms (0, 1, 2, and 3), one obtains a chiral molecule. The chirality in this case arises solely by the mass distribution of its nuclei, while the electron distribution is still essentially achiral. This chirality is the thinnest one synthesized so far and was assessed by ROA in 2007.[2]
References
Forbes, Kayn A. (2019-03-14). "Raman Optical Activity Using Twisted Photons" (PDF). Physical Review Letters. 122 (10): 103201. Bibcode:2019PhRvL.122j3201F. doi:10.1103/PhysRevLett.122.103201. PMID 30932650.
Haesler, Jacques; Schindelholz, Ivan; Riguet, Emmanuel; Bochet, Christian G.; Hug, Werner (2007). "Absolute configuration of chirally deuterated neopentane" (PDF). Nature. 446 (7135): 526–529. doi:10.1038/nature05653. PMID 17392783. S2CID 4423560.
Bibliography
Laurence D. Barron, Fujiang Zhu, Lutz Hecht, George E. Tranter, Neil W. Isaacs, Raman optical activity: An incisive probe of molecular chirality and biomolecular structure, Journal of Molecular Structure, 834–836 (2007) 7–16.
See also
Linear dichroism
Magnetic circular dichroism
Optical activity
Optical isomerism
Optical rotation
Optical rotatory dispersion
Hyper Rayleigh Scattering Optical Activity
Two-photon circular dichroism
Vibrational circular dichroism
External links
Two Kings of Chirality by Dermot Martin. Laboratory News.http://www.labnews.co.uk/article/2028647/two_kings_of_chirality
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FT-IR Raman Resonance Raman Rotational Rotational–vibrational Vibrational Vibrational circular dichroism
UV–Vis–NIR
Ultraviolet–visible Fluorescence Vibronic Near-infrared Resonance-enhanced multiphoton ionization (REMPI) Raman optical activity spectroscopy Raman spectroscopy Laser-induced
X-ray and
photoelectron
Energy-dispersive X-ray spectroscopy Photoelectron Atomic Emission X-ray photoelectron spectroscopy EXAFS
Nucleon
Radiowave
NMR Terahertz ESR/EPR Ferromagnetic resonance
Others
Acoustic resonance spectroscopy Auger spectroscopy Astronomical spectroscopy Cavity ring-down spectroscopy Circular dichroism spectroscopy Coherent anti-Stokes Raman spectroscopy Cold vapour atomic fluorescence spectroscopy Conversion electron Mössbauer spectroscopy Correlation spectroscopy Deep-level transient spectroscopy Dual-polarization interferometry Electron phenomenological spectroscopy EPR spectroscopy Force spectroscopy Fourier-transform spectroscopy Glow-discharge optical emission spectroscopy Hadron spectroscopy Hyperspectral imaging Inelastic electron tunneling spectroscopy Inelastic neutron scattering Laser-induced breakdown spectroscopy Mössbauer spectroscopy Neutron spin echo Photoacoustic spectroscopy Photoemission spectroscopy Photothermal spectroscopy Pump–probe spectroscopy Saturated spectroscopy Scanning tunneling spectroscopy Spectrophotometry Time-resolved spectroscopy Time-stretch Thermal infrared spectroscopy Video spectroscopy Vibrational spectroscopy of linear molecules
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Raman spectroscopy
Techniques
Coherent anti-Stokes Raman spectroscopy Raman optical activity Resonance Raman spectroscopy Rotating-polarization coherent anti-Stokes Raman spectroscopy Spatially offset Raman spectroscopy Stimulated Raman spectroscopy Surface-enhanced Raman spectroscopy Tip-enhanced Raman spectroscopy Transmission Raman spectroscopy
Applications
Raman amplification Raman cooling Raman laser Raman microscope SHERLOC Stimulated Raman adiabatic passage
Theory
Depolarization ratio Four-wave mixing Nonlinear optics Raman scattering Rayleigh scattering Rule of mutual exclusion Stokes shift
Journals
Journal of Raman Spectroscopy Vibrational Spectroscopy
Hellenica World - Scientific Library
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