Raman optical activity (ROA) is a vibrational

spectroscopic Spectroscopy is the field of study that measures and interprets electromagnetic spectra. In narrower contexts, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum. Spectrosc ...

technique that is reliant on the difference in intensity of Raman scattered right and left circularly polarised light due to molecular

chirality Chirality () is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is distinguishable fro ...

History of Raman optical activity

The field began with the doctoral work of Laurence D. Barron with

Peter Atkins Peter William Atkins (born 10 August 1940) is an English chemist and a Fellow of Lincoln College at the University of Oxford. He retired in 2007. He is a prolific writer of popular chemistry textbooks, including ''Physical Chemistry'', ''Ino ...

at the

University of Oxford The University of Oxford is a collegiate university, collegiate research university in Oxford, England. There is evidence of teaching as early as 1096, making it the oldest university in the English-speaking world and the List of oldest un ...

and was later further developed by Barron with David Buckingham at the

University of Cambridge The University of Cambridge is a Public university, public collegiate university, collegiate research university in Cambridge, England. Founded in 1209, the University of Cambridge is the List of oldest universities in continuous operation, wo ...

. More developments, including important contributions to the development of practical Raman optical activity

instruments Instrument may refer to: Science and technology * Flight instruments, the devices used to measure the speed, altitude, and pertinent flight angles of various kinds of aircraft * Laboratory equipment, the measuring tools used in a scientific lab ...

, were made by Werner Hug of the

University of Fribourg The University of Fribourg (; ) is a public university located in Fribourg, Switzerland. The roots of the university can be traced back to 1580, when the notable Jesuit Peter Canisius founded the Collège Saint-Michel in the City of Fribourg ...

, and Lutz Hecht with Laurence Barron at the

University of Glasgow The University of Glasgow (abbreviated as ''Glas.'' in Post-nominal letters, post-nominals; ) is a Public university, public research university in Glasgow, Scotland. Founded by papal bull in , it is the List of oldest universities in continuous ...

Theory of Raman optical activity

The basic principle of Raman optical activity is that there is interference between light waves scattered by the

polarizability Polarizability usually refers to the tendency of matter, when subjected to an electric field, to acquire an electric dipole moment in proportion to that applied field. It is a property of particles with an electric charge. When subject to an elect ...

and

optical activity Optical rotation, also known as polarization rotation or circular birefringence, is the rotation of the orientation of the plane of polarization about the optical axis of linearly polarized light as it travels through certain materials. Circul ...

tensor In mathematics, a tensor is an algebraic object that describes a multilinear relationship between sets of algebraic objects associated with a vector space. Tensors may map between different objects such as vectors, scalars, and even other ...

s 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

wavenumber In the physical sciences, the wavenumber (or wave number), also known as repetency, is the spatial frequency of a wave. Ordinary wavenumber is defined as the number of wave cycles divided by length; it is a physical quantity with dimension of ...

s 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 A biomolecule or biological molecule is loosely defined as a molecule produced by a living organism and essential to one or more typically biological processes. Biomolecules include large macromolecules such as proteins, carbohydrates, lipi ...

structure and behaviour in aqueous solution. It has been used to study

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

nucleic acid Nucleic acids are large biomolecules that are crucial in all cells and viruses. They are composed of nucleotides, which are the monomer components: a pentose, 5-carbon sugar, a phosphate group and a nitrogenous base. The two main classes of nuclei ...

carbohydrate A carbohydrate () is a biomolecule composed of carbon (C), hydrogen (H), and oxygen (O) atoms. The typical hydrogen-to-oxygen atomic ratio is 2:1, analogous to that of water, and is represented by the empirical formula (where ''m'' and ''n'' ...

and

virus A virus is a submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are ...

structures. Though the method does not reveal information to the atomic resolution of

crystallographic Crystallography is the branch of science devoted to the study of molecular and crystalline structure and properties. The word ''crystallography'' is derived from the Ancient Greek word (; "clear ice, rock-crystal"), and (; "to write"). In J ...

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 Raman spectroscopy () (named after physicist C. V. Raman) is a Spectroscopy, spectroscopic technique typically used to determine vibrational modes of molecules, although rotational and other low-frequency modes of systems may also be observed. Ra ...

and

circular dichroism Circular dichroism (CD) is dichroism involving circular polarization, circularly polarized light, i.e., the differential Absorption (electromagnetic radiation), absorption of left- and right-handed light. Left-hand circular (LHC) and right-hand ci ...

. 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.

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.

References

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.

External links

* Two Kings of Chirality by Dermot Martin. Laboratory News.http://www.labnews.co.uk/article/2028647/two_kings_of_chirality {{Raman spectroscopy Raman spectroscopy