Interference Results in Inaccurate Raman Spectroscopic Analysis of Vitamin B12

Plenty of natural products are complex organic molecules. Regardless of this intricacy, researchers are typically able to investigate them using spectroscopic techniques. Nevertheless, a team of scientists has found that caution should be taken using Raman spectroscopy to analyze specific chiral molecules (molecules that have handedness; i.e., they can exist in two “mirror image” kinds of each other). The study, released in the journal Angewandte Chemie, reveals that interference with circularly polarized light can falsify results.

Vitamin B12 is necessary for numerous bodily functions. It contributes to energy metabolism, and also it has a role to play in the nervous system and blood cells. It can also alternatively be bonded to other materials and also is non-toxic. These top qualities suggest that some chemists consider its great potential as a transport medium on which particular drugs could “piggyback” to arrive at their target location.

To use vitamin B12 in such a complex drug-transport layout, however, needs dependable analysis methods. One of the methods used to examine vitamin B12 is Raman spectroscopy, which is based on measuring light spread by molecules utilized to determine vibrational modes. However, this method is not flawless. Malgorzata Baranska from the Jagiellonian College in Krakow, Poland, and also collaborators have discovered a prospective source of flaws in the Raman spectroscopy of vitamin B12.

Many organic materials, like vitamin B12, have chirality or handedness, which can be observed via other interactions with polarized light. These molecules absorb and spread right and left-circularly polarized light differently and can have specific Raman optical activity spectra – referred to as a distinction in the scattering of the circularly polarized light. For the team’s analysis, they picked a variety of vitamin B12 by-products with different functional groups.

Because the structure of the selected molecules was similar, the team presumed the spectra to be similar as well. However, in a few of the measurements, optical activity changed considerably as the concentration of the substances in their solutions shifted. The scientists are alert that if this phenomenon is not considered in other investigations, it could lead to data misinterpretation.

As Baranska and her team went on to uncover, this unforeseen concentration dependency could be credited to circular dichroism. “The left- as well as right-circularly polarized light, is taken in different ways by a chiral medium, before and on the focal range of the laser beam in the measurement cell,” Baranska says. The resulting outcome might bring about an extra (false) Raman optical activity of the chiral solute. The group thinks, “this phenomenon has been either overlooked or misunderstood in earlier research studies.”

Baranska and her colleagues are fast to add that this issue is not overwhelming. The interference can be modeled computationally and then extracted from the data, or the measurement itself could be adjusted to take account of the interference.

The team additionally claims that, while they demonstrated this phenomenon for vitamin B12 analogs, the procedure is also applicable to various other light-absorbing chiral molecules.

Originally published on Phys.org. Read the original article.

Reference: Ewa Machalska et al, Recognition of the True and False Resonance Raman Optical Activity, Angewandte Chemie International Edition (2021). DOI: 10.1002/anie.202107600