Warwick introduces service to measure optical activity

By Wai Lang Chu

- Last updated on GMT

Related tags Enantiomer Stereochemistry

Warwick Analytical Services has made available a service that
allows the investigation and measurement of the optical activity of
samples with an accuracy of +/- 0.002 degrees for optical rotations
of less than 1 degree.

The sheer accuracy of this service could provide new insights into the optical activity of newly synthesised compounds, quantitative analysis of sugars, quality control of pharmaceutical drugs for enantiomeric purity and monitoring of enzymatic reactions.

Using polarimetry, the instrumentation operates at five wavelengths and all measurements of optical rotation are of the highest possible accuracy and precision.

Where samples are scarce use of an ultra microbalance combined with a 100mm micro cell allows accurate measurement from only 2ml of solution.

Optical activity of substances, especially drugs, must be determined early on in the drug discovery process as its chirality property may have an effect to the drug's efficacy.

A compound is chiral when it cannot be superimposed on its mirror image The pair of mirror imaged non-superimposable compounds are known as enantiomers.

Even though very similar still, different enatiomers of the same chiral drug can have very different pharmological effects, mainly because the proteins they bind to are also chiral.

If the substance exhibits nochirality and thus no effect on the function of the molecule then it should be safe to use in a racemic mixture.

If chirality is involved in biological activity then the use of a racemic mixture can be dangerous.

An example of the dangers of chirality occurred in early 1960's when a synthetic tranquilliser thalidomide was widely prescribed as a sedative. Some pregnant women later gave birth to deformed children.

The drug was administered as a racemic mixture. Later it was found that one isomer was teratogenic and interfered with DNA metabolism, while the other isomer was safe.

Though the L-isomer produced the teratogenic effect, and severe foetal abnormalities, but the situation still unclear because thalidomide racemises (interchange between isomers) rapidly in vivo.

>Warwick's​ Optical Rotation service uses a Perkin Elmer 341 Polarimeter. This high-resolution instrument has an accuracy of ±0.0020.

The rotation can be measured at 5 wavelengths, 589nm, 578nm, 546nm, 436nm and 365nm and the Polarimeter cell is temperature controlled with a Peltier unit, normally operated at 25°C.

The measurement of optical rotation is important in characterising newly synthesised compounds as well as quality control, especially of pharmacological substances, which may depend on their enantiomeric purity

Additionally, Warwick's use of an ultra microbalance combined with a 100mm micro cell allows accurate measurement with only 2ml of solution.

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