Understanding Chirascan Systems

• The Light Source: A Xenon Arc Lamp

Chirascan systems use a 150W Xenon arc lamp as the light source, which produces high-intensity ultraviolet (UV) and visible light. This ensures a high signal-to-noise ratio, enabling high-quality data. 

However, exposure of oxygen to UV light can produce ozone, which can degrade optical components. To counteract this, the system features an Active Nitrogen Management System (ANMS) to purge oxygen from the optical pathway.

• The Monochromator: Precision Polarisation Selection

Unlike conventional dual-prism spectrometers, Chirascan systems not only utilise two prisms, but a dual-polarising monochromator, which offers purer polarised light.

•  Photoelastic Modulator (PEM): Generating Circularly Polarised Light 

A crucial step in CD spectroscopy is converting linearly polarised light into circularly polarised light. This is achieved using a Photoelastic Modulator (PEM), which modulates the phase shift between orthogonal components of the light wave. By controlling this modulation, the system alternates between left- and right-circularly polarised light at a high frequency. 

• The Sample Interaction: Measuring Circular Dichroism

Once the circularly polarised light interacts with a chiral sample, the differential absorption of left- and right-handed circularly polarised light is measured. This difference is what generates the characteristic CD spectrum, which provides insights into the secondary and tertiary structure of proteins, protein-ligand interactions, and other molecular properties.

• High-Sensitivity Detection

Chirascan systems are designed for maximum sensitivity and precision. The advanced models, the Chirascan V100 and Q100 incorporate a solid-state detector (large-area avalanche photodiode, LAAPD) to achieve exceptional signal quality. This detector synchronises with the PEM frequency to accurately capture data with minimal noise.