Introduction

While CD measurements are typically obtained to analyze the secondary structure of proteins, CD can also be used to determine the configuration of organic compounds and coordination of metal complexes with optically active ligands.

J-1500 CD Spectrometer

This application note will compare CD spectra obtained using the OneDrop microsampling disc with a conventional cell, for organic compounds with an absorption band in the ultraviolet (UV) region and metal complexes with an absorption band in the UV and Visible regions.

Experimental

Measurement conditions for organic compounds (Figure 1)
Sample volume: 10 µL(MSD), 400 µL (Conventional cell)
Path length: 1 mm
Bandwidth: 1 nm
Data Interval: 0.1 nm
Scan speed: 100 nm/min
D.I.T.: 2 sec
Accumulation: 4 times (MSD), 1 time (Conventional cell)

Measurement conditions for metal complexes (Figure 2)
Sample volume: 10 µL(MSD), 400 µL (Conventional cell)
Path length: 1 mm
Bandwidth: 1 nm
Data Interval: 0.1 nm
Scan speed: 200 nm/min
D.I.T.: 2 sec
Accumulation: 9 times (MSD), 1 time (Conventional cell)

Diagram of procedure for using the microsampling disc

Keywords

One-drop measurement, Circular Dichroism, Organic compound, Metal-complex

Results

The CD spectra depicted in Figures 1 and 2 compare the results obtained using the MSD and a conventional cell for organic compounds and metal complexes, respectively. Both the organic compounds and metal complexes’ data show good correlation between spectra measured with the 10 µL volume microsampling disk (blue) and 400 µL volume conventional cell (green), each with a 1 mm path length.

Figure 1. CD spectra of (A) (1S)-(+)-10-Camphorsulfonid acid, ammounium salt and (B) D-Pantolactone using a microsampling disk (blue) and cylindrical cell (green).

Figure 2. CD spectra of (A) 2(+)D-[Coen₃]Cl3NaCl-6H₂O and (B) 0.25 M NiSO₄+0.36 M Rochelle salt using a microsampling disk (blue) and cylindrical cell (green).

Conclusion

This application note demonstrates that the OneDrop microsampling disk provides reliable spectra for CD spectroscopy measurements in volume-limited samples