Analytical Sciences

Refining Calibration Procedures of Circular Dichroism Spectrometer to Improve Usability

Kumiko SAKAI-KATO,*1 Kohki YOSHIDA,*1 Takashi OHGITA,*2 Yuki TAKECHI-HARAYA,*3 Yosuke DEMIZU,*4 and Hiroyuki SAITO*2

*1 School of Pharmacy, Kitasato University, 5-9-1 Shirokane, Minato, Tokyo 108-8641, Japan
*2 Department of Biophysical Chemistry, Kyoto Pharmaceutical University, 5 Misasagi-Nakauchi-cho, Yamashina, Kyoto 607-8414, Japan
*3 Division of Drugs, National Institute of Health Sciences, 3-25-26 Tonomachi, Kawasaki, Kawasaki 210-9501, Japan
*4 Division of Organic Chemistry, National Institute of Health Sciences, 3-25-26 Tonomachi, Kawasaki, Kawasaki 210-9501, Japan

Circular dichroism (CD) is a technique used for conformational studies of peptides and proteins. We studied the specific calibration procedures of CD spectrometers based on procedures specified in the European Pharmacopoeia. We aimed to develop procedures to improve the usability of CD, in addition to reducing adverse effects on users’ health. The use of ethanol instead of 1,4-dioxane as the solvent for isoandrosterone was examined. Both solvents yielded the same maximum value of +3.3 for molar CD. We also studied a two-point calibration method using (1S)-(+)-ammonium 10-camphorsulfonate instead of (1S)-(+)-10-camphorsulfonic acid, which is a hygroscopic compound. Both compounds yielded similar results and the values for (1S)-(+)-ammonium 10-camphorsulfonate of 2.39 ± 0.04 and –4.92 ± 0.06 at 290.5 and 192.5 nm, respectively, were within the criteria defined in the European Pharmacopoeia. The inter-laboratory repeatability was also acceptable. These studies provide specific procedures for calibrating CD spectrometers for drug development.

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