Measurement of a Complex Forming Reaction of Nickel Sulfate and Rochelle Salt Probed by Stopped-Flow CD Spectroscopy

Download PDF May 31, 2017

Introduction

Stopped-flow CD is a well-known method to probe the unfolding and refolding processes of proteins in order to obtain secondary structure information on a millisecond time scale. Stopped-flow CD can also be used outside the realm of protein dynamics, to observe complex-forming reactions. Transition metal complexes typically exhibit absorption bands in the visible to near-infrared region of the spectrum and CD measurements can be used to probe structural changes that occurr in this region.

This application note demonstrates the measurement of the complex-forming reaction of nickel sulfate and Rochelle salt using a High Speed Stopped-Flow system consisting of a J-1500 CD spectrometer and a SFS-562T stopped-flow accessory.

J-1500 Circular Dichroism Spectrophotometer
J-1500 CD Spectrometer

Keywords

J-1500, circular dichroism, stopped-flow, SFS-562T, transition metal complexes, kinetics, infrared, visible, chemical

Results

Measurement Conditions 
Measurement wavelength1 nm
Path length2 mm
Spectral bandwidth5 nm and 10 nm
Data pitch1 msec
Accumulations75 and 50 times
Response time2 msec
Syringe 10.24 M nickel sulfate
Syringe 20.36 M Rochelle salt
Mixing ratio100 µL:100 µL
Total flow rate5 mL/sec

Figure 1 illustrates the CD spectra of 1:1 solution sample of nickel sulfate and Rochelle salt. The CD spectrum exhibits a single, broad peak from the ultraviolet (UV)-visible to near infrared (NIR) region.

Figure 1. CD spectra of 0.24 M nickel sulfate and 0.36 M Rochelle salt in a 10 mm path length cell.

The stopped-flow CD spectra of nickel sulfate and Rochelle salt are shown in Figure 2-4. The data illustrated in Figure 2 were obtained at 720 nm and Figure 3 were obtained at 1000 nm. Figure 4 shows both the spectra obtained at 720 and 1000 nm for comparison. After 100 msec the data for both wavelengths begin to level off, indicating that the complexforming reaction is complete. This also means that the data measured at both 720 and 1000 nm observe the same reaction process.

Figure 2. The complex formation of nickel sulfate and Rochelle salt as measured by stopped-flow CD at 720 nm
Figure 3. The complex formation of nickel sulfate and Rochelle salt as measured by stopped-flow CD at 1000 nm
Figure 4. The complex formation of nickel sulfate and Rochelle salt as measured by stopped-flow CD at 720 nm (blue) and 1000 nm (green)

Conclusion

This application note demonstrates that the J-1500 CD spectrometer and SFS-562T stopped-flow accessory can be used to monitor complex-forming reactions and their completion time.

References

  1. Miyake, H., Sugimoto, H., Tamiaki, H., and H. Tsukube, (2005) Chem. Commun., 429104293.
  2. Miyake, H., Kamon, H., Ikuko, M., Sugimoto, H., and H. Tsukube, (2008), JACS, 130, 792-793

About the Author

Leah Pandiscia received her PhD from Drexel University where she studied Biophysical Chemistry. She is a Spectroscopy Applications Scientist at JASCO.