J 815 s spectropolarimeter

Samples for CD measurements were prepared by mixing equal volumes of HEWL dissolved in D₂O, pD 7,4 at 2∙10⁻³ wt. % concentration and sodium mellitate solution in D₂O of the same molar concentration and pD as the HEWL solution. A quartz cuvette with a 10-mm-optical pathway placed in a PC-controlled Peltier unit was used to collect spectra on Jasco J-815 S spectropolarimeter (Jasco, Japan). Each spectrum was obtained through the accumulation of five independent scans at selected temperature. The temperature in the cell was increased through the Peltier module in a stepwise manner (typically at the rate of 10°C / 15 min). After reaching the highest temperature (85 ^oC) cell was gradually cooled down to 25 ^oC within 30 minutes and the final CD spectrum was collected.

For far-UV circular dichroism (CD) measurements of soluble (non-aggregated) samples, neutral pH stock solutions were diluted 100 times with deionized water (or GdnHCl solution, as specified in figure captions) to the final albumin concentration of 0.025 wt. % and subsequently placed in 1 mm quartz cuvettes. For near-UV CD measurements, the concentration of albumin was set at 0.75 wt. %. As aggregated protein tends to precipitate over time, it was desirable to carry out CD measurement of magnetically stirred samples of {BSA}, {BSA-AuNC}, and {BSA-Alk} which required 10 mm quartz cuvettes and further 10-times dilution of the sample to compensate for the increased optical density. All measurements were carried out at 25 ^oC by accumulation and averaging of 10 CD spectra independently collected on Jasco J-815 S spectropolarimeter (Jasco, Japan).

For circular dichroism
(CD) measurements of fresh aqueous solutions of peptide samples (typically
at a 0.21 mg/mL concentration), 1 mm quartz cuvettes were used. All
CD spectra corrected for the buffer signal were acquired at room temperature
by the accumulation of 5 independent spectra (at a 200 nm/s scanning
rate) on a J-815 S spectropolarimeter from Jasco Corp. (Tokyo, Japan).