Omnic program

The Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectra at room temperature was measured on a Nicolet iS50 FTIR spectrophotometer equipped with one pass diamond crystal ATR module (Thermo Fisher Scientific, Waltham, MA). The spectrometer was purged with N₂ to remove the contribution of atmospheric water vapor and CO₂ from all spectra. Each spectrum was an average of 100 scans at room temperature with a resolution of 2 cm^-1 in the spectral range of 4000–400 cm⁻¹. At indicated time points (0h–144h), 5 μl protein samples were taken out of the incubator and dropped on top of the ATR crystal. Raw data corresponding to amide-I region (1700–1600 cm^-1) were deconvoluted by using the Fourier self-deconvolution (FSD) method. The deconvoluted spectra in the amide-I region were subsequently subject to Gaussian curve-fitting procedure in order to quantify the secondary structure content in aS. The water component was subtracted from each of the sample spectra. Data analysis was performed with Omnic program (Thermo Fisher Scientific, MA) and OriginPro 2015 (OriginLab Corporation, MA), according to the manufacturers’ instructions.

FT-IR spectra were recorded on a Nicolet™ iS™ 5 FTIR Spectrometer (Thermo Scientific, Waltham, MA, USA), with a horizontal device for attenuated reflectance and diamond crystal, on a spectral window ranging from 4000 to 400 cm⁻¹, at a spectral resolution of 2 cm⁻¹. Spectra were recorded without any sample preparation and were processed with the OMNIC program (Thermo Scientific, Waltham, MA, USA).

Diffuse reflectance IR spectra (DRIFT) were recorded at room temperature using a NICOLET protégé 460 spectrometer (Thermo Scientific, Waltham, MA, USA) with a diffuse-reflectance attachment in the range of 6000–400 cm^–1 with a step of 4 cm^–1. For a satisfactory signal-to-noise ratio, 500 spectra were accumulated. CaF₂ powder was used as a standard. Before measuring the spectra, samples in granular form (fraction 50–200 mesh) were subjected to thermal vacuum treatment at a temperature of 450 °C for 2 h (heating rate 5 °C/min) to remove physically adsorbed gases and water. Carbon monoxide was used as a test molecule for the electronic state of metals. Adsorption was carried out at room temperature and equilibrium CO pressure of 15 Torr. The intensity of the bands in the spectra was expressed in Kubelka–Munk units. Data collection and processing were carried out using the OMNIC program (Thermo Scientific, Waltham, MA, USA). The spectra of adsorbed CO were presented as the difference between those recorded after and before adsorption.