Tensor 27 fourier transform spectrometer

HoxG protein solutions were transferred into a homemade, gas-tight, and temperaturecontrolled (10°C) transmission cell equipped with two sandwiched CaF₂ windows separated by a Teflon spacer with an optical pathlength of 50 μm. Spectra with a resolution of 2 cm⁻¹ were recorded on a Tensor 27 Fourier-Transform spectrometer (Bruker) equipped with an MCT (liquid nitrogen-cooled mercury-cadmium-telluride) detector. The cell compartment was purged with dried air. For a single spectrum 200 individual scans were averaged. A buffer spectrum was used as reference for calculating the corresponding absorbance spectra. OPUS software version 7.5 from Bruker was used for data analysis. For the cofactor-stability experiments, IR spectra of as-isolated HoxG protein solution 35 mg/ml (500 μM) and a threefold higher concentrated sample were recorded consecutively for 7 h.

The infrared spectra were recorded on a Tensor 27 Fourier-transform spectrometer Bruker (Ettlingen, Germany) in a range of 4000–400 cm⁻¹ with an optical resolution of 4 cm⁻¹ and an accumulation of 32 scans using KBr pressed pellets.

The reflectanceI) solar spectrum range (0.3–2.5 μm) of the coating was obtained by a Shimadzu UV3600 UV/VIS/NIR spectrophotometer with an integration sphere (module 150 mm), while the reflectance spectra in the range of 2.5–25 μm were measured by a Bruker Tensor 27 Fourier Transform spectrometer equipped with an integrating sphere (A562-G/Q) using a gold plate as a standard. Then, the absorptance α and emittance ε were obtained by Equations (1) and (2): $$\alpha =\frac{{{\displaystyle \int }}_{0.3}^{2.5}{I}_s\left(\lambda \right)\left[1-R\left(\lambda \right)\right]d\lambda }{{{\displaystyle \int }}_{0.3}^{2.5}{I}_s\left(\lambda \right)d\lambda }$$
$$\epsilon =\frac{{{\displaystyle \int }}_{2.5}^{25}{I}_b\left(\lambda \right)\left[1-R\left(\lambda \right)\right]d\lambda }{{{\displaystyle \int }}_{2.5}^{25}{I}_b\left(\lambda \right)d\lambda }$$
where λ is the wavelength, I_s(λ) is the solar radiation power at AM1.5, R(λ) is the spectral reflectance of sample, and I_b(λ) is the spectral black body emissive power at room temperature.
The thermal stability of the solar selective absorbing coating was evaluated by the performance criterion (PC), which was calculated from the obtained α and ε according to the following Equation (3):

where Δα = α_(aged) − α_(unaged) and Δε = ε(_aged) − ε(_unaged). Once the PC increases to be higher than 0.05, the solar selective absorbing coating is identified as having failed.