The CD spectra of all BSA formulations showed negative bands at 222 nm and 208 nm and a positive band at 193 nm, characteristic of a high ↵-helical content (see ESI). The amide I band (1700-1600 cm 1 ) of the FTIR spectrum showed an asymmetric feature centred at approximately ⇠1658 cm 1 , (Figure ), which is characteristic of a high ↵-helical content. No significant changes were observed upon heat treatment of the mAb formulations in the peak positions or intensities in the CD (Figure ) or FTIR spectra (Figure ) (see ESI). The CD spectra for the F6 and F7 mAb formulations exhibited a typical spectra with a broad negative band at 218 nm characteristic of beta-sheet secondary structure. Similarly, the amide I band of the FTIR spectrum showed an asymmetric band centred at ⇡ 1640 cm 1 , with shoulders at approximately 1670 cm 1 and 1690 cm 1 (Figure ), which is characteristic of the high -sheet content, estimated to be for example 56 ± 8% for unheated F6 (see ESI). 3.1.3. Solid State Nuclear Magnetic Resonance Spectroscopy (ssNMR) Solid State NMR is a well established method for studying protein formulations. To investigate the structural changes on the molecular scale, 13 C CP-MAS spectra of the BSA formulations before and after heating, and with the addition of 0.04% polysorbate 80 were acquired and compared to pure BSA and a physical mixture of the formulation components (for the THz-TDS spectra of the physical mix see ESI). When comparing the spectrum of the formulation with the one of the pure protein, no significant chemical shift differences can be observed that could imply any major changes in the structure of the protein. In contrast, the signals of the anomeric carbon atoms were clearly shifted. This can be explained by the formation of an amorphous structure of the sugar in the buffer upon freeze-drying compared to the crystalline structure of the sugar in the physical mixture. Additionally, the signal line shapes of histidine and sucrose were found to be significantly sharper in the physical mixture compared to those ob- Previous studies have shown that the investigation of T 1 and T 1⇢ can provide insight to changes in protein mobility in the presence of sugars. By comparing the values of T 1 and T 1⇢ of the sugar and proteins, one can obtain information about phase separation in the sample on the length scale of 2 5 nm (T 1⇢ ) and 20 50 nm (T 1 ). . Equal relaxation times indicate homogeneous phases, whereas different relaxation times imply separated phases. Figure shows an overview of the measured T 1 and T 1⇢ relaxation times of the formulations and pure BSA.