Fig 3. Representative absorbance spectra of AMB-PEG 2 and unconjugated AMB formulations prepared in buffers with varying hydrophobicity.

20 mM AMB-PEG 2 and unconjugated AMB formulations were prepared in DMSO and resuspended in 20% and 48% ACN buffers containing 4.3% acetic acid, as well as PBS-EDTA, to a final concentration of 2 mM AMB. As buffer hydrophobicity increases with higher ACN concentrations, the A₃₄₈/A₄₀₉ ratio decreases, implying that AMB-PEG is increasingly in its monomeric form. As AMB-PEG 1 and 2 have similar UV-visible absorption profiles, with identical peak height ratios in all buffers tested, data for AMB-PEG 1 is not shown. AMB-PEG formulations that have been subjected to buffer exchange to PBS-EDTA through a 10 kDa centrifugal filter have the same UV-visible absorption spectra as the initial formulation of AMB-PEG in PBS-EDTA, which contains 10% DMSO.