Drug binding to human serum albumin (HSA) has been characterized by a spin-labeling and continuous-wave (CW) EPR spectroscopic approach. Specifically, the contribution of functional groups (FGs) in a compound on its albumin-binding capabilities is quantitatively described. Molecules from different drug classes are labeled with EPR-active nitroxide radicals (spin-labeled pharmaceuticals (SLPs)) and in a screening approach CW-EPR spectroscopy is used to investigate HSA binding under physiological conditions and at varying ratios of SLP to protein. Spectral simulations of the CW-EPR spectra allow extraction of association constants (KA ) and the maximum number (n) of binding sites per protein. By comparison of data from 23 SLPs, the mechanisms of drug-protein association and the impact of chemical modifications at individual positions on drug uptake can be rationalized. Furthermore, new drug modifications with predictable protein binding tendency may be envisaged.

A systematic study on the self-assembled solution system of human serum albumin (HSA) and paramagnetic doxyl stearic acid (5-DSA and 16-DSA) ligands is reported covering the broad pH range 0.7–12.9, mainly using electron paramagnetic resonance (EPR) methods. It is tested to which extent the pH-induced conformational isomers of HSA reveal themselves in continuous wave (CW) EPR spectra from this spin probing approach in comparison to an established spin-labeling strategy utilizing 3-maleimido proxyl (5-MSL). Most analyses are conducted on empirical levels with robust strategies that allow for the detection of dynamic changes of ligand, as well as protein. Special emphasis has been placed on the EPR spectroscopic detection of a molten globule (MG) state of HSA that is typically found by the fluorescent probe 8-Anilino- naphthalene-1-sulfonic acid (ANS). Moreover, four-pulse double electron-electron resonance (DEER) experiments are conducted and substantiated with dynamic light scattering (DLS) data to determine changes in the solution shape of HSA with pH. All results are ultimately combined in a detailed scheme that describes the pH-induced functional phase space of HSA.

A highly efficient approach for the synthesis of polyester-based networks via aza-Michael addition of primary amines to ⊍,⊎-unsaturated (vinyl) end groups of poly(glycerol adipate) (PGA) was achieved. By acylation of PGA with 6-(Fmoc-amino)hexanoic acid side chains via Steglich esterification, protected amine-functionalized PGA was obtained. This was followed by the removal of fluorenylmethyloxycarbonyl (Fmoc) protecting groups and the synthesis of PGA-based networks under catalyst-free conditions. The successful conjugate addition of primary amines to vinyl end groups and network formation were confirmed using 13 C magic angle spinning NMR and Fourier transform infrared spectroscopy. Network heterogeneity and defects were quantitatively investigated using 1 H double-quantum NMR spectroscopy. Finally, a hydrogel was prepared with potential biomedical applications. Supporting information may be found in the online version of this article.

A large number (63) of well‐defined nitroxide radicals, all phenol‐based TEMPO and PROXYL esters, were synthesized using different strategies based on well‐established Steglich esterifications. All of these radicals can be used as spin probes (SPs) and spin labels (SLs) for electron paramagnetic resonance (EPR) spectroscopy of supramolecular systems. Depending on the nature of the functional group(s) on each SP/SL, the synthesized nitroxide radicals serve as polyphilic molecular “toolbox” for the EPR‐spectroscopic detection and characterization of specific types of interactions, e. g. π–π interactions, sulfur‐sulfur interactions, hydrogen bonding, electrostatic and dipole‐dipole interactions, and van der Waals and hydrophobic interactions, in the presence of the selected supramolecular systems of interest (e. g. proteins, peptides). For each synthesized SP/SL the water solubility was gravimetrically determined for use in aqueous solution at pH 7.

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