Identifying how small molecular acceptors pack with polymer donors in thin and thick (bulk) films is critical to understanding the nature of electrical doping by charge transfer. In this study, the packing structure of the molecular acceptor tetrafluorotetracyanoquinodimethane (F4TCNQ) with the semiconducting polymer poly­(2,5-bis­(3-tetradecylthiophen-2-yl)­thieno­[3,2-b]­thiophene) (PBTTT-C14) is examined. A combination of solid-state NMR, synchrotron X-ray scattering, and optical spectroscopy was used to determine the packing motif for blends of PBTTT-C14 and F4TCNQ in thin and bulk films. These results indicate that F4TCNQ and PBTTT-C14 order in a cofacial arrangement where charge transfer is near 100% efficient in the solid state. These results provide crucial insights into the structures and compositions of ordered domains in doped semiconducting polymers and suggest a model for the microstructure where the location of the molecular acceptors are correlated rather than randomly dispersed.

Flexible on the outside: The functional structure of the transport protein in human blood, human serum albumin (HSA), was characterized by distance measurements with double electron–electron resonance (DEER) spectroscopy on spin‐labeled fatty acids that are bound to HSA. The functional protein structure derived has a more rigid inner core, while the surface of the protein shows much greater structural flexibility.

This article highlights the occurrence and nature of nanoscale inhomogeneities in thermoresponsive polymers and focuses on different experimental techniques for their observation and characterization. Such inhomogeneities can be regarded as nanoscopic domains of collapsed polymer segments (or of a small number of unimers), which provide a nonpolar, hydrophobic interior. Continuous wave (CW) electron paramagnetic resonance (EPR) spectroscopy on amphiphilic reporter molecules (spin probes) as an intrinsically local technique is particularly emphasized. In combination with different ensemble-averaging methods, it provides a holistic understanding of the often inhomogeneous nanoscale processes during the temperature-induced collapse of a thermoresponsive polymer.

The effect of several ionic liquids (ILs) on the solution structure of human serum albumin (HSA) is revealed by continuous wave electron paramagnetic resonance (EPR) spectroscopy and nanoscale distance measurements with double electron-electron resonance (DEER) spectroscopy. HSA, the most abundant protein in human blood, is able to bind and transport multiple fatty acids (FAs). Using spin-labeled FA, the uptake of the FA by the protein and their spatial distribution in the protein can be monitored. The FA distribution provides an indirect yet effective way to characterize the structure of the protein in solution. Addition of imidazolium-based ILs to an aqueous solution of HSA/FA conjugates is accompanied by significant destabilization and unfolding of the protein's tertiary structure. In contrast, HSA maintains its tertiary structure when choline dihydrogenphosphate (dhp) is added. The comparison of FA distance distributions in HSA with and without choline dhp surprisingly revealed that with this IL, the FA anchoring units are in better agreement with the crystallographic data. Furthermore, the FA entry point distribution appears widened and more asymmetric than in pure buffer. These results indicate that choline dhp as a cosolvent may selectively stabilize HSA conformations closer to the crystal structure out of the overall conformational ensemble.