71HIGHLIGHTS 2020

Mechanism of Crystal Formation in Ruddlesden Popper Sn-Based Perovskites, J. Dong (a), S. Shao (a), S. Kahmann (a), A.J. Rommens (a), D. Hermida-Merino (b),

G.H. ten Brink (b), M.A. Loi (a) and G. Portale (a), Adv. Funct. Mater. 30, 2001294 (2020); https://doi.org/10.1002/ adfm.202001294.

(a) University of Groningen (The Netherlands) (b) Netherlands Organization for Scientific Research (NWO)

[1] https://www.nrel.gov/pv/module-efficiency.html. [2] F. Hao et al., Nat. Photonics 8, 489 (2014). [3] S. Shao et al., Adv. Energy Mater. 8, 1702019 (2018). [4] J.J. van Franeker et al., Adv. Funct. Mater. 27, 1702516 (2017). [5] Q. Hu et al., Nat. Commun. 8, 15688 (2017).

MYOSIN MOTOR DYNAMICS CONTROL THE STRENGTH AND DURATION OF THE HEARTBEAT

Despite their importance for human health, the molecular mechanisms that regulate the heartbeat in response to the changing needs of the body have remained obscure. X-ray movies of molecular structural changes in beating heart muscle have now uncovered these mechanisms, with potential implications for the treatment of the failing heart.

PRINCIPAL PUBLICATION AND AUTHORS

REFERENCES

crystallites in the bulk of the drying solution occurring in the 3D system and induces preferential alignment of the crystallites growing from the air-polymer interface. This results in the formation of an orientated 3D-like structure responsible for a PCE increase in the 2D/3D thin films [3]. Contrary to what was believed, the reason for the formation of this oriented structure is not a templating from 2D crystallised seeds,

but rather the active coordination role at the edge of the growing crystals of the PEA+ cations. The data highlight the difference between the Sn- and Pb-based perovskites, especially in the sequence of precursors and intermediate phases involved in the thin-film crystal-formation process, and suggest that efforts should certainly be focused on understanding the nature of the disordered colloidal precursors in Sn halide solutions.

Cardiovascular disease continues to be the leading cause of death worldwide, and is frequently associated with heart failure. Efforts to develop better therapeutics for heart failure have been held back by limited understanding of the normal control of contraction on the timescale of the heartbeat. Now, improved angular resolution at the ID02 beamline combined with low-noise rapid-readout detectors has enabled diffraction movies of beating heart muscle cells to be recorded with 20-ms time resolution. The results show that the time course and strength of contraction in the heart are determined by novel myosin filament-based control mechanisms, which can now be targeted for developing new therapies for heart disease.

Heart muscle cells are formed from long strings of sarcomeres (Figure 57a). At the center of each sarcomere is a centrosymmetric myosin filament (Figure 57b, white rectangle) containing two arrays of myosin motors with an axial periodicity of 14.5 nm. These myosin motors interact cyclically with the overlapping actin filaments to pull them towards the midpoint (M) of the myosin filament to drive contraction of the heart muscle. The centrosymmetric

structure of the myosin filament generates interference fringes (Figure 57c, blue) that sample the X-ray reflection produced by a single array of motors (Figure 57b-c, red) to give finely-spaced subpeaks (Figure 57c, black). By measuring these subpeaks during the contraction of heart muscle (Figure 57d, black), it was possible to determine the interference distance (Figure 57b, ID) between the two arrays of diffracting motors and the length of the diffracting array.

Nearly all the 49 layers of motors in each half myosin filament were found to contribute to the 14.5-nm reflection in the relaxed phase between heart beats (Figure 58a). In this OFF state of the myosin filament, most of the motors are inactivated by folding onto the filament surface (Figure 58a, pink). Some motors are also helically ordered (Figure 58a, dark pink) in relaxed heart muscle, but only in the central zone of each half-filament containing myosin binding protein-C (the C-zone, Figure 58a, green; labelled with a green fluorescent antibody in Figure 57a). When the heart muscle starts to contract, the non-helical motors at the tips of the filament are activated first, stressing the regions