Cryojet

Diffraction data were collected at 110 K on an Oxford Diffraction SuperNova diffractometer with MoK_α radiation (λ=0.71073 Å) using a EOS CCD camera. The crystal of ^EtReP^Br was cooled with an Oxford Instruments Cryojet. Diffractometer control, data collection, initial unit cell determination, frame integration and unit-cell refinement was carried out with “CrysAlisPro”.[30 ] Face-indexed absorption corrections were applied using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm.[31 ] OLEX2[32 ] was used for overall structure solution, refinement and preparation of computer graphics and publication data. Within OLEX2, the algorithm used for structure solution was “charge-flipping” using the superflip program.[33 ] Refinement by full-matrix least-squares used the SHELXL-97[34 ] algorithm within OLEX2.[32 ] All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were placed using a “riding model” and included in the refinement at calculated positions. Crystal data and structure refinement details (see the Supporting Information, Table S4), selected bond distances and angles (Table S5) and details about the X-ray crystal structure refinement are given in the Supporting Information.

The equipment required for SRXRF analysis is available as part of the general user facility at the Advanced Photon Source (APS, Argonne National Laboratory, Argonne, IL) beamline 2-ID-D. Upon mounting onto a custom holder in a liquid nitrogen bath, the neuron-containing SiN window was quickly placed in the center of a Cryojet (Oxford Instruments) that convectively cooled the sample with cold nitrogen gas maintained at 100°K. To prevent frosting of the sample, the cold nitrogen jet was surrounded by a dry nitrogen jet at ambient temperature placed inside a chamber with a continuous flow of dry nitrogen. A monochromatic X-ray beam was focused on the specimen using a Fresnel zone plate. Energy of the incident X-ray beam was 10 keV allowing excitation of zinc, potassium, sulfur, and other transition elements. A scan area containing neurons of interest was located by the coordinates obtained from the observation in cryo light microscope and further defined by a coarse 2-D scan viewed using the MAPS software (see below). A final high resolution scan was performed with a pixel step size of 0.25 μm and a 250 msec dwell time.

To obtain single crystals of D-U hyd, 15 mg of a dry ground equimolar mixture of D and U was dissolved in 5 mL of methanol. Single-crystals were grown after solvent evaporation at room temperature. Single crystal measurements were performed on an Oxford Diffraction Xcalibur Nova R (microfocus Cu tube) equipped with an Oxford Instruments CryoJet liquid nitrogen cooling device. Program package CrysAlis^PRO70 was used for data reduction and numerical absorption correction. The structures was solved using SHELXS97 and refined with SHELXL-2017.⁷⁷ The model was refined using the full-matrix least-squares refinement; all non-hydrogen atoms were refined anisotropically. Hydrogen atoms were located in a difference Fourier map and refined as a mixture of free-restrained and riding entities. The co-crystallized water molecule (O3) is disordered over two positions (designated as A and B) with respective occupancies of 63% and 37%. Molecular geometry calculations were performed by PLATON⁷¹ (link) and molecular graphics were prepared using ORTEP-3,⁷² and Mercury.⁷³ (link) Crystallographic and refinement data for D-U hyd is shown in Figure S15. The structure has been deposited in the Cambridge Crystallographic Data Center (CCDC) as no. 2059340.