Intrinsic glassy-metallic transport in an amorphous coordination polymer.

Conducting organic materials, such as doped organic polymers1, molecular conductors2,3 and emerging coordination polymers4, underpin technologies ranging from displays to flexible electronics5. Realizing high electrical conductivity in traditionally insulating organic materials necessitates tuning their electronic structure through chemical doping6. Furthermore, even organic materials that are intrinsically conductive, such as single-component molecular conductors7,8, require crystallinity for metallic behaviour. However, conducting polymers are often amorphous to aid durability and processability9. Using molecular design to produce high conductivity in undoped amorphous materials would enable tunable and robust conductivity in many applications10, but there are no intrinsically conducting organic materials that maintain high conductivity when disordered. Here we report an amorphous coordination polymer, Ni tetrathiafulvalene tetrathiolate, which displays markedly high electronic conductivity (up to 1,200 S cm-1) and intrinsic glassy-metallic behaviour. Theory shows that these properties are enabled by molecular overlap that is robust to structural perturbations. This unusual set of features results in high conductivity that is stable to humid air for weeks, pH 0-14 and temperatures up to 140 °C. These findings demonstrate that molecular design can enable metallic conductivity even in heavily disordered materials, raising fundamental questions about how metallic transport can exist without periodic structure and indicating exciting new applications for these materials.

Correlation-driven phenomena in periodic molecular systems from variational two-electron reduced density matrix theory.

Correlation-driven phenomena in molecular periodic systems are challenging to predict computationally not only because such systems are periodically infinite but also because they are typically strongly correlated. Here, we generalize the variational two-electron reduced density matrix (2-RDM) theory to compute the energies and properties of strongly correlated periodic systems. The 2-RDM of the unit cell is directly computed subject to necessary N-representability conditions such that the unit-cell 2-RDM represents at least one N-electron density matrix. Two canonical but non-trivial systems, periodic metallic hydrogen chains and periodic acenes, are treated to demonstrate the methodology. We show that while single-reference correlation theories do not capture the strong (static) correlation effects in either of these molecular systems, the periodic variational 2-RDM theory predicts the Mott metal-to-insulator transition in the hydrogen chains and the length-dependent polyradical formation in acenes. For both hydrogen chains and acenes, the periodic calculations are compared with previous non-periodic calculations with the results showing a significant change in energies and increase in the electron correlation from the periodic boundary conditions. The 2-RDM theory, which allows for much larger active spaces than are traditionally possible, is applicable to studying correlation-driven phenomena in general periodic molecular solids and materials.

Extended Protein Ions Are Formed by the Chain Ejection Model in Chemical Supercharging Electrospray Ionization.

Supercharging electrospray ionization can be a powerful tool for increasing charge states in mass spectra and generating unfolded ion structures, yet key details of its mechanism remain unclear. The structures of highly extended protein ions and the mechanism of supercharging were investigated using ion mobility-mass spectrometry. Head-to-tail-linked polyubiquitins (Ubq1-11) were used to determine size and charge state scaling laws for unfolded protein ions formed by supercharging while eliminating amino acid composition as a potential confounding factor. Collisional cross section was found to scale linearly with mass for these ions and several other monomeric proteins, and the maximum observed charge state for each analyte scales with mass in agreement with an analytical charge state scaling law for protein ions with highly extended structures that is supported by experimental gas-phase basicities. These results indicate that these highly unfolded ions can be considered quasi-one-dimensional, and collisional cross sections modeled with the Trajectory Method in Collidoscope show that these ions are significantly more extended than linear α-helices but less extended than straight chains. The effect of internal disulfide bonds on the extent of supercharging was probed using bovine serum albumin, ß-lactoglobulin, and lysozyme, each of which contains multiple internal disulfide bonds. Reduction of the disulfide bonds led to a marked increase in charge state upon supercharging without significantly altering folding in solution. This evidence supports a supercharging mechanism in which these proteins unfold before or during evaporation of the electrospray droplet and ionization occurs by the Chain Ejection Model.

Collidoscope: An Improved Tool for Computing Collisional Cross-Sections with the Trajectory Method.

Ion mobility-mass spectrometry (IM-MS) can be a powerful tool for determining structural information about ions in the gas phase, from small covalent analytes to large, native-like or denatured proteins and complexes. For large biomolecular ions, which may have a wide variety of possible gas-phase conformations and multiple charge sites, quantitative, physically explicit modeling of collisional cross sections (CCSs) for comparison to IMS data can be challenging and time-consuming. We present a "trajectory method" (TM) based CCS calculator, named "Collidoscope," which utilizes parallel processing and optimized trajectory sampling, and implements both He and N2 as collision gas options. Also included is a charge-placement algorithm for determining probable charge site configurations for protonated protein ions given an input geometry in pdb file format. Results from Collidoscope are compared with those from the current state-of-the-art CCS simulation suite, IMoS. Collidoscope CCSs are within 4% of IMoS values for ions with masses from ~18 Da to ~800 kDa. Collidoscope CCSs using X-ray crystal geometries are typically within a few percent of IM-MS experimental values for ions with mass up to ~3.5 kDa (melittin), and discrepancies for larger ions up to ~800 kDa (GroEL) are attributed in large part to changes in ion structure during and after the electrospray process. Due to its physically explicit modeling of scattering, computational efficiency, and accuracy, Collidoscope can be a valuable tool for IM-MS research, especially for large biomolecular ions. Graphical Abstract ᅟ.