Multinuclear Solid-State Magnetic Resonance as a Sensitive Probe of Structural Changes upon the Occurrence of Halogen Bonding in Co-crystals

Although the understanding of intermolecular interactions, such as hydrogen bonding, is relatively well-developed, many additional weak interactions work both in tandem and competitively to stabilize a given crystal structure. Due to a wide array of potential applications, a substantial effort has been invested in understanding the halogen bond. Here, we explore the utility of multinuclear (13C, 14/15N, 19F, and 127I) solid-state magnetic resonance experiments in characterizing the electronic and structural changes which take place upon the formation of five halogen-bonded co-crystalline product materials. Single-crystal X-ray diffraction (XRD) structures of three novel co-crystals which exhibit a 1:1 stoichiometry between decamethonium diiodide (i.e., [(CH3)3N+(CH 2)10N+(CH3)3][2 I -]) and different para-dihalogen-substituted benzene moieties (i.e., p-C6X2Y4, X=Br, I; Y=H, F) are presented. 13C and 15N NMR experiments carried out on these and related systems validate sample purity, but also serve as indirect probes of the formation of a halogen bond in the co-crystal complexes in the solid state. Long-range changes in the electronic environment, which manifest through changes in the electric field gradient (EFG) tensor, are quantitatively measured using 14N NMR spectroscopy, with a systematic decrease in the 14N quadrupolar coupling constant (CQ) observed upon halogen bond formation. Attempts at 127I solid-state NMR spectroscopy experiments are presented and variable-temperature 19F NMR experiments are used to distinguish between dynamic and static disorder in selected product materials, which could not be conclusively established using solely XRD. Quantum chemical calculations using the gauge-including projector augmented-wave (GIPAW) or relativistic zeroth-order regular approximation (ZORA) density functional theory (DFT) approaches complement the experimental NMR measurements and provide theoretical corroboration for the changes in NMR parameters observed upon the formation of a halogen bond

Manufacturing in the time of COVID-19: an assessment of barriers and enablers

Pandemics and other forms of epidemic outbreaks are a unique case of manufacturing risk typified by high uncertainty, increasing propagation and long-term disruption to manufacturers, supply chain actors as well as the end-users and consumers. For manufacturing the COVID-19 disruption scope has been largely two-fold; an endogenous disruption of manufacturing processes and systems as well as extreme shifts in demand and supply caused by exogenous supply chain disruption. Existing literature on disruptions in manufacturing suggests that pandemics are qualitatively different from typical disruptions. There is no literature available to manufacturing practitioners that identify the barriers and enablers of manufacturing resilience, especially with regards to pivoting of the manufacturing sector in response to a pandemic. This study draws on an extensive survey collected during the COVID-19 pandemic. The respondents were employees of manufacturing firms in all regions of the world who had engaged in manufacturing during the pandemic or had opted out from manufacturing due to various identified reasons. By collating their responses, we offer to practitioners and policymakers an analysis for identifying a best-practice framework for pivoting successfully as a response to major manufacturing disruptions

Polymorphs of Theophylline Characterized by DNP Enhanced Solid-State NMR

We show how dynamic nuclear polarization (DNP) enhanced solid-state NMR spectroscopy can be used to characterize polymorphs and solvates of organic solids. We applied DNP to three polymorphs and one hydrated form of the asthma drug molecule theophylline. For some forms of theophylline, sample grinding and impregnation with the radical-containing solution, which are necessary to prepare the samples for DNP, were found to induce polymorphic transitions or desolvation between some forms. We present protocols for sample preparation for solid-state magic-angle spinning (MAS) DNP experiments that avoid the polymorphic phase transitions in theophylline. These protocols include cryogrinding, grinding under inert atmosphere, and the appropriate choice of the impregnating liquid. By applying these procedures, we subsequently demonstrate that two-dimensional correlation experiments, such as H-1-C-13 and H-1-N-15 HETCOR or C-13-C-13 INADEQUATE, can be obtained at natural isotopic abundance in reasonable times, thus enabling more advanced structural characterization of polymorphs

Weak Halogen Bonding in Solid Haloanilinium Halides Probed Directly via Chlorine-35, Bromine-81, and Iodine-127 NMR Spectroscopy

A series of monohaloanilinium halides exhibiting weak halogen bonding (XB) has been prepared and characterized by ³⁵Cl, ⁸¹Br, and ¹²⁷I solid-state nuclear magnetic resonance (SSNMR) spectroscopy in magnetic fields of up to 21.1 T. The quadrupolar and chemical shift (CS) tensor parameters for halide ions (Cl^–, Br^–, I^–) which act as electron density donors in the halogen bonds of these compounds are measured to provide insight into the possible relationship between halogen bonding and NMR observables. The NMR data for certain series of related compounds are strongly indicative of when such compounds pack in the same space group, thus providing practical structural information. Careful interpretation of the NMR data in the context of novel and previously available X-ray crystallographic data, and new gauge-including projector-augmented-wave density functional theory (GIPAW DFT) calculations has revealed several notable trends. When a series of related compounds pack in the same space group, it has been possible to interpret trends in the NMR data in terms of the strength of the halogen bond. For example, in isostructural series, the halide quadrupolar coupling constant was found to increase as the halogen bond weakens. In the case of a series of haloanilinium bromides, the ⁸¹Br isotropic chemical shift and CS tensor span both decrease as the bromide–halogen XB is weakened. These trends were reproduced using both GIPAW DFT and cluster-model calculations of the bromide ion magnetic shielding tensor. Such trends are particularly exciting given the well-known role that NMR has played historically in the characterization of hydrogen bonding

Oxygen-17 NMR Spectroscopy of Water Molecules in Solid Hydrates

Oxygen-17 solid-state NMR studies of waters of hydration in crystalline solids are presented. The 17O quadrupolar coupling and chemical shift (CS) tensors, and their relative orientations, are measured experimentally at room temperature for ď Ą-oxalic acid dihydrate, barium chlorate monohydrate, lithium sulfate monohydrate, potassium oxalate monohydrate, and sodium perchlorate monohydrate. The 17O quadrupolar coupling constants (CQ) range from 6.6 to 7.35 MHz and the isotropic chemical shifts range from -17 to 19.7 ppm. The oxygen CS tensor spans vary from 25 to 78 ppm. These represent the first complete CS and electric field gradient tensor measurements for water coordinated to metals in the solid state. Gauge-including projector-augmented wave density functional theory calculations overestimate the values of CQ, likely due to librational dynamics of the water molecules. Computed CS tensors only qualitatively match the experimental data. The lack of strong correlations between the experimental and computed data, and between these data and any single structural feature is attributed to motion of the water molecules and to the relatively small overall range in the NMR parameters relative to their measurement precision. Nevertheless, the isotropic chemical shift, quadrupolar coupling constant, and CS tensor span clearly differentiate between the samples studied, and establish a â fingerprintâ 17O spectral region for water coordinated to metals in solids.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Na+ mobility in sodium strontium silicate fast ion conductors

We present the first direct evidence of Na-ion mobility in sodium strontium silicate fast ion conductors, based on variable temperature 23Na solid state NMR spectroscopy and spin-lattice relaxation measurements

Three-Dimensional Structure Determination of Surface Species by DNP Enhanced Solid-state NMR

International audienceThree-dimensional molecular structures determined from single crystals by diffraction methods transformed Chemistry in the twentieth century, leading to today’s structure based understanding of the field. However, if the system under investigation is located at a surface, as in many of the most interesting functional materials today, the problem of structure determination is largely unsolved. Such samples are encountered with increasing frequency, particularly in the area of energy and catalysis, so that there is a critical need to provide new methods for structural characterization of surfaces. Solid-state Nuclear Magnetic Resonance (NMR) spectroscopy would be the method of choice for surface characterization if it were not that the detection limit of NMR is too low to allow the study of many modern materials. The sensitivity of NMR is thus the major limitation to surface structure determination. We have recently introduced an approach using Dynamic Nuclear Polarization (DNP) under Magic Angle Spinning (MAS) to greatly enhance NMR signals of surfaces. With the recent introduction of polarizing agents of high molecular weight like TEKPOL signal enhancement factors of two orders of magnitude (between 100 and 200 in mesoporous materials) are routinely obtained at magnetic fields of 5−9.4 T and sample temperatures of ca. 80−105 K.Here we show that the gain provided by DNP surface enhanced NMR spectroscopy (SENS) is sufficient to enable the implementation with high sensitivity of a series of multi-dimensional correlation experiments (including HETCOR, 29Si-29Si INADEQUATE, 13C-{15N} and 29Si-{15N} REDOR) that allow us to solvethe three-dimensional structure of organic fragments incorporated on a silica surface. Using a total of 8 internuclear constraints, we could determine the structure ofa Pt complex, used asprototypical metal site for moleculary-defined supported catalyst

Three-Dimensional Structure Determination of Surface Sites

Lenaic Leroux is acknowledged for technical assistance at the CRMN. Prof. Paul Tordo and Dr. Olivier Ouari are thanked for providing TEKPo12.International audienceThe spatial arrangement of atoms is directly linked to chemical function. A fundamental challenge in surface chemistry and catalysis relates to the determination of three-dimensional structures with atomic-level precision. Here we determine the three-dimensional structure of an organometallic complex on an amorphous silica surface using solid-state NMR measurements, enabled through a dynamic nuclear polarization surface enhanced NMR spectroscopy approach that induces a 200-fold increase in the NMR sensitivity for the surface species. The result, in combination with EXAFS, is a detailed structure for the surface complex determined with a precision of 0.7 angstrom. We observe a single well-defined conformation that is folded toward the surface in such a way as to include an interaction between the platinum metal center and the surface oxygen atoms

Effects of hospital funding reform on wait times for hip fracture surgery: a population-based interrupted time-series analysis

Abstract Background Health care funding reforms are being used worldwide to improve system performance but may invoke unintended consequences. We assessed the effects of introducing a targeted hospital funding model, based on fixed price and volume, for hip fractures. We hypothesized the policy change was associated with reduction in wait times for hip fracture surgery, increase in wait times for non-hip fracture surgery, and increase in the incidence of after-hours hip fracture surgery. Methods This was a population-based, interrupted time series analysis of 49,097 surgeries for hip fractures, 10,474 for ankle fractures, 1,594 for tibial plateau fractures, and 40,898 for appendectomy at all hospitals in Ontario, Canada between April 2012 and March 2017. We used segmented regression analysis of interrupted monthly time series data to evaluate the impact of funding reform enacted April 1, 2014 on wait time for hip fracture repair (from hospital presentation to surgery) and after-hours provision of surgery (occurring between 1700 and 0700 h). To assess potential adverse consequences of the reform, we also evaluated two control procedures, ankle and tibial plateau fracture surgery. Appendectomy served as a non-orthopedic tracer for assessment of secular trends. Results The difference (95 % confidence interval) between the actual mean wait time and the predicted rate had the policy change not occurred was − 0.46 h (-3.94 h, 3.03 h) for hip fractures, 1.46 h (-3.58 h, 6.50 h) for ankle fractures, -3.22 h (-39.39 h, 32.95 h) for tibial plateau fractures, and 0.33 h (-0.57 h, 1.24 h) for appendectomy (Figure 1; Table 3). The difference (95 % confidence interval) between the actual and predicted percentage of surgeries performed after-hours − 0.90 % (-3.91 %, 2.11 %) for hip fractures, -3.54 % (-11.25 %, 4.16 %) for ankle fractures, 7.09 % (-7.97 %, 22.14 %) for tibial plateau fractures, and 1.07 % (-2.45 %, 4.59 %) for appendectomy. Conclusions We found no significant effects of a targeted hospital funding model based on fixed price and volume on wait times or the provision of after-hours surgery. Other approaches for improving hip fracture wait times may be worth pursuing instead of funding reform