The Vibrational Spectrum of Parabanic Acid by Inelastic Neutron Scattering Spectroscopy and Simulation by Solid-State DFT

The incoherent inelastic neutron scattering spectrum of parabanic acid was measured and simulated using solid-state density functional theory (DFT). This molecule was previously the subject of low-temperature X-ray and neutron diffraction studies. While the simulated spectra from several density functionals account for relative intensities and factor group splitting regardless of functional choice, the hydrogen-bending vibrational energies for the out-of-plane modes are poorly described by all methods. The disagreement between calculated and observed out-of-plane hydrogen bending mode energies is examined along with geometry optimization differences of bond lengths, bond angles, and hydrogen-bonding interactions for different functionals. Neutron diffraction suggests nearly symmetric hydrogen atom positions in the crystalline solid for both heavy-atom and N−H bond distances but different hydrogen-bonding angles. The spectroscopic results suggest a significant factor group splitting for the out-of-plane bending motions associated with the hydrogen atoms (N−H) for both the symmetric and asymmetric bending modes, as is also supported by DFT simulations. The differences between the quality of the crystallographic and spectroscopic simulations by isolated-molecule DFT, cluster-based DFT (that account for only the hydrogen-bonding interactions around a single molecule), and solid-state DFT are considered in detail, with parabanic acid serving as an excellent case study due to its small size and the availability of high-quality structure data. These calculations show that hydrogen bonding results in a change in the bond distances and bond angles of parabanic acid from the free molecule values

Examination of Phencyclidine Hydrochloride via Cryogenic Terahertz Spectroscopy, Solid-State Density Functional Theory, and X-ray Diffraction

The terahertz (THz) spectrum of phencyclidine hydrochloride from 7.0 to 100.0 cm−1 has been measured at cryogenic (78.4 K) temperature. The complete structural analysis and vibrational assignment of the compound have been performed employing solid-state density functional theory utilizing eight generalized gradient approximation density functionals and both solid-state and isolated-molecule methods. The structural results and the simulated spectra display the substantial improvement obtained by using solid-state simulations to accurately assign and interpret solid-state THz spectra. A complete assignment of the spectral features in the measured THz spectrum has been completed at a VWN-BP/DNP level of theory, with the VWN-BP density functional providing the best-fit solid-state simulation of the experimentally observed spectrum. The cryogenic THz spectrum contains eight spectral features that, at the VWN-BP/DNP level, consist of 15 infrared-active vibrational modes. Of the calculated modes, external crystal vibrations are predicted to account for 42% of the total spectral intensity

Differential effects of chronic methamphetamine treatment on high-frequency oscillations and responses to acute methamphetamine and NMDA receptor blockade in conscious mice

Dysregulation of high-frequency neuronal oscillations has been implicated in the pathophysiology of schizophrenia. Chronic methamphetamine (METH) use can induce psychosis similar to paranoid schizophrenia. The current study in mice aimed to determine the effect of chronic METH treatment on ongoing and evoked neuronal oscillations. C57BL/6 mice were treated with METH or vehicle control for three weeks and implanted with extradural recording electrodes. Two weeks after the last METH injection, mice underwent three EEG recording sessions to measure ongoing and auditory-evoked gamma and beta oscillatory power in response to an acute challenge with METH (2 mg/kg), the NMDA receptor antagonist MK-801 (0.3 mg/kg), or saline control. A separate group of mice pretreated with METH showed significantly greater locomotor hyperactivity to an acute METH challenge, confirming long-term sensitisation. Chronic METH did not affect ongoing or evoked gamma or beta power. Acute MK-801 challenge reduced ongoing beta power whereas acute METH challenge significantly increased ongoing gamma power. Both MK-801 and METH challenge suppressed evoked gamma power. Chronic METH treatment did not modulate these acute drug effects. There were minor effects of chronic METH and acute METH and MK-801 on selected components of event-related potential (ERP) waves. In conclusion, chronic METH treatment did not exert neuroplastic effects on the regulation of cortical gamma oscillations in a manner consistent with schizophrenia, despite causing behavioural sensitisation

Site-Specific CO₂ Adsorption and Zero Thermal Expansion in an Anisotropic Pore Network

Detailed neutron powder diffraction (NPD) experiments were carried out on the parent and CO2 adsorbed Mg-MOF-74 (MOF: metal–organic framework). Data collected at low temperature revealed two CO2 adsorption sites on the pore surface and multiple changes in the framework as a function of CO2 loading. Upon heating the samples to room temperature, the data revealed minimal changes in expansivity upon adsorption of up to 0.94 CO2/Mg (≈ 25% mass fraction). Further, temperature-dependent data collected on the bare framework reveals net zero thermal expansion between 10 and 475 K

Water Adsorption in Porous Metal–Organic Frameworks and Related Materials

Water adsorption in porous materials is important for many applications such as dehumidification, thermal batteries, and delivery of drinking water in remote areas. In this study, we have identified three criteria for achieving high performing porous materials for water adsorption. These criteria deal with condensation pressure of water in the pores, uptake capacity, and recyclability and water stability of the material. In search of an excellently performing porous material, we have studied and compared the water adsorption properties of 23 materials, 20 of which are metal–organic frameworks (MOFs). Among the MOFs are 10 zirconium­(IV) MOFs with a subset of these, MOF-801-SC (single crystal form), −802, −805, −806, −808, −812, and −841 reported for the first time. MOF-801-P (microcrystalline powder form) was reported earlier and studied here for its water adsorption properties. MOF-812 was only made and structurally characterized but not examined for water adsorption because it is a byproduct of MOF-841 synthesis. All the new zirconium MOFs are made from the Zr₆O₄(OH)₄(−CO₂)_<i>n</i> secondary building units (<i>n</i> = 6, 8, 10, or 12) and variously shaped carboxyl organic linkers to make extended porous frameworks. The permanent porosity of all 23 materials was confirmed and their water adsorption measured to reveal that MOF-801-P and MOF-841 are the highest performers based on the three criteria stated above; they are water stable, do not lose capacity after five adsorption/desorption cycles, and are easily regenerated at room temperature. An X-ray single-crystal study and a powder neutron diffraction study reveal the position of the water adsorption sites in MOF-801 and highlight the importance of the intermolecular interaction between adsorbed water molecules within the pores

Separation of Xylene Isomers through Multiple Metal Site Interactions in Metal–Organic Frameworks

Purification of the C8 alkylaromatics o-xylene, m-xylene, p-xylene, and ethylbenzene remains among the most challenging industrial separations, due to the similar shapes, boiling points, and polarities of these molecules. Herein, we report the evaluation of the metal–organic frameworks Co2(dobdc) (dobdc4– = 2,5-dioxido-1,4-benzenedicarboxylate) and Co2(m-dobdc) (m-dobdc4– = 4,6-dioxido-1,3-benzenedicarboxylate) for the separation of xylene isomers using single-component adsorption isotherms and multicomponent breakthrough measurements. Remarkably, Co2(dobdc) distinguishes among all four molecules, with binding affinities that follow the trend o-xylene > ethylbenzene > m-xylene > p-xylene. Multicomponent liquid-phase adsorption measurements further demonstrate that Co2(dobdc) maintains this selectivity over a wide range of concentrations. Structural characterization by single-crystal X-ray diffraction reveals that both frameworks facilitate the separation through the extent of interaction between each C8 guest molecule with two adjacent cobalt­(II) centers, as well as the ability of each isomer to pack within the framework pores. Moreover, counter to the presumed rigidity of the M2(dobdc) structure, Co2(dobdc) exhibits an unexpected structural distortion in the presence of either o-xylene or ethylbenzene that enables the accommodation of additional guest molecules

Separation of Xylene Isomers through Multiple Metal Site Interactions in Metal–Organic Frameworks

Purification of the C₈ alkylaromatics <i>o</i>-xylene, <i>m</i>-xylene, <i>p</i>-xylene, and ethylbenzene remains among the most challenging industrial separations, due to the similar shapes, boiling points, and polarities of these molecules. Herein, we report the evaluation of the metal–organic frameworks Co₂(dobdc) (dobdc^4– = 2,5-dioxido-1,4-benzenedicarboxylate) and Co₂(<i>m</i>-dobdc) (<i>m</i>-dobdc^4– = 4,6-dioxido-1,3-benzenedicarboxylate) for the separation of xylene isomers using single-component adsorption isotherms and multicomponent breakthrough measurements. Remarkably, Co₂(dobdc) distinguishes among all four molecules, with binding affinities that follow the trend <i>o</i>-xylene > ethylbenzene > <i>m</i>-xylene > <i>p</i>-xylene. Multicomponent liquid-phase adsorption measurements further demonstrate that Co₂(dobdc) maintains this selectivity over a wide range of concentrations. Structural characterization by single-crystal X-ray diffraction reveals that both frameworks facilitate the separation through the extent of interaction between each C₈ guest molecule with two adjacent cobalt­(II) centers, as well as the ability of each isomer to pack within the framework pores. Moreover, counter to the presumed rigidity of the M₂(dobdc) structure, Co₂(dobdc) exhibits an unexpected structural distortion in the presence of either <i>o</i>-xylene or ethylbenzene that enables the accommodation of additional guest molecules

Separation of Xylene Isomers through Multiple Metal Site Interactions in Metal–Organic Frameworks

Purification of the C₈ alkylaromatics <i>o</i>-xylene, <i>m</i>-xylene, <i>p</i>-xylene, and ethylbenzene remains among the most challenging industrial separations, due to the similar shapes, boiling points, and polarities of these molecules. Herein, we report the evaluation of the metal–organic frameworks Co₂(dobdc) (dobdc^4– = 2,5-dioxido-1,4-benzenedicarboxylate) and Co₂(<i>m</i>-dobdc) (<i>m</i>-dobdc^4– = 4,6-dioxido-1,3-benzenedicarboxylate) for the separation of xylene isomers using single-component adsorption isotherms and multicomponent breakthrough measurements. Remarkably, Co₂(dobdc) distinguishes among all four molecules, with binding affinities that follow the trend <i>o</i>-xylene > ethylbenzene > <i>m</i>-xylene > <i>p</i>-xylene. Multicomponent liquid-phase adsorption measurements further demonstrate that Co₂(dobdc) maintains this selectivity over a wide range of concentrations. Structural characterization by single-crystal X-ray diffraction reveals that both frameworks facilitate the separation through the extent of interaction between each C₈ guest molecule with two adjacent cobalt­(II) centers, as well as the ability of each isomer to pack within the framework pores. Moreover, counter to the presumed rigidity of the M₂(dobdc) structure, Co₂(dobdc) exhibits an unexpected structural distortion in the presence of either <i>o</i>-xylene or ethylbenzene that enables the accommodation of additional guest molecules

Separation of Xylene Isomers through Multiple Metal Site Interactions in Metal–Organic Frameworks

Purification of the C₈ alkylaromatics <i>o</i>-xylene, <i>m</i>-xylene, <i>p</i>-xylene, and ethylbenzene remains among the most challenging industrial separations, due to the similar shapes, boiling points, and polarities of these molecules. Herein, we report the evaluation of the metal–organic frameworks Co₂(dobdc) (dobdc^4– = 2,5-dioxido-1,4-benzenedicarboxylate) and Co₂(<i>m</i>-dobdc) (<i>m</i>-dobdc^4– = 4,6-dioxido-1,3-benzenedicarboxylate) for the separation of xylene isomers using single-component adsorption isotherms and multicomponent breakthrough measurements. Remarkably, Co₂(dobdc) distinguishes among all four molecules, with binding affinities that follow the trend <i>o</i>-xylene > ethylbenzene > <i>m</i>-xylene > <i>p</i>-xylene. Multicomponent liquid-phase adsorption measurements further demonstrate that Co₂(dobdc) maintains this selectivity over a wide range of concentrations. Structural characterization by single-crystal X-ray diffraction reveals that both frameworks facilitate the separation through the extent of interaction between each C₈ guest molecule with two adjacent cobalt­(II) centers, as well as the ability of each isomer to pack within the framework pores. Moreover, counter to the presumed rigidity of the M₂(dobdc) structure, Co₂(dobdc) exhibits an unexpected structural distortion in the presence of either <i>o</i>-xylene or ethylbenzene that enables the accommodation of additional guest molecules

Separation of Xylene Isomers through Multiple Metal Site Interactions in Metal–Organic Frameworks

Purification of the C₈ alkylaromatics <i>o</i>-xylene, <i>m</i>-xylene, <i>p</i>-xylene, and ethylbenzene remains among the most challenging industrial separations, due to the similar shapes, boiling points, and polarities of these molecules. Herein, we report the evaluation of the metal–organic frameworks Co₂(dobdc) (dobdc^4– = 2,5-dioxido-1,4-benzenedicarboxylate) and Co₂(<i>m</i>-dobdc) (<i>m</i>-dobdc^4– = 4,6-dioxido-1,3-benzenedicarboxylate) for the separation of xylene isomers using single-component adsorption isotherms and multicomponent breakthrough measurements. Remarkably, Co₂(dobdc) distinguishes among all four molecules, with binding affinities that follow the trend <i>o</i>-xylene > ethylbenzene > <i>m</i>-xylene > <i>p</i>-xylene. Multicomponent liquid-phase adsorption measurements further demonstrate that Co₂(dobdc) maintains this selectivity over a wide range of concentrations. Structural characterization by single-crystal X-ray diffraction reveals that both frameworks facilitate the separation through the extent of interaction between each C₈ guest molecule with two adjacent cobalt­(II) centers, as well as the ability of each isomer to pack within the framework pores. Moreover, counter to the presumed rigidity of the M₂(dobdc) structure, Co₂(dobdc) exhibits an unexpected structural distortion in the presence of either <i>o</i>-xylene or ethylbenzene that enables the accommodation of additional guest molecules