Browsing by Author "Novelli, G"
Now showing 1 - 6 of 6
Results Per Page
Sort Options
- ItemAccurate H-atom parameters for the two polymorphs of L-histidine at 5, 105 and 295 K(International Union of Crystallography, 2021-10-01) Novelli, G; McMonagle, CJ; Kleemiss, F; Probert, MR; Puschmann, H; Grabowsky, S; Maynard-Casely, HE; McIntyre, GJ; Parsons, SThe crystal structure of the monoclinic polymorph of the primary amino acid L-histidine has been determined for the first time by single-crystal neutron diffraction, while that of the orthorhombic polymorph has been reinvestigated with an untwinned crystal, improving the experimental precision and accuracy. For each polymorph, neutron diffraction data were collected at 5, 105 and 295 K. Single-crystal X-ray diffraction experiments were also performed at the same temperatures. The two polymorphs, whose crystal packing is interpreted by intermolecular interaction energies calculated using the Pixel method, show differences in the energy and geometry of the hydrogen bond formed along the c direction. Taking advantage of the X-ray diffraction data collected at 5 K, the precision and accuracy of the new Hirshfeld atom refinement method implemented in NoSpherA2 were probed choosing various settings of the functionals and basis sets, together with the use of explicit clusters of molecules and enhanced rigid-body restraints for H atoms. Equivalent atomic coordinates and anisotropic displacement parameters were compared and found to agree well with those obtained from the corresponding neutron structural models.© International Union of Crystallography
- ItemCarbon molecules in space: a thermal equation of state study of solid hexamethylenetetramine(Australian Institute of Physics, 2020-02-04) Novelli, G; McIntyre, GJ; Maynard-Casely, HE; Marshall, WG; Kamenev, KV; Parsons, SProperties such as compressibility, thermo-elasticity and the energy landscape remain unknown for many organic compounds under conditions encountered on extraterrestrial planets and moons and in space. In this study, a thermal Equation of State (EoS) for the crystalline solid hexamethylenetetramine was determined by neutron powder diffraction in the temperature and pressure ranges of 113-480 K and 0-5 GPa, respectively. The material was chosen as a molecular model for its high symmetry and its property of remaining in the same phase throughout the experimental conditions selected to simulate the planetary environments. Equations of States (EoSs) show how the thermodynamic variables of temperature (T), pressure (P) and volume (V) are inter-related. The ideal gas law, PV = nRT, is an example of an EoS which is used as a simple but effective model to explain the properties of gases. More complex EoSs, where the assumption of ideality is relaxed, can be applied to solids in order to describe how the geometry and energy transform when they experience dramatic changes in their environment. Such information acquires enormous importance in planetary materials science, where scientists are trying to understand the fate of carbon, the fourth most abundant element in our galaxy, in the context of the origin of life and planetary environments. Despite the large heterogeneity of galactic and interstellar regions, the organic chemistry of the universe seems to follow common pathways. Molecules of high astrobiological and astrophysical relevance such as amino acids, polyaromatic hydrocarbons, and N-heterocycles have been identified across the solar system, but how they behave under such varied conditions is a question yet to be answered. Key to our approach was the determination of how the internal energy (U), entropy (S) and the Gibbs free energy (G) vary with pressure not only computationally, but also, and for the first time, experimentally. A new method has been developed, able to transform directly variable-PT crystallographic data into thermodynamic information. Although it is quite common to model thermal expansion at ambient pressure with a VTEoS, and compression at ambient temperature using a PV-EoS, determinations of PVT-EoSs are much less common, particularly for organic materials. This paucity of PTV-EoSs reflects the difficulty of varying pressure and temperature simultaneously in crystallographic experiments, especially at reduced temperatures. The task was addressed in this study by the variable-temperature insert for the Paris-Edinburgh press available on the PEARL instrument at the ISIS Neutron Spallation Source (UK). The results were successfully combined with periodic DFT (Figure 1) and other semiempirical calculations, where pressure and temperature can be included at little time cost, enabling the stability profile of the material to be understood, right down to the level of individual intermolecular interactions.
- ItemCurrent high-pressure capabilities at ACNS and future plans(Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Maynard-Casely, HE; Booth, N; Shumack, A; Baldwin, C; White, R; Rule, KC; McIntyre, GJ; Novelli, GHigh-pressure (>1 Kbar) is a marvellous variable, which can reveal mechanical properties, structural transitions and exotic behaviours. This pairs very well with neutron scattering, where the highly penetrating nature of neutron beams is idea for accessing sample within complex sample environments. The Australian Centre for Neutron Scattering (ACNS) has developed a number of capabilities for high-pressure experiments, mainly revolving around the use of our Paris-Edinburgh press but more recently with miniature diamond-anvil cells. Some of these, such as our ability to compress radioactive samples as well as combining high-pressure and high-electric fields are unique in the world. Here we review the high pressure capabilities at ACNS, and outline some directions for capabilities and measurements.
- ItemEffect of high pressure on the crystal structures of polymorphs of l-histidine(American Chemical Society, 2020-11-06) Novelli, G; Maynard-Casely, HE; McIntyre, GJ; Warren, MR; Parsons, SThe effect of pressure on the crystal structures of the two ambient-pressure polymorphs of the amino acid l-histidine has been investigated. Single-crystal diffraction measurements, up to 6.60 GPa for the orthorhombic form I (P212121) and 6.85 GPa for the monoclinic form II (P21), show their crystal structures undergo isosymmetric single-crystal-to-single-crystal first-order phase transitions at 4.5 and 3.1 GPa to forms I′ and II′, respectively. Although the similarity in crystal packing and intermolecular interaction energies between the polymorphs is remarkable at ambient conditions, the manner in which each polymorph responds to pressure is different. Form II is found to be more compressible than form I, with bulk moduli of 11.6(6) GPa and 14.0(5) GPa, respectively. The order of compressibility follows the densities of the polymorphs at ambient conditions (1.450 and 1.439 g cm–3 for phases I and II, respectively). The difference is also related to the space-group symmetry, the softer monoclinic form having more degrees of freedom available to accommodate the change in pressure. In the orthorhombic form, the imidazole-based hydrogen atom involved in the H-bond along the c-direction swaps the acceptor oxygen atom at the transition to phase I′; the same swap occurs just after the phase transition in the monoclinic form and is also preceded by a bifurcation. Concurrently, the H-bond and the long-range electrostatic interaction along the b-direction form a three-centered H-bond at the I to I′ transition, while they swap their character during the II to II′ transition. The structural data were interpreted using periodic-density-functional theory, symmetry-adapted perturbation theory, and semiempirical Pixel calculations, which indicate that the transition is driven by minimization of volume, the intermolecular interactions generally being destabilized by the phase transitions. Nevertheless, volume calculations are used to show that networks of intermolecular contacts in both phases are very much less compressible than the interstitial void spaces, having bulk moduli similar to moderately hard metals. The volumes of the networks actually expand over the course of both phase transitions, with the overall unit-cell-volume decrease occurring through larger compression of interstitial void space. © 2020 American Chemical Society
- ItemInvestigating carbon molecules with pressure-volume-temperature equations of state(Australian Nuclear Science and Technology Organisation, 2019-09-03) Novelli, G; McIntyre, GJ; Maynard-Casely, HE; Funnell, NP; Marshall, WG; Kamenev, KV; Parsons, SWe are interested in intermolecular interactions which determine thermodynamic stability in crystalline solids and their response to changes in the external conditions. In no area is this information of more importance than in planetary materials science, where scientists are trying to understand the fate of carbon in the context of the origin of life and/or the varied planetary surfaces observed. Molecules of high astrobiological and astrophysical relevance, such as amino acids (1), polyaromatic hydrocarbons, and N-heterocycles (2), have been identified across the Universe but how they behave under such varying conditions is a question yet to be answered. Key to our approach is the determination of the internal-energy, entropy and the Gibbs free energy - not only computationally but also, and for the first time, experimentally. We have developed a new method that transforms variable-pressure (P)-temperature (T) crystallographic data into thermodynamic information. Equations of State (EoSs) are the models of choice to fit these data, describing how pressure, temperature, and volume (V) are inter related in solid phases. Although it is quite common to model thermal expansion at ambient pressure with a VT equation of state (EoS), and compression at ambient temperature using a PV-EoS, determinations of PVT-EoSs are much less common, particularly for molecular materials (3). The paucity of PVT-EoSs reflects the difficulty in varying pressure and temperature simultaneously in crystallographic experiments, especially at reduced temperatures. These difficulties are addressed by the variable temperature insert for the Paris-Edinburgh press available on the PEARL instrument at the ISIS Neutron Spallation Source (4) and by the cryofurnace for the Merrill-Bassett cell available on the KOALA instrument at the ANSTO OPAL reactor (5). The results can then be combined with Periodic DFT and other semi-empirical calculations, where pressure and temperature can be included at little time cost, enabling the stability profile of a material to be understood, right down to the level of individual intermolecular interactions. Many classes of structure-directing intermolecular interactions involve hydrogen atoms: hydrogen bonds are an obvious example, but hydrogens can also be involved in dispersion and electrostatic interactions. The responses of different kind of crystalline organics containing these interactions, such as hexamethylenetetramine, naphthalene, histidine, and alanine are to be studied using powder and single-crystal neutron diffraction up to 5 GPa and between 105-480 K. We are specifically using neutron diffraction for the experiments because of its sensitivity to locate hydrogen atoms. Additionally, the penetrating nature of neutron radiation means that complete, high-quality data can be obtained for samples in elaborate extreme-conditions environments.
- ItemUse of a miniature diamond-anvil cell in a joint x-ray and neutron high-pressure study on copper sulfate pentahydrate(International Union of Crystallography, 2022-01) Novelli, G; Kamenev, KV; Maynard-Casely, HE; Parsons, S; McIntyre, GJSingle-crystal X-ray and neutron diffraction data are usually collected using separate samples. This is a disadvantage when the sample is studied at high pressure because it is very difficult to achieve exactly the same pressure in two separate experiments, especially if the neutron data are collected using Laue methods where precise absolute values of the unit-cell dimensions cannot be measured to check how close the pressures are. In this study, diffraction data have been collected under the same conditions on the same sample of copper(II) sulfate pentahydrate, using a conventional laboratory diffractometer and source for the X-ray measurements and the Koala single-crystal Laue diffractometer at the ANSTO facility for the neutron measurements. The sample, of dimensions 0.40 × 0.22 × 0.20 mm3 and held at a pressure of 0.71 GPa, was contained in a miniature Merrill–Bassett diamond-anvil cell. The highly penetrating diffracted neutron beams passing through the metal body of the miniature cell as well as through the diamonds yielded data suitable for structure refinement, and compensated for the low completeness of the X-ray measurements, which was only 24% on account of the triclinic symmetry of the sample and the shading of reciprocal space by the cell. The two data-sets were combined in a single `XN' structure refinement in which all atoms, including H atoms, were refined with anisotropic displacement parameters. The precision of the structural parameters was improved by a factor of up to 50% in the XN refinement compared with refinements using the X-ray or neutron data separately. Published under an open-access licence.