Michael T. Ruggiero

Measuring the Elasticity of Poly-l-Proline Helices with Terahertz Spectroscopy.

Abstract The rigidity of poly‐l‐proline is an important contributor to the stability of many protein secondary structures, where it has been shown to strongly influence bulk flexibility. The experimental Youngs moduli of two known poly‐l‐proline helical forms, right‐handed all‐cis (Form I) and left‐handed all‐trans (Form II), were determined in the crystalline state by using an approach that combines terahertz time‐domain spectroscopy, X‐ray diffraction, and solid‐state density functional theory. Contrary to expectations, the helices were found to be considerably less rigid than many other natural and synthetic polymers, as well as differing greatly from each other, with Youngs moduli of 4.9 and 9.6 GPa for Forms I and II, respectively.

Piezo-optic tensor of crystals from quantum-mechanical calculations

An automated computational strategy is devised for the ab initio determination of the full fourth-rank piezo-optic tensor of crystals belonging to any space group of symmetry. Elastic stiffness and compliance constants are obtained as numerical first derivatives of analytical energy gradients with respect to the strain and photo-elastic constants as numerical derivatives of analytical dielectric tensor components, which are in turn computed through a Coupled-Perturbed-Hartree-Fock/Kohn-Sham approach, with respect to the strain. Both point and translation symmetries are exploited at all steps of the calculation, within the framework of periodic boundary conditions. The scheme is applied to the determination of the full set of ten symmetry-independent piezo-optic constants of calcium tungstate CaWO4, which have recently been experimentally reconstructed. Present calculations unambiguously determine the absolute sign (positive) of the π61 constant, confirm the reliability of 6 out of 10 experimentally determined constants and provide new, more accurate values for the remaining 4 constants.

Examination of l-Glutamic Acid Polymorphs by Solid-State Density Functional Theory and Terahertz Spectroscopy

The ability of l-glutamic acid to crystallize in two different forms has long been the subject of study due to its commercial importance. While a solvent-mediated phase transformation between the α and β polymorphs is the prevailing theory, recent reports indicate a thermal solid-solid transformation between the two may be possible. However, determining accurate thermodynamic stabilities of these crystals has been challenging. Here new low-temperature single-crystal X-ray diffraction data coupled to solid-state density functional theory simulations have enabled a detailed description to be achieved for the energetic parameters governing the stabilization of the two l-glutamic acid solids. The temperature-dependent Gibbs free-energy curves show that α-glutamic acid is the preferred form at low temperatures (<222 K) and the β form is most stable at ambient temperatures. Terahertz time-domain spectroscopy was utilized to evaluate the quality of the intermolecular force modeling as well as to provide characteristic low-frequency spectral data that can be used for quantification of polymorph mixtures or crystal growth monitoring.

Evaluation of Range-Corrected Density Functionals for the Simulation of Pyridinium-Containing Molecular Crystals.

The problem of nonlocal interactions in density functional theory calculations has in part been mitigated by the introduction of range-corrected functional methods. While promising solutions, the continued evaluation of range corrections in the structural simulations of complex molecular crystals is required to judge their efficacy in challenging chemical environments. Here, three pyridinium-based crystals, exhibiting a wide range of intramolecular and intermolecular interactions, are used as benchmark systems for gauging the accuracy of several range-corrected density functional techniques. The computational results are compared to low-temperature experimental single-crystal X-ray diffraction and terahertz spectroscopic measurements, enabling the direct assessment of range correction in the accurate simulation of the potential energy surface minima and curvatures. Ultimately, the simultaneous treatment of both short- and long-range effects by the ωB97-X functional was found to be central to its rank as the top performer in reproducing the complex array of forces that occur in the studied pyridinium solids. These results demonstrate that while long-range corrections are the most commonly implemented range-dependent improvements to density functionals, short-range corrections are vital for the accurate reproduction of forces that rapidly diminish with distance, such as quadrupole-quadrupole interactions.

Origins of contrasting copper coordination geometries in crystalline copper sulfate pentahydrate

Metal-aqua ion ([M(H2O)n](X+)) formation is a fundamental step in mechanisms that are central to enzymatic and industrial catalysis. Past investigations of such ions have yielded a wealth of information regarding their properties, however questions still exist involving the exact structures of these complexes. A prominent example of this is hexaaqua copper(II) ([Cu(H2O)6](2+)), with the solution versus gas-phase configurations under debate. The differences are often attributed to the intermolecular interactions between the bulk solvent and the aquated complex, resulting in structures stabilized by extended hydrogen-bonding networks. Yet solution phase systems are difficult to study due to the lack of atomic-level positional details. Crystalline solids are ideal models for comparative study, as they contain fixed structures that can be fully characterized using diffraction techniques. Here, crystalline copper sulfate pentahydrate (CuSO4·5H2O), which contains two unique copper-water geometries, was studied in order to elucidate the origin of these contrasting hydrated metal envrionments. A combination of solid-state density functional theory and low-temperature X-ray diffraction was used to probe the electronic origins of this phenomenon. This was accomplished through implementation of crystal orbital overlap population and crystal orbital Hamiltonian population analyses into a developmental version of the CRYSTAL14 software. These new computational methods help highlight the delicate interplay between electronic structure and metal-water geometries.

Glass-Transition Temperature of the β-Relaxation as the Major Predictive Parameter for Recrystallization of Neat Amorphous Drugs

Recrystallization of amorphous drugs is currently limiting the simple approach to improve solubility and bioavailability of poorly water-soluble drugs by amorphization of a crystalline form of the drug. In view of this, molecular mobility, α-relaxation and β-relaxation processes with the associated transition temperatures Tgα and Tgβ, was investigated using dynamic mechanical analysis (DMA). The correlation between the transition temperatures and the onset of recrystallization for nine amorphous drugs, stored under dry conditions at a temperature of 296 K, was determined. From the results obtained, Tgα does not correlate with the onset of recrystallization under the experimental storage conditions. However, a clear correlation between Tgβ and the onset of recrystallization was observed. It is shown that at storage temperature below Tgβ, amorphous nifedipine retains its amorphous form. On the basis of the correlation, an empirical correlation is proposed for predicting the onset of recrystallization for drugs stored at 0% RH and 296 K.

Structure searching methods: general discussion

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Structure searching methods: general discussion Matthew Addicoat, Claire Adjiman, Mihails Arhangelskis, Gregory Beran, Gerit Brandenburg, Doris Braun, Virginia Burger, Asbjoern Burow, Chris Collins, Andrew Cooper, et al.

Applications of crystal structure prediction – inorganic and network structures: general discussion

1 Applications of crystal structure prediction – inorganic and network structures: general discussion Virginia Burger, Frederik Claeyssens, Daniel Davies, Graeme Day, Matthew S. Dyer, Alan Hare, Yi Li, Caroline Mellot-Draznieks, John Mitchell, Sharmarke Mohamed, Artem R. Oganov, Sarah Price, Michael Ruggiero, Matthew Ryder, German Sastre, Christian Schön, Peter Spackman, Scott Woodley and Qiang Zhu

Research Data Supporting: Intermolecular Anharmonicity in Molecular Crystals: Interplay Between Experimental Low-Frequency Dynamics and Quantum Quasi-Harmonic Simulations of Solid Purine

Variable temperature THz-TDS and low-frequency Raman data DFT-predicted low-frequency spectra Crystallographic information

CCDC 1587065: Experimental Crystal Structure Determination

Related Article: Michael T. Ruggiero, Juraj Sibik, J. Axel Zeitler, and Timothy M. Korter|2016|J.Phys.Chem.A|120|7490|doi:10.1021/acs.jpca.6b05702