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Dive into the research topics where Patrick Derollez is active.

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Featured researches published by Patrick Derollez.


Journal of Physics: Condensed Matter | 1990

Structure of succinonitrile in its plastic phase

Patrick Derollez; J Lefebvre; M. Descamps; W Press; H Fontaine

The structure of succinonitrile in its orientationally disordered phase was reexamined through extended X-ray diffraction measurements. It was solved by using both the analytic procedures of symmetry-adapted functions and a Frenkel model assuming discrete orientations. A possible translation-rotation coupling was included in this latter case via an offset vector e. The study confirms that the nitrogen atoms are localised along the fourfold axis of the cubic cell but evidences a strong offset of the centre of mass for gauche conformations. It is shown that this can be explained by steric hindrance between some configurations of neighbouring molecules.


Journal of Physical Chemistry B | 2011

Low- and High-Frequency Raman Investigations on Caffeine: Polymorphism, Disorder and Phase Transformation

Alain Hédoux; Anne-Amandine Decroix; Yannick Guinet; Laurent Paccou; Patrick Derollez; M. Descamps

Raman investigations are carried out both in crystalline forms of caffeine and during the isothermal transformation of the orientationally disordered form I into the stable form II at 363 K. The time dependence of the Raman spectrum exhibits no significant change in the intramolecular regime (above 100 cm(-1)), resembling the spectrum of the liquid state. By contrast, significant changes are observed below 100 cm(-1), and the low-frequency spectra of forms I and II are observed to be different from that of the liquid. The temperature dependence of the 5-600 cm(-1) spectrum gives information on the static disorder through the analysis of collective motions, while information on dynamic disorder are obtained from the study of the 555 cm(-1) band corresponding to internal vibrations in the pyrimidine ring. This analysis indubitably reveals that form II is also orientationally disordered with a local molecular arrangement that mimics that in form I and the liquid state. The comparison of the low-frequency spectra recorded in theophylline and form II of caffeine allows one to describe the stable form of caffeine from the packing arrangement of anhydrous theophylline with the consideration of reorientational molecular disorder.


Acta Crystallographica Section B-structural Science | 2005

Ab initio structure determination of the high-temperature phase of anhydrous caffeine by X-ray powder diffraction

Patrick Derollez; Natália T. Correia; Florence Danède; Frédéric Capet; F. Affouard; Jacques Lefebvre; M. Descamps

The high-temperature phase I of anhydrous caffeine was obtained by heating and annealing the purified commercial form II at 450 K. This phase I can be maintained at low temperature in a metastable state. A powder X-ray diffraction pattern was recorded at 278 K with a laboratory diffractometer equipped with an INEL curved position-sensitive detector CPS120. Phase I is dynamically orientationally disordered (the so-called plastic phase). The Rietveld refinements were achieved with rigid-body constraints. It was assumed that on each site, a molecule can adopt three preferential orientations with equal occupation probability. Under a deep undercooling of phase I, below 250 K, the metastable state enters in a glassy crystal state.


Carbohydrate Research | 2011

Solid state amorphization kinetic of alpha lactose upon mechanical milling

Vincent Caron; J.F. Willart; Ronan Lefort; Patrick Derollez; Florence Danède; M. Descamps

It has been previously reported that α-lactose could be totally amorphized by ball milling. In this paper we report a detailed investigation of the structural and microstructural changes by which this solid state amorphization takes place. The investigations have been performed by Powder X-ray Diffraction, Solid State Nuclear Magnetic Resonance ((13)C CP-MAS) and Differential Scanning Calorimetry. The results reveal the structural complexity of the material in the course of its amorphization so that it cannot be considered as a simple mixture made of a decreasing crystalline fraction and an increasing amorphous fraction. Heating this complexity can give rise to a fully nano-crystalline material. The results also show that chemical degradations upon heating are strongly connected to the melting process.


Acta Crystallographica Section B-structural Science | 2010

Ab initio structure determination of phase II of racemic ibuprofen by X-ray powder diffraction.

Patrick Derollez; Emeline Dudognon; F. Affouard; Florence Danède; Natália T. Correia; M. Descamps

Annealing of the quenched ibuprofen at 258 K yielded a new crystalline form, called phase II. Powder X-ray diffraction patterns of this phase II were recorded with a laboratory diffractometer equipped with an INEL G3000 goniometer and a curved position-sensitive detector CPS120. The starting structural model was found by a Monte-Carlo simulated annealing method. The final structure was obtained through Rietveld refinements with rigid-body constraints for the phenyl group and soft restraints on the other interatomic bond lengths and bond angles. The cell volume is 5% larger than that of the conventional phase I at 258 K. It is also shown that the orientation of the propanoic acid group is drastically changed with respect to phase I, leading to strong modifications of the orientation of the O-H...O hydrogen bonds with respect to the chains of dimers. These structural considerations could explain the metastable character of this phase II.


Acta Crystallographica Section B-structural Science | 2005

Structure determination of the stable anhydrous phase of α-lactose from X-ray powder diffraction

Cyril Platteau; Jacques Lefebvre; F. Affouard; J.F. Willart; Patrick Derollez; Franck Mallet

The stable anhydrous form of α-lactose has been obtained by the dehydration of α-lactose monohydrate in methanol. An X-ray powder diffraction pattern was recorded at room temperature with a laboratory diffractometer equipped with an INEL curved sensitive detector CPS120. The starting structural model of this form was found by a Monte-Carlo simulated annealing method. The structure was obtained through Rietveld refinements and the minimization of crystalline energy for the localization of the H atoms of the hydroxyl groups. Soft restraints were applied to bond lengths and angles. Networks of O—H⋯O hydrogen bonds account for the crystalline cohesion. A comparison is made between the hydrogen-bond networks of this form and those of the monohydrate and hygroscopic anhydrous forms of α-lactose.


Acta Crystallographica Section B-structural Science | 2004

Ab initio structure determination of the hygroscopic anhydrous form of α-lactose by powder X-ray diffraction

Cyril Platteau; Jacques Lefebvre; F. Affouard; Patrick Derollez

Annealing of alpha-lactose monohydrate at 408 K yielded a mixture of this compound with hygroscopic anhydrous alpha-lactose. A powder X-ray diffraction pattern of this mixture was recorded at room temperature. The starting structural model of hygroscopic alpha-lactose was found by a Monte Carlo simulated-annealing method. The final structure was obtained through Rietveld refinements, with soft restraints on interatomic bond lengths and bond angles, and crystalline energy minimization to locate the H atoms of the hydroxy groups. The crystalline cohesion is achieved by networks of O-H...O hydrogen bonds that differ from those of the monohydrate phase. The width of the Bragg peaks is interpreted by a phenomenological microstructural approach in terms of isotropic size effects and anisotropic strain effects.


Journal of Pharmaceutical Sciences | 2013

Polymorphic Transformation of Anhydrous Caffeine upon Grinding and Hydrostatic Pressurizing Analyzed by Low-Frequency Raman Spectroscopy

Alain Hédoux; Yannick Guinet; Laurent Paccou; Florence Danède; Patrick Derollez

Low-frequency Raman investigations were carried out upon pressurizing and grinding both crystalline forms of anhydrous caffeine at room temperature. These investigations have led to the detection of metastable states under stress. Upon moderated hydrostatic compression, only form I transform into a metastable state characterized by a Raman band-shape resembling that of form II. Above 2 GPa, both pressurized forms convert into an identical disordered state, suggesting a pressure-induced amorphization. In contrast to hydrostatic compression, grinding induces transformation of each phase into the other, leading to an intermediate state only stabilized under long enough grinding. The origin of these metastable states induced by stress was related to the disordered nature of both crystalline forms of caffeine and the stability conditions at room temperature of form I.


International Journal of Pharmaceutics | 2011

Raman spectroscopy of racemic ibuprofen: Evidence of molecular disorder in phase II

Alain Hédoux; Yannick Guinet; Patrick Derollez; Emeline Dudognon; Natália T. Correia

Low- and high-frequency Raman experiments in the 5-200 cm(-1) and 600-1800 cm(-1) ranges were carried out in the crystalline and amorphous states of ibuprofen. Low-frequency investigations indubitably reveal the existence of a molecular disorder in the metastable phase (phase II), through the observation of quasielastic contribution below 30 cm(-1), and the absence of phonon peaks in the Raman susceptibility which mimics the density of vibrational states of an amorphous state. High-frequency Raman spectra indicate a local order in phase II similar to that in the glassy state. Both dynamic and static molecular disorder could contribute to the Raman signatures of the disorder in crystalline phase II. Raman investigations suggest that phase II can be considered as a transient metastable state in the devitrification process of ibuprofen upon heating from a far from equilibrium state toward the stable phase I.


Journal of Chemical Physics | 2013

Vibrational and structural properties of amorphous n-butanol: a complementary Raman spectroscopy and X-ray diffraction study.

Alain Hédoux; Yannick Guinet; Laurent Paccou; Patrick Derollez; Florence Danède

Raman spectroscopy and X-ray diffraction experiments were performed in the liquid, undercooled liquid, and glassy states of n-butanol. Clear correlated signatures are obtained below the melting temperature, from both temperature dependences of the low-wavenumber vibrational excitations and the intermediate-range order characterized by a prepeak detected in the different amorphous states. It was found that these features are related to molecular associations via strong hydrogen bonds, which preferentially develop at low temperature, and which are not compatible with the long-range order of the crystal. This study provides information on structural heterogeneities developing in hydrogen-bonded liquids, associated to the undercooled regime and the inherent glass transition. The analysis of the isothermal abortive crystallization, 2 K above the glass transition temperature, has given the opportunity to analyze the early stages of the crystallization and to describe the origin of the frustration responsible for an uncompleted crystallization.

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