Ivo Rietveld - Profile on Academia.edu (original) (raw)

Papers by Ivo Rietveld

Structural Chemistry, 2011

L-Tyrosine alkyl esters are used as prodrugs for L-tyrosine. Although prodrugs are often designed... more L-Tyrosine alkyl esters are used as prodrugs for L-tyrosine. Although prodrugs are often designed for their behavior in solution, understanding their solid-state properties is the first step in mastering drug delivery. The crystal structure of L-tyrosine methyl ester has been determined and compared to published structures of L-tyrosine and its ethyl and n-butyl esters. It is almost isostructural with the other esters: it crystallizes in the orthorhombic chiral space group P2 1 2 1 2 1 , a = 5.7634(15) Å , b = 12.111(2) Å , c = 14.3713(19) Å , V = 1003.1(4) Å 3 with Z 0 = 1. Their main packing motif is a C(9) infinite hydrogen-bond chain, but the conformation of L-tyrosine methyl ester is different from the other two: eclipsed versus U-shaped, respectively. The published structure of the ethyl ester, which was incomplete, has been confirmed by X-ray powder diffraction data. Because L-tyrosine methyl ester is very stable (28 years stored at room temperature), and its hydrolysis rate is relatively low, it should be one of the better prodrugs among the alkyl esters of tyrosine.

International Journal of Pharmaceutics, 2012

Aging of drug molecules is generally studied following regulatory procedures, i.e. under forced c... more Aging of drug molecules is generally studied following regulatory procedures, i.e. under forced conditions and for relatively limited storage time; therefore naturally aged samples are rare and provide scientific reference data beyond regulatory considerations. Tienoxolol was studied after 25 years of storage in the dark under ambient conditions. About 86% of the samples still consisted of tienoxolol and the main impurity (13%) was caused by the hydrolysis of the ester moiety. Protection from humidity is therefore important. Other sensitive groups containing nitrogen and sulfur appear to be quite stable with less than 0.8% conversion over 25 years. In addition, the crystal structure has been solved. Tienoxolol orange needles were found to crystallize in the orthorhombic noncentrosymmetric space group Iba2, indicating that the crystal is a racemic compound. The unit cell parameters at room temperature are a = 10.069(5) Å, b = 45.831(10) Å, and c = 9.822(5) Å and the unit cell volume is 4533(3) Å 3 with Z = 8.

Triethylenetetramine Dihydrochloride: Interactions and Conformations in Two Anhydrous Structures and a Hydrate

Crystal Growth & Design, 2015

ABSTRACT Triethylenetetramine is a polyamine type chelating ligand for copper(II), which is curre... more ABSTRACT Triethylenetetramine is a polyamine type chelating ligand for copper(II), which is currently used, mainly in its dihydrochloride form, as an alternative to d-penicillamine against Wilsons disease. Because knowledge about the solid-state behavior of pharmaceuticals is a prerequisite for the development of an effective dosage form, the crystal structures of two triethylenetetramine dihydrochloride polymorphs have been determined, and the infrared spectra and thermal expansion have been studied. No suitable crystals could be obtained of the two anhydrous forms, for which the structures have been solved from X-ray powder diffraction. Form I is monoclinic P2(1)/n with the cell parameters a = 11.0475(4) angstrom, b = 4.87475(16) angstrom, c = 11.1178(4) angstrom, and beta = 106.9826(13)degrees leading to V = 572.63(3) angstrom(3) with Z = 2. Form II is also monoclinic P2(1)/c with cell parameters a = 10.6734(6) angstrom, b = 12.3613(6) angstrom, c = 9.8479(7) angstrom, and beta = 115.985(3)degrees leading to a unit-cell volume of V = 1167.95(12) angstrom(3) with Z = 4. A recurring structural element is a ionic interaction between two chloride ions and two ammonium groups each organized in a diamond pattern present in the dihydrate (the salt is hygroscopic) and anhydrous form I. The molecular conformations are different in both anhydrous forms and in the dihydrate. Comparison of the thermal expansions demonstrates that form I has the smallest thermal expansion and thus possesses the strongest intermolecular interactions.

Crystal growth and physical properties of the organic salt benzimidazolium 3-nitrophthalate

From the point of view of crystal growth and design, it is interesting to study the effect of dif... more From the point of view of crystal growth and design, it is interesting to study the effect of different isomers on the resulting structure. Single crystals of the organic salt benzimidazolium 3-nitrophthalate (BZD + ·mNPA −) have been grown by slow evaporation from methanol solution. Single crystal X-ray diffrac-tion demonstrated that the crystal structure belongs to the monoclinic system with space group P2 1 /c. The properties of the functional groups have been studied by FTIR spectroscopy, FT-Raman spectral analysis and 1 H and 13 C NMR spectroscopy. The emission spectra of BZD + ·mNPA − were recorded in different solvents ; they exhibit a negative solvatochromatic effect when the polarity of the solvent is increased. The thermal stability, dielectric constant and dielectric loss have been investigated and the HOMO and LUMO energy levels have been calculated using density functional theory (DFT). The crystal structure of BZD + ·mNPA − has been compared with that of benzimidazolium 2-nitroterephthalate (BZD + ·NTPh −). The interactions of the isomers 3-nitrophthalate or 2-nitroterephthalate salts with benzimidazolium are very similar ; however, the different positions of the carboxyl groups on the benzene rings changes the layout of the structure, which leads to undulating sheets for 3-nitrophthalate and flat antiparallel sheets for 2-nitrotherephthalate. The salt decomposes at around 180 °C.

Crystal Growth Design, Jun 1, 2011

Thermochimica Acta, Nov 20, 2010

The properties of dextrorotatory and racemic camphor have been investigated as a function of temp... more The properties of dextrorotatory and racemic camphor have been investigated as a function of temperature and composition. A thorough literature survey has been undertaken for temperatures and enthalpies of all transitions and for structural information of the phases existing under ordinary pressure. The transition temperatures and enthalpies have been measured with differential scanning calorimetry. Cell parameters of all phases have been determined as a function of temperature up to the melt and the specific volume of liquid camphor has been determined. A temperature-composition phase diagram is presented containing all condensed-phase transitions, including an analysis of the melting transition. The melting point of racemic camphor is at least 2 K lower than the melting point of d-(and l-) camphor at 451 ± 2 K, whereas the melting enthalpy is the same within error. Below the melting point, mixtures of solid d-and l-camphor are solid solutions. Because the structures of the racemic compound near the melting point and the solid solution are equivalent for time and volume averaged measurements, they cannot be distinguished. One could call this a case of 'critical symmetry'.

Crystal Growth & Design

3,4-Diaminopyridine is an active pharmaceutical ingredient for the treatment of Lambert−Eaton mya... more 3,4-Diaminopyridine is an active pharmaceutical ingredient for the treatment of Lambert−Eaton myasthenic syndrome (LEMS). It is 3,4-diaminopyridine dihydrogen phosphate that has become the active ingredient of choice. As part of a larger study for the development of this drug, solid-state studies have been carried out. At room temperature, the crystals are monoclinic (C2/c). Dihydrogen phosphate anions H 2 PO 4 − form infinite chains parallel to the b axis, and these chains can be considered as macroanions (H 2 PO 4)∞. The organic cations form hydrogen bonds with the macroanions bridging them together. A negative thermal expansion is observed along the [103] direction in the crystal, which coincides with the direction of chains of interchanging anions and cations. The crystal packing shows similarities with the hydrogen tartrate salt as illustrated by a Hirshfeld surface analysis. This phosphate and this tartrate salt are also the two diaminopyridine salts that have been selected fo...

Quencher distribution analysis in heterogeneous systems using time-resolved phosphorometry

Porphyrin-based dendritic oxygen sensors

Fluorescence and physical properties of the organic salt 2-chloro-4-nitrobenzoate–3-ammonium-phenol

Chemical Physics, 2015

Rotigotine: Unexpected Polymorphism with Predictable Overall Monotropic Behavior

Journal of Pharmaceutical Sciences, 2015

Crystallization of polymorphs still has a touch of art, as even prior observations of polymorphs ... more Crystallization of polymorphs still has a touch of art, as even prior observations of polymorphs do not guarantee their crystallization. However, once crystals of various polymorphs have been obtained, their relative stabilities can be established with a straightforward thermodynamic approach even if the conclusion will depend on the quality of the experimental data. Rotigotine is an active pharmaceutical ingredient, which has suffered the same setback as Ritonavir: a sudden appearance of a more stable crystalline polymorph than the one used for the formulation. Although the cause of the defect in the formulation was quickly established, the interpretation of the phase behavior of rotigotine has been lacking in clarity. In the present paper, data published in the patents resulting from the discovery of the new polymorph have been used to establish the pressure-temperature phase diagram of the two known solid forms of rotigotine. The analysis clearly demonstrates that form II is the stable solid phase and form I is metastable in the entire pressure-temperature domain: form I is overall monotropic in relation to form II. Thus, it was a sensible decision of European Medicines Agency to ask for a reformulation, as the first formulation was metastable even if crystallization appeared to be very slow. © 2015 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci.

Physical and chemical stability of triethylenetetramine dihydrochloride, an API against Wilson’s disease

MATEC Web of Conferences, 2013

Supporting Information-Rimonabant

Lornithinium aketoglutarate crystal structure

Two extreme cases of volume change on melting are considered (see Ubbelohde) : 7 and 16 %. They a... more Two extreme cases of volume change on melting are considered (see Ubbelohde) : 7 and 16 %. They are combined with two extreme cases of volumic thermal expansion for the liquid (L) phase: 0.8 × 10 --3 K --1 and 2 × 10 --3 K --1 . 1 This gives four combinations with different dP/dT slopes for the A--L and B--L equilibrium curves.

Crystal structure and thermal expansion of N,N,N',N'-Tetrakis-(1,2,4)triazol-1 ylmethyl-ethane-1,2-diamine, a triazole derivative with antifungal properties

Structural Chemistry

The crystal structure of N,N,N',N'-Tetrakis-(1,2,4)triazol-1-ylmethyl-ethane-1,2-diamine ... more The crystal structure of N,N,N',N'-Tetrakis-(1,2,4)triazol-1-ylmethyl-ethane-1,2-diamine has been fully determined at six different temperatures by X-ray single-crystal diffraction and the thermal expansion has been determined from 100 K to ambient temperature. The expansion is anisotropic and it is negative in one direction of the unit cell. The supramolecular structure formed by weak hydrogen bonds of the type C-H∙∙∙N resembles a trellis analogous to that observed in other systems purely organic with stronger hydrogen bonds.

$Research paper thumbnail of Differentiating amorphous mixtures of cefuroxime axetil and copovidone by X-ray diffraction and differential scanning calorimetry$

Annales Pharmaceutiques Françaises

La dispersion solide amorphe moléculaire, formée par le céfuroxime axétil et la copovidone dans l... more La dispersion solide amorphe moléculaire, formée par le céfuroxime axétil et la copovidone dans le rapport massique céfuroxime axétil/copovidone = 71/29, est comparée à ces deux constituants purs amorphes et à leur mélange mécanique dans le même rapport. Les examens calorimétriques montrent que tous ces matériaux sont vitreux. Les profils de diffraction des rayons X montrent que la dispersion solide est différente du mélange mécanique. Plus généralement, on montre comment la notion d’écart à l’additivité peut être utilisée pour caractériser l’originalité des dispersions solides.

Supplementary Information