Bicalutamide polymorphs I and II

For a complete picture of the phase behavior of a compound exhibiting dimorphism, not only the temperature but also the pressure, the second variable of the Gibbs energy, should be taken into account. Because volume reflects the dependence of the Gibbs energy on pressure, investigating the specific volumes of a compound provides information on its phase behavior under pressure. This can be quantified using the Clapeyron equation, which leads to a so-called topological pressure–temperature phase diagram. Bicalutamide is used as a sample case and with literature data its topological phase diagram has been constructed. Even though the phase relationship between bicalutamide’s two known solid phases is monotropic at ordinary pressure, it becomes enantiotropic at higher pressure. The steep slope of the solid–solid equilibrium in the P–T diagram, 22.5 MPa K^?1, indicates that pressure has virtually no influence on it and that it is mainly entropy driven.     

Tyrosine alkyl esters as prodrug: the structure and intermolecular interactions of <Emphasis Type="SmallCaps">l</Emphasis>-tyrosine methyl ester compared to <Emphasis Type="SmallCaps">l</Emphasis>-tyrosine and its ethyl and <Emphasis Type="Italic">n</Emphasis>-butyl esters

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 P2₁2₁2₁, a = 5.7634(15) Å, b = 12.111(2) Å, c = 14.3713(19) Å, V = 1003.1(4) Å³ with Z′ = 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.     

Crystal structure and thermal expansion of N,N,N′,N′-tetrakis-[(1H,2,4-triazol-1-yl)methyl]-ethane-1,2-diamine

Structural Chemistry - The crystal structure of N,N,N′,N′-tetrakis-[(1H,2,4-triazol-1-yl)methyl]-ethane-1,2-diamine has been fully determined at six different temperatures by X-ray...     

Phenomenology of Polymorphism: IV. The Trimorphism of Ferrocene and the Overall Metastability of Its Triclinic Phase

Structural and thermodynamic data reported in the literature for the three crystalline phases of ferrocene are used to build a topological representation of its (p, T) phase diagram. Two phases (orthorhombic and monoclinic) exhibit stable phase regions whose temperature ranges increase with increasing pressure. The triclinic phase is found to be metastable at any temperature and pressure. In fact, in the (p, T) diagram, it is not associated with any state of lowest energy although it transforms into the monoclinic phase according to a transition which is reversible. This transition occurs in the phase region where the orthorhombic phase is the stable one.     

Electrophoretic behavior of a highly water-soluble dendro[60]fullerene

The aim of the present study was to develop an analytical method for measuring amounts of a dendro[60]fullerene (DF) which is a highly water-soluble [60]fullerene derivative. We tried to define a straightforward methodology using capillary zone electrophoresis, a method which, to our knowledge, has not yet been used to that purpose. Preliminary assays showed that DF has almost the same mobility than the electroosmotic flow (EOF) but in the opposite direction. Attempts were carried out to reduce the EOF and positive results were obtained by adding hydroxypropylcellulose to the background electrolyte. In order to define optimal operating conditions, a Taguchi experimental plan was used to study simultaneously the effects of the main parameters that are pH, ionic strength, methanol amount and hydroxypropylcellulose concentration. Two parameters are of the utmost importance as to their effect on the migration time and separation efficiecy: pH and ionic strength whose actions are opposite.     

Decagonal C60 crystals grown from n-hexane solutions: solid-state and aging studies

Decagonal C₆₀ crystals grown from n-hexane solutions correspond to an orthorhombic 1:1 solvate (a=10.249 , b=31.308 , c=10.164 ). It forms with negative excess volume ( per formula unit) and transforms on heating into fcc C₆₀ (desolvation enthalpy of +50.6 kJ per solvate mole, close to the sublimation enthalpy for pure n-hexane) while n-hexane desorption from fcc C₆₀ is accompanied by an enthalpy of +48.6 kJ per solvent mole. Thus solvate formation is preferred to solvent adsorption. Orthorhombic C₆₀·1 n-hexane undergoes no degradation when stored in air for 9 years at room temperature in the dark.     

Uniaxial negative thermal expansion in crystals of tienoxolol

The thermal expansion of tienoxolol has been investigated by X-ray powder diffraction up to its melting temperature. The data indicate that the expansion is anisotropic and even negative in one direction of the unit cell. The supramolecular structure formed by hydrogen-bonds reflects that of a trellis, which explains the observed behavior of tienoxolol crystals.