Search Results

You are looking at 1 - 7 of 7 items for

  • Author or Editor: M. Caira x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract  

Complexes between members of a homologous series of alkylparabens and b-cyclodextrin (b-CD) have been prepared by both kneading and co-precipitation methods and their behaviour studied by differential scanning calorimetry (DSC), thermogravimetric (TG), infrared (IR) and powder X-ray diffraction (PXRD) techniques. PXRD revealed that complexation did occur by both the kneading and co-precipitation methods. DSC and IR techniques confirmed these results and TG indicated the presence and number of water molecules in each complex.

Restricted access

Abstract  

Hydrated inclusion complexes of the hosts β-CD (CD=cyclodextrin), γ-CD and permethylated β-CD with the guest clofibric acid were analysed by TG and DSC methods to characterise their dehydration behaviours. Activation energies for dehydration of the β- and γ-CD clofibric acid complexes, determined by isothermal thermogravimetry, are significantly lower (∼20-25%) than those for the corresponding uncomplexed hydrated CDs. These data can be reconciled with X-ray structural data which show that H2O molecules in the complexes occupy different crystal sites from those occupied in the parent CDs.

Restricted access

Abstract  

Two polymorphs of the bronchodilator tulobuterol (2-chloro-α-[[(1,1-dimethylethyl)- amino]-methyl]benzenemethanol) with melting points differing by ~10 K were isolated and characterized by thermal analysis (HSM, TG, DSC), as well as powder and single crystal X-ray diffraction. Analysis of melting data for Forms 1 and 2 revealed a monotropic relationship, with ΔG 0, the Gibbs free energy difference at the melting temperature of the lower melting form, less than 1 kJ mol-1. This small difference is reconciled with known structural features in the crystals of the two forms. The hydrogen bonding capacity of the tulobuterol molecule is fully utilised in both polymorphs in forming a common trimeric unit via three strong O-H···N interactions. Consequently only weak intermolecular forces characterize the packing of the trimers in the monoclinic polymorph (Form 1, P21/n, Z =12) and the triclinic polymorph (Form 2, P(-1),Z =6).

Restricted access

Abstract  

Salbutamol laurate is a novel salt form of the well-known bronchodilator salbutamol (albuterol). Its polymorphism and inclusion in (2-hydroxypropyl)-β-cyclodextrinwere investigated by thermogravimetry, differential scanning calorimetry, infrared and powder X-ray diffraction techniques. Two polymorphic forms of the salt were identified. Conditions for inclusion complex formation between the salt and (2-hydroxypropyl)-β-cyclodextrin, namely prolonged co-grinding and kneading, were established by a combination of the above methods.

Restricted access

Abstract  

The thermal and structural characteristics of two crystal forms of ambroxol, (trans-((amino-2-dibromo-3,5-benzyl)amino)-4-cyclohexanol), a drug with remarkable mucolytic and expectorant properties marketed in several drug products, were investigated. Form II (m.p. 92.4C) is obtained by spontaneous cooling from a hot water/ethanol solution while Form I (m.p. 99.5C) slowly separates from the mother liquor. The two forms can be identified by PXRD and DSC analyses. On the basis of both thermal and structural data the thermodynamic relationship of enantiotropy was deduced. No metastable (Form I)?stable (Form II) conversion was observed upon storage at ambient conditions. Form I crystallizes in the space group P21/n (alternative setting of P21/c) with Z=8. Form II crystallizes in the space group P21/c with Z=4 and a significantly different crystal packing arrangement from that in Form I. A third crystalline modification, Form III (space group P21/c with Z=16) was detected on cooling a single crystal of Form I down to -70C. On warming to ambient temperature Form III was found to revert to Form I. This reversible single crystal to single crystal transition was structurally characterised and found to involve subtle changes in the types and extent of molecular disorder as well as the hydrogen bonding arrangement.

Restricted access

Abstract  

Isostructural solvates of the 1:1 molecular complex between the antibacterial drugs tetroxoprim (TXP) and sulfametrole (SMTR) with formulae TXPSMTRCH3OH (I), TXPSMTRC2H5OH (II) and TXPSMTRH2O (III), were investigated to establish their propensity for guest exchange. Separate exposure of powdered (I), (II) and (III) to a saturated atmosphere of each solvent of the complementary solvate pair at ambient temperature resulted in reversible solvent exchange in all cases. DSC and TG were the methods of choice for monitoring the exchange processes since (I)-(III) have distinct onset temperatures of desolvation and characteristic mass losses. Interpretation of the results in terms of the known locations of the solvent molecules in crystals of (I)-(III) led to the conclusion that solvent exchange probably proceeds by a co-operative mechanism involving material transport through channels while the common host framework is maintained.

Restricted access

Abstract

A hydrated form of theophylline-7-acetic acid obtained by recrystallization from water is described and characterized in terms of thermal properties, physical stability with respect to relative humidity and dehydration kinetics. The hydrate resulted to be stable at ambient conditions. Fitting of experimental dehydration data to solid state reaction equations suggests a three dimensional phase boundary reaction proceeding from the surface of the crystal inward along three dimensions. The relevant activation energy calculated from the Arrhenius plot is 173 kJ/mol.

Restricted access