Optical spectroscopic studies of the polymorphic forms of 1, 4-dihydroxyanthraquinone

The present study is focused on estimation of transition temperature and stability of various forms of lamivudine. The forms were recrystallized from variety of solvents and preliminarily identification on the basis of SEM revealed existence of three forms (Forms I, II, III). DSC scans of Forms I and III show that these are metastable and undergo heat mediated transformation to Form IH and Form IIIH, respectively. Form II is phase pure with single sharp melting endotherm at 178.6°C. The thermal events are visually observed by hot stage microscopy. Enthalpy of solution of the forms is endothermic and magnitude varies in the order Form II > Form IL > Form IIIL suggesting Form IIIL to be least crystalline which is well correlated with XRPD data. The transition temperature of the polymorphic pairs IL/IH and IIIL/IIIH derived from enthalpy of solution and solubility data revealed monotropy whereas enantiotropy exists in IIIH/II. The slurry experiments showed Form II to be thermodynamically most stable. Forms IL and IIIL though stable in water are converted to Form II in ethanol, acetonitrile, and propanol after 1 day. Form IIIL is converted to Form IL in water after 7 days and the observation is of importance as this instability can effect the pharmaceutical preparations whereas Form IL shows a balance between stability and solubility.

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Infrared and Raman spectroscopic studies of the polymorphic forms of nickel, cobalt and ferric molybdates

Infrared Physics ◽

10.1016/0020-0891(87)90072-8 ◽

1987 ◽

Vol 27 (5) ◽

pp. 309-315 ◽

Cited By ~ 41

Author(s):

S.Sheik Saleem

Keyword(s):

Spectroscopic Studies ◽

Raman Spectroscopic ◽

Nickel Cobalt ◽

Polymorphic Forms

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Polymorphic phase transition of a membrane protein - analysis of continuous diffuse electron diffraction intensity

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100142451 ◽

1986 ◽

Vol 44 ◽

pp. 166-167

Author(s):

Douglas L. Dorset ◽

Andrew K. Massalski

Keyword(s):

Molecular Sieve ◽

Three Dimensional ◽

Pore Geometry ◽

Two Dimensional ◽

Diffraction Intensity ◽

Polymorphic Phase Transition ◽

E Coli ◽

Crystallographic Study ◽

Hexagonal Form ◽

Polymorphic Forms

Matrix porin, the ompF gene product of E. coli, has been the object of a electron crystallographic study of its pore geometry in an attempt to understand its function as a membrane molecular sieve. Three polymorphic forms have been found for two-dimensional crystals reconstituted in phospholipid, two hexagonal forms with different lipid content and an orthorhombic form coexisting with and similar to the hexagonal form found after lipid loss. In projection these have been shown to retain the same three-fold pore triplet geometry and analyses of three-dimensional data reveal that the small hexagonal and orthorhombic polymorphs have similar structure as well as unit cell spacings.

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