scholarly journals Polymorphic Forms of Lamivudine: Characterization, Estimation of Transition Temperature, and Stability Studies by Thermodynamic and Spectroscopic Studies

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Renu Chadha ◽  
Poonam Arora ◽  
Swati Bhandari
Keyword(s):  
Transition Temperature ◽  
Enthalpy Of Solution ◽  
Pharmaceutical Preparations ◽  
Spectroscopic Studies ◽  
Stability Studies ◽  
Order Form ◽  
Phase Pure ◽  
Melting Endotherm ◽  
Polymorphic Forms ◽  
Stable Forms

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.

scholarly journals An Insight into Thermodynamic Relationship Between Polymorphic Forms of Efavirenz

2012 ◽  
Vol 15 (2) ◽  
pp. 234 ◽  
Author(s):  
Renu Chadha ◽  
Poonam Arora ◽  
Anupam Saini ◽  
Dharamvir Singh Jain
Keyword(s):  
Transition Temperature ◽  
Fusion Rule ◽  
Solution Calorimetry ◽  
Enthalpy Of Fusion ◽  
Solubility Data ◽  
Enthalpies Of Solution ◽  
Thermally Induced ◽  
Preferential Formation ◽  
Polymorphic Forms ◽  
Stable Forms

Purpose: The aim of the work is to study the crystallization of efavirenz to understand the preferential formation of various polymorphic forms, to establish their identity, to study the transformation between the polymorphic forms on heating and to determine their free energy. Methods: Slow crystallization from different solvents under controlled conditions was employed to prepare various crystalline forms. The TGA and DSC were used to study their thermal behavior and inter-conversion of these forms. The calorimetrically determined enthalpies of solution and solubility data are utilized to determine the transition temperatures. Results: Six polymorphic forms of efavirenz are identified and characterized completely. The TGA scans of all the forms did not show any mass loss indicating absence of hydrate or solvate. The thermally induced transformations are observed in the DSC scans of five forms II-VI indicating them to be metastable which are converted to stable higher melting forms. The melting temperature and enthalpy of fusion of lower melting (FormL) and higher melting forms (FormH) reveal that four of these polymorphic pairs are monotropically related. The enthalpies of solution of FormL are found to be more exothermic as compared to corresponding FormH. The transition temperature (Tt) determined using enthalpy of solution and solubility data was found to be higher than the melting of both the forms except for polymorphic pair VIL/VIH. The effect of ΔCp on transition temperature is also reported. Conclusions: The form I is found to be thermodymanically most stable but least soluble. The forms II-V are metastable and are converted irreversibly to stable forms. The enthalpy of fusion rule and virtual transition temperature provided complementary evidence for the existence of monotropy in these polymorphic pairs. However, enantiotropy is demonstrated in VIL/VLH pair and is well established in our study. Novelty: The present study reveals the thermodynamic aspects of various isolated polymorphic forms of efavirenz. Solution calorimetry along with other techniques is used to study the transformation of one form to another. The emphasis is laid on determination of transition temperature of various polymorphic pairs which has not been reported earlier. This article is open to POST-PUBLICATION REVIEW. Registered readers (see “For Readers”) may comment by clicking on ABSTRACT on the issue’s contents page.

Polymorphism of pharmaceuticals

2020 ◽  
pp. 342-375
Author(s):  
Joel Bernstein
Keyword(s):  
Ionic Liquids ◽  
Pharmaceutical Preparations ◽  
Phase Changes ◽  
New Techniques ◽  
Solvent Selection ◽  
Crystal Forms ◽  
Rate Of Dissolution ◽  
Amorphous Forms ◽  
Stable Forms ◽  
Chemical Microscopy

Chapter 7 deals with polymorphism in pharmaceuticals. Following a discussion of the problem of determining the statistics of the occurrence of polymorphism in pharmaceuticals, I present a discussion and examples of the connection between polymorphism and the rate of dissolution and solubility, bioavailability, and the importance of phase changes and mixtures of forms in pharmaceutical preparations. I survey some of the considerations and techniques involved in screening for crystal forms: solvent selection, specific screening for solvates and hydrates, gel crystallization, crystallization in ionic liquids, the challenge of difficult to obtain stable forms and unstable new forms, and the outlook on new techniques and conditions for crystallization. The chapter also deals with polymorphism in pharmaceutical co-crystals, excipients, and amorphous forms and the importance and utility of chemical microscopy in the study of polymorphism of pharmaceuticals.

scholarly journals Spectrofluorometric Determination of Verapamil Hydrochloride in Pharmaceutical Preparations and Human Plasma Using Organized Media: Application to Stability Studies

2006 ◽  
Vol 89 (6) ◽  
pp. 1565-1572 ◽  
Author(s):  
Mohamed Walash ◽  
Fathalla Belal ◽  
Nahed El-Enany ◽  
Amina Abdelsalam
Keyword(s):  
Human Plasma ◽  
Biological Fluids ◽  
Sodium Dodecyl ◽  
Pharmaceutical Preparations ◽  
Pharmaceutical Formulations ◽  
Official Method ◽  
Stability Studies ◽  
Verapamil Hydrochloride ◽  
Spiked Human Plasma

Abstract A highly sensitive spectrofluorometric method was developed for the determination of verapamil hydrochloride (VP HCl) in pharmaceutical formulations and biological fluids. The proposed method is based on investigation of the fluorescence spectral behavior of VP HCl in micellar systems, such as sodium dodecyl sulfate (SDS) and β-cyclodextrin (β-CD). In aqueous solutions of borate buffer of pH 9 and 8.5, VP HCl was well incorporated into SDS and β-CD, respectively, with enhancement of its native fluorescence. The fluorescence was measured at 318 nm after excitation at 231 nm. The fluorescence intensity enhancements were 183 and 107% in SDS and in β-CD, respectively. The fluorescence-concentration plots were rectilinear over the range of 0.020.2 and 0.020.25 μg/mL, with lower detection limits of 5.58 × 103 and 3.62 × 103 μg/mL in SDS and β-CD, respectively. The method was successfully applied to the analysis of commercial tablets and the results were in good agreement with those obtained with the official method. The method was further applied to the determination of VP HCl in real and spiked human plasma. The mean % recoveries in the case of spiked human plasma (n 4) was 92.59 3.11 and 88.35 2.55 using SDS and β-CD, respectively, while that in real human plasma (n 3) was 90.17 6.93 and 89.17 6.50 using SDS and β-CD, respectively. The application of the method was extended to the stability studies of VP HCl after exposureto ultraviolet radiation and upon oxidation with hydrogen peroxide.

Flux-Assisted Preparation of Powdered Bismuth Superconductors

1989 ◽  
Vol 169 ◽  
Author(s):  
R. H. Arendt ◽  
M. F. Garbauskas ◽  
L. L. Schilling
Keyword(s):  
Transition Temperature ◽  
Reaction Temperature ◽  
Solvent Content ◽  
Phase Pure ◽  
Post Synthesis ◽  
Powdered Form

AbstractResults are presented on efforts to prepare both the 80K, Bi2CaSr2Cu2Oz (2122), and 11 OK, (Bi,Pb)2Ca2Sr2Cu3Oz (2223), transition temperature bismuth superconducting species in either phase pure or nearly phase pure, powdered form using either equimolar NaCI-KCI or NaBiOz as molten fluxes. Data are presented on the effects of variation of the reaction temperature and duration, solvent content, relative CaO and CuO contents, and of post-synthesis anneals of the product materials.

scholarly journals X-ray Absorption Spectroscopic studies of Single Crystal SrFeO3-δ

2014 ◽  
Vol 70 (a1) ◽  
pp. C1527-C1527
Author(s):  
Shang Hsien Hsieh ◽  
Mukta Vinayak Limaye ◽  
Shashi Bhushan Singh ◽  
Yu Cheng Shao ◽  
Yu Fu Wang ◽  
...  
Keyword(s):  
Transition Temperature ◽  
Single Crystal ◽  
Thermal Hysteresis ◽  
Spectroscopic Studies ◽  
Temperature Dependent ◽  
Zone Method ◽  
Edge Structure ◽  
X Ray ◽  
Length Changes ◽  
X Ray Absorption

We have prepared a high quality single crystal of SrFeO3-δ (δ ~ 0.14) by the floating-zone method to study the electronic and atomic structures using temperature-dependent x-ray absorption near-edge structure (XANES), x-ray linear dichroism (XLD), and extended x-ray absorption fine structure (EXAFS) at the O K-edge, Fe L3,2- and K-edge. Resistivity measurements indicate that the SrFeO2.86 shows an anisotropic behavior, and thermal hysteresis behavior between 70 K and 40 K. The temperature dependent Fe K-edge EXAFS studies shows that the Fe-O bond length changes in ab-plane below transition temperature. The XLD results illustrate that as temperature is reduced from room temperature to below the transition temperature, the preferential occupancy of Fe majority-spin eg orbitals changes from the 3d3z2-r2 to 3dx2-y2, but restore to 3dx2-y2 after thermal hysteresis. Experimental findings suggest that the charge transfer during thermal hysteresis is induced by lattice distortions of the FeO6 octahedra in SrFeO2.86.

Preparation of YBa2Cu3O7−x using barium hydroxide flux

1990 ◽  
Vol 5 (12) ◽  
pp. 2755-2758 ◽  
Author(s):  
N. Coppa ◽  
A. Kebede ◽  
J. W. Schwegler ◽  
I. Perez ◽  
R. E. Salomon ◽  
...  
Keyword(s):  
Transition Temperature ◽  
Liquid Phase ◽  
Barium Hydroxide ◽  
Bunsen Burner ◽  
High Quality ◽  
Heat Treated ◽  
Phase Pure ◽  
Hydroxide Flux ◽  
Conventional Methods ◽  
Response Field

High quality bulk YBa2Cu3O7−x was synthesized by fusing stoichiometric amounts of yttrium and copper nitrates and barium hydroxide in air, using an ordinary Bunsen burner. The starting materials go through a short-lived liquid phase yielding a solid black product which was subsequently heat treated (900 °C, 18–24 h in air, followed by 500 °C, 5 h in O2). These materials were greater than 99% phase pure with CuO as the only other phase and they exhibited a transition temperature of 92 K, a 15.5% perfect diamagnet response (field cooled). This synthesis represents an improvement over the much more labor and time intensive conventional methods in that it allows high quality materials of various compositions to be prepared quickly.

Evaluation of non-isothermal methods in stability studies of human insulin pharmaceutical preparations

2009 ◽  
Vol 49 (4) ◽  
pp. 916-922 ◽  
Author(s):  
Alexis Oliva ◽  
Marta Suárez ◽  
Juan Ramón Hernández ◽  
Matías Llabrés ◽  
José B. Fariña
Keyword(s):  
Human Insulin ◽  
Pharmaceutical Preparations ◽  
Stability Studies
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