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.

Enthalpic analysis of the CaTiSiO5 system

2006 ◽  
Vol 60 (4) ◽  
Author(s):  
I. Nerád ◽  
L. Kosa ◽  
E. Mikšíková ◽  
K. Adamkovičová
Keyword(s):  
Experimental Data ◽  
Acid Solution ◽  
Hydrofluoric Acid ◽  
Solution Calorimetry ◽  
Enthalpy Of Fusion ◽  
Drop Calorimetry ◽  
Enthalpies Of Solution ◽  
Hydrofluoric Acid Solution ◽  
Relative Enthalpy

AbstractThe relative enthalpy of titanite and enthalpy of CaTiSiO5 melt have been measured using drop calorimetry between 823 K and 1843 K. Enthalpies of solution of titanite and CaTiSiO5 glass have been measured by the use of hydrofluoric acid solution calorimetry at 298 K. Enthalpy of vitrification at 298 K, δvitr H(298 K) = (80.7 ± 3.4) kJ mol−1, and enthalpy of fusion at the temperature of fusion 1656 K, δfus H(1656 K) = (139 ± 3) kJ mol−1, of titanite have been determined from experimental data. The obtained enthalpy of fusion is considerably higher than up to the present published values of this quantity.

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 Isolation of active subforms of α2-macroglobulin

1985 ◽  
Vol 229 (1) ◽  
pp. 227-232 ◽  
Author(s):  
J F Chlebowski ◽  
K Williams
Keyword(s):  
Differential Scanning Calorimetry ◽  
Anion Exchange ◽  
Functional Properties ◽  
Anion Exchange Chromatography ◽  
Exchange Chromatography ◽  
Scanning Calorimetry ◽  
Thermally Induced ◽  
Binding Stoichiometry ◽  
Α2 Macroglobulin ◽  
Stable Forms

Anion-exchange chromatography is shown to permit resolution and separation of subforms of the serum glycoprotein alpha 2-macroglobulin. The subforms differ dramatically in their stability as judged by differential scanning calorimetry, undergoing thermally induced unfolding at temperatures of 61 and 69 degrees C respectively. In addition, the proteinase-binding stoichiometry of the subforms differs by a factor of 2, with the more- and less-stable forms binding 2 and 1 mol of proteinase per mol of tetramer respectively. The calorimetric stability of the two forms is differentially affected on treatment with neuraminidase, suggesting that the nature of glycosylation may in part account for the observed differences in physical and functional properties.

THE SYSTEM LITHIUM SULPHATE – AMMONIUM SULPHATE – WATER

1954 ◽  
Vol 32 (7) ◽  
pp. 696-707 ◽  
Author(s):  
A. N. Campbell ◽  
W. J. G. McCulloch ◽  
E. M. Kartzmark
Keyword(s):  
Transition Temperature ◽  
Ammonium Sulphate ◽  
Room Temperature ◽  
Double Salt ◽  
Enthalpies Of Solution ◽  
Lithium Sulphate ◽  
Solubility Isotherms ◽  
Ternary Eutectics ◽  
Sulphate Water

The binary eutectics Li2SO4•H2O–ice and (NH4)2SO4–ice as well as the ternary eutectics Li2SO4•H2O–Li2SO4•(NH4)2SO4–ice and (NH4)2SO4–Li2SO4•(NH4)2SO4–ice have been determined as to temperature and composition. The complete solubility isotherms at 0.1°, 71.8°, and 95.2 °C. have been investigated. The enthalpies of solution of lithium sulphate monohydrate, of ammonium sulphate, and of double salt have been determined (in water at room temperature), and from these data, as well as from the solubility isotherms, it has been shown that the temperature of the transition of the double salt, Li2SO4•(NH4)2SO4, to its component single salts (in the presence of water) is approached by lowering the temperature, but this transition temperature is still far from reached when the system freezes completely.

Polymorphic forms of bendamustine hydrochloride: crystal structure, thermal properties and stability at ambient conditions

2019 ◽  
Vol 75 (6) ◽  
pp. 933-941
Author(s):  
Pablo Gaztañaga ◽  
Ricardo Baggio ◽  
Daniel Roberto Vega
Keyword(s):  
Crystal Structure ◽  
Fusion Rule ◽  
Polymorphic Form ◽  
Heat Of Fusion ◽  
High Humidity ◽  
Ambient Conditions ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Molecular Conformations ◽  
Polymorphic Forms

Crystallographic, thermal and stability analyses are presented of three different anhydrated forms of bendamustine hydrochloride [(I), (III) and (IV)] and a fourth, monohydrated one (II). Since form (I) presents the higher melting point and the higher heat of fusion, according to the `heat of fusion' rule it should be the most stable in thermodynamic terms [Burger & Ramberger (1979). Mikrochim. Acta, 72, 259–271], though it is unstable in high-humidity conditions. The monohydrate structure (II), in turn, dehydrates by heating and topotactically transform into anhydrate (III). This latter form appears as less stable than anhydrate (I), to which it is linked via a monotropic relationship. For these three different forms, the crystal structure has been determined by single crystal X-ray diffraction. The crystal structures and molecular conformations of forms (II) and (III) are quite similar, as expected from the topotactic transformation linking them; furthermore, under high-humidity conditions, form (III) shows changes compatible with a transformation into form (II) within 24 h. The crystal structure of form (I) is different from the other two. The remaining polymorphic form (IV) could only be obtained as a powder, from which its crystalline structure could not be determined. The relative thermodynamic stability of the different crystalline forms was determined by differential scanning calorimetry and thermogravimetrical studies, and their stability under different humidity conditions analysed.

Polymorphism of felodipine co-crystals with 4,4′-bipyridine

CrystEngComm ◽  
2014 ◽  
Vol 16 (29) ◽  
pp. 6603-6611 ◽  
Author(s):  
Artem O. Surov ◽  
Katarzyna A. Solanko ◽  
Andrew D. Bond ◽  
Annette Bauer-Brandl ◽  
German L. Perlovich
Keyword(s):  
Blocking Agent ◽  
Solution Calorimetry ◽  
Molar Ratio ◽  
X Ray Diffraction ◽  
X Ray ◽  
Molar Ratios ◽  
Hirshfeld Surfaces ◽  
Channel Blocking ◽  
Polymorphic Forms ◽  
Hirshfeld Surfaces Analysis

The calcium-channel blocking agent felodipine forms co-crystals with 4,4′-bipyridine with 1 : 1 and 2 : 1 molar ratios. The co-crystal with 1 : 1 molar ratio exists in two polymorphic forms. The co-crystals polymorphism was investigated by X-ray diffraction, DSC, solution calorimetry and Hirshfeld surfaces analysis.

Thermische Zersetzung und Lösungskalorimetrie von Ammoniumneodymbromiden / Thermal Decomposition and Solution Calorimetry of Ammonium Neodymium Bromides

1999 ◽  
Vol 54 (10) ◽  
pp. 1283-1294 ◽  
Author(s):  
C. Hennig ◽  
H. Oppermann
Keyword(s):  
Thermal Decomposition ◽  
Pressure Measurement ◽  
Total Pressure ◽  
Solid Phase ◽  
Solution Calorimetry ◽  
Enthalpies Of Solution ◽  
Pressure Measurements ◽  
Tabulated Data

The thermal decomposition equilibria of ammonium neodymium bromides (NH4)3NdBr6, (NH4)2NdBr5 and NH4Nd2Br7 have been investigated by total pressure measurements. The thermodynamical data of these solid phase complexes have been derived from the decomposition functions. The standard enthalpies of solution in 4N HBr (aq.) of (NH4)3NdBr6, (NH4)2NdBr5, NH4Nd2Br7, NdBr3 and Nd2O3 were measured. On the basis of these values and tabulated data, the standard enthalpies at 298 K of the ammonium neodymium bromides were derived and compared with the results obtained from the total pressure measurements.Data by total pressure measurement: ΔH°B((NH4)3 NdBr6,f,298) = -399,1 ± 4,9 kcal/mol; S°((NH4)3NdBr6,f,298) = 153,4 ± 7,4 cal/K.mol; ΔH°B((NH4)2NdBr5,f,298) = -343,0 ± 4,4 kcal/mol; S°((NH4)2,NdBr5,f,298) = 109,9 ± 6,8 cal/K.mol; ΔH°B(NH4Nd2Br7,f,298) = -484,0 ± 5,1 kcal/mol; S°(NH4Nd2Br7,f,298) = 127,9 ± 6,6 cal/K.mol.Data by solution calorimetry: ΔH°B(NdBr3,f,298) = -208,7 ± 1,6 kcal/mol; ΔH°B((NH4)3- NdBr6,f,298) = -404,8 ± 2,7 kcal/mol; ΔH°B((NH4)2NdBr5,f,298) = -344,2 ± 2,4 kcal/mol; ΔH°B(NH4Nd2Br7,f,298) = -482,7 ± 3,7 kcal/mol.

Eutectoid Al-51at%Zn Alloy Studied by Isothermal Mechanical Spectroscopy

2012 ◽  
Vol 184 ◽  
pp. 167-172 ◽  
Author(s):  
Andre Rivière ◽  
Veronique Pelosin ◽  
Michel Gerland
Keyword(s):  
Transition Temperature ◽  
Low Frequency ◽  
Mechanical Spectroscopy ◽  
Thermally Induced ◽  
Atom Diffusion ◽  
Thermally Activated ◽  
Relaxation Parameters ◽  
Zn Alloy ◽  
Large Frequency ◽  
Internal Friction Spectra

sothermal mechanical spectroscopy measurements were performed in an Al-51 at % Zn alloy at various temperatures below and above the eutectoid transition temperature: during a heating the α-β eutectoid mixture changes into α solid solution at 550 K. Damping experiments were performed in a very large frequency range (10-5– 50 Hz) between room temperature and 673 K. Internal friction spectra performed between 200 K and 540 K, exhibit two thermally activated relaxation peaks (P1 and P2). P1 decreases and disappears with the increase of measurement temperature while P2 appears and increases. P2 totally disappears above the eutectoid transition temperature. Above 550 K, a new peak (P3) is evidenced at very low frequency. The relaxation parameters of P3 (limit relaxation time τ0= 9×10-7and activation energy H = 105 kJ/mole (1.1 eV)) allow to associate this peak with the motion of sub grain boundaries. P1 and P2 (τ0≈ 10-7and H ≈ 70 kJ/mole (0.75 eV) for both peaks) are associated with a thermally induced atom diffusion across the α-β interface.

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