| 1. |
- Croker, Denise, et al.
(författare)
-
Understanding the p-toluenesulfonamide / triphenylphosphine oxide crystal chemistry: a new 1:1 cocrystal and ternary phase diagram
- 2012
-
Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 12:2, s. 869-875
-
Tidskriftsartikel (refereegranskat)abstract
- A novel 1:1 cocrystal between p-toluenesulfonamide and triphenylphosphine oxide has been prepared and structurally characterized. This 1:1 cocrystal was observed to form during solid state grinding experiments, with subsequent formation of a known 3:2 cocrystal in the presence of excess sulfonamide. Both cocrystals are stable in the solid state. The ternary phase diagram for the two coformers was constructed in two different solvents: acetonitrile and dichloromethane. Examination of these diagrams clarified solution crystallization of both the newly discovered 1:1 cocrystal and the previously reported 3:2 cocrystal, and identified regions of stability for each cocrystal in each solvent. The choice of solvent was found to have a significant effect on the position of the solid state regions within a cocrystal system.
|
|
| 2. |
- Maher, Anthony, et al.
(författare)
-
Investigation of the Solid-State Polymorphic Transformations of Piracetam
- 2012
-
Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 12:12, s. 6223-6233
-
Tidskriftsartikel (refereegranskat)abstract
- The solid-state polymorphic transformations of 2-oxo-1-pyrrolidine acetamide (piracetam) were investigated using a combination of off-line and online techniques: differential scanning calorimetry (DSC), high temperature X-ray diffraction (HT-XRD), thermal analysis, and hot-stage optical microscopy. Form II and Form III were each observed to transform directly to Form I upon heating, with Form II transforming at a slightly lower temperature. The transformation of both polymorphs to Form I was observed to cause physical cracking of the crystals as well as changing the optical properties. Form I consistently transformed to Form II when cooled. The molecular rearrangements required for the transformation from Form I to Form II were found to be more energetically favorable than those required for the transformation to Form III. The transformation from the metastable Form II to the stable Form III was not observed in the solid-state, while the Form II-Form III transition temperature was found to be higher than the transition temperature of both polymorphs to Form I.
|
|
| 3. |
- Maher, Anthony, et al.
(författare)
-
Solubility of form III piracetam in a range of solvents
- 2010
-
Ingår i: Journal of Chemical and Engineering Data. - : American Chemical Society (ACS). - 0021-9568 .- 1520-5134. ; 55:11, s. 5314-5318
-
Tidskriftsartikel (refereegranskat)abstract
- The polymorph known as Form III of 2-oxo-1-pyrrolidine acetamide (piracetam) was isolated by cooling crystallization from methanol and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). Form III is the thermodynamically stable polymorph of piracetam in the range of this solubility study. The solubility of Form III was determined by gravimetrically measuring the amount of Form III which was contained in a volume of saturated solution over the temperature range (278 to 323) K, following evaporation of the solvent. Five solvents were examined: methanol, ethanol, 2-propanol, acetone, and 1,4-dioxane. The results showed that the solubility values correlated positively with solvent polar characteristics from a qualitative point of view; an increase in solubility of Form 111 was observed with increasing solvent polarity and solvent acidity. As the number of carbons in the n-alcohols increases, the polarity of the solvent and its hydrogen donation ability decreases and so does the solubility of Form III in the solvent. 1,4-Dioxane and acetone are relatively nonpolar and non-hydrogen bond donating solvents compared to the n-alcohols, and accordingly Form III is much less soluble in these.
|
|
| 4. |
- Maher, Anthony, et al.
(författare)
-
Solution-mediated polymorphic transformation : Form II to Form III piracetam in organic solvents
- 2014
-
Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 14:8, s. 3967-3974
-
Tidskriftsartikel (refereegranskat)abstract
- The solution-mediated polymorphic transformation from Form II to Form III 2-oxo-1-pyrrolidine acetamide (piracetam) was investigated in seven organic solvents over the temperature range of 5–50 °C. The transformation rate increased as a function of temperature, agitation, and the solubility of piracetam in the host solvent. However, this trend was reversed in 2-propanol. Molecular modeling demonstrated that 2-propanol forms interactions with piracetam molecules in solution stronger than those formed by other solvents, thereby retarding the nucleation and growth of FIII(6.525) during the transformation in this solvent.
|
|
| 5. |
- Mealey, Donal, et al.
(författare)
-
Crystal nucleation of salicylic acid in organic solvents
- 2015
-
Ingår i: CrystEngComm. - : Royal Society of Chemistry (RSC). - 1466-8033. ; 17:21, s. 3961-3973
-
Tidskriftsartikel (refereegranskat)abstract
- The crystal nucleation of salicylic acid was explored in a range of solvents using induction time and metastable zone width measurements. In total 3100 experiments were performed to collect statistically valid nucleation results. The lognormal cumulative probability function provided a representative fit for both induction time and metastable zone width distributions. At equal driving force the induction time is found to increase in the order chloroform, ethyl acetate, acetonitrile, acetone, methanol and acetic acid, and this order agrees with the order of increasing interfacial energy The metastable zone width (MSZW) value (expressed as supersaturation driving force) was highest in acetic acid followed by a lower value in methanol, consistent with the induction time results. In ethyl acetate, acetonitrile and acetone the corresponding MSZW values were lower but the order among these three solvents varied depending on the cooling rate and saturation temperature. A novel format for comparing the induction time and MSZW experiments is presented. The analysis reveals that the time of nucleation in the metastable zone width experiments is also dependent on the time of transforming clusters into nuclei, and not only governed by the rate of supersaturation generation. The relative influence of this transformation time depends on the solvent and the cooling rate.
|
|
| 6. |
- Munroe, Aina, et al.
(författare)
-
Analysis of FII crystals of Sulphathiazole : Epitaxial growth of FII on FIV
- 2011
-
Ingår i: CrystEngComm. - : Royal Society of Chemistry (RSC). - 1466-8033. ; 13:3, s. 831-834
-
Tidskriftsartikel (refereegranskat)abstract
- This work describes the phenomenon of a less stable polymorph wedged as a middle layer in a more stable polymorph of sulfathiazole. Isolation of the pure FII polymorph of sulfathiazole consistently yielded crystals with a distinctive middle layer. Raman spectroscopy and X-ray diffraction have identified this middle layer as another polymorph of sulfathiazole, namely FIV. The solubilities of FII and FIV sulfathiazole are almost identical, with FIV slightly more soluble. It is thought that this causes FIV to nucleate first, followed by the epitaxial growth of FII. A morphological examination of the crystals demonstrated that the (100) face of the FII crystal matches the (101) face of the FIV crystal. It is proposed that the similarity of these faces supports the epitaxial growth of the FII polymorph on the surface of the FIV polymorph.
|
|
| 7. |
|
|
| 8. |
- O'Mahony, Marcus, et al.
(författare)
-
Examining Solution and Solid State Composition for the Solution Mediated Polymorphic Transformation of Carbamazepine and Piracetam
- 2012
-
Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505.
-
Tidskriftsartikel (refereegranskat)abstract
- Solution-mediated polymorphic transformations (SMPT) of the pharmaceutical compounds carbamazepine and piracetam have been investigated. Seeded transformation experiments were performed, and the solution concentration was monitored by in situ infrared spectroscopy using a calibration free method. Solid samples were also taken over time, and the percentage of metastable and stable polymorphic phases were determined using off line quantitative powder X-ray diffraction analysis. Solution and solid state data were compared for each compound. In the case of carbamazepine, the SMPT from FI to FIII was identified as being controlled by the growth of the stable FIII polymorph. For piracetam, the SMPT was also identified as being controlled by growth of the stable polymorph, but with a more considerable induction time for nucleation of the stable phase. This paper demonstrates how the rate determining steps of the SMPT can be identified if both solution and solid phase data are recorded. The results are compared with other studies reported in the literature and rationalized into four principal scenarios.
|
|
