The Experts below are selected from a list of 105 Experts worldwide ranked by ideXlab platform
M M De Villiers - One of the best experts on this subject based on the ideXlab platform.
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Comparison of high sensitivity micro differential scanning calorimetry with X-ray powder diffractometry and FTIR spectroscopy for the characterization of pharmaceutically relevant non-crystalline materials.
Die Pharmazie, 2006Co-Authors: Mingna Song, W. Liebenberg, M M De VilliersAbstract:In this study, high sensitivity micro differential scanning calorimetry (MDSC) in the scanning of dynamic mode was compared to X-ray powder diffractometry (XRPD) for quantifying amorphous nifedipine in mixtures crystalline nifedipine. This technique was also compared with FTIR for quantifying polymorph A of Chloramphenicol Palmitate (CAP) and poly DL-lactide-co-glycolide) (PLGA) in pharmaceutical formulations. The limit of determination (LOD) achieved by MDSC were 0.06% compared to 5% for XRPD quantification of amorphous nifedipine and 0.02% compared to 7% for IR quanitfication of polymorph A of CAP. As little as 0.165 mg PLGA could be measured in excipients mixtures. Desirable linearity and repeatability were established in all cases.
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An analysis of fine grinding and aggregation of poorly soluble drug powders in a vibrating ball mill
Pharmazie, 1996Co-Authors: M M De Villiers, L. R. TiedtAbstract:Ball mills are used extensively in the pharmaceutical industry as a simple, economical and rapid means of particle size reduction. In this study a laboratory vibrating ball mill was used to mill relatively large (300-400μm) crystals of the poorly soluble drugs furosemide, acetaminophen and Chloramphenicol palminate. It was found that prolonged grinding in this type of mill resulted in a practical limit in particle size reduction within a relatively short time (30 min). Grinding also caused the aggregation of the milled furosemide and Chloramphenicol Palmitate but not acetaminophen particles. To evaluate aggregation the milling process was described by a first-order breakage model and deviation from this model was attributed to aggregation. These results were confirmed by microscopic evaluation of the powders and by comparing mean volume particle sizes of aggregates and dispersed particles for statistically significant differences
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kinetic study of the solid state thermal interconversion of the polymorphic forms of Chloramphenicol Palmitate
Drug Development and Industrial Pharmacy, 1993Co-Authors: M M De Villiers, J G Van Der Watt, A P LotterAbstract:AbstractKinetic studies revealed that the solid-state thermal interconversion of polymorphic forms of Chloramphenicol Palmitate at different temperatures followed apparent zeroorder kinetics. The transformation between the metastable forms C and B was faster than the subsequent transformation of form B to form A. However, starting with form B the transformation to form A was slower than the transformation of form B, formed by the transformation of form C, to form A. The rate constant (k0) plotted versus temperature (K) according to the Arrhenius equation was linear. There were significant differences in the activation energy and other thermodynamic parameters.
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The interconversion of the polymorphic forms of Chloramphenicol Palmitate (CAP) as a function of environmental temperature
Drug Development and Industrial Pharmacy, 1991Co-Authors: M M De Villiers, J G Van Der Watt, A P LotterAbstract:AbstractWhen polymorph B of Chloramphenicol Palmitate (CAP) is heated at 82 °C for 1600 minutes it changes completely to the less soluble and less bioavailable polymorph A. When polymorph C, the most soluble polymorph, is grinded for a prolonged period it changes to polymorph A through B. We investigated the effect of the environmental temperature on the interconversion of polymorph C. This was done to determine the effect that heat generated during grinding could have on polymorph C.Samples of polymorph C was kept at 50 and 75 °C respectively. At predetermined intervals samples were withdrawn and differential scanning colorimetric (DSC) curves and Xray powder diffractograms recorded.Both samples changed to polymorph B but only the sample kept at 75 °C changed into A during the time the experiment was run. Therefore temperature control during storage and handling, especially grinding, of polymorph C and B is recommended to prevent conversion to the poorly soluble and less bioavailable polymorph A.
A P Lotter - One of the best experts on this subject based on the ideXlab platform.
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kinetic study of the solid state thermal interconversion of the polymorphic forms of Chloramphenicol Palmitate
Drug Development and Industrial Pharmacy, 1993Co-Authors: M M De Villiers, J G Van Der Watt, A P LotterAbstract:AbstractKinetic studies revealed that the solid-state thermal interconversion of polymorphic forms of Chloramphenicol Palmitate at different temperatures followed apparent zeroorder kinetics. The transformation between the metastable forms C and B was faster than the subsequent transformation of form B to form A. However, starting with form B the transformation to form A was slower than the transformation of form B, formed by the transformation of form C, to form A. The rate constant (k0) plotted versus temperature (K) according to the Arrhenius equation was linear. There were significant differences in the activation energy and other thermodynamic parameters.
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The interconversion of the polymorphic forms of Chloramphenicol Palmitate (CAP) as a function of environmental temperature
Drug Development and Industrial Pharmacy, 1991Co-Authors: M M De Villiers, J G Van Der Watt, A P LotterAbstract:AbstractWhen polymorph B of Chloramphenicol Palmitate (CAP) is heated at 82 °C for 1600 minutes it changes completely to the less soluble and less bioavailable polymorph A. When polymorph C, the most soluble polymorph, is grinded for a prolonged period it changes to polymorph A through B. We investigated the effect of the environmental temperature on the interconversion of polymorph C. This was done to determine the effect that heat generated during grinding could have on polymorph C.Samples of polymorph C was kept at 50 and 75 °C respectively. At predetermined intervals samples were withdrawn and differential scanning colorimetric (DSC) curves and Xray powder diffractograms recorded.Both samples changed to polymorph B but only the sample kept at 75 °C changed into A during the time the experiment was run. Therefore temperature control during storage and handling, especially grinding, of polymorph C and B is recommended to prevent conversion to the poorly soluble and less bioavailable polymorph A.
J G Van Der Watt - One of the best experts on this subject based on the ideXlab platform.
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kinetic study of the solid state thermal interconversion of the polymorphic forms of Chloramphenicol Palmitate
Drug Development and Industrial Pharmacy, 1993Co-Authors: M M De Villiers, J G Van Der Watt, A P LotterAbstract:AbstractKinetic studies revealed that the solid-state thermal interconversion of polymorphic forms of Chloramphenicol Palmitate at different temperatures followed apparent zeroorder kinetics. The transformation between the metastable forms C and B was faster than the subsequent transformation of form B to form A. However, starting with form B the transformation to form A was slower than the transformation of form B, formed by the transformation of form C, to form A. The rate constant (k0) plotted versus temperature (K) according to the Arrhenius equation was linear. There were significant differences in the activation energy and other thermodynamic parameters.
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The interconversion of the polymorphic forms of Chloramphenicol Palmitate (CAP) as a function of environmental temperature
Drug Development and Industrial Pharmacy, 1991Co-Authors: M M De Villiers, J G Van Der Watt, A P LotterAbstract:AbstractWhen polymorph B of Chloramphenicol Palmitate (CAP) is heated at 82 °C for 1600 minutes it changes completely to the less soluble and less bioavailable polymorph A. When polymorph C, the most soluble polymorph, is grinded for a prolonged period it changes to polymorph A through B. We investigated the effect of the environmental temperature on the interconversion of polymorph C. This was done to determine the effect that heat generated during grinding could have on polymorph C.Samples of polymorph C was kept at 50 and 75 °C respectively. At predetermined intervals samples were withdrawn and differential scanning colorimetric (DSC) curves and Xray powder diffractograms recorded.Both samples changed to polymorph B but only the sample kept at 75 °C changed into A during the time the experiment was run. Therefore temperature control during storage and handling, especially grinding, of polymorph C and B is recommended to prevent conversion to the poorly soluble and less bioavailable polymorph A.
Maria Christina Gamberini - One of the best experts on this subject based on the ideXlab platform.
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Structural, electronic, thermodynamical and charge transfer properties of Chloramphenicol Palmitate using vibrational spectroscopy and DFT calculations.
Spectrochimica acta. Part A Molecular and biomolecular spectroscopy, 2012Co-Authors: Rashmi Mishra, Anubha Srivastava, Anamika Sharma, Poonam Tandon, Cecilia Baraldi, Maria Christina GamberiniAbstract:Abstract The global problem of advancing bacterial resistance to newer drugs has led to renewed interest in the use of Chloramphenicol Palmitate (C 27 H 42 Cl 2 N 2 O 6 ) [Palmitic acid alpha ester with d -threo-(-),2-dichloro-N-(beta-hydroxy-alpha-(hydroxymethyl)-p-nitrophenethyl)acetamide also known as Detereopal]. The characterization of the three polymorphic forms of Chloramphenicol Palmitate (CPP) was done spectroscopically by employing FT-IR and FT-Raman techniques. The equilibrium geometry, various bonding features, and harmonic wavenumbers have been investigated for most stable form A with the help of DFT calculations and a good correlation was found between experimental data and theoretical values. Electronic properties have been analyzed employing TD-DFT for both gaseous and solvent phase. The theoretical calculation of thermodynamical properties along with NBO analysis has also been performed to have a deep insight into the molecule for further applications.
David J.w. Grant - One of the best experts on this subject based on the ideXlab platform.
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Estimating the relative stability of polymorphs and hydrates from heats of solution and solubility data
Journal of pharmaceutical sciences, 2001Co-Authors: David J.w. GrantAbstract:The transition temperature, T(t), of polymorphs is estimated from both their heats of solution and solubilities (or intrinsic dissolution rates) determined at any one temperature (e.g., ambient). At a given temperature, T, the enthalpy difference, DeltaH, between polymorphs, I and II, is equal to the difference between their heats of solution, whereas the free energy difference, DeltaG, can be estimated by the equation, DeltaG = -RTln (c(I)/c(II)) or DeltaG = -RTln (J(I)/J(II)), where c is the solubility and J is the intrinsic dissolution rate. The entropy difference, DeltaS, is evaluated as (DeltaH - DeltaG)/T. Because the heat capacity difference,DeltaC(p) between polymorphs is small enough to be neglected, the transition temperature may be estimated by the equation, T(t) = DeltaH/DeltaS. The thermodynamic stability relationships of the polymorphs (i.e., whether they are enantiotropes or monotropes) are predicted from the value of T(t) and the melting temperature. The T(t) values for auranofin, carbamazepine, Chloramphenicol Palmitate, cyclopenthiazide, gepirone hydrochloride, lamivudine, MK571, premafloxacin, sulfamerazine, sulfamethoxazole, sulfathiazole, and urapidil, were calculated from reported values of the heats of solution and solubilities (or dissolution rates). The stability relationships deduced from the calculated values of T(t) are in good agreement with those reported using other methods, such as differential scanning calorimetry and interpretation of melting data.