Snake skin is a viable and readily available material as a model for human skin. Pharmaceutical applications use shed snake skin to study the effects of sunscreens on exposure to UV radiation (e.g. benzophenone on Boa integument). In order to understand the effects of radiation or drug transport through this model skin, one must determine its basic physical properties. This preliminary study evaluated two types of snake skin, namely Cuban Boa a 'dark' skin (Epicrates angulifer) and Green tree python a 'light' skin (Morelia viridis). Previous studies by other investigators have used pig, rabbit and snake skin as a human skin substitute. The structure of both snake skins was comparable based on IR spectroscopy and were functionally amino acids and moisture. Photomicrography by light and scanning electron microscopy revealed strong anatomic similarities. Morphologically there were two structures visible, namely a cellular and hinge-fibrous area. The thermal techniques indicated a phase transition at 35-75°C, which is associated with lipid melting. There was an 8 and 12% mass loss for the light skin and dark skin, respectively, which is interpreted, in part, as moisture loss at <100°C. The physical and analytical properties establish a base line that will be used in the future to differentiate various sunscreen types, such as benzophenone and octyl salicylate. Study was also done to determine the effect of an application of a commercially available sunscreen using SEM.
Authors:K. Chatterjee, D. Dollimore, and K. Alexander
Hydroxy benzoic acids were subjected to rising temperature thermogravimetric analysis. After optimizing the procedural variables,
the kinetics of decomposition was determined and methyl paraben was taken as the calibration compound to characterize the
evaporation patterns for the ortho and meta derivatives. The Eact values for ortho, meta and para derivatives were 64.8, 78.2, and 119.1 kJ mol–1, respectively. The Antoine and Langmuir equations were utilized to determine the coefficient of evaporation k, which was 1245250.8, units being in the SI system. The vapor pressure plots were generated for the ortho and meta derivatives; ΔHvap for these two compounds were obtained as 66.7 and 80.4 kJ mol–1, respectively.
Authors:S. Lerdkanchanaporn, D. Dollimore, and K. Alexander
In a previous publication, the thermogravimetric (TG) analysis of ascorbic acid was considered. Simultaneously with the production
of the TG data, time-temperature plots were also generated on the work station which allowed the process to be classified
as exothermic or endothermic and identified the energy change with the reaction sequence. This aspect is investigated in the
present study. To maximize the energy change, the model mixtures were assessed at a mass ratio of 1∶1. The analytical implications
of this approach are explored. To avoid complications in this kind of analysis, the present study is restricted to the behavior
of binary systems heat treated in nitrogen.
This project investigated the interaction between poly-L-lactic acid (PLLA) and several therapeutic agents. Low percentage crystallinity PLLA (melt-pressed, molded and drawn) was
studied. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were used to characterize the crystallinity and
thermal properties in a thermal cycling process. Repeatable melting and crystallization events were observed. The thermal
properties of a drug-polymer combination using PLLA and an acidic, basic, neutral and zwitterionic material were investigated.
A sufficient quantity of the drug must be present in the polymer to be observed thermally. Release of atropine sulfate from
a PLLA tablet showed a two-phase process.
scanning calorimetry (DSC) is a thermal analytical tool for preformulation
studies. Extrapolated melting temperature (TP)
and heat of fusion (ΔHf)
can be used as parameters for optimizing the DSC performance. Two model pharmaceuticals
acetaminophen and nicotinamide are used in this study. Using a factorial design
for the experimental model and matrix analysis the results, the effect of
sample mass, heating rate and the nitrogen flow rate were evaluated on the
and TP values. Two
levels for each of the procedural variables were used as a balanced experimental
design with two sample sizes, two heating rates and two nitrogen flow rates.
It was found that the change in the heating rate caused significant changes
in the ΔHf
values but not the Tp
values for acetaminophen. However, no significant effect was found for the Tp value but ΔHf value was affected to a
certain extent for nicotinamide.
Authors:P. Aggarwal, D. Dollimore, and K. Alexander
Ingredients used in the manufacture of perfumes can be investigated by thermogravimetry. In this study the evaporation of
methyl benzoate was investigated using a simultaneous TG-DTA unit. A rising temperature method of thermal analysis was used
for the study. The rate of evaporation of the ingredient was calculated from a simple plot of percentage mass lossvs. time. A derivative plot of the same was used to calculate the coefficient of evaporation in a controlled atmosphere and regulated
air flow rate. In a series of programmed temperature runs on the TGDTA unit it was shown that the evaporation process is zero
order, and that the evaporation coefficients at each temperature can be fitted into the Arrhenius equation. The energy of
activation, Eact can be calculated from the slope of the line. It was found to be 47 kJ mol−1. This value was compared and shown to approach the enthalpy of vaporization as calculated using the Troutons or Clausius
Five poorly soluble drugs namely hydrochlorothiazide, menadione, propylthiouracil, quinine sulfate and sulfamerazine were
used to evaluate the ability of an index (Ic) based on the van't Hoff equation to predict the eutectic composition at a higher heating rate than previously published.
The term Ic is a dimensionless index which has been defined in the literature and is used to predict eutectic composition. This current
work uses this study to determine if the correlation holds true at the higher heating rate of 10C min-1. The maximum deviation was observed for quinine sulfate, for which the predicted eutectic composition was 10% lower than
what was observed with the DSC. It can be concluded that the Index developed here has a good correlation with the experimentally
determined eutectic composition.
Authors:M. Samtani, D. Dollimore, and K. Alexander
The effects of procedural variables on dolomite decomposition in carbon dioxide were investigated. The partial pressure of carbon dioxide causes dolomite decomposition to split into a two-stage process. It was observed that the first stage of dolomite decomposition is progressively displaced to higher temperatures with an increase in heating rate. However, the second stage is not affected significantly by changes in the heating rate. These studies also indicate that decrepitation analysis on dolomite in CO2 provides better information as compared to experiments in other atmospheres. The flow rate of the purge gas does not influence the thermal behavior of dolomite.
Authors:A. Hazra, K. Alexander, D. Dollimore, and A. Riga
The present study was aimed at determining the kinetics of evaporation and establishing vapor pressure curves for both single and multi-component systems by thermogravimetry (TG) and differential scanning calorimetry (DSC). Essential oils (e.g. lavender oil, orange oil, clove oil and eucalyptus oil, etc.) are typically multi-component systems consisting of various volatile pure components (e.g. linalyl acetate, limonene, cinnamaldehyde, etc.) which resemble single component systems. In this study linalyl acetate was taken as the calibration compound for TG. The vapor pressure curves for the pure substances were plotted using TG and vapor pressure plots for clove oil and eucalyptus oil were constructed using DSC. The thermodynamic and kinetic parameters of the pure compounds were compared to that of the multi-component systems to quantitatively and qualitatively measure the influence of different compounds on each other. The k-value from the vapor pressure data for linalyl acetate was calculated as 112006 Pa kg0.5mol0.5s-1 m-2 K-0.5. The vapor pressure values were used to determine the Antoine constants using the SPSS 10.0 software.
Authors:A. Vora, A. Riga, D Dollimore, and K. Alexander
This study attempts to identify the degradative process which folic acid undergoes in the solid-state under thermal stress.
In order to facilitate the process, the various pieces of the chemical structure, namely, p-amino benzoic acid, pterin and glutamic acid as both its d- and l-isomers were investigated as separate entities. These structured solid-state pieces were then compared to the composite solid
state folic acid degradative curves in order to identify the peaks seen and provide direction for the interpolation of the
degradative mechanism. It was observed that none of the structural pieces could be superimposed as assumed earlier and hence
an attempt was made to identify the decomposition products using various analytical techniques such as infrared spectroscopy,
mass spectroscopy and X-ray diffraction which suggested that the glutamic acid fragment is lost first as evidenced by acid
loss and amide enhancement in the IR spectra. The vitamin was ultimately degrading to carbon fragments and that further identification
was not necessary.