Dielectric Thermal Analysis (DETA) of drugs, proteins and amino acids reveals a strongly linear conductivity increase prior
to and peaking at the melt, associated with dielectric viscoelastic properties of the material. Premelt onset and peak are
shown to depend on thermal history. Comparisons of neat amino acid samples to samples heated to 150 °C; dried in a desiccator;
or heated above their melting point and cooled show significant premelt and melt shifts. Melts are also correlated with phase
transitions observed by Differential Scanning Calorimetry (DSC). Activation energies attributed to charging in the premelt
for amino acids were typically 250 J/mole.
Authors:Satya Girish Avula, Kenneth Alexander, and Alan Riga
A eutectic is formed from a mixture of two or more solids and has a melting point lower than that of each of its constituents. It is generally represented by a phase diagram where the liquid and solid phases impact upon each other with a value known as the eutectic point. In pharmaceuticals, poor water solubility is a major obstacle for releasing new dosage forms into the market. Eutectic formation overcomes these problems. Preparation of a phase diagram by Differential Scanning Calorimetry can determine eutectic properties, but it is tedious. A modified Van't Hoff (VH) equation was used in this study. Devalina Law developed a dimensionless index for the VH equation. The difference in melting points of an excipient polymer and drug are divided by the slope of the VH equation. In previous studies, five excipient–drug compositions were evaluated. The final index relationship was in good agreement except for the salt, quinine sulfate. In order to test the validity of the VH index, further studies of PEG with acetylsalicylic acid, acetaminophen, diflunisal, dimenhydrinate, ketoconazole, and mefenamic acid were performed.
This study examines the polymerization of dental monomers catalyzed by synthesized acylphosphine oxides in a differential
scanning calorimetry (DSC) cell. This research focuses on establishing a relationship between radicals generated by the acylphosphine
oxide photoinitiators and the kinetic reaction rates of methyl methacrylate (MMA) and acrylamide (ACM), a model monomer. The
thermal stability of mono- and di-acylphosphine oxides was examined by DSC. Endothermic melting and exothermic polymerization
reactions initiated with the two initiators were recorded. The acrylamide model system laid the ground work for the critical
evaluation of the synthesized new initiators of mono (2,4,6-trimethylbenzoyl) diphenylphosphine oxide, and bis(2,4,6-trimethylbenzoyl)
phenylphosphine oxide. The bis(acyl) phosphine oxide photoinitiator was more reactive than the mono-(acyl) phosphine oxide
with methyl methacrylates under laboratory conditions. In exothermic reactions, temperatures rose higher and more rapidly
for bis(acyl) phosphine oxide initiated reactions than mono-(acyl) phosphine oxide initiated reactions.
Advances in science and technology are now at the heart of the global economy, but the number of students earning degrees in the sciences, technology, engineering, and math (STEM) fields has stalled. According to the National Association for Colleges and Employers (NACE), programs have been initiated nationwide to nurture interest in the sciences, including research competitions, co-ops and internships, and K-12 STEM education. Senior thermal analysis scientists are not only researchers, they are role models, mentors and teachers intimately involved in the recruitment and training of young scientists. The authors present guidelines for thermal analysis research project planning for high school students, undergraduate students and master’s and doctoral candidates. Project planning includes developmentally appropriate techniques, methods, instruments, scope and significance. Case studies illustrate examples of short-term, concrete materials analysis projects tailored to younger student researchers, as well as master’s level projects making significant contributions to the state of the science and innovative doctoral research. In addition to designing projects for students at all levels, senior thermal analysis scientists can use specific teaching and training techniques to help young scientists develop their abilities in the lab and at the podium.
Authors:Amanda Santos, Gilberto Chierice, Kenneth Alexander, Alan Riga, and Ellen Matthews
Eugenol is the main volatile compound extracted oil from clove bud, Syzygiumaromaticum L., and used in traditional medicine, as a bactericide, fungicide, anesthetic, and others. Its extraction was performed using
hydrodistillation which is the most common extraction technique. Its components and thermal behavior were evaluated using
gas chromatography (GC) and differential scanning calorimetry (DSC), which provide a better characterization of these natural
compounds. This extracted product was compared to the standard eugenol results. The GC results suggested ~90% eugenol was
found in the total extracted oil, and some of its boiling characteristics were 270.1 °C for peak temperature and 244.1 J g−1 for the enthalpy variation.
Authors:Ronaldo Nunes, Felipe Semaan, Alan Riga, and Éder Cavalheiro
The thermal properties of verapamil hydrochloride (VRP) and its physical association as binary mixtures with some common excipients
were evaluated. Thermogravimetry (TG) was used to determine the thermal mass loss, as well as to study the kinetics of VRP
thermal decomposition, using the Flynn-Wall-Ozawa model. Based on their frequent use in pharmacy, five different excipients
(microcrystalline cellulose, magnesium stearate, hydroxypropyl methylcellulose, polyvinylpyrrolidone and talc) were blended
with VRP. Samples were prepared by mixing the analyte and excipients in a proportion of 1:1 (m/m). DSC curves for pure VRP
presented an endothermic event at 143 ± 2 °C (ΔHmelt = 132 ± 4 J g−1), which corresponds to the melting (literature Tm = 143.7 °C, ΔHmelt = 130.6 J g−1). Comparisons among the observed results for each compound and their binary physical mixtures presented no relevant changes.
This suggests no interaction between the drug and excipient.
Authors:Cheila G. Mothé, Michelle G. Mothé, Alan T. Riga, and Kenneth S. Alexander
Thermal properties of some shedded snake skins in comparison with human skins are represented by thermogravimetry (TG), derivative thermogravimetry (DTG), and differential thermal analysis (DTA) to predict process condition as dermal pathway for administration of drugs or it be used as model membranes for permeation studies. Thermal behavior by TG/DTG and DTA curves for four kinds of shedded snake skins as Boelens Python (BP), Eastern Indigo Snake (EIS), Emerald Tree Boa (ETB), and Cascavel (CBR) were similar in relation to their decomposition temperatures at 100 °C and 230–400 °C of its constituents, however, their properties were different in the residue content (inorganic or carbonaceous substances). Similar thermal properties were also exhibited by human skins’ samples, however, they presented different residue and constituents’ content.
Authors:Noufissa Zanati, Michael Mathews, Indika Perera, John Moran, Jean Boutros, Alan Riga, and Mekki Bayachou
The long-term goal of this investigation is to study the effects of increased cholesterol levels on the molecular activity
of membrane-bound enzymes such as nitric oxide synthase, that are critical in the functioning of the cardiovascular system.
In this particular investigation, we used differential scanning calorimetry (DSC) and dielectric thermal analysis (DETA) to
study the effect of added cholesterol on melting/recrystallization and dielectric behavior, respectively, of phosphatidylcholine
(PC) bilayered thin films. We also used electrochemical methods to investigate the effect of added cholesterol on the redox
behavior of the oxygenase domain of nitric oxide synthase as a probe embedded in the PC films. The results show that added
cholesterol in the PC films seems to depress the molecular dynamics as indicated by lowered current responses in the presence
of cholesterol as well as a slight increase of the transition temperature in the overall two-phase regime behavior observed
in PC–cholesterol films. These results are rationalized in the context of the general DSC and DETA behaviors of the PC–chol
Authors:Libby Yoerg, M. Ellen Matthews, Lakshmi Kaza, Naullage Indika Perera, David W. Ball, John Moran, and Alan T. Riga
Three aldohexose monosaccharides, d-glucose, d-mannose, and d-galactose, were examined by scanning temperature dielectric analysis (DEA) from ambient temperatures through their melts. Phase transitions, including glass transition (Tg) and melting temperature (Tm), were evaluated by differential scanning calorimetry (DSC). The monosaccharides were found to exhibit thermally-induced dielectric loss spectra in their amorphous-solid phase before melting. Activation energies for electrical charging of each of the monosaccharides were calculated from an Arrhenius plot of the tan delta (e″/e′, dielectric loss factor/relative permittivity) peak frequency versus reciprocal temperature in Kelvin. The DEA profiles were also correlated with the DSC phase diagrams, showing the changes in electrical behavior associated with solid–solid and solid–liquid transitions.