Cholesterol Levels and Activity of Membrane Bound Proteins: Characterization by Thermal and Electrochemical Methods

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 films

Thermal Analysis of Model Bio-Polymers: Poly-L-Lactic Acid and Shedded Snake Skins

Biological polymers, or biopolymers, are of great interest in medical research. Compatibility of materials placed in the human body is important because of the known rejection of many thermoplastics. However, polypropylene, a classic thermoplastic, used in hernia repairs is typically not rejected. Researchers are constantly seeking biopolymers which are accepted by the human body. One very popular polymer that is being studied in our laboratories is poly-L-lactic acid. Poly-L-lactic Acid (PLLA) is an optically active, biocompatible and biodegradable polymer that has been widely investigated as an artificial cell scaffold material. In its most crystalline form, PLLA is highly anisotropic and is one of the most piezoelectric polymers known. Conversely, amorphous PLLA exhibits little, if any, piezoelectric behavior. Compression molded PLLA films can be endowed with varying amounts of crystalline character and piezoelectricity by uniaxially stretching the polymer in a hot air bath. Understanding the precise crystalline architecture of PLLA that results from tensile drawing is important for constructing cell scaffolds that have highly tailored biodegradation and cell guiding properties. In our work here, we investigate the changes in the thermal properties of PLLA at draw ratios between 1 and 5.5 using differential scanning calorimetry (DSC). The crystallinity of the compression molded undrawn starting material and drawn films are characterized using wide angle X-ray diffraction analysis. Our DSC results show an increase in percent crystallinity with increasing draw up to a draw ratio of 4.0. At greater draw ratios, there is a decrease in the crystalline character exhibited by PLLA. There is a growing interest in employing the transdermal pathway for administration of drugs. In order to develop knowledge of the drug transport properties or the effects of sun radiation on human skin, one needs a practical human skin model. We propose that shedded snake skins are biological polymers which fit the need and are readily available. We have developed in our laboratories a correlation in the thermal properties by TG, DTG and DTA between the human and shedded snake skins. Based on these correlations, we are studying the effects of chemicals and radiation on shedded snake skin as predictive model membranes for human skin behavior. The present study concerns the evaluation of various shedded snake skins by Thermal Mechanical Analysis (TMA). The low temperature TMA will be used to verify the effectiveness of sun screen creams and lotions

Thermal Analysis of Model Bio-Polymers: Poly-L-Lactic Acid and Shedded Snake Skins

Biological polymers, or biopolymers, are of great interest in medical research. Compatibility of materials placed in the human body is important because of the known rejection of many thermoplastics. However, polypropylene, a classic thermoplastic, used in hernia repairs is typically not rejected. Researchers are constantly seeking biopolymers which are accepted by the human body. One very popular polymer that is being studied in our laboratories is poly-L-lactic acid. Poly-L-lactic Acid (PLLA) is an optically active, biocompatible and biodegradable polymer that has been widely investigated as an artificial cell scaffold material. In its most crystalline form, PLLA is highly anisotropic and is one of the most piezoelectric polymers known. Conversely, amorphous PLLA exhibits little, if any, piezoelectric behavior. Compression molded PLLA films can be endowed with varying amounts of crystalline character and piezoelectricity by uniaxially stretching the polymer in a hot air bath. Understanding the precise crystalline architecture of PLLA that results from tensile drawing is important for constructing cell scaffolds that have highly tailored biodegradation and cell guiding properties. In our work here, we investigate the changes in the thermal properties of PLLA at draw ratios between 1 and 5.5 using differential scanning calorimetry (DSC). The crystallinity of the compression molded undrawn starting material and drawn films are characterized using wide angle X-ray diffraction analysis. Our DSC results show an increase in percent crystallinity with increasing draw up to a draw ratio of 4.0. At greater draw ratios, there is a decrease in the crystalline character exhibited by PLLA. There is a growing interest in employing the transdermal pathway for administration of drugs. In order to develop knowledge of the drug transport properties or the effects of sun radiation on human skin, one needs a practical human skin model. We propose that shedded snake skins are biological polymers which fit the need and are readily available. We have developed in our laboratories a correlation in the thermal properties by TG, DTG and DTA between the human and shedded snake skins. Based on these correlations, we are studying the effects of chemicals and radiation on shedded snake skin as predictive model membranes for human skin behavior. The present study concerns the evaluation of various shedded snake skins by Thermal Mechanical Analysis (TMA). The low temperature TMA will be used to verify the effectiveness of sun screen creams and lotions

Evaluation of the light polymerization efficiency of copolymers used in dental formulations by differential scanning calorimetry

Different compositions of visible-light-curable triethylene glycol dimethacrylate/bisglycidyl methacrylate copolymers used in dental resin formulations were prepared through copolymerization photoinitiated by a camphorquinone/ethyl 4-dimethylaminobenzoate system irradiated with an Ultrablue IS light-emitting diode. The obtained copolymers were evaluated with differential scanning calorimetry. From the data for the heat of polymerization, before and after light exposure, obtained from exothermic differential scanning calorimetry curves, the light polymerization efficiency or degree of conversion of double bonds was calculated. The glass-transition temperature also was determined before and after photopolymerization. After the photopolymerization, the glass-transi-tion temperature was not well defined because of the breadth of the transition region associated with the properties of the photocured dimethacrylate. The glass-transition temperature after photopolymerization was determined experimentally and compared with the values determined with the Fox equation. In all mixtures, the experimental value was lower than the calculated value. Scanning electron microscopy was used to analyze the morphological differences in the prepared copolymer structures. (C) 2007 Wiley Periodicals, Inc

Predicting Interactive Behavior of Cytokines and Their Receptors by Dielectric Thermal Analysis and Thermogravimetry

Cytokines and soluble cytokine receptors serve as important protein biomarkers for chronic and infectious disease diagnosis. The development of biosensors capable of detecting cytokines or their soluble receptors in patient bodily fluids is a growing area of research. In an ongoing series of studies to understand the thermal analytical behavior of cytokines and their soluble receptors, dielectric thermal analysis (DETA) and thermogravimetry (TG) were used in investigations to determine if differentiations based on dielectric properties (e.g., conductivity) of the proteins could be identified. Permittivity (ε′) and dielectric loss factor (ε′) measurements were performed over a frequency range of 0.1-300,000 Hz. Up to 20 min, water associated with the samples was conductive, interacting with the proteins and affecting the temperature-dependent relaxation spectra of proteins. A trend analysis revealed differences between surface charge at 0.1 Hz and bulk charge at 300,000 Hz. In addition, the greatest change detected among proteins was due to the conductivity (dielectric loss factor). Beyond a 20 min drying time, the observed conductivity was due to intrinsic properties of the proteins with limited dependence on frequency. A 100% water loss was obtained for samples within 20-30 min by TG. Sample drying by TG could serve as a preparatory step in drying protein samples for further DETA and DSC analysis. © 2011 Akadémiai Kiadó, Budapest, Hungary

Thermally-induced Dielectric Relaxation Spectra in Three Aldohexose Monosaccharides

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 (T g) and melting temperature (T m), 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

Human Cytokines Characterized by Dielectric Thermal Analysis, Thermogravimetry, and Differential Scanning Calorimetry

Malaria affects over 500 million people worldwide leading to 1-2 million deaths each year, the majority of whom are children. Four Plasmodium species cause malaria in humans. To properly diagnose, and correctly treat malarial infections, accurate diagnosis of infection is required. Proper diagnosis of infection will result in a reduction of morbidity, mortality, and of drug resistant parasites. However, the current tests for malaria diagnosis do not efficiently identify the appropriate human and parasite biomarkers associated with disease. Detection of specific inflammatory mediators such as cytokines associated with malaria pathogenesis will aid the determination of disease progression, disease prognosis, and the early diagnosis of malaria infection. In this study, we used dielectric thermal analysis (DETA), thermogravimetric analysis, and differential scanning calorimetry (DSC) to characterize five human cytokines (IL-1α, IL-2, IL-4, IL-6, and IL-10), to demonstrate how their thermoanalytical properties can be investigated for sensor design. Analysis for DETA was performed at a frequency range of 0.1-300,000 Hz. Permittivity and loss factor measurements were used to calculate tan δ values. Peak frequencies were used to determine dielectric signatures for each cytokine. The peak frequencies were different for each cytokine analyzed. In addition, activation energies were frequency dependent for IL-2 but frequency independent for the remaining four cytokines. Cytokines were also examined using DSC which established variance in heat of crystallization and heat of fusion of solvent among the five cytokines. A noticeable differentiation was observed with IL-1α among the other four cytokines when analyzed using trend analysis. Detection of unique dielectric signals will aid development of sensitive dielectric sensors capable of detecting cytokines in various human samples. © 2012 Akadémiai Kiadó, Budapest, Hungary

Thermal Behavior and Signature Patterns of Human Cytokine and Soluble Cytokine Receptors Investigated Using Dielectric Thermal Analysis and Thermogravimetry

Cytokines are small regulatory proteins secreted mostly by cells of the immune system. Cytokines participate in anti-inflammatory and pro-inflammatory processes in the body and in responses to host exposure to pathogens. In this study, the thermal behavior of human recombinant cytokines and soluble cytokine receptors; IFNγ, TNFα, IL-1 receptor antagonist, soluble TNF-receptor types 1 and 2, and sIL-2 receptor α were analyzed by dielectric thermal analysis at 37 °C and by thermogravimetry. Measurements were performed at a frequency range of 0.1-300,000 Hz. Permittivity and loss factor measurements were used to calculate mobility of charges (tan δ values) in the proteins from Debye plots. Peak frequencies and polarization times were used to determine dielectric signatures for each cytokine and receptor. Peak frequencies and polarization times were obtained for each cytokine and receptor analyzed. Detection of unique dielectric signatures of the proteins will aid development of sensitive dielectric sensors capable of detecting cytokines and soluble cytokine receptors in various human samples for malaria diagnosis. © 2011 Akadémiai Kiadó, Budapest, Hungary