Thermolytic Processes Research Articles

Effects of Medications on Heat Loss Capacity in Chronic Disease Patients: Health Implications Amidst Global Warming.

Pharmacological agents used to treat or manage diseases can modify the level of heat strain experienced by chronically ill and elderly patients via different mechanistic pathways. Human thermoregulation is a crucial homeostatic process that maintains body temperature within a narrow range during heat stress through dry (i.e., increasing skin blood flow) and evaporative (i.e., sweating) heat loss, as well as active inhibition of thermogenesis, which is crucial to avoid overheating. Medications can independently and synergistically interact with aging and chronic disease to alter homeostatic responses to rising body temperature during heat stress. This review focuses on the physiologic changes, with specific emphasis on thermolytic processes, associated with medication use during heat stress. The review begins by providing readers with a background of the global chronic disease burden. Human thermoregulation and aging effects are then summarized to give an understanding of the unique physiologic changes faced by older adults. The effects of common chronic diseases on temperature regulation are outlined in the main sections. Physiologic impacts of common medications used to treat these diseases are reviewed in detail, with emphasis on the mechanisms by which these medications alter thermolysis during heat stress. The review concludes by providing perspectives on the need to understand the effects of medication use in hot environments, as well as a summary table of all clinical considerations and research needs of the medications included in this review. SIGNIFICANCE STATEMENT: Long-term medications modulate thermoregulatory function, resulting in excess physiological strain and predisposing patients to adverse health outcomes during prolonged exposures to extreme heat during rest and physical work (e.g., exercise). Understanding the medication-specific mechanisms of altered thermoregulation has importance in both clinical and research settings, paving the way for work toward refining current medication prescription recommendations and formulating mitigation strategies for adverse drug effects in the heat in chronically ill patients.

Thermolytic degradation of methylmethionine and implications for its role in DMS and MeCl formation in hypersaline environments

Environmental context Methyl chloride and dimethyl sulfide are important atmospheric trace gases, but their biogeochemical contributions to the atmosphere are not fully understood. The amino acid derivative methyl methionine has been hypothesised to be a precursor of these two atmospheric gases, especially in drying salt-lake environments. We found methyl chloride and dimethyl sulfide in salt crystals and soil samples of hypersaline lakes, suggesting that a thermal decay of methyl methionine could be one of the formation mechanisms responsible. Abstract Volatile organic halocarbons (VOXs) and volatile organosulfur compounds (VOSCs) play an important role in the chemical processes of the lower atmosphere. However, biogeochemical release mechanisms from terrestrial environments are complex and the current knowledge of the origin and fluxes of these compounds is incomplete. This study presents data from worldwide sampling campaigns to hypersaline salt lakes to investigate terrestrial sources for atmospheric VOXs and VOSCs. The hypothesis was tested if methionine or methylmethionine could potentially serve as a precursor for methyl chloride and dimethyl sulfide formation in salt-lake environments. Next to methyl chloride, emissions from hypersaline soil samples incubated in headspace vials showed an array of VOSCs including dimethylsulfide and dimethyldisulfide. Additionally, methyl chloride and dimethyl sulfide were released from fluid inclusions of halite crystals after grinding and purge-and-trap headspace gas chromatography–mass spectrometry analysis. An abiotic mechanism for their formation is conceivable owing to the fast response of emission on heating freeze-dried samples at 40°C. Furthermore, the compounds trapped in fluid inclusions of halite crystals correspond to those compounds originally formed in the immediately subjacent soils. Based on the thermolytic degradation of methylmethionine, the activation energies for methyl chloride and dimethyl sulfide are calculated from their Arrhenius plots. Additionally, structurally related substances were analysed and a degradation mechanism is postulated. Results indicate that thermolytic processes could play an important role in salt-lake environments on desiccation.

Phase formation of REBa 2Cu 3O 7− δ (RE: Y 0.5Gd 0.5, Y 0.5Nd 0.5, Nd 0.5Gd 0.5) superconductors from nanopowders synthesised via co-precipitation

Phase formation of REBa 2Cu 3O 7− δ (RE: Y 0.5Gd 0.5, Y 0.5Nd 0.5, Nd 0.5Gd 0.5) superconductors synthesised via co-precipitation (COP) method were investigated by thermogravimetric analysis (TGA), differential thermal analysis (DTA) and X-ray diffraction (XRD) analysis. All samples showed identical thermal decomposition behaviour from the thermogram in which 5 major weight losses were observed. However, XRD of the samples at different heat treatment temperatures showed different diffraction patterns indicating different thermolytic processes. Meanwhile, transmission electron microscopy and surface area analysis revealed that the powders obtained from COP have particle sizes ranging from 7 to 12 nm with relatively large surface area. Molar ratios of prepared samples obtained were near to the theoretical values as confirmed by elemental analyses using X-ray fluorescence (XRF). The T C( R=0) for sintered YGd, YNd and NdGd were 87 K, 86 K and 90 K, respectively. Surface morphological study via scanning electron microscope showed the structures of samples were dense and non porous.

Modeling the body temperature throughout the day with a two-term function

A two-term function with potential and exponential terms is proposed to model the body temperature throughout the day. These terms can be related to thermogenic and thermolytic processes that are opposite but simultaneous. The first term, a potential function, reflects that the heat gain process is predominant; the second term is a negative exponential function and reflects the predominance of heat dissipation. The function also provides the time of the inflection between thermal opposite processes. The proposed two-term function and a cosine function were fitted to 335 temperature series of 24-h duration recorded in humans and animals. The percentage of variance accounted for by the two-term function was higher than that for the cosine approximation for the total sample and for those series whose shape was asymmetrical (n=75). Nevertheless, no significant differences between the percentage of variance accounted for by the two functions were found for those series whose shape was symmetrical (n=260). The results of different subgroups that differed in experimental conditions are discussed.

Kinetic data imprecisions in photochemical rate calculations: Means, medians, and temperature dependence

The uncertainty in computed species concentrations resulting from measurement imprecision in reaction rate components is investigated in two tropospheric photochemical models. In this study, which extends Thompson and Stewart [1991], we perform statistical analysis on reaction rate coefficients to focus on two aspects of model uncertainty: (1) the change in the magnitude of concentration uncertainty as temperature varies throughout a model grid and (2) the difference resulting from selection of mean, as opposed to median, rates for model calculations. Reaction rates are treated as realizations of random variables having statistical properties given by component terms and their imprecisions. These assumptions lead to expressions for probability distributions of bimolecular rates and for the high‐ and low‐pressure limits for termolecular and thermolytic processes. They also imply that bimolecular rates and high‐ and low‐pressure limits used in photochemical models correspond to median values taken from a lognormal distribution. We derive analytic expressions for mean values, which are always larger than the medians, an intrinsic property of lognormal variables. We suggest that comparison of species concentrations computed using median and mean rates can provide some measure of the effect of rate imprecision in multidimensional models. We also find that the temperature dependence derived for the imprecision in bimolecular rates differs from that given in standard references, with our expression giving a smaller increase in imprecision as temperatures deviate from 298 K. Results are illustrated using a box and a one‐dimensional (1‐D) model.

Kallikrein, nitric oxide and the vascular responses of the submaxillary glands in rats exposed to heat.

During exposure of normal rats to an ambient temperature of 36 degrees C or 40 degrees C, body temperature increases; thermolytic processes are set up and saliva is spread on the skin. In Wistar rats, thermolytic salivation started when body temperature was above 39 degrees C. This water loss was associated with a loss of body weight. A 10% reduction of plasma volume was observed in animals exposed to 40 degrees C but no change was observed in those exposed to 36 degrees C. Body weight loss was reduced by hexamethonium, atropine, prazosin, HOE 140, a bradykinin-antagonist, and NG-nitro-L-arginine (NOARG), a NO synthase inhibitor. The weight and blood content of the submaxillary glands, which are the main effectors of the thermolytic processes, increased as a function of the ambient temperature. The increase of blood content was enhanced by hexamethonium but reduced by atropine and NOARG. The weight increase was inhibited by hexamethonium, prazosin, HOE 140 and NOARG. At an ambient temperature of 40 degrees C, a large swelling developed around the submaxillary glands, resulting in a distention of the surrounding soft tissues. This local oedema fluid contained low levels of endogenous proteins but accumulated exogenous labelled albumin. This swelling was enhanced by atropine but decreased by hexamethonium, trasylol, HOE 140, NOARG, ketoprofen, a cyclooxygenase inhibitor, and prazosin. In kininogen deficient rats, the blood content of submaxillary glands increased as a function of ambient temperature. No increase in glandular weight and no swelling of the of the soft tissues were observed. After atropine, the weight of the glands increased and a swelling of the soft tissues appeared.(ABSTRACT TRUNCATED AT 250 WORDS)

ChemInform Abstract: New Routes to Thioketenes and Propadienethione by Flash Vacuum Thermolysis.

AbstractThe retro‐Diels‐Alder reaction under f.v.p. conditions is applied to the synthesis of simple unstabilized thioketenes (II) and (VIII).

New routes to thioketenes and propadienethione by flash vacuum thermolysis

The retro-Diels-Alder reaction under flash vacuum thermolysis (FVT) conditions was applied to the synthesis of simple unstabilized thioketenes. Alternatively, these reactive thiocarbonyl compounds were obtained by FVT elimination of methyltrimethylsilyl sulfide from silylated ketene dithioacetals (and for thioketene itself from methyl trimethylsilyl dithioacetate). A synthesis of propadienethione associating these two thermolytic processes is also reported. The thermolysis products were identified by low temperature IR spectroscopy and immediate quenching with gaseous dimethylamine leading to the corresponding thioamides. In the case of propadienethione, further reaction with the methanethiol formed in situ was observed.

Thermal exchanges during sleep in anhidrotic ectodermal dysplasia

Anhidrotic ectodermal dysplasia is a congenital syndrome characterized by the absence of sweat glands. A sweating test was performed on such a patient and proved his inability to sweat. Thermal exchanges during night sleep were then measured in this patient and compared with data obtained from a healthy control subject. Ambient conditions were as follows: dry bulb temperature 32.2 degrees C, relative humidity 30%-40%, wind speed 0.7 m.s-1. Polysomnographic recordings showed normal sleep patterns in both subjects, but a "first night effect" in the patient. Rectal (Tre) and mean skin (Tsk) temperatures and loss of mass were monitored continuously throughout the 8-h sleep recording. Loss of mass averaged 34.1 g.h-1 in the patient vs 78.1 g.h-1 in the control subject. No relationship with sleep stages was observed in the patient, in contrast to the control subject who experienced a decrease in evaporation during rapid eye movement sleep. Body temperatures varied little in the patient, but decreased until the 6th h of sleep in the control subject. On two occasions there was a 0.3 degrees C fall in the Tre of the patient during two slow wave sleep (SWS) phases, while Tsk and loss of mass did not change. As thermolytic processes had not varied on these two occasions, it was concluded that the fall in Tre indicated a concomitant decrease in metabolic heat production, in agreement with the assumption that SWS represented a state of energy conservation.

A study of the use of Y 2O 3 doped ZrO 2 membranes for solar electrothermal and solarthermal separations

We measured ion and (implicitly) electron hole conductivities and O 2 semipermeabilities and their activation energies of commercial slip-cast Y 2O 3 doped ZrO 2 under conditions simulating their practical application. We believe that this material shows promise as an O 2 semipermeable membrane for ROC and electro-ROC type water splitters, as well as components of devices for the gas-phase electrolytic separation of metals (Zn in this study) from their oxides. The higher activation energy for hole transport vis-à-vis ion transport and the associated transition from electrically-dominated to pressure-dominated transport of O 2 across such membranes makes an almost continuous transition from electrolytic to thermolytic processes possible. This is especially important in solar processes, where, at high temperatures, the difference between electrochemical and thermochemical processes fades away. This transition greatly increases the latitude with which process variables can be adjusted for optimization.

Organic chemistry by infrared lasers: 5. Pulsed CO 2 laser induced photoablative decomposition of biomass materials

Pulsed CO 2 laser irradiation of pulverized corn cobs, oak leaves, pine sawdust and processed cotton in an evacuated sealed system at 1077 cm −1 affords a limited number of low molecular weight chemicals. The product mixture is very nearly the same in each reaction. The product ratios vary somewhat depending upon the initial biomass material used. The major gaseous products identified are CO, CO 2, CH 4, C 2H 2, C 2H 4, C 2H 6, C 3H 6, H 2O, acetaldehyde and acrolein. Irradiation at 1054 cm −1 or 944 cm −1 or under atmospheric conditions does not change the results significantly. The latter seems to indicate an ablative process wherein the cellulosic material decomposes by expelling neutral low molecular weight fragments from the biomass surface where high concentrations of radicals seem to be formed during, or very shortly after laser irradiation. Comparison with known thermolytic processes of biomass materials indicates that the laser induced ablation may be more controlled than pyrolysis. The results suggest the possibility of using the laser method for the continuous production of some of the low molecular weight chemicals and for studying the modes of decomposition of biomass materials.

Implications of the large surface area to body mass ratio on the heat balance of the greater glider (Petauroides volans: Marsupialia)

1. In a study of thermoregulation in the greater glider, a small arboreal marsupial with large gliding membranes, metabolic rate (MR), skin and deep body temperature (Tsk,Tb), and respiratory and total evaporative heat loss (Eex,Etot) were measured in relation to ambient temperature (Ta). 2. Although the surface area is twice that of marsupials of similar body weight, MR was not significantly different from the average marsupial metabolic rate. This must be attributed to an excellent thermal insulation and behavioural factors. 3. AtTa above the thermoneutral point, at 20°C, the greater glider became hyperthermic.Tb increased from 35.4°C at 20°CTa to 39.1°C at 40°C. At 30°C, 55% of MR was dissipated by evaporation. This proportion increased to 105% at 35°C and 132% of MR at 40°C. The increase inEtot was accompanied by intense licking of extremities and the ventral body surface.Eex dissipated only 12% of MR at 40°C irrespective of an 8-fold increase in respiratory frequency from a basal value of 18 breaths·min−1. 4. It is concluded that the greater glider can utilize its gliding membranes to reduce heat losses by increasing the insulative layer around the body surface. At highTa, a clear contrast between the inefficient use of water for evaporative thermolytic processes, mainly salivation, and the limited availability of water in its arboreal habitat becomes evident.

Use of the kinetic isotope effect as a test for homogeneous unimolecular gas phase reactions in thermolytic processes

Experiments are described employing the kinetic isotope effect to discriminate between homogeneous and heterogeneous surface catalyzed reactions. Advantage is taken of the differences in isotope effect expected between the nonequilibrium statistical weight isotope effect (NESWIE) observed at low pressures and the conventional isotope effect observed at higher pressures for molecules containing up to approximately 15 atoms. No change in isotope effect as a function of pressure is expected for surface-catalyzed processes. The k/sub H//k/sub D/ ratio for the thermal decomposition of diketene to ketene in a flow system is reported. At low pressures a value of k/sub H//k/sub D/ of 0.91 was obtained while at pressures of 140 mm, k/sub H//k/sub D/ was found to be 1.04 at 420/sup 0/C.

The Application of Thermolytic Reactions for the Syntheses of Fluoro-Organic Compounds

Methods for synthesising fluoro-organic compounds with the aid of thermolytic processes are discussed. High-temperature transformations of fluorinated saturated and unsaturated compounds, as well as of aromatic and heterocyclic compounds are considered. 1. Thermolysis of Saturated Compounds 1.1. Alkanes 1.2. Cycloalkanes 1.3. Fluorinated Polymers 2. Thermolysis of Unsaturated Compounds 2.1. Alkenes and Alkynes 2.2. Cycloalkenes 2.3. Thermolysis of Unsaturated Compounds in the Presence of Difluorocarbene Sources 3. Thermolysis of Aromatic and Heterocyclic Compounds 3.1. Aromatic and Heterocyclic Compounds 3.2. Reactions with Polytetrafluoroethene and Potassium Fluoride 3.3. Reactions with Fluoroalkenes 3.3.1. Hexafluorobenzene (F-Benzene) 3.3.2. Reactions of Compounds with Functional Groups 3.4. Reactions with Sources of Radicals 4. Other Reactions 4.1. Pyrolysis of Carboxylic Acids and their Derivatives 4.2. Miscellaneous Reactions