Differential scanning calorimetry (DSC) is a useful tool for studying the nucleation rate-limited kinetics of crystallization from the melt. However, applying popular isoconversional methods of thermal analysis to such calorimetric data often yields incorrect values of the activation energy, Ea. Against this backdrop, we investigate the classical dataset for the temperature-dependent rate of crystallization of piperine from the melt [Tammann G. Ueber die Abhangigkeit der Zahl der Kerne, welche sich in verschiedenen unterk & uuml;hlten Fl & uuml;ssigkeiten bilden, von der Temperatur. Z. Phys. Chem. 1898;25: 441-479] to demonstrate that the Turnbull-Fisher (T-F) equation describing nucleation kinetics generates meaningful Ea values, across the entire temperature range, only when it is decoupled from isoconversional or Arrhenius analysis. This is accomplished by digitizing, replotting, and subsequently analyzing the Tammann dataset through application of the T-F equation, alone, the T-F equation used in conjunction with isoconversional analysis, and, lastly, the T-F equation combined with the Arrhenius equation. While the latter two methodologies are discussed thoroughly in a recent work [Vyazovkin S, Sbirrazzuoli N. Non-isothermal crystallization kinetics by DSC: Practical overview. Processes. 2023;11:1438], our goal is to reveal that the fundamental problem with those approaches that results in reporting of negative activation energies is that they are reliant on the assumption of Arrhenius kinetics. That is because T-F kinetics can exhibit both Arrhenius (at large supercooling from the melt) and non-Arrhenius (at moderate supercooling) behavior, depending on the temperature. Consistent with the predictions of classical nucleation theory (CNT), Ea values for nucleation rate-limited conversions are generally positive even though the specific rate often increases at higher degrees of cooling. Reports of negative activation energies are simply a mathematical artifact caused by ignoring the mismatch between Arrhenius and T-F kinetics.

Kinetics of condensed-phase processes are routinely studied by methods based on the general rate equation. It is demonstrated here that, for the kinetic analysis, two degrees of conversion should be employed: (i) the degree of conversion used in classical kinetics, alpha kin , conventionally defined as the reacted amount of a reactant normalized to its initial amount; (ii) the thermoanalytical degree of conversion, alpha, defined as the thermoanalytical effect observed at temperature T (or at time t for isothermal measurements) divided by the total thermoanalytical effect. For elementary reactions, alpha kin = alpha so that the general rate equation is a true rate equation describing the mechanism of the reaction. For complex processes, alpha kinand alpha differ considerably in general; they are equivalent for some special cases only. In this case, the general rate equation represents the single-step approximation. The values of alpha thus describe the kinetics of heat exchange (for DSC) or mass loss (for TG) and so do the kinetic parameters obtained from the treatment of experimental data. Even though no mechanistic conclusions should be drawn from such kinetic parameters, they still enable us to model the kinetics of complex processes from the point of view of the quantity measured.

Differential scanning calorimetry (DSC) is a useful tool for studying nucleation rate-limited kinetics of crystallization from the melt. However, applying popular isoconversional methods of thermal analysis to such calorimetric data yields incorrect values of the effective activation energy, E_a. Investigating the classical dataset for the temperature-dependent rate of crystallization of piperine from the melt [Tammann, G. Ueber die Abhängigkeit der Zahl der Kerne, welche sich in verschiedenen unterkühlten Flüssigkeiten bilden, von der Temperatur. Z. Phys. Chem. 1898, 25, 441-479], we demonstrate that the Turnbull-Fisher (T-F) equation generates meaningful E_a values, across a broad temperature range, only when it is decoupled from isoconversional analysis. The problem with isoconversional methods is that they are reliant on Arrhenius kinetics, whereas T-F kinetics can exhibit either Arrhenius or non-Arrhenius behavior, depending on the temperature. Consistent with classical nucleation theory (CNT), E_a values for nucleation rate-limited conversions are positive even though the rate typically increases at higher degrees of cooling.

Mathematical correctness and applicability of the methods based on the general rate equation (GRE) are analyzed from the viewpoint of the new concept of understanding GRE as a formal mathematical tool. It is taken into account that, in kinetic analysis, it is necessary to discriminate between the kinetic and thermoanalytical degrees of conversion. In principle, all the methods based on GRE describe the kinetics of the change of thermoanalytical effects, i.e., the heat consumption/evolution for DSC or mass decrease for TG. For elementary processes, the kinetic and thermoanalytical degrees of conversion coincide so that conclusions on kinetics can be drawn from the thermoanalytical data. For complex processes, the kinetic and thermoanalytical degrees of conversion may differ considerably and they coincide only for special cases. Hence, for complex processes, the thermoanalytical kinetic data describe rather the change of the thermoanalytical effects than the mechanism of the process under study. No mechanistic conclusions should be drawn from the values of individual kinetic parameters, particularly from the values of activation energy.

Calcium lignosulfonate (CaL) as biopolymer filler was incorporated into rubber matrices based on acrylonitrile-butadiene rubber (NBR) and styrene-butadiene rubber (SBR) in concentration scale ranging from 10 to 60 phr. The work was aimed at investigation of CaL content on crosslink density and mechanical properties of the composites. Subsequently, the composites were kept in hot air chamber for 7 days at 70 °C and 100 °C and the influence of thermooxidative ageing on the change of cross-link density and mechanical properties was investigated. Kinetics of thermal oxidation was studied by non-isothermal differential scanning calorimetry. The achieved results showed that the changes in modulus and elongation at break were in close connection with the changes in crosslink density before ageing as well as after ageing. When compared to the SBR based reference, the crosslink density of the composite with maximum CaL content decreased by about 62

Delayed ettringite formation (DEF) is a deleterious reaction which can result in expansion and cracking of concrete. The reaction occurs in the cement paste and is associated with the recrystallisation of the ettringite at a later age after hardening of the concrete. As ettringite is an expansive phase and as recrystallisation occurs in the hardened state, its formation may lead to cracking of the concrete. Laboratory tests of DEF induced expansion use specific conditions to initiate expansion which include elevating the alkali and sulphate contents (1

Conventional toxicological methods and integrated transcriptomic analysis were used to comprehensively assess the potential health hazard of residual metal nanoparticles accumulated in the body due to poor solubility.

Here we suggest that integral isoconversional method, when applied in a mathematically correct way, can lead to satisfactory results with the least number of adjustable parameters. Differential and incremental methods are used in cases when the apparent activation energy, E, varies with degree of conversion, α. However, in some cases the observed E(α) dependence can spuriously be induced by small variations in α(T) curves and there is only little to no benefit gained from allowing arbitrary change of E between adjacent conversion levels. As a result, the E(α) dependences are highly “fragile” and subject to minor variations in the experimental data. On the other hand, when the activation energy is optimized globally for all isoconversional levels, a significantly more robust estimate is obtained and the agreement between the experimental and simulated data is still plausible. The approach is demonstrated on two datasets which were evaluated with both variable E(α) dependence and with constant value of E.

During ICTAC2020, a workshop was held on “Good laboratory practice in thermal analysis and calorimetry” for young researchers and beginners under the aegis of the Education Committee of ICTAC. Thermal analysis (TA) covers relationship between large number of sample properties and the temperature. Naturally, there is some technique for each property of the sample bringing versatility in TA. This review is devoted to the Workshop and has been refined for the benefit of the readers so that it helps them in obtaining useful qualitative and quantitative information about the effects of heat treatments on materials of all kinds. Recent trends in DSC, TG-FTIR, TG-MS, DMA, kinetics and nanocalorimetry have also been covered in this article.

It is demonstrated here that the concept of variable activation energy is mathematically not fully correct. Further it is shown that general rate equation is a formal mathematical tool for the description of thermoanalytical kinetic data. The temperature function, k ( T ), is not the rate constant in general and the conversion function, f ( α ), may not reflect the mechanism in case of complex processes. Both, k ( T ) and f (α), are functions enabling to describe the kinetic hypersurface. For the complex processes, the physical meaning of parameters occurring in both functions is unclear. Hence, no mechanistic conclusions should be drawn from the values of an individual kinetic parameter; particularly, just from the values of activation energy. The conclusions can be drawn from the quantities with a clear physical meaning such as the values of isoconversional times, isoconversional temperatures, conversion, reaction rate, etc., i.e., the quantities that can be accessible experimentally. These quantities can be recovered and modeled from known kinetic parameters. It is proved here that the right temperature function may not be necessarily the Arrhenius equation for a complex process.

In this work, a novel procedure for fast assessment of the material residual stability is proposed. The method resides in integral isoconversional kinetic analysis of the thermal oxidation of unaged material employing the Berthelot–Hood temperature function. Subsequently, the obtained conversion-independent kinetic parameter D is also employed for samples aged in various regimes. The value of conversion-dependent parameter A for aged samples is calculated from the oxidation onset temperature measured at 5 °C min−1. The residual stabilities are then calculated as a simple ratio of the parameter A of aged material to that of the unaged one. The method has been applied and verified for the samples of low-density polyethylene aged by thermal, radiation and combined ageing. The method can also be employed for high-throughput screening of the effect of various stabilizers and antioxidants in a given organic matrix.

Data suitable for assembling a physiologically-based pharmacokinetic (PBPK) model for nanoparticles (NPs) remain relatively scarce. Therefore, there is a trend in extrapolating the results of in vitro and in silico studies to in vivo nanoparticle hazard and risk assessment. To evaluate the reliability of such approach, a pharmacokinetic study was performed using the same polyethylene glycol-coated gold nanoparticles (PEG-AuNPs) in vitro and in vivo. As in vitro models, human cell lines TH1, A549, Hep G2, and 16HBE were employed. The in vivo PEG-AuNP biodistribution was assessed in rats. The internalization and exclusion of PEG-AuNPs in vitro were modeled as first-order rate processes with the partition coefficient describing the equilibrium distribution. The pharmacokinetic parameters were obtained by fitting the model to the in vitro data and subsequently used for PBPK simulation in vivo. Notable differences were observed in the internalized amount of Au in individual cell lines compared to the corresponding tissues in vivo, with the highest found for renal TH1 cells and kidneys. The main reason for these discrepancies is the absence of natural barriers in the in vitro conditions. Therefore, caution should be exercised when extrapolating in vitro data to predict the in vivo NP burden and response to exposure.

In the manuscripts dealing with thermoanalytical kinetics, many flaws, mistakes, and misconceptions are encountered repeatedly. In this paper, frequent flaws encountered in manuscript of kinetic papers are reviewed, mainly those originating in the false interpretation of the general rate equation, improper employment of integral isoconversional methods, conclusions drawn from the values of a single kinetic parameter, absence of error estimation and application of single-heating rate methods. Assessment of the quality of kinetic treatment is also noticed. Some experimental imperfections that could lead to incorrect values of kinetic parameters are mentioned.

The rate constants for (L)-N-acetyl homocysteine thiolactone enantiomerization have been obtained from batch-wise studies and by dynamic gas chromatography of racemic mixtures. Results from the batch-wise experiments show that the kinetics of racemization at 150 degrees C is the same for vials made of glass, silanized glass or Teflon-coated glass so that the vial surface exhibited no effect on the kinetics of racemization. From the temperature dependence of the rate constants the preexponential factor, activation energy, the activation Gibbs energy and activation entropy have been obtained from transition state theory. The catalytic effect of G-DP, G-BP and B-DP GC chiral stationary phases on racemization has been observed and quantified by the values of rate constants; B-DP exhibited the greatest activity. The Eyring activation parameters obtained from batch-wise experiment were compared with theoretical values acquired from quantum chemical modelling. Agreement between the experimental and calculated values of activation Gibbs energy, activation enthalpy and activation entropy is good. The dynamic gas chromatography of racemic mixture on chiral B-DP, G-DP and G-BP capillary columns indicate that the rate constants of forward and reverse reactions are different in chiral environments. The greatest accelerating effect in the process of enantiomerization has been identified for G-BP both in the batch-wise experiments and by the dynamic gas chromatography. (C) 2021 Published by Elsevier B. V.

Plastic ingestion by various organisms within different trophic levels, including humans, is becoming a serious problem worldwide. Plastic waste samples are often found concentrated in an organism’s digestive tract and can be degraded and further translocate to the surrounding tissue or circulatory systems and accumulate in food chains. In the present work, we report a detailed chemical analysis and degradation state evaluation of a relatively large piece of plastic waste found in the gastrointestinal tract of a Wels catfish (Silurus glanis L.) caught in the Bodrog River (Danube River basin), eastern Slovakia. Chemical analysis by surface-sensitive X-ray photoelectron spectroscopy (XPS) was performed to identify the surface composition of the digested plastic piece. Micro-Fourier transform infrared (μFTIR) spectroscopy showed that the plastic waste was oxidized low-density polyethylene (LDPE), with some nylon fibers adhered on the surface. Glyceraldehyde adhered onto LDPE was also detected, which might come from the carbohydrate metabolism of that fish. A morphology study by digital optical microscopy indicated solid inorganic particles attached to the surface of LDPE. A degradation study by differential scanning calorimetry (DSC) showed considerable oxidation of LDPE, leading to fragmentation and disintegration of the plastic waste material.

Despite the obvious advantages of gold nanoparticles for biomedical applications, controversial and incomplete toxicological data hamper their widespread use. Here, we present the results from an in vivo toxicity study using gold nanoparticles coated with polyethylene glycol (PEG-AuNPs). The pharmacokinetics and biodistribution of PEG-AuNPs were examined in the rat’s liver, lung, spleen, and kidney after a single i.v. injection (0.7 mg/kg) at different time intervals. PEG-AuNPs had a relatively long blood circulation time and accumulated primarily in the liver and spleen, where they remained for up to 28 days after administration. Increased cytoplasmic vacuolation in hepatocytes 24 h and 7 days after PEG-AuNPs exposure and apoptotic-like cells in white splenic pulp 24 h after administration has been detected, however, 28 days post-exposure were no longer observed. In contrast, at this time point, we identified significant changes in lipid metabolism, altered levels of liver injury markers, and elevated monocyte count, but without marked biological relevance. In blood cells, no DNA damage was present in any of the studied time intervals, with the exception of DNA breakage transiently detected in primary kidney cells 4 h post-injection. Our results indicate that the tissue accumulation of PEG-AuNPs might result in late toxic effects.

Microfluidic technology is a valuable tool for realizing more in vitro models capturing cellular and organ level responses for rapid and animal-free risk assessment of new chemicals and drugs. Microfluidic cell-based devices allow high-throughput screening and flexible automation while lowering costs and reagent consumption due to their miniaturization. There is a growing need for faster and animal-free approaches for drug development and safety assessment of chemicals (Registration, Evaluation, Authorisation and Restriction of Chemical Substances, REACH). The work presented describes a microfluidic platform for in vivo-like in vitro cell cultivation. It is equipped with a wafer-based silicon chip including integrated electrodes and a microcavity. A proof-of-concept using different relevant cell models shows its suitability for label-free assessment of cytotoxic effects. A miniaturized microscope within each module monitors cell morphology and proliferation. Electrodes integrated in the microfluidic channels allow the noninvasive monitoring of barrier integrity followed by a label-free assessment of cytotoxic effects. Each microfluidic cell cultivation module can be operated individually or be interconnected in a flexible way. The interconnection of the different modules aims at simulation of the whole-body exposure and response and can contribute to the replacement of animal testing in risk assessment studies in compliance with the 3Rs to replace, reduce, and refine animal experiments.

at the age of 80.This was after a long scientific career of nearly 50 years in the field of thermal analysis where he became one of its pioneers.