• Energy Research

Crystalline solids are integral to a broad range of natural science and engineering applications and their Gibbs free energy is an important parameter in modeling their thermodynamics. However, predicting for solids remains a difficult task and an under-explored field in high-throughput thermochemistry. In this work, we benchmark the performance of the newest generation of machine learning (ML) predictions, machine learning interatomic potentials (MLIPs), and density functional theory in predicting within the harmonic and quasi-harmonic approximations against experimental data from 100–2500 K and for up to 784 compounds. Furthermore, these calculations are fed to a reaction network (RN) from which experimentally informed predictions can be made. We find that predictions of made by MLIPs display promising performance but with the help of the RN, simpler methods show similar or better performance. Nonetheless, we show that much of the calculated and experimental data for still lack the accuracy and precision required for some thermodynamic modeling applications. Finally, we apply the RN to predict the room temperature Gibbs free energy of formation and find that it performs satisfactorily but that improvements need to be made before these predictions can be used as reliable indicators of thermodynamic stability in general applications.

BACKGROUND Lead is still a major environmental and occupational health hazard, since it is extensively used in the production of paints, gasoline and cosmetics. This causes the metal to be ubiquitous in the environment, being found in the air, soil, and water, from which it can enter the human body by inhalation or ingestion. Absorbed lead is capable of altering the calcium levels in bone. The aim of this study was to demonstrate the effect of lead on bone calcium levels by measuring the reaction constant, Gibbs free energy, and enthalpy. METHODS This study was of pure experimental design using 100 male albino rats (Rattus norvegicus). The experimental animals were assigned by simple randomization to two groups, one group receiving lead acetate orally at a dosage of 100 mg/ kgBW, while the other group did not receive lead acetate. The intervention was given for 4 weeks and the rats were observed weekly for measurement of bone calcium levels by the permanganometric method. RESULTS This study found that k1 (hydroxyapatite dissociation rate constant) was 0.90 x 10-3 dt-1, and that k2 (hydroxyapatite association rate constant) was 6.16 x 10-3 dt-1 for the control group, whereas for the intervention group k1 = 26.20 x 10-3 dt-1 and k2 = 16.75 x 10-3 dt-1. Thermodynamically, the overall reaction was endergonic and endothermic (ΔG > 0 and ΔH > 0). CONCLUSIONS Lead exposure results in increased dissociation rate of bone in comparison with its association rate. Overall, the reaction was endergonic and endothermic (ΔG > 0 and ΔH > 0).

The shift of incubation temperature in anoxic paddy soil from 30 to 15 degrees C resulted in a reversible decrease of the methane production rate and of the H2 steady state partial pressure. Only at 30 degrees C but not at 17 degrees C, total CH4 production rates were enhanced by the addition of H2, acetate, or cellulose compared to the control. Apparent activation energies which were calculated from the temperature dependence of CH4 production were higher in presence than in absence of excess H2. Decrease of temperature caused a decrease of the H2 turnover rate constant and of the Gibbs free energy of H2-dependent methanogenesis, and also resulted in a smaller contribution of H2 to total methanogenesis. However, H2-dependent methanogenesis was significantly stimulated by excess H2 and slightly inhibited by acetate at low as well as high temperature. The results show that H2-producing bacteria were limited by temperature to a greater extent than the methanogens so that the methanogenic microbial community in paddy soil was limited by the supply of H2. At lows as well as high temperatures, excess H2 apparently enabled part of the methanogenic community to shift from acetate-dependent to H2-dependent CH4 had only this effect, but with increasing temperature, excess H2 additionally stimulated total methanogenic activity and eventually even growth. (IFU)

Objetivou-se determinar as propriedades termodinâmicas de grãos de feijão danificados. Foram utilizados grãos com teor de água inicial de 53,85% (b.s.); parte dos grãos foi utilizada para se obter as isotermas de dessorção, enquanto que a outra foi submetida a secagem até o teor de água de 5,26% (b.s.), para que a mesma fosse submetida ao processo de adsorção. Para a indução da danificação foi utilizado um Stein Breakage Tester. Para obter o teor de água de equilíbrio, os grãos foram colocados em câmara climática cujas temperaturas foram de 20, 30, 40 e 50 ± 1 ºC combinadas com umidades relativas de 30, 40, 50, 70 e 90 ± 3%. Na dessorção, os grãos danificados apresentaram menor entalpia diferencial quando comparados com a testemunha enquanto o inverso foi observado na adsorção. A danificação mecânica provocou a formação de um número maior de sítios disponíveis de sorção, resultando em maiores valores de entropia diferencial na adsorção e menores valores na dessorção quando comparados com a testemunha. A danificação mecânica não teve efeito sobre a energia livre de Gibbs. This study aims to determine the thermodynamic properties of damaged beans. Grains with initial moisture content of 53.85% (d.b.) were used. A part of the grains was used to obtain the desorption isotherms, while another part was subjected to drying until a moisture content of 5.26% (d.b.) was achieved; therefore, it was subjected to the adsorption process. To induce damage, a Stein breakage tester was used. To obtain the equilibrium moisture content, grains were placed in a climatic chamber whose temperatures were 20, 30, 40, and 50 ± 1 °C combined with a relative humidity of 30, 40, 50, 70, and 90 ± 3%. Although in the desorption process, damaged grains had a lower differential enthalpy compared with the control, the reverse behavior was observed in the adsorption process. Mechanical damage caused the formation of a greater number of available adsorption sites, resulting in higher differential entropy values in adsorption and lower values in desorption compared with the control. The mechanical damage had no effect on the Gibbs free energy.

The nutritional and functional benefits offered by whey protein α-lactalbumin justify the great interest in its manufacture in large quantities at a high purity level. Hydroxyapatite is a calcium phosphate material able to adsorb proteins and can be synthesized at low production cost. Therefore, this work evaluated the adsorption of α-lactalbumin on hydroxyapatite using solid-liquid phase equilibrium data reported as adsorption isotherms. Van't Hoff's thermodynamics analysis showed that the adsorption process is entropically driven.

A value for the free energy of activation, or ï„G for the inversion of groups on the imino nitrogen of the title compounds was calculated from data obtained from variable temperature NMR. The coalescence temperature, Tc, is obtained as the temperature at which the non-equivalent methyl resonances of the title compounds collapse to a singlet. ï„G is calculated from ï„G =2.3RTc(10.32 + logTc/k) Eq.3 derived from the Eyring Equation. p-Methoxyphenylimino-2,2,4,4-tetramethyl 3-cyclobutanone (4) is found to possess an energy of activation equal to that of 18.55 kcal/mole with its temperature of coalescence at 118C. p-Nitrophenylimino-2,2,4,4-tetramethyl 3-cyclobutanone (5) is found to have an energy of activation for inversion to be 14.25 kcal/mole. The coalescence temperature found for the nitro derivative was found to be subsequently lower than that of the methoxy, 35C. The ï„G value of N-(2,2,4,4-tetramethyl-3 -cyclobutanone)-p-toluenesulfonamide (16) was found to have a value no greater than 16.42 kcal/mole with a corresponding Tc value of 76C. Whereas, the N-(3,3-Dichloro-2,2,4,4-tetramethyl-3-cyclobutanone)- toluenesulfonamide (17) yielded a value of 15.32 kcal/mole for the inversion energy. The Tc was found to be 56C. The data support the hypothesis that lone pair orbital interaction in the transition state affect the free energy of inversion of groups attached to the imino nitrogen.

June 1968. ; Sponsored by the National Science Foundation GA930.

Recent advances in genome editing and metabolic engineering enabled a precise construction of de novo biosynthesis pathways for high-value natural products. One important design decision to make for the engineering of heterologous biosynthesis systems is concerned with which foreign metabolic genes to introduce into a given host organism. Although this decision must be made based on multifaceted factors, a major one is the suitability of pathways for the endogenous metabolism of a host organism, in part because the efficacy of heterologous biosynthesis is affected by competing endogenous pathways. To address this point, we developed an open-access web server called MRE (metabolic route explorer) that systematically searches for promising heterologous pathways by considering competing endogenous reactions in a given host organism. MRE utilizes reaction Gibbs free energy information. However, 25% of the reactions do not have accurate estimations or cannot be estimated. To address this issue, we developed a method called FC (fingerprint contribution) to provide a more accurate and complete estimation of the reaction free energy. To rationally design a productive heterologous biosynthesis system, it is essential to consider the suitability of foreign reactions for the specific endogenous metabolic infrastructure of a host. For a given pair of starting and desired compounds in a given chassis organism, MRE ranks biosynthesis routes from the perspective of the integration of new reactions into the endogenous metabolic system. For each promising heterologous biosynthesis pathway, MRE suggests actual enzymes for foreign metabolic reactions and generates information on competing endogenous reactions for the consumption of metabolites. The URL of MRE is http://www.cbrc.kaust.edu.sa/mre/. Accurate and wide-ranging prediction of thermodynamic parameters for biochemical reactions can facilitate deeper insights into the workings and the design of metabolic systems. Here, we introduce a machine learning method, referred to as fingerprint contribution (FC), with chemical fingerprint-based features for the prediction of the Gibbs free energy of biochemical reactions. From a large pool of 2D fingerprint-based features, this method systematically selects a small number of relevant ones and uses them to construct a regularized linear model. FC is freely available for download at http://sfb.kaust.edu.sa/Pages/Software.aspx.