Thermodynamic Study on Biomimetic Legionella gormanii Bacterial Membranes.

The presented studies were aimed at determining the interactions in model membranes (Langmuir monolayers) created of phospholipids (PL) isolated from Legionella gormanii bacteria cultured with (PL + choline) or without (PL - choline) choline and to describe the impact of an antimicrobial peptide, human cathelicidin LL-37, on PL's monolayer behavior. The addition of choline to the growth medium influenced the mutual proportions of phospholipids extracted from L. gormanii. Four classes of phospholipids-phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylglycerol (PG), cardiolipin (CL), and their mixtures-were used to register compression isotherms with or without the LL-37 peptide in the subphase. Based on them the excess area (Ae), excess (ΔGe), and total (ΔGm) Gibbs energy of mixing were determined. The thermodynamic analyses revealed that the PL - choline monolayer showed greater repulsive forces between molecules in comparison to the ideal system, while the PL + choline monolayer was characterized by greater attraction. The LL-37 peptide affected the strength of interactions between phospholipids' molecules and reduced the monolayers stability. Accordingly, the changes in interactions in the model membranes allowed us to determine the difference in their susceptibility to the LL-37 peptide depending on the choline supplementation of bacterial culture.

The Acid Roles of PtSn@Al2O3 in the Synthesis and Performance of Propane Dehydrogenation.

In this study, a PtSn/Al2O3 catalyst with bimetallic uniform distribution in the sphere was synthesized. The PDH performance and characterization analyses, such as with FTIR, XPS, and NH3-TPD, were investigated. The effects of acid on the PDH performance were analyzed. Citric acid (CA) acted as a competing adsorbent in the preparation process of the PtSn/Al2O3 catalyst to synthesize the uniform catalyst. Water washing and alkali-treated samples were also studied. SEM line scanning revealed that increased the apparent concentration of Pt metal from 0.23 to 0.30 with citric acid. In contrast to the fresh PtSn/Al2O3 catalyst, the addition of citric acid increased the PDH selectivity from 74% to 93%. After alkali or water washing treatments, the catalyst's selectivity further increased to 96%. Strong acid sites promoted the breaking of C-C bonds during the PDH reaction, resulting in more methane and ethylene byproducts, and decreased catalyst selectivity for fresh PtSn/Al2O3. From the PDH reaction thermodynamic analysis, a relatively sub-atmospheric pressure environment with a lower propane pressure could be the reasonable choice.

Comparing the influence of explicit and implicit solvation models on site-specific thermodynamic stability of proteins.

Understanding the molecular basis for protein stability requires a thermodynamic analysis of protein folding. Thermodynamic analysis is often performed by sampling many atomistic conformations using molecular simulations that employ either explicit or implicit water models. However, it remains unclear to what extent thermodynamic results from different solvation models are reliable at the molecular level. In this study, we quantify the influence of both solvation models on folding stability at the individual backbone and side chain resolutions. We assess the residue-specific folding free energy components of a ß-sheet protein and a helical protein using trajectories resulting from TIP3P explicit and generalized Born/surface area implicit solvent simulations of model proteins. We found that the thermodynamic discrepancy due to the implicit solvent mostly originates from charged side chains, followed by the under-stabilized hydrophobic ones. In contrast, the contributions of backbone residue in both proteins were comparable for explicit and implicit water models. Our study lays out the foundation for detailed thermodynamic assessment of solvation models in the context of protein simulation.

Definition of an Index Parameter To Screen Highly Functional Enzymes Derived from a Biochemical and Thermodynamic Analysis of Ancestral meso-Diaminopimelate Dehydrogenases.

Sequence-based protein design approaches are being adopted to generate highly functional enzymes; however, screening the enzymes remains a time-consuming task. In this study, by analyzing the enzymatic properties of four ancestral meso-2,6-diaminopimelate dehydrogenases (AncDAPDHs), AncDAPDH-N1, -N2, -N3, and -N4, we attempted to define a new index parameter that is helpful for efficiently screening the enzymes. Biochemical and thermodynamic analyses indicated that only AncDAPDH-N4 exhibited greater thermal stability than and activity similar to those of native DAPDHs. Structural and sequence comparisons between DAPDH from Corynebacterium glutamicum (CgDAPDH) and the AncDAPDHs suggested that "quality of mutations" is a potential index parameter. In fact, the mutations introduced from CgDAPDH to AncDAPDH-N4 correlated highly with the mutations accumulated during the evolution process from mesophiles to thermophiles. These results suggest that, although there are several exceptions, the correlation coefficient can be used as an index parameter for screening high-functioning enzymes from sequence data.

Spectroscopy of Laser-Induced Dielectric Breakdown Plasma in Mixtures of Air with Inert Gases Ar, He, Kr, and Xe.

The generation of ozone and nitrogen oxides by laser-induced dielectric breakdown (LIDB) in mixtures of air with noble gases Ar, He, Kr, and Xe is investigated using OES and IR spectroscopy, mass spectrometry, and absorption spectrophotometry. It is shown that the formation of NO and NO2 noticeably depends on the type of inert gas; the more complex electronic configuration and the lower ionization potential of the inert gas led to increased production of NO and NO2. The formation of ozone occurs mainly due to the photolytic reaction outside the gas discharge zone. Equilibrium thermodynamic analysis showed that the formation of NO in mixtures of air with inert gases does not depend on the choice of an inert gas, while the equilibrium concentration of the NO+ ion decreases with increasing complexity of the electronic configuration of an inert gas.

Using greenhouse gases in the synthesis gas production processes: Thermodynamic conditions.

The work concerns the thermodynamic analysis of CH4 reforming with various oxidants (CO2, H2O, O2) in the technological variants DRM (Dry Reforming of Methane) and TRM (Tri-reforming of Methane) technological variants. Both processes of synthesis gas production (raw material for the production of value-added products) are problematic in terms of environmental protection. In the process, two components of greenhouse gases are used as a substrate: CO2 and CH4. The influence of temperature, pressure, and the molar ratio of oxidants to methane on the efficiency of both processes was analyzed using the deterministic method: raw material conversion, product efficiency and selectivity - H2 and CO, and the value of the H2/CO ratio characterizing the suitability of the synthesis gas for various syntheses. The problem of carbon deposition tendency in DRM was minimized through the selection of operational process conditions, and in the case of TRM, it was fully reduced. The deterministic method of non-linear programming by defining the objective function with constraints helped formulate allowed one the values of TRM parameters: complete reduction of the coking problem, maintaining the H2/CO ratio at the desired level - 2 and CO2 conversion equal to 90%, led to a hydrogen efficiency of over 90%. This efficiency can be obtained at the process temperature T = 273 K, with a pressure of 1 atm, and the molar ratios of oxidants to methane: CH4/CO2/H2O/O2 = 1/0.36/0.77/0.01.

Solubility and Thermodynamic Analysis of Isotretinoin in Different (DMSO + Water) Mixtures.

The solubility and solution thermodynamics of isotretinoin (ITN) (3) in numerous {dimethyl sulfoxide (DMSO) (1) + water (H2O) (2)} combinations were studied at 298.2-318.2 K under fixed atmospheric pressure of 101.1 kPa. A shake flask methodology was used to determine ITN solubility, and correlations were made using the "van't Hoff, Apelblat, Buchowski-Ksiazczak λh, Yalkowsky-Roseman, Jouyban-Acree, and Jouyban-Acree-van't Hoff models". In mixtures of {(DMSO (1) + H2O (2)}, the solubility of ITN in mole fractions was enhanced with the temperature and DMSO mass fraction. The mole fraction solubility of ITN was highest in neat DMSO (1.02 × 10-1 at 318.2 K) and lowest in pure H2O (3.14 × 10-7 at 298.2 K). The output of computational models revealed good relationships between the solubility data from the experiments. The dissolution of ITN was "endothermic and entropy-driven" in all of the {(DMSO (1) + H2O (2)} mixtures examined, according to the positive values of measured thermodynamic parameters. Enthalpy was discovered to be the driving force behind ITN solvation in {(DMSO (1) + H2O (2)} combinations. ITN-DMSO displayed the highest molecular interactions when compared to ITN-H2O. The outcomes of this study suggest that DMSO has a great potential for solubilizing ITN in H2O.

In crystallo thermodynamic analysis of conformational change of the topaquinone cofactor in bacterial copper amine oxidase.

In the catalytic reaction of copper amine oxidase, the protein-derived redox cofactor topaquinone (TPQ) is reduced by an amine substrate to an aminoresorcinol form (TPQamr), which is in equilibrium with a semiquinone radical (TPQsq). The transition from TPQamr to TPQsq is an endothermic process, accompanied by a significant conformational change of the cofactor. We employed the humid air and glue-coating (HAG) method to capture the equilibrium mixture of TPQamr and TPQsq in noncryocooled crystals of the enzyme from Arthrobacter globiformis and found that the equilibrium shifts more toward TPQsq in crystals than in solution. Thermodynamic analyses of the temperature-dependent equilibrium also revealed that the transition to TPQsq is entropy-driven both in crystals and in solution, giving the thermodynamic parameters that led to experimental determination of the crystal packing effect. Furthermore, we demonstrate that the binding of product aldehyde to the hydrophobic pocket in the active site produces various equilibrium states among two forms of the product Schiff-base, TPQamr, and TPQsq, in a pH-dependent manner. The temperature-controlled HAG method provides a technique for thermodynamic analysis of conformational changes occurring in protein crystals that are hardly scrutinized by conventional cryogenic X-ray crystallography.

Structural Characterization of Cis- and Trans-Pt(NH3)2Cl2 Conjugations with Chitosan Nanoparticles.

The conjugation of chitosan 15 and 100 KD with anticancer drugs cis- and trans-Pt (NH3)2Cl2 (abbreviated cis-Pt and trans-Pt) were studied at pH 5-6. Using multiple spectroscopic methods and thermodynamic analysis to characterize the nature of drug-chitosan interactions and the potential application of chitosan nanoparticles in drug delivery. Analysis showed that both hydrophobic and hydrophilic contacts are involved in drug-polymer interactions, while chitosan size and charge play a major role in the stability of drug-polymer complexes. The overall binding constants are Kch-15-cis-Pt = 1.44 (±0.6) × 105 M-1, Kch-100-cis-Pt = 1.89 (±0.9) × 105 M-1 and Kch-15-trans-Pt = 9.84 (±0.5) × 104 M-1, and Kch-100-trans-Pt = 1.15 (±0.6) × 105 M-1. More stable complexes were formed with cis-Pt than with trans-Pt-chitosan adducts, while stronger binding was observed for chitosan 100 in comparison to chitosan 15 KD. This study indicates that polymer chitosan 100 is a stronger drug carrier than chitosan 15 KD in vitro.

A thermodynamic understanding of the salt-induced B-to-Z transition of DNA containing BZ junctions.

Z-DNA has attracted interest due to its distinctive left-handed helical structure. This non-canonical DNA structure is able to form transiently and plays an important role in cellular processes such as transcriptional regulation and DNA recombination. Alternating purine-pyrimidine sequences are well known to form Z-DNA under high-salt conditions, but the detailed mechanism of B-to-Z transition of DNA containing BZ junctions under these conditions is not well understood. Here, using single-molecule FRET and circular dichroism experiments, we studied the effect of BZ junctions on Z-DNA formation under high-salt conditions. Further thermodynamic analysis revealed that a discrepancy of different DNA substrates in the presence and absence of BZ junctions in Z-DNA formation can be attributed mainly to the competition between enthalpy and entropy. Salt-induced B-to-Z transition is entropically favored in the presence of BZ junctions and is enthalpically favored in their absence. This thermodynamic information provides a deeper understanding of Z-DNA formation of DNA containing BZ junctions.

An exploration of the interaction mechanism of Direct Red 80 with α-Amylase at the molecular level.

The use and production of Direct Red 80 (DR80) dye are growing rapidly, and a large amount of dye wastewater is discharged into the soil without treatment. DR80 accumulated in soil or sludge can lead to enzyme poisoning, inhibit microbial activity, and affect the transformation of substances in the soil. In this research, the interaction mechanism between DR80 and α-Amylase (a typical enzyme in soil and sludge) was investigated by multi-spectra, molecular docking, thermodynamics analysis and enzyme activity experiment. The results of UV-visible and resonance light scattering (RLS) spectra showed that the skeleton of α-Amylase became loosened and unfolded under the exposure of Direct Red. The size of α-Amylase was smaller and α-Amylase became dispersed under high concentration of DR80. Molecular docking and thermodynamic analysis showed that DR80 bound to the surface of domain A rather than the active site of α-Amylase in the form of hydrogen bonds, and the binding process was an exothermic reaction. In addition, the inhibition of α-Amylase activity by DR80 was verified by enzyme activity experiment. These results indicate that DR80 has an effect on the structure and function of α-Amylase at molecular level, which means that the toxicity of DR80 should receive more attention.

Insight into the mechanism of thermostabilization of GH10 xylanase from Bacillus sp. strain TAR-1 by the mutation of S92 to E.

The mechanism of thermostabilization of GH10 xylanase, XynR, from Bacillus sp. strain TAR-1 by the mutation of S92 to E was investigated. Thermodynamic analysis revealed that thermostabilization was driven by the decrease in entropy change of activation for thermal inactivation. Crystallographic analysis suggested that this mutation suppressed the fluctuation of the amino acid residues at position 92-95.

Bovine ß-casein binding studies of a Schiff base ligand: fluorescence and circular dichroism approaches.

In this study, a Schiff base derived from a heterocyclic moiety was synthesized and characterized. The in vitro binding behaviour of this ligand with ß-casein (ß-CN) was investigated using biophysical techniques. For evaluation, thermodynamics variables of interactions between the Schiff base ligand and ß-CN, such as fluorescence at different temperatures, were measured. The results showed that the Schiff base ligand possessed considerable associated binding to ß-CN and that the procedure was enthalpy driven. The ß-CN conformation was also changed to give a further unfolded structure. Fluorescence resonance energy transfer was used to estimate the interval between donor (ß-CN) and acceptor (Schiff base ligand). All these experimental results proposed that ß-CN might act as carrier protein for the Schiff base ligand to deliver it to the target molecules.

Experimental Solubility of Ketoconazole, Validation Models, and In vivo Prediction in Human Based on GastroPlus.

The study aimed to identify a suitable cosolvent + water mixture for subcutaneous (sub-Q) delivery of ketoconazole (KETO). The solubility was assessed for several dimethyl acetamide (DMA) + water mixtures at T = 293.2 to 318.2 K and pressure P = 0.1 MPa. The experimental solubility (xe) was validated using the Van 't Hoff and Yalkowsky models and functional thermodynamic parameters (enthalpy ΔsolH°, entropy ΔsolS°, and Gibbs free energy ΔsolG°). The in vitro drug release study was performed at physiological pH, and the data served as the input to GastroPlus, which predicted the in vivo performance of KETO dissolved in a DMA + water cosolvent mixture for sub-Q delivery in human. The maximum solubility (mole fraction) of KETO (9.81 × 10-1) was obtained for neat DMA at 318.2 K whereas the lowest value (1.7 × 10-5) was for pure water at 293.2 K. An apparent thermodynamic analysis based on xe gave positive values for the functional parameters. KETO dissolution requires energy, as evidenced by the high positive values of ΔsolH° and ΔsolG°. Interestingly, ΔsolG° progressively decreased with increasing concentration of DMA in the DMA + water mixture, suggesting that the DMA-based molecular interaction improved the solubilization. Positive values of ΔsolG° and ΔsolS° for each DMA + water cosolvent mixture corroborated the endothermic and entropy-driven dissolution. GastroPlus predicted better absorption of KETO through sub-Q delivery than oral delivery. Hence, the DMA + water mixture may be a promising system for sub-Q delivery of KETO to control topical and systemic fungal infections.

Stirling Refrigerating Machine Modeling Using Schmidt and Finite Physical Dimensions Thermodynamic Models: A Comparison with Experiments.

The purpose of the study is to show that two simple models that take into account only the irreversibility due to temperature difference in the heat exchangers and imperfect regeneration are able to indicate refrigerating machine behavior. In the present paper, the finite physical dimensions thermodynamics (FPDT) method and 0-D modeling using the Schmidt model with imperfect regeneration were applied in the study of a ß type Stirling refrigeration machine.The 0-D modeling is improved by including the irreversibility caused by imperfect regeneration and the finite temperature difference between the gas and the heat exchangers wall. A flowchart of the Stirling refrigerator exergy balance is presented to show the internal and external irreversibilities. It is found that the irreversibility at the regenerator level is more important than that at the heat exchangers level. The energies exchanged by the working gas are expressed according to the practical parameters, necessary for the engineer during the entire project. The results of the two thermodynamic models are presented in comparison with the experimental results, which leads to validation of the proposed FPDT model for the functional and constructive parameters of the studied refrigerating machine.

Performances of Transcritical Power Cycles with CO2-Based Mixtures for the Waste Heat Recovery of ICE.

In the waste heat recovery of the internal combustion engine (ICE), the transcritical CO2 power cycle still faces the high operation pressure and difficulty in condensation. To overcome these challenges, CO2 is mixed with organic fluids to form zeotropic mixtures. Thus, in this work, five organic fluids, namely R290, R600a, R600, R601a, and R601, are mixed with CO2. Mixture performance in the waste heat recovery of ICE is evaluated, based on two transcritical power cycles, namely the recuperative cycle and split cycle. The results show that the split cycle always has better performance than the recuperative cycle. Under design conditions, CO2/R290(0.3/0.7) has the best performance in the split cycle. The corresponding net work and cycle efficiency are respectively 21.05 kW and 20.44%. Furthermore, effects of key parameters such as turbine inlet temperature, turbine inlet pressure, and split ratio on the cycle performance are studied. With the increase of turbine inlet temperature, the net works of the recuperative cycle and split cycle firstly increase and then decrease. There exist peak values of net work in both cycles. Meanwhile, the net work of the split cycle firstly increases and then decreases with the increase of the split ratio. Thereafter, with the target of maximizing net work, these key parameters are optimized at different mass fractions of CO2. The optimization results show that CO2/R600 obtains the highest net work of 27.43 kW at the CO2 mass fraction 0.9 in the split cycle.

Influences of Different Architectures on the Thermodynamic Performance and Network Structure of Aircraft Environmental Control System.

The environmental control system (ECS) is one of the most important systems in the aircraft used to regulate the pressure, temperature and humidity of the air in the cabin. This study investigates the influences of different architectures on the thermal performance and network structure of ECS. The refrigeration and pressurization performances of ECS with four different architectures are analyzed and compared by the endoreversible thermodynamic analysis method, and their external and internal responses have also been discussed. The results show that the connection modes of the heat exchanger have minor effects on the performance of ECSs, but the influence of the air cycle machine is obvious. This study attempts to abstract the ECS as a network structure based on the graph theory, and use entropy in information theory for quantitative evaluation. The results provide a theoretical basis for the design of ECS and facilitate engineers to make reliable decisions.

Thermodynamic Analysis and Optimization of a Novel Power-Water Cogeneration System for Waste Heat Recovery of Gas Turbine.

A power-water cogeneration system based on a supercritical carbon dioxide Brayton cycle (SCBC) and reverse osmosis (RO) unit is proposed and analyzed in this paper to recover the waste heat of a gas turbine. In order to improve the system performance, the power generated by SCBC is used to drive the RO unit and the waste heat of SCBC is used to preheat the feed seawater of the RO unit. In particular, a dual-stage cooler is employed to elevate the preheating temperature as much as possible. The proposed system is simulated and discussed based on the detailed thermodynamic models. According to the results of parametric analysis, the exergy efficiency of SCBC first increases and then decreases as the turbine inlet temperature and split ratio increase. The performance of the RO unit is improved as the preheating temperature rises. Finally, an optimal exergy efficiency of 52.88% can be achieved according to the single-objective optimization results.

Beta Type Stirling Engine. Schmidt and Finite Physical Dimensions Thermodynamics Methods Faced to Experiments.

The paper presents experimental tests and theoretical studies of a Stirling engine cycle applied to a ß-type machine. The finite physical dimension thermodynamics (FPDT) method and 0D modeling by the imperfectly regenerated Schmidt model are used to develop analytical models for the Stirling engine cycle. The purpose of this study is to show that two simple models that take into account only the irreversibility due to temperature difference in the heat exchangers and imperfect regeneration are able to indicate engine behavior. The share of energy loss for each is determined using these two models as well as the experimental results of a particular engine. The energies exchanged by the working gas are expressed according to the practical parameters, which are necessary for the engineer during the entire project, namely the maximum pressure, the maximum volume, the compression ratio, the temperature of the heat sources, etc. The numerical model allows for evaluation of the energy processes according to the angle of the crankshaft (kinematic-thermodynamic coupling). The theoretical results are compared with the experimental research. The effect of the engine rotation speed on the power and efficiency of the actual operating machine is highlighted. The two methods show a similar variation in performance, although heat loss due to imperfect regeneration is evaluated differently.

Thermodynamic Evaluation and Sensitivity Analysis of a Novel Compressed Air Energy Storage System Incorporated with a Coal-Fired Power Plant.

A novel compressed air energy storage (CAES) system has been developed, which is innovatively integrated with a coal-fired power plant based on its feedwater heating system. In the hybrid design, the compression heat of the CAES system is transferred to the feedwater of the coal power plant, and the compressed air before the expanders is heated by the feedwater taken from the coal power plant. Furthermore, the exhaust air of the expanders is employed to warm partial feedwater of the coal power plant. Via the suggested integration, the thermal energy storage equipment for a regular CAES system can be eliminated and the performance of the CAES system can be improved. Based on a 350 MW supercritical coal power plant, the proposed concept was thermodynamically evaluated, and the results indicate that the round-trip efficiency and exergy efficiency of the new CAES system can reach 64.08% and 70.01%, respectively. Besides, a sensitivity analysis was conducted to examine the effects of ambient temperature, air storage pressure, expander inlet temperature, and coal power load on the performance of the CAES system. The above work proves that the novel design is efficient under various conditions, providing important insights into the development of CAES technology.