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This study explores the possibility of using Luffa Cylindrica Cords to remove Copper from aqueous effluents. The removal of copper was investigated in both batch and continuous processes. Batch mode adsorption studies were performed by varying parameters such as contact time, pH, initial copper concentration and temperature. The different adsorption models Langmuir, Freundlich, Elivoch and Temkin were used for the mathematical description of the adsorption equilibrium, and it was found that the very well - equipped experimental data for the Langmuir model (R2=0.961), the pseudo - first - order and pseudo - second - order kinetic models were applied to the experimental data. The experimental data fitted very well the pseudo-second-order kinetic model (R2= 0.965) and also followed the model of intra particle diffusion for concentrations between 5 and 50 mg/L), whereas diffusion is not the only rate - control step. Finally the thermodynamic parameters for the adsorption of copper onto cords were also determined. The negative sign of S° shows the decreased randomness at the solid - solution interface during adsorption, and the negative sign of H° indicates that the adsorption process is exothermic. The negative sign of G° confirms the spontaneous nature of the adsorption process, physical reaction. [ABSTRACT FROM AUTHOR]

Austenite formation was numerically investigated using Thermo-Calc/DICTRA in a deformed ferrite/pearlite microstructure to produce dual-phase steels. This work aims to better understand how the interface conditions (local equilibrium with negligible partitioning—LENP—or local equilibrium with partitioning—LEP) control the austenite growth kinetics during the intercritical annealing. Inspired by our experimental observations, two nucleation sites were considered. The austenite formed from pearlite islands showed a regime transition from LENP to LEP when the holding stage started. For the growth of austenite from isolated carbides, three stages were identified during the heating stage: first, slow growth under LEP; then, fast growth under LENP; and finally, after dissolution of the carbide, slow growth again. LENP and LEP interface conditions may coexist thanks to these regime transitions. In the case of competition, LEP conditions hinder austenite growth while it is promoted by LENP interface conditions. Such differences in growth kinetics explain, in part, the morphogenesis of dual-phase microstructures. [ABSTRACT FROM AUTHOR]

Several missions have reported complex alteration mineralogies on early Mars, which preserve environmental records of multiple water-rock-atmosphere interactions. The MSL and M2020 missions in Gale and Jezero have identified Fe and Mn-bearing secondary phases. These elements are used as tracers for the redox conditions on both Earth and Mars. However, to fully understand the short-lived and local-scale processes observed on Mars, it is necessary to go beyond thermodynamic models and experiments. Enhancing our ability to interpret the redox and hydrological conditions from the observed phase assemblage requires understanding the evolution of Fe and Mn during weathering. This study reports the results of kinetic alteration experiments and geochemical models conducted under Mars-like conditions. We tested variable pO 2 , pCO 2 , temperatures, and starting solutions. The results suggest that Fe is more mobile on Mars than on Earth, with a pseudo-equilibrium concentration that is kinetically controlled by dissolution and oxidation rates. Despite some initially modeled siderite precipitation, no siderite precipitation was observed in the altered powder. Solutions with higher acid concentrations were primarily controlled by dissolution kinetics, with both Fe and Mn being mobile, even when a minor amount of P, Fe, and S bearing secondary phases are formed. Based on our experimental results, we updated the model and conducted two large-scale sensitivity tests on our kinetic simulation. We confirmed that our experiments were too high in pO 2 for siderite to form; however, we found that over a range of clearly oxidizing conditions from an equilibrium standpoint, Fe and Mn are mostly mobile, and siderite precipitation can occur. We were able to determine the pO 2 , pCO 2 and the temporal space where Fe-oxide or siderite predominate or coexist, constraining the meaning of reducing or oxidizing conditions. Moreover, we also observed that siderite formation would require a much longer water residence time than Fe-oxide to precipitate, interpreted as higher weathering rates, or later evaporation required to effectively precipitate under any conditions. On ancient Mars, both Fe and Mn would be relatively mobile and prone to be leached from their host rock. Observing siderite or oxide would not primarily be a redox marker but would be a clue to a different hydrological regime. At the planetary scale, it would be challenging to form authigenic siderite during alteration. Although siderite would not indicate the presence of a particularly reducing atmosphere and that Mn-oxides are mainly pH controlled and do not require terrestrial-level amounts of oxygen, a collocated precipitation of siderite and Mn-oxides could also provide valuable information to constrain the redox environment of the ancient Mars. • Iron and Manganese are much more mobile on Mars than on Earth. • Concentrations are controlled by steady-state equilibrium between kinetic rates. • Siderite can form in oxidizing conditions compared to previous equilibrium models. • The pO2 and pCO2 window for the formation of siderite or Fe-oxide was determined. • Siderite precipitation is more of a clue of a change in hydrology than in redox. [ABSTRACT FROM AUTHOR]

[Display omitted] Photoswitchable surfactants are used in the design of many light-responsive colloids and/or self-assemblies. Photo-isomerization enables to control molecular equilibrium, and triggers transient reorganizations with possibly out-of-equilibrium intermediate states that have been overlooked. Here, we address this question by an in depth structural investigation of intermediate lipid-surfactant assemblies that occur during fast isothermal photo-triggered transition in lipid:surfactant mixtures. The structural parameters of mixed assemblies of azobenzene-containing cationic surfactant (AzoTMA) and dioleoylphosphatidylcholine (DOPC) lipids were studied by light scattering and time-resolved small angle X-ray scattering. Structural and compositional information about the assemblies and unimers in bulk were determined at the photostationary states, as well as at intermediate kinetic states formed during UV or blue light illumination. DOPC:AzoTMA systems form mixed assemblies representative of phospholipid:cationic surfactant mixtures, that evolve from spheroid, to rod-like micelles, and vesicles with increasing DOPC fraction. Transient assemblies detected during the photo-triggered kinetics are similar to the ones found in stationary states. But changes of AzoTMA unimers in bulk can be considerably faster than mass reorganizations of the mixed assemblies, suggesting that out-of-equilibrium conditions are transiently reached. Mass reorganization of the surfactant-enriched assemblies is much faster than in the lipid enriched ones, providing insight into the role of lipids in a slow reorganization of the assemblies. [ABSTRACT FROM AUTHOR]

The possible evolutionary significance of pyrophosphate (PPi) has been discussed since the early 1960s. Lipmann suggested that PPi could have been an ancient currency or a possible environmental source of metabolic energy at origins, while Kornberg proposed that PPi vectorializes metabolism because ubiquitous pyrophosphatases render PPi forming reactions kinetically irreversible. To test those ideas, we investigated the reactions that consume phosphoanhydride bonds among the 402 reactions of the universal biosynthetic core that generates amino acids, nucleotides, and cofactors from H2, CO2, and NH3. We find that 36% of the core's phosphoanhydride hydrolyzing reactions generate PPi, while no reactions use PPi as an energy currency. The polymerization reactions that generate ~80% of cell mass – protein, RNA, and DNA synthesis – all generate PPi, while none use PPi as an energy source. In typical prokaryotic cells, aminoacyl tRNA synthetases (AARS) underlie ~80% of PPi production. We show that the irreversibility of the AARS reaction is a kinetic, not a thermodynamic effect. The data indicate that PPi is not an ancient energy currency and probably never was. Instead, PPi hydrolysis is an ancient mechanism that imparts irreversibility, as Kornberg suggested, functioning like a ratchet's pawl to vectorialize the life process toward growth. The two anhydride bonds in nucleoside triphosphates offer ATP-cleaving enzymes an option to impart either thermodynamic control (Pi formation) or kinetic control (PPi formation) upon reactions. This dual capacity explains why nature chose the triphosphate moiety of ATP as biochemistry's universal energy currency. [ABSTRACT FROM AUTHOR]

The effects of solution‐state dielectric and intermolecular interactions on the degree of charge separation provide a route to understanding the switching properties and concentration dependence of donor–acceptor Stenhouse adducts (DASAs). Through solvatochromic analysis of the open‐form DASA in conjunction with X‐ray diffraction and computational theory, we have analyzed the ionic character of a series of DASAs. First‐ and third‐generation architectures lead to a higher zwitterionic resonance contribution of the open form and a zwitterionic closed form, whereas the second‐generation architecture possesses a less charge‐separated open form and neutral closed form. This can be correlated with equilibrium control and photoswitching solvent compatibility. As a result of the high contribution of the zwitterionic resonance forms of first‐ and third‐generation DASAs, we were able to control their switching kinetics by means of ion concentration, whereas second‐generation DASAs were less affected. Importantly, these results show how the previously reported concentration dependence of DASAs is not universal, and that DASAs with a more hybrid structure in the open form can achieve photoswitching at high concentrations. [ABSTRACT FROM AUTHOR]

Dynamics in complexes of porphyrin cage compounds and viologen‐derived guest molecules are investigated by selective exchange NMR spectroscopy (1D EXSY). Exchange rates were found to be independent of excess guest concentration, revealing a dissociative exchange mechanism, which is accompanied by negative activation entropies, indicating significant reorganization of the host–guest complex during dissociation. Nonsymmetric viologen guests with bulky head groups had more unidirectional binding and slower exchange rates than guests with less‐bulky head groups. Thermodynamic and kinetic studies revealed that the exchange process is primarily driven by the thermodynamics of binding and that guest binding can be influenced by introducing steric and electronic groups on the host. Exchange studies with guests bearing a polymer chain revealed that both slippage and full dissociation takes place and the rate constants for both processes were determined. The slippage rate constant revealed that for smaller guests exchange takes place nearly exclusively under thermodynamic control. [ABSTRACT FROM AUTHOR]

he mechanistic details of the aldol addition of N‐amino cyclic carbamate (ACC) hydrazones is provided herein from both an experimental and computational perspective. When the transformation is carried out at room temperature the anti‐aldol product is formed exclusively. Under these conditions the anti‐ and syn‐aldolate intermediates are in equilibrium and the transformation is under thermodynamic control. The anti‐aldolate that leads to the anti‐aldol product was calculated to be 3.7 kcal mol−1 lower in energy at room temperature than that leading to the syn‐aldol product, which sufficiently accounts for the exclusive formation of the anti‐aldol product. When the reaction is conducted at −78 °C it is under kinetic control and favors formation of the syn‐aldol addition product. In this case, it was found that a solvent separated aza‐enolate anion and aldehyde form a σ‐intermediate in which the lithium cation is coordinated to the aldehyde. The σ‐intermediate collapses with a very small activation barrier to form the β‐alkoxy hydrazone intermediate. The chiral nonracemic lithium aza‐enolate discriminates between the two diastereotopic faces of the pro‐chiral aldehyde, and there is no rapid direct pathway that interconverts the two diastereomeric intermediates. Consequently, the reaction does not follow the Curtin–Hammett principle and the stereochemical outcome at low temperature instead depends on the relative energies of the two σ‐intermediates. [ABSTRACT FROM AUTHOR]

Abstract As part of an ongoing program to constrain the factors affecting phase stability in nuclear waste containment glasses, the thermodynamic and kinetic factors influencing molybdenum oxide solubility in a borosilicate melt have been studied. A simplified system has been chosen to study how Mo oxide is transferred from solid effluent residues (calcines) to glass. The model calcines used are pure Na 2 MoO 4 and a more complex mixture of Na 2 MoO 4 and Al-bearing phases. These solid residues are mixed with a borosilicate glass frit and heat treated isothermally at temperatures in the range 700–1000 °C for times ranging from 2 min to 8 h. The mineralogy of the mixtures has been followed as a function of temperature and time using XRD and 27Al and 23Na MAS NMR spectroscopy, while the structure and composition of the amorphous phase have been studied by 11B MAS NMR and electron microprobe. The results obtained illustrate that while the dissolution of Al-rich calcines can modify the structure of the borosilicate network this does not affect either the MoO 3 content of the liquid at saturation, or the characteristic time-scale required to reach saturation. In detail, the variation of the Mo content of the liquid at saturation can be described by an Arrhenian temperature dependence with an activation energy of 30 ± 5 kJ/mol and the time-scale required to reach saturation, can be described by an exponential function of time. This time-scale also shows Arrhenian temperature dependence with an activation energy of 225 ± 25 kJ/mol, a value identical within uncertainty to that associated with viscous flow. Using the experimental results, a numerical model for dissolution along variable temperature-time paths has been developed. These models indicate that for systems that are capable of complete dissolution grain-size is one of the most important parameter controlling the efficiency of the dissolution process. [ABSTRACT FROM AUTHOR]

The founding principles of protein folding introduced by Christian Anfinsen, together with the numerous mechanistic investigations that followed, assume that protein folding is a thermodynamically controlled process. On the other hand, this review underscores the fact that thermodynamic control is far from being the norm in protein folding, as long as one considers an extended chemical-potential landscape encompassing aggregates, in addition to native, unfolded and intermediate states. Here, we highlight the key role of kinetic trapping of the protein native state relative to unfolded, intermediate and, most importantly, aggregated states. We propose that kinetic trapping serves an important role in biology by protecting the bioactive states of a large number of proteins from deleterious aggregation. In the event that undesired aggregates were somehow formed, specialized intracellular disaggregation machines have evolved to convert any aberrant populations back to the native state, thus restoring a fully bioactive and aggregation-protected protein cohort. [ABSTRACT FROM AUTHOR]

Dyes are ranked as an important class of pollutants which affect the aesthetic property of the environment when present even in very low concentrations. This study was carried out to explore the potential use of an agricultural waste (Marula seed husk) to decontaminate methylene blue (MB) from aqueous solution. The effect of change in water chemistry was also examined. The influence of basic adsorption parameters such as contact time, temperature, dosage, pH and particle size on the efficiency of adsorption were investigated. Langmuir and Freundlich isotherms were used to describe the equilibrium data while Pseudo first, second order and Elovich kinetic models were used to evaluate the kinetics of the adsorption process. Thermodynamic parameters such as change in enthalpy (ΔH°), entropy (ΔS°) and Gibbs free energy (ΔG°) were evaluated. Natural surface water showed higher MB removal efficiency than de-ionized water. The sorption process was favored more in alkaline pH range (7-10). The dye adsorption process was found to be endothermic, while ΔG° was negative implying that the reaction is spontaneous. Functional group analyses on the adsorbent showed the presence of hydroxyl, carbonyl and carboxyl groups. The Langmuir equilibrium model best described the adsorption process based on the linearized coefficient. The Pseudo second order model best described the kinetics of the reaction. [ABSTRACT FROM AUTHOR]

Present study deals with the synthesis of Zn/Al Layered double hydroxide (LDH) intercalated cellulose (CL) nanocomposite. The CL-Zn/Al LDH nanocomposite was characterized by XRD, FTIR, BET, TEM and AFM. XRD analysis showed the crystalline nature of LDH nanocomposite. TEM analysis confirmed the formation of a sheet like structure of LDH. The synthesized CL-Zn/Al LDH nanocomposite was found to have a capacity of rapid uptake of Y 3+ , La 3+ and Ce 3+ . Kinetic experiments revealed that equilibrium was achieved in 10 min for Y 3+ , La 3+ and Ce 3+ . The kinetic data was well predicted by pseudo second order with higher correlation coefficient (R 2 ) compared to pseudo first order. The adsorption capacities of Y 3+ , La 3+ and Ce 3+ was found to be 102.25, 92.51 and 96.25 mg/g, respectively, according to Langmuir model. Analysis of thermodynamic studies for Y 3+ , La 3+ and Ce 3+ showed that the process of adsorption is spontaneous and endothermic in nature. The CL-Zn/Al LDH nanocomposite revealed a good reusability up to five cycles. The CL-Zn/Al LDH showed good adsorption and selectivity for Y 3+ , La 3+ and Ce 3+ in the presence of other ions. Therefore, CL-Zn/Al LDH nanocomposite has a great potential to be used for the adsorption of Y 3+ , La 3+ and Ce 3+ . [ABSTRACT FROM AUTHOR]

Due to the difficulty in controlling thermodynamics and kinetics of the growth for branched bimetallic metal alloy nanocrystals in a solution system, understanding the growth mechanisms of this class of nanostructures is critical for their shape-controlled synthesis. Herein, we report an approach to control over shape of branched PtNi alloy nanocrystals by tuning the molar ratio of Pt to Ni in an oleyamine solution. The detailed analyses confirmed that the morphologies of PtNi alloy nanocrystals evolve from dendrites (less than 5 at% Ni) to multipods (5–10 at% Ni) to star shapes (10–20 at% Ni) and finally to polyhedrons (100 at% Ni) as the nickel content in PtNi alloy nanocrystals increase. During the morphology evolution, the growth mechanism changes from oriented attachment growth to a new mechanism combining oriented attachment and anisotropic overgrowth, then to kinetically controlled overgrowth and finally to thermodynamic control growth. More importantly, we find that the growth of branched PtNi alloy nanocrystals is always along the [220] direction, and the growth direction determines the number of branches in nanocrystals. Electrochemical results show that highly branched PtNi alloy nanocrystals exhibit significantly enhanced electrocatalytic activity and durability compared with commercial Pt catalysts. These in-depth findings will provide new hints to precisely control synthesis of highly branched PtNi nanocrystals. • The shape of branched PtNi alloy nanocrystals are tuned by adjusting atom ratio of Pt to Ni precursor. • The presence of nickel in the Pt4+-oleylamine system has a strong influence on Pt reduction kinetics. • The growth of the branched PtNi alloy nanocrystals is always along the (220) direction. • The branched PtNi alloy catalysts exhibit a high MOR activity compared to commercial Pt/C catalysts. [ABSTRACT FROM AUTHOR]

Removal of Ni(II) ions from aqueous solution was carried out using brassica oleracea botrylis leaves (cauliflower leaves) and was characterized by SEM, XRD and EDAX techniques. The effect of solution pH, contact time, initial metal ion concentration and temperature was investigated in a systematic manner. Various thermodynamic parameters such as ΔG°, ΔH° and ΔS° have also been evaluated and it has been found that the adsorption process was spontaneous, endothermic and randomness in nature. The equilibrium data were analyzed by using Langmuir, Freundlich, Temkin and D-R isotherm models. Among these isotherm models Freundlich model was fitted well with its good correlation coefficient. The experimental data were analyzed by kinetic parameters such as Lagergen pseudo-first order and pseudo-second order models and found that the biosorption of Ni(II) followed pseudo-second order model by its good correlation coefficient values which are very close to unity. Desorption and recovery of the adsorbent was found that 12%. The results concluded that the BOBL powder was an efficient, eco-friendly and economically cheap adsorbent in the removal of Ni(II) ions from the aqueous solution. [ABSTRACT FROM AUTHOR]

Polyaniline/silver nanocomposite (PANI/AgNPs) was synthesized by the chemical oxidative polymerization of aniline with ammonium peroxydisulphate in acidic medium of sulfuric acid (1 M). The surface of polyaniline is modified by silver nanoparticles. Samples were prepared at various molar ratios of silver nitrate to PANI ranging from 1 to 2.5. The emeraldine base was oxidized to pernigraniline, where the silver nitrate was reduced to metallic silver. The modified surface of PANI was confirmed by the scanning electron microscopy (SEM), Energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), FT-IR and thermogravemetric analysis (TGA). The efficiency of polyaniline/silver nanoparticles for the adsorptive removal of brilliant green (BG) from aqueous solutions, has been evaluated with respect to several experimental conditions. These conditions are contact time, initial BG concentration, temperature and nanocomposite dosage. The experimental data were analyzed by the Langmuir, Freundlich, and Tempkin isotherm models. The Langmuir isotherm fits the experimental data very well due to the homogeneous distribution of active sites onto PANI/AgNPs surface. The thermodynamic parameters such as Gibbs free energy, entropy and enthalpy changes of the ongoing adsorption process indicated the feasibility and endothermic nature of BG adsorption. The kinetics study revealed that adsorption of BG onto PANI/AgNPs follows the pseudo-second order kinetic model. [ABSTRACT FROM AUTHOR]

In this work, an experimental study of CO2 hydrate formation kinetics was undertaken, the effects of stirring rate and initial pressure on the hydrate formation rate were investigated. The results showed that a stirring rate of 600 rpm was optimum for increasing the CO2 hydrate formation rate, especially at lower temperatures. The effects of additives on the hydrate formation rate were also investigated. Three surfactants: Sodium Dodecyl Sulfate (SDS), Dodecyl Trimethyl Ammonium Bromide (DTAB) and Triton X-100 (TX-100), were tested. DTAB and TX-100 were new surfactants for investigation into CO2 hydrate formation kinetics. SDS and DTAB did not significantly affect the hydrate formation rate at concentrations of 300 and 500 ppm, whereas SDS increased, and DTAB insignificantly decreased the hydrate formation rate at 1000 ppm. Furthermore, TX-100 negligibly decreased the hydrate formation rate at 300 and 500 ppm, but significantly decreased the rate at 1000 ppm. In contrast, the application of thermodynamic additives, tetrahydrofuran (THF) and tetra-n-butyl ammonium bromide (TBAB), at low concentrations, increased the hydrate formation rate, and these additives affected the rate of hydrate formation in a manner similar to kinetic promoters. [ABSTRACT FROM AUTHOR]

Regioselectivity and yields of Yamaguchi cyclization of (15S,16S)-15,16-dihydroxy-otadecyl-(6Z,9Z,12Z)-trienoic acid and its saturated homologue have been compared at different temperatures and concentrations. For the unsaturated species the regioselectivity of cyclization depends on temperature to such an extent that the preferred regioisomer changes as the temperature changes, whereas for the saturated homologue the even-membered ring turns out to be always the preferred one. Molecular mechanics is used to interpret these findings. For both dihydroxyacids, there is experimental evidence that the yields of the two monocyclic regioisomers are thermodynamically controlled, unlike those of the analogue monohydroxy lactones. The higher cyclization yield of the unsaturated monohydroxyacid is interpreted in terms of conformational pre-organization. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]