Negative Values Of DeltaG Research Articles

Thermodynamic sensitivity analysis of CO2 reforming of methane based on equilibrium predictions

Thermodynamic sensitivity analysis was conducted to evaluate the selectivity dry reforming of methane (DRM) with respect to other competing side reactions in terms of Gibbs energy minimization and equilibrium reactor compositions. Spontaneity of each reaction was evaluated by their corresponding changes in Gibbs energy as a function of reactor temperature from 100 – 1000 °C. At temperatures above 700 °C, all reactions considered with the exception of the Boudouard reaction are spontaneous due to their negative deltaG values. Equilibrium compositions were computed for 40 kmol of feed (CO2 + CH4) to determine its sensitivity to occurrence of reverse water-gas-shift (RWGS) reaction and changes in feed CO2/CH4 ratio. The presence of RWGS reaction results to higher reactant conversion accompanied by more severe carbon formation. The H2/CO ratio was however not affected by its occurrence. At CO2/CH4 feed ratio of 2, the product ratio was barely affected and at minimal carbon formation while CO2/CH4 ratio value of 0.5 produced a lot of carbon especially at high temperatures due to the prevalence of CH4 cracking. DRM is thus more preferable at temperatures above 700 °C, devoid of RWGS and high feed CH4.

Spectroscopic studies of interaction between biologically synthesized silver nanoparticles and bovine serum albumin.

Binding interaction of biologically synthesized silver nanoparticles with bovine serum albumin (BSA) has been investigated by UV-Vis and fluorescence spectroscopic techniques. UV-Vis analysis implies the formation of the ground state complex between BSA and silver nanoparticles. The analysis of fluorescence spectrum and fluorescence intensity indicates that silver nanoparticles (SNP) have a strong ability to quench the intrinsic fluorescence of BSA by dynamic quenching mechanisms. The number of binding sites 'n' and binding constants 'K' were determined at different temperatures based on fluorescence quenching. The thermodynamic parameters namely deltaH, deltaG, and deltaS were calculated at different temperatures (20, 30, and 40 degrees C) and the results indicate that both hydrophobic and electrostatic interactions were predominantly present in the SNP-BSA complex. Negative deltaG values imply that the binding process is spontaneous.

Investigation on the Interaction of Prulifloxacin with Human Serum Albumin: A Spectroscopic Analysis

The interaction between prulifloxacin (PUFX) and human serum albumin (HSA) was investigated under simulated physiologic conditions with fluorescence spectra. The fluorescence quenching process of HSA may be mainly governed by a static quenching mechanism. The apparent binding constant K(b) between PUFX and HSA at different temperatures were 2.08+/-1.04, 2.74+/-0.50, and 4.98+/-1.61x10(8) l/mol. The thermodynamic parameters, with a negative value of DeltaG(0), revealed that the binding is a spontaneous process. A binding distance R of 1.19 nm between donor and acceptor was obtained from the Fŏrster energy transfer theory.

Iso‐guanine quintet complexes coordinated by mono valent cations (Na+, K+, Rb+, and Cs+)

The geometric structures, the interaction energies, the vibrational characteristics, and the electronic structures of the complexes of the isoguanine (isoG) quintet coordinated with mono valent cations (Na(+), K(+), Rb(+), and Cs(+)) have been studied based on the nonplanar models. The geometry of the local minimum structure of the Na(+)-isoG quintet complex deviates significantly from the planar structure. The geometric characteristics of the Na(+)-isoG quintet complex support the experimental findings that Na(+) is unlikely to induce the formation of the isoG quintet-based pentaplexes. Similar to the guanine tetraplexes, the ionic selectivity of the isoG quintet-based pentaplexes is largely dominated by the hydration energy of the cations. After hydration correction, the positive value of the free energy difference for the formation of the Na(+)-isoG quintet complex (DeltaG(f)) suggests that the isoG quintet is unable to capture the hydrated Na(+). The negative values of DeltaG(f) for the K(+) and Rb(+) complexes implies that both ions have the tendency to be inserted into the isoG pentaplexes. This study suggests that, to elucidate the high Cs(+) selectivity of isoG pentaplexes, it is necessary to extend the model from the isoG quintet to the isoG decamer.

Studies on indium sorption from iodide medium by polyurethane foam

The sorption behavior of indium iodide onto polyether-based polyurethane (PUF) foam was investigated. The system shows rapid kinetics and maximum sorption from a meaningful range of either acidic or basic media and achieves distribution ratios above 10(4) L kg-1 ([KI] > 0.6 mol kg-1). Sorption equilibrium analysis indicates tetraiodo-indate (MInI4) as the main species sorbed on the foam matrix. A Langmuir isotherm was successfully fitted and values of (1.55±0.02) x 10-1 mol kg-1 and (7.0±1.3) x 10(4) L g-1 were obtained for the saturation capacity Ks and adsorption coefficient b, respectively. The temperature effect was evaluated and the thermodynamic parameters calculated. The values of the equilibrium constant, Kc, decreased with increasing temperature. The negative values of deltaG, deltaH and deltaS indicate a spontaneous and exothermic chemisorption process favored at low temperatures.