Standard Gibbs Free Energy Change Research Articles

Electrochemical and spectrophotometric study on neodymium ions in molten alkali chloride mixtures

The thermodynamic stability of Nd(III) complex in various molten alkali chlorides at 923 K was studied by electrochemical analysis. The standard Gibbs free energy change of the Nd 3+ formation, Δ G 3 / 0 ∘ , decreased by adding MCl (M = Na, K, Rb, or Cs) into LiCl. The Nd(III) complex was more stable in an alkali chloride mixture with larger averaged cationic radius. This means that the stability is controlled by the polarizing power of solvent cations. The electronic absorption spectrum of the hypersensitive f– f transition of Nd 3+ was investigated to know the change in its coordination environments. The oscillator strength of the 4 G 5/2, 2 G 7/2 ← 4 I 9/2 transition and the degree of the energy splitting in electronic energy levels were estimated. The results suggested that the octahedral symmetry of the NdCl 6 3− complex was more distorted in the melt with higher LiCl content, and the distortion was depressed by decreasing the polarizing power of solvent cations. The local structure around Nd 3+ was significantly correlated with the thermodynamic stability of the Nd(III) complex in molten alkali chlorides.

Thermodynamics of chromite ore oxidative roasting process

To explicate the thermodynamics of the chromite ore lime-free roasting process, the thermodynamics of reactions involved in this process was calculated and the phrases of sinter with different roasting times were studied. The thermodynamics calculation shows that all the standard Gibbs free energy changes of the reactions to form Na2CrO4, Na2O·Fe2O3, Na2O·Al2O3 and Na2O·SiO2 via chromite ore and Na2CO3 are negative, and the standard Gibbs free energy changes of the reactions between MgO, Fe2O3 and SiO2 released from chromite spinel to form MgO·Fe2O3 and MgO·SiO2 are also negative at the oxidative roasting temperatures (1 173–1 473 K). The phrase analysis of the sinter in lime-free roasting process shows that Na2O·Fe2O3, Na2O·Al2O3 and Na2O·SiO2 can be formed in the first 20 min, but they decrease in contents and finally disappear with the increase of roasting time. The final phase compositions of the sinter are Na2CrO4, MgO·Fe2O3, MgO·SiO2 and MgO. The results indicate that Na2CrO4 can be formed easily via the reaction of Na2CO3 with chromite ore. Na2O·Fe2O3, Na2O·Al2O3 and Na2O·SiO2 can be formed as intermediate compounds in the roasting process and they can further react with chromite ore to form Na2CrO4. MgO released from chromite ore may react with iron oxides and silicon oxide to form stable compounds of MgO·Fe2O3 and MgO·SiO2, respectively.

Synthesis and characterization of carboxymethyl-polyaminate chitosan and its adsorption behavior toward a reactive dye

Carboxymethyl-polyaminate chitosan (DETA-CMCHS), a novel kind of amphoteric chitosan derivative, was prepared and characterized by elemental analysis, and by IR and 1H NMR spectroscopy. The adsorption behavior of Reactive Blue (RB2) on DETA-CMCHS was also studied. Results showed that the maximum value of adsorption capacity was 1185.71mg/g at pH 3. The adsorption kinetic behavior was fitted with a second-order reaction rate equation. The adsorption was an exothermic, irreversible and entropy-reduced process according to thermodynamic parameters, such as standard Gibbs free-energy change, enthalpy change, and entropy change, all of which were calculated from adsorption equilibrium data.

Thermodynamics of the Amphiphilic Drug, Amitriptyline Hydrochloride-Surfactant/Polymer Systems at the Cloud Point

Herein, we report the energetics of clouding in amphiphilic drug, amitriptyline hydrochloride (AMT—a tricyclic antidepressant drug), in the presense of surfactants and polymers. Surfactants/polymers are extensively used in drug delivery as drug carriers. The cloud point (CP) of an amphiphile can be considered as the limit of its solubility. The clouding components release their solvated water and separate out from the solution. Hence, the standard Gibbs free energy change of solubilization is evaluated from the relation . For all the additives, is found to be positive. However, and values are negative as well as positive depending upon the type and nature of the additive and the results are discussed on the basis of these factors.

Experiment and Prediction: A Productive Symbiosis in Studies on the Thermodynamics of DNA Oligomers

Recently, we reported the kinetics of hybridization of cDNA dodecamers (Carrillo-Nava, E., Mejía-Radillo, Y., and Hinz, H.-J. Biochemistry 2008, 47, 13153-13157). In this study, we provide the thermodynamic reaction parameters of those dodecamers as well as a comparison with parameters for 24-mers designed from two identical dodecamers in tandem arrangement. The thermodynamic properties were determined by isothermal titration calorimetry (ITC), differential scanning microcalorimetry (DSC), and UV melting studies. On the basis of the results from our kinetic studies, fitting algorithms of DSC and UV melting profiles employed the two-state assumption for the duplex to a single strand dissociation reaction. The formation of both 12-mer and 24-mer duplexes is strongly enthalpy driven at all temperatures. At identical temperatures, the hybridization enthalpy of the 24-mer is within error limits twice that of the 12-mer. Duplex formation is always associated with a significant negative heat capacity change, ΔC(p), which, on a mass basis, is comparable to that observed for protein folding. Only a small part of the favorable reaction enthalpy appears as a standard Gibbs free energy change due to large compensating negative entropy changes linked to duplex formation. On the basis of the results of the present studies, it appears to be absolutely essential for a proper analysis of thermodynamic parameters of oligonucleotide hybridization reactions to combine low temperature ITC measurements of binding enthalpies with DSC and UV melting studies to obtain an accurate assessment of standard Gibbs energy changes or, equivalently, hybridization constants over a broad temperature range. The experimental thermodynamic parameters were compared with theoretical estimates based on nearest-neighbor approximations employing temperature-independent enthalpies. Good agreement between experimental and predicted ΔG° values is observed at ambient temperatures (20-30 °C), as long as helix formation is associated with small molar heat capacity changes. If the experimental ΔC(p) values determined by ITC are taken into account, significant deviations occur.

Mineralization of Trace Nitro/Chloro/Methyl/Amino-Aromatic Contaminants in Wastewaters by Advanced Oxidation Processes

It has great significance to investigate the degradation of aromatic contaminants as they are highly carcinogenic and nondegradable pollutants in drinking water. In this paper, the mineralization orders of the representative nitro/chloro/methyl/amino-aromatic contaminants with oxidants (·OH, H2O2, ·O−, O2,O3) in advanced oxidation processes (AOPs) are investigated based on the calculated standard molar Gibbs free energy changes of reaction (ΔrGm0) and the results are consistent with those from previous experimental results, electrophilic substitution orientation rules of the Hammett equation, and predicted results with a quantitative structure−activity relationship (QSAR). In addition, the quantitative function relationship between the degradation rate (r) of the aromatic contaminants and the thermodynamic driving force (ΔrGm0) is analyzed in order to investigate the degradation kinetics more rigorously.

Kinetics, Mechanistic, Equilibrium, and Thermodynamic Studies on the Adsorption of Acid Red Dye from Wastewater by γ-Fe2O3 Nanoadsorbents

The presence of dyestuffs in wastewater poses an environmental concern since these organic contaminants are toxic to aquatic and non-aquatic life. In addition, these contaminants are difficult to remove or biodegrade, which poses a challenge to the conventional wastewater treatment techniques. In this work, the adsorption of acid red dye 27 (AR27) onto γ-Fe2O3 nanoadsorbents was studied for the removal of red dye from aqueous solutions by the batch-adsorption technique. The experiments were carried out at different conditions of contact time, initial AR27 concentration, temperature, co-existing ions, and solution pH. It was found that the adsorption was a rapid process, and equilibrium was achieved in less than 4 minutes. The removal of AR27 decreased with the increase in solution pH and temperature. Furthermore, the addition of chloride and nitrate anions has no remarkable influence on AR27 removal efficiency. On the other hand, the effects of sulfate and bicarbonate anions on the removal of AR27 were significant. The adsorption equilibrium data fitted very well using Langmuir and Freundlich adsorption isotherm models. The data obtained from adsorption isotherms at different temperatures were used to calculate thermodynamic quantities of adsorption, such as standard Gibbs free energy change , enthalpy change , and entropy change . The adsorption process was found to be spontaneous, exothermic and physical in nature. The results indicate that γ-Fe2O3 nanoadsorbents could be employed for the removal of dyes from wastewater.

Theoretical Study on Thermodynamic Hydrogen Isotope Effect of VQ2 (Q=H, D and T)

Abstract Based on ab-initio principle and pseudo-potential plain wave function combined with density function theory, crystal lattice dynamical characteristics and thermodynamical functions of V, VH 2 , VD 2 and VT 2 were calculated. The thermodynamical isotope effect was analyzed based on those calculated data. Calculation results show that both difference of vibration frequency of atoms in V Q 2 ( Q =H, D and T) and difference of oscillation frequency of hydrogen isotopes are mainly responsible for the hydrogen isotope effect. The standard Gibbs free energy change of the absorption reaction rises from −50 kJ/mol to 140 kJ/mol with the temperature increasing from 10 K to 1000 K. The equilibrium pressure climbs drastically when temperature is higher than room temperature. Within the whole temperature range, only inverse hydrogen isotope effect is found

Electrochemical behavior of 1-ferrocenyl-3-phenyl-2-propen-1-one on glassy carbon electrode and evaluation of its interaction parameters with DNA

The electrochemical behavior of 1-ferrocenyl-3-phenyl-2-propen-1-one (ferrocenylone) and its interaction with DNA was studied by a glassy carbon electrode using cyclic voltammetry (CV) technique. The results from CV were supported by UV-Visible spectroscopy performed under the similar conditions. The positive peak potential shift in CV and the bathochromic shift in the UV-Vis absorption spectra suggested an intercalative mode of binding. The binding constant (K = 1.39 ± 0.02 × 104 mol-1 L) and the binding site size (0.53 bp) were obtained from voltammetric data which leads to a standard Gibbs free energy change (ΔGo= -RT lnK) of -23.64 kJ mol-1 and hence indicated the spontaneity of the binding interaction. The values of binding constants obtained from UV-Vis absorption and CV measurements, 1.26 ± 0.01 × 104 and 1.39 ± 0.02 × 104 mol-1 L respectively, were in close agreement.

Thermodynamics and Mechanism of the Block Copolymer Micelle Shuttle between Water and an Ionic Liquid

The micelle shuttle utilizing block copolymer micelles as nanocarriers for transportation between water and a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]), is examined in detail. Rhodamine B, a dye with a high molar absorptivity and fluorescence quantum yield, is conjugated to a short poly(1,2-butadiene) homopolymer and then loaded in amphiphilic poly((1,2-butadiene)-block-ethylene oxide) (PB-PEO) block copolymer micelles. The round-trip transportation of the micelles between water and the ionic liquid is simply triggered by temperature; it is fully reversible, quantitative, and without leakage. Quantitative fluorescence analysis reveals that the micelle distribution in the biphasic system has a very strong temperature dependence, which is favorable for control of the transportation. The standard Gibbs free energy change (DeltaG(o)), standard enthalpy change (DeltaH(o)), and standard entropy change (DeltaS(o)) of the micelle shuttle are extracted from the temperature dependence of the micelle distribution. Both DeltaH(o) and DeltaS(o) are positive, indicating an entropy-driven process. The slow yet spontaneous micelle shuttle is explored under quiescent conditions to understand the transfer kinetics. Both of the two-way transfers involve three steps, formation of micelle-concentrated [EMIM][TFSI]/water droplets in the initial phase, sedimentation/creaming of the droplets to the interface, and diffusion of the micelles to the destination phase. A detailed mechanism for the transfer is therefore proposed.

A novel tool to facilitate the learning of thermodynamic principles by undergraduate students of the biological area

This study describes the application and evaluation of a novel didactic tool (thermodynamic device) developed for students in the area of biology who have conceptual deficiencies that render the learning of thermodynamic principles difficult. Systems of communicant vessels with equal and different compartments were constructed to correlate the equilibrium constant of the reactions and reagent/product ratios with the concept of standard and nonstandard Gibbs free energy changes (ΔG° and ΔG, respectively). The communicating vessels were filled respectively with equal and different volumes of a dye aqueous solution followed by the opening of a faucet that coupled the vessels. This procedure allows liquid flux leading to the movement of internal propellers. The movement of the propellers turns on an electronic circuit that processes the information to exhibit the energy released by the movement of the solution toward equilibrium. The thermodynamic device was evaluated regarding the efficiency of content comprehension and retention of the gain by challenging students to answer five subjective questions 1 week after a regular teaching module about thermodynamics. The overall mean score obtained by the students who accessed the thermodynamic device (7.0) was significantly higher (p < 0.01) than the mean score of the control group (3.4). The thermodynamic device increased twofold the percentage of students who gave more than 50% correct answers. The efficiency of the didactic tool was also evaluated and corroborated by objective questions. In conclusion, the use of the thermodynamic device was highly effective in improving the understanding of thermodynamic principles by undergraduate biology students.

Solubility of CO 2 in dialkylimidazolium dialkylphosphate ionic liquids

The solubility of carbon dioxide in room temperature ionic liquids (RTILs), dialkylimidazolium dialkylphosphates, was measured at 313–333 K and at pressures close to atmospheric pressure, from which Henry's law coefficients, standard Gibbs free energy, enthalpy, and entropy changes of solvation were derived. The CO 2 solubility in the dialkylimidazolium dialkylphosphate was found to increase with increasing chain length of the alkyl groups on the cation and/or the anion as was similarly found in other RTILs. Among various dialkylimidazolium dialkylphosphates tested, 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][Et 2PO 4]) and 1-butyl-3-methylimidazolium dibutylphosphate ([BMIM][Bu 2PO 4]) exhibited the comparable or better capability of dissolving CO 2 in comparison with that of [BMIM][BF 4], but their absorption capacities were still lower than that of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][Tf 2N]).

A New Competitive Adsorption Isothermal Model of Heavy Metals in Soils

Abstract A new competitive adsorption isothermal model (CAIM) was developed for the coexistent and competitive binding of heavy metals to the soil surface. This model extended the earlier adsorption isothermal models by considering more than one kind of ion adsorption on the soil surface. It was compared with the Langmuir model using different conditions, and it was found that CAIM, which was suitable for competitive ion adsorption at the soil solid-liquid surface, had more advantages than the Langmuir model. The new competitive adsorption isothermal model was used to fit the data of heavy metal (Zn and Cd) competitive adsorption by a yellow soil at two temperatures. The results showed that CAIM was appropriate for the competitive adsorption of heavy metals on the soil surface at different temperatures. The fitted parameters of CAIM had explicit physical meaning. The model allowed for the calculation of the standard molar Gibbs free energy change, the standard molar enthalpy change, and the standard molar entropy change of the competitive adsorption of the heavy metals, Zn and Cd, by the yellow soil at two temperatures using the thermodynamic equilibrium constants.

Performance of sulfate-dependent anaerobic ammonium oxidation

The performance of sulfate-dependent anaerobic ammonium oxidation was studied. The results showed that both SO42− and NH4+ were chemically stable under anaerobic conditions. They did not react with each other in the absence of biological catalyst (sludge). The anaerobic digested sludge cultivated in an anaerobic reactor for three years took on the ability of oxidizing ammonium with sulfate anaerobically. The average reduction of sulfate and ammonium was 71.67 mg·L−1 and 56.82 mg·L−1 at high concentrations. The reaction between SO42− and NH4+ was difficult, though feasible, due to its low standard Gibbs free energy change. The experiment demonstrated that high substrate concentrations and low oxidation-reduction potential (ORP) may be favourable for the biological reaction.

Effects of solubilization of short and medium-chain molecules in the self-assembly of two amphiphilic drugs in solution

The effect of short and medium chain length alcohols ethanol, propanol, and butanol on the thermodynamic properties of aqueous solutions of the ionic amphiphilic antidepressants imipramine and clomipramine hydrochlorides has been investigated at T = 293 K. Critical concentrations of the drugs were obtained from ultrasound velocity measurements. Experimental results have shown a strong dependence of the ultrasound velocity with the alcohol concentration and chain length. Differences in the aggregate properties of both amphiphiles arise from the presence of the extra Cl − substituent on the ring system of clomipramine. Density and ultrasound measurements have been used to obtain the apparent molar volumes, V φ , and isentropic apparent molar compressibilities, K ϕ (S), for the aqueous drug/water–alcohol solutions. The distribution coefficient of the amount solubilized between water and the aggregates, K, has been determined using an indirect method based on the pseudo-phase model by using apparent molar volume values. This method allows the calculation of the distribution coefficients at concentrations below saturation. The standard molar Gibbs free energy change on transfer from the aqueous to the micellar, Δ G ∘ , phase was calculated from the partition coefficient. The results have highlighted the structural differences between both amphiphiles.

EXAFS studies on adsorption irreversibility of Zn(II) on TiO 2: Temperature dependence

Adsorption irreversibility of Zn(II) on TiO 2 at various temperatures was studied using a combination of classical macroscopic methods and extended X-ray absorption fine structure (EXAFS) spectroscopy. When the temperature was increased from 5 to 40 °C, the Zn(II) adsorption capacity increased by 130%, and adsorbed Zn(II) became more reversible. The standard Gibbs free energy change ( Δ G 0 ) of the adsorption reaction at 5, 20, and 40 °C was determined to be − 19.58 ± 0.30 , − 22.28 ± 0.10 , and − 25.14 ± 0.21 kJ mol −1 , respectively. And the standard enthalpy ( Δ H 0 ) and entropy ( Δ S 0 ) were 24.55 ± 2.91 kJ mol −1 and 159.13 ± 0.53 J mol −1 K −1 , respectively. EXAFS spectra results showed that the hydrated Zn(II) was adsorbed through fourfold coordination with an average Zn O bond distance of 1.98 ± 0.01 Å . Two Zn Ti atomic distances of 3.25 ± 0.02 and 3.69 ± 0.03 Å were observed, which corresponded to an edge-sharing linkage mode (strong adsorption) and a corner-sharing linkage mode (weak adsorption), respectively. As the temperature increased from 5 to 40 °C, the number of strong adsorption sites ( N 1 ) remained relatively constant while the number for the weak adsorption sites ( N 2 ) increased by 31%. These results indicate that the net gain in adsorption capacity and the decreased adsorption irreversibility at elevated temperatures were due to the increase in available weak adsorption sites ( N 2 ) or the decrease in the ratio of N 1 / N 2 . Both the macroscopic sorption/desorption equilibrium data and the molecular level evidence of this study suggest that in a given environmental system (e.g., soils or natural waters) zinc and other similar heavy metals are likely more mobile at higher temperatures.

Free Energies of Formation of Metal Clusters and Nanoparticles from Molecular Simulations: Aln with n = 2−60

Efficient simulation methods are presented for determining the standard Gibbs free energy changes for the reactions, M + Mn-1 ↔ Mn (R1), involved in the formation of atomic clusters and nanoparticles (also called particles) in the vapor phase. The standard Gibbs free energy of formation (ΔfG°) of a particle is obtained from these Gibbs free energy changes (ΔG°) by a recursion relationship using the experimental ΔfG° of the monomer. In the present study, this method has been applied to reactions involving Aln particles with n = 2−60. This method has been validated for n = 2, where the experimental thermodynamic properties of Al2 have been recompiled using the latest available experimental or highly accurate theoretical data. For n = 2−4, two completely different approaches, a Monte Carlo configuration integral (MCCI) integration of partition functions and a Monte Carlo direct simulation of the equilibrium constants (MCEC), employing four well-validated potential energy functions have been used to calculate ΔG° of R1. Excellent agreement is observed for these two methods. Although different potential energy functions give different stage-1 results for n ≤ 10, three high-level correction (HLC) terms, namely, a correction for the potential energy difference of the global minima, another for the electronic excitation contribution, and a third based on calculating isomeric−rovibrational contribution, have been applied to mitigate deficiencies in the potential energy functions. For n = 2, good agreement has been found between the corrected simulation results and experimental data. For larger n, the more efficient MCEC method has been used. Finally, accurate ΔG° of R1 and thus ΔfG° of Aln particles with n = 2−60 have been determined. This is the first example of the determination of nanoparticle free energies of formation.

Phase relationship of complex multi-component system in chromate cleaner production

The phase relationships of the complex multi-component systems in the liquid-phase oxidization and separation process related with the chromate cleaner production are investigated theoretically and experimentally. The phase diagram of main system FeCr2O4-KOH-O-2 of oxidization process and the relationship of its standard Gibbs free energy change with temperature are calculated. A series of phase diagrams of the separation process at different temperatures, such as K(Na)OH-K(Na)(2)CrO4-H2O, KOH-KAlO2-H2O, K(Na)OH-K(Na)(2)CO3-H2O, K(Na)OH-K(Na)HCO3-H2O and K(Na)HCO3-K(Na)(2)CrO4-H2O have also been calculated. Some experiments are carried out to verify the calculated results. Our results showed that the sub-molten salt media are suitable for the oxidization and separation processes; FeCr2O4 can be oxidized across a wide range of temperature; K(Na)(2)CrO4 can be separated from K(Na)AlO2 system at appropriate temperature and proper concentration; the crystallization of carbonate is easier than that of K(Na)(2)CrO4.

Adsorption of micelle forming and non-micelle forming surfactants on the adsorbents of different nature

Wastewater treatment is considered to be a part of mineralization processes of man-caused substance. The mineralization of substance, in turn, is an inclusion of vital functions products, waste and metabolites into the continual natural cycles of substance and energy exchange. Study of water-soluble organic substances adsorption in order to find effective and cheap adsorbents both natural and artificially created is an important problem of the XXI century. Due to the increasing use and global scale of production of surfactant detergents being pollutants of water bodies, grounds and soils, adsorption of both micelle forming surfactant detergents (anionic sodium dodecylsulfate SDS, cationic cetyltrimethylammonium bromide CTAB and non-ionic Triton X-100) and non-micelle forming surfactants—aliphatic alcohols ( n-butanol, n-pentanol and n-hexanol) on aluminum oxide (of analytical grade) and natural mineral shungite was studied in this paper. Isotherms of adsorption were found according to the data of surface tension obtained. The Gibbs–Langmuir adsorption model constant values were determined for surfactants at both the air/water interface and at the water/adsorbent interface studied. Critical micellization concentrations of the solutions of surfactants also were determined by the tensiometric and the conductometric methods. The most effective hydrophilic and hydrophobic adsorbents are revealed for alcohols and micelle forming surfactants. The given results on surfactant adsorption, in particular, on aluminum oxide, are interpreted on the basis for Nechaev's conceptions (1989) about the connection of adsorption ability of organic molecules with resonance potential of adsorbents. For thermodynamic estimation of adsorbents efficiency the standard Gibbs free energy change of adsorption and the standard Gibbs free energy change of micellization were calculated. Comparison of the Gibbs free energies values for micelle forming surfactants shows that wastewater treatment from cationic CTAB is effective using both powders of shungite and aluminum oxide. Another case is wastewater treatment from SDS and Triton X-100 for which aluminum oxide is non-effective while shungite is still efficient. Data obtained are considered to be a component part of colloido-chemical base of purification of sewage polluted with surfactants.

A thermodynamic study of ketoreductase-catalyzed reactions 4. Reduction of 2-substituted cyclohexanones in n-hexane

The equilibrium constants K for the ketoreductase-catalyzed reduction reactions (2-substituted cyclohexanone + 2-propanol = cis- and trans-2-substituted cyclohexanol + acetone) have been measured in n-hexane as solvent. The 2-substituted cyclohexanones included in this study are: 2-methylcyclohexanone, 2-phenylcyclohexanone, and 2-benzylcyclohexanone. The equilibrium constants K for the reactions with 2-methylcyclohexanone were measured over the range T = 288.15 to 308.05 K. The thermodynamic quantities at T = 298.15 K are: K = (2.13 ± 0.06); Δ r G m ∘ = - ( 1.87 ± 0.06 ) kJ · mol - 1 ; Δ r H m ∘ = - ( 6.56 ± 2.68 ) kJ · mol - 1 ; and Δ r S m ∘ = - ( 15.7 ± 9.2 ) J · K - 1 · mol - 1 for the reaction involving cis-2-methylcyclohexanol, and K = (10.7 ± 0.2); Δ r G m ∘ = - ( 5.87 ± 0.04 ) kJ · mol - 1 ; Δ r H m ∘ = - ( 2.54 ± 1.8 ) kJ · mol - 1 ; and Δ r S m ∘ = ( 11.2 ± 6.4 ) J · K - 1 · mol - 1 for the reaction involving trans-2-methylcyclohexanol. The standard molar Gibbs free energy changes Δ r G m ∘ for the reactions ( trans-2-substituted cyclohexanol = cis-2-substituted cyclohexanol) in n-hexane have also been calculated and compared with the literature data that pertain to reactions in the gas phase and at higher temperatures. Experiments carried out with a chiral column demonstrated that the enzymatic reduction of 2-phenylcyclohexanone catalyzed by the ketoreductase used in this study is not stereoselective.