O2 Binding to Heme is Strongly Facilitated by Near‐Degeneracy of Electronic States

This paper reports the computed O₂ binding to heme, which for the first time explains experimental enthalpies for this process of central importance to bioinorganic chemistry. All four spin states along the relaxed Fe? O₂‐binding curves were optimized using the full heme system with dispersion, thermodynamic, and scalar‐relativistic corrections, applying several density functionals. When including all these physical terms, the experimental enthalpy of O₂ binding (?59 kJ mol^?1) is closely reproduced by TPSSh‐D3 (?66 kJ mol^?1). Dispersion changes the potential energy surfaces and leads to the correct electronic singlet and heptet states for bound and dissociated O₂. The experimental activation enthalpy of dissociation (～82 kJ mol^?1) was also accurately computed (～75 kJ mol^?1) with an actual barrier height of ～60 kJ mol^?1 plus a vibrational component of ～10 and ～5 kJ mol^?1 due to the spin‐forbidden nature of the process, explaining the experimentally observed difference of ～20 kJ mol^?1 in enthalpies of binding and activation. Most importantly, the work shows how the nearly degenerate singlet and triplet states increase crossover probability up to ～0.5 and accelerate binding by ～100 times, explaining why the spin‐forbidden binding of O₂ to heme, so fundamental to higher life forms, is fast and reversible.     

Exploring antibiotic resistant mechanism by microcalorimetry

In an effort to probe the reaction of antibiotic hydrolysis catalyzed by B3 metallo-??-lactamase (M??L), the thermodynamic parameters of penicillin G hydrolysis catalyzed by M??L L1 from Stenotrophomonas maltophilia were determined by microcalorimetric method. The values of activation free energy ??G _?? ^?? are 88.26, 89.44, 90.49, and 91.57?kJ?mol^?1 at 293.15, 298.15, 303.15, and 308.15?K, respectively, activation enthalpy ??H _?? ^?? is 24.02?kJ?mol^?1, activation entropy ??S _?? ^?? is ?219.2511?J?mol^?1?K^?1, apparent activation energy E is 26.5183?kJ?mol^?1, and the reaction order is 1.0. The thermodynamic parameters reveal that the penicillin G hydrolysis catalyzed by M??L L1 is an exothermic and spontaneous reaction.     

Interconversion of the Tautomers of 2-Benzylidene-4-Methyl-3-Oxo-Pentanoic Acid Phenylamide During Gas Chromatography

Tautomerization of 2-benzylidene-4-methyl-3-oxo-pentanoic acid phenylamide has been studied by NMR and GC-MS. The two tautomers were separated on an HP-5 column, which enabled the kinetic and the thermodynamic behavior of on-column interconversion to be investigated. The enol-to-imide tautomerization was found to occur primarily in the stationary phase. By treating the column as a reactor, the interconversion was investigated as a function of retention time and oven temperature. This enabled determination of the rate constant (0.0605 s^?1) by monitoring the increase of the less gas stable tautomer at a constant temperature of 260 °C and determination of the activation energy of the reaction for the net tautomerization (52.0 kJ mol^?1), because it was found that the reaction obeyed pseudo first-order kinetics. The enthalpy and the entropy changes (?H=1.68 kJ mol^?1, ?S=3.54 J K^?1 mol^?1) for the enol-to-imide reaction in the stationary phase were also obtained.     

Isoconversional kinetic study of alachlor and metolachlor vaporization by thermal analysis

The vaporization kinetics of two acetamide pesticides, namely alachlor and metolachlor, was studied by thermogravimetric analysis under nonisothermal conditions (using heating rates between 1.0 and 10 K min^?1). A model‐free isoconversional method of kinetic analysis was proposed, and activation energy dependences on the extent of conversion α for nonisothermal experiments were given. An increase in activation energy is shown for alachlor from 50 to 60 kJ mol^?1, while E values do not significantly vary in the range α > 0.1: 63 kJ mol^?1 for metolachlor while 60 kJ mol^?1 for alachlor. At the end of vaporization (0.9 < α < 1.0), the activation energies are in close agreement with the enthalpies of vaporization calculated from DSC measurements. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 74–80, 2005     

Exploring antibiotic resistant mechanism by microcalorimetry II

In an effort to understand the reaction of antibiotic hydrolysis with B2 metallo-??-lactamases (M??Ls), the thermodynamic parameters of imipenem hydrolysis catalyzed by metallo-??-lactamase ImiS from Aeromonas veronii bv. sobria were determined by microcalorimetric method. The values of activation free energy $ \Updelta G_{ \ne }^{\theta } $ are 86.400?±?0.043, 87.543?±?0.034, 88.772?±?0.024, and 89.845?±?0.035?kJ?mol^?1 at 293.15, 298.15, 303.15, and 308.15?K, respectively, activation enthalpy $ \Updelta H_{ \ne }^{\theta } $ is 18.586?±?0.009?kJ?mol^?1, activation entropy $ \Updelta S_{ \ne }^{\theta } $ is ?231.34?±?0.12?J?mol^?1?K^?1, apparent activation energy E is 21.084?kJ?mol^?1, and the reaction order is 1.5. The thermodynamic parameters reveal that the imipenem hydrolysis catalyzed by metallo-??-lactammase ImiS is an exothermic and spontaneous reaction.     

Surface and bulk conduction and thermodynamic properties of ionic salt CsH<Subscript>5</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

Transport properties of ionic salt CsH₅(PO₄)₂ are studied by the impedance method. The salt’s bulk conductivity ranges from 10^?8 to 10^?4 S cm^?1 in the temperature interval 90 to 145°C. The apparent activation energy is high (1.6–2.0 eV). The conductivity is slightly anisotropic: it is maximum in the [001] direction and minimum in the [100] direction (～5.6 and 1 times × 10^?6 S cm^?1, respectively, at 130°C). The conductivity of polycrystalline samples is higher by 1–2 orders of magnitude, and the activation energy drops to 1.05 eV due to the formation of a pseudoliquid layer with a high proton mobility at the intercrystallite boundary. The salt’s thermodynamic properties are examined by differential scanning calorimetry and thermogravimetry. No phase transitions are discovered in the salt up to the melting point (151.6°C), with the melting enthalpy equal to ～34 kJ mol^?1. The crystallization occurs at lower temperatures (107°C) and the crystallization enthalpy (?18 kJ mol^?1) is lower than the melting enthalpy. The melting is accompanied by slow decomposition of the salt. Factors affecting the proton transport in the salt are analyzed.     

Kinetische untersuchung der reversiblen dimerisierung von o-phenylendioxidimethylsilan

The reversible dimerisation of o-phenylenedioxydimethylsilane (2,2-dimethyl-1,3,2-benzodioxasilole) has been studied by ¹H NMR spectroscopy. The kinetics of this reaction can be described quantitatively by a bimolecular 10-ring formulation reaction and a monomolecular backreaction. The thermodynamic and kinetic parameters are: ΔH⁰ = ?43 kJ mol^?1; ΔS⁰ = ?112 J mol^?1 K^?1; ΔG⁰₂₉₈ = ?9.6 kJ mol^?1; ΔH³₂₉₈ = 57 kJ mol^?1; ΔS³₂₉₈ = ?129 J mol^?1 K^?1; ΔG³₂₉₈ = 96 kJ mol^?1; E_a = 60 kJ mol^?1; A = 3.17 × 10⁶ l mol^?1 s^?1. Remarkable is the low activation energy of formation of the ten-membered ring, considering that two SiO bonds have to be cleaved during the reaction. Transition states and possible structures of the ten-membered heterocycle are discussed.     

On the mechanism of the chromium carbonyl photocatalyzed watergas shift reaction

The chromium hexacarbonyl catalyzed watergas shift reaction is accelerated by UV irradiation and inhibited by increased CO pressure. An activation energy of 30 kJ mol^?1 has been determined for the photochemical and one of 145 kJ mol^?1 for the thermal reaction. Light accelerates the conversion of Cr(CO)₆ into [Cr(CO)₅ formate]^?, which is thermally activated, as evidenced by in situ IR and UV spectroscopy.     

The influence of reagents solvation on enthalpy change of glycine-ion protonation and silver(I) glycine-ion complexation in aqueous-dimethylsulfoxide solutions

The thermal decomposition process and non-isothermal decomposition kinetic of glyphosate were studied by the Differential thermal analysis (DTA) and Thermogravimetric analysis (TGA). The results showed that the thermal decomposition temperature of glyphosate was above 198?°C. And the decomposition process was divided into three stages: The zero stage is the decomposition of impurities, and the mass loss in the first and second stage may be methylene and carbonyl, respectively. The mechanism function and kinetic parameters of non-isothermal decomposition of glyphosate were obtained from the analysis of DTA?CTG curves by the methods of Kissinger, Flynn?CWall?COzawa, Distributed activation energy model, Doyle and ?atava-?esták, respectively. In the first stage, the kinetic equation of glyphosate decomposition obtained showed that the decomposition reaction is a Valensi equation of which is two-dimensional diffusion, 2D. Its activation energy and pre-exponential factor were obtained to be 201.10?kJ?mol^?1 and 1.15?×?10¹⁹?s^?1, respectively. In the second stage, the kinetic equation of glyphosate decomposition obtained showed that the decomposition reaction is a Avrami?CErofeev equation of which is nucleation and growth, and whose reaction order (n) is 4. Its activation energy and pre-exponential factor were obtained to be 251.11?kJ?mol^?1 and 1.48?×?10²¹?s^?1, respectively. Moreover, the results of thermodynamical analysis showed that enthalpy change of ??H ^??, entropy change of ??S ^?? and the change of Gibbs free energy of ??G ^?? were, respectively, 196.80?kJ?mol^?1,107.03?J?mol^?1?K^?1, and 141.77?kJ?mol^?1 in the first stage of the process of thermal decomposition; and 246.26?kJ?mol^?1,146.43?J?mol^?1?K^?1, and 160.82?kJ?mol^?1 in the second stage.     

Conductivity of crosslinked poly(N-vinylpyrrolidone) gel film containing surfactant as electrolyte salt

New polymeric solid electrolyte films, consisting of crosslinked poly(N-vinylpyrrolidone) (PVPD) as matrix, and surfactant, sodium deoxycholate (NaDC), lithium deoxycholate (LiDC), sodium laulylsulfate (R₁₂OSO₃Na), or sodium palmitate (R₁₅COONa) as electrolyte salt, are prepared; their basic structure and conductivity dependence on temperature are reported. The structure of the electrolytes is amorphous. Their conductivity is 3.1 × 10^?5 S cm^?1 (containing NaDC), 8.42 × 10^?6 S cm^?1 (LiDC), 2.18 × 10^?4 S cm^?1 (R₁₂OSO₃Na), and 7.27 × 10^?5 S cm^?1 (R₁₅COONa) at 20°C. Their temperature dependence of the conductivity is similar to that of liquid electrolyte rather than that of usual polymeric solid electrolyte, i.e., the WLF-type dependence. The values of activation energy of conductivity (E_a) were PVPD, 25.5 kJ mol^?1; PVPD/NaDC, 21.4 kJ mol^?1; PVPD/LiDC, 25.3 kJ mol^?1; PVPD/R₁₂OSO₃Na, 17.2 kJ mol^?1; PVPD/R₁₅COONa, 18.7 kJ mol^?1. © 1993 John Wiley & Sons, Inc.     

Thermal decomposition and non-isothermal decomposition kinetics of carbamazepine

The thermal stability and kinetics of isothermal decomposition of carbamazepine were studied under isothermal conditions by thermogravimetry (TGA) and differential scanning calorimetry (DSC) at three heating rates. Particularly, transformation of crystal forms occurs at 153.75°C. The activation energy of this thermal decomposition process was calculated from the analysis of TG curves by Flynn-Wall-Ozawa, Doyle, distributed activation energy model, ?atava-?esták and Kissinger methods. There were two different stages of thermal decomposition process. For the first stage, E and logA [s^?1] were determined to be 42.51 kJ mol^?1 and 3.45, respectively. In the second stage, E and logA [s^?1] were 47.75 kJ mol^?1 and 3.80. The mechanism of thermal decomposition was Avrami-Erofeev (the reaction order, n = 1/3), with integral form G(α) = [?ln(1 ? α)]^1/3 (α = ～0.1–0.8) in the first stage and Avrami-Erofeev (the reaction order, n = 1) with integral form G(α) = ?ln(1 ? α) (α = ～0.9–0.99) in the second stage. Moreover, ΔH ^≠, ΔS ^≠, ΔG ^≠ values were 37.84 kJ mol^?1, ?192.41 J mol^?1 K^?1, 146.32 kJ mol^?1 and 42.68 kJ mol^?1, ?186.41 J mol^?1 K^?1, 156.26 kJ mol^?1 for the first and second stage, respectively.     

The structure and dissociation pathways of protonated methanol: An ab initio molecular orbital study

Ab initio molecular orbital calculations with moderately large polarization basis sets and including valence-electron correlation have been used to examine the structure and dissociation mechanisms of protonated methanol [CH₃OH₂]⁺. Stable isomers and transition structures have been characterized using gradient techniques. Protonated methanol is found to be the only stable isomer in the [CH₅O]⁺ potential surface. There is no evidence for a tightly-bound complex, [HOCH₂]⁺…?H₂, analogous to the preferred structure [CH₃]⁺…?H₂ of [CH₅]⁺. Protonated methanol is found to possess a pyramidal arrangement of bonds at the oxygen atom with a barrier to inversion of 8kJ mol^?1. The lowest energy fragmentation pathways are dissociation into methyl cation and water (predicted to require 284 kJ mol^?1 with zero reverse activation energy) and loss of molecular hydrogen (endothermic by 138 kJ mol^?1 but with a reverse activation barrier of 149 kJ mol^?1). The results offer a possible explanation as to why production of [CH₂OH]⁺ from the reaction of methyl cation with water is not observed. Other dissociation processes examined include loss of a hydrogen atom to yield the methylenoxonium radical cation or methanol radical cation (requiring 441 and 490 kJ mol^?1, respectively) and loss of a proton to yield neutral methanol (requiring 784 kJ mol^?1).     

The effects of additives on the thermal decomposition of azodicarbonamide

The thermal decomposition of azodicarbanamide containing a promotor and pigments is studied by thermal analysis. The promotor used was the “Standere” 3450 containing zinc and cadmium, the activation energies ranged from 25.1 to 38.2 kJ mol^?1 with different ratios. Six pigments are studied giving a range of activation energy values from 45.3 to 156.8 kJ mol^?1.     

Surface segregation measurements of In and S impurities from a dilute Cu(In,S) ternary alloy

The surface segregation of In and S from a dilute Cu(In,S) ternary alloy were measured using Auger electron spectroscopy coupled with a linear programmed heater. The alloy was linearly heated and cooled at constant rates. Segregation data of a linear heat run showed surface segregation of In that reached a maximum surface coverage of 25% followed by S, which reached a coverage of 30%. It was found that after In had reached a maximum surface coverage, it started to desegregate as soon as the S enriched the surface until In was completely replaced by S. The segregation parameters, namely, the pre‐exponential factor (D₀), activation energy (Q), segregation energy (ΔG?) and interaction energy (Ω) were extracted from the measured segregation data for both In and S segregation in Cu by simulating the measured segregation data with a theoretical segregation model (modified Darken model). The segregation parameters obtained for In segregation in Cu are D₀ = 1.8 ± 0.5 × 10^?5 m² s^?1, Q = 184.3 ± 1.0 kJ.mol^?1, ΔG? = ?61.4 ± 1.4 kJ.mol^‐1, Ω_Cu?In = 3.0 ± 0.4 kJ.mol^?1; for S segregation in Cu the parameters are D₀ = 8.9 ± 0.5 × 10^?3 m² s^?1, Q = 212.8 ± 3.0 kJ.mol^?1, ΔG? = ?120.0 ± 3.5 kJ.mol^?1, Ω_Cu?S = 23.0 ± 2.0 kJ mol^?1 and the In and S interaction parameter is Ω_In?S = ?4.0 ± 0.5 kJ.mol^?1. The initial parameters used for the Darken calculations were extracted from fits performed with the Fick's and Guttmann model. Copyright © 2013 John Wiley & Sons, Ltd.     

Electrochemical reduction of ytterbium in perchloric media

The electrochemical behavior of Yb³⁺ in perchloric media was studied by cyclic voltammetry and current reversal chronopotentiometry at several temperatures. The results show that the reversible electrochemical reduction of Yb³⁺ is followed by homogeneous reactions. The experimentally determined diffusion coefficients of ytterbic ion are 0.41×10^?5, 0.48×10^?5 and 0.53×10^?5 cm² s^?1 at 4.2, 9.2 and 14.7°C, respectively, in 0.5 M NaClO₄ solutions. From these data a value of 16 kJ mol^?1 (3830 cal mol^?1) was obtained for the activation energy for diffusion of ytterbic ion. From the activation energy the diffusion coefficient of ytterbic ion at 25.0°C was estimated. The value of 0.67×10^?5 cm² s^?1 was obtained. In all the experiments the initial pH was maintained at 4.1.     

Reaction of energetic hydrogen atoms with 1-chloropropane

The reaction of photochemically generated energetic hydrogen atoms with 1-chloropropane, reaction (1), has been examined for translational energies of H* in the range 40 to 110 kJ mol^?1. Integral probabilities for reaction (1) have been determined, and the phenomenological threshold energy is 47 ± 10 kJ mol^?1. The moderating effect of CO₂ on reaction (1) for hydrogen atoms of initial energy 108 kJ mol^?1 has also been studied. © 1993 John Wiley & Sons, Inc.     

Kinetic study of polyurethanes formation by using differential scanning calorimetry

Kinetics of polyurethane formation between several polyols and isocyanates with dibutyltin dilaurate (DBTDL) as the curing catalyst, were studied in the bulk state by differential scanning calorimetry (DSC) using an improved method of interpretation. The molar enthalpy of urethane formation from secondary hydroxyl groups and aliphatic isocyanates is 72±3 kJ mol^-1 and for aromatic isocyanates it is 55±2 kJ mol^-1 . In the case of a single second order reaction for aliphatic isocyanates reaction, activation energy is 70±5 kJ mol^-1 with oxypropylated polyols and 50±3 kJ mol^-1 with Castor oil. For aromatic isocyanates and oxypropylated polyols the activation energy is higher around 77 kJ mol^-1 . In the case of two parallel reactions (situation for IPDI and TDI 2-4) best fits are observed considering two different activation energies.     

Investigation of the Removal of Lead by Adsorption onto 1‐(2‐Thiazolylazo)‐2‐Naphthol (TAN) Imbedded Polyurethane Foam from Aqueous Solution

A new preconcentration method is presented for lead on TAN‐loaded polyurethane foam (PUF) and its measurement by differential pulse anodic stripping voltammetry (DPASV). The optimum sorption conditions of 1.29 × 10^?5 M solution of Pb(II) ions on TAN‐loaded PUF were investigated. The maximum sorption was observed at pH 7 with 20 minutes equilibrated time on 7.25 mg mL^?1 of TAN‐loaded foam. The kinetic study indicates that the overall sorption process was controlled by the intra‐particle diffusion process. The validity of Freundlich, Langmuir and Dubinin ‐ Radushkevich adsorption isotherms were tested. The Freundlich constants 1/n and K_F are evaluated to be 0.45 ±0.04 and (1.03 +0.61) × 10^?3 mol g^?1, respectively. The monolayer sorption capacity and adsorption constant related to the Langmuir isotherm are (1.38 ± 0.08) × 10^?5 mol g^?1 and (1.46 ± 0.27) × 10⁵ L mol^?1, respectively. The mean free energy of Pb(II) ions sorption on‐TAN loaded PUF is 11.04 ± 0.28 kJ mol^?1 indicating chemisorption phenomena. The effect of temperature on the sorption yields thermodynamics parameters of ΔH, ΔS and ΔG at 298 K that are 15.0 ± 1.4 kJ mol^?1, 74 ±5 J mol^?1 K^?1 and ‐7.37 ± 0.28 kJ mol^?1, respectively. The positive values of enthalpy (ΔH) and entropy (ΔS) indicate the endothermic sorption and stability of the sorbed complexes are entropy driven. However, the negative value of Gibb's free energy (ΔG) indicates the spontaneous nature of sorption. On the basis of these data, the sorption mechanism has been postulated. The effect of different foreign ions on the sorption and desorption studies were also carried out. The method was successfully applied for the determination of lead from different water samples at ng levels.     

The use of freshwater fish scale of the species Leporinus elongatus as adsorbent for anionic dyes

Fish scale of the species Leporinus elongatus was tested as an adsorbent for anionic Remazol dyes. Characterization has suggested that hydroxyl, phosphate, amides I, II, and III, and carbonate groups are the potential sites of adsorption. From solution calorimetry, values of thermal effects, Q _int, and amount of dye that interacts, n _int, were determined. The adsorption order observed was Yellow-dye/scale?>?Red-dye/scale?>?Blue-dye/scale. The Q _int and n _int data were successfully adjusted to the Langmuir isotherm model. The dyes removals by fish scale are exothermic processes (from ?83 to ?199?kJ?mol^?1) with negative entropies and are thermodynamically spontaneous. The thermodynamic results suggest that the interactions at scale/anionic dye interfaces occur mainly by surface reactions. It was finding that fish scale is a new and suitable sorbent material for recovery and biosorption/adsorption of anionic dyes from aqueous solutions.     

Non-isothermal Kinetics of the Thermal Decomposition of 3-Nitro-1,2,4-triazol-5-one Magnesium Complex

Introduction3 Nitro 1,2 ,4 triazol 5 one (NTO)metalcomplexeshavemanyspecialstructuresandsomepotentialusesinammunition .1 4 Wepreviouslypreparedanddeterminedthecrystalstructureofitsmagnesiumcomplex ,5andinthispaper ,wediscusseditsthermalbehaviorbyDSCandTG/DTGtechniquesandstudieditsnon isothermalkineticsbythemeansoftheKissingermethod ,theOzawamethod ,thedifferentialmethodandtheintegralmethod .ExperimentalSample[Mg(H2 O) 6 ](NTO) 2 ·2H2 Owaspreparedasfollows :AcalculatedamountofMg(OH…