p-Chloroacetophenone: A study of enolization kinetics

The reaction rate of enolization of p-chloroacetophenone has been studied in the presence of amino acids, namely, β-alanine, DL-alanine, L-alanine, and glycine. Maximum reaction rate was observed in the case of β-alanine at 22M concentration. The effects of parameters such as effect of ketone concentration, effect of dielectric constant, effect of catalysts, etc., have been found to exert a significant effect on the reaction rate. The effect of temperature was studied in the range of 313–328?K, and several thermodynamic parameters such as entropy (ΔS^≠), enthalpy (ΔH^≠), energy of activation (ΔE_a), and Gibbs free energy (ΔF^≠) were found to be ?10.32?e.u., 17.87?cal?mol^?1, 19.24?kcal?mol^?1, and 21.20?cal?mol^?1, respectively. The reaction rate increased from 1.9 to 5.8?min^?1 on increasing the percentage of dimethylformamide from 10 to 50% (v/v).     

Reactive separation of p-nitro phenol (PNP) from aqueous solution using tri-n-butyl phosphate: equilibrium and COSMO-RS studies

ABSTRACT

The present study is aimed to optimized diluent type, tri-n-butyl phosphate (TBP) composition and temperature for the reactive extraction of p-nitro phenol (PNP) in two different PNP concentration ranges [(0.00036–0.00646) kmol·m^?3 and (0.00646–0.01437) kmol·m^?3] as found in industrial effluents. 1-Octanol is investigated as the best diluent with TBP based on COSMO-RS theory. Equilibrium study based on mass action law is performed to find the insights of extraction mechanisms, equilibrium constant (K = 295.12 k·mol^?1) and stoichiometry (m:n = 1:1) as also confirmed by FTIR. Thermodynamic parameters, enthalpy (ΔH°), and entropy (ΔS°) are determined 27.51 K J mol^?1 and ?50.21 J mol^?1 K^?1, respectively.     

Molecular and thermodynamic basis for EGCG‐Keratin interaction‐part II: Experimental investigation

In Part I, we reported all‐atom, fully solvated molecular dynamics (MD) simulations of epigallocatechin‐3‐gallate (EGCG) binding to keratin. Herein, we report the second part of experimental investigation on EGCG binding to keratin using ultrafiltration and isothermal titration calorimetry (ITC). The thermodynamic equilibrium of EGCG binding to keratin has been quantitatively determined using ultrafiltration and high‐performance liquid chromatography?UV/vis. The relationship confirms multilayer binding of EGCG to keratin which was observed in MD simulations. By combining the ultrafiltration and ITC data, the thermodynamic parameters of EGCG binding to keratin have been quantified. The obtained free energy of the first layer binding (ΔG = ?6.37 kcal mol^?1) is shown in excellent agreement with that obtained from computer simulations (ΔG = ?6.20 kcal mol^?1) presented in Part I. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4824–4827, 2013     

Equilibrium bulk polymerization of 1,3-dioxolan

Cationic bulk polymerization of 1,3-dioxolan has been carried out in sealed ampoules using a high vacuum technique. The polymerization is initiated with triethyl oxonium hexafluorophosphate and the equilibrium between monomer and active polymer is attained within a few hours. Specific volumes of pure monomer and polymer in solution of its own monomer have been measured. Equilibrium measurements have been performed in the 40° to 141·4°C temperature range and the ceiling temperature is estimated to be 144° ± 2°C. The effect of short polymer chains on the equilibrium is discussed briefly. Values of ΔG_lc, the free energy of polymerization of one mole of pure liquid monomer to one base-mole of amorphous polymer, are computed making allowance for the non-ideal mixing. Respective values of ?17.5 ± 0.8 kJ/mol and ?47.9 ± 2.2JK^?1mol^?1 are deduced for the corresponding ΔH_lc and ΔS_lc. ΔG_lc is also computed from published data on equilibrium polymerization of 1,3-dioxolan in various solvents and the combined results for both types of polymerization yield ΔH_lc = ?16.7 ± 0.5kJ/mol and ΔS_lc = ?45.8 ± 1.5JK^?1mol^?1 for the 20° to 140°C range.     

Influence of Fatty Acid Desaturation on Spontaneous Acyl Migration in 2-Monoacylglycerols

The effect of desaturation from the C9 to the C15 carbon of 2-monoacylglycerol (2-MAG) fatty acids on spontaneous acyl migration is described. Three 2-MAG species, 2-monooleoylglycerol (C18:1 cis-Δ9), 2-monolinoleoylglycerol (C18:2 cis-Δ9,12), and 2-monolinolenoylglycerol (C18:3 cis-Δ9,12,15) were synthesized by lipase-catalyzed ethanolysis of their respective triacylglycerols and isolated in >60?% yield and at 2-MAG purities of >95?% relative to 1-monoacylglycerol (1-MAG). ¹H-NMR spectroscopy was used to monitor the spontaneous acyl migration of the 2-MAG species over a temperature range from 20 to 80?°C. The relative energies of activation calculated from the Arrhenius relationships of the 2-MAG acyl migration rate constants were 73.3, 68.0, and 72.9?kJ?mol^?1 for the three 2-MAG species, respectively. Density functional calculations performed using the B3LYP functional at the 6-31+G* basis set on the three ketal ring intermediate of the three 2-MAG species followed a similar trend with a lack of relative energetic preference associated with the degree of desaturation. The kinetically determined relative activation energies were approximately twofold higher than the theoretical relative Gibbs free energies of the intermediates, suggesting that other factors influence acyl migration. In general, increasing desaturation after the C9 carbon of 2-MAG fatty acids had no appreciable effect on acyl migration rates.     

Kinetics of thermal inactivation of transglutaminase from a newly isolated Bacillus circulans BL32

BACKGROUND: This paper describes the modeling of the kinetics of thermal inactivation of transglutaminase (TGase) from a newly isolated Bacillus circulans BL32, isolated from the Amazon environment. The purified enzyme was incubated at temperatures ranging from 30 to 70 °C and values of the thermodynamic inactivation parameters, such as activation energy (ΔE), activation enthalpy (ΔH), activation entropy (ΔS), and free energy (ΔG) for thermal inactivation, were calculated. RESULTS: The kinetics of TGase thermo‐inactivation followed a Lumry–Eyring model. The enzyme was very stable up to 50 °C, with approximately 50% of activity remaining after heating for 12 h. It was completely inactivated by incubation at 70 °C for 2 min. ΔE for TGase was 350.5 kJ mol^?1. ΔH and ΔS for thermo‐inactivation of the TGase were 347.8 kJ mol^?1 and 744 J mol^?1 K^?1 at 50 °C, respectively. Dynamic light scattering measurements suggest that the thermal inactivation of this microbial TGase can be partially attributed to the formation of aggregates. CONCLUSION: These results provide useful information about the thermal characteristics of the microbial TGase from B. circulans BL32 and indicate that this enzyme could be a good candidate for industrial applications. Copyright © 2009 Society of Chemical Industry     

Examining the preparation and characterization of coatings based on linear aromatic terpoly(methoxy‐cyanurate‐thiocyanurate)s

Two series of terpoly(methoxy‐cyanurate‐thiocyanurate)s based on thiodiphenol and dithiodiphenyl sulfide and on dihydroxydiphenyl ether and dithiodiphenyl ether, were prepared in good yield and purity and fully characterized. Most of the resulting polymers, formed at room temperature using phase transfer catalysis, can be cast into films with good resilience and thermal stability (some examples suffer practically no mass loss when held isothermally at 190 °C and only display appreciable losses when held continuously at 225 °C). Char yields of 53%?61% are achieved in nitrogen depending on backbone structure. Some problems were encountered with solubility, particularly with copolymers, which limited molecular weight analysis, but values of M_n = 8000–13 000 g mol^?1 were obtained for the polymers based on thiodiphenol and dithiodiphenyl sulfide, and M_n = 5000–13 000 g mol^?1 for the polymers based on dihydroxydiphenyl ether and dithiodiphenyl ether. DSC reveals polymerization exotherms with maxima at 184–207 °C (ΔH_p = 43–59 kJ mol^?1), which are believed to be due to isomerization of the cyanurate to the isocyanurate (activation energies span 159–195 kJ mol^?1). Molecular simulation shows that diphenylether and diphenylsulfide display very similar conformational energy surfaces and would therefore be expected to adopt similar conformations, but the diphenylsulfide offers less resistance to deformations that increase the proximity of the two phenyl rings and results in more resilient films. © 2013 Society of Chemical Industry     

The Adsorption of a Polystyrene-b-Polyisoprene Block Copolymer at the n-Hexadecane/Air Interface

Surface-tension measurements were used to investigate the surface adsorption and micellisation of a polystyrene-b-polyisoprene block copolymer in n-hexadecane which is a selectively bad solvent for polystyrene. Measurements were made over a range of concentrations (1.29–2.88)x10^?4 mol dm^?3 and temperatures 25–40°C. The block copolymer was found to be positively adsorbed at the n-hexadecane/air interface. The linearity of plots of γ against In c just below the critical micelle concentration (c.m.c.) indicated an approximately constant surface concentration. The area per block copolymer molecule at the surface had an average value of 4.1 nm². A plot of In (c.m.c.) against T^?1 gave a value for the standard enthalpy of micellisation of -41.9.3.0 kJ per mole of copolymer chains. The standard entropy contribution (-TΔSΔ) to the standard free energy of micellisation was found to be 19.7.3.0 kJ mol^?1. These thermodynamic values are in good agreement with results obtained earlier for this system by light scattering and calorimetry.     

Kinetic study of anionic polymerization of butadiene in a polar solvent

The kinetics of the propagation reaction for the polymerization of butadiene initiated by cumyl potassium in tetrahydrofuran solution at several temperatures have been studied. Kinetic data and electrolytic behaviour indicate that polybutadienyl free ions assume the whole of the propagation reaction. At 0°C, the respective rate constants for ion-pairs and free ions are 1 l mol^?1 s^?1 and 4.8 × 10⁴ l mol^?1 s^?1 respectively. The ionic dissociation constant is 7.8 × 10^?9 mol/l. The activation energy of the propagation reaction for free ions is 6.5 kcal/mol.     

Synthesis,characterization, conductivity,band gap,and kinetic of thermal degradation of poly‐4‐[(2‐mercaptophenyl) imino methyl] phenol

The oxidative polycondensation reaction conditions of 4‐[(2‐mercaptophenyl) imino methyl] phenol (2‐MPIMP) were studied in an aqueous acidic medium between 40 and 90°C by using oxidants such as air, H₂O₂, and NaOCl. The structures of the synthesized monomer and polymer were confirmed by FTIR, ¹H NMR, ¹³C NMR, and elemental analysis. The characterization was made by TGA‐DTA, size exclusion chromatography (SEC) and solubility tests. At the optimum reaction conditions, the yield of poly‐4‐[(2‐mercaptophenyl) imino methyl]phenol (P‐2‐MPIMP) was found to be 92% for NaOCl oxidant, 84% for H₂O₂ oxidant 54% for air oxidant. According to the SEC analysis, the number‐average molecular weight (M_n), weight‐average molecular weight (M_w), and polydispersity index values of P‐2‐MPIMP were found to be 1700 g mol^?1, 1900 g mol^?1, and 1.118, using H₂O₂; 3100 g mol^?1, 3400 g mol^?1, and 1.097, using air; and 6750 g mol^?1, 6900 g mol^?1, and 1.022, using NaOCl, respectively. According to TG analysis, the weight losses of 2‐MPIMP and P‐2‐MPIMP were found to be 95.93% and 76.41% at 1000°C, respectively. P‐2‐MPIMP showed higher stability against thermal decomposition. Also, electrical conductivity of the P‐2‐MPIMP was measured, showing that the polymer is a typical semiconductor. The highest occupied molecular orbital, the lowest unoccupied molecular orbital, and the electrochemical energy gaps (E′_g) of 2‐MPIMP and P‐2‐MPIMP were found to be ?6.13, ?6.09; ?2.65, ?2.67; and 3.48, 3.42 eV, respectively. Kinetic and thermodynamic parameters of these compounds investigated by MacCallum‐Tanner and van Krevelen methods. The values of the apparent activation energies of thermal decomposition (E_a), the reaction order (n), pre‐exponential factor (A), the entropy change (ΔS*), enthalpy change (ΔH*), and free energy change (ΔG*) were calculated from the TGA curves of compounds. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Polypentadecalactone prepared by lipase catalysis: crystallization kinetics and morphology

BACKGROUND: This work addresses the need to better understand the crystallization kinetics and morphology of poly (ω‐pentadecalactone) (PPDL). This polyester has promising mechanical properties and a unique structure that resembles that of polyethylene. PPDL is a member of the poly(ω‐hydroxy fatty acid) family, which can be derived from biobased feedstocks. RESULTS: PPDL (M_n = 34 000 g mol^?1 and dispersity D = M_w/M_n = 2.7) was synthesized using enzyme catalysis. Equilibrium melting enthalpy and equilibrium melting point were determined using extrapolation techniques, being 227 J g^?1 and 101 °C, respectively. In addition, the equilibrium melting point ( ) was found to be 109.3 °C by the nonlinear Hoffman‐Weeks plot. For , the lateral surface free energy (σ), fold surface free energy (σ_e) and fold work (q) are 10.4 erg cm^?2, 47.5 erg cm^?2 and 2.6 kcal mol^?1, respectively; while for , they are 25.1 erg cm^?2, 46.6 erg cm^?2 and 2.6 kcal mol^?1, respectively. The results indicated the existence of a regime I to regime II transition during crystallization at about 80 °C. Polarized optical microscopy and AFM provided further evidence for the regime I–II transition. In regime I, coarse spherulites were formed through splaying out and occasional branching of lamellae, as well as stacking of lamellae through screw dislocation. In contrast, in regime II, banded spherulites were formed through crystal twisting. CONCLUSION: Morphological changes in PPDL at spherulitic and lamellar levels in regimes I and II were confirmed by differential scanning calorimetry, POM and AFM. Copyright © 2009 Society of Chemical Industry     

Kinetic parameters of the electrode reaction of chloropenta-amminecobalt(III) ions at a gold electrode

The cathodic reduction of chloropenta-amminecobalt(III) ions at active gold electrodes has been studied in 0.1 M HClO₄ + 0.1 M NaClO₄ by means of the potentiostatic method. Chloropentaamminecobalt(III) ions gave one irreversible reduction wave in the double layer potential region of gold electrodes. The kinetic parameters of the electrode reaction were measured at 5, 15, 25, 35 and 45°C, and the activation energy was calculated to be 19 kcal mol^?1 for the electron transfer process and 4.5 kcal mol^?1 for the diffusion process.     

Molecular orbital conformational energy calculations of the aromatic heterocyclic poly(5,5′-bibenzoxazole-2,2′ diyl-1,4-phenylene) and poly(2,5-benzoxazole)

Interest in potential high-performance polymers, leading to characterization and development of the rodlike poly(p-phenylene benzobisoxazoles) (PBO) and poly(p-phenylene benzobisthiazoles) (PBT), has recently been extended to a related group of polymers referred to as AAPBO, ABPBO, AAPBT, and ABPBT. In this study, geometry-optimized CNDO/2 molecular orbital calculations have been carried out on AAPBO and ABPBO model compounds to determine conformational energies as a function of rotation about each type of rotatable bond within the repeat units. For AAPBO, which contains two types of rotatable bonds per repeat unit, the bond between the benzoxazole group and p-phenylene group prefers the coplanar conformation with a barrier to free rotation of 2.1 kcal mol^?1, while the bond between the benzoxazole groups prefers a conformation approximately 60 degrees away from coplanarity with a barrier to coplanarity and to free rotation of 3.6 kcal mol^?1. For ABPBO, which contains only the former type of rotatable bond per repeat unit, the coplanar conformations were preferred with a barrier to free rotation of 1.6 kcal mol^?1. These results are in excellent agreement with the results of both theoretical and experimental studies on the structurally analogous PBO. They are also consistent with the liquid crystalline behavior found for ABPBO but not for AAPBO.     

Temperature effects on polyphenol oxidase activity in organic solvents with low water content

The effect of temperature studies on polyphenol oxidase immobilized on glass beads were carried out in organic solvents. The optimum temperature for catalysis depended on the solvent and varied in a range from 26°C for dichloromethane to 50°C for toluene, benzene and 1,1,1-trichloroethane. Optimum temperature and activation energy were independent of the water content of the system whereas the inactivation energies decreased as the water content of the system was decreased. The enzyme was stable in toluene up to 50°C although residual activity depended on the water content of the system. Thermoinactivation of polyphenol oxidase in toluene gave an activation energy for enzyme decay of 111.5 kcal mol^?1 which is consistent with a conformational process. Among the agents employed to protect the enzyme against thermal denaturation 1 % (w/v) short-chain polyols added to the buffer and 0.5 mmol dm^?3 p-nitrophenol added to toluene more than doubled the half-life of the enzyme.     

Cyclopinolenic acids: Synthesis,derivatives and thermal properties

The two isomeric cyclopinolenic acids (CP-1 and CP-2), components of distilled tall oil, have been synthesized by means of an intramolecular Diels-Alder reaction of isomers of 5,10,12-octadecatrienoic esters, themselves synthesized in a stereocontrolled manner. The 5cis,10-trans,12trans isomer cyclizes at 200°C to a 1:3 mixture of esters of CP-1 and CP-2. At 200°C, the 5cis,10trans,12cis isomer is unreactive, but at 240°C it gives the same CP-1 + CP-2 ester mixture, presumably by way of prior isomerization to the 5cis,10trans,12trans isomer. A subambient thermal study of CP-1 and CP-2 and their derivatives shows that the compounds, excluding CP-1, lack crystalline structures or melting points, and display glass transitions only, below −80°C for esters and below −50°C for the carboxylic acids.     

Effect of temperature on linolenic acid loss and 18:3 Δ9-cis, Δ12-cis, Δ15-trans formation in soybean oil

Oil was extracted from soybeans, degummed, alkalirefined and bleached. The oil was heated at 160, 180, 200, 220 and 240°C for up to 156 h. Fatty acid methyl esters were prepared by boron trifluoride-catalyzed transesterification. Gas-liquid chromatography with a cyanopropyl CPSil88 column was used to separate and quantitate fatty acid methyl esters. Fatty acids were identified by comparison of retention times with standards and were calculated as area % and mg/g oil based on 17:0 internal standard. The rates of 18:3ω3 loss and 18:3 Δ9-cis, Δ12-cis, Δ15-trans (18:3c,c,t) formation were determined, and the activation energies were calculated from Arrhenius plots. Freshly prepared soy oil had 10.1% 18:3ω3 and no detectable 18:3c,c,t. Loss of 18:3ω3 followed apparent first-order kinetics. The first-order rate constants ranged from .0018±.00014 min⁻¹ at 160°C to .083±.0033 min⁻¹ at 240°C. The formation of 18:3c,c,t did not follow simple kinetics, and initial rates were estimated. The initial rates (mg per g oil per h) of 18:3c,c,t formation ranged from 0.0031±0.0006 at 160°C to 2.4±.24 at 240°C. The Arrhenius activation energy for 18:3ω3 loss was 82.1±7.2 kJ mol⁻¹. The apparent Arrhenius activation energy for 18:3c,c,t formation was 146.0±13.0 kJ mol⁻¹. The results indicate that small differences in heating temperature can have a profound affect on 18:3c,c,t formation. Selection of appropriate deodorization conditions could limit the amount of 18:3c,c,t produced.     

Nanocrystalline growth activation energy of alumina polymorphs synthesised by mechanochemical technique

Abstract

Al₂O₃ nanopowders were synthesised via mechanochemical method using AlCl₃ and CaO as raw materials. The effect of thermal treatment on the structural evolutions and morphological characteristics of the nanopowders was investigated using X-ray diffractometry, transmission electron microscopy, scanning electron microscopy, differential thermal analysis and Rietveld refinement. The results showed that the average crystallite size of Al₂O₃ was <100 nm up to ～1200°C. The activation energy for Al₂O₃ nanocrystallite growth during calcinations was calculated to be ～22?598 and 30?195 J mol^?1 for η- and κ-alumina respectively, while for α-Al₂O₃, it was 8373 and 34?131 J mol^?1 at temperatures up to 1200°C and >1200°C respectively. The mechanism of nanocrystalline growth of Al₂O₃ polymorphs during annealing is also discussed.     

Photoresponsive peptide and polypeptide systems: Part 9. Synthesis and reversible photochromism of azo aromatic poly(L-α,ω-diaminobutyric acid)

Poly(L-α,ω-diaminobutyric acid) having azo aromatic side chains was synthesized by the water-soluble carbodiimide procedure. The photoresponsive properties of the polypeptide poly[N⁷-p-(phenylazo)benzoyl-L -α,ω-diaminobutyric acid] (PPABLDBA) due to the trans (about 71%, under visible light) cis (under ultraviolet light) photoisomerization of the azo aromatic moieties in the side chains were investigated by absorption and circular dichroism spectroscopy in hexafluoro-2-propanol (HFIP). The starting slightly turbid solution of trans-PPABLDBA becomes clear on irradiation at 360 nm, accompanied by photoconversion of the conformer of the azo moieties to cis. The backbone conformation of PPABLDBA in HFIP is right-handed helical (helical content, about 60%) when the azo moieties are trans (71%), while the conformation is random coil when cis. The backbone conformational transition of PPABLDBA from helical to coil is mostly reversible under the influence of light.     

Oxidation of lipids: III. Oxidation of methyl linoleate in solution

The effects of oxygen pressure, substrate concentration and solvent on the rate and products of oxidation of methyl linoleate were studied at 50 C with azobisisobutyronitrile as a radical initiator. The absolute and quantitative numbers for oxygen uptake, substrate disappearance, and formation of conjugated diene and hydroperoxides were measured. Under the present conditions, 4 conjugated diene hydroperoxides, 13-hydroperoxy-9-cis, 11-trans-(2a), 13-hydroperoxy-9-trans, 11-trans-(3a), 9-hydroperoxy-10-trans, 12-cis-(4a), and 9-hydroperoxy-10-trans, 12-trans-(5a) octadecadienoic acid methyl esters, were formed almost quantitatively. The rate of oxidation decreased with decreasing oxygen pressure. However, the ratio ofcis,trans totrans,trans hydroperoxides, (2a+4a)/(3a+5a), was independent of oxygen pressure, and this ratio increased with increasing methyl linoleate concentration, as found recently by Porter. Further, the rate of oxidation and the ratio ofcis,trans/trans,trans hydroperoxides were dependent on solvent and increased with an increase in dielectric constant of solvent. A mechanism of methyl linoleate oxidation consistent with these results is discussed. Presented at the 15th Symposium on Oxidation Reactions, Nagoya, October 1981.     

Kinetic and thermodynamic investigation of Arthrospira (Spirulina) platensis fed‐batch cultivation in a tubular photobioreactor using urea as nitrogen source

BACKGROUND: Fed‐batch culture allows the cultivation of Arthrospira platensis using urea as nitrogen source. Tubular photobioreactors substantially increase cell growth, but the successful use of this cheap nitrogen source requires a knowledge of the kinetic and thermodynamic parameters of the process. This work aims at identifying the effect of two independent variables, temperature (T) and urea daily molar flow‐rate (U), on cell growth, biomass composition and thermodynamic parameters involved in this photosynthetic cultivation. RESULTS: The optimal values obtained were T = 32 °C and U = 1.16 mmol L^?1 d^?1, under which the maximum cell concentration was 4186 ± 39 mg L^?1, cell productivity 541 ± 5 mg L^?1 d^?1 and yield of biomass on nitrogen 14.3 ± 0.1 mg mg^?1. Applying an Arrhenius‐type approach, the thermodynamic parameters of growth (ΔH* = 98.2 kJ mol^?1; ΔS* = ? 0.020 kJ mol^?1 K^?1; ΔG* = 104.1 kJ mol^?1) and its thermal inactivation ( kJ mol^?1; kJ mol^?1 K^?1; kJ mol^?1) were estimated. CONCLUSIONS: To maximize cell growth T and U were simultaneously optimized. Biomass lipid content was not influenced by the experimental conditions, while protein content was dependent on both independent variables. Using urea as nitrogen source prevented the inhibitory effect already observed with ammonium salts. Copyright © 2012 Society of Chemical Industry