A Combined Effect of Thermal and Enzymatic Racemization for d‐Aspartic Acid to l‐Aspartic Acid by High‐Performance Liquid Chromatography Assay

The racemization of d ‐aspartic acid to l ‐aspartic acid has been successfully performed with a coupled enzyme system at 90 °C and a pH of about 4.0 by the assay of high‐performance liquid chromatography. This coupled enzymatic racemization is a successive two‐step reaction first induced by d ‐amino acid oxidase and a subsequent coupled reaction by an aminotransferase clonezyme with the help of coenzyme pyridoxal 5′‐phosphate and cosubstrate l ‐glutamate. Due to the very high temperature, part of the l ‐aspartic acid is produced by the thermal effect. In fact the thermal racemization for aspartic acid can proceed from either d ‐ or l ‐aspartic acid via an intermediate fumaric acid and leads to the formation of d ,l ‐malic acid. The formation of α‐oxalacetic acid formed irreversibly from d ‐aspartic acid with d ‐amino acid oxidase can induce a side reaction to l ‐alanine. The thermal effect may also be responsible for the production of d ‐, and l ‐alanine.     

Kinetics of amino acid racemization (epimerization) in the dentine of fossil and modern bear teeth

The present study examines the question of whether heating experiments on modern bear teeth dentine model the pattern of D /L racemization in fossil teeth. Using samples of modern bear teeth dentine heated at 65°C, 85°C (up to 53 days), and 105°C (up to 71 days), and three independently dated fossil bear teeth, we have compared the modes of racemization induced by temperature in the modern samples and by time on the fossil samples. We have studied seven amino acids (aspartic and glutamic acids, alanine, valine, leucine, isoleucine, and phenylalanine) that follow a reversible first‐order kinetic model of racemization (epimerization) either at low or high temperature. We have estimated the Arrhenius parameters, the activation energy E_a and the frequency factor A, first based on the heating experiments, and later including the fossil data. Valine shows no appreciable differences in E_a and A in both estimations, and could then be used with confidence in dating studies. In a lesser extension this also applies to alanine, phenylalanine, leucine, and glutamic acid. Aspartic acid shows a great difference between the temperature‐induced and the time‐induced racemization kinetic models, and it should be used with special care in dating studies, since diagenetic racemization in aspartic acid is extremely sensitive to the thermal history of the site. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 576–591, 2003     

Trimetaphosphate‐Induced Addition of Aspartic Acid to Oligo(glutamic acid)s

When a solution containing 0.01M decaglutamic acid, 0.1–1.0M aspartic acid, 1.0M MgCl₂, and 0.5M sodium trimetaphosphate is allowed to stand at temperatures in the range 0–50°, addition products containing up to ten aspartic acid residues are formed. Addition occurs to the side‐chain carboxy moieties, not to the terminal amine of the decaglutamic acid. A number of other amino acids including glutamic acid, glycine, and histidine fail to react with decaglutamic acid under the same conditions. We believe that the activation of aspartic acid leads to the formation of a cyclic anhydride that is the key intermediate in the reaction.     

Macroporous zirconia particles prepared by subcritical water in batch and flow processes

Porous zirconia particles were synthesized through a low-temperature hydrothermal synthesis process. Under hydrothermal conditions, water can control the direction of crystal growth, morphology, particle size, and size distribution because thermodynamics and transport properties can be controlled by pressure and temperature. In a batch process, the hydrothermal synthesis was conducted at 200–300 °C and 30 MPa with an SUS-304 tube as the reactor. At the same reaction pressure, experiments were also performed for a flow process with temperatures of 180–200 °C. The synthesized products were calcined and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The results showed that the macroporous zirconia particles that were formed had pore diameters around 419 nm. The XRD pattern indicated that the products were composed of zirconium oxide particles with monoclinic, tetragonal, and cubic structures.     

Study on Production of Amino Acids from Bean Dregs by Hydrolysis in Sub-critical Water

This study investigated the production of value‐added amino acids from bean dregs by hydrolysis in subcritical water. It was investigated that the effect of reaction temperature, reaction time and CO₂ on amino acid concentration in the hydrolysates of bean dregs. The product of amino acid was determined by Amino Acid Analyzer. The results show that a variety of amino acids are produced. The concentrations of arginine, lysine and alanine were relatively high in the hydrolysate. Temperature and time have a great influence on the hydrolysis reaction. The effects of reaction temperature and time on concentration of different amino acids vary. The addition of carbon dioxide led to an increase in amino acid yield due to the acceleration of acid hydrolyzed catalysis steps. The highest yield of total amino acids is 22% (0.22 g/g of dry bean dregs) at 330°C and 30 min. This method may provide a practical and economical solution for the disposal of bean dregs wastes.     

Alumina catalyzed reactions of amino acids

Thermal reactions of glycine (Gly), alanine (Ala), leucine (Leu), valine (Val) and proline (Pro) adsorbed on activated alumina were studied by means of thermal analysis. In the absence of alumina, decomposition of amino acids was detected as a sharp endotherm above 200°C, whereas no thermal effects were detectable by differential thermal analysis (DTA) and differential scanning calorimetry (DSC) for amino acid/alumina mixtures. This could be explained by a continuous amino acid condensation to peptides and simultaneous absorption of formed water by alumina, the latter being gradually released at higher temperatures. Thermogravimetry (TG) and differential thermogravimetry (DTG) measurements revealed that the reactions of the amino acids adsorbed on alumina surface were spread over a wide range of temperatures. The catalysis of peptide bond formation on alumina surface at 85°C was proven directly by the identification of the reaction products, mainly dipeptides and cyclic anhydrides. This revised version was published online in August 2006 with corrections to the Cover Date.     

The unimolecular elimination kinetics of benzaldoxime in the gas phase

The kinetics of the gas‐phase elimination of benzaldoxime was determined in a static reaction system over the temperature and pressure range 350°C–400°C and 56–140 Torr, respectively. The products obtained were benzonitrile and water. The reaction was found to be homogeneous, unimolecular, and tend to obey a first‐order rate law. The observed rate coefficient is represented by the following Arrhenius equation: According to kinetic and thermodynamic parameters, the reaction proceeds through a concerted, semi‐polar, four‐membered cyclic transition state type of mechanism. © 2007 Wiley Periodicals, Inc. 39: 145–147, 2007     

Reactions of platinum(II) dipicolinate complex with amino acids—chelation and isomerization

The kinetic course of the reactions of [Pt(dipic_tr)Cl]^? (where H₂dipic = pyridine‐2,6‐dicarboxylic acid; bonded in tridentate mode) with glycine, β‐alanine, and L‐histidine was followed at 25°C in aqueous medium at pH 3.00–10.73 at I = 0.5 mol dm^?3 (LiClO₄) spectrophotometrically and through ¹H NMR spectral analysis. The selectivity of platinum(II) toward the amino acids with regard to chelation and isomerization is controlled by donor atoms and steric properties. The aquation equilibrium of the designated platinum(II) complex also affects the binding rate in the case of glycine and β‐alanine. The reaction products have been isolated and characterized through ¹H NMR spectra. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 262–270, 2002     

Synthesis of linear and hyperbranched poly(etherketone)s containing flexible oxyethylene spacers

As an alternative to strong acid reaction media for the Friedel–Crafts acylation for a polymer‐forming reaction, a mild polyphosphoric acid (PPA) with optimized amount of phosphorous pentoxide (P₂O₅) has been tested for the polymerization of AB monomers 4‐(2‐phenoxyethoxy)benzoic acid and 3‐(2‐phenoxyethoxy)benzoic acid, and an AB₂ monomer 3,5‐bis(2‐phenoxyethoxy)benzoic acid. The reaction progress of AB₂ monomer was conveniently traced by FTIR spectroscopy monitoring aromatic ketone (C?O) stretching bands arisen from carboxylic acid groups at the chain ends and carbonyl groups in the backbone as a function of reaction time at 110 °C. The resultant linear and hyperbranched polymers containing flexible oxyethylene spacers, which were prone to be hydrolyzed in strong acids at elevated temperature, displayed high intrinsic viscosities. Thus, the reaction medium PPA/P₂O₅ mixture as an electrophilic substitution reaction was indeed benign not to depolymerize growing polymer molecules but strong enough for the direct generation of carbonium ion from carboxylic acid to promote efficient polymerization. The resultant hyperbranched poly(etherketone) (PEK) displayed the best solubility among samples. All PEKs showed good thermal stability; glass transition temperatures were in the range of 90–117 °C; 5% weight loss generally occurred at greater than 345 °C in air. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5112–5122, 2007     

Capillary gas chromatography of tert-butyldimethlysilylamino acids with PTV injection

The programmable temperature vaporizing injector (PTV) has been used to study the effects of injection temperature and initial heating period on the FID response factors of TBDMS derivatives of 17 protein amino acids. The relative response factors were calculated for injection temperatures of 50°C, 90°C, 160°C, 220°C, and 260°C with different initial heating periods (1 s, 5 s, and 10 s) and the results compared with the values obtained for the calculated response factors obtained under classical split injection conditions (300°C, continuous). Except for expected peak broadening effects, the initial heating period does not seem to have significative effects on relative peak areas. The response to the derivatives of alanine, glycine, α-aminobutyric acid, valine, proline, methionine, cysteine, phenylalanine, asparagine, and arginine was only slightly affected by increasing the injection temperature whereas the response factors for the derivatives of serine, threonine, glutamic acid, lysine, histidine, tyrosine, and tryptophan were strongly dependent upon initial injection temperatures, decreasing rapidly at temperatures above 160°C. The cold split-splitless injection is clearly advantageous over the classical hot injection techniques for the analysis of this type of aminoacid derivative.     

Effect of reaction conditions on product distribution from the co-pyrolysis of α-amino acids with glucose

The effect of reaction conditions on product distribution from the co-pyrolysis of amino acids with glucose was studied. Three different amino acids, proline, tryptophan and asparagine, were studied. Some experiments were also conducted with aspartic acid, glutamic acid and glutamine. Equimolar binary mixtures of each amino acid and glucose were pyrolyzed at 300 °C to obtain low temperature char (LTC) and low temperature tar (LTT). The LTC in each case was then pyrolyzed further at 625 °C to obtain high temperature char (HTC) and high temperature tar (HTT). In a few experiments, the LTT and HTT were also pyrolyzed at 870 °C (secondary cracking) to obtain the final tars (LTFT and HTFT, respectively) and study the formation of polycyclic aromatic compounds (PACs) via secondary reactions. Experiments were also conducted at different amino acid/glucose molar ratio or at a temperature of 200 °C. All the experiments were performed in an inert atmosphere. The extent of interaction between the amino acids and glucose was determined by comparing the observed results to that calculated from the separate pyrolyses of amino acids and glucose. At 200 °C, the co-pyrolysis led to lower LTC yields relative to the calculated yields. At 300 and 625 °C the yields of LTC and HTC were mostly higher whereas those of LTT and HTT were lower than the calculated yields, except for asparagine and aspartic acid where the observed and calculated LTC yields were comparable. Although proline formed no char in the absence of glucose, it gave a significant amount of nitrogen-containing char when co-pyrolyzed with glucose. The pyrolysis tars contained a number of nitrogenous products not observed from the pyrolysis of amino acids alone. After the secondary cracking, the product changed from mainly single-ring heterocycles to PACs and, in some cases, PAHs.     

Cyclic polypeptides by thermal polymerization of α‐amino acid N‐carboxyanhydrides

The NCAs of the following five amino acids were polymerized in bulk at 120 °C without addition of a catalyst or initiator: sarcosine (Sar), L ‐alanine (L ‐Ala), D ,L ‐phenylalanine (D ,L ‐Phe), D ,L ‐leucine (D ,L ‐Leu) and D ,L ‐valine (D,L ‐Val). The virgin reaction products were characterized by viscosity measurements ¹³C NMR spectroscopy and MALDI‐TOF mass spectrometry. In addition to numerous low molar mass byproducts cyclic polypeptides were formed as the main reaction products in the mass range above 800 Da. Two types of cyclic oligo‐ and polypeptides were detected in all cases with exception of sarcosine NCA, which only yielded one class of cyclic polypeptides. The efficient formation of cyclic oligo‐ and polypeptides explains why high molar mass polymers cannot be obtained by thermal polymerizations of α‐amino acid NCAs. Various polymerization mechanisms were discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4012–4020, 2008     

Synthesis and radical ring‐opening polymerization of vinylcyclopropanes derived from amino acids with hydrophobic moieties

Six 1,1‐disubstituted vinylcyclopropanes (VCP) were synthesized from glycine and amino acids bearing hydrophobic moieties, l ‐alanine, l ‐valine, l ‐leucine, l ‐isoleucine, and l ‐phenylalanine. These VCP derivatives efficiently underwent radical ring‐opening polymerization to afford the corresponding polymers bearing trans‐vinylene moiety in the main chains and the amino acid‐derived chiral moieties in the side chains. The polymers were film‐formable, and in the films of polymers bearing the glycine‐ and alanine‐derived side chains, presence of hydrogen bonding was confirmed by IR analysis. Thermogravimetric analysis of the polymers revealed that the temperatures of 5% weight loss were higher than 300 °C. Differential scanning calorimetry clarified that the polymers were amorphous ones showing glass transition temperatures in a range of 48–80 °C. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3996–4002     

Crystal transition from hydrated chitosan and chitosan/monocarboxylic acid complex to anhydrous chitosan investigated by X‐ray diffraction

We have studied the crystal transition behaviors from hydrated chitosan to anhydrous chitosan by X‐ray diffraction analyses. Hydrated chitosan prepared by deacetylation of crustacean α‐chitin was subjected to the two conversion methods, hydrothermal treatment and high‐humidity treatment via chitosan/monocarboxylic acid complex. The transition by hydrothermal treatment progressed with increasing treatment temperature and time, and the rapid transition occurred above 200 °C. Chitosan/acetic acid complex and chitosan/formic acid complex were prepared by immersing hydrated chitosan in acid solution. The transition from chitosan/acetic acid complex to anhydrous chitosan in high relative humidity condition proceeded with increasing temperature and was complete at 80 °C for 1 h, whereas chitosan/formic acid complex did not convert to anhydrous chitosan under the same conditions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1065–1069     

Effect of Polycondensation Reaction Conditions on the Properties of Thermotropic Liquid‐Crystalline Copolyester

In this study a range of wholly aromatic copolyesters based on kink m‐acetoxybenzoic acid (m‐ABA) monomer (33 mol%) and equimolar‐linear p‐acetoxybenzoic acid (p‐ABA), hydroquinone diacetate (HQDA) and terephthalic acid (TPA) monomers (67 mol%) have been synthesized by melt polycondensation reaction process at 280°C and 260°C for different time intervals. Characterization of copolyesters were performed by solution viscosity measurement, wide–angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), hot‐stage polarized light microscopy, proton‐nuclear magnetic resonance analysis (¹H‐NMR). According to the results obtained, copolyesters showed thermotropic liquid crystalline behavior in an appropriate temperature range. The copolyesters were prepared in high yields. It was observed that the intrinsic viscosities of the copolyesters are increased regularly with increasing polymerization time and temperature. All the copolyesters were soluble in a trifluoroacetic acid/dichloromethane (30:70 v/v) except the copolyesters which were synthesized at 280°C in 5 h. According to the WAXD results; the degree of crystallinity of copolyesters were found to be between 5–15%. DSC and hot stage polarized light microscopy results showed that all the copolyesters are melt processable and a significant molecular interaction exist in a very broad temperature range (160°C and 165°C) in the nematic mesophase. The T_g values are increased with an increasing polycondensation reaction time and temperature and they were observed between 93–126°C. Fibers prepared by a hand‐spinning technique from the polymer melt exhibit well‐developed fibrillar structure parallel to the fiber axis.     

Dynamic hydrothermal synthesis of xonotlite from acid-extracting residues of circulating fluidized bed fly ash

This investigation was made to examine how the conditions of hydrothermal synthesis influence the crystal structure of xonotlite and its morphology. For synthesis, we used acid residues after extracting the alumina from circulating fluidized bed fly ash as raw material, as far as we know, that no one used before. Staring with Ca/Si = 1, hydrothermal temperatures were between 180 and 260 °C. The samples were characterized in terms of mineralogical composition (XRD), morphological analysis (SEM), and thermal gravimetric and differential thermal analyses. During the 72 h synthesis at 240 °C, well formed xonotlite fibers of 10–15 μm long were obtained. Under the same conditions, but at 200 °C, the obtained xonotlite was poorly formed. The results indicated that the residue could be used to prepare pure xonotlite. Different hydrothermal temperatures and holding times have a great impact on crystallinity and morphology of xonotlite.     

Mimicking the prebiotic acidic hydrothermal environment: One‐pot prebiotic hydrothermal synthesis of glucose phosphates

Prebiotic acidic hydrothermal conditions were mimicked, and biological phosphate esters such as glucose‐1‐phosphate, glucose‐6‐phosphate, and glucose‐di‐phosphate were synthesized under hydrothermal conditions, in the presence of a mixture of montmorillonite and kaolinite. Phosphorus was incorporated into the biological world under hydrothermal conditions, leading to the formation of phosphate esters. The synthesis was successfully carried out within a temperature range of 100–160°C. Both isomers of glucose phosphate were obtained, with some detectable amount of glucose‐di‐phosphate. Selected mixture of montmorillonite and kaolinite was found to be essential for the reaction. No products were detected without this catalyst mixture. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:186–191, 2011; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.20675     

Experimental and theoretical study of the homogeneous,unimolecular gas‐phase elimination kinetics of 2‐furoic acid

The kinetics of the gas‐phase elimination kinetics of CO₂ from furoic acid was determined in a static system over the temperature range 415–455°C and pressure range 20–50 Torr. The products are furan and carbon dioxide. The reaction, which is carried out in vessels seasoned with allyl bromide and in the presence of the free‐radical suppressor toluene and/or propene, is homogeneous, unimolecular, and follows a first‐order rate law. The observed rate coefficient is expressed by the following Arrhenius equation: log k₁(s^?1) = (13.28 ± 0.16) ? (220.5 ± 2.1) kJ mol^?1 (2.303 RT)^?1. Theoretical studies carried out at the B3LYP/6‐31++G** computational level suggest two possible mechanisms according to the kinetics and thermodynamic parameters calculated compared with experimental values. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 298–306, 2007     

Recovery of Algal Oil from Marine Green Macro-algae Enteromorpha intestinalis by Acidic–Hydrothermal Process

In this study, the recovery of algal oil from Enteromorpha intestinalis based on an acidic–hydrothermal reaction was investigated. Overall, the algal oil yield after the acidic–hydrothermal reaction was increased under the conditions of high reaction temperature, high catalyst concentration, and long reaction time within the tested ranges. Significantly, catalyst concentration, compared with reaction temperature and time, less affected algal oil recovery. The optimal acidic–hydrothermal reaction conditions for production of algal oil from E. intestinalis were as follows—200 °C reaction temperature, 2.92 % catalyst concentration, 54 min reaction time. Under these conditions, an 18.6 % algal oil yield was obtained. By increasing the combined severity factor, the algae oil recovery yield linearly increased.     

Effect of curing accelerators on thermal imidization of polyamic acids at low temperature

The effect of new additives on the thermal conversion of a range of polyamic acids to polyimides at temperatures lower than 100°C was investigated using infrared spectroscopy. Additives such as m-hydroxybenzoic acid, p-hydroxyphenylacetic acid, and p-hydroxybenzenesulfonic acid were found to be highly effective as curing catalysts or accelerators. The degree of imidization of polyamic acids in the presence of additives increased with an increase in the reaction temperature, and complete imidization was achieved at 140–200°C. The reaction was characterized by a rapid rate that slowed with time. © 1996 John Wiley & Sons, Inc.