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Differential Scanning Calorimetry Analysis (differential + scanning_calorimetry_analysis)
Selected AbstractsCrystal structure of highly thermostable glycerol kinase from a hyperthermophilic archaeon in a dimeric formFEBS JOURNAL, Issue 10 2008Yuichi Koga The crystal structure of glycerol kinase from the hyperthermophilic archaeon Thermococcus kodakaraensis (Tk-GK) in a dimeric form was determined at a resolution of 2.4 Å. This is the first crystal structure of a hyperthermophilic glycerol kinase. The overall structure of the Tk-GK dimer is very similar to that of the Escherichia coli glycerol kinase (Ec-GK) dimer. However, two dimers of Ec-GK can associate into a tetramer with a twofold axis, whereas those of Tk-GK cannot. This may be the reason why Tk-GK is not inhibited by fructose 1,6-bisphosphate, because the fructose 1,6-bisphosphate binding site is produced only when a tetrameric structure is formed. Differential scanning calorimetry analyses indicate that Tk-GK is a highly thermostable protein with a melting temperature (Tm) of 105.4 °C for the major transition. This value is higher than that of Ec-GK by 34.1 °C. Comparison of the crystal structures of Tk-GK and Ec-GK indicate that there is a marked difference in the number of ion pairs in the ,16 helix. Four ion pairs, termed IP1,IP4, are formed in this helix in the Tk-GK structure. To examine whether these ion pairs contribute to the stabilization of Tk-GK, four Tk-GK and four Ec-GK derivatives with reciprocal mutations at the IP1,IP4 sites were constructed. The determination of their stabilities indicates that the removal of each ion pair does not affect the stability of Tk-GK significantly, whereas the mutations designed to introduce one of these ion pairs stabilize or destabilize Ec-GK considerably. These results suggest that the ion pairs in the ,16 helix contribute to the stabilization of Tk-GK in a cooperative manner. [source] Lipase-mediated Acidolysis of Fully Hydrogenated Soybean Oil with Conjugated Linoleic AcidJOURNAL OF FOOD SCIENCE, Issue 1 2004J. Ortega ABSTRACT: Interesterification (acidolysis) of fully hydrogenated soybean oil (melting point = 69.9 °C) with conjugated linoleic acid (CLA) was carried out in a batch reactor at 75 °C. Lipases from Candida antarctica, Rhizomucor miehei, Pseudomonas sp., and Thermomyces lanuginosus were used at 5% (wt/wt) of the total substrate load. The lipase from Rhizomucor miehei produced the fastest reaction rates, and the greatest extent of incorporation of CLA residues in acylglycerols was achieved in 12 h. Lipases from C. antarctica and T. lanuginosus produced slower initial rates, and maximum extents of incorporation of CLA residues were achieved in 24 h. The lipase from Pseudomonas sp. produced the slowest initial rate. The corresponding maximum extent of incorporation was reached in 48 h. Differential scanning calorimetry analysis of the triacylglycerol (TAG) fractions produced by C. antarctica, R. miehei, and T. lanuginosus lipases after purification by solid phase extraction showed little variation in melting point (60.4 °C, 62.8 °C, and 60.1 °C, respectively). By contrast, the corresponding TAG fraction produced by the Pseudomonas sp. lipase melted at 48.4 °C. The positional distribution of the TAGs produced by the lipase from Pseudomonas sp. differed appreciably from those produced by the other enzymes. [source] Synthesis, crystallization, and morphology of star-shaped poly(,-caprolactone)JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2005Jing-Liang Wang Abstract Six-arm star-shaped poly(,-caprolactone) (sPCL) was successfully synthesized via the ring-opening polymerization of ,-caprolactone with a commercial dipentaerythritol as the initiator and stannous octoate (SnOct2) as the catalyst in bulk at 120 °C. The effects of the molar ratios of both the monomer to the initiator and the monomer to the catalyst on the molecular weight of the polymer were investigated in detail. The molecular weight of the polymer linearly increased with the molar ratio of the monomer to the initiator, and the molecular weight distribution was very low (weight-average molecular weight/number-average molecular weight = 1.05,1.24). However, the molar ratio of the monomer to the catalyst had no apparent influence on the molecular weight of the polymer. Differential scanning calorimetry analysis indicated that the maximal melting point, cold crystallization temperature, and degree of crystallinity of the sPCL polymers increased with increasing molecular weight, and crystallinities of different sizes and imperfect crystallization possibly did not exist in the sPCL polymers. Furthermore, polarized optical microscopy analysis indicated that the crystallization rate of the polymers was in the order of linear poly(,-caprolactone) (LPCL) > sPCL5 > sPCL1 (sPCL5 had a higher molecular weight than both sPCL1 and LPCL, which had similar molecular weights). Both LPCL and sPCL5 exhibited a good spherulitic morphology with apparent Maltese cross patterns, whereas sPCL1 showed a poor spherulitic morphology. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5449,5457, 2005 [source] Preparation of novel polyindene/polyoxymethylene blends and investigation of their propertiesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Tenzile Zilhan Cabuk Abstract In this study, the conducting homopolymer of indene was synthesized by a chemical polymerization method in a nonaqueous medium, and polyindene (PIn)/polyoxymethylene (POM) blends were prepared. The physical, chemical, thermal, and spectral properties of the synthesized homopolymer and their blends were investigated. The conductivities of PIn and the PIn/POM blends were measured with a four-probe technique. The conductivity of PIn was determined as 1.16 × 10,5 S/cm, whereas the conductivities of the PIn/POM blends were determined to be in the range 3.16 × 10,6 to 9.8 × 10,6 S/cm. From Gouy scale magnetic susceptibility measurements, we found that PIn and the PIn/POM blends had polaron natures. The amount of Fe (milligrams per gram) in the PIn and PIn/POM structures were determined by inductively coupled plasma,optic emission spectrometry. Fourier transform infrared spectra were taken to analyze the structural properties of PIn and the PIn/POM blends. The thermal properties of PIn and PIn/POM blends were investigated with thermogravimetric analysis and differential scanning calorimetry analyses, and we found that they showed adequate thermal stability. According to the initial decomposition temperature among the blends, the blend including 16% PIn had the highest decomposition temperature with 244°C. The morphological structures of the PIn, POM, and blends were clarified with scanning electron microscopy. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Effect of Organic Modification on the Compatibilization Efficiency of Clay in an Immiscible Polymer BlendMACROMOLECULAR RAPID COMMUNICATIONS, Issue 20 2005Suprakas Sinha Ray Abstract Summary: This communication describes the effect of organic modifier miscibility with the matrices, and the effect of the initial interlayer spacing of the organoclay, on the overall morphology and properties of an immiscible polycarbonate/poly(methyl methacrylate) blend. By varying the organic-modifier-specific interactions with the blend matrices at the same time as changing the initial interlayer spacing of the organoclay, different levels of compatibilization were revealed. The evidence for the interfacial compatibilization of the organoclay was assessed by scanning electron microscopy observations and was supported by differential scanning calorimetry analyses. The effect on the level of clay exfoliation was also examined. Differential scanning calorimetry scans of virgin, montmorillonite, and various organically modified montmorillonite-compatibilized 40PC/60PMMA blends [source] Tensile and lignocellulosic properties of Prosopis chilensis natural fabricJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010G. Venkata Reddy Abstract The uniaxial natural fabric Prosopis chilensis was treated with NaOH (alkali), poly (vinyl alcohol) (PVA), and polycarbonate (PC) solutions. The Prosopis chilensis fabric belongs to Leguminosae family. The properties of ligno-cellulosic fabric and the effect of sodium hydroxide (NaOH) treatment were evaluated using thermal analysis by means of thermogravimetric and differential scanning calorimetry analysis, Autonated total reflection-fourier transform infrared spectroscopy, X-ray diffraction (XRD), and field emission scanning electron microscopy. Tensile properties of the untreated and fabric treated with NaOH, PVA, and PC were also studied to assess their performance. The fabric has good thermal resistance on alkali treatment. The FTIR method indicates lowering the hemi cellulose and lignin content by alkali treatment. Further, the XRD studies reveal that crystallinity of the fabric increases on alkali treatment. Tensile properties of the fabric were enhanced on treatments with NaOH, PVA, and PC treatments. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Influence of stereochemistry on the thermal properties of partially cycloaliphatic polyamidesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2002Bert Vanhaecht Abstract The effects of the partial substitution of 1,4-disubstituted cyclohexane monomers for linear aliphatic monomers in polyamides are discussed. More specifically, the relation between the stereochemistry of the cycloaliphatic residues and the thermal properties [melting temperature (Tm) and crystallization temperature (Tcr)] was investigated. For this purpose, two different types of copolyamides were synthesized: in polyamides 12.6, the adipic acid residues were partially replaced by cis/trans -1,4-cyclohexanedicarboxylic acid (1,4-CHDA), whereas in polyamides 4.14, the 1,4-diaminobutane residues were partially substituted with cis/trans -1,4-diaminocyclohexane (1,4-DACH). For both systems, increasing the degree of substitution of cycloaliphatic residues for linear aliphatic residues resulted in a rise of both Tm and Tcr. This points to the isomorphous crystallization of the linear and cycloaliphatic residues. In contrast to the use of 1,4-DACH as a comonomer, 1,4-CHDA residues showed isomerization upon thermal treatment of the polyamides. This isomerization of the cyclohexane residues influenced the thermal properties of the copolyamides. The use of a nonisomerizing cis,trans mixture of 1,4-DACH exhibited the large influence of the stereochemistry of the cycloaliphatic residues on the Tm of the copolyamides. For both the 1,4-CHDA- and 1,4-DACH-based copolyamides, differential scanning calorimetry analysis revealed that recrystallization occurs during melting. This exothermal effect becomes less pronounced with an increasing content of rigid cycloaliphatic residues. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1962,1971, 2002 [source] Synthesis of new photoresponsive polyesters containing norbornadiene residues by the polyaddition of donor,acceptor norbornadiene dicarboxylic acid diglycidyl ester with dicarboxylic acids and their photochemical propertiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2001Yousuke Konno Abstract A donor,acceptor norbornadiene derivative, 5-(4-methoxyphenyl)-1,4,6,7,7-pentamethyl-2,5-norbornadiene-2,3-dicarboxylic acid diglycidyl ester (D,A NDGE), was synthesized by the reaction of the cesium salt of 5-(4-methoxyphenyl)-1,4,6,7,7-pentamethyl-2,5-norbornadiene-2,3-dicarboxylic acid with epibromohydrin in N -methyl- pyrrolidone (NMP). The polyaddition reactions of D,A NDGE with certain dicarboxylic acids were carried out with tetrabutylammonium bromide as a catalyst in NMP, producing corresponding polyesters containing D,A norbornadiene (NBD) residues in the main chain in fair to good yields. The photoisomerization of the D,A NBD residues in the polyesters proceeded very smoothly, forming the corresponding quadricyclane groups. The photoreactivities of the D,A NBD residues in the polymer were 50 times higher than those of the NBD residues in the film state and 60 times higher than those in a tetrahydrofuran solution. The stored energy in the quadricyclane groups of the polymers was about 45,55 kJ/mol according to differential scanning calorimetry analysis of the irradiated polymer films. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2683,2690, 2001 [source] A Scalable Route to Highly Functionalized Multi-Walled Carbon Nanotubes on a Large ScaleMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 8 2008Xianhong Chen Abstract A scalable and solvent-free chemical process to obtain highly functionalized and dispersible multi-walled carbon nanotubes is reported. Highly functionalized multi-walled carbon nanotubes have been prepared using in situ generated aryl diazonium salts in the presence of ammonium persulfate and 2,2,-azoisobutyronitrile by solvent-free techniques. In the Raman spectra of the resulting materials, characteristic peaks, the D- and G-bands, are shifted by about 10 cm,1 to lower frequencies. At the same time, the relative intensity ratios between the D- and G-bands increase in comparison to that in the spectrum of the purified product. Fourier-transform infrared spectroscopy reveals the presence of the functional groups on the surface. Transmission electron microscopy images directly confirm the significant build-up of sidewall organic moieties on the treated materials. The weight loss of various functional moieties determined by thermogravimetry,differential scanning calorimetry analysis is about 18,33%. The dispersibility of the functionalized materials in solvents, such as chloroform, tetrahydrofuran, and water, is obviously improved. [source] | |||||||||||||