The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Enis S Džunuzovic - One of the best experts on this subject based on the ideXlab platform.
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improvement of epoxy resin properties by incorporation of tio2 nanoparticles surface modified with gallic acid esters
Materials & Design, 2014Co-Authors: Tijana S Radoman, Jasna V Džunuzovic, K Jeremic, Branimir N Grgur, Dejan Milicevic, Ivanka G Popovic, Enis S DžunuzovicAbstract:Abstract Epoxy resin/titanium dioxide (epoxy/TiO 2 ) nanocomposites were obtained by incorporation of TiO 2 nanoparticles surface modified with gallic acid esters in epoxy resin. TiO 2 nanoparticles were obtained by acid catalyzed hydrolysis of titanium isopropoxide and their structural characterization was performed by X-ray diffraction and transmission electron microscopy. Three gallic acid esters, having different hydrophobic part, were used for surface modification of the synthesized TiO 2 nanoparticles: propyl, hexyl and lauryl gallate. The gallate chemisorption onto surface of TiO 2 nanoparticles was confirmed by Fourier transform infrared and ultraviolet–visible spectroscopy, while the amount of surface-bonded Gallates was determined using thermogravimetric analysis. The influence of the surface modified TiO 2 nanoparticles, as well as the length of hydrophobic part of the gallate used for surface modification of TiO 2 nanoparticles, on glass transition temperature, barrier, dielectric and anticorrosive properties of epoxy resin was investigated by differential scanning calorimetry, water vapor transmission test, dielectric spectroscopy, electrochemical impedance spectroscopy and polarization measurements. Incorporation of surface modified TiO 2 nanoparticles in epoxy resin caused increase of glass transition temperature and decrease of the water vapor permeability of epoxy resin. The water vapor transmission rate of epoxy/TiO 2 nanocomposites was reduced with increasing hydrophobic part chain length of gallate ligand. Dielectric constant of examined nanocomposites was influenced by gallate used for the modification of TiO 2 nanoparticles. The nanocomposites have better anticorrosive properties than pure epoxy resin, because the surface modified TiO 2 nanoparticles react as oxygen scavengers, which inhibit steel corrosion by cathodic mechanism.
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characterization of in situ prepared nanocomposites of ps and tio2 nanoparticles surface modified with alkyl Gallates effect of alkyl chain length
Polymer Composites, 2013Co-Authors: Enis S Džunuzovic, Jasna V Džunuzovic, Milena Marinoviccincovic, K Jeremic, Tijana S Radoman, Ljubisa Nikolic, Jovan M NedeljkovicAbstract:Incorporation of surface modified TiO2 nanoparticles into polystyrene (PS) matrix was achieved by in situ bulk radical polymerization of styrene. The surface of TiO2 nanoparticles was modified with four amphiphilic esters of the gallic acid (octyl, decyl, lauryl and cetyl gallate), which have different lengths of hydrophobic alkyl chain (C8–C16). FTIR and UV-Vis spectroscopy measurements confirmed the formation of a charge transfer complex between surface Ti atoms and gallic esters. Microstructural characterization of the synthesized nanocomposites revealed that the best dispersion of TiO2 nanoparticles in PS was achieved when the TiO2 surface was modified with octyl gallate. The presence of surface modified TiO2 nanoparticles by different alkyl Gallates does not have an influence on the molecular weight and glass transition temperature of PS matrix. On the other hand, thermal and thermo-oxidative stability of PS were significantly improved by incorporation of surface modified TiO2 nanoparticles. The most pronounced improvement of thermal and thermo-oxidative stability was observed for TiO2 nanoparticles surface modified with octyl gallate. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers
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influence of surface modified tio2 nanoparticles by Gallates on the properties of pmma tio2 nanocomposites
European Polymer Journal, 2012Co-Authors: Enis S Džunuzovic, Jasna V Džunuzovic, Aleksandar D Marinkovic, Milena Marinoviccincovic, K Jeremic, Jovan M NedeljkovicAbstract:Nanocomposites based on poly(methyl methacrylate) (PMMA) and TiO2 nanoparticles were synthesized by in situ radical polymerization of MMA in solution. The surface of TiO2 nanoparticles was modified with four gallic acid esters (octyl, decyl, lauryl and cetyl gallate). The content of Gallates present on the surface of TiO2 was calculated from the TGA results. The influence of length of hydrophobic tail of amphiphilic alkyl Gallates on dis- persability of surface modified TiO2 nanoparticles in PMMA matrix, the molecular weight and glass transition temperature of PMMA, as well as the thermal stability of the prepared PMMA/TiO2 nanocomposites in nitrogen and air was investigated. The influence of content of TiO2 nanoparticles on the properties of these nanocomposites was also examined. The formation of a charge transfer complex between the surface Ti atoms and the Gallates was confirmed by FTIR and UV spectroscopy. TEM micrographs of the PMMA/TiO2 nano- composites revealed that degree of TiO2 aggregation can be significantly lowered by increasing the length of aliphatic part of the used Gallates. The molecular weight of PMMA slightly decreases with the increase of TiO2 content, indicating that used TiO2 nanoparticles act as radical scavengers during the polymerization of MMA. The presence of surface mod- ified TiO2 nanoparticles do not have an influence on the mobility of PMMA chain segments leading to the same values of glass transition temperature for all investigated samples. Thermal and thermo-oxidative stability of the PMMA matrix are improved by introducing TiO2 nanoparticles modified with Gallates.
Tomihiko Higuti - One of the best experts on this subject based on the ideXlab platform.
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triple combinations of lower and longer alkyl Gallates and oxacillin improve antibiotic synergy against methicillin resistant staphylococcus aureus
Antimicrobial Agents and Chemotherapy, 2009Co-Authors: Hirofumi Shibata, Naokatu Arakaki, Tatsuro Nakano, Anowar Khasru M Parvez, Yoshihiro Furukawa, Akio Tomoishi, Shingo Niimi, Tomihiko HigutiAbstract:Using liposome systems, we found that Gallates with short alkyl chains were located in the external medium and those with longer alkyl chains were located in the surface region of lipid bilayer. Combinations of these Gallates remarkably reduced oxacillin MICs against methicillin-resistant Staphylococcus aureus to below the antibiotic breakpoint (≤2 μg/ml).
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alkyl Gallates intensifiers of β lactam susceptibility in methicillin resistant staphylococcus aureus
Antimicrobial Agents and Chemotherapy, 2005Co-Authors: Hirofumi Shibata, Kyoko Kondo, Ryo Katsuyama, Kazuyoshi Kawazoe, Yoichi Sato, Kotaro Murakami, Yoshihisa Takaishi, Naokatu Arakaki, Tomihiko HigutiAbstract:We found that ethyl gallate purified from a dried pod of tara (Caesalpinia spinosa) intensified β-lactam susceptibility in methicillin-resistant and methicillin-sensitive strains of Staphylococcus aureus (MRSA and MSSA strains, respectively). This compound and several known alkyl Gallates were tested with MRSA and MSSA strains to gain new insights into their structural functions in relation to antimicrobial and β-lactam susceptibility-intensifying activities. The maximum activity of alkyl Gallates against MRSA and MSSA strains occurred at 1-nonyl and 1-decyl gallate, with an MIC at which 90% of the isolates tested were inhibited of 15.6 μg/ml. At concentrations lower than the MIC, alkyl Gallates synergistically elevated the susceptibility of MRSA and MSSA strains to β-lactam antibiotics. Such a synergistic activity of the alkyl Gallates appears to be specific for β-lactam antibiotics, because no significant changes were observed in the MICs of other classes of antibiotics examined in this study. The length of the alkyl chain was also associated with the modifying activity of the alkyl Gallates, and the optimum length was C5 to C6. The present work clearly demonstrates that the length of the alkyl chain has a key role in the elevation of susceptibility to β-lactam antibiotics.
Tsutomu Nakayama - One of the best experts on this subject based on the ideXlab platform.
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efficient synthesis of theaflavin 3 gallate by a tyrosinase catalyzed reaction with epicatechin and epigallocatechin gallate in a 1 octanol buffer biphasic system
Journal of Agricultural and Food Chemistry, 2018Co-Authors: Asako Naraikanayama, Yoshinori Uekusa, Fumiyuki Kiuchi, Tsutomu NakayamaAbstract:Theaflavins, the orange-red pigments contained in black tea, have attracted attention as a result of their health-promoting effects. However, their synthetic preparation, in which the enzymatic oxidation of catechol-type catechin is followed by the quinone-induced oxidative dimerization of selectively combined catechol- and pyrogallol-type catechins, provides only a low yield. In the present study, we found that a 1-octanol/buffer biphasic system improved the yield of theaflavin 3-gallate in a tyrosinase-catalyzed synthetic reaction with (-)-epicatechin and (-)-epigallocatechin gallate. When the enzymatic reaction proceeded in a buffer solution, oxidized (-)-epigallocatechin gallate was preferentially used for self-dimerization. However, self-dimerization was suppressed in the octanol phase, allowing oxidized (-)-epigallocatechin gallate to participate in coupling with (-)-epicatechin quinone, leading to effective production of theaflavin 3-gallate. Furthermore, the preferential localization of theaflavin 3-gallate in the octanol phase prevented (-)-epicatechin-quinone-induced degradation.
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Efficient Synthesis of Theaflavin 3‑Gallate by a Tyrosinase-Catalyzed Reaction with (−)-Epicatechin and (−)-Epigallocatechin Gallate in a 1‑Octanol/Buffer Biphasic System
2018Co-Authors: Asako Narai-kanayama, Yoshinori Uekusa, Fumiyuki Kiuchi, Tsutomu NakayamaAbstract:Theaflavins, the orange–red pigments contained in black tea, have attracted attention as a result of their health-promoting effects. However, their synthetic preparation, in which the enzymatic oxidation of catechol-type catechin is followed by the quinone-induced oxidative dimerization of selectively combined catechol- and pyrogallol-type catechins, provides only a low yield. In the present study, we found that a 1-octanol/buffer biphasic system improved the yield of theaflavin 3-gallate in a tyrosinase-catalyzed synthetic reaction with (−)-epicatechin and (−)-epigallocatechin gallate. When the enzymatic reaction proceeded in a buffer solution, oxidized (−)-epigallocatechin gallate was preferentially used for self-dimerization. However, self-dimerization was suppressed in the octanol phase, allowing oxidized (−)-epigallocatechin gallate to participate in coupling with (−)-epicatechin quinone, leading to effective production of theaflavin 3-gallate. Furthermore, the preferential localization of theaflavin 3-gallate in the octanol phase prevented (−)-epicatechin-quinone-induced degradation
Jovan M Nedeljkovic - One of the best experts on this subject based on the ideXlab platform.
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characterization of in situ prepared nanocomposites of ps and tio2 nanoparticles surface modified with alkyl Gallates effect of alkyl chain length
Polymer Composites, 2013Co-Authors: Enis S Džunuzovic, Jasna V Džunuzovic, Milena Marinoviccincovic, K Jeremic, Tijana S Radoman, Ljubisa Nikolic, Jovan M NedeljkovicAbstract:Incorporation of surface modified TiO2 nanoparticles into polystyrene (PS) matrix was achieved by in situ bulk radical polymerization of styrene. The surface of TiO2 nanoparticles was modified with four amphiphilic esters of the gallic acid (octyl, decyl, lauryl and cetyl gallate), which have different lengths of hydrophobic alkyl chain (C8–C16). FTIR and UV-Vis spectroscopy measurements confirmed the formation of a charge transfer complex between surface Ti atoms and gallic esters. Microstructural characterization of the synthesized nanocomposites revealed that the best dispersion of TiO2 nanoparticles in PS was achieved when the TiO2 surface was modified with octyl gallate. The presence of surface modified TiO2 nanoparticles by different alkyl Gallates does not have an influence on the molecular weight and glass transition temperature of PS matrix. On the other hand, thermal and thermo-oxidative stability of PS were significantly improved by incorporation of surface modified TiO2 nanoparticles. The most pronounced improvement of thermal and thermo-oxidative stability was observed for TiO2 nanoparticles surface modified with octyl gallate. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers
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influence of surface modified tio2 nanoparticles by Gallates on the properties of pmma tio2 nanocomposites
European Polymer Journal, 2012Co-Authors: Enis S Džunuzovic, Jasna V Džunuzovic, Aleksandar D Marinkovic, Milena Marinoviccincovic, K Jeremic, Jovan M NedeljkovicAbstract:Nanocomposites based on poly(methyl methacrylate) (PMMA) and TiO2 nanoparticles were synthesized by in situ radical polymerization of MMA in solution. The surface of TiO2 nanoparticles was modified with four gallic acid esters (octyl, decyl, lauryl and cetyl gallate). The content of Gallates present on the surface of TiO2 was calculated from the TGA results. The influence of length of hydrophobic tail of amphiphilic alkyl Gallates on dis- persability of surface modified TiO2 nanoparticles in PMMA matrix, the molecular weight and glass transition temperature of PMMA, as well as the thermal stability of the prepared PMMA/TiO2 nanocomposites in nitrogen and air was investigated. The influence of content of TiO2 nanoparticles on the properties of these nanocomposites was also examined. The formation of a charge transfer complex between the surface Ti atoms and the Gallates was confirmed by FTIR and UV spectroscopy. TEM micrographs of the PMMA/TiO2 nano- composites revealed that degree of TiO2 aggregation can be significantly lowered by increasing the length of aliphatic part of the used Gallates. The molecular weight of PMMA slightly decreases with the increase of TiO2 content, indicating that used TiO2 nanoparticles act as radical scavengers during the polymerization of MMA. The presence of surface mod- ified TiO2 nanoparticles do not have an influence on the mobility of PMMA chain segments leading to the same values of glass transition temperature for all investigated samples. Thermal and thermo-oxidative stability of the PMMA matrix are improved by introducing TiO2 nanoparticles modified with Gallates.
K Jeremic - One of the best experts on this subject based on the ideXlab platform.
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improvement of epoxy resin properties by incorporation of tio2 nanoparticles surface modified with gallic acid esters
Materials & Design, 2014Co-Authors: Tijana S Radoman, Jasna V Džunuzovic, K Jeremic, Branimir N Grgur, Dejan Milicevic, Ivanka G Popovic, Enis S DžunuzovicAbstract:Abstract Epoxy resin/titanium dioxide (epoxy/TiO 2 ) nanocomposites were obtained by incorporation of TiO 2 nanoparticles surface modified with gallic acid esters in epoxy resin. TiO 2 nanoparticles were obtained by acid catalyzed hydrolysis of titanium isopropoxide and their structural characterization was performed by X-ray diffraction and transmission electron microscopy. Three gallic acid esters, having different hydrophobic part, were used for surface modification of the synthesized TiO 2 nanoparticles: propyl, hexyl and lauryl gallate. The gallate chemisorption onto surface of TiO 2 nanoparticles was confirmed by Fourier transform infrared and ultraviolet–visible spectroscopy, while the amount of surface-bonded Gallates was determined using thermogravimetric analysis. The influence of the surface modified TiO 2 nanoparticles, as well as the length of hydrophobic part of the gallate used for surface modification of TiO 2 nanoparticles, on glass transition temperature, barrier, dielectric and anticorrosive properties of epoxy resin was investigated by differential scanning calorimetry, water vapor transmission test, dielectric spectroscopy, electrochemical impedance spectroscopy and polarization measurements. Incorporation of surface modified TiO 2 nanoparticles in epoxy resin caused increase of glass transition temperature and decrease of the water vapor permeability of epoxy resin. The water vapor transmission rate of epoxy/TiO 2 nanocomposites was reduced with increasing hydrophobic part chain length of gallate ligand. Dielectric constant of examined nanocomposites was influenced by gallate used for the modification of TiO 2 nanoparticles. The nanocomposites have better anticorrosive properties than pure epoxy resin, because the surface modified TiO 2 nanoparticles react as oxygen scavengers, which inhibit steel corrosion by cathodic mechanism.
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characterization of in situ prepared nanocomposites of ps and tio2 nanoparticles surface modified with alkyl Gallates effect of alkyl chain length
Polymer Composites, 2013Co-Authors: Enis S Džunuzovic, Jasna V Džunuzovic, Milena Marinoviccincovic, K Jeremic, Tijana S Radoman, Ljubisa Nikolic, Jovan M NedeljkovicAbstract:Incorporation of surface modified TiO2 nanoparticles into polystyrene (PS) matrix was achieved by in situ bulk radical polymerization of styrene. The surface of TiO2 nanoparticles was modified with four amphiphilic esters of the gallic acid (octyl, decyl, lauryl and cetyl gallate), which have different lengths of hydrophobic alkyl chain (C8–C16). FTIR and UV-Vis spectroscopy measurements confirmed the formation of a charge transfer complex between surface Ti atoms and gallic esters. Microstructural characterization of the synthesized nanocomposites revealed that the best dispersion of TiO2 nanoparticles in PS was achieved when the TiO2 surface was modified with octyl gallate. The presence of surface modified TiO2 nanoparticles by different alkyl Gallates does not have an influence on the molecular weight and glass transition temperature of PS matrix. On the other hand, thermal and thermo-oxidative stability of PS were significantly improved by incorporation of surface modified TiO2 nanoparticles. The most pronounced improvement of thermal and thermo-oxidative stability was observed for TiO2 nanoparticles surface modified with octyl gallate. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers
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influence of surface modified tio2 nanoparticles by Gallates on the properties of pmma tio2 nanocomposites
European Polymer Journal, 2012Co-Authors: Enis S Džunuzovic, Jasna V Džunuzovic, Aleksandar D Marinkovic, Milena Marinoviccincovic, K Jeremic, Jovan M NedeljkovicAbstract:Nanocomposites based on poly(methyl methacrylate) (PMMA) and TiO2 nanoparticles were synthesized by in situ radical polymerization of MMA in solution. The surface of TiO2 nanoparticles was modified with four gallic acid esters (octyl, decyl, lauryl and cetyl gallate). The content of Gallates present on the surface of TiO2 was calculated from the TGA results. The influence of length of hydrophobic tail of amphiphilic alkyl Gallates on dis- persability of surface modified TiO2 nanoparticles in PMMA matrix, the molecular weight and glass transition temperature of PMMA, as well as the thermal stability of the prepared PMMA/TiO2 nanocomposites in nitrogen and air was investigated. The influence of content of TiO2 nanoparticles on the properties of these nanocomposites was also examined. The formation of a charge transfer complex between the surface Ti atoms and the Gallates was confirmed by FTIR and UV spectroscopy. TEM micrographs of the PMMA/TiO2 nano- composites revealed that degree of TiO2 aggregation can be significantly lowered by increasing the length of aliphatic part of the used Gallates. The molecular weight of PMMA slightly decreases with the increase of TiO2 content, indicating that used TiO2 nanoparticles act as radical scavengers during the polymerization of MMA. The presence of surface mod- ified TiO2 nanoparticles do not have an influence on the mobility of PMMA chain segments leading to the same values of glass transition temperature for all investigated samples. Thermal and thermo-oxidative stability of the PMMA matrix are improved by introducing TiO2 nanoparticles modified with Gallates.
