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Sanket B. Dusunge - One of the best experts on this subject based on the ideXlab platform.
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Thiolated xyloglucan: Synthesis, characterization and evaluation as mucoadhesive in situ gelling agent
Carbohydrate Polymers, 2013Co-Authors: Hitendra S. Mahajan, Vinod Kumar Tyagi, Ravindra R. Patil, Sanket B. DusungeAbstract:The objective of present study was to enhance bioadhesive potential of xyloglucan by thiolation. Thiolation of xyloglucan was achieved with esterification with thioglycolic acid. Thiolated xyloglucan was characterized by NMR, DSC, and XRD analysis. Thiolated xyloglucan was determined to possess 4 mmol of thiol groups/g of polymer by Ellman's method. Comparative evaluation of mucoadhesive property of ondansetron containing in situ gel system of xyloglucan and thiolated xyloglucan using sheep nasal mucosa revealed higher ex vivo bioadhesion time of thiolated xyloglucan as compared to xyloglucan. Improved mucoadhesive property of thiolated xyloglucan over the xyloglucan can be attributed to the formation of disulfide bond between mucus and thiolated xyloglucan. Ex vivo permeation study conducted using sheep nasal showed improved drug permeation in formulation based on thiolated xyloglucan. In conclusion, thiolation of xyloglucan improves its bioadhesion and drug permeation without affecting the resultant gel properties. © 2012 Elsevier Ltd.
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Thiolated xyloglucan: Synthesis, characterization and evaluation as mucoadhesive in situ gelling agent.
Carbohydrate Polymers, 2012Co-Authors: Hitendra S. Mahajan, Vinod Kumar Tyagi, Ravindra R. Patil, Sanket B. DusungeAbstract:Abstract The objective of present study was to enhance bioadhesive potential of xyloglucan by thiolation. Thiolation of xyloglucan was achieved with esterification with thioglycolic acid. Thiolated xyloglucan was characterized by NMR, DSC, and XRD analysis. Thiolated xyloglucan was determined to possess 4 mmol of thiol groups/g of polymer by Ellman's method. Comparative evaluation of mucoadhesive property of ondansetron containing in situ gel system of xyloglucan and thiolated xyloglucan using sheep nasal mucosa revealed higher ex vivo bioadhesion time of thiolated xyloglucan as compared to xyloglucan. Improved mucoadhesive property of thiolated xyloglucan over the xyloglucan can be attributed to the formation of disulfide bond between mucus and thiolated xyloglucan. Ex vivo permeation study conducted using sheep nasal showed improved drug permeation in formulation based on thiolated xyloglucan. In conclusion, thiolation of xyloglucan improves its bioadhesion and drug permeation without affecting the resultant gel properties.
Heinrich Vahrenkamp - One of the best experts on this subject based on the ideXlab platform.
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Tris(thioimidazolyl)borate-zinc-thiolate complexes for the modeling of biological thiolate alkylations.
Inorganic Chemistry, 2005Co-Authors: Mohamed M. Ibrahim, Jan Seebacher, Gunther Steinfeld, Heinrich VahrenkampAbstract:The S3Zn−SR coordination of thiolate-alkylating enzymes such as the Ada DNA repair protein was reproduced in tris(thioimidazolyl)borate-zinc-thiolate complexes TtiRZn−SR‘. Four different TtiR ligands and nine different Thiolates were employed, yielding a total of 12 new complexes. In addition, one TtiRZn−SH complex and two thiolate-bridged [TtiR-SEt-TtiR]+ complexes were obtained. A selection of six thiolate complexes was converted with methyl iodide to the corresponding methyl thioethers and TtiRZn−I. According to a kinetic analysis these reactions are second-order processes, which implies that the alkylations are likely to occur at the zinc-bound Thiolates. They are much faster than the alkylations of zinc Thiolates with N3 or N2S tripod ligands. The most reactive thiolate, TtiXylZn−SEt, reacts slowly with trimethyl phosphate in a nonpolar medium at room temperature, yielding methyl-ethyl-thioether and TtiXylZn−OPO(OMe)2 which can be converted back to the thiolate complex with NaSEt. This is the closest...
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Biomimetic Thiolate Alkylation with Zinc Pyrazolylbis(thioimidazolyl)borate Complexes
European Journal of Inorganic Chemistry, 2005Co-Authors: Mohamed M. Ibrahim, Jan Seebacher, Guosen He, Boumahdi Benkmil, Heinrich VahrenkampAbstract:The NS2ZnX coordination in thiolate-alkylating zinc enzymes is reproduced in (tripod)ZnX complexes with substituted pyrazolylbis(thioimidazolyl)borate tripod ligands. Intermediate (tripod)Zn nitrates and perchlorates are converted into (tripod)Zn Thiolates, including the biologically relevant homocysteinate. Methylation with CH3I converts these to (tripod)ZnI and the corresponding thioethers CH3SR, including methionine. A kinetic investigation has shown the alkylations to be intramolecular SN2 processes that take place at the zinc-bound Thiolates. They are considerably faster for the (NS2)Zn Thiolates than for the (N2S)- and (N3)Zn-Thiolates with similar pyrazolylborate-derived tripod ligands, in agreement with Nature’s choice of an NS2 donor set for zinc. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
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Zinc-thiolate complexes of the bis(pyrazolyl)(thioimidazolyl)hydroborate tripods for the modeling of thiolate alkylating enzymes.
Inorganic Chemistry, 2005Co-Authors: Mian Ji, Boumahdi Benkmil, Heinrich VahrenkampAbstract:The new tripod ligands bis(pyrazolyl)(3-tert-butyl-2-thioimidazol-1-yl)hydroborate (L1) and bis(pyrazolyl)(3-isopropyl-2-thioimidazol-1-yl)hydroborate (L2), together with zinc nitrate or zinc chloride and the corresponding Thiolates, have yielded a total of 17 zinc−thiolate complexes. These comprise aliphatic as well as aromatic Thiolates and a cysteine derivative. Structure determinations have confirmed the tetrahedral ZnN2S2 coordination in the complexes. Upon reaction with methyl iodide, the species L1·Zn−SR are slowly converted to L1·Zn−I and the free thioethers CH3SR. A kinetic analysis has shown these alkylations to be about 1 order of magnitude slower than those of the tris(pyrazolyl)borate complexes TpPh,MeZn−SR. Alkylations with trimethyl phosphate were found to proceed very slowly even in DMSO at 80 °C.
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alcohol and aldehyde adducts of zinc Thiolates structural modeling of alcoholdehydrogenase
Inorganic Chemistry, 1999Co-Authors: Bodo Muller, Astrid Schneider, Markus Tesmer, Heinrich VahrenkampAbstract:: Bis(pentafluorothiophenolato)zinc (1) and bis(2,4,6-triisopropylthiophenolato)zinc (2) can be combined with nitrogen-containing derivatives of benzyl alcohol and benzaldehyde to form (N,O-chelate) zinc Thiolates. 2-Pyridylmethanol as well as 2-quinolylmethanol (HetMeOH) yield [(HetMeO)Zn(SR)](4) (3, 4) having a cyclo-Zn(4)(m-O)(4) backbone and only terminal SR. Likewise, thiolate 1 and 2-(dimethylamino)benzyl alcohol form zwitterionic [(dimethylammoniobenzylato)Zn(SR)(2)](2) (5) with bridging alkoxide and terminal thiolate. In contrast, 6-picolylmethanol (PicMeOH) and thiolate 1 result in [(PicMeOH)Zn(SC(6)F(5))(2)] (6) containing zinc in a tetrahedral ZnNS(2)O, environment. Simple aromatic aldehydes form polymeric complexes [(RCHO)Zn(SC(6)F(5))(2)] (7: R = p-tolyl, 8: R = mesityl) with a [Zn-S](infinity) backbone. Chelating aldehydes (CA) yield mononuclear complexes with tetrahedral ZnNS(2)O coordination [(CA)Zn(SC(6)F(5))(2)] (9, CA = pyridine-2-carbaldehyde; 10, CA = 6-methylpyridine-2-carbaldehyde; 11, CA = 6-methoxypyridine-2-carbaldehyde; 12, CA = quinoline-2-carbaldehyde; 13, CA = 2-(dimethylamino)benzaldehyde). In contrast, N-methylimidazole-2-carbaldehyde (ImA) is coordinated twice in tetrahedral [(ImA)(2)Zn(SC(6)F(5))(2)] (14) lacking any Zn-O interactions. Pyridine-2,6-dicarbaldehyde (PDA) forms trigonal bipyramidal [(PDA)Zn(SC(6)F(5))(2)] (15) with ZnNO(2)S(2) ligation. The structures of 3, 4, 6, 8, 10, 11, 13, and 14 were determined crystallographically, and the structures of 5 and 15 were deduced from those of the corresponding ZnBr(2) complexes. The ZnNS(2)O coordination pattern observed for the enzyme has been reproduced to a very good approximation. In complexes 6 and 10, which are almost superimposable, it is realized for both the corresponding alcohol and aldehyde.
Hitendra S. Mahajan - One of the best experts on this subject based on the ideXlab platform.
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Thiolated xyloglucan: Synthesis, characterization and evaluation as mucoadhesive in situ gelling agent
Carbohydrate Polymers, 2013Co-Authors: Hitendra S. Mahajan, Vinod Kumar Tyagi, Ravindra R. Patil, Sanket B. DusungeAbstract:The objective of present study was to enhance bioadhesive potential of xyloglucan by thiolation. Thiolation of xyloglucan was achieved with esterification with thioglycolic acid. Thiolated xyloglucan was characterized by NMR, DSC, and XRD analysis. Thiolated xyloglucan was determined to possess 4 mmol of thiol groups/g of polymer by Ellman's method. Comparative evaluation of mucoadhesive property of ondansetron containing in situ gel system of xyloglucan and thiolated xyloglucan using sheep nasal mucosa revealed higher ex vivo bioadhesion time of thiolated xyloglucan as compared to xyloglucan. Improved mucoadhesive property of thiolated xyloglucan over the xyloglucan can be attributed to the formation of disulfide bond between mucus and thiolated xyloglucan. Ex vivo permeation study conducted using sheep nasal showed improved drug permeation in formulation based on thiolated xyloglucan. In conclusion, thiolation of xyloglucan improves its bioadhesion and drug permeation without affecting the resultant gel properties. © 2012 Elsevier Ltd.
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Thiolated xyloglucan: Synthesis, characterization and evaluation as mucoadhesive in situ gelling agent.
Carbohydrate Polymers, 2012Co-Authors: Hitendra S. Mahajan, Vinod Kumar Tyagi, Ravindra R. Patil, Sanket B. DusungeAbstract:Abstract The objective of present study was to enhance bioadhesive potential of xyloglucan by thiolation. Thiolation of xyloglucan was achieved with esterification with thioglycolic acid. Thiolated xyloglucan was characterized by NMR, DSC, and XRD analysis. Thiolated xyloglucan was determined to possess 4 mmol of thiol groups/g of polymer by Ellman's method. Comparative evaluation of mucoadhesive property of ondansetron containing in situ gel system of xyloglucan and thiolated xyloglucan using sheep nasal mucosa revealed higher ex vivo bioadhesion time of thiolated xyloglucan as compared to xyloglucan. Improved mucoadhesive property of thiolated xyloglucan over the xyloglucan can be attributed to the formation of disulfide bond between mucus and thiolated xyloglucan. Ex vivo permeation study conducted using sheep nasal showed improved drug permeation in formulation based on thiolated xyloglucan. In conclusion, thiolation of xyloglucan improves its bioadhesion and drug permeation without affecting the resultant gel properties.
Jeffrey R Reimers - One of the best experts on this subject based on the ideXlab platform.
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gold surfaces and nanoparticles are protected by au 0 thiyl species and are destroyed when au i Thiolates form
Proceedings of the National Academy of Sciences of the United States of America, 2016Co-Authors: Jens Ulstrup, Arnab Halder, Jeffrey R Reimers, Michael J Ford, Noel S. HushAbstract:The synthetic chemistry and spectroscopy of sulfur-protected gold surfaces and nanoparticles is analyzed, indicating that the electronic structure of the interface is Au(0)–thiyl, with Au(I)–Thiolates identified as high-energy excited surface states. Density-functional theory indicates that it is the noble character of gold and nanoparticle surfaces that destabilizes Au(I)–Thiolates. Bonding results from large van der Waals forces, influenced by covalent bonding induced through s–d hybridization and charge polarization effects that perturbatively mix in some Au(I)–thiolate character. A simple method for quantifying these contributions is presented, revealing that a driving force for nanoparticle growth is nobleization, minimizing Au(I)–thiolate involvement. Predictions that Brust–Schiffrin reactions involve thiolate anion intermediates are verified spectroscopically, establishing a key feature needed to understand nanoparticle growth. Mixing of preprepared Au(I) and thiolate reactants always produces Au(I)–thiolate thin films or compounds rather than monolayers. Smooth links to O, Se, Te, C, and N linker chemistry are established.
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Gold surfaces and nanoparticles are protected by Au(0)–thiyl species and are destroyed when Au(I)–Thiolates form
Proceedings of the National Academy of Sciences, 2016Co-Authors: Jeffrey R Reimers, Jens Ulstrup, Arnab Halder, Michael J Ford, Noel S. HushAbstract:The synthetic chemistry and spectroscopy of sulfur-protected gold surfaces and nanoparticles is analyzed, indicating that the electronic structure of the interface is Au(0)-thiyl, with Au(I)-Thiolates identified as high-energy excited surface states. Density-functional theory indicates that it is the noble character of gold and nanoparticle surfaces that destabilizes Au(I)-Thiolates. Bonding results from large van der Waals forces, influenced by covalent bonding induced through s-d hybridization and charge polarization effects that perturbatively mix in some Au(I)-thiolate character. A simple method for quantifying these contributions is presented, revealing that a driving force for nanoparticle growth is nobleization, minimizing Au(I)-thiolate involvement. Predictions that Brust-Schiffrin reactions involve thiolate anion intermediates are verified spectroscopically, establishing a key feature needed to understand nanoparticle growth. Mixing of preprepared Au(I) and thiolate reactants always produces Au(I)-thiolate thin films or compounds rather than monolayers. Smooth links to O, Se, Te, C, and N linker chemistry are established.
Noel S. Hush - One of the best experts on this subject based on the ideXlab platform.
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gold surfaces and nanoparticles are protected by au 0 thiyl species and are destroyed when au i Thiolates form
Proceedings of the National Academy of Sciences of the United States of America, 2016Co-Authors: Jens Ulstrup, Arnab Halder, Jeffrey R Reimers, Michael J Ford, Noel S. HushAbstract:The synthetic chemistry and spectroscopy of sulfur-protected gold surfaces and nanoparticles is analyzed, indicating that the electronic structure of the interface is Au(0)–thiyl, with Au(I)–Thiolates identified as high-energy excited surface states. Density-functional theory indicates that it is the noble character of gold and nanoparticle surfaces that destabilizes Au(I)–Thiolates. Bonding results from large van der Waals forces, influenced by covalent bonding induced through s–d hybridization and charge polarization effects that perturbatively mix in some Au(I)–thiolate character. A simple method for quantifying these contributions is presented, revealing that a driving force for nanoparticle growth is nobleization, minimizing Au(I)–thiolate involvement. Predictions that Brust–Schiffrin reactions involve thiolate anion intermediates are verified spectroscopically, establishing a key feature needed to understand nanoparticle growth. Mixing of preprepared Au(I) and thiolate reactants always produces Au(I)–thiolate thin films or compounds rather than monolayers. Smooth links to O, Se, Te, C, and N linker chemistry are established.
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Gold surfaces and nanoparticles are protected by Au(0)–thiyl species and are destroyed when Au(I)–Thiolates form
Proceedings of the National Academy of Sciences, 2016Co-Authors: Jeffrey R Reimers, Jens Ulstrup, Arnab Halder, Michael J Ford, Noel S. HushAbstract:The synthetic chemistry and spectroscopy of sulfur-protected gold surfaces and nanoparticles is analyzed, indicating that the electronic structure of the interface is Au(0)-thiyl, with Au(I)-Thiolates identified as high-energy excited surface states. Density-functional theory indicates that it is the noble character of gold and nanoparticle surfaces that destabilizes Au(I)-Thiolates. Bonding results from large van der Waals forces, influenced by covalent bonding induced through s-d hybridization and charge polarization effects that perturbatively mix in some Au(I)-thiolate character. A simple method for quantifying these contributions is presented, revealing that a driving force for nanoparticle growth is nobleization, minimizing Au(I)-thiolate involvement. Predictions that Brust-Schiffrin reactions involve thiolate anion intermediates are verified spectroscopically, establishing a key feature needed to understand nanoparticle growth. Mixing of preprepared Au(I) and thiolate reactants always produces Au(I)-thiolate thin films or compounds rather than monolayers. Smooth links to O, Se, Te, C, and N linker chemistry are established.
