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K C Gupta - One of the best experts on this subject based on the ideXlab platform.
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Polymer-supported Schiff Base complexes in oxidation reactions
Coordination Chemistry Reviews, 2009Co-Authors: K C Gupta, Alekha Kumar Sutar, Chu-chieh LinAbstract:Polymer-supported Schiff Base complexes of metal ions show high catalytic activity in comparison to their unsupported analogues. The catalytic activity of metal complexes of different types of Schiff Base was analyzed and presented in this review. The manganese(III) Schiff Base complexes exhibited high catalytic activity in the oxidation of alkenes and alkanes both in homogeneous and heterogeneous conditions. Similarly, the Schiff Base complexes of iron(III), cobalt(II), nickel(II), copper(II) and zinc(II) ions have been used as catalysts in the epoxidation of cyclohexene and oxidation of phenol. Polymer-supported iron(III) Schiff Base complexes have demonstrated higher activity than unsupported and polymer-supported Schiff Base complexes of other metal ions. Similarly, the polymer-supported salen complexes of ruthenium(III), iron(III) and Schiff Base complexes of molybdenum carbonyls have been used successfully as catalysts in the oxidation of cyclo-octene. The oxidation of styrene, limonene, stilbene, benzene and its alkyl derivatives, adamantane, benzyl alcohol, etc. was catalyzed significantly by polymer-supported Schiff Base complexes of different metal ions. The recyclability of polymer-supported Schiff Base complexes has also been evaluated and presented in this review. The thermal and moisture stability of polymer-supported Schiff Base complexes is responsible for their high activities in reactions involving high temperatures.
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Polymer-supported Schiff Base complexes in oxidation reactions
Coordination Chemistry Reviews, 2009Co-Authors: K C Gupta, Alekha Kumar Sutar, Chu-chieh LinAbstract:Polymer-supported Schiff Base complexes of metal ions show high catalytic activity in comparison to their unsupported analogues. The catalytic activity of metal complexes of different types of Schiff Base was analyzed and presented in this review. The manganese(III) Schiff Base complexes exhibited high catalytic activity in the oxidation of alkenes and alkanes both in homogeneous and heterogeneous conditions. Similarly, the Schiff Base complexes of iron(III), cobalt(II), nickel(II), copper(II) and zinc(II) ions have been used as catalysts in the epoxidation of cyclohexene and oxidation of phenol. Polymer-supported iron(III) Schiff Base complexes have demonstrated higher activity than unsupported and polymer-supported Schiff Base complexes of other metal ions. Similarly, the polymer-supported salen complexes of ruthenium(Ill), iron(Ill) and Schiff Base complexes of molybdenum carbonyls have been used successfully as catalysts in the oxidation of cyclo-octene. The oxidation of styrene, limonene, stilbene. benzene and its alkyl derivatives, adamantane, benzyl alcohol, etc. was catalyzed significantly by polymer-supported Schiff Base complexes of different metal ions. The recyclability of polymer-supported Schiff Base complexes has also been evaluated and presented in this review. The thermal and moisture stability of polymer-supported Schiff Base complexes is responsible for their high activities in reactions involving high temperatures. (C) 2009 Elsevier B.V. All rights reserved
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catalytic activities of Schiff Base transition metal complexes
Coordination Chemistry Reviews, 2008Co-Authors: K C Gupta, Alekha Kumar SutarAbstract:Abstract Many Schiff Base complexes of metal ions show high catalytic activity. Chiral Schiff Base complexes are more selective in various reactions such as oxidation, hydroxylation, aldol condensation and epoxidation. The catalytic activity of metal complexes of binaphthyl, binaphthol and their combinations with salen Schiff Base is presented in this review. The pyridyl bis(imide) and pyridine bis(imine) complexes of cobalt(II), iron(II) ions have been used as catalysts in the polymerization of ethylene and propylene. The phenoxy-imine (FI) complexes of zirconium, titanium and vanadium and Schiff Base complexes of nickel(II) and palladium(II) were also used as catalysts in the polymerization of ethylene. Schiff Base complexes of metal ions were catalytic in ring opening polymerization processes at low temperature. Schiff Base complexes also catalyzed the oxidation of sulfides, thioanisoles, aldehydes, phenol and styrene. Schiff Base complexes in super critical carbon dioxide (ScCO2) and in the presence of polar solvents were active catalysts. Schiff Base complexes showed significant activity in catalyzing allylic alkylations, hydrosilation, the decomposition of hydrogen peroxide, isomerization, and annulation and carbonylation reactions. The high thermal and moisture stabilities of many Schiff Base complexes were useful attributes for their application as catalysts in reactions involving at high temperature.
Chu-chieh Lin - One of the best experts on this subject based on the ideXlab platform.
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Polymer-supported Schiff Base complexes in oxidation reactions
Coordination Chemistry Reviews, 2009Co-Authors: K C Gupta, Alekha Kumar Sutar, Chu-chieh LinAbstract:Polymer-supported Schiff Base complexes of metal ions show high catalytic activity in comparison to their unsupported analogues. The catalytic activity of metal complexes of different types of Schiff Base was analyzed and presented in this review. The manganese(III) Schiff Base complexes exhibited high catalytic activity in the oxidation of alkenes and alkanes both in homogeneous and heterogeneous conditions. Similarly, the Schiff Base complexes of iron(III), cobalt(II), nickel(II), copper(II) and zinc(II) ions have been used as catalysts in the epoxidation of cyclohexene and oxidation of phenol. Polymer-supported iron(III) Schiff Base complexes have demonstrated higher activity than unsupported and polymer-supported Schiff Base complexes of other metal ions. Similarly, the polymer-supported salen complexes of ruthenium(III), iron(III) and Schiff Base complexes of molybdenum carbonyls have been used successfully as catalysts in the oxidation of cyclo-octene. The oxidation of styrene, limonene, stilbene, benzene and its alkyl derivatives, adamantane, benzyl alcohol, etc. was catalyzed significantly by polymer-supported Schiff Base complexes of different metal ions. The recyclability of polymer-supported Schiff Base complexes has also been evaluated and presented in this review. The thermal and moisture stability of polymer-supported Schiff Base complexes is responsible for their high activities in reactions involving high temperatures.
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Polymer-supported Schiff Base complexes in oxidation reactions
Coordination Chemistry Reviews, 2009Co-Authors: K C Gupta, Alekha Kumar Sutar, Chu-chieh LinAbstract:Polymer-supported Schiff Base complexes of metal ions show high catalytic activity in comparison to their unsupported analogues. The catalytic activity of metal complexes of different types of Schiff Base was analyzed and presented in this review. The manganese(III) Schiff Base complexes exhibited high catalytic activity in the oxidation of alkenes and alkanes both in homogeneous and heterogeneous conditions. Similarly, the Schiff Base complexes of iron(III), cobalt(II), nickel(II), copper(II) and zinc(II) ions have been used as catalysts in the epoxidation of cyclohexene and oxidation of phenol. Polymer-supported iron(III) Schiff Base complexes have demonstrated higher activity than unsupported and polymer-supported Schiff Base complexes of other metal ions. Similarly, the polymer-supported salen complexes of ruthenium(Ill), iron(Ill) and Schiff Base complexes of molybdenum carbonyls have been used successfully as catalysts in the oxidation of cyclo-octene. The oxidation of styrene, limonene, stilbene. benzene and its alkyl derivatives, adamantane, benzyl alcohol, etc. was catalyzed significantly by polymer-supported Schiff Base complexes of different metal ions. The recyclability of polymer-supported Schiff Base complexes has also been evaluated and presented in this review. The thermal and moisture stability of polymer-supported Schiff Base complexes is responsible for their high activities in reactions involving high temperatures. (C) 2009 Elsevier B.V. All rights reserved
H G Khorana - One of the best experts on this subject based on the ideXlab platform.
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The retinylidene Schiff Base counterion in bacteriorhodopsin.
The Journal of biological chemistry, 1991Co-Authors: T Marti, S J Rösselet, Henning Otto, Maarten P. Heyn, H G KhoranaAbstract:Abstract Previous studies of bacteriorhodopsin have indicated interactions between Asp-85, Asp-212, Arg-82, and the retinylidene Schiff Base. The counterion environment of the Schiff Base has now been further investigated by using single and double mutants of the above amino acids. Chromophore regeneration from bacterioopsin proceeds to a normal extent in the presence of a single aspartate or glutamate residue at position 85 or 212, whereas replacement of both charged amino acids in the mutant Asp-85----Asn/Asp-212----Asn abolishes the binding of retinal. This indicates that a carboxylate group at either residue 85 or 212 is required as counterion for formation and for stabilization of the protonated Schiff Base. Measurements of the pKa of the Schiff Base reveal reductions of greater than 3.5 units for neutral single mutants of Asp-85 but only decreases of less than 1.2 units for corresponding substitutions of Asp-212, relative to the wild type. Substitutions of Asp-85 show large red shifts in the absorption spectrum that are partially reversible upon addition of anions, whereas mutants of Asp-212 display minor red shifts or blue shifts. We conclude, therefore, that Asp-85 is the retinylidene Schiff Base counterion in wild-type bacteriorhodopsin. In the mutant Asp-85----Asn/Asp-212----Asn formation of a protonated Schiff Base chromophore is restored in the presence of salts. The spectral properties of the double mutant are similar to those of the acid-purple form of bacteriorhodopsin. Upon addition of salts the folded structure of wild-type and mutant proteins can be stabilized at low pH in lipid/detergent micelles. The data indicate that exogenous anions serve as surrogate counterions to the protonated Schiff Base, when the intrinsic counterions have been neutralized by mutation or by protonation.
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The role of the retinylidene Schiff Base counterion in rhodopsin in determining wavelength absorbance and Schiff Base pKa.
Proceedings of the National Academy of Sciences of the United States of America, 1991Co-Authors: Thomas P. Sakmar, R R Franke, H G KhoranaAbstract:Glu-113 serves as the retinylidene Schiff Base counterion in bovine rhodopsin. Purified mutant rhodopsin pigments were prepared in which Glu-113 was replaced individually by Gln (E113Q), Asp (E113D), Asn (E113N), or Ala (E113A). E113Q, E113N, and E113A existed as pH-dependent equilibrium mixtures of unprotonated and protonated Schiff Base (PSB) forms. The Schiff Base pKa values determined by spectrophotometric titration were 6.00 (E113Q), 6.71 (E113N), and 5.70 (E113A). Thus, mutation of Glu-113 markedly reduced the Schiff Base pKa. The addition of NaCl promoted the formation of a PSB in E113Q and E113A. An exogenously supplied solute anion replaced Glu-113 to compensate for the positive charge of the PSB in these mutants. The lambda max values of the PSB forms of the mutants in NaCl were 496 nm (E113Q), 506 nm (E113A), 510 nm (E113D), and 520 nm (E113N). To evaluate the effect of different types of solute anions on lambda max values, mutants were prepared in sodium salts of halides, perchlorate, and a series of carboxylic acids of various sizes and acidity. The lambda max values of E113Q and E113A depended on the solute anion present and ranged from 488 nm to 522 nm for E113Q and from 486 nm to 528 nm for E113A. The solute anion affected the lambda max values of E113N and E113D to lesser degrees. The reactivities of the mutants to hydroxylamine were also studied. Whereas rhodopsin was stable to hydroxylamine in the dark, E113N reacted slowly and E113Q reacted rapidly under these conditions, indicating structural differences in the Schiff Base environments. The lambda max values and solute anion dependencies of the Glu-113 mutants indicate that interactions between Schiff Base and its counterion play a significant role in determining the lambda max of rhodopsin.
Kin Shing Chan - One of the best experts on this subject based on the ideXlab platform.
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Binucleating Ligands: Synthesis of Acyclic Achiral and Chiral Schiff Base−Pyridine and Schiff Base−Phosphine Ligands
The Journal of Organic Chemistry, 1996Co-Authors: Fung Lam, Kin Shing ChanAbstract:5-tert-Butyl-3-(2‘-pyridyl)salicyaldehyde and 5-tert-butyl-3-(diphenylphosphino)salicyaldehyde were synthesized from 4-tert-butylphenol in good overall yields. Condensation of the salicyaldehydes with 2,3-diamino-2,3-dimethylbutane afforded the desired dinucleating Schiff Base−pyridine and Schiff Base−phosphine ligands, respectively. 5-tert-Butyl-3-(2‘-pyridyl)salicyaldehyde reacted with optically active 1,2-diaminocyclohexanes to give chiral dinucleating Schiff Base−pyridine ligands.
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Synthesis of acyclic dinucleating Schiff Base-pyridine and Schiff Base-phosphine ligands
Tetrahedron Letters, 1995Co-Authors: Fung Lam, Kin Shing ChanAbstract:Abstract 5-tert-butyl-3-pyridyl-salicyaldehyde and 5-tert-butyl-3-diphenylphosphino-salicyaldehyde have been synthesized from 4-tert-butylphenol in good overall yields. Condensation of the salicyaldehydes with 2,3-diamino-2-3-dimethylbutane afforded the desired dinucleating Schiff Base-pyridine and Schiff Base-phosphine ligands respectively.
Alekha Kumar Sutar - One of the best experts on this subject based on the ideXlab platform.
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Polymer-supported Schiff Base complexes in oxidation reactions
Coordination Chemistry Reviews, 2009Co-Authors: K C Gupta, Alekha Kumar Sutar, Chu-chieh LinAbstract:Polymer-supported Schiff Base complexes of metal ions show high catalytic activity in comparison to their unsupported analogues. The catalytic activity of metal complexes of different types of Schiff Base was analyzed and presented in this review. The manganese(III) Schiff Base complexes exhibited high catalytic activity in the oxidation of alkenes and alkanes both in homogeneous and heterogeneous conditions. Similarly, the Schiff Base complexes of iron(III), cobalt(II), nickel(II), copper(II) and zinc(II) ions have been used as catalysts in the epoxidation of cyclohexene and oxidation of phenol. Polymer-supported iron(III) Schiff Base complexes have demonstrated higher activity than unsupported and polymer-supported Schiff Base complexes of other metal ions. Similarly, the polymer-supported salen complexes of ruthenium(III), iron(III) and Schiff Base complexes of molybdenum carbonyls have been used successfully as catalysts in the oxidation of cyclo-octene. The oxidation of styrene, limonene, stilbene, benzene and its alkyl derivatives, adamantane, benzyl alcohol, etc. was catalyzed significantly by polymer-supported Schiff Base complexes of different metal ions. The recyclability of polymer-supported Schiff Base complexes has also been evaluated and presented in this review. The thermal and moisture stability of polymer-supported Schiff Base complexes is responsible for their high activities in reactions involving high temperatures.
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Polymer-supported Schiff Base complexes in oxidation reactions
Coordination Chemistry Reviews, 2009Co-Authors: K C Gupta, Alekha Kumar Sutar, Chu-chieh LinAbstract:Polymer-supported Schiff Base complexes of metal ions show high catalytic activity in comparison to their unsupported analogues. The catalytic activity of metal complexes of different types of Schiff Base was analyzed and presented in this review. The manganese(III) Schiff Base complexes exhibited high catalytic activity in the oxidation of alkenes and alkanes both in homogeneous and heterogeneous conditions. Similarly, the Schiff Base complexes of iron(III), cobalt(II), nickel(II), copper(II) and zinc(II) ions have been used as catalysts in the epoxidation of cyclohexene and oxidation of phenol. Polymer-supported iron(III) Schiff Base complexes have demonstrated higher activity than unsupported and polymer-supported Schiff Base complexes of other metal ions. Similarly, the polymer-supported salen complexes of ruthenium(Ill), iron(Ill) and Schiff Base complexes of molybdenum carbonyls have been used successfully as catalysts in the oxidation of cyclo-octene. The oxidation of styrene, limonene, stilbene. benzene and its alkyl derivatives, adamantane, benzyl alcohol, etc. was catalyzed significantly by polymer-supported Schiff Base complexes of different metal ions. The recyclability of polymer-supported Schiff Base complexes has also been evaluated and presented in this review. The thermal and moisture stability of polymer-supported Schiff Base complexes is responsible for their high activities in reactions involving high temperatures. (C) 2009 Elsevier B.V. All rights reserved
