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Pradip K Bhowmik - One of the best experts on this subject based on the ideXlab platform.
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Poly(Pyridinium Salt)s with organic counterions derived from 3,3′-dimethylnaphthidine: Thermal, liquid crystalline, and optical properties
Journal of Polymer Research, 2015Co-Authors: Robin Jose, Dat P. Truong, Pradip K BhowmikAbstract:A poly(Pyridinium Salt) was synthesized from 4,4′-(1,4-phenylene)bis(2,6-diphenylpyrilium)tosylate and 3,3′-dimethylnaphthidine. Tosylate counterion was exchanged with other organic counterions such as triflimide, 1-napthalenesulfonate, and 2-napthalenesulfonate in DMSO to yield a total of four poly(Pyridinium Salt)s. Their chemical structures were established by using various spectroscopic techniques. Gel permeation chromatography showed that their number-average molecular weights (Mn) were in the range of 56–76 kg/mol and polydispersities in the range of 1.09–1.32. Their thermal stabilities ranged from 290 to 425 °C, under nitrogen atmosphere. Even though these polymers didn’t show thermotropic liquid crystalline phases, counterion-dependent lyotropic liquid-crystalline phase were observed in some polar aprotic solvents above their critical concentrations. Each of these polymers emitted green light (500–572 nm) both in solutions and solid states as observed by UV–vis and photoluminescent spectroscopies.
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poly Pyridinium Salt s with organic counterions derived from 3 3 dimethylnaphthidine thermal liquid crystalline and optical properties
Journal of Polymer Research, 2015Co-Authors: Robin Jose, Dat Truong, Pradip K BhowmikAbstract:A poly(Pyridinium Salt) was synthesized from 4,4′-(1,4-phenylene)bis(2,6-diphenylpyrilium)tosylate and 3,3′-dimethylnaphthidine. Tosylate counterion was exchanged with other organic counterions such as triflimide, 1-napthalenesulfonate, and 2-napthalenesulfonate in DMSO to yield a total of four poly(Pyridinium Salt)s. Their chemical structures were established by using various spectroscopic techniques. Gel permeation chromatography showed that their number-average molecular weights (Mn) were in the range of 56–76 kg/mol and polydispersities in the range of 1.09–1.32. Their thermal stabilities ranged from 290 to 425 °C, under nitrogen atmosphere. Even though these polymers didn’t show thermotropic liquid crystalline phases, counterion-dependent lyotropic liquid-crystalline phase were observed in some polar aprotic solvents above their critical concentrations. Each of these polymers emitted green light (500–572 nm) both in solutions and solid states as observed by UV–vis and photoluminescent spectroscopies.
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solution thermal and optical properties of bis Pyridinium Salt s as ionic liquids
Materials Chemistry and Physics, 2013Co-Authors: Tae Soo Jo, Pradip K BhowmikAbstract:Abstract Bis(Pyridinium Salt)s containing different alkyl chain lengths and various organic counterions were prepared by the ring-transmutation reaction of bis(pyrylium tosylate) with aliphatic amines in dimethyl sulfoxide at 130–135 °C for 18 h and their tosylate counterions were exchanged to other anions such as triflimide, methyl orange, and dioctyl sulfosuccinate by the metathesis reaction in a common organic solvent. Their chemical structures were established by using 1H, 19F, and 13C NMR spectra. The thermal properties of bis(Pyridinium Salt)s were studied by DSC and TGA measurements. Some of the dicationic Salts provided low melting points below 100 °C and some of them displayed amorphous properties. Polarized optical microscopy studies revealed the crystal structures prior to melting temperatures in some cases. Their optical properties were examined by using UV–Vis and photoluminescent spectrometers; and they emitted blue light both in the solution and solid states regardless of their microstructures, counterions, and the polarity of organic solvents. However, most of these Salts exhibited hypsochromic shifts in their emission peaks in the solid state when compared with those of their solution spectra. Due to unique properties of methyl orange anion as a pH indicator, two of the Salts showed different color change in varying concentrations of triflic acid in common organic solvents, demonstrating their potential use as an acid sensor in methanol, acetonitrile and acetone.
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Dispersion of Single‐Walled Carbon Nanotubes with Poly(Pyridinium Salt)s Containing Various Rigid Aromatic Moieties
Macromolecular Chemistry and Physics, 2012Co-Authors: Tae Soo Jo, Pradip K Bhowmik, Longzhou MaAbstract:Dispersions of single-walled carbon nanotubes (SWNTs) with several poly(Pyridinium Salt)s containing various aromatic diamine moieties are prepared via a non-covalent coagulation in DMSO. The interactions between SWNTs and polymers are characterized with various spectroscopic techniques. The 1H NMR spectra suggest that strong interactions exist. The UV−Vis absorption spectra are independent of the incorporation of SWNTs. The resulting composites display high quenching efficiency in the photoluminescent properties; and transmission electron microscopy studies reveal the well-dispersed SWNTs in the ionic polymer matrices. The enhanced thermal stability of the composites is determined by thermogravimetric analysis. The fully grown lyotropic LC properties of the poly(Pyridinium Salt)s are disrupted by the introduction of SWNTs.
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synthesis and characterization of poly Pyridinium Salt s derived from various aromatic diamines
Polymer, 2012Co-Authors: Tae Soo Jo, Alexi K Nedeltchev, Bidyut Biswas, Pradip K BhowmikAbstract:Abstract Several poly(Pyridinium Salt)s containing various aromatic diamine moieties and tosylate counterions were prepared by the ring-transmutation polymerization reaction of bis(pyrylium tosylate) with aromatic diamines in dimethyl sulfoxide at 130−135 °C for 48 h and their tosylate counterions were exchanged to triflimide polymers by a metatheses reaction in an organic solvent. Their chemical structures were established by using various spectroscopic techniques. Their number-average molecular weights (Mn) were in the range of 38–46 kg/mol and polydispersities in the range of 1.13–1.43 as determined by gel permeation chromatography. They showed excellent thermal stabilities in nitrogen in the range of 326–477 °C. They exhibited lyotropic liquid-crystalline phase in polar aprotic and protic organic solvents above their critical concentrations depending on their microstructures and counterions. Their optical properties were examined by using UV–Vis and photoluminescent spectroscopy, which revealed that some polymers emitted UV light, some emitted blue light, and some emitted green light (both in solutions and solid states) depending on their microstructures, counterions, and on solvent polarity of organic solvents.
Frank W Harris - One of the best experts on this subject based on the ideXlab platform.
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aromatic poly Pyridinium Salt s part 3 photoreduction in amide solvents
Polymer, 2002Co-Authors: Stephen Z D Cheng, Frank W HarrisAbstract:Abstract UV–Vis irradiation of bis(Pyridinium Salt) model compounds and poly(Pyridinium Salt)s in amide solvents result in dramatic changes in their UV–Vis spectra. The absorption maximum near 342 nm, characteristic of Pyridinium rings, disappears, while an absorption maximum near 500 nm appears and then disappears. During this process, the solutions change from yellow to dark red to light yellow. The inherent viscosities of the poly(Pyridinium Salt)s also decrease dramatically under UV–Vis irradiation. Both the color changes and the viscosity decreases are unaffected by the nature of the Pyridinium Salt counter anion. However, they are dramatically affected by the presence of pendent substituents. Electron-withdrawing groups increase the rate at which these changes take place, while electron-donating groups retard them. It is speculated that the photodecomposition proceeds through the initial formation of radical cations. It is also speculated that the amide groups may serve as reducing agents providing electrons in the electron transfer process. Evidence for this comes from the fact that a poly(Pyridinium Salt) containing pendent amide groups underwent photoreduction in DMSO in marked contrast to other poly(Pyridinium Salt)s that are photostable in this solvent.
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aromatic poly Pyridinium Salt s part 2 synthesis and properties of organo soluble rigid rod poly Pyridinium triflate s
Polymer, 2000Co-Authors: Shel Ann X Huang, Stephen Z D Cheng, Kathy C Chuang, Frank W HarrisAbstract:Abstract A bis[pyrylium tetrafluoromethanesulfonate (triflate)], i.e. p -bis[4-(2,6-diphenylpyrylium)]benzene ditriflate) ( 3 ), has been prepared and polymerized with a series of aromatic diamines. The polymerizations, which were carried out in a dimethylsulfoxide (DMSO)/toluene mixture at 150°C for 3–4 h, were significantly faster than previous polymerizations of an analogous bis(pyrylium tetrafluoroborate). The poly(Pyridinium triflate)s ( 5 ) obtained were soluble in polar aprotic solvents and had inherent viscosities that ranged from 8.3 to 18.7 dl/g (0.1 g/dl in DMSO at 30.0±0.1° C ). The rigid-rod polymers obtained from all- para -catenated diamines had viscosities comparable to those of other rigid-rod polyheterocyclics. All of the polymers could be solution cast into tough thin films that had moduli of 2.3–5.5 GPa. The poly(Pyridinium triflate)s ( 5 ) were significantly more thermally and thermooxidatively stable than analogous poly(Pyridinium tetrafluoroborate)s. The polymers underwent 5% weight losses near 451°C in nitrogen and near 461°C in air when subjected to thermal gravimetric analysis at a heating rate of 10°C/min. The differences in the poly(Pyridinium Salt) stabilities were shown to be due to the differences in the stabilities of the counter ions.
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aromatic poly Pyridinium Salt s synthesis and structure of organo soluble rigid rod poly Pyridinium tetrafluoroborate s
Polymer, 1994Co-Authors: Frank W Harris, Kathy C Chuang, Shel Ann X Huang, James J Janimak, Stephen Z D ChengAbstract:Abstract A series of phenylated, aromatic poly(Pyridinium tetrafluoroborate)s has been prepared by the polymerization of 4,4′-(1,4-phenylene)bis(2,6-diphenylpyrylium tetrafluoroborate) with aromatic diamines in a dimethylsulfoxide/toluene mixture at 145–150°C. The water generated by the transformation of the pyrylium rings to Pyridinium rings was distilled from the reaction mixture as a water/toluene azeotrope. All- para -catenated, rigid-rod polymers with inherent viscosities as high as 4.9 dl g −1 were obtained that were soluble in polar aprotic solvents. The polymers could be solution cast into tough, flexible films. Although the glass transition temperatures of the poly(Pyridinium Salt)s were difficult to detect with differential scanning calorimetry, they displayed distinctive melting endotherms with minima above 380°C. Thermogravimetric analysis showed that the polymers began to decompose near 360°C prior to melting. Wide-angle X-ray diffraction analysis revealed that the chains were packed in a structure similar to that of a smectic liquid crystalline glass.
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design of anhydrous electrorheological er suspensions based on i2 doped poly Pyridinium Salt
Journal of Polymer Science Part B, 1994Co-Authors: Weiching Yu, Montgomery T Shaw, Xiaoyan Huang, Frank W HarrisAbstract:A rigid-rod aromatic poly (Pyridinium Salt) [(C 5 H 2 N + [Ph] 2 )-Ph-(C 5 H 2 N + [Ph] 2 )-Ph-Ph] n was synthesized and doped with iodine for making anhydrous electrorheological (ER) fluids. The I 2 -doped particles were further processed into ones having insulating skins. Dielectric properties and current densities of the suspensions containing these particles were studied to elucidate the roles of conductivity of the dispersed phase in the ER suspension
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Design of anhydrous electrorheological (ER) suspensions based on I2‐doped poly(Pyridinium Salt)
Journal of Polymer Science Part B, 1994Co-Authors: Weiching Yu, Montgomery T Shaw, Xiaoyan Huang, Frank W HarrisAbstract:A rigid-rod aromatic poly (Pyridinium Salt) [(C 5 H 2 N + [Ph] 2 )-Ph-(C 5 H 2 N + [Ph] 2 )-Ph-Ph] n was synthesized and doped with iodine for making anhydrous electrorheological (ER) fluids. The I 2 -doped particles were further processed into ones having insulating skins. Dielectric properties and current densities of the suspensions containing these particles were studied to elucidate the roles of conductivity of the dispersed phase in the ER suspension
Alexi K Nedeltchev - One of the best experts on this subject based on the ideXlab platform.
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synthesis and characterization of poly Pyridinium Salt s derived from various aromatic diamines
Polymer, 2012Co-Authors: Tae Soo Jo, Alexi K Nedeltchev, Bidyut Biswas, Pradip K BhowmikAbstract:Abstract Several poly(Pyridinium Salt)s containing various aromatic diamine moieties and tosylate counterions were prepared by the ring-transmutation polymerization reaction of bis(pyrylium tosylate) with aromatic diamines in dimethyl sulfoxide at 130−135 °C for 48 h and their tosylate counterions were exchanged to triflimide polymers by a metatheses reaction in an organic solvent. Their chemical structures were established by using various spectroscopic techniques. Their number-average molecular weights (Mn) were in the range of 38–46 kg/mol and polydispersities in the range of 1.13–1.43 as determined by gel permeation chromatography. They showed excellent thermal stabilities in nitrogen in the range of 326–477 °C. They exhibited lyotropic liquid-crystalline phase in polar aprotic and protic organic solvents above their critical concentrations depending on their microstructures and counterions. Their optical properties were examined by using UV–Vis and photoluminescent spectroscopy, which revealed that some polymers emitted UV light, some emitted blue light, and some emitted green light (both in solutions and solid states) depending on their microstructures, counterions, and on solvent polarity of organic solvents.
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solution thermal and optical properties of new poly Pyridinium Salt s derived from conjugated quinoline diamines
Journal of Polymer Science Part A, 2011Co-Authors: Alexi K Nedeltchev, Pradip K BhowmikAbstract:Several new poly(Pyridinium Salt)s with quinoline diamine moieties in their backbones with tosylate and triflimide counterion were prepared by either a ring-transmutation polymerization reaction with bis(pyrylium tosylate) with a series of isomeric quinoline diamines in dimethyl sulfoxide (DMSO) for 48 h at 130–140 °C or a metathesis reaction of the tosylate polymers with lithium triflimide in DMSO at about 60 °C. Their chemical structures were confirmed by FTIR, 1H and 13C NMR spectroscopy, and elemental analysis. Their number-average molecular weights (Mn) were in the range of 18,000–58,000, and their polydispersities were in the range of 1.12–1.53 as determined by gel permeation chromatography. They had thermal stability in the temperature range of 353–455 °C and glass-transition temperatures >240 °C. They had good solubility in common organic solvents and were characterized with polarizing optical microscopy (POM) studies for their lyotropic liquid-crystalline properties. Their light-emission properties were examined by spectrofluorometry in both the solution and film states. Their quantum yields were also determined. Additionally, their morphologies in the thin-film states and melt-drawn fibers were examined with POM, scanning electron microscopy, and transmission electron microscopy techniques. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011
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solution thermal and optical properties of novel poly Pyridinium Salt s derived from conjugated pyridine diamines
Journal of Polymer Science Part A, 2010Co-Authors: Alexi K Nedeltchev, Pradip K BhowmikAbstract:Several novel poly(Pyridinium Salt)s with heterocy- clic pyridine moieties in their backbones with tosylate and trifli- mide counterions were prepared by either ring-transmutation polymerization reaction of phenylated-bis(pyrylium tosylate) with isomeric pyridine diamines of 4-phenyl-2,6-bis(4-amino- phenyl)pyridine in dimethyl sulfoxide (DMSO) for 48 h at 130- 140 � C or by metathesis reaction of the respective tosylate polymers with lithium triflimide in DMSO at about 60 � C. Their chemical structures were characterized by FTIR, 1 H, 13 C NMR spectroscopy, and elemental analysis. Their number-average molecular weights (Mn) were in the range of 8,000-51,000 and their polydispersities in the range of 1.18-2.13 as determined by gel permeation chromatography. They had excellent ther- mal stabilities of 340-458 � C and high glass transition tempera- tures >200 � C. As they showed good solubilities in common organic solvents, their solution properties were also character- ized for their lyotropic liquid-crystalline properties with polariz- ing optical microscopy (POM) studies. Their photoluminescent properties were examined by using a spectrofluorometer in both solution and solid states. Their quantum yields were rather low, which were in the range of 1.3-2.0%. Additionally, hand-drawn fibers from the melts were examined to determine their morphologies with a number of microscopic techniques including POM, scanning electron microscopy, and transmis- sion electron microscopy. V C 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4408-4418, 2010
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solution thermal and optical properties of new poly Pyridinium Salt s derived from bisquinoline diamines
Polymer Chemistry, 2010Co-Authors: Alexi K Nedeltchev, Pradip K BhowmikAbstract:Several novel poly(Pyridinium Salt)s with heterocyclic bisquinoline moieties having both tosylate and triflimide counterions were prepared by either ring-transmutation or metathesis reaction. Their chemical structures were established by using 1H and 13C NMR, FTIR and elemental analysis. Their number-average molecular weights (Mn) ranged from 53,000 to 79,000 and their polydispersities ranged from 1.30 to 3.24 as determined by gel permeation chromatography. They had excellent thermal stabilities in the temperature range of 336–447 °C and glass transition temperatures in the range of 119–174 °C. They had good solubilities in common organic solvents and in several cases their critical concentrations (*C) were exceeded to form lyotropic liquid-crystalline phases. Additionally, they emitted light in the blue and green region in both solution and solid state. Their quantum yields were also determined by using a spectrofluorometer.
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poly Pyridinium Salt s with organic counterions derived from an aromatic diamine containing tetraoxyethylene units exhibiting amphotropic liquid crystalline and photoluminescence properties
Journal of Applied Polymer Science, 2009Co-Authors: Pradip K Bhowmik, Alexi K Nedeltchev, Hari D Mandal, Jose A Jimenezhernandez, Patrick M McgannonAbstract:Several poly(Pyridinium Salt)s containing various organic counterions and tetraoxyethylene units in their backbones were synthesized by either ring-transmutation polymerization reaction of 4,4'-(1,4-phenylene)bis(2,6-diphenylpyrylium tosylate) with bis(2-(2-(4-aminophenoxy)ethoxy)ethyl) ether on heating in dimethyl sulfoxide or metathesis reaction of the tosylate polymer with the corresponding lithium or sodium Salts in acetonitrile. Their chemical structures were determined by 1H-NMR and 13C-NMR spectroscopy, and elemental analyses. Their number-average molecular weights and polydispersity indices were in the range of 34,000–52,000 and 1.14–1.38, respectively, as determined by gel permeation chromatography. They were characterized both for their thermotropic and lyotropic liquid-crystalline properties by using differential scanning calorimetry and polarizing optical microscopy. As these polymers exhibited liquid-crystalline phase both in the melt and in solutions, they are classified as an amphotropic class of ionic polymers. Their light-emitting properties in a large number of organic solvents that ranged from nonpolar to polar solvents and in films cast from methanol and acetonitrile were also studied by using spectrofluorometry. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010
Stephen Z D Cheng - One of the best experts on this subject based on the ideXlab platform.
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aromatic poly Pyridinium Salt s part 3 photoreduction in amide solvents
Polymer, 2002Co-Authors: Stephen Z D Cheng, Frank W HarrisAbstract:Abstract UV–Vis irradiation of bis(Pyridinium Salt) model compounds and poly(Pyridinium Salt)s in amide solvents result in dramatic changes in their UV–Vis spectra. The absorption maximum near 342 nm, characteristic of Pyridinium rings, disappears, while an absorption maximum near 500 nm appears and then disappears. During this process, the solutions change from yellow to dark red to light yellow. The inherent viscosities of the poly(Pyridinium Salt)s also decrease dramatically under UV–Vis irradiation. Both the color changes and the viscosity decreases are unaffected by the nature of the Pyridinium Salt counter anion. However, they are dramatically affected by the presence of pendent substituents. Electron-withdrawing groups increase the rate at which these changes take place, while electron-donating groups retard them. It is speculated that the photodecomposition proceeds through the initial formation of radical cations. It is also speculated that the amide groups may serve as reducing agents providing electrons in the electron transfer process. Evidence for this comes from the fact that a poly(Pyridinium Salt) containing pendent amide groups underwent photoreduction in DMSO in marked contrast to other poly(Pyridinium Salt)s that are photostable in this solvent.
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aromatic poly Pyridinium Salt s part 2 synthesis and properties of organo soluble rigid rod poly Pyridinium triflate s
Polymer, 2000Co-Authors: Shel Ann X Huang, Stephen Z D Cheng, Kathy C Chuang, Frank W HarrisAbstract:Abstract A bis[pyrylium tetrafluoromethanesulfonate (triflate)], i.e. p -bis[4-(2,6-diphenylpyrylium)]benzene ditriflate) ( 3 ), has been prepared and polymerized with a series of aromatic diamines. The polymerizations, which were carried out in a dimethylsulfoxide (DMSO)/toluene mixture at 150°C for 3–4 h, were significantly faster than previous polymerizations of an analogous bis(pyrylium tetrafluoroborate). The poly(Pyridinium triflate)s ( 5 ) obtained were soluble in polar aprotic solvents and had inherent viscosities that ranged from 8.3 to 18.7 dl/g (0.1 g/dl in DMSO at 30.0±0.1° C ). The rigid-rod polymers obtained from all- para -catenated diamines had viscosities comparable to those of other rigid-rod polyheterocyclics. All of the polymers could be solution cast into tough thin films that had moduli of 2.3–5.5 GPa. The poly(Pyridinium triflate)s ( 5 ) were significantly more thermally and thermooxidatively stable than analogous poly(Pyridinium tetrafluoroborate)s. The polymers underwent 5% weight losses near 451°C in nitrogen and near 461°C in air when subjected to thermal gravimetric analysis at a heating rate of 10°C/min. The differences in the poly(Pyridinium Salt) stabilities were shown to be due to the differences in the stabilities of the counter ions.
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aromatic poly Pyridinium Salt s synthesis and structure of organo soluble rigid rod poly Pyridinium tetrafluoroborate s
Polymer, 1994Co-Authors: Frank W Harris, Kathy C Chuang, Shel Ann X Huang, James J Janimak, Stephen Z D ChengAbstract:Abstract A series of phenylated, aromatic poly(Pyridinium tetrafluoroborate)s has been prepared by the polymerization of 4,4′-(1,4-phenylene)bis(2,6-diphenylpyrylium tetrafluoroborate) with aromatic diamines in a dimethylsulfoxide/toluene mixture at 145–150°C. The water generated by the transformation of the pyrylium rings to Pyridinium rings was distilled from the reaction mixture as a water/toluene azeotrope. All- para -catenated, rigid-rod polymers with inherent viscosities as high as 4.9 dl g −1 were obtained that were soluble in polar aprotic solvents. The polymers could be solution cast into tough, flexible films. Although the glass transition temperatures of the poly(Pyridinium Salt)s were difficult to detect with differential scanning calorimetry, they displayed distinctive melting endotherms with minima above 380°C. Thermogravimetric analysis showed that the polymers began to decompose near 360°C prior to melting. Wide-angle X-ray diffraction analysis revealed that the chains were packed in a structure similar to that of a smectic liquid crystalline glass.
Patrick S Mariano - One of the best experts on this subject based on the ideXlab platform.
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Observations Made in Exploring a Pyridinium Salt Photochemical Approach to the Synthesis of (+)-Lactacystin
Bulletin of The Korean Chemical Society, 2008Co-Authors: Jiwen Zhou, Patrick S Mariano, Maozhen Gong, Ung Chan YoonAbstract:The key step in a strategy for the synthesis of (+)-lactacystin involving photocyclization reaction of a cyclopenta-fused Pyridinium Salt has been probed by using a model substrate. Observations made in this effort led to the discovery of a highly unusual cascade process that leads to stereoselective formation of an interesting tricyclic carbamate. The results of this study are presented and discussed in the context of a (+)-lactacystin synthetic approach.
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observations made in exploring a Pyridinium Salt photochemical approach to the synthesis of lactacystin
Bulletin of The Korean Chemical Society, 2008Co-Authors: Jiwen Zhou, Patrick S Mariano, Maozhen Gong, Ung Chan YoonAbstract:The key step in a strategy for the synthesis of (+)-lactacystin involving photocyclization reaction of a cyclopenta-fused Pyridinium Salt has been probed by using a model substrate. Observations made in this effort led to the discovery of a highly unusual cascade process that leads to stereoselective formation of an interesting tricyclic carbamate. The results of this study are presented and discussed in the context of a (+)-lactacystin synthetic approach.
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stereoselective synthesis of polyhydroxylated indolizidines based on Pyridinium Salt photochemistry and ring rearrangement metathesis
Journal of Organic Chemistry, 2004Co-Authors: Ling Song, Eileen N Duesler, Patrick S MarianoAbstract:Ruthenium-catalyzed ring rearrangement metathesis (RRM) reactions of stereochemically diverse, differentially protected 4-N-allylacetamidocyclopenten-3,5-diols, prepared by using Pyridinium Salt photochemistry, have been explored as part of a program to develop novel routes for the synthesis of polyhydroxylated indolizidines. The RRM reactions, which produce selectively protected 1-acetyl-2-allyl-3-hydroxy-1,2,3,6-tetrahydropyridines, were found to take in high yields and with high levels of regioselectivity. The significance of RRM reactions of 4-N-allylacetamidocyclopenten-3,5-diols in the context of polyhydroxylated indolizidine synthesis is demonstrated by an application to the concise preparation of the potent glycosidase inhibitor, (−)-swainsonine.
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a novel approach to the synthesis of amino sugars routes to selectively protected 3 amino 3 deoxy aldopentoses based on Pyridinium Salt photochemistry
Journal of Organic Chemistry, 2002Co-Authors: Haiyan Lu, Ling Song, Zhuoyi Su, Patrick S MarianoAbstract:A new approach for the synthesis of selectively blocked 3-amino-3-deoxyaldopentoses is presented. The strategy is based on employment of a Pyridinium Salt photocyclization−aziridine ring-opening sequence to prepare stereochemically defined, enantiomerically enriched aminocyclopentendiol derivatives. Ring-opening reactions transform these substances into terminally differentiated aminopolyols, which serve as precursors to the target amino-aldopentoses. The utility of this strategy is demonstrated by its application to the syntheses of protected derivatives of d- and l-3-amino-3-deoxyxylose, l-3-amino-3-deoxyarabinose, and a late-stage intermediate in a potential route to N-acetylneuraminic acid.
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a concise synthesis of the allosamizoline aminocyclopentitol based on Pyridinium Salt photochemistry
Tetrahedron Letters, 2001Co-Authors: Haiyan Lu, Patrick S MarianoAbstract:Abstract The (−)-allosamizoline aminocyclopentitol was prepared by use of a route featuring Pyridinium Salt photochemical synthesis of the aminocyclopentene core, enzymatic desymmetrization, Wittig rearrangement to introduce the hydroxymethyl side chain, and regiocontrolled epoxide ring opening.
