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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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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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synthesis and characterization of poly pyridinium salt s with organic Counterions exhibiting both thermotropic liquid crystalline and light emitting properties
Journal of Polymer Science Part A, 2006Co-Authors: Pradip K Bhowmik, Alexi K NedeltchevAbstract:Two poly(pyridinium salt)s with bulky organic Counterions (tosylate and triflimide) were synthesized by either the ring-transmutation polymerization reaction of 4,4‘-(1,4-phenylene)bis(2,6-diphenylpyrylium tosylate) with 1,12-diaminododecane on heating in dimethyl sulfoxide (DMSO) at 145−150 °C for 24 h or the metathesis reaction of the corresponding tosylate polymer with lithium triflimide in a common organic solvent such as acetonitrile. Their polyelectrolyte behavior in DMSO was determined by solution viscosity measurements, and their chemical structures were determined by Fourier transform infrared and Fourier transform NMR spectroscopy. They were characterized for their thermotropic liquid-crystalline properties with a number of experimental techniques. Poly(pyridinium salt) with tosylate as a counterion had a crystal-to-smectic phase transition at 116 °C that persisted up to its decomposition temperature. The corresponding polymer with triflimide as a counterion had not only lower crystal-to-smectic...
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synthesis and characterization of poly pyridinium salt s with organic Counterions exhibiting both thermotropic liquid crystalline and light emitting properties
Macromolecules, 2004Co-Authors: Pradip K Bhowmik, James J Cebe, Ivan K Nedeltchev, Shinwoong Kang, Satyendra KumarAbstract:Two poly(pyridinium salt)s with bulky organic Counterions (tosylate and triflimide) were synthesized by either the ring-transmutation polymerization reaction of 4,4'-(1,4-phenylene)bis(2,6-diphenylpyrylium tosylate) with 1,12-diaminododecane on heating in dimethyl sulfoxide (DMSO) at 145-150 °C for 24 h or the metathesis reaction of the corresponding tosylate polymer with lithium triflimide in a common organic solvent such as acetonitrile. Their polyelectrolyte behavior in DMSO was determined by solution viscosity measurements, and their chemical structures were determined by Fourier transform infrared and Fourier transform NMR spectroscopy. They were characterized for their thermotropic liquid-crystalline properties with a number of experimental techniques. Poly(pyridinium salt) with tosylate as a counterion had a crystal-to-smectic phase transition at 116 °C that persisted up to its decomposition temperature. The corresponding polymer with triflimide as a counterion had not only lower crystal-to-smectic phase transition at 80 °C but also a smectic-to-isotropic transition at about 180 °C. Both of these transitions were well below its decomposition temperature. It had better thermal stability than that of the corresponding tosylate polymer. Their fluorescence property in solutions of tetrahydrofuran and methanol as well as in the solid state was also included in this study.
Ralph H Colby - One of the best experts on this subject based on the ideXlab platform.
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dielectric and viscoelastic responses of imidazolium based ionomers with different Counterions and side chain lengths
Macromolecules, 2014Co-Authors: Hyeok U Choi, Yuesheng Ye, David Salasde La Cruz, Karen I Winey, Yossef A Elabd, James Runt, Ralph H ColbyAbstract:A molecular-level understanding of dynamics in imidazolium-based ionomers with different Counterions and side chain lengths was investigated using X-ray scattering, oscillatory shear, and dielectric relaxation spectroscopy (DRS). Variations of the counterion size and side chain length lead to changes in glass transition temperature (Tg), extent of ionic aggregation, and dielectric constant, with consequences for ion transport. A physical model of electrode polarization is used to determine the number density of simultaneously conducting ions and their mobility. Imidazolium-based ionomers with larger counterion and longer side chain have lower Tg, resulting in higher ionic conductivity and mobility. The ionic mobility is coupled to ion motions that are directly measured as a second segmental process in DRS, as these are observed to share the same Vogel temperature. Time–temperature superposition (tTS) was applied to create linear viscoelasticity master curves and to investigate the delay in chain motion re...
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counterion dynamics in polyester sulfonate ionomers with ionic liquid Counterions
Macromolecules, 2011Co-Authors: Gregory J Tudryn, Shihwa Wang, Ralph H ColbyAbstract:Conventional sodium cations (Na+) in sulfonated polyester ionomers were replaced with ammonium-based ionic liquid Counterions. Counterion dynamics were measured by dielectric spectroscopy and linear viscoelastic response via oscillatory shear. Ion exchange from sodium Counterions to ionic liquid Counterions such as tetramethylammonium and tetrabutylammonium showed an order of 104 increase in conductivity compared with sodium Counterions, primarily attributed to weaker ionic interactions that lower the glass transition temperature. Electrode polarization was used in conjunction with the 1953 Macdonald model to determine the number density of conducting Counterions and their mobility. Conductivity and mobility exhibit Vogel−Fulcher−Tammann (VFT) temperature dependences and both increased with counterion size. Conducting counterion concentrations showed Arrhenius temperature dependences, with activation energy reduced as counterion size increased. When ether−oxygen was incorporated into the mobile cation str...
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counterion dynamics in polyurethane carboxylate ionomers with ionic liquid Counterions
Chemistry of Materials, 2011Co-Authors: Shihwa Wang, Ralph H ColbyAbstract:Polyurethane carboxylate ionomers based on poly(ethylene glycol) (Mn = 600) with sodium and various ammonium, phosphonium and imidazolium cations are synthesized for systematic comparison of different cationic Counterions. Generally, larger cations act as plasticizers, lowering Tg because of weaker Coulombic force for ion associations (acting as physical cross-links). Tg can be reduced from 47 °C to −6 °C when replacing Na+ with large ether-oxygen containing ammonium without changing polymer composition and the lower Tg can enhance ionic conductivity by 5 orders of magnitude. Ionic conductivity has a stronger correlation with segmental relaxation than Tg, suggesting that counterion motion is coupled to the poly(ethylene oxide) local motions. An electrode polarization model is used to quantify the conducting ion concentration and mobility. All cation mobility follows VFT behavior, whereas conducting ion concentration has an Arrhenius temperature dependence, with slope providing activation energy and interc...
Li Yu - One of the best experts on this subject based on the ideXlab platform.
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aggregation behavior of imidazolium based surface active ionic liquids with photoresponsive cinnamate Counterions in the aqueous solution
Langmuir, 2015Co-Authors: Yanhui Bi, Qiongzheng Hu, Liuchen Zhao, Li YuAbstract:Two imidazolium-based surface active ionic liquids (SAILs) with photoresponsive cinnamate aromatic Counterions, viz. 1-dodecyl-3-methylimidazolium cinnamate ([C12mim][CA]) and 1-dodecyl-3-methylimidazolium para-hydroxy-cinnamate ([C12mim][PCA]), were newly synthesized, and their self-assembly behaviors in aqueous solutions were systematically explored. Results of surface tension and conductivity measurements show that both [C12mim][CA] and [C12mim][PCA] display a superior surface activity in aqueous solutions compared to the common imidazolium-based SAIL, 1-dodecyl-3-methylimidazolium bromide (C12mimBr), which implies the incorporation of cinnamate aromatic Counterions can promote the micellar formation. Furthermore, [C12mim][CA] shows higher surface activity due to the higher hydrophobicity of its counterion in comparison to [C12mim][PCA] that has a hydroxyl group. Both hexagonal liquid-crystalline phase (H1) and cubic liquid-crystalline phase (V2) were constructed in the [C12mim][CA] aqueous solutions. In contrast, the [C12mim][PCA]/H2O system only exhibits a single hexagonal liquid-crystalline phase (H1) in a broad concentration region. These lyotropic liquid crystal (LLC) phases were comprehensively characterized by polarized optical microscopy (POM), small-angle X-ray scattering (SAXS), and rheometer. Investigation on the temperature-dependent self-assembly nanostructures demonstrates that the higher temperature leads to a looser arrangement. Under UV irradiation, trans-cis photoisomerization of the phenylalkene group results in inferior surface activity of the prepared SAILs in aqueous solution with higher cmc values. Moreover, UV light irradiation induces obvious change of the structural parameters without altering the LLC phases. This work is expected to enrich the investigations of phase behaviors formed in SAILs systems and receive particular attention due to their unique properties and potential applications in drug delivery, biochemistry, materials science, etc.
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experimental and dft studies on the aggregation behavior of imidazolium based surface active ionic liquids with aromatic Counterions in aqueous solution
Langmuir, 2015Co-Authors: Wenwen Xu, Tao Wang, Ni Cheng, Qiongzheng Hu, Yanhui Bi, Yanjun Gong, Li YuAbstract:Two imidazolium-based surface-active ionic liquids with aromatic Counterions, namely, 1-dodecyl-3-methylimidazolium salicylate (C12mimSal) and 1-dodecyl-3-methylimidazolium 3-hydroxy-2-naphthoate (C12mimHNC), were synthesized, and their aggregate behavior in aqueous solutions was systematically explored. Surface tension and conductivity measurements indicate that both C12mimSal and C12mimHNC show superior surface activity compared to the common imidazolium-based SAIL with the same hydrocarbon chain length, 1-dodecyl-3-methylimidazolium bromide (C12mimBr). This result demonstrates that the incorporation of aromatic Counterions favors the formation of micelles. C12mimHNC displays a higher surface activity than C12mimSal, resulting from the different hydrophobicities of the Counterions. In comparison with C12mimBr, C12mimSal not only can form hexagonal liquid-crystalline phase (H1) in aqueous solution, but also exhibits a broad region of cubic liquid-crystalline phase (V2) at higher concentration. As for the C12mimHNC/H2O system, a lamellar liquid-crystalline (L(α)) phase was observed. These lyotropic liquid crystals (LLCs) were characterized by polarized optical microscopy (POM) and small-angle X-ray scattering (SAXS). Structural parameters calculated from SAXS patterns suggest that a higher concentration of the SAIL leads to a denser arrangement whereas a higher temperature results in the opposite effect. The rheological results manifest that the formed H1 phase in the C12mimSal/H2O system exhibits an impressive viscoelastic behavior, indicated by a modulus (G' and G″) that is 1 order of magnitude higher than that of C12mimBr. Density functional theory (DFT) calculations reveal that C12mimSal has a more negative interaction energy with a water molecule and the Sal(-) counterion presents a stronger electronegativity than the HNC(-) counterion. The specific phase behavior of the C12mimSal/H2O and C12mimHNC/H2O systems can be attributed to the strong synergic interaction between the imidazolium cation and the aromatic counterion, including electrostatic attraction, hydrophobic interaction, and especially π-π interaction.
Eduardo Zeiger - One of the best experts on this subject based on the ideXlab platform.
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the role of sucrose in guard cell osmoregulation
Journal of Experimental Botany, 1998Co-Authors: Lawrence D Talbott, Eduardo ZeigerAbstract:Stomatal apertures are regulated by changes in the solute content of guard cells. The identity of the solutes involved in guard cell osmoregulation has been the subject of much study. Early consensus in the field held that carbohydrates derived from starch constitute the principal osmoticum. This starch-sugar hypothesis has been replaced by the present paradigm of guard cell osmoregulation by K + and its Counterions. Recent studies, however, show that both K + and sucrose are primary guard cell osmotica, and that the use of these two solutes is separated into two distinct phases in which one or the other constitutes the dominant osmoticum. In the intact leaf, opening at the beginning of a daily cycle is supported by K + and its Counterions, malate 2- and Cl - . Malate 2- is the dominant counterion in growth chamber-grown leaves, whereas Cl - predominates in a greenhouse environment. In the second half of the daily cycle, K + content in guard cells decreases drastically and sucrose becomes the dominant solute. Manipulation of stomatal apertures by altering ambient CO 2 concentration shows that either K + or sucrose accumulation can sustain rapid opening. The functional implications of two distinct osmoregulatory phases of stomatal movements remains to be elucidated. The guard cell content of K + , its Counterions, and sucrose can be modulated by at least three osmoregulatory pathways in guard cells. Experimental conditions favouring three distinct pathways have been established, but major uncertainties remain about the control of guard cell solute content in the intact leaf.
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central roles for potassium and sucrose in guard cell osmoregulation
Plant Physiology, 1996Co-Authors: Lawrence D Talbott, Eduardo ZeigerAbstract:Osmoregulation in guard cells of intact, attached Vicia faba leaves grown under growth chamber and greenhouse conditions was studied over a daily light cycle of stomatal movements. Under both growth conditions guard cells had two distinct osmoregulatory phases. In the first (morning) phase, opening was correlated with K+ uptake and, to a lesser extent, sucrose accumulation. In the second (afternoon) phase, in which apertures were maximal, K+ content declined and sucrose became the dominant osmoticum. Reopening of the stomata after a CO2-induced closure was accompanied by accumulation of either K+ or sucrose, depending on the time of day, indicating that a single environmental signal may use multiple osmoregulatory pathways. Malate accumulation, correlated with K+ uptake, was detected under growth chamber but not greenhouse conditions, whereas Cl- was the main K+ counterion in the greenhouse. These results indicate that guard-cell osmoregulation in the intact leaf depends on at least two different osmoregulatory pathways, K+ transport and sucrose metabolism. Furthermore, the relative importance of the K+ Counterions malate and Cl- appears to be environment-dependent.
J. Ruan - One of the best experts on this subject based on the ideXlab platform.
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determination of inorganic pharmaceutical Counterions using hydrophilic interaction chromatography coupled with a corona cad detector
Journal of Pharmaceutical and Biomedical Analysis, 2009Co-Authors: Zhihong Huang, M.a. Richards, R. Francis, Ruben Lozano, J. RuanAbstract:A simple generic approach was investigated for the determination of inorganic pharmaceutical Counterions in drug substances using conventional high performance liquid chromatographic (HPLC) instruments. An intuitive approach combined Corona® charged aerosol detection (CAD) with a polymer-based zwitterionic stationary phase in the hydrophilic interaction chromatography (HILIC) mode. Two generic methods based on this HILIC/CAD technique were developed to quantitate Counterions such as Cl−, Br−, SO42−, K+, Ca2+ and Mg2+ in different pharmaceutical compounds. The development and capability of this HILIC/CAD technique analysis were examined. HILIC/CAD was compared to ion chromatography (IC), the most commonly used methodology for pharmaceutical counterion analysis. HILIC/CAD was found to have significant advantages in terms of: (1) being able to quantitate both anions and cations simultaneously without a need to change column/eluent or detection mode; (2) imposing much less restriction on the allowable organic percentage of the eluents than IC, and therefore being more appropriate for analysis of Counterions of poorly water-soluble drugs; (3) requiring minimal training of the operating analysts. The precision and accuracy of counterion analysis using HILIC/CAD was not compromised. A typical precision of <2.0% was observed for all tested inorganic Counterions; the determinations were within 2.0% relative to the theoretical counterion amount in the drug substance. Additionally, better accuracy was shown for Cl− in several drug substances as compared to IC. The main drawback of HILIC/CAD is its unsuitability for many of the current silica-based HILIC columns, because slight dissolution of silica leads to high baseline noise in the CAD detector. As a result of the universal detection characteristics of Corona® CAD and the unique separation capabilities of a zwitterionic stationary phase, an intuitive and robust HPLC method was developed for the generic determination of various Counterions in different drug substances. HILIC/CAD technique is a useful alternative methodology, particularly for determination of Counterions in low-solubility drugs.
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Determination of inorganic pharmaceutical Counterions using hydrophilic interaction chromatography coupled with a Corona® CAD detector
Journal of Pharmaceutical and Biomedical Analysis, 2009Co-Authors: Zhihong Huang, M.a. Richards, R. Francis, Y. Zha, Rogelio Lozano, J. RuanAbstract:A simple generic approach was investigated for the determination of inorganic pharmaceutical Counterions in drug substances using conventional high performance liquid chromatographic (HPLC) instruments. An intuitive approach combined Corona® charged aerosol detection (CAD) with a polymer-based zwitterionic stationary phase in the hydrophilic interaction chromatography (HILIC) mode. Two generic methods based on this HILIC/CAD technique were developed to quantitate Counterions such as Cl-, Br-, SO4\n2-, K+, Ca2+ and Mg2+ in different pharmaceutical compounds. The development and capability of this HILIC/CAD technique analysis were examined. HILIC/CAD was compared to ion chromatography (IC), the most commonly used methodology for pharmaceutical counterion analysis. HILIC/CAD was found to have significant advantages in terms of: (1) being able to quantitate both anions and cations simultaneously without a need to change column/eluent or detection mode; (2) imposing much less restriction on the allowable organic percentage of the eluents than IC, and therefore being more appropriate for analysis of Counterions of poorly water-soluble drugs; (3) requiring minimal training of the operating analysts. The precision and accuracy of counterion analysis using HILIC/CAD was not compromised. A typical precision of
