The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform
Zhiyong Zhou - One of the best experts on this subject based on the ideXlab platform.
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elucidation of the structures of tributyl phosphate li complexes in the presence of fecl3 via uv visible raman and ir spectroscopy and the method of Continuous Variation
Chemical Engineering Science, 2013Co-Authors: Zhiyong ZhouAbstract:Abstract The method of Continuous Variation, in conjunction with UV–visible, Raman and infrared spectroscopy, has been applied to the structural characterization of complexes resulting from tributyl phosphate (TBP), Li+ and FeCl3 in an organic extraction solvent. Data derived from various spectroscopic analyses confirmed the presence of FeCl4− in the solvent, and also demonstrated that the combination of Li+ and FeCl3 produces LiFeCl4. From the method of Continuous Variation, it was determined that more than one complex results during the extraction of Li+ from aqueous solution, and that these complexes have the general structural formula LiFeCl4·nTBP, where n is greater than or equal to 1. The coordination mode of the complex was investigated by applying a curve-fitting algorithm to the IR spectra of the organic solvent following the extraction of various cations. The results showed that high molecular weight organic cations are produced by the coordination of the TBP extractant and the cation, and that the selective recovery of Li+ occurs via an ion association reaction involving the organic cation and the FeCl4− anion. Finally, the structural formulae of the complexes formed during the extraction were confirmed to be [Li(TBP)(H2O)3]+·FeCl4– and [Li(TBP)2(H2O)2]+·FeCl4–, and the planar and stereo structures of both are given.
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Elucidation of the structures of tributyl phosphate/Li complexes in the presence of FeCl3 via UV–visible, Raman and IR spectroscopy and the method of Continuous Variation
Chemical Engineering Science, 2013Co-Authors: Zhiyong ZhouAbstract:Abstract The method of Continuous Variation, in conjunction with UV–visible, Raman and infrared spectroscopy, has been applied to the structural characterization of complexes resulting from tributyl phosphate (TBP), Li+ and FeCl3 in an organic extraction solvent. Data derived from various spectroscopic analyses confirmed the presence of FeCl4− in the solvent, and also demonstrated that the combination of Li+ and FeCl3 produces LiFeCl4. From the method of Continuous Variation, it was determined that more than one complex results during the extraction of Li+ from aqueous solution, and that these complexes have the general structural formula LiFeCl4·nTBP, where n is greater than or equal to 1. The coordination mode of the complex was investigated by applying a curve-fitting algorithm to the IR spectra of the organic solvent following the extraction of various cations. The results showed that high molecular weight organic cations are produced by the coordination of the TBP extractant and the cation, and that the selective recovery of Li+ occurs via an ion association reaction involving the organic cation and the FeCl4− anion. Finally, the structural formulae of the complexes formed during the extraction were confirmed to be [Li(TBP)(H2O)3]+·FeCl4– and [Li(TBP)2(H2O)2]+·FeCl4–, and the planar and stereo structures of both are given.
David B Collum - One of the best experts on this subject based on the ideXlab platform.
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method of Continuous Variation characterization of alkali metal enolates using 1h and 19f nmr spectroscopies
Journal of the American Chemical Society, 2014Co-Authors: Laura L Tomasevich, David B CollumAbstract:The method of Continuous Variation in conjunction with 1H and 19F NMR spectroscopies was used to characterize lithium and sodium enolates solvated by N,N,N′,N′-tetramethylethyldiamine (TMEDA) and tetrahydrofuran (THF). A strategy developed using lithium enolates was then applied to the more challenging sodium enolates. A number of sodium enolates solvated by TMEDA or THF afford exclusively tetramers. Evidence suggests that TMEDA chelates sodium on cubic tetramers.
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structure determination using the method of Continuous Variation lithium phenolates solvated by protic and dipolar aprotic ligands
Journal of Organic Chemistry, 2013Co-Authors: Laura L Tomasevich, David B CollumAbstract:The method of Continuous Variation (MCV) was used in conjunction with 6Li NMR spectroscopy to characterize four lithium phenolates solvated by a range of solvents, including N,N,N′,N′-tetramethylethylenediamine, Et2O, pyridine, protic amines, alcohols, and highly dipolar aprotic solvents. Dimers, trimers, and tetramers were observed, depending on the precise lithium phenolate–solvent combinations. Competition experiments (solvent swaps) provide insights into the relative propensities toward mixed solvation.
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lithium phenolates solvated by tetrahydrofuran and 1 2 dimethoxyethane structure determination using the method of Continuous Variation
Journal of the American Chemical Society, 2009Co-Authors: Timothy S De Vries, Lara R Liou, Jocelyn M Gruver, Anandarup Goswami, Emily Jayne, David B CollumAbstract:The method of Continuous Variation in conjunction with 6Li NMR spectroscopy was used to characterize lithium phenolates solvated by tetrahydrofuran and 1,2-dimethoxyethane. The strategy relies on the formation of ensembles of homo- and heteroaggregated phenolates. The symmetries and concentration dependencies of the heteroaggregates attest to the aggregation numbers of the homoaggregates. The structurally diverse phenols afford substrate- and solvent-dependent combinations of lithium phenolate monomers, dimers, trimers, tetramers, and pentamers. We discuss the refinement of protocols for characterizing O-lithiated species. Computational studies examine further the substituent and solvent dependencies of aggregation.
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structures of β amino ester enolates new strategies using the method of Continuous Variation
Journal of the American Chemical Society, 2008Co-Authors: Lara R Liou, Anne J Mcneil, Gilman E S Toombes, David B CollumAbstract:The solution structures of four enolates derived from β-amino esters are investigated using 6Li NMR spectroscopy in conjunction with the method of Continuous Variation (method of Job). Ensembles of homo- and heteroaggregated enolates are generated by mixing enantiomers of a single enolate (R/S mixtures), opposite antipodes of two different enolates (R/S′ mixtures), and the same antipodes of two different enolates (R/R′ mixtures). The numbers of observable aggregates and their dependence on the mole fraction of the two enolates confirm the hexamer assignments. Inherent symmetries observable in the 6Li NMR spectra show the stereochemistry of chelation about the hexagonal drum.
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lithium enolates of simple ketones structure determination using the method of Continuous Variation
Journal of the American Chemical Society, 2008Co-Authors: Lara R Liou, Anne J Mcneil, Antonio Ramirez, Gilman E S Toombes, Jocelyn M Gruver, David B CollumAbstract:The method of Continuous Variation in conjunction with 6Li NMR spectroscopy was used to characterize lithium enolates derived from 1-indanone, cyclohexanone, and cyclopentanone in solution. The strategy relies on forming ensembles of homo- and heteroaggregated enolates. The enolates form exclusively chelated dimers in N,N,N‘,N‘-tetramethylethylenediamine and cubic tetramers in tetrahydrofuran and 1,2-dimethoxyethane.
Roma Tauler - One of the best experts on this subject based on the ideXlab platform.
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multivariate extension of the Continuous Variation and mole ratio methods for the study of the interaction of intercalators with polynucleotides
Analytica Chimica Acta, 2000Co-Authors: M Vives, Raimundo Gargallo, Roma TaulerAbstract:Abstract A recently proposed approach for the study of the intercalation equilibria of drugs and polynucleotides is applied to ethidium bromide and poly(inosinic)–poly(cytidylic) acid. The procedure consists of the extension of the Continuous Variation and mole-ratio methods by recording all the UV–VIS absorption, fluorescence and circular dichroism spectra for a set of solutions containing a range of polynucleotide:dye concentration ratios. The whole set of spectroscopic data matrices was simultaneously analyzed by a multivariate curve resolution method based on alternating least squares. This procedure allowed the detection of the intercalation complex, the recovery of the concentration profiles and pure spectra for each species and the calculation of the polynucleotide:dye ratio in the complex and the apparent equilibrium constant. The intercalation sites occur every three base pairs and the value for the logarithm of the apparent equilibrium constant at 37°C in 0.26 M NaCl was 4.6±0.1 M −1 .
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study of the intercalation equilibrium between the polynucleotide poly adenylic poly uridylic acid and the ethidium bromide dye by means of multivariate curve resolution and the multivariate extension of the Continuous Variation and mole ratio method
Analytical Chemistry, 1999Co-Authors: M Vives, Raimundo Gargallo, Roma TaulerAbstract:The intercalation equilibrium between the polynucleotide poly(adenylic)-poly(uridylic) acid and the dye ethidium bromide was studied using molecular absorption spectrophotometry, spectrofluorimetry, and circular dichroism. The presence of an intercalation complex, its pure spectrum, and its concentration profile were clearly deduced using Multivariate Curve Resolution and a multivariate extension of the classical Continuous Variation and mole-ratio methods. The value of the polynucleotide/dye ratio (rpoly/dye) in the intercalation complex and of its apparent formation log constant were estimated to be 4 and 6.2, respectively. The proposed multivariate methodology allowed an accurate qualitative and quantitative description of the intercalation process.
P K Mohanty - One of the best experts on this subject based on the ideXlab platform.
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Continuously Varying Critical Exponents Beyond Weak Universality
Scientific Reports, 2017Co-Authors: N. Khan, Anupam Midya, Prabhat Mandal, P. Sarkar, P K MohantyAbstract:Renormalization group theory does not restrict the form of Continuous Variation of critical exponents which occurs in presence of a marginal operator. However, the Continuous Variation of critical exponents, observed in different contexts, usually follows a weak universality scenario where some of the exponents (e.g., β, γ, ν) vary keeping others (e.g., δ, η) fixed. Here we report ferromagnetic phase transition in (Sm1−yNdy)0.52Sr0.48MnO3 (0.5 ≤ y ≤ 1) single crystals where all three exponents β, γ, δ vary with Nd concentration y. Such a Variation clearly violates both universality and weak universality hypothesis. We propose a new scaling theory that explains the present experimental results, reduces to the weak universality as a special case, and provides a generic route leading to Continuous Variation of critical exponents and multi-criticality.
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Continuously Varying Critical Exponents Beyond Weak Universality
arXiv: Statistical Mechanics, 2016Co-Authors: N. Khan, Anupam Midya, Prabhat Mandal, P. Sarkar, P K MohantyAbstract:We show, from magnetization measurements, that the the critical exponents \beta, \gamma and \delta of the ferromagnetic to paramagnetic transition in [Sm_{1-y}Nd_{y}]_{0.52}[Sr]_{0.48}MnO_3 vary Continuously with Nd concentration (y>0.4) and the critical line eventually ends at the Heisenberg universality class in three dimension when y=1. Continuous Variation of these three critical exponents violate both universality and weak universality hypothesis. We propose a new scaling ansatz which explains the observed Variation of exponents and suggests that the y-dependence of critical exponents does not lead to new universality, rather they are only Heisenberg fixed points with rescaled exponents. The proposed scaling hypothesis includes weak universality as a special case and provides a generic route leading to Continuous Variation of critical exponents and multicriticality.
Martine Grice - One of the best experts on this subject based on the ideXlab platform.
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the dynamics of intonation categorical and Continuous Variation in an attractor based model
PLOS ONE, 2019Co-Authors: Simon Roessig, Doris Mucke, Martine GriceAbstract:The framework of dynamical systems offers powerful tools to understand the relation between stability and variability in human cognition in general and in speech in particular. In the current paper, we propose a dynamical systems approach to the description of German nuclear pitch accents in focus marking to account for both the categorical as well as the Continuous Variation found in intonational data. We report on results from 27 native speakers and employ an attractor landscape to represent pitch accent types in terms of f0 measures in a Continuous dimension. We demonstrate how the same system can account for both the categorical Variation (relative stability of one prosodic category) as well as the Continuous Variation (detailed modifications within one prosodic category). The model is able to capture the qualitative aspects of focus marking such as falling vs. rising pitch accent types as well as the quantitative aspects such as less rising vs. more rising accents in one system by means of scaling a single parameter. Furthermore, speaker group specific strategies are analysed and modelled as differences in the scaling of this parameter. Thus, the model contributes to the ongoing debate about the relation between phonetics and phonology and the importance of Variation in language and speech.