Quantitative Electron Paramagnetic Resonance Study of the Motion, Adsorption, and Aggregation of TEMPOL Radicals in the Nanopores of Dry Cotton

and, Ronald S. Rock; Roduner, Emil; Batchelor, S. N.

doi:10.1021/jp011995q

Cited by 18 publications

(56 citation statements)

References 14 publications

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“…For T-OH at 75% RH and 323 K, the values are constant at 1.9 G up to a loading of 10 -4 mol kg -1 , then rise to 2.8 G by 10 -3 mol kg -1 , which is ascribed to population of different microdomains with increased loading. 5,6 The temperature dependence is small, but lowering the RH causes a large increase in ∆H + for intermediate loadings (5 × 10 -5 to 5 × 10 -4 mol kg -1 ), which reflects the dependence of the motion on water content for these microdomains. For T-NH 3 + , which from the behavior of its coupling constants is close to T-OH, this is not observed.…”

Section: Rotational Motion and Low Field Line Widthmentioning

confidence: 99%

“…11 EPR spin probing has been insightful, giving the micropolarity and microviscosity of the amorphous regions, showing the existence of microdomains of different character and allowing quantification of the equilibrium between radicals absorbed in the bulk amorphous regions and adsorbed onto the crystallite surfaces. 5,6 A pertinent criticism of the work is that it has all been done with only a single type of probe radical, 4-hydroxy-TEMPO (Table 1), and the results may change with different probes. Such effects may be particularly important in complex supramolecular structures such as cotton.…”

Section: Introductionmentioning

confidence: 99%

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Effect of Charge on Spin Probe Interaction and Dynamics in the Nanopores of Cotton

Frantz¹,

Wendland²,

Roduner³

et al. 2007

J. Phys. Chem. C

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To understand the effect of charge on spin probe interactions and dynamics in the nanopores of cotton, an electron paramagnetic resonance (EPR) study of 4-amino-TEMPO (T-NH 2 ) and 4-carboxy-TEMPO (T-COOH) nitroxide radicals deposited on dry cotton has been conducted. Spectra are recorded as a function of probe loading (2 × 10 -5 to 10 -2 mol kg -1 ), temperature (293-333 K), and relative humidity (RH, 6 and 75%) and compared to results from the neutral probe 4-hydroxy TEMPO (T-OH). The effective internal pH of the cotton was measured using codeposited indicator dyes, which showed that both probes were charged, T-COO -and T-NH 3 + , at loadings up to and including 10 -3 mol kg -1 . Three components contribute to the spectra, corresponding to (a) mobile radicals absorbed in the bulk amorphous regions, (b) slowly moving radicals adsorbed on the crystallite surfaces in cotton, and (c) aggregated radicals. Independent of loading, the mobile T-NH 3 + experience a highly polar aqueous-like environment at 75% RH, which became much less polar at 6% RH as water was removed from the cotton. An analogous but much smaller drop in polarity was found for T-COO -, ascribed to the higher hydrogen-bonding ability of the probe, binding water more effectively. The rotational correlation time of mobile T-NH 3 + and T-COO -radicals had much larger activation energies than T-OH and different loading dependencies. This was ascribed to interactions with the 5.3 mmol kg -1 of carboxylic acid groups in cotton, so that the charged probes monitor different aspects of the cellulose chain relaxation. The enthalpy and entropy of the adsorption equilibrium between mobile and adsorbed radicals was extracted at 10 -3 mol kg -1 . Values were independent of humidity except for T-COO -, because of its stronger interactions with water. Both the T-NH 3 + and the T-COO -probes preferentially adsorb on less constricted binding sites than T-OH. At 10 -2 mol kg -1 , the carboxy probe becomes predominately protonated, T-COOH, radically changing the spectra observed, with a much greater fraction of mobile radicals. For the amino probe, the spectra at 10 -2 mol kg -1 are dominated by aggregated radicals.

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Section: Rotational Motion and Low Field Line Widthmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effect of Charge on Spin Probe Interaction and Dynamics in the Nanopores of Cotton

Frantz¹,

Wendland²,

Roduner³

et al. 2007

J. Phys. Chem. C

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“…Electron paramagnetic resonance (EPR) spin probing [19][20][21][22][23] has proved to be particularly useful. Electron paramagnetic resonance (EPR) spin probing [19][20][21][22][23] has proved to be particularly useful.…”

Section: New Insights Into Substrate Structurementioning

confidence: 99%

“…The nitroxide EPR spectra were surprisingly complex and dynamic [20][21][22][23], with the radicals found in at least three different environments, as depicted in Figure 1. For TEMPOL, at low loadings of up to~5 9 10 À3 mol kg À1 , the radicals existed in an equilibrium between being adsorbed on the surface of the crystallite or freely mobile within the amorphous regions [21,22].…”

Section: New Insights Into Substrate Structurementioning

confidence: 99%

New insights into dye chemistry and physics

Batchelor

2015

Coloration Technology

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A review of the academic dye research performed by the Port Sunlight group and its coworkers over the past 15 years is presented. The work is focused on three areas: (1) substrate structure; (2) dye interactions in aqueous solution and on substrates; (3) dye degradation and products. For substrates, a detailed model of the nanoenvironment experienced by chemicals within cellulose fibre is given, showing the different environments and remarkable mobility of absorbed chemicals. Advanced nuclear magnetic resonance diffusion measurements provide the complex pathways by which compounds find their way in and out of the fibre. For dye interaction, detailed theoretical and experimental studies are reported on three model dye systems, the anionic monoazo dye Orange II, the bisazo anionic dye CI Direct Blue 1, and cationic monoazo thiazolium dyes, providing a comprehensive picture of their structure. A quantitative mechanism of dye binding to cellulose is shown. Resonance Raman provides an effective forensic tool for dye identification, even from single fibres. The products and kinetics of Orange II dye degradation by one-electron reduction in aqueous solution is given, with the identification of an indophenol dye end-product. In cellulosic materials the reduction mechanism is similar to solution, when the higher microviscosity is accounted for. Hydrolysis of thiazolium dyes occurs at both aromatic rings of the dye but on different timescales. Measurement and calculations of the electronic structures of one-electron-reduced and -oxidised dyes are presented. The mechanism of photooxidation by sunlight of azo dyes in cotton is delineated.

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“…Spin probing experiments, where a stable nitroxide radical is doped into the fiber and its EPR spectrum recorded, give useful information. [2][3][4] Here a detailed spin probe study of two important synthetic fibers, Nylon 6,6 and Elastane, is reported. Nylon 6,6 is formed from polyhexamethylenediamide, 5 and Elastane is formed from polyurethane-poly(ethylene glycol) copolymers: 6 Nylon 6,6 is 50% crystalline, as measured by X-ray diffraction, 5,7 and hence is 50% amorphous.…”

Section: Introductionmentioning

confidence: 99%

Free Radical Motion in the Supramolecular Structure of Nylon 6,6 and Elastane, Studied by Quantitative Spin Probing

2007

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An electron paramagnetic resonance investigation of the nano-environment within Nylon 6,6 and Elastane fibers, using the TEMPOL (4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy) nitroxide radical as a spin probe is reported as a function of radical loading, temperature, and relative humidity. Within Elastane, only rapidly rotating radicals are observed and assigned to radicals absorbed in the bulk amorphous regions. Within Nylon, slowly moving radicals are found which are thought to be adsorbed on the surface of crystallites. From simulation of the spectra, the rotational correlation times are extracted, and the activation energy and preexponential factor for the motion are obtained from the temperature dependence. For both fibers, the activation energy was much lower than in liquids and showed small but pronounced variation with the fiber water content. The local polarity experienced by the probe was extracted from the spectra via the hyperfine constant and indicated a nonaqueous polar environment more or less independent of water content. These effects are rationalized in terms of the chain relaxations in the fibers. At high radical loadings (>10 -2 mol kg -1 ) in Nylon, strong spin exchange effects were seen and assigned to the onset of radical aggregation in the fiber; however, in Elastane, there was no evidence of spin exchange up to a loading of 5 × 10 -2 mol kg -1 .

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Quantitative Electron Paramagnetic Resonance Study of the Motion, Adsorption, and Aggregation of TEMPOL Radicals in the Nanopores of Dry Cotton

Cited by 18 publications

References 14 publications

Effect of Charge on Spin Probe Interaction and Dynamics in the Nanopores of Cotton

Effect of Charge on Spin Probe Interaction and Dynamics in the Nanopores of Cotton

New insights into dye chemistry and physics

Free Radical Motion in the Supramolecular Structure of Nylon 6,6 and Elastane, Studied by Quantitative Spin Probing

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