Electron Spin Echo Modulation Research Articles

Electron spin resonance, electron spin echo modulation, and electron nuclear double resonance studies of the photoionization of N-alkyl-N,N',N'-trimethylbenzidine in anionic and cationic micelles

N-Alkyl-N,N',N'-trimethylbenzidines (C[sub n]TMB, n = 1-6, 8) were synthesized and photoionized in rapidly frozen anionic and cationic micelles. The photoyields of the cation radicals were investigated by electron spin resonance spectroscopy. Electron spin echo modulation spectroscopy and proton matrix electron nuclear double resonance were used to determine the relative location of the photoproduced cation radical with respect to the deuterated aqueous interface. No dependence on the photoyield as a function of the electron donor alkyl chain length is observed, although increasing the alklyl chain length on the benzidine moiety moves its location toward the aqueous interface. The lack of a photoyield trend is interpreted in terms of the solubilization geometry, which determines the paths of electron escape to form charge-separated products. An electron escape cone defined as the solid angle formed from the center of the electron donor moiety through the width of the spin distribution that interests the interface changes only slowly as a function of radical location over a limited range. Hence, the photoyield is little changed. 34 refs., 7 figs., 1 tab.

Mixed micelles of SDS/C12E6 and DTAC/C12E6 surfactants

Electron spin echo modulation (ESEM) of x-doxylstearic acid spin probes (x-DSA, x = 5, 7, 10, 12, and 16) in mixed micellar solutions of ionic and nonionic surfactants has been studied as a function of the doxyl position along the alkyl chain of the stearic acid spin probe and of the mixed micellar composition. The mixed micellar systems investigated were sodium dodecyl sulfate (SDS) or dodecyltrimethylammonium chloride (DTAC) with hexakis(ethylene glycol) monododecyl ether (C[sub 12]E[sub 6]), selectively deuterated along the poly(ethylene glycol) group (C[sub 12]D[sub 6]) or along the alkyl chain ((CD)[sub 12]E[sub 6]) in H[sub 2]O and D[sub 2]O. The average probe conformation and probe location in the pure surfactants and in the mixed micelles are reported as a function of the doxyl position, x. Modulation effects due to the interactions of the probe unpaired electron with deuterium in D[sub 2]O give direct evidence that the hydration is maximized for an equimolar mixture of SDS/C[sub 12]E[sub 6] mixed micelles. It is also found that the polar head groups of SDS and DTAC surfactants are located in the ethylene oxide region of the C[sub 12]E[sub 6] surfactant. A comparative analysis of the deuterium modulation depth, arising from deuteriums located inmore » the alkyl chain or in the ethylene oxide groups of the nonionic surfactant, shows that SDS polar head groups are located at the surface of the mixed micelle, close to the second ethylene oxide group of C[sub 12]E[sub 6], while DTAC polar head groups are located deeper inside the mixed micelle, at the 5th-6th ethylene oxide group of the nonionic surfactant. These results provide an explanation at the molecular level of the different thermodynamical behavior found for mixed micelles of anionic-nonanionic and cationic-nonionic surfactants. 44 refs., 8 figs.« less

Solvate structures in water‐methanol solutions of MRI contrast agents: Electron spin echo envelope modulation in gadolinium chelates

Electron Spin Echo Envelope Modulation (ESEEM) data are reported for three gadolinium (III) chelates, Gd-EDTA, Gd-DTPA, and Gd-TTHA, in frozen D2O/CH3OD glasses. This series includes Gd-DTPA, an MRI contrast agent that is in clinical use. Three-pulse electron spin echo modulation patterns can be modeled to yield geometrical information; e.g., distances and numbers of Gd+3-OD interactions. Interpreted by a spherical shell model, the data for Gd-TTHA are accounted for by Gd+3 surrounded by seven deuterons at an effective distance of 3.9 A. We attribute these deuterons to second-coordination sphere solvent molecules, since it is likely that Gd+3 is fully coordinated by a TTHA ligand. For analysis of ESEEM from Gd-EDTA and Gd-DTPA, the second-sphere structures of Gd-EDTA, Gd-DTPA, and Gd-TTHA are assumed equivalent. 2H-ESEEM from inner-sphere solvent molecules gives the effective distance between deuterons and Gd+3 to be approximately 2.7 A for the inner-sphere water in both EDTA and DTPA complexes. The results of simulations also give the isotropic hyperfine and quadrupole coupling constants for solvent deuterium in these systems. Possible sources of error in the determination of r and q by this method are discussed.

ChemInform Abstract: An Electron Magnetic Resonance Study on the Photoionization of N‐ Alkylphenothiazines in Dioctadecyldimethylammonium Chloride Frozen Vesicles: The Effect of Urea, 1,3‐Dimethylurea, 1,3‐Diethylurea, and 1, 1′,3,3′‐Tetramethylurea.

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Comparative electron spin resonance and electron spin echo modulation studies of the photoionization of positively and negatively charged and neutral alkylphenothiazines in cationic dioctadecyldimethylammonium chloride, neutral dipalmitoylphosphatidylcholine, and anionic dihexadecyl phosphate vesicles at 77 K

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTComparative electron spin resonance and electron spin echo modulation studies of the photoionization of positively and negatively charged and neutral alkylphenothiazines in cationic dioctadecyldimethylammonium chloride, neutral dipalmitoylphosphatidylcholine, and anionic dihexadecyl phosphate vesicles at 77 KYoung Soo Kang, Hugh J. D. McManus, and Larry KevanCite this: J. Phys. Chem. 1993, 97, 9, 2027–2033Publication Date (Print):March 1, 1993Publication History Published online1 May 2002Published inissue 1 March 1993https://doi.org/10.1021/j100111a049RIGHTS & PERMISSIONSArticle Views103Altmetric-Citations20LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (792 KB) Get e-Alerts

Electron paramagnetic resonance and electron spin echo modulation spectroscopic studies on the location and adsorbate interactions of paramagnetic Pd ion species in PdII-exchanged K-L zeolite

Dehydration and adsorbate (O2, H2O, CD3OH, CH3OD, CH3CH2OD, C2D4, CO) interactions of paramagnetic palladium ion species in PdII-exchanged K-L channel type zeolite are studied by electron paramagnetic resonance (EPR) and electron spin echo modulation (ESEM) spectroscopies. The EPR spectrum of an activated sample at ca. 400–500 °C shows the formation of one PdI species which has g∥= 2.821 and g⊥= 2.125 and which is suggested to be located at the centre of double eight rings of the L zeolite framework. Adsorption of oxygen on an activated sample oxidizes the reduced PdI to PdII interacting with a superoxide ion. Equilibration with methanol or ethanol results in a broad isotropic EPR signal which is attributed to the formation of small charged palladium clusters. ESEM shows that the Pd clusters coordinate to one molecule of methanol or ethanol. EPR and ESEM results indicate that equilibration with C2D forms a new PdI species with g∥= 2.661 and g⊥= 2.125 coordinating to one molecule of ethene. Adsorption of carbon monoxide results in a complex containing two molecules of carbon monoxide based upon resolved 13C superhyperfine and analysis of 13C modulation.

Location of palladium(I) species and adsorbate interactions in PdH-SAPO 5 molecular sieve determined by electron spin resonance and electron spin echo modulation spectroscopies

Electron spin resonance (SSR) and electron spin echo modulation (SSSM) have been used to determine the location of Pd + and its interaction with water, methanol, and hydrogen in PdH-SAPO-5. After activation at 600 o C two different Pd + species are observed: A (g ∥=2.96) and B (g ∥=2.68) with a common g ⊥=2.13. The adsorption of water on activated samples results in the decomposition ofwater with formation of O 2 - and the simultaneous disappearance of the B signal

Electron paramagnetic resonance, electron spin echo modulation and electron nuclear double resonance studies on the photoionization of N-alkylphenothiazines in cetyltrimethylammonium bromide–alcohol reverse micelles. Effects of alkyl chain length of alkylphenothiazines, reverse micellar water pool size and cosurfactant alcohol

Neutral N-alkylphenothiazines (PCn, n= 1, 3, 6, 9, 12, 16) are solubilized and photoionized in cetyltrimethylammonium bromide (CTAB)–alcohol reverse micelles at 77 K to investigate the optimum photoionization conditions by varying the cosurfactant alcohol, reverse micellar water pool size and pendant alkyl chain length. The photo-produced radicals are identified and quantified by electron paramagnetic resonance (EPR). The relative locations from deuteriated water at the interface are monitored by deuteron electron spin echo modulation (ESEM) and proton matrix electron nuclear double resonance (ENDOR).The photoyields and deuteron modulation depths of PCn compounds show a U-shaped trend with increasing pendant alkyl chain length which indicates U-shaped conformations for the longer alkyl chains. The photoyields of the PCn compounds decrease with the water to surfactant mole ratio and correlate with decreasing deuteron modulation depths which indicate an increasing distance from the phenothiazine moiety to deuteriated interface water. The deeper penetration is attributed to a decreased packing density of the interface region of the reverse micelles. This is supported by decreasing ENDOR linewidths with increasing water pool size.A change of cosurfactant alcohol from butanol to octanol slightly decreases the photoyield and the deuteron modulation depths. This reflects deeper solubilization and a decreased rate of photoinduced radical conversion.

Anionic coordination involvement in solid-state ion-exchanged CuH-SAPO-n(n= 5, 11 and 34) molecular sieves

High-temperature solid-state ion exchange has been performed with H-SAPO-5 and various copper(II) compounds. Electron paramagnetic resonance (EPR) shows that this technique introduces CuII cations by ion exchange into H-SAPO-5, producing (S)Cu(F)H-SAPO-5 and (S)Cu(O)H-SAPO-5, where (S) indicates solid-state ion exchange and the subscripts F and O indicate the copper sources CuF2 and CuO used in the solid-state reaction. The EPR parameters for both hydrated and dehydrated samples of (S)Cu(F)H-SAPO-5 and (S)Cu(O)H-SAPO-5 vs.(L)CuH-SAPO-5, where (L) indicates liquid-state ion exchange, show differences which are suggested to be due to anion involvement in the coordination of copper(II). This is supported by electron spin echo modulation data which show that the distances between CuII and several adsorbates in (S)Cu(F)H-SAPO-5 are shorter than those for (L)CuH-SAPO-5 by 0.02–0.04 nm. Similar differences are observed for (S)Cu(F)H-SAPO-34 and (S)Cu(Cl)H-SAPO-34 vs.(L)CuH-SAPO-34 and for (S)Cu(O)H-SAPO-11 vs.(L)CuH-SAPO-11. The g anisotropy also supports a decrease in symmetry owing to anion involvement.

Electron paramagnetic resonance and proton matrix electron nuclear double resonance studies of N,N,N′,N′-tetramethylbenzidine photoionization in sodium dodecyl sulfate micelles: structural effects of added alcohols

An electron nuclear double resonance and electron paramagnetic resonance study of photogenerated N,N,N′,N′-tetramethylbenzidine (TMB) cation in frozen suspensions of sodium dodecyl sulfate micelles containing various concentrations of alcohols has been undertaken. The alcohols used in the study were ethanol, propan-2-ol, butan-1-ol and octan-1-ol. Experiments were performed with both the deuteriated and protonated analogues of these molecules. The photoyields were determined from double integration of the first-derivative electron paramagnetic resonance spectra. The location of the TMB cation relative to the micelle interface was determined from the proton matrix electron nuclear double resonance (H-ENDOR) linewidth at 140 K. In general, the TMB radical cation was observed to have a broader H-ENDOR linewidth for samples in which the protonated alcohol was used. This difference increased when longer-chained alcohols were used. The results demonstrate that the shorter chain length alcohols are located at the micellar interface, whereas both butan-1-ol and octan-1-ol intercalate deeper into the hydrocarbon interior of the micelle. The photoyield grew with alcohol addition up to 50 mmol dm–3, after which the yield decreased. The maximum yield was obtained in samples with short-chain alcohols. These results showed that the yield depended on the degree of disruption of the micelle/water interface. Although hydration of the interface stabilizes the photogenerated cation thus increasing the yield, this effect competes with the disruption of the interfacial region and concomitant decrease of the negative surface charge. The lower negative surface charge helps increase back electron transfer. The results from this ENDOR study are consistent with recent work involving electron spin echo modulation spectroscopy, which showed greater water penetration into the micellar interface upon addition of alcohol.

Electron spin resonance and electron spin echo studies of copper(II) ion location and coordination geometry in Na-, K-, and Rb-SAPO 42

Cu(II) ions in Na + , K + , K + , and Rb + cationic forms of SAPO-42 are investigated. The various Cu(II) species generated after dehydration and exposure to absorbates are examined with electron spin resonance and electron spin echo modulation techniques. The results are interpreted in terms of Cu(II) ion location and coordination geometry. The conclusions are compared to those of Cu(II) ions in zeolite A, which is the aluminosilicate structural analog of SAPO-42

An electron magnetic resonance study on the photoionization of N-alkylphenothiazines in dioctadecyldimethylammonium chloride frozen vesicles: the effect of urea, 1,3-dimethylurea, 1,3-diethylurea, and 1,1',3,3'-tetramethylurea

Photoionization of N-alkylphenothiazines was carried out in frozen dioctadecyldimethylammonium chloride (DODAC) vesicle suspensions to which various concentrations of urea, 1,3-dimethylurea (DMU), 1,3-diethylurea (DEU), 1,1{prime},3,3{prime}-tetramethylurea (TMU) had been added. The photoproduced cation radical yields were investigated by electron spin resonance (ESR). Electron spin echo modulation (ESEM) and electron nuclear double resonance (ENDOR) spectroscopies were used to probe the microenvironment of the photoproduced cation. The concentration of each of the urea derivatives was systematically varied. Urea, DMU, and DEU showed a similar trend in the photoyield versus concentration, with the highest yield obtained at 1 M additive. For TMU the photoyield of phenothiazine increased as a function of additive concentration. The different photoyield trends are explained in terms of the effect of urea on the DODAC vesicule interface. This interpretation is supported by the ESEM and ENDOR studies. Urea and its derivatives appear to interact with water through the {open_quotes}direct mechanism{close_quotes}. The ESR data for these species suggest that impregnation for the vesicle interface with urea decreases the strength of the photoproduced cation-water interactions which leads to a decrease in the photoyield. The ESE and ENDOR results for TMU suggest that this bulky additive opens up the vesicle interface to water penetration.more » The steady increase in the photoyield with TMU concentration together with the ESEM and ENDOR results support this interpretation of the ESR data. 49 refs., 10 figs.« less

Electron spin resonance and electron spin echo modulation studies of copper(II) ions in the aluminosilicate chabazite: a comparison of copper(II) cation location and adsorbate interaction with isostructural silicoaluminophosphate-34

This study focuses on Cu(II) ions exchanged in the aluminosilicate zeolite chabazite. The various Cu(II) species formed after dehydration, rehydration, and exposure to adsorbates are characterized by electron spin resonance and electron spin echo modulation spectroscopies. These results are interpreted in terms of Cu(II) ion location and adsorbate interaction. The results of this study are compared to the results found earlier for SAPO-34, chabazite`s structural analog from the silicoaluminophosphate group. In a hydrated sample of chabazite the Cu(II) ions are found to be in a near octahedral environment coordinated to three nonequivalent water molecules and three framework oxygens. The most probable location of the Cu(II) ion in a hydrated sample is above the plane of the six-membered ring slightly displaced into the ellipsoidal cavity. A somewhat similar location and coordination is found for Cu(II) ions in H-SAPO-34. A feature common to both CuH-chabazite and CuH-SAPO-34 is the generation of two distinct Cu(II) species upon dehydration. It is found that Cu(II) cations in chabazite interact with the various adsorbate molecules in a similar manner as Cu(II) cation in H-chabazite and three molecules of ethanol and three propanol molecules. Only the Cu(II) ions located in the hexagonal rings after dehydration were foundmore » to complex with ethylene. The differences observed in the interaction of the Cu(II) in with water, propanol, and ehtylene between SAPO-34 and chabazite can be related to the differing cation densities of these two materials. 32 refs., 7 figs., 21 tabs.« less

Comparative electron magnetic resonance, electron spin echo modulation, and electron nuclear double resonance studies of the photoionization of N-alkylphenothiazines in variously charged micelles and vesicles

Photoirradiation of N-alkylphenothiazines (PC n , n=1, 3, 6, 9, 12, 16) in cationic dodecyltrimethylammonium bromide and anionic sodium dodecyl sulfate micelles and in cationic dioctadecyldimethylammonium bromide, neutral dihexadecanoyl-phorphatidylcholine, and anionic dihexadecyl phosphate vesicles was carried out to study the effect of varying the length of a pendant alkyl chain on the photoionization yield. Electron spin resonance spectroscopy was used to measure the photoyield of the alkylphenothiazine cation radical. A secondary surfactant alkyl radical and the methyl radical were also observed

Electron spin resonance and electron spin echo modulation spectroscopic studies on the structure and reactivity of palladium(I) species in SAPO-11 molecular sieves

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTElectron spin resonance and electron spin echo modulation spectroscopic studies on the structure and reactivity of palladium(I) species in SAPO-11 molecular sievesChul Wee Lee, Jong Sung Yu, and Larry KevanCite this: J. Phys. Chem. 1992, 96, 19, 7747–7751Publication Date (Print):September 1, 1992Publication History Published online1 May 2002Published inissue 1 September 1992https://doi.org/10.1021/j100198a047RIGHTS & PERMISSIONSArticle Views97Altmetric-Citations12LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (590 KB) Get e-Alerts

Pulsed EPR studies of the type 2 copper binding site in the mercury derivative of laccase.

The nuclear modulation effect in pulsed EPR spectroscopy was used to study the type 2 copper binding site in the mercury derivative of laccase (MDL) in which the type 1 copper is substituted by Hg(II). By comparing the three-pulse electron spin-echo modulations and Fourier transform spectra of MDL and several model compounds, we conclude that the imidazole groups of two histidyl amino acid residues are equatorially coordinated to Cu(II) in the type 2 site. Computer simulations of these data suggest that the remote nonbonding nitrogens of the two imidazoles possess nuclear quadrupole parameters e2qQ = 1.47 MHz and eta = 0.83. A(iso) values of these two nitrogens are not identical, being 1.5 and 2.0 MHz. We have also used samples of the enzyme exchanged with D2O to examine the coordination of the water to the type 2 copper site. The deuterium modulation that is resolved by taking the ratio of the time domain ESEEM data from native and D2O-exchanged enzyme indicates that there is an equatorial water ligand, and further data show that this water is displaced by azide.

Photoionization of neutral alkylphenothiazines in positive, neutral, and negatively charged vesicles: effects of the addition of cholesterol and alkyl chain length

The photoionization of alkylphenothiazines in cationic dioctadecyldimethylammonium chloride (DODAC), neutral dipalmitoylphosphatidylcholine (DPPC), and anionic dihexadecylphosphate (DHP) vesicles of different surface charge, after addition of cholesterol, was studied by electron spin resonance (ESR) and electron spin echo modulation (ESEM) methods

Solid-state ion exchange in H-SAPO-34: electron spin resonance and electron spin echo modulation studies of copper(II) location and adsorbate interaction

ESR and ESEM are used in this paper to study Cu(II) ion location and interaction with water, alcohols, ammonia, and ethylene in the solid-state reactions of H-SAPO-34 with various copper compounds (CuO, CuCl{sub 2}, CuF{sub 2}). The Cu(II) ions migrate from the exterior to the interior of the molecular sieve similar to an aqueous ion exchange method. Two types of Cu(II) complexes form during the adsorption of methanol, but only one complex type forms with the rest of the adsorbates. Cu(II) interactions with other adsorbate molecules are also discussed. 20 refs., 3 figs., 2 tabs.

Electron spin echo modulation studies of doxylstearic acid spin probes in frozen dihexadecyl phosphate and dioctadecyldimethylammonium chloride vesicles: interaction of the spin probe with deuterated water and effects of cholesterol addition

Electron spin echo studies have been carried out for a series of x-doxylstearic acid (x=5, 7, 10, 12, and 16) and 3-doxyl-5α-cholestane spin probes in frozen deuterated aqueous solutions of anionic dihexadecyl phosphate (DHP) vesicles and cationic dioctadecyldimethylammonium chloride (DODAC) vesicles. Modulation effects due to interactions of the spin probe nitroxide group with D 2 O at the vesicle interface give distance-based information which can be used to draw conclusions about the ordering and chain packing of the vesicles

Evaluation of manganese(II) framework substitution in MnAPO-11 and Mn-impregnated AlPO4-11 molecular sieves by electron spin resonance and electron spin-echo modulation spectroscopy

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEvaluation of manganese(II) framework substitution in MnAPO-11 and Mn-impregnated AlPO4-11 molecular sieves by electron spin resonance and electron spin-echo modulation spectroscopyGuillaume Brouet, Xinhua Chen, Chul Wee Lee, and Larry KevanCite this: J. Am. Chem. Soc. 1992, 114, 10, 3720–3726Publication Date (Print):May 1, 1992Publication History Published online1 May 2002Published inissue 1 May 1992https://doi.org/10.1021/ja00036a022RIGHTS & PERMISSIONSArticle Views192Altmetric-Citations58LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (786 KB) Get e-Alerts Get e-Alerts