Electron Spin Echo Modulation Studies Research Articles

Electron spin resonance and electron spin echo modulation studies of Fe-containing mesoporous MCM-48 molecular sieves

Through electron spin resonance (ESR) and electron spin echo modulation (ESEM) studies, three Fe(III) species are found in liquid ion-exchanged Fe-MCM-48 and synthesized FeMCM-48. Species A with ESR parameters gA = 4.30 with a line width of 160 G is observed in hydrated samples. This species is accompanied by a shoulder atg = 7.60 and is assigned to distorted tetrahedral Fe(III) likely located at framework defect sites. Species B is a broad peak centered at gB = 2.00 and is assigned to distorted octahedral Fe(III) located at extraframework sites. This species is also observed in dehydrated samples. Species C is a very narrow isotropic signal at gC = 4.30 with a line width of 30 G and is only observed in synthesized mesophase materials. It is consistent with rhombic Fe(III) with zero field parametersD andE corresponding toD/E =1/3 and is assigned to tetrahedral Fe(III) located at framework sites. Framework Fe(III) in FeMCM-48 is less accessible to ND3 than is extraframework Fe(III) in Fe-MCM-48. On the basis of deuterium ESEM data, framework Fe(III) in synthesized FeMCM-48 directly coordinates to two D2O or CH3OD molecules and interacts more weakly with two more molecules. However, no deuterium ESEM is observed for extraframework Fe(III) in ion-exchanged Fe-MCM-48 with adsorbed D2O or CH3OD. It is also found that Fe(III) is incorporated into the framework of FeMCM-48 at an early stage of the formation of the MCM-48 mesostructure.

Electron Spin Resonance and Electron Spin Echo Modulation Studies of Adsorbate Interactions with Cupric Ion on the Aluminum Content in Cu−AlMCM-41 Materials

Employing electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopy, adsorbate interactions are studied in two types of ion-exchanged Cu−AlMCM-41 materials. One is structurally ordered Cu−AlMCM-41(60)-I, Cu−AlMCM-41(40)-I, Cu−AlMCM-41(20)-I, and the other is less structurally ordered Cu−AlMCM-41(15)-II. Four Cu(II) species are observed by ESR. Species A with ESR parameters g∥A = 2.406, A∥A = 0.0145 cm-1, and g⊥A = 2.081 is assigned to octahedral Cu(II) and is observed in hydrated Cu−AlMCM-41. Species B with g∥B = 2.317, A∥B = 0.0176 cm-1, and g⊥B = 2.076 is assigned to distorted octahedral Cu(II) and is observed in dehydrated samples. Species C with g∥C = 2.430, A∥C = 0.0125 cm-1, and g⊥C = 2.091 is also assigned to octahedral Cu(II) and is observed after adsorption of CH3OD. Species D contains square planar D1 Cu(II) with g∥D1 = 2.280, A∥D1 = 0.0168 cm-1, and g⊥D = 2.058, and distorted octahedral D2 Cu(II) with g∥D2 = 2.249 and A∥D2 = 0.0190 cm-1 after adsorption of ammonia. The...

Electron Spin Resonance and Electron Spin Echo Modulation Studies on the Formation and Adsorbate Interactions of Ni(Ι) in Synthetic Clinoptilolite

Electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopies were used to study the formation of Ni(Ι) by various reduction methods and various adsorbate interactions of Ni(Ι) in synthetic clinoptilolite, in which Ni(ΙΙ) was ion-exchanged into extraframework sites of clinoptilolite. Thermal reduction by dehydration at 573 K shows a single species assigned to Ni(Ι) ions. Two isolated Ni(Ι) ions are observed after hydrogen reduction at 623 K. Adsorption of methanol on hydrogen-reduced NiNaK−Clino forms a Ni(Ι)−(CD3OH)n complex resulting from the interaction of methanol with one of the isolated Ni(Ι) ions. Adsorption of ammonia on hydrogen-reduced NiNaK−Clino produces a prominent Ni(Ι)−(ND3)n complex by interaction with both Ni(Ι) ions. The 13C hyperfine structure and ESEM analysis parameters after 13CO adsorption indicate that Ni(Ι) interacts with one CO molecule and forms a Ni(Ι)−(CO)1 complex. Two Ni(Ι)−(C2D4)n complexes are generated after adsorption of ethylene on dehydrated Ni(II)NaK−Clino and subsequent heating below 623 K. At higher temperature, these species disappear with the concomitant formation of two Ni(Ι)−(C4D8)n complexes, indicating ethylene dimerization. 2D ESEM confirms the coordination of Ni(Ι) with butene. Adsorption of NO on dehydrated Ni(II)NaK−Clino produces two Ni(Ι)−NO+ complexes formed by transfer of the odd electron from NO to Ni(ΙΙ) ions. Along with two Ni(Ι)−NO+ species, another species assigned to the NO radical is also observed in NiNaK−Clino after NO adsorption on Ni(II)NaK−Clino and NaK−Clino.

Electron Spin Resonance and Electron Spin−Echo Modulation Studies of Synthesized NiAPSO-34 Molecular Sieve and Comparison with Ion-Exchanged NiH−SAPO-34 Molecular Sieve

The formation of monovalent nickel in NiAPSO-34 where nickel is believed to be incorporated into the framework of SAPO-34, and its interaction with several adsorbates are compared to Ni(I) species formed in NiH−SAPO-34, where Ni(II) is incorporated by solid-state ion exchange into known extraframework sites using electron spin resonance (ESR) and electron spin−echo modulation (ESEM) spectroscopies. Dehydration at temperatures above 573 K and hydrogen treatment at 573 K as well as γ-irradiation at 77 K produce one nickel species assigned by ESR as isolated Ni(I) in the two samples. Even though the ESR parameters of isolated Ni(I) species are similar after reduction, NiAPSO-34 and NiH−SAPO-34 show noticeable differences in their ESR characteristics after adsorption of various adsorbates, suggesting that Ni(I) in these two materials is in different sites. As a supplement to this, ESEM studies of 31P and 27Al, used to ascertain the location of the incorporated paramagnetic transition metal ion, also show significant differences in the modulation patterns. Simulation of the 31P modulation observed for NiH−SAPO-34 shows two nearest-neighbor phosphorus atoms at 3.9 Å and three next-nearest-neighbor phosphorus atoms at 6.5 Å, indicating that Ni(I) is at site II‘ in the chabazite cage near a six ring window after reduction. The 31P simulation for NiAPSO-34 shows three nearest-neighbor phosphorus atoms at a distance of 4 Å and two next-nearest-neighbor phosphorus atoms at 5.3 Å. This is consistent with Ni(I) ions substituting into a framework phosphorus site. In as-synthesized NiAPSO-34, the nickel ion is possibly also coordinated to additional waters to give distorted octahedral coordination. On dehydration, tetrahedrally coordinated nickel in a framework site of SAPO-34 is formed.

ESR and ESEM studies of Mn-containing MCM-41 materials

Abstract Through electron spin resonance (ESR) and electron spin echo modulation (ESEM) studies, three Mn(II) species are found in three kinds of Mn-containing MCM-41 materials: ion-exchanged Mn-MCM-41, synthesized MnMCM-41 and synthesized MnMCM-41(Ca) with subsequent CaCl 2 exchange. Mn(II) species I with a well-resolved sextet centered at g =2.007 has distorted octahedral symmetry and is observed in hydrated ion-exchanged Mn-MCM-41 and in synthesized calcined MnMCM-41. Mn(II) species II with g =5.2 and 3.2 is observed in dehydrated Mn-MCM-41 and MnMCM-41; attributed to zero field interactions. Both species I and II correspond to extra-framework Mn(II). Mn(II) species III, with a symmetric line at g =2.004 and a broad line-width of 250 to 350 G is assigned to framework sites. Extra-framework Mn(II) species I and II coordinate with four D 2 O and are accessible to water, but framework Mn(II) species III coordinates with only three D 2 O and is less accessible to water.

Electron Spin Resonance and Electron Spin Echo Modulation Studies on Reducibility, Location, and Adsorbate Interactions of Ni(I) in Ni(II)-Exchanged SAPO-34

Electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopies were used to study the reducibility, location, and adsorbate interactions of Ni(I) in NiH−SAPO-34, in which Ni(II) was introduced into extraframework sites of SAPO-34 by partial ion exchange of H(I) by Ni(II). After dehydration at temperatures above 573 K as well as after γ-irradiation at 77 K, one nickel species assigned as isolated Ni(I) by ESR is observed. Along with the isolated Ni(I) species, a second species assigned to Ni(I)−(H2)n is also observed after hydrogen reduction at 573 K. Adsorption of water into reduced NiH−SAPO-34 forms an axially symmetric Ni(I)−(O2)n complex indicating water decomposition by Ni(I). Adsorption of methanol into reduced NiH−SAPO-34 forms two Ni(I)-methanol complexes suggested to be located at two different sites in the chabazite structure. Similarly, two Ni(I)−(C2D4)n complexes, the predominant one exhibiting axial symmetry and the other one having rhombic symmetry, are formed after eth...

Quenching of excited states of pyrene derivatives by amphiphilic nitroxide radicals in cationic micellar solutions. Dynamics and location of the guest molecules in the aggregates

Steady-state and nanosecond time-resolved studies have been performed on fluorescence quenching of excited pyrene sulfonic acid and pyrene butyric acid (PBA and PSA, respectively, in the form of sodium salts) by n-doxylstearic methyl esters ( n-DSE, n=5, 10, 12) in aqueous solution of cationic micelles of hexadecyltrimethylammonium chloride (HTAC, 0.1 M). The results are compared with those reported earlier for pyrene (P) as a luminophore (Szajdzinska-Pietek and Wolszczak, Chem. Phys. Lett., 270 (1997) 527). It is shown that PBA/ n-DSE and PSA/ n-DSE luminophore/quencher pairs, unlike P/ n-DSE pairs, are not suitable for determination of the micellar aggregation number, neither by the ‘quasi-static’ method of Turro—Yekta nor by the dynamic method of Infelt—Tachiya. It is suggested that the fluorescence decay curves in the examined systems can be adequately described in terms of dispersive kinetics using the time-dependent rate coefficient for intramicellar quenching process. The average location of the luminophore and the quencher molecules in the aggregates is discussed, considering previous findings of electron spin echo modulation studies of n-doxylstearic acid spin probes in micellar systems.

Electron spin resonance and electron spin echo modulation studies of Cu(II) cation locations and adsorbate interactions in ionexchanged Cu-MCM-22 zeolite

MCM-22 is a medium-pore high-silica-containing zeolite. Its unique structure contains two noninterconnected channel systems with potential for transition metal-based heterogeneous catalysis. Paramagnetic Cu(II) cation is ionexchanged into MCM-22 to act as a probe for electron spin resonance and electron spin echo modulation spectroscopic methods to verify the location of the ion-exchangeable sites. The electron spin resonance spectra of dehydrated Cu-MCM-22 are strikingly well-resolved and exhibit features related to both 63Cu and 65Cu nuclei. Interactions with water, ammonia, methanol, pyridine, benzene, cyclohexylamine and triethylamine adsorbed on Cu-MCM-22 are studied. Three types of ion-exchangeable extra framework site are identified.

Quenching of pyrene fluorescence by amphiphilic nitroxide radicals embedded in cationic micelles

Steady-state and nanosecond time-resolved studies have been carried out on the fluorescence quenching of excited pyrene by n-doxylstearic methyl esters ( n-DSE, n = 5, 10, 12) in an aqueous solution of cationic micelles of hexadecyltrimethylammonium chloride (HTAC, 0.1 M). The aggregation number ( N = 114 ± 6) and the rate constants of intramicellar quenching (1.4 × 10 7, 1.3 × 10 7 and 1.05 × 10 7 s −1 for 5-, 10- and 12-DSE respectively) have been determined. The results are discussed in terms of the average location of the luminophore and the quencher molecules in the aggregates, considering previous findings of electron spin echo modulation studies of n-doxylstearic acid spin probes in micellar systems.

CuIIlocation and adsorbate interaction in CuII-exchangedsynthetic Na-omega gallosilicate EPR and electron spin echo modulation studies

The location of CuII and its interaction with adsorbates in CuII-exchanged synthetic Na-omega gallosilicate have been studied by EPR and electron spin echo modulation (ESEM) spectroscopies. These results are compared with those of CuII-exchanged Na-omega aluminosilicate and also those of L and offretite gallosilicates of similar channel type and size, and the differences are discussed. In general, similar results to those for CuNa-omega gallosilicate are obtained for CuNa-omega aluminosilicate. It is concluded that, in fresh hydrated omega material, CuII is in a main channel coordinating to three water molecules and to framework oxygens in the main channel wall. A minor CuII diaquo species not seen in the gallosilicate is observed in the aluminosilicate. Upon evacuation at increasing temperature, CuII moves from the main channel to a gmelinite cage. Dehydration at 410°C produces one CuII species located in a six-ring window of a gmelinite cage, based on a lack of broadening of its EPR lines by oxygen. In L and offretite gallosilicates, there is evidence for back migration of CuII from a hexagonal prism into a main channel to coordinate with adsorbates. However, in omega the back migration from a gmelinite cage to a main channel seems to be blocked, as shown by very slow changes in the EPR spectra and differing coordination numbers for methanol, ethanol and propanol to CuII when alcohols are adsorbed. CuII does not form a complex with propanol or larger adsorbates in omega gallosilicate. It is suggested that, in omega, small adsorbates must diffuse into a gmelinite cage where CuII is located, to form CuII–adsorbate complexes. The slow changes in the EPR spectra correspond to the time for adsorbate diffusion into a gmelinite cage. CuII interacts with one molecule each of ethylene and acetonitrile, based on EPR and ESEM analyses. CuII forms a square-planar complex containing four molecules of ammonia, based on resolved nitrogen superhyperfine coupling.

Electron Spin Resonance and Electron Spin Echo Modulation Studies on Photoinduced Charge Separation from N-Alkylphenothiazines in Sodium Dodecyl Sulfate Micelles: Effect of α- and β-Cyclodextrin Addition

Photoinduced electron transfer from N-alkylphenothiazines (PCn, n = 3, 9, 12, 16) to D2O at a micellar interface was monitored versus the alkyl chain length of PCn and versus cyclodextrin (CD) addi...

Synthesis, electron paramagnetic resonance and electron spin echo modulation studies on synthesized NiAPSO-41 molecular sieve and comparison with ion-exchanged NiH-SAPO-41 molecular sieve

A. M. Prakash, M. Hartmann and L. Kevan, J. Chem. Soc., Faraday Trans., 1997, 93, 1233 DOI: 10.1039/A606398E

Electron spin echo modulation study of the Type I copper protein rusticyanin and its mutant variant His85Ala Implications for the general analysis of weak 14Nsuperhyperfine interactions

Electron spin echo modulation (ESEEM) spectra were recorded at 500 MHz intervals for the Type I protein rusticyanin and its engineered variant His85Ala, which lacks one of the two imidazole ligands to copper. The Zeeman and g-value dependence of the spectral peaks were systematically mapped and accurately predicted that low intensity lines in the wild type (w.t.) spectrum were combination lines, as verified in the His85Ala spectra. Analysis reveals that the w.t. ESEEM spectra are attributable to a pair of HisNε only, and the NQI parameters e2Qq and η are 1.37 ± 0.03 MHz and 0.90 ± 0.05 for both HisNε in the w.t. protein. The nuclear hyperfine interaction is estimated as 1.8 MHz, and includes a dipolar interaction of 0.5 MHz. The principal difference between the two imidazole nitrogen couplings is manifest in the dispersion of the combination lines, which suggests non-equivalent orientations of the respective superhyperfine tensors (or tilt of the imidazole ring). The protocol demonstrates a general procedure for accurately determining superhyperfine parameters from powder ESEEM spectra. Finally, peak shifts among ESEEM spectra of His85Ala–X (X = H2O, Cl−, Br−) demonstrate that the imidazole ligand powder superhyperfine spectrum is sensitive to chemical effects in the metal's ligand sphere, thus suggesting that the method may be used for evaluation in molecular design.

Silver atoms and clusters in molecular sieves and clays

Electron spin resonance (ESR) and electron spin echo modulation (ESEM) studies on small paramagnetic silver clusters generated radiolytically in molecular sieves and clays are reviewed. Special attention is paid to the role of framework structure with respect to cluster nuclearity and stability. In general, geometrical size constraints play a crucial role and molecular sieves with cage-like structures with small openings between the cages such as A and rho zeolites stabilize cationic silver clusters more efficiently than channel-like zeolite structures. In addition, other factors like total cation capacity, type of cocation and/or molecular adsorbate in the cages can affect the silver agglomeration process to a great extent. The mechanism of silver agglomeration in irradiated molecular sieves and clays based on the ESR results is described as well as the reactivity of tetrameric and hexameric silver clusters with various molecular adsorbates.

Electron Spin Resonance and Electron Spin Echo Modulation Studies of Cu(II) Ion Coordination and Adsorbate Interaction in Ion-Exchanged AlMCM-41 Mesoporous Materials

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTElectron Spin Resonance and Electron Spin Echo Modulation Studies of Cu(II) Ion Coordination and Adsorbate Interaction in Ion-Exchanged AlMCM-41 Mesoporous MaterialsAndreas Poppl, Martin Hartmann, and Larry KevanCite this: J. Phys. Chem. 1995, 99, 47, 17251–17258Publication Date (Print):November 1, 1995Publication History Published online1 May 2002Published inissue 1 November 1995https://doi.org/10.1021/j100047a032RIGHTS & PERMISSIONSArticle Views128Altmetric-Citations41LEARN 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 (954 KB) Get e-Alerts

Electron Spin Resonance and Electron Spin Echo Modulation Studies of the Incorporation of Macrocyclic-Complexed Cupric Ions into Siliceous MCM-41

Electron Spin Resonance and Electron Spin Echo Modulation Studies of the Incorporation of Macrocyclic-Complexed Cupric Ions into Siliceous MCM-41

Electron Spin Resonance and Electron Spin Echo Modulation Study of Ni(I) in Silicoaluminophosphate Type 5: Adsorbate Interactions and Evidence for the Framework Incorporation of Ni(I)

Electron Spin Resonance and Electron Spin Echo Modulation Study of Ni(I) in Silicoaluminophosphate Type 5: Adsorbate Interactions and Evidence for the Framework Incorporation of Ni(I)

Electron Spin Resonance and Electron Spin Echo Modulation Studies of Cupric Ion Ion-Exchanged into Siliceous MCM-41

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTElectron Spin Resonance and Electron Spin Echo Modulation Studies of Cupric Ion Ion-Exchanged into Siliceous MCM-41Andreas Poeppl, Mike Newhouse, and Larry KevanCite this: J. Phys. Chem. 1995, 99, 24, 10019–10023Publication Date (Print):June 1, 1995Publication History Published online1 May 2002Published inissue 1 June 1995https://doi.org/10.1021/j100024a051RIGHTS & PERMISSIONSArticle Views114Altmetric-Citations32LEARN 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 (579 KB) Get e-Alerts

Electron Spin Echo Modulation Studies of Doxylstearic Acid Spin Probes in Frozen Vesicle Solutions: Interaction of the Spin Probe with 31P in the Surfactant Headgroups

Electron Spin Echo Modulation Studies of Doxylstearic Acid Spin Probes in Frozen Vesicle Solutions: Interaction of the Spin Probe with 31P in the Surfactant Headgroups

Electron Spin Resonance and Electron Spin Echo Modulation Studies of Ni(I) in Silicoaluminophosphate Type 11: Reducibility and Location of Nickel Ions during Various Degrees of Dehydration

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTElectron Spin Resonance and Electron Spin Echo Modulation Studies of Ni(I) in Silicoaluminophosphate Type 11: Reducibility and Location of Nickel Ions during Various Degrees of DehydrationNaoto Azuma and Larry KevanCite this: J. Phys. Chem. 1995, 99, 14, 5083–5088Publication Date (Print):April 1, 1995Publication History Published online1 May 2002Published inissue 1 April 1995https://doi.org/10.1021/j100014a031RIGHTS & PERMISSIONSArticle Views84Altmetric-Citations21LEARN 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 (574 KB) Get e-Alerts