Electron Spin Echo Modulation Research Articles

Coordination Features and Affinity of the Cu2+ Site in the α-Synuclein Protein of Parkinson’s Disease

Parkinson's disease (PD) is the second most prevalent age-related, neurodegenerative disorder, affecting >1% of the population over the age of 60. PD pathology is marked by intracellular inclusions composed primarily of the protein α-synuclein (α-syn). These inclusions also contain copper, and the interaction of Cu(2+) with α-syn may play an important role in PD fibrillogenesis. Here we report the stoichiometry, affinity, and coordination structure of the Cu(2+)-α-syn complex. Electron paramagnetic resonance (EPR) titrations show that monomeric α-syn binds 1.0 equiv of Cu(2+) at the protein N-terminus. Next, an EPR competition technique demonstrates that α-syn binds Cu(2+) with a K(d) of ≈0.10 nM. Finally, EPR and electron spin echo modulation (ESEEM) applied to a suite of mutant and truncated α-syn constructs reveal a coordination sphere arising from the N-terminal amine, the Asp2 amide backbone and side chain carboxyl group, and the His50 imidazole. The high binding affinity identified here, in accord with previous measurements, suggests that copper uptake and sequestration may be a part of α-syn's natural function, perhaps modulating copper's redox properties. The findings further suggest that the long-range interaction between the N-terminus and His50 may have a weakening effect on the interaction of α-syn with lipid membranes, thereby mobilizing monomeric α-syn and hastening fibrillogenesis.

ChemInform Abstract: Synthesis and Characterization of Mn-Containing Cubic Mesoporous MCM-48 and AlMCM-48 Molecular Sieves.

Employing electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopy, five Mn(II) species are found in three kinds of Mn-containing MCM-48 materials: ion-exchanged Mn−MCM-48, synthesized MnMCM-48, and synthesized MnMCM-48(Ca) with subsequent CaCl2 exchange. Mn(II) species I with a well-resolved sextet centered at g = 2.00 has distorted octahedral symmetry and is observed in hydrated ion-exchanged Mn−MCM-48 and in synthesized calcined MnMCM-48. Mn(II) species II with a group of single peaks between g = 11.32 and 2.62 with possible distorted tetrahedral symmetry and a significant zero field contribution is observed in dehydrated Mn−MCM-48 and in MnMCM-48. Mn(II) species III with a symmetric line at g = 2.00 and a line width around 410 G is assigned to tetrahedral symmetry and is observed in MnMCM-48(Ca) and in MnAlMCM-48(Ca). Mn(II) species IV with a sextet centered from 4.11 to 4.34 also has distorted octahedral symmetry and is obtained in partially dehydrated Mn−MCM-48 and Mn−AlM...

Application of ESEEM to study the structure of free radicals

Manifestations of the hyperfine interaction of paramagnetic particles in their electron spin echo signal decay were comprehensively discussed. Mechanochemically activated calcium gluconate was studied using electron spin echo modulation phenomenon and electron-nuclear double resonance techniques and quantum-chemical calculations. Three possible structures are obtained for free radicals in calcium gluconate. To specify the structure of radicals, further investigations are needed.

Electron Spin Echo Study of Molecular Structure and Dynamics: New Approaches Based on Spontaneous Fluctuations of Magnetic Interactions

Modulation phenomena that take place during electron spin echo signal decay have long been used in structural studies of free radicals and their environment. These phenomena are based on coherent dynamic effects, arising from simultaneous excitation (by microwave pulses) of two or more transitions in the EPR spectrum. Recently, a new source of stimulated electron spin echo (ESE) modulation was discovered due to spontaneous changes in the magnetic parameters of radicals during the operation of the pulse sequence. For monoradicals, these changes are caused by intramolecular motions. For radical pairs, additional mechanisms are longitudinal relaxation of spin counterparts and transformations of the paramagnetic partners during chemical reactions. Promising applications of this phenomenon to structural studies of radicals and radical pairs in solids and to investigations of their mobility and chemical transformations are considered.

Intramembrane Polarity by Electron Spin Echo Spectroscopy of Labeled Lipids

The association of water (D 2O) with phospholipid membranes was studied by using pulsed-electron spin resonance techniques. We measured the deuterium electron spin echo modulation of spin-labeled phospholipids by D 2O in membranes of dipalmitoyl phosphatidylcholine with and without 50 mol% of cholesterol. The Fourier transform of the relaxation-corrected two-pulse echo decay curve reveals peaks, at one and two times the deuterium NMR frequency, that arise from the dipolar hyperfine interaction of the deuterium nucleus with the unpaired electron spin of the nitroxide-labeled lipid. For phosphatidylcholine spin-labeled at different positions down the sn-2 chain, the amplitude of the deuterium signal decreases toward the center of the membrane, and is reduced to zero from the C-12 atom position onward. At chain positions C-5 and C-7 closer to the phospholipid headgroups, the amplitude of the deuterium signal is greater in the presence of cholesterol than in its absence. These results are in good agreement with more indirect measurements of the transmembrane polarity profile that are based on the 14N-hyperfine splittings in the conventional continuous-wave electron spin resonance spectrum.

ESR, ESEM을 이용한 이온 교환된 MoH-SAPO-34에 대한 Mo의 화학종, 위치 및 흡착상호작용에 관한 연구

<TEX>$MoO_3$</TEX>와 H-SAPO-34의 고체상 반응은 상자기성의 Mo(V) 화학종을 띤다. 탈수하면 Mo(V) 화학 종이 약하게 나타나지만 계속적으로 활성화 시키면 ESR로 규명할 수 있는 <TEX>$Mo(V)_{5c}$</TEX>와 <TEX>$Mo(V)_{6c}$</TEX>와 같은 Mo(V) 화학종이 생성된다. ESR과 ESEM 자료들은 <TEX>$(MoO_2)^+$</TEX>나 <TEX>$(MoO)^{3+}$</TEX> 같은 옥소-몰리브덴 화학 종을 보여준다. <TEX>$(MoO_2)^+$</TEX> 화학 종이 다음과 같이 더 합리적인 것 같이 보여진다. H-SAPO-34는 낮은 골격전하를 갖기 때문에 높은 양전하를 갖는 <TEX>$(MoO)^{3+}$</TEX>는 쉽게 안정화 되지 못한다. 소성된 H-SAPO-34와 도데카몰리브덴 규산 용액 사이의 용액 상태 반응은 단지 <TEX>$MoO^{2+}$</TEX> 화학 종만을 발생한다. 마름모형 ESR 신호는 <TEX>$D_2O$</TEX>, <TEX>$CD_3OH$</TEX>, <TEX>$CH_3CH_2OD$</TEX>와 <TEX>$ND_3$</TEX>를 흡착할 때 관측되었다. Mo(V) 화학 종의 배위구조와 위치는 트리 펄스 전자 스핀반향 자료로 측정하였다. MoH-SAPO-34에 메탄올, 에틸렌 암모니아와 물이 흡착될 때 3분자, 1분자, 1분자와 1분자가 <TEX>$(MoO_2)^+$</TEX>에 각각 직접 배위하였다. A solid-state reaction of <TEX>$MoO_3$</TEX> with as-synthesized H-SAPO-34 generated paramagnetic Mo(V) species. The dehydration resulted in weak Mo(V) species, and subsequent activation resulted in the formation of Mo(V) species such as <TEX>$Mo(V)_{5c}$</TEX> and <TEX>$Mo(V)_{6c}$</TEX> that are characterized by ESR. The data of ESR and ESEM show the oxomolybdenum species, to be <TEX>$(MoO_2)^+$</TEX> or <TEX>$(MoO)^{3+}$</TEX>. The <TEX>$(MoO_2)^+$</TEX> species seems to be more probable. Since H-SAPO-34 has a low framework negative charge, <TEX>$(MoO)^{3+}$</TEX> with a high positive charge can not be easily stabilized. A solution reaction between the solution of silico-molybdic acid and calcined H-SAPO-34 resulted in only <TEX>$(MoO_2)^+$</TEX> species. A rhombic ESR signal is observed on adsorption of <TEX>$D_2O$</TEX>, <TEX>$CD_3OH$</TEX>, <TEX>$CH_3Ch_2OD$</TEX> and <TEX>$ND_3$</TEX>. The Location and coordination structure of Mo(V) species has been determined by three-pulse electron spin-echo modulation data and their simulations. After the adsorption of methanol, ethylene, ammonia, and water for MoH-SAPO-34, three molecules, one molecule, one and one molecule, respectively, are directly coordinated to <TEX>$(MoO_2)^+)$</TEX>.

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.

Adsorbate interactions of Cu(II) in mesoporous Cu-GaMCM-41 studied by electron spin resonance and electron spin echo modulation

Gallium-containing mesoporous MCM-41 materials (GaMCM-41) were synthesized by adjusting the gel equilibrium between the source gallosilicate mixture and a GaMCM-41 phase using an organic acid. The location of Cu(II) exchanged into the mesoporous GaMCM-41 and its interactions with various adsorbate molecules were investigated by electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopies. The results are compared with those of Cu-AlMCM-41. In a fresh, hydrated Cu-GaMCM-41, Cu(II) is octahedrally coordinated to six water molecules and is located in a cylindrical channel and rotates rapidly at room temperature. Evacuation removes some of these water molecules, leaving the Cu(II) coordinated to fewer water molecules and anchored to oxygens in the channel wall. Dehydration produces one Cu(II) species located on the internal wall of a channel which is accessible to oxygen as evidenced by broadening of its ESR lines by oxygen. Adsorption of water, methanol, ammonia, pyridine, aniline, acetonitrile, benzene and ethylene on dehydrated Cu-GaMCM-41 materials causes changes in the ESR spectra of Cu(II), indicating complex formation with these adsorbates. Cu(II) fully coordinates with a maximum coordination number of polar adsorbates in MCM-41 mesopores. Cu(II) forms a complex with six molecules of methanol as evidenced by an isotropic room temperature ESR signal and ESEM data. Cu(II) forms square planar complexes with four molecules of ammonia, pyridine and aniline based on resolved nitrogen superhyperfine interactions and other ESR parameters. However, Cu(II) forms a complex with six molecules of acetonitrile based on the ESR parameters and ESEM data. Interestingly, Cu(II) does not fully coordinate with nonpolar molecules. Cu(II) interacts directly with only one molecule of benzene, and only part of Cu(II) interacts indirectly with one molecule of ethylene based on ESR and ESEM analyses.

Structure and Adsorbate Interactions of Vanadium in a Vanadium Silicate (VS-1) Molecular Sieve

A medium pore vanadium silicate molecular sieve VS-1 with the ZSM-5 structure was studied by electron spin resonance (ESR) and electron spin−echo modulation (ESEM) spectroscopies to determine the vanadium structure and interaction with various adsorbate molecules. The VS-1 material is compared with ion-exchanged VO2+-ZSM-5 and impregnated V/silicalite-1 materials. As-synthesized VS-1 contains two vanadyl species with distorted octahedral coordination. Deviating from earlier assignments, we assign one of these species to VO(H2O)2+ based on ESEM results. The other species is suggested to be a similar complex in which the water molecule is replaced by a hydroxyl ion interacting with a tetrapropylammonium ion. The VO2+ ions oxidize to V5+ on calcination and then form a V5+···H2O complex after room-temperature hydration. Calcined, hydrated VS-1, after dehydration at elevated temperature, shows vanadyl species with square pyramidal geometry involving four framework oxygens. High-temperature H2 or CO treatment o...

Reaction of NO with copper ions in Cu(II)-exchanged ZSM-5 zeolite: electron spin resonance, electron spin echo modulation and Fourier transform infrared spectroscopy

Dehydration of Cu(II)-exchanged ZSM-5 and rehydration have been studied by electron spin resonance (ESR) and electron spin echo modulation (ESEM). The ESEM results indicate that Cu(II) is present in hydrated Cu-ZSM-5 as paramagnetic Cu(II)–OH − with five coordinated water molecules. Upon thermal dehydration, the ESR intensity decreases by about 85%, and it is suggested that Cu(I) and Cu(II)–O − are formed among other possible species. The remaining isolated paramagnetic Cu(II) is identified by ESR as three different species: I, II and III with g ‖ values of 2.314, 2.301 and 2.272, respectively. After NO adsorption onto dehydrated Cu-ZSM-5, NO interactions with Cu(I), Cu(II)–O − and Cu(II) have been studied by ESR and fourier transform infrared spectroscopy. It is suggested that Cu(II)–O − interacts with NO to form Cu(I)–(NO 2) and that further interaction with NO yields Cu(II)–(NO 2)(NO). Cu(I) is also suggested to react with one or two NO to form Cu(I)–NO and Cu(I)–(NO) 2 of which the latter further transforms to Cu(II)–(N 2O)O −. Among the three paramagnetic Cu(II) ions, only species III reacts with NO to form Cu(II)–NO; the other two Cu(II) species are inactive toward NO adsorption. A schematic mechanism based on these and earlier results is proposed for NO adsorption, interaction and transformation over Cu-ZSM-5.

Formation and Adsorbate Interactions of Paramagnetic Pd(I) Species in Pd(II)-Exchanged NaK- and H-Clinoptilolite

The formation of monovalent palladium in PdNaK-clinoptilolite where Pd(II) is introduced into extraframework sites as [Pd(NH3)4]2+ by liquid-state ion exchange at 298 K, is compared to that observed in PdH-clinoptilolite where Pd(II) is incorporated by solid-state ion exchange at 823 K, using electron spin resonance (ESR) and electron spin−echo modulation (ESEM) spectroscopies. Dehydration at 473 K produces one Pd(I) species in PdH-clinoptilolite but no ESR signal in PdNaK-clinoptilolite. This indicates that the stability of Pd(I) between PdH-clinoptilolite and PdNaK-clinoptilolite is different, probably due to the different locations and environments of Pd in these systems. Hydrogen reduction of Pd(II) in these two materials after activation reveals that Pd(II) ions in PdNaK-clinoptilolite occupy relatively accessible sites in comparison to those in PdH-clinoptilolite. The interactions of Pd(I) formed by thermal reduction of PdH-clinoptilolite with various adsorbates are also studied. The ESR studies cou...

Recruitment of a Foreign Quinone into the A1 Site of Photosystem I: II. STRUCTURAL AND FUNCTIONAL CHARACTERIZATION OF PHYLLOQUINONE BIOSYNTHETIC PATHWAY MUTANTS BY ELECTRON PARAMAGNETIC RESONANCE AND ELECTRON-NUCLEAR DOUBLE RESONANCE SPECTROSCOPY

Electron paramagnetic resonance (EPR) and electron-nuclear double resonance studies of the photosystem (PS) I quinone acceptor, A(1), in phylloquinone biosynthetic pathway mutants are described. Room temperature continuous wave EPR measurements at X-band of whole cells of menA and menB interruption mutants show a transient reduction and oxidation of an organic radical with a g-value and anisotropy characteristic of a quinone. In PS I complexes, the continuous wave EPR spectrum of the photoaccumulated Q(-) radical, measured at Q-band, and the electron spin-polarized transient EPR spectra of the radical pair P700(+) Q(-), measured at X-, Q-, and W-bands, show three prominent features: (i) Q(-) has a larger g-anisotropy than native phylloquinone, (ii) Q(-) does not display the prominent methyl hyperfine couplings attributed to the 2-methyl group of phylloquinone, and (iii) the orientation of Q(-) in the A(1) site as derived from the spin polarization is that of native phylloquinone in the wild type. Electron spin echo modulation experiments on P700(+) Q(-) show that the dipolar coupling in the radical pair is the same as in native PS I, i.e. the distance between P700(+) and Q(-) (25.3 +/- 0.3 A) is the same as between P700(+) and A(1)(-) in the wild type. Pulsed electron-nuclear double resonance studies show two sets of resolved spectral features with nearly axially symmetric hyperfine couplings. They are tentatively assigned to the two methyl groups of the recruited plastoquinone-9, and their difference indicates a strong inequivalence among the two groups when in the A(1) site. These results show that Q (i) functions in accepting an electron from A(0)(-) and in passing the electron forward to the iron-sulfur clusters, (ii) occupies the A(1) site with an orientation similar to that of phylloquinone in the wild type, and (iii) has spectroscopic properties consistent with its identity as plastoquinone-9.

Incorporation of Transition Metal Ions into MeAPO/MeAPSO Molecular Sieves

The synthetic incorporation of transition metal ions into aluminophosphate and silicoaluminophosphate molecular sieve frameworks is studied by electron spin−echo modulation (ESEM) spectroscopy. Based mainly on bulk chemical composition of the product, it has been suggested that divalent and trivalent metal ions such as Mn(II), Co(II), Cr(III), and Fe(III) substitute for framework aluminum sites. On the basis of 31P ESEM results, we originally suggested a framework phosphorus site for the incorporation of metal ions such as Ni(II) and Cr(III) in NiAPSO-5 and CrAPSO-5 molecular sieves. This site was later supported for other metal ions such as Ti(IV), V(IV), and Cu(II). In this work, we have extended such studies to Mn(II) and Fe(III) to better understand the metal substitution sites in AlPO4 frameworks. Irrespective of the particular metal ion, the 31P ESEM spectra of MeAPO/MeAPSO molecular sieves can be interpreted best on the basis of metal incorporation at a framework phosphorus site. Strong 27Al modula...

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...

Automatic spin-Hamiltonian diagonalization for electronic doublet coupled to anisotropic nuclear spins applied in one- and two-dimensional electron spin-echo simulations

We explore the possibility of putting together some earlier theoretical inventions in electron paramagnetic resonance (EPR) into an efficient method leading to accurate explicit expressions of echo modulation spectra in one and two dimensions. The resulting “automatic” diagonalization of the high-field spin-Hamiltonian gives a quick method for Electron spin-echo modulation computations. It accounts accurately for the effects of nonaxial electron Zeeman and hyperfine coupling tensors to an arbitrary system of nuclei in any relative orientations, including also the secular part of the quadrupole tensors in the computation of the modulation frequencies. Explicit expressions for the time-resolved signals, involving a single geometric parameter, particularly useful in economizing powder simulations of multipulse sequences like hyperfine sublevel correlation spectroscopy (HYSCORE), are presented. Finally, implementation in a complete package including fundamental EPR-line shape, primary-echo, stimulated-echo, and HYSCORE simulations and application to computations in experimentally interesting model systems is demonstrated. ©2000 John Wiley & Sons, Inc. Concepts Magn Reson 12: 410–433, 2000

Synthesis and Characterization of Mn-Containing Cubic Mesoporous MCM-48 and AlMCM-48 Molecular Sieves

Employing electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopy, five Mn(II) species are found in three kinds of Mn-containing MCM-48 materials: ion-exchanged Mn−MCM-48, synthesized MnMCM-48, and synthesized MnMCM-48(Ca) with subsequent CaCl2 exchange. Mn(II) species I with a well-resolved sextet centered at g = 2.00 has distorted octahedral symmetry and is observed in hydrated ion-exchanged Mn−MCM-48 and in synthesized calcined MnMCM-48. Mn(II) species II with a group of single peaks between g = 11.32 and 2.62 with possible distorted tetrahedral symmetry and a significant zero field contribution is observed in dehydrated Mn−MCM-48 and in MnMCM-48. Mn(II) species III with a symmetric line at g = 2.00 and a line width around 410 G is assigned to tetrahedral symmetry and is observed in MnMCM-48(Ca) and in MnAlMCM-48(Ca). Mn(II) species IV with a sextet centered from 4.11 to 4.34 also has distorted octahedral symmetry and is obtained in partially dehydrated Mn−MCM-48 and Mn−AlM...

Electron Spin Resonance and Electron Spin Echo Modulation Studies of Ion-Exchanged NiH−SAPO-17 and NiH−SAPO-35 Molecular Sieves: Comparison with Ion-Exchanged NiH−SAPO-34 Molecular Sieve

Erionite-like silicoaluminophosphate molecular sieve SAPO-17 and levyne-like SAPO-35, in which Ni ions were incorporated via solid-state ion-exchange into known extraframework sites, have been studied by electron spin resonance (ESR) and electron spin echo modulation (ESEM). The Ni ion reducibility, location, and interaction with several adsorbates have been investigated. Among these adsorbates, the interaction with nitric oxide was emphasized and compared to that of Ni ion with NO in the previously studied chabazite-like SAPO-34. Room-temperature adsorption of C2D4 on NiH−SAPO-17 after dehydration at 573 K, oxygen treatment at 823 K, evacuation, and subsequent hydrogen treatment at 573 K produces two Ni−ethylene complexes. Carbon monoxide adsorption gives rise to a Ni(I)−(CO)n complex with unresolved 13C hyperfine lines. Following the kinetics of nitric oxide adsorption on NiH−SAPO-17 shows that initially, a Ni(I)−(NO)+ complex, a NO radical, and a new species which appears to be another NO species are g...

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.

Synthesis and Characterization of Mesoporous Chromium-Containing Silica Tube Molecular Sieves CrMCM-41

A series of mesoporous chromium-containing silica tube molecular sieves (CrMCM-41) with variable Si/Cr ratios have been synthesized and characterized by powder X-ray diffraction (XRD), electron probe microanalysis (EPMA), Fourier transform infrared spectroscopy (FTIR), diffuse reflectance UV−visible spectroscopy (UV−vis), electron spin resonance (ESR), electron spin-echo modulation (ESEM), Raman spectroscopy, 29Si magic-angle-spinning nuclear magnetic resonance (MAS NMR), and N2 adsorption measurements. XRD, EPMA, UV−vis, and ESR show that the as-synthesized CrMCM-41 materials have the MCM-41 structure and contain only atomically dispersed Cr(III). FTIR, UV−vis, and Raman reveal that Cr(VI) monochromate exists in calcined CrMCM-41. 29Si MAS NMR and N2 adsorption show that part of the chromium is incorporated into the MCM-41 structure. ESR shows that Cr(VI)−O2- exists in calcined CrMCM-41 and transforms to Cr(V) after evacuation above 150 °C. The interaction of Cr(V) with O2, CO, C2D4, ND3, CD3OH, and D2O was studied. Cr(V) occurs at two different sites. At one site, Cr(V) coordinates with one molecule of O2, CO, and D2O to form square pyramidal complexes and reacts with C2D4, CD3OH, and ND3 to be reduced to Cr(III). At the other site, Cr(V) is inert to O2, CO, and C2D4 while it coordinates with two molecules of ND3 to form six-coordinated complexes and coordinates with one molecule of CD3OH.

Location and Adsorbate Interactions of Vanadium in VAPO-5 Molecular Sieve Studied by Electron Spin Resonance and Electron Spin Echo Modulation Spectroscopies

Large-pore vanadium-incorporated aluminophosphate molecular sieve VAPO-5 has been studied by electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopies to determine the vanadium location and interaction with various adsorbate molecules. As-synthesized VAPO-5 contains two paramagnetic vanadyl species A and B with distorted octahedral coordination. After calcination in O2 and exposure to moisture, only species A is observed with reduced intensity. Species A is identified as a VO(H2O)32+ complex coordinated to two framework oxygens bonded to aluminum. Species B is observed only in as-synthesized VAPO-5. Species B is suggested to be similar to species A in which one of the water ligands is replaced by hydroxyl interacting with a protonated amine. When calcined, hydrated VAPO-5 is dehydrated at elevated temperature, species A loses its water ligands and transforms to VO2+ ions coordinated to two framework oxygens (species C). Species C reduces its intensity significantly after treatment with O2 at high temperature, thus suggesting oxidation of V4+ to V5+. High-temperature H2 treatment of a previously oxidized sample shows more than one vanadium species. Weak 31P ESEM is observed in both as-synthesized and dehydrated VAPO-5. Simulation of the 31P ESEM spectrum of dehydrated VAPO-5 shows one phosphorus nucleus at 4.4 Å from the vanadium ion. Strong 27Al ESE modulations are observed in both as-synthesized and dehydrated VAPO-5, which suggests that the vanadium ion is located at sites nearer to framework aluminum than to phosphorus. These observations lead to the conclusion that vanadium incorporated into AlPO4-5 occupies a framework phosphorus site probably as a localized defect. When dehydrated VAPO-5 makes contact with D2O at room temperature, the ESR signal of species A is observed. This species is identified as a VO(D2O)32+ complex from the 2D ESEM spectrum. Adsorption of ND3 on VAPO-5 generates a new vanadium species F identified as a VO(ND3)22+ complex. Adsorption of deuterated methanol on dehydrated VAPO-5 results in another new vanadium species G, which is identified as a VO(CD3OH)22+ complex. When deuterated ethylene is adsorbed on dehydrated VAPO-5, another new vanadium species H identified as VO(C2D4)12+ is observed. Possible coordination geometries of these various complexes are discussed.