Accurate Determination of Interstrand Distances and Alignment in Amyloid Fibrils by Magic Angle Spinning NMR
Marc A. Caporini†§, Vikram S. Bajaj†, Mikhail Veshtort†, Anthony Fitzpatrick‡, Cait E. MacPhee‡, Michele Vendruscolo‡, Christopher M. Dobson‡, and Robert G. Griffin*†
J. Phys. Chem. B, 2010, 114 (42), pp 13555–13561
DOI: 10.1021/jp106675h
Publication Date (Web): October 6, 2010
Copyright © 2010 American Chemical Society
Abstract: Amyloid fibrils are structurally ordered aggregates of proteins whose formation is associated with many neurodegenerative and other diseases. For that reason, their high-resolution structures are of considerable interest and have been studied using a wide range of techniques, notably electron microscopy, X-ray diffraction, and magic angle spinning (MAS) NMR. Because of the excellent resolution in the spectra, MAS NMR is uniquely capable of delivering site-specific, atomic resolution information about all levels of amyloid structure: (1) the monomer, which packs into several (2) protofilaments that in turn associate to form a (3) fibril. Building upon our high-resolution structure of the monomer of an amyloid-forming peptide from transthyretin (TTR105−115), we introduce single 1-13C labeled amino acids at seven different sites in the peptide and measure intermolecular carbonyl−carbonyl distances with an accuracy of 0.11 A. Our results conclusively establish a parallel, in register, topology for the packing of this peptide into a β-sheet and provide constraints essential for the determination of an atomic resolution structure of the fibril. Furthermore, the approach we employ, based on a combination of a double-quantum filtered variant of the DRAWS recoupling sequence and multispin numerical simulations in SPINEVOLUTION, is general and should be applicable to a wide range of systems.
Solid-State NMR Study of Cysteine on Gold Nanoparticles
Anuji Abraham, Eugene Mihaliuk, Bharath Kumar, Justin Legleiter, and Terry Gullion*
Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506, United States
J. Phys. Chem. C, 2010, 114 (42), pp 18109–18114
DOI: 10.1021/jp107112b
Publication Date (Web): September 30, 2010
Copyright © 2010 American Chemical Society
Abstract: Solid-state NMR spectroscopy is used to characterize the interaction of l-cysteine with gold nanoparticles. The experiments show that there are two types of cysteine in the gold−cysteine complex, with nearly equal populations. We postulate that cysteine forms a two-layer boundary around the gold nanoparticles. The first layer is made of cysteine molecules forming a thiolate bond with the gold surface and having its charged amino and carboxyl groups oriented away from the gold surface. The second layer has its amino and carboxyl groups oriented toward the first layer and its sulfur group oriented away from the gold particles.
Pore Size Distribution Analysis of Mesoporous TiO2 Spheres by 1H Nuclear Magnetic Resonance (NMR) Cryoporometry
Su-Yeol Ryu, Dong Suk Kim, Jae-Deok Jeon, and Seung-Yeop Kwak*
J. Phys. Chem. C, 2010, 114 (41), pp 17440–17445
DOI: 10.1021/jp105496h
Publication Date (Web): September 21, 2010
Copyright © 2010 American Chemical Society
Abstract: Mesoporous TiO2 spheres with various pore sizes were prepared by varying the calcination temperature in the range of 300−700 °C. Increasing calcination temperature was found to increase the crystal size, decrease the surface area, and increase the pore size. The morphologies of mesoporous TiO2 spheres consist of well-defined spherical shapes of monodisperse sizes near 0.8 μm. To determine the pore size distributions (PSDs) of these mesoporous TiO2 spheres, 1H nuclear magnetic resonance (NMR) cryoporometry and Barrett−Joyner−Halenda (BJH) analysis were conducted. NMR cryoporometry is based on the theory of the melting point depression (MPD) of a probe molecule confined within a pore, which is dependent on the pore diameter. MPD was determined by analyzing the variation of the NMR spin−echo intensity with temperature. From the resulting spin−echo intensity versus temperature (I−T) curves, it was found that the maximum MPD of a probe molecule confined within the pores of mesoporous TiO2 decreases with increasing calcination temperature; that is, the pore size increases with increasing calcination temperature. Because mesoporous TiO2 spheres consist of aggregates of nanocrystallite TiO2 and mesopores located at intercrystallites, an increase in the calcination temperature induces an increase in the crystallite size and, thus, in the pore size because the small pores collapse and the large pores increase in size. We also confirmed by BJH analysis that the pore size of mesoporous TiO2 increases with increasing calcination temperature. This trend is in agreement with our 1H NMR cryoporometry results. Overall, these findings indicate that NMR cryoporometry is a very effective method for determining the PSDs of mesoporous TiO2 spheres.
Defect Functionalization of Hexagonal Boron Nitride Nanosheets
Yi Lin*†, Tiffany V. Williams‡, Wei Cao§, Hani E. Elsayed-Ali§, and John W. Connell‡
J. Phys. Chem. C, 2010, 114 (41), pp 17434–17439
DOI: 10.1021/jp105454w
Publication Date (Web): September 21, 2010
Copyright © 2010 American Chemical Society
Abstract:A pristine hexagonal boron nitride (h-BN) powder sample with layered crystalline sheetlike particles of 1−10 μm in lateral sizes and a few hundred nanometers in thicknesses was mechanically treated using a ball-mill to intentionally introduce defect sites. The h-BN was ball-milled for various times and subsequently was functionalized with a long alkyl chain amine via Lewis acid−base interactions between the amino groups and the boron atoms of h-BN to obtain soluble amine-attached nanosheet samples as the products. The functionalized h-BN nanosheet samples were characterized via various microscopic and spectroscopic techniques. The results strongly support a direct correlation between increasing defect site concentrations of the h-BN nanosheet samples and improved reaction efficiency with the amine. This suggests the enhanced reactivity of defect boron atoms in comparison to conjugated ones on an unperturbed h-BN plane. NMR investigations provided the strongest evidence supporting the hypothesis that the amino groups reacted with the h-BN at specific defect sites induced by ball-milling. The mechanistic implications are discussed.
Access to Well-Defined Ruthenium Mononuclear Species Grafted via a Si−Ru Bond on Silane Functionalized Silica†
Fernando Rascn‡, Romain Berthoud‡, Raphal Wischert‡, Wayne Lukens§, and Christophe Copret*‡
J. Phys. Chem. C, Article ASAP
DOI: 10.1021/jp1064962
Publication Date (Web): September 20, 2010
Copyright © 2010 American Chemical Society
Abstract: A functionalized silica with T3 silane surface groups (i.e., (≡SiO)3Si−H) was prepared and interacted with Ru(cod)(cot), resulting in the formation of monometallic surface species attached to the surface via a Si−Ru bond, according to EXAFS spectroscopy, infrared spectroscopy, and solid-state NMR.
Time-Resolved and Site-Specific Insights into Migration Pathways of Li+ in α-Li3VF6 by 6Li 2D Exchange MAS NMR
M. Wilkening*†, E. E. Romanova†‡, S. Nakhal§, D. Weber§, M. Lerch§, and P. Heitjans†
J. Phys. Chem. C, 2010, 114 (44), pp 19083–19088
DOI: 10.1021/jp103433h
Publication Date (Web): September 14, 2010
Copyright © 2010 American Chemical Society
Abstract: Two-dimensional (2D) exchange nuclear magnetic resonance (NMR) spectroscopy carried out under magic angle spinning (MAS) conditions is ideally suited to study site-specific Li diffusion parameters of cathode materials required for the target-oriented development of so-called high-energy density 4 V-lithium-ion batteries. In the present study, we took advantage of Li NMR hyperfine shifts to record temperature-variable 1D and mixing-time dependent 2D exchange MAS 6Li NMR spectra on α-Li3VF6 serving as both a potential cathode material as well as an application-oriented model substance with three magnetically inequivalent Li sites. By comparing the NMR results with structural details of the material we were able to obtain detailed insights into the migration pathways and Li exchange rates which are of the order of some hundreds of Li jumps per second at approximately 340 K. Site-specific Li jump rates τ−1 reveal the electrochemically active sites and provide information how to modify the material in order to increase its relatively low Li diffusivity found at room temperature.
Adsorbate Effect on AlO4(OH)2 Centers in the Metal−Organic Framework MIL-53 Investigated by Solid-State NMR Spectroscopy
Christian Lieder, Sabine Opelt, Michael Dyballa, Harald Henning, Elias Klemm, and Michael Hunger*
J. Phys. Chem. C, 2010, 114 (39), pp 16596–16602
DOI: 10.1021/jp105700b
Publication Date (Web): September 10, 2010
Copyright © 2010 American Chemical Society
Abstract:1H and 27Al MAS NMR spectroscopies have been applied for studying the effect of water molecules, nitrogen bases, and o-xylene on the hydroxyl protons of bridging AlOH groups and framework aluminum atoms in the metal−organic framework (MOF) MIL-53. For water molecules adsorbed on the low-temperature form MIL-53lt, two 1H MAS NMR signals were found indicating the formation of different O−H···O hydrogen bonds to neighboring oxygen atoms, such as to carboxylic oxygens. Upon adsorption of the nitrogen bases acetonitrile, ammonia, and pyridine, a linear increase of the quadrupole coupling constant, CQ, of the framework aluminum atoms in dehydrated MIL-53 from CQ = 8.5 MHz (unloaded material) to maximum 10.8 MHz (pyridine-loaded material) as a function of the proton affinity of the adsorbates was observed. Adsorption of o-xylene led to three stepwise changes of the quadrupole coupling constants, CQ, of framework aluminum atoms in dehydrated MIL-53. While the first two stepwise changes of the CQ values (CQ = 8.0 and 8.7 MHz) occur for o-xylene loadings of lower than 4 molecules per unit cell and for all AlO4(OH)2 centers, the third change of the CQ value to 9.4 MHz was observed for o-xylene loadings higher than 4 o-xylene molecules per unit cell and for maximum 50% of the framework aluminum atoms. This third adsorbate-induced change of the CQ value of framework aluminum atoms in MIL-53 is accompanied by a significant decrease of the adsorbate mobility
Impact of Controlling the Site Distribution of Al Atoms on Catalytic Properties in Ferrierite-Type Zeolites†
Yuriy Romn-Leshkov, Manuel Moliner, and Mark E. Davis*
Chemical Engineering, California Institute of Technology, Pasadena, California 91125
J. Phys. Chem. C, Article ASAP
DOI: 10.1021/jp106247g
Publication Date (Web): September 9, 2010
Copyright © 2010 American Chemical Society
Abstract: Zeolites with the ferrierite (FER) topology are synthesized using a combination of tetramethylammonium (TMA) cations with differently sized cyclic amines (pyrrolidine (Pyr), hexamethyleneimine (HMI), and 1,4-diazabicyclo[2.2.2]octane (DAB)). Using these organic structure-directing agents (SDAs), low Si/Al ratios and concentrated synthesis mixtures favor the crystallization of FER materials. Increasing the size of the cyclic amine or decreasing the aluminum content leads to the crystallization of other phases or the creation of excessive amounts of connectivity defects. TMA cations play a decisive role in the synthesis of the FER materials, and their presence allows the use of HMI to synthesize FER. Proton MAS NMR is used to quantify the accessibility of pyridine to acid sites in these FER samples, where it is found that the FER+HMI+TMA sample contains only 27% acid sites in the 8-MR channels, whereas FER+Pyr and FER+Pyr+TMA contain 89% and 84%, respectively. The constraint index (CI) test and the carbonylation of dimethyl ether (DME) with carbon monoxide are used as probe reactions to evaluate how changes in the aluminum distribution in these FER samples affect their catalytic behavior. Results show that the use of Pyr as an SDA results in the selective population of acid sites in the 8-MR channels, whereas the use of HMI generates FER zeolites with an increased concentration of acid sites in the 10-MR channels.
Showing posts with label Jounal of Physical Chemistry C. Show all posts
Showing posts with label Jounal of Physical Chemistry C. Show all posts
Thursday, December 02, 2010
Tuesday, May 11, 2010
Journal of Physical Chemistry C, vol. 114, Issue 18
The Role of the Cluster on the Relaxation of Endohedral Fullerene Cage Carbons: A NMR Spin−Lattice Relaxation Study of an Internal Relaxation Reagent
Sabrina Klod, Lin Zhang and Lothar Dunsch*
J. Phys. Chem. C, 2010, 114 (18), pp 8264–8267
DOI: 10.1021/jp101218p
Abstract: The endohedral cluster fullerenes Ih-Sc3N@C80, Ih-Y3N@C80, and Ih-Lu3N@C80 were investigated with respect to the strategy of an internal relaxation reagent by following the cluster size effects and the influence of f-electrons on the carbon relaxation. For endohedral nitride cluster fullerenes of Ih-C80 cage symmetry increased relaxation rates are observed. In general, the enlarged cage size increases the relaxation of the carbons. The encapsulated metal atoms give an additional dipole−dipole interaction to the relaxation rate of the carbon atoms depending on their magnetic character. For different metals the increased nitride cluster size is one reason for the observed stronger dipole−dipole interaction. In contrast, a higher shielding of a metal nucleus by its electron shell leads to a reduced magnetic effect. The negative charge on the cage increases the electron density, thus decreasing T1. In temperature-dependent studies, the diffusion is fast compared to the rotation of the molecule at higher temperatures which is typical for the spherical shape of the fullerene cage. Thus, only a minor deformation of the cage by the endohedral voluminous cluster is found. The shape of the cage is preserved and less influenced by the type and size of the cluster.
Fabrication of Hierarchical Channel Wall in Al-MCM-41 Mesoporous Materials to Enhance Their Adsorptive Capability: Why and How?
Fang Na Gu†‡, Feng Wei†, Jia Yuan Yang†, Ying Wang*‡ and Jian Hua Zhu*†
Key Laboratory of Mesoscopic Chemistry of MOE, College of Chemistry and Chemical Engineering, and Ecomaterials and Renewable Energy Research Center (ERERC), Nanjing University, Nanjing 210093, China
J. Phys. Chem. C, 2010, 114 (18), pp 8431–8439
DOI: 10.1021/jp1009143
Abstract:To overcome the inefficiency of mesoporous materials in the adsorption of small molecules, this article reports the effort how to create hierarchical channel wall in Al-MCM-41 and more important, how to distinguish the contribution of the newly formed micropores in adsorption by the mesoporous materials. Fabrication of hierarchical channel wall is realized through extracting framework aluminum of sample by acid leach to create micropores and defects, providing the fine geometric confinement toward tiny targets. The influence of original Al content of Al-MCM-41 on the controlled dealumination was studied, and X-ray diffraction, N2 adsorption−desorption, 27Al and 29Si MAS NMR, Fourier transform IR techniques were employed to characterize the resulting samples. Besides, volatile nitrosamine N-nitrosopyrrolidine (NPYR) was chosen as a probe to assess the adsorption of the resulting samples. Hierarchical channel wall in Al-MCM-41 significantly increased its ability to trap NPYR, and for the first time the adsorptive contribution of newly formed micropores and defects in the mesoporous silica was distinguished by the instantaneous adsorption under the carrier gas with different flow rate, which is beneficial for developing new functional materials to protect environment.
Structure, Connectivity, and Configurational Entropy of GexSe100−x Glasses: Results from 77Se MAS NMR Spectroscopy
E. L. Gjersing and S. Sen*, B. G. Aitken
J. Phys. Chem. C, 2010, 114 (18), pp 8601–8608
DOI: 10.1021/jp1014143
Abstract:High-resolution 77Se MAS NMR spectroscopy has been conducted at 11.7 T to investigate the short-and intermediate- range structure and chemical order in binary GexSe100−x glasses with 5 ≤ x ≤ 33.33. Four distinct Se environments are observed for the first time, corresponding to Se−Se−Se and Ge−Se−Se linkages as well as Ge−Se−Ge sites where the Se atom is shared by two GeSe4 tetrahedra in either corner-sharing or edge-sharing configuration. Assignments of corner and edge-shared tetrahedra were made based on the 77Se MAS NMR spectrum of crystalline β-GeSe2. Analysis of the compositional variation of the relative concentrations of these Se sites indicates that the structure of GexSe100−x glasses in this composition range can be described as a randomly interconnected network of GeSe4 tetrahedra and chains of Se atoms. The implications of this structural model are discussed in relation to the composition dependence of the glass-forming ability and kinetic fragility of the corresponding parent liquids.
Sabrina Klod, Lin Zhang and Lothar Dunsch*
J. Phys. Chem. C, 2010, 114 (18), pp 8264–8267
DOI: 10.1021/jp101218p
Abstract: The endohedral cluster fullerenes Ih-Sc3N@C80, Ih-Y3N@C80, and Ih-Lu3N@C80 were investigated with respect to the strategy of an internal relaxation reagent by following the cluster size effects and the influence of f-electrons on the carbon relaxation. For endohedral nitride cluster fullerenes of Ih-C80 cage symmetry increased relaxation rates are observed. In general, the enlarged cage size increases the relaxation of the carbons. The encapsulated metal atoms give an additional dipole−dipole interaction to the relaxation rate of the carbon atoms depending on their magnetic character. For different metals the increased nitride cluster size is one reason for the observed stronger dipole−dipole interaction. In contrast, a higher shielding of a metal nucleus by its electron shell leads to a reduced magnetic effect. The negative charge on the cage increases the electron density, thus decreasing T1. In temperature-dependent studies, the diffusion is fast compared to the rotation of the molecule at higher temperatures which is typical for the spherical shape of the fullerene cage. Thus, only a minor deformation of the cage by the endohedral voluminous cluster is found. The shape of the cage is preserved and less influenced by the type and size of the cluster.
Fabrication of Hierarchical Channel Wall in Al-MCM-41 Mesoporous Materials to Enhance Their Adsorptive Capability: Why and How?
Fang Na Gu†‡, Feng Wei†, Jia Yuan Yang†, Ying Wang*‡ and Jian Hua Zhu*†
Key Laboratory of Mesoscopic Chemistry of MOE, College of Chemistry and Chemical Engineering, and Ecomaterials and Renewable Energy Research Center (ERERC), Nanjing University, Nanjing 210093, China
J. Phys. Chem. C, 2010, 114 (18), pp 8431–8439
DOI: 10.1021/jp1009143
Abstract:To overcome the inefficiency of mesoporous materials in the adsorption of small molecules, this article reports the effort how to create hierarchical channel wall in Al-MCM-41 and more important, how to distinguish the contribution of the newly formed micropores in adsorption by the mesoporous materials. Fabrication of hierarchical channel wall is realized through extracting framework aluminum of sample by acid leach to create micropores and defects, providing the fine geometric confinement toward tiny targets. The influence of original Al content of Al-MCM-41 on the controlled dealumination was studied, and X-ray diffraction, N2 adsorption−desorption, 27Al and 29Si MAS NMR, Fourier transform IR techniques were employed to characterize the resulting samples. Besides, volatile nitrosamine N-nitrosopyrrolidine (NPYR) was chosen as a probe to assess the adsorption of the resulting samples. Hierarchical channel wall in Al-MCM-41 significantly increased its ability to trap NPYR, and for the first time the adsorptive contribution of newly formed micropores and defects in the mesoporous silica was distinguished by the instantaneous adsorption under the carrier gas with different flow rate, which is beneficial for developing new functional materials to protect environment.
Structure, Connectivity, and Configurational Entropy of GexSe100−x Glasses: Results from 77Se MAS NMR Spectroscopy
E. L. Gjersing and S. Sen*, B. G. Aitken
J. Phys. Chem. C, 2010, 114 (18), pp 8601–8608
DOI: 10.1021/jp1014143
Abstract:High-resolution 77Se MAS NMR spectroscopy has been conducted at 11.7 T to investigate the short-and intermediate- range structure and chemical order in binary GexSe100−x glasses with 5 ≤ x ≤ 33.33. Four distinct Se environments are observed for the first time, corresponding to Se−Se−Se and Ge−Se−Se linkages as well as Ge−Se−Ge sites where the Se atom is shared by two GeSe4 tetrahedra in either corner-sharing or edge-sharing configuration. Assignments of corner and edge-shared tetrahedra were made based on the 77Se MAS NMR spectrum of crystalline β-GeSe2. Analysis of the compositional variation of the relative concentrations of these Se sites indicates that the structure of GexSe100−x glasses in this composition range can be described as a randomly interconnected network of GeSe4 tetrahedra and chains of Se atoms. The implications of this structural model are discussed in relation to the composition dependence of the glass-forming ability and kinetic fragility of the corresponding parent liquids.
Monday, July 27, 2009
Journal of Physical Chemistry C, vol. 113, Issues 25-30
29Si NMR Relaxation of Silicated Nanoparticles in Tetraethoxysilane−Tetrapropylammonium Hydroxide−Water System (TEOS−TPAOH−H2O)
Mohamed Haouas*†, David P. Petry†‡, Michael W. Anderson‡ and Francis Taulelle†
Institut Lavoisier de Versailles, Universit de Versailles-St. Quentin en Yvelines, Versailles, J. Phys. Chem. C, 2009, 113 (25), pp 10838–10841
DOI: 10.1021/jp903454f
Abstract: Silicon-29 longitudinal (T1) and transverse (T2) NMR relaxation times have been measured in the clear solution precursor of silicalite-1 of composition 25 TEOS−5 TPAOH−400 H2O. The nanoparticles as well as the silicate oligomers are giving rise to observable resonances. An unusually long T1 relaxation time of 126 s is observed for Q4 in nanoparticles. Proper care for acquisition is therefore required for quantifying the distribution of Qn of the nanoparticles, an essential measurement to follow the nanoparticles connectivity evolution.
Clathrate Hydrate Formation: Dependence on Aqueous Hydration Number
Steven F. Dec*
J. Phys. Chem. C, 2009, 113 (28), pp 12355–12361
DOI: 10.1021/jp9009977
Abstract: The formation of methane−ethane (C1−C2) clathrate hydrate was studied with high-resolution, solid-state 13C NMR and density functional theory techniques. The 13C NMR experiments yield a number of significant findings: (1) the hydration number of C2(aq) is 26, (2) the initial quantity of C2−51262 sI hydrate cages outnumber C1−512 cages at 274 K, (3) C1−C2 sII hydrate forms at a C1−C2 gas phase composition where only sI hydrate is thermodynamically stable, (4) the initial composition of C1−C2 sII hydrate at 268 K contains less than the original amount of C1, (5) a quasi-liquid water layer solvating both C1 and C2 exists at 268 K, (6) any C1(qll) and C2(qll) present at 253 K is too small to be detected, (7) the initial amounts of C1−C2 sI and sII hydrates formed at 253 K are much smaller than those formed at 268 and 274 K, and (8) C1(aq), C2(aq) and C1(qll), C2(qll) facilitate the formation of C1−C2 sI and sII clathrate hydrate at 268 and 274 K, respectively. On the basis of these experimental observations, a model is developed that states that the aqueous hydration number of the most water-soluble clathrate hydrate former controls the structure of the clathrate hydrate that forms during the initial stages of the clathrate hydrate formation reaction. For methane−ethane clathrate hydrate, this means that ethane in a water liquid phase or quasi-liquid layer eliminates or adds two water molecules to its hydration shell to form the ethane-filled 51262 or 51264 cage building blocks of structure I or structure II clathrate hydrate, respectively. Density functional theory computations on methane-filled 512, 51262, and 51264 and ethane-filled 51262, 51263, and 51264 clathrate hydrate cages yield the stabilization energy of the gas-filled cages and provide theoretical evidence consistent with the experimentally based clathrate hydrate formation model. The proposed model is found to explain the results of other clathrate hydrate formation reactions.
Hierarchical Meso-/Macroporous Aluminum Phosphonate Hybrid Materials as Multifunctional Adsorbents
Tian-Yi Ma, Xue-Jun Zhang and Zhong-Yong Yuan*
J. Phys. Chem. C, 2009, 113 (29), pp 12854–12862
DOI: 10.1021/jp903412m
Abstract: Inorganic−organic hybrid aluminum phosphonate (AlPPh) materials with hierarchical meso-/macroporous structure were synthesized by using two different kinds of organophosphonic acids: amino tri(methylene phosphonic acid) and bis(hexamethylenetriamine)-penta(methylenephosphonic acid). The preparation was accomplished both with and without the assistance of surfactant F127. All the samples possess a uniform macroporous (500−2000 nm) structure of mesoporous (4−5 nm) framework, which were characterized by SEM, TEM, N2 sorption, XRD, TGA-DSC, elemental analysis, MAS NMR, and FT-IR spectroscopy techniques. The as-prepared AlPPh materials were used as multifunctional adsorbents for the efficient removal of heavy metal ions (e.g., Cu2+) and the adsorption of proteins (e.g., lysozyme). The heavy metal ion adsorption results show that the AlPPh materials have a large adsorption capacity, comparable to those of previous reported Cu(II)-adsorbents made up of functionalized mesoporous silica. The isotherms for lysozyme adsorption are of type L (Langmuir isotherm), and different monolayer capacities were calculated using Langmuir equation. The differences between the metal ion and the lysozyme adsorption were mainly caused by the nature of inorganic ions and proteins and the interactions between the adsorbents and adsorbates. The synthesized AlPPh hybrid materials were confirmed to be useful multifunctional adsorbents for both metal ions and proteins.
Observation of Distinct Surface AlIV Sites and Phosphonate Binding Modes in γ-Alumina and Concrete by High-Field 27Al and 31P MAS NMR
George W. Wagner*† and Roderick A. Fry‡§
J. Phys. Chem. C, 2009, 113 (30), pp 13352–13357
DOI: 10.1021/jp902474z
Publication Date (Web): July 1, 2009
Abstract: High loadings of nerve agent-related phosphonic acids adsorbed on γ-Al2O3 and concrete examined by 31P MAS NMR and high-field 27Al MAS NMR reveal the presence of several phosphonate−surface binding modes and greatly improved resolution of multiple AlIV sites. Some of the resolved AlIV sites are sensitive to surface hydroxylation/dehydroxylation are attributed to surface AlIV−OH groups (apparently having been observed for the first time). Although the number of surface AlIV sites detected by high-field 27Al MAS NMR (three) is in agreement with current surface models, their dehydroxylation behavior does not entirely concur with proposed dehydroxylation mechanisms. The various phosphonate−alumina surface species detected by 31P MAS NMR are consistent with those previously observed by IR techniques. In concrete, the formation of an aluminophosphonate species is directly observed, consistent with the recalcitrant extraction behavior exhibited by adsorbed phosphonates in environmental matrices.
Mohamed Haouas*†, David P. Petry†‡, Michael W. Anderson‡ and Francis Taulelle†
Institut Lavoisier de Versailles, Universit de Versailles-St. Quentin en Yvelines, Versailles, J. Phys. Chem. C, 2009, 113 (25), pp 10838–10841
DOI: 10.1021/jp903454f
Abstract: Silicon-29 longitudinal (T1) and transverse (T2) NMR relaxation times have been measured in the clear solution precursor of silicalite-1 of composition 25 TEOS−5 TPAOH−400 H2O. The nanoparticles as well as the silicate oligomers are giving rise to observable resonances. An unusually long T1 relaxation time of 126 s is observed for Q4 in nanoparticles. Proper care for acquisition is therefore required for quantifying the distribution of Qn of the nanoparticles, an essential measurement to follow the nanoparticles connectivity evolution.
Clathrate Hydrate Formation: Dependence on Aqueous Hydration Number
Steven F. Dec*
J. Phys. Chem. C, 2009, 113 (28), pp 12355–12361
DOI: 10.1021/jp9009977
Abstract: The formation of methane−ethane (C1−C2) clathrate hydrate was studied with high-resolution, solid-state 13C NMR and density functional theory techniques. The 13C NMR experiments yield a number of significant findings: (1) the hydration number of C2(aq) is 26, (2) the initial quantity of C2−51262 sI hydrate cages outnumber C1−512 cages at 274 K, (3) C1−C2 sII hydrate forms at a C1−C2 gas phase composition where only sI hydrate is thermodynamically stable, (4) the initial composition of C1−C2 sII hydrate at 268 K contains less than the original amount of C1, (5) a quasi-liquid water layer solvating both C1 and C2 exists at 268 K, (6) any C1(qll) and C2(qll) present at 253 K is too small to be detected, (7) the initial amounts of C1−C2 sI and sII hydrates formed at 253 K are much smaller than those formed at 268 and 274 K, and (8) C1(aq), C2(aq) and C1(qll), C2(qll) facilitate the formation of C1−C2 sI and sII clathrate hydrate at 268 and 274 K, respectively. On the basis of these experimental observations, a model is developed that states that the aqueous hydration number of the most water-soluble clathrate hydrate former controls the structure of the clathrate hydrate that forms during the initial stages of the clathrate hydrate formation reaction. For methane−ethane clathrate hydrate, this means that ethane in a water liquid phase or quasi-liquid layer eliminates or adds two water molecules to its hydration shell to form the ethane-filled 51262 or 51264 cage building blocks of structure I or structure II clathrate hydrate, respectively. Density functional theory computations on methane-filled 512, 51262, and 51264 and ethane-filled 51262, 51263, and 51264 clathrate hydrate cages yield the stabilization energy of the gas-filled cages and provide theoretical evidence consistent with the experimentally based clathrate hydrate formation model. The proposed model is found to explain the results of other clathrate hydrate formation reactions.
Hierarchical Meso-/Macroporous Aluminum Phosphonate Hybrid Materials as Multifunctional Adsorbents
Tian-Yi Ma, Xue-Jun Zhang and Zhong-Yong Yuan*
J. Phys. Chem. C, 2009, 113 (29), pp 12854–12862
DOI: 10.1021/jp903412m
Abstract: Inorganic−organic hybrid aluminum phosphonate (AlPPh) materials with hierarchical meso-/macroporous structure were synthesized by using two different kinds of organophosphonic acids: amino tri(methylene phosphonic acid) and bis(hexamethylenetriamine)-penta(methylenephosphonic acid). The preparation was accomplished both with and without the assistance of surfactant F127. All the samples possess a uniform macroporous (500−2000 nm) structure of mesoporous (4−5 nm) framework, which were characterized by SEM, TEM, N2 sorption, XRD, TGA-DSC, elemental analysis, MAS NMR, and FT-IR spectroscopy techniques. The as-prepared AlPPh materials were used as multifunctional adsorbents for the efficient removal of heavy metal ions (e.g., Cu2+) and the adsorption of proteins (e.g., lysozyme). The heavy metal ion adsorption results show that the AlPPh materials have a large adsorption capacity, comparable to those of previous reported Cu(II)-adsorbents made up of functionalized mesoporous silica. The isotherms for lysozyme adsorption are of type L (Langmuir isotherm), and different monolayer capacities were calculated using Langmuir equation. The differences between the metal ion and the lysozyme adsorption were mainly caused by the nature of inorganic ions and proteins and the interactions between the adsorbents and adsorbates. The synthesized AlPPh hybrid materials were confirmed to be useful multifunctional adsorbents for both metal ions and proteins.
Observation of Distinct Surface AlIV Sites and Phosphonate Binding Modes in γ-Alumina and Concrete by High-Field 27Al and 31P MAS NMR
George W. Wagner*† and Roderick A. Fry‡§
J. Phys. Chem. C, 2009, 113 (30), pp 13352–13357
DOI: 10.1021/jp902474z
Publication Date (Web): July 1, 2009
Abstract: High loadings of nerve agent-related phosphonic acids adsorbed on γ-Al2O3 and concrete examined by 31P MAS NMR and high-field 27Al MAS NMR reveal the presence of several phosphonate−surface binding modes and greatly improved resolution of multiple AlIV sites. Some of the resolved AlIV sites are sensitive to surface hydroxylation/dehydroxylation are attributed to surface AlIV−OH groups (apparently having been observed for the first time). Although the number of surface AlIV sites detected by high-field 27Al MAS NMR (three) is in agreement with current surface models, their dehydroxylation behavior does not entirely concur with proposed dehydroxylation mechanisms. The various phosphonate−alumina surface species detected by 31P MAS NMR are consistent with those previously observed by IR techniques. In concrete, the formation of an aluminophosphonate species is directly observed, consistent with the recalcitrant extraction behavior exhibited by adsorbed phosphonates in environmental matrices.
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