J. Am. Chem. Soc., 2009, 131 (12), pp 4490–4498

Determining the Effects of Lipophilic Drugs on Membrane Structure by Solid-State NMR Spectroscopy: The Case of the Antioxidant Curcumin

Jeffrey Barry, Michelle Fritz, Jeffrey R. Brender, Pieter E. S. Smith, Dong-Kuk Lee† and Ayyalusamy Ramamoorthy*

Abstract
Curcumin is the active ingredient of turmeric powder, a natural spice used for generations in traditional medicines. Curcumin’s broad spectrum of antioxidant, anticarcinogenic, antimutagenic, and anti-inflammatory properties makes it particularly interesting for the development of pharmaceutical compounds. Because of curcumin’s various effects on the function of numerous unrelated membrane proteins, it has been suggested that it affects the properties of the bilayer itself. However, a detailed atomic-level study of the interaction of curcumin with membranes has not been attempted. A combination of solid-state NMR and differential scanning calorimetry experiments shows curcumin has a strong effect on membrane structure at low concentrations. Curcumin inserts deep into the membrane in a transbilayer orientation, anchored by hydrogen bonding to the phosphate group of lipids in a manner analogous to cholesterol. Like cholesterol, curcumin induces segmental ordering in the membrane. Analysis of the concentration dependence of the order parameter profile derived from NMR results suggests curcumin forms higher order oligomeric structures in the membrane that span and likely thin the bilayer. Curcumin promotes the formation of the highly curved inverted hexagonal phase, which may influence exocytotic and membrane fusion processes within the cell. The experiments outlined here show promise for understanding the action of other drugs such as capsaicin in which drug-induced alterations of membrane structure have strong pharmacological effects.

C & E News: 7Li Solid-State NMR Studies of Batteries

http://pubs.acs.org/cen/news/87/i13/8713news4.html

J. Phys Chem B and C, vol. 113, Issue 12

Nothing from J Phys Chem B this time around.

Diffusion in Confined Dimensions: Li+ Transport in Mixed Conducting TiO2−B Nanowires
Martin Wilkening*†, Christopher Lyness‡, A. Robert Armstrong‡ and Peter G. Bruce‡§

J. Phys. Chem. C, 2009, 113 (12), pp 4741–4744
DOI: 10.1021/jp8107792
Copyright © 2009 American Chemical Society
Abstract: The precise determination of diffusion parameters plays a key role in Li battery research and is a rather complex problem when electrode materials, i.e., mixed conductors, have to be investigated. In the present contribution, we show how stimulated echo nuclear magnetic resonance (NMR) can be used to go beyond the limits of standard NMR methods for the characterization of dynamic properties of one of the most promising new electrode materials viz. Li intercalated TiO2−B nanowires. It turned out that Li self-diffusion is very slow with an activation energy of 0.48(1) eV. Obviously, the shorter diffusion length compensates for this low mobility so that, nonetheless, facile incorporation and removal of Li is possible when the nanowires are used in an ion battery.



Probing the Incorporation of Ti(IV) into the BEA Zeolite Framework by XRD, FTIR, NMR, and DR UV−jp810722bis

Jean-Philippe Nogier†‡, Yannick Millot†‡, Pascal P. Man†‡, Tetsuya Shishido§, Michel Che# and Stanislaw Dzwigaj*
J. Phys. Chem. C, 2009, 113 (12), pp 4885–4889
DOI: 10.1021/jp8099829
Copyright © 2009 American Chemical Society
Abstract: The method (Dzwigaj, S., et al. Chem. Commun. 1998, 87) proposed earlier to incorporate V(V) ions into the BEA zeolite framework at the solid−liquid interface from V precursors in aqueous solution has been successfully extended to the solid−gas interface and titanium, with TiCl4 vapor as the precursor. The use of TiCl4 vapor has the advantage to restrict the speciation of titanium to this single species and to lead to a significant amount of Ti (5 Ti wt %) determined by chemical analysis. The incorporation of Ti into the SiBEA zeolite framework is evidenced by XRD. The reaction of TiCl4 vapor with H-bonded and terminal SiO−H groups of vacant T-atom sites is monitored by FTIR, 29Si MAS NMR, 1H−29Si CP MAS NMR and 1H MAS NMR. The presence of tetrahedral Ti(IV) as the main titanium species is evidenced by diffuse reflectance UV−vis. A possible pathway for the formation of framework tetrahedral Ti(IV) in TiSiBEA is proposed.

Macromolecules, v42, issue 6

Dipolar and Bond Vector Correlation Function of Linear Polymers Revealed by Field Cycling 1H NMR: Crossover from Rouse to Entanglement Regime

A. Herrmann†, V. N. Novikov‡ and E. A. Rssler*†
Macromolecules, 2009, 42 (6), pp 2063–2068

Abstract: We apply field cycling NMR to study segmental reorientation dynamics in melts of linear 1,4-polybutadiene (PB) in the entanglement regime (M ≥ Me). Dispersion data of the spin−lattice relaxation time T1(ω) are transformed to the susceptibility representation χ′′(ω) = ω/T1(ω), and using frequency temperature superposition master curves χ′′(ωτs) are constructed which reflect spectral contributions from glassy as well as polymer specific dynamics. The correlation time τs is determined by glassy dynamics. Transforming χ′′(ωτs) into the time domain and studying the crossover from Rouse to entanglement regime, the full dipolar or segmental reorientational correlation function F2(t/τs) is presented covering six decades in amplitude and 8 decades in time. Assuming F2(t) ub(t)ub(0)2 the bond vector correlation function b(t) = ub(t)ub(0) is obtained. Reaching Z = M/Me ≤ 9, comparison with theoretical predictions by the tube-reptation model as well as renormalized Rouse theory reveals significant discrepancies whereas good agreement is found with simulations. The crossover to entanglement dynamics appears to be very protracted.




1H HRMAS NMR Study on Phase Transition of Poly(N-isopropylacrylamide) Gels with and without Grafted Comb-Type Chains

Geying Ru†‡, Nian Wang†‡, Shaohua Huang† and Jiwen Feng*†
Macromolecules, 2009, 42 (6), pp 2074–2078

Abstract: Phase transition occurring in three different types of poly(N-isopropylacrylamide) gelsnormal cross-linked gel, comb-type grafted gel, and comb-type grafted gel with styrene-modified comb chainshas been investigated by variable-temperature measurements of 1H NMR spectra and spin−spin relaxation time. Three different gels exhibit distinct collapse behaviors in response to increasing temperature. For the normal gel, remarkable network shrinking occurs in a relatively narrow temperature range from 32 to 35 °C. For the styrene-modified comb-type gel, overall chain shrinkage appears in a very broad temperature range from 22 to 35 °C in which the styrene-modified comb chains shrink at lower temperatures (22−32 °C) than the backbone networks (32−35 °C). In the comb-type gel without styrene modification, however, the backbone networks shrink first (at 32−35 °C) on heating, followed by collapsing of comb chains (at 35−36 °C). During shrinkage of backbone networks the comb chains are expulsed from the main gel networks which is revealed by abnormal T2 increase of comb chains. T2 measurements also reveal that the styrene-modified comb-type gel in the equilibrium swelling state has more rigid network structure than both conventional gel and comb-type gel without styrene modification.

J Phys Chem B and C, vol 113, issues 10-11

Nothing in the two issues of J Phys Chem C this time around

Alamethicin Topology in Phospholipid Membranes by Oriented Solid-state NMR and EPR Spectroscopies: a Comparison

Evgeniy S. Salnikov†‡, Marta De Zotti§, Fernando Formaggio§, Xing Li, Claudio Toniolo§, Joe D. J. ONeil, Jan Raap, Sergei A. Dzuba*† and Burkhard Bechinger*‡

J. Phys. Chem. B, 2009, 113 (10), pp 3034–3042
Abstract: Alamethicin, a hydrophobic peptide that is considered a paradigm for membrane channel formation, was uniformly labeled with 15N, reconstituted into oriented phosphatidylcholine bilayers at concentrations of 1 or 5 mol %, and investigated by solid-state NMR spectroscopy as a function of temperature. Whereas the peptide adopts a transmembrane alignment in POPC bilayers at all temperatures investigated, it switches from a transmembrane to an in-plane orientation in DPPC membranes when passing the phase transition temperature. This behavior can be explained by an increase in membrane hydrophobic thickness and the resulting hydrophobic mismatch condition. Having established the membrane topology of alamethicin at temperatures above and below the phase transition, ESEEM EPR was used to investigate the water accessibility of alamethicin synthetic analogues carrying the electron spin label TOAC residue at one of positions 1, 8, or 16. Whereas in the transmembrane alignment the labels at positions 8 and 16 are screened from the water phase, this is only the case for the latter position when adopting an orientation parallel to the surface. By comparing the EPR and solid-state NMR data of membrane-associated alamethicin it becomes obvious that the TOAC spin labels and the cryo-temperatures required for EPR spectroscopy have less of an effect on the alamethicin−POPC interactions when compared to DPPC. Finally, at P/L ratios of 1/100, spectral line broadening due to spin−spin interactions and thereby peptide oligomerization within the membrane were detected for transmembrane alamethicin.


JOEL TANG!!!!

Impact of Reduction on the Properties of Metal Bisdithiolenes: Multinuclear Solid-State NMR and Structural Studies on Pt(tfd)2 and Its Reduced Forms

Joel A. Tang†, Elzbieta Kogut‡, Danielle Norton‡, Alan J. Lough§, Bruce R. McGarvey†, Ulrich Fekl*‡ and Robert W. Schurko*†
J. Phys. Chem. B, 2009, 113 (11), pp 3298–3313

Abstract: Transition-metal dithiolene complexes have interesting structures and fascinating redox properties, making them promising candidates for a number of applications, including superconductors, photonic devices, chemical sensors, and catalysts. However, not enough is known about the molecular electronic origins of these properties. Multinuclear solid-state NMR spectroscopy and first-principles calculations are used to examine the molecular and electronic structures of the redox series [Pt(tfd)2]z– (tfd = S2C2(CF3)2; z = 0, 1, 2; the anionic species have [NEt4]+ countercations). Single-crystal X-ray structures for the neutral (z = 0) and the fully reduced forms (z = 2) were obtained. The two species have very similar structures but differ slightly in their intraligand bond lengths. 19F−195Pt CP/CPMG and 195Pt magic-angle spinning (MAS) NMR experiments are used to probe the diamagnetic (z = 0, 2) species, revealing large platinum chemical shielding anisotropies (CSA) with distinct CS tensor properties, despite the very similar structural features of these species. Density functional theory (DFT) calculations are used to rationalize the large platinum CSAs and CS tensor orientations of the diamagnetic species using molecular orbital (MO) analysis, and are used to explain their distinct molecular electronic structures in the context of the NMR data. The paramagnetic species (z = 1) is examined using both EPR spectroscopy and 13C and 19F MAS NMR spectroscopy. Platinum g-tensor components were determined by using solid-state EPR experiments. The unpaired electron spin densities at 13C and 19F nuclei were measured by employing variable-temperature 13C and 19F NMR experiments. DFT and ab initio calculations are able to qualitatively reproduce the experimentally measured g-tensor components and spin densities. The combination of experimental and theoretical data confirm localization of unpaired electron density in the π-system of the dithiolene rings.



Location of a Metallic Cation Complexed in a Calixarene Cavity As Determined by Calixarene 13C Spin Relaxation. Application to Cesium and Thallium Complexed by p-Sulfonatocalix[4]arene in Water

Diana Cuc†, Sabine Bouguet-Bonnet†, Nicole Morel-Desrosiers‡, Jean-Pierre Morel‡, Pierre Mutzenhardt† and Daniel Canet*†

J. Phys. Chem. B, 2009, 113 (11), pp 3499–3503
Abstract: This study deals with the exact location of the monovalent metal cations Cs+ and Tl+ which are complexed by the p-sulfonatocalix[4]arene in water. This determination rests on the measurements of longitudinal relaxation times of carbon-13 not directly bonded to protons. The difference between the relaxation times of the free calixarene and of the complex definitely demonstrates that the monovalent metal cation is well inside the calixarene cavity. These features are in fact enhanced by the presence of paramagnetic species which act in a different way in the complexed form. Experimental results also show without any ambiguity that the calixarene cavity is essentially hydrophobic. Finally, it is observed that thallium is more mobile than cesium within the calixarene cavity.

Macromolecules, v42, issue 5

Determination of the Structure of a Novel Anion Exchange Fuel Cell Membrane by Solid-State Nuclear Magnetic Resonance Spectroscopy

Xueqian Kong, Kuldeep Wadhwa, John G. Verkade and Klaus Schmidt-Rohr*
Macromolecules, 2009, 42 (5), pp 1659–1664

Abstract: A novel anion exchange fuel cell membrane was successfully synthesized by chemically attaching proazaphosphatranium/phosphatranium cations under microwave treatment to the sulfonic groups of Nafion-F. Solid-state nuclear magnetic resonance (NMR) techniques were employed to determine the actual structure and composition of this anion exchange membrane. 31P NMR showed two main signals with a 2:1 intensity ratio and chemical shift changes of +89 and +46 ppm, respectively, from the main peak of phosphatranium chloride. 1H−31P heteronuclear correlation (HetCor) NMR and 1H−31P recoupling experiments indicated that the proton originally bonded to phosphorus in phosphatranium chloride is replaced in the major component of the Nafion−proazaphosphatranium/phosphatranium composite. 19F NMR experiments showed that the fluorine in the −SO2F group of the Nafion-F precursor is fully replaced. 31P{19F} rotational-echo double-resonance (REDOR) experiments measured a P−F internuclear distance of 0.4 nm, which showed that the proazaphosphatranium is covalently attached to Nafion through a S−P bond. 13C NMR and 1H−13C HetCor spectra indicated that the proazaphosphatranium structure is maintained even after the microwave treatment at 180 °C and also showed indications of entrapped dimethylformamide solvent.

Magnetic Resonance in Chemistry (MRC), up to March 9, 2009

Magnetic Resonance in Chemistry (MRC), up to March 9, 2009

Using hyperbolic secant pulses to assist characterization of chemical shift tensors for half-integer spin quadrupolar nuclei in MAS powder samples

by Thomas T. Nakashima, Roshanak Teymoori, Roderick E. Wasylishen

online March 9, 2009

Determination of the NMR anisotropic magnetic shielding parameters from magic angle spinning, MAS, powder samples containing half-integer spin quadrupolar nuclei is achieved by analysis of the difference spectrum obtained with and without application of a hyperbolic secant pulse. Application of a hyperbolic secant pulse to any spinning sideband associated with the central transition, mI = 1/2 to mI = - 1/2, results in 'saturation' of the entire central transition manifold. Similarly, if one spinning sideband associated with the mI = 3/2 to mI = 1/2 and mI = - 1/2 to mI = - 3/2 satellite transitions is perturbed, the entire satellite manifold associated with these transitions is 'saturated' while the central transition is enhanced by population transfer. Three 'difference spectrum' techniques are employed to selectively yield the spinning sidebands associated predominantly from the central transition. The success of these difference techniques is first demonstrated by examining 51V NMR spectra of three metavanadate salts and 59Co NMR spectra of Co(acac)3. The vanadium and cobalt chemical shift tensors in these compounds have spans between 400 and 1400 ppm. Because the hyperbolic secant techniques proposed here yielded results that are in good agreement with earlier reports, they have been applied to characterize the 51V chemical shift tensor of the dimer of bis(N, N-dimethylhydroxamido)-hydroxooxovanadate, {V(O)(ONMe2)2}2O, whose chemical shift tensor has not been previously reported.

DOI: http://dx.doi.org/10.1002/mrc.2413

J. Med. Chem., 2009, 52 (5), pp 1263–1267

Detection of Metabolite Changes in C6 Glioma Cells Cultured with Antimitotic Oleyl Glycoside by 1H MAS NMR

Isabel Garca-lvarez, Leoncio Garrido, Ernesto Doncel-Prez, Manuel Nieto-Sampedro and Alfonso Fernndez-Mayoralas

Abstract
The synthetic glycoside, oleyl N-acetyl-α-d-glucosaminide (1), was previously shown to exhibit antimitotic activity on rat (C6) and human (U-373) glioma lines. To obtain information about its mechanism of action, metabolite changes in C6 glioma cells were analyzed after treatment with 1 using high-resolution magic angle spinning 1H NMR. Compound 1 caused either a decrease or an increase in the intensity of the signal assigned to coenzyme A (CoA) metabolites depending on the concentration used. The data obtained from the 1H NMR spectra of cells cultured with 1, combined with those obtained after treatment with oleic acid (an inhibitor of acetyl-CoA carboxylase) and phenyl butyrate (a known antineoplastic agent), suggest that 1 may be altering the metabolism of fatty acids and induce apoptosis of C6 glioma cells. These results point to NMR spectroscopy as an efficient technique for monitoring the response of the cells to therapeutic agents.

J. Am. Chem. Soc., 2009, 131 (9), pp 3317–3330

Solid-State Chlorine NMR of Group IV Transition Metal Organometallic Complexes
Aaron J. Rossini, Ryan W. Mills, Graham A. Briscoe†, Erin L. Norton, Stephen J. Geier, Ivan Hung, Shaohui Zheng, Jochen Autschbach and Robert W. Schurko

Abstract
Static solid-state 35Cl (I = 3/2) NMR spectra of the organometallic compounds Cp2TiCl2, CpTiCl3, Cp2ZrCl2, Cp2HfCl2, Cp*2ZrCl2, CpZrCl3, Cp*ZrCl3, Cp2ZrMeCl, (Cp2ZrCl)2μ-O, and Cp2ZrHCl (Schwartz’s reagent) have been acquired at 9.4 T with the quadrupolar Carr−Purcell Meiboom−Gill (QCPMG) sequence in a piecewise manner. Spectra of several samples have also been acquired at 21.1 T. The electric field gradient (EFG) tensor parameters, the quadrupolar coupling constant (CQ) and quadrupolar asymmetry parameter (ηQ), are readily extracted from analytical simulations of the spectra. The 35Cl EFG and chemical-shift tensor parameters are demonstrated to be sensitive probes of metallocene structure and allow for differentiation of monomeric and oligomeric structures. First-principles calculations of the 35Cl EFG parameters successfully reproduce the experimental values and trends. The origin of the observed values of CQ(35Cl) are further examined with natural localized molecular orbital (NLMO) analyses. The combination of experimental and theoretical methods applied to the model compounds are employed to structurally characterize Schwartz’s reagent (Cp2ZrHCl), for which a crystal structure is unavailable. Aside from a few select examples of single-crystal NMR spectra, this is the first reported application of solid-state 35Cl NMR spectroscopy to molecules with covalently bound chlorine atoms. It is anticipated that the methodology outlined herein will find application in the structural characterization of a wide variety of chlorine-containing transition-metal and main-group systems.

J. Am. Chem. Soc., 2009, 131 (9), pp 3164–3165

Hyperpolarized 1H NMR Employing Low γ Nucleus for Spin Polarization Storage
Eduard Y. Chekmenev, Valerie A. Norton, Daniel P. Weitekamp and Pratip Bhattacharya

Abstract
Here, we demonstrate the utility of low gamma nuclei for spin storage of hyperpolarization followed by proton detection, which theoretically can provide up to (gamma[1H]/gamma[X])2 gain in sensitivity in hyperpolarized biomedical MR. This is exemplified by hyperpolarized 1-13C sites of 2,2,3,3-tetrafluoropropyl 1-13C-propionate-d3 (TFPP), 13C T1 = 67 s in D2O, and 1-13C-succinate-d2, 13C T1 = 105 s in D2O, pH 11, using PASADENA. In a representative example, the spin polarization was stored on 13C for 24 and 70 s, respectively, while the samples were transferred from a low magnetic field polarizer operating at 1.76 mT to a 4.7 T animal MR scanner. Following sample delivery, the refocused INEPT pulse sequence was used to transfer spin polarization from 13C to protons with an efficiency of 50% for TFPP and 41% for 1-13C-succinate-d2 increasing the overall NMR sensitivity by a factor of 7.9 and 6.5, respectively. The low gamma nuclei exemplified here by 13C with a T1 of tens of seconds acts as an efficient spin polarization storage, while J-coupled protons are better for NMR detection.

Chem. Mater., 2009, 21 (5), pp 856–861

6Li MAS NMR Investigation of Electrochemical Lithiation of RuO2: Evidence for an Interfacial Storage Mechanism

Emilie Bekaert, Palani Balaya, Sevi Murugavel, Joachim Maier and Michel Mntrier

Abstact
Nanocrystalline RuO2 was electrochemically lithiated using a 6Li-enriched negative electrode, and selected samples at various states of lithiation-delithiation were characterized ex situ by 6Li magic-angle spinning nuclear magnetic resonance (6Li MAS NMR). In the first plateau (up to one Li per RuO2), a signal with considerable shift and loss of intensity is observed, showing a strongly paramagnetic character for the LiRuO2 phase. A signal due to solid electrolyte interphase (SEI) appears at 0 ppm on this first plateau, but significantly grows only on the subsequent conversion plateau (from 1 to 4 Li/RuO2). Li2O is detected only at the very end of the latter plateau. On further lithiation (4 to 5.5 Li/RuO2), the magnitude of the Li2O signal remains constant, and a new signal at 4 ppm appears, that we can assign to interfacial Li hypothesized earlier in this system. Upon subsequent delithiation, NMR shows that the interfacial Li first disappears, then Li2O also disappears, and the reconstructed Li-RuO2 phase is clearly different from the one formed during the initial lithiation of RuO2. Besides, the SEI signal slightly changes but does not decrease in magnitude upon delithiation. NMR results are in satisfactory agreement with the characteristic features of the proposed “job-sharing” mechanism.

Nature

Nature 458, 102-105 (5 March 2009) doi:10.1038/nature07814;

Protein structure determination in living cells by in-cell NMR spectroscopy
Daisuke Sakakibara1,2,11, Atsuko Sasaki1,2,11, Teppei Ikeya1,3,11, Junpei Hamatsu1,2, Tomomi Hanashima1, Masaki Mishima1,2, Masatoshi Yoshimasu4, Nobuhiro Hayashi5,12, Tsutomu Mikawa6, Markus Wälchli7, Brian O. Smith8, Masahiro Shirakawa2,9, Peter Güntert1,3,10 & Yutaka Ito1,2,6

Abstract: Investigating proteins 'at work' in a living environment at atomic resolution is a major goal of molecular biology, which has not been achieved even though methods for the three-dimensional (3D) structure determination of purified proteins in single crystals or in solution are widely used. Recent developments in NMR hardware and methodology have enabled the measurement of high-resolution heteronuclear multi-dimensional NMR spectra of macromolecules in living cells (in-cell NMR)1, 2, 3, 4, 5. Various intracellular events such as conformational changes, dynamics and binding events have been investigated by this method. However, the low sensitivity and the short lifetime of the samples have so far prevented the acquisition of sufficient structural information to determine protein structures by in-cell NMR. Here we show the first, to our knowledge, 3D protein structure calculated exclusively on the basis of information obtained in living cells. The structure of the putative heavy-metal binding protein TTHA1718 from Thermus thermophilus HB8 overexpressed in Escherichia coli cells was solved by in-cell NMR. Rapid measurement of the 3D NMR spectra by nonlinear sampling of the indirectly acquired dimensions was used to overcome problems caused by the instability and low sensitivity of living E. coli samples. Almost all of the expected backbone NMR resonances and most of the side-chain NMR resonances were observed and assigned, enabling high quality (0.96 ångström backbone root mean squared deviation) structures to be calculated that are very similar to the in vitro structure of TTHA1718 determined independently. The in-cell NMR approach can thus provide accurate high-resolution structures of proteins in living environments.

J Phys Chem C, vol 113, Issues 8 and 9

Structure−Property Relations in Mixed-Network Glasses: Multinuclear Solid State NMR Investigations of the System xAl2O3:(30 − x)P2O5:70SiO2

Bruce G. Aitken* and Randall E. Youngman, Rashmi R. Deshpande and Hellmut Eckert*

J. Phys. Chem. C, 2009, 113 (8), pp 3322–3331
DOI: 10.1021/jp809208m
Abstract: New mixed-network glasses along the composition line xAl2O3−(30 − x)P2O5−70SiO2 have been prepared and characterized in terms of their density, thermal expansion coefficient, refractive index, and characteristic temperatures. The compositional changes in these macroscopic properties have been correlated with structural information, obtained via Raman spectroscopy and state-of-the-art solid state NMR techniques, including 27Al, 29Si, and 31P magic-angle spinning (MAS) NMR, 27Al triple quantum MAS NMR, as well as static 31P spin echo decay spectroscopy. In addition, the extent of P−O−Al connectivity has been quantified on the basis of 27Al{31P} rotational echo double resonance (REDOR) and 31P{27Al} rotational echo adiabatic passage double resonance (REAPDOR) measurements. Both the macroscopic and the structural properties show nonlinear dependences on x, including abrupt changes at a nominal Al/P ratio of 1 (x = 0.15), where no glasses can be formed by melt quenching under the conditions used in this study. The structure of phosphorus-rich glasses (Al/P <> 1), where the alumina component is involved in Al−O−P, Al−O−Si, and possibly also Al−O−Al linkages. All of these results indicate that the structure of these glasses is dominated by the strong mutual affinity of the phosphorus oxide and alumina components. To quantify this affinity, the experimental REDOR and REAPDOR results have been compared with a cluster model assuming that both components react completely under formation of aluminum phosphate-like domains, thereby maximizing the number of Al−O−P linkages. Both the REDOR and the REAPDOR results show, however, clear deviations from such a structural scenario, supporting a more homogeneous glass structure with a certain degree of connectivity randomization.




Preferential Adsorption of Lower-Charge Glutamate Ions on Layered Double Hydroxides: An NMR Investigation

Marc X. Reinholdt*†§, Panakkattu K. Babu†‡ and R. James Kirkpatrick†
J. Phys. Chem. C, 2009, 113 (9), pp 3378–3381

Abstract: 13C MAS NMR spectroscopy of isotopically enriched samples of the layered double hydroxide hydrotalcite (HT) [(Mg2Al)(OH)6A−,nH2O, where A− is a counteranion that may bear different charges] exchanged with glutamate (Glu) shows an unexpected preferential adsorption of the lower-charged species (Glu1−) relative to the higher-charged species (Glu2−) by a layered double hydroxide (LDH) compound. At pH 11.0, the Glu1−/Glu2− ratio is about 0.44, an order of magnitude greater than expected in solution. Previous studies of phosphate and carbonate exchange onto LDH compounds (refs 25 and 26) show a strong preference for the higher-charged anion. The preference for Glu1−, in which the amine site is protonated, may be due in part to −NH3+ allowing for an energetically more favorable H-bonding network among the anions, the metal hydroxide substrate, and the interlayer and surface water molecules compared to −NH2. Changes in the pH and the pKa of Glu near the HT surface and due to nanoconfinement may also play important roles. These results suggest that the interactions dominating the exchange of amino acids and proteins onto LDH compounds may be quite different from those that control the exchange of small inorganic anions.




Homogeneously-Alloyed CdTeSe Single-Sized Nanocrystals with Bandgap Photoluminescence
Ruibing Wang†, Olivier Calvignanello†, Christopher I. Ratcliffe†, Xiaohua Wu‡, Donald M. Leek†, Md. Badruz Zaman†, David Kingston§, John A. Ripmeester† and Kui Yu*†

J. Phys. Chem. C, 2009, 113 (9), pp 3402–3408

Abstract: Homogeneously alloyed ternary CdTeSe magic-sized nanocrystals (MSNs) with bandgap emission were synthesized in 1-octadecene (ODE) via a noninjection one-pot approach featuring synthetic reproducibility and large-scale capability. The noninjection approach used cadmium acetate dihydrate (Cd(OAc)2·2H2O), elemental selenium, and elemental tellurium as Cd, Se, and Te sources, respectively. The growth of the CdTeSe nanocrystals was carried out at temperatures from 120 to 200 °C for several hours in a reaction flask containing the reactants together with a long-chain fatty acid as capping ligands and ODE as the reaction medium. During synthesis, the CdTeSe nanocrystals exhibited persistent bandgap and did not grow in size anymore after their formation, either with longer growth periods or higher reaction temperature. Also, they exhibit an absorption doublet with 288 meV energy difference between the two peaks; the first excitonic transition peak is at 520 nm and bandgap photoemission peak at 524 nm with full width at half-maximum (fwhm) of ca. 20 nm. Both the growth pattern and the optical properties suggest that they are magic-sized and thus termed as single-sized. Nuclear magnetic resonance (NMR), with sensitivity to local environment, provided valuable information regarding the structure and composition of the nanocrystals. Solid-state 13C cross polarization/magic angle spinning (CP/MAS) NMR spectra showed that the carboxylate capping ligand is firmly attached to the crystal, and 1H decoupled 113Cd MAS spectra, with and without CP, distinguished between the surface Cd species and the Cd inside a nanocrystal. The 113Cd NMR results also confirmed, unambiguously, that the nanocrystals are homogeneously alloyed ternary CdTeSe, with 113Cd resonances located between those of CdTe and CdSe nanocrystals indicating a stoichiometry of approximately 1Se:1Te ratio throughout the whole nanocrystal. XRD supported that they are ternary-alloyed CdTeSe rather than binary CdTe or CdSe, with a wurtzite crystal structure. In addition, both energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) supported an approximate stoichiometric ratio of 1Se:1Te of the CdTeSe nanocrystals.



27Al NMR Chemical Shifts in Oxide Crystals: A First-Principles Study
Minseok Choi*†, Katsuyuki Matsunaga†‡, Fumiyasu Oba† and Isao Tanaka*†‡

J. Phys. Chem. C, 2009, 113 (9), pp 3869–3873
DOI: 10.1021/jp810484j
Abstract: In the framework of density functional theory using periodic boundary conditions, 27Al nuclear magnetic resonance (NMR) parameters of 20 aluminum sites in 12 aluminum-containing crystalline oxides, i.e., Al2O3, LiAlO2, SiAl2O5, MgAl2O4, YAlO3, AlVO4, and their polymorphs, are investigated. The present method excellently reproduces the 27Al NMR parameters and the well-known empirical correlation of the isotropic chemical shifts, δiso, of 27Al nuclei with its number of coordinating oxygen atoms, i.e., coordination number. Through systematic calculations, we demonstrate that the mean Al−O bond order, QAl−O, can be a better parameter to correlate with 27Al δiso than merely averaged bond length or the coordination number. The relationship between δiso and QAl−O is also found to be valid for α-Al2O3 under hydrostatic pressures in which the coordination number is unchanged from six.

J Phys Chem B vol. 113, Issues 8 and 9

31P NMR Investigation of Backbone Dynamics in DNA Binding Sites†

Ye Tian‡, Michael Kayatta§, Katharine Shultis, Alejandro Gonzalez§, Leonard J. Mueller‡ and Mary E. Hatcher*

J. Phys. Chem. B, 2009, 113 (9), pp 2596–2603
DOI: 10.1021/jp711203m
Abstract: The backbone conformation of DNA plays an important role in the indirect readout mechanisms for protein−DNA recognition events. Thus, investigating the backbone dynamics of each step in DNA binding sequences provides useful information necessary for the characterization of these interactions. Here, we use 31P dynamic NMR to characterize the backbone conformation and dynamics in the Dickerson dodecamer, a sequence containing the EcoRI binding site, and confirm solid-state 2H NMR results showing that the C3pG4 and C9pG10 steps experience unique dynamics and that these dynamics are quenched upon cytosine methylation. In addition, we show that cytosine methylation affects the conformation and dynamics of neighboring nucleotide steps, but this effect is localized to only near neighbors and base-pairing partners. Last, we have been able to characterize the percent BII in each backbone step and illustrate that the C3pG4 and C9pG10 favor the noncanonical BII conformation, even at low temperatures. Our results demonstrate that 31P dynamic NMR provides a robust and efficient method for characterizing the backbone dynamics in DNA. This allows simple, rapid determination of sequence-dependent dynamical information, providing a useful method for studying trends in protein−DNA recognition events.




Molecular Mechanism for Formation of Polyaniline Lamella from a Lyotropic Liquid Crystal: An NMR Study

Li Shi, Xiaodong Wu*, Lude Lu, Xujie Yang and Xin Wang*
J. Phys. Chem. B, 2009, 113 (9), pp 2725–2733
DOI: 10.1021/jp9002824

Abstract: Polyaniline (PANI) microlamellas with an average interlamellar distance of 2.6 nm were prepared from a nematic lyotropic liquid crystal system composed by sodium dodecyl sulfate (SDS) aqueous solution. To reveal the formation mechanism of these lamellas, a series of NMR studies have been performed. At first, variable-temperature (VT) 13C NMR experiments have suggested that, prior to polymerization, anilines are predominantly located in the vicinity of the SDS polar head region with a limited mobility at low temperature, whereas they become more mobile and penetrate into the SDS hydrophobic domain at elevated temperature. Subsequent in situ 13C NMR measurements at 310 K have indicated that the overall polymerization can be taken place in two stages. In the beginning, the reaction sites are within the SDS micelles, resulting in the formation of oligomeric PANI species with benzenoid and quinoid structures. Interestingly, these oligomeric species fall off from the micellar hydrophobic domains and reorganize into layered structures with the support of SDS. In the second stage, further polymerization can be continued within the interlayers. This paper provides a good example in studying the roles of surfactants at the nucleation stage qualitatively during the synthesis of morphology-specific polymers with the application of NMR techniques, a period difficult to be examined by other approaches currently.