Sideband Intensities Research Articles

Acceleration of indirect detection 195Pt solid-state NMR experiments by sideband selective excitation or alternative indirect sampling schemes

The measurement of the of chemical shift (CS) tensors via solid-state NMR (ssNMR) spectroscopy has proven to be a powerful probe of structure for organic molecules, biomolecules, and inorganic materials. However, when measuring the NMR spectra of heavy spin-1/2 isotopes the chemical shift anisotropy (CSA) is commonly on the order of thousands of parts per million, which makes acquisition of NMR spectra difficult due to the low NMR sensitivity imposed by the breadth of the signals and challenges in uniformly exciting the NMR spectrum. We have recently shown that complete 195Pt NMR spectra could be rapidly measured by using 195Pt saturation or excitation selective long pulses (SLP) with multiple rotor-cycle durations and RF fields less than 50 kHz into 1H{195Pt} or 1H-31P{195Pt} PE S-RESPDOR, TONE D-HMQC-4, J-resolved, and J-HMQC pulse sequences. The SLP only provide signal or dephasing when they are applied on resonance with a spinning sideband. The magic angle spinning 195Pt NMR spectrum is reconstructed in the sideband selective NMR experiments by acquiring 1D NMR spectra at variable 195Pt pulse offsets. In this work, we present a detailed investigation of the specific pulse conditions required for the ideal performance of sideband selective experiments. Sideband selective experiments are shown to be able to accurately reproduce MAS NMR spectra with minimal distortions of relative sideband intensities. It is also demonstrated that a 195Pt NMR spectrum indirectly detected with HMQC can be rapidly obtained by acquiring a single rotor cycle of indirect dimension evolution points. We dub this method One Rotor Cycle of Acquisition (ORCA) HMQC. Sideband selective experiments and ORCA HMQC experiments are shown to provide a one order of magnitude improvement in experiment times as compared to conventional wideline HMQC experiments.

Optically detected magnetic resonance of nitrogen-vacancy centers in vertical diamond Schottky diodes

Diamond solid-state devices are very attractive to electrically control the charge state of nitrogen-vacancy (NV) centers. In this work, p-type vertical diamond Schottky diodes (VDSDs) are introduced as a platform to electrically control the interconversion between the neutral charge NV (NV0) and negatively charged NV (NV−) centers. The photoluminescence of NV centers generated by ion implantation in VDSDs shows an increase in NV− zero phonon line (ZPL) and phonon sideband intensities with reverse voltage, whereas the NV0 ZPL intensity decreases. Thus, NV centers embedded in VDSDs are converted into NV− under reverse bias voltage. Moreover, the optically detected magnetic resonance (ODMR) of NV− exhibits an increase in the ODMR contrast with reverse bias voltage and splitting of the resonance dips. Since no magnetic field is applied, the dip splitting in the ODMR spectrum is ascribed to the Stark effect induced by the interaction of NV− with the electric field existing within the depletion region of VDSDs.

Dynamical Birefringence: Electron-Hole Recollisions as Probes of Berry Curvature

The direct measurement of Berry phases is still a great challenge in condensed matter systems. The bottleneck has been the ability to adiabatically drive an electron coherently across a large portion of the Brillouin zone in a solid where the scattering is strong and complicated. We break through this bottleneck and show that high-order sideband generation (HSG) in semiconductors is intimately affected by Berry phases. Electron-hole recollisions and HSG occur when a near-band gap laser beam excites a semiconductor that is driven by sufficiently strong terahertz (THz)-frequency electric fields. We carried out experimental and theoretical studies of HSG from three GaAs/AlGaAs quantum wells. The observed HSG spectra contain sidebands up to the 90th order, to our knowledge the highest-order optical nonlinearity observed in solids. The highest-order sidebands are associated with electron-hole pairs driven coherently across roughly 10% of the Brillouin zone around the \Gamma point. The principal experimental claim is a dynamical birefringence: the sidebands, when the order is high enough (> 20), are usually stronger when the exciting near-infrared (NIR) and the THz electric fields are polarized perpendicular than parallel; the sideband intensities depend on the angles between the THz field and the crystal axes in samples with sufficiently weak quenched disorder; and the sidebands exhibit significant ellipticity that increases with increasing sideband order, despite nearly linear excitation and driving fields. We explain dynamical birefringence by generalizing the three-step model for high order harmonic generation. The hole accumulates Berry phases due to variation of its internal state as the quasi-momentum changes under the THz field. Dynamical birefringence arises from quantum interference between time-reversed pairs of electron-hole recollision pathways.

Application of the Mössbauer effect to the study of subnanometer harmonic displacements in thin solids

We measure subnanometer displacements of thin samples vibrated by piezotransducer. Samples contain $^{57}$Fe nuclei, which are exposed to 14.4 keV $\gamma$-radiation. Vibration produces sidebands from a single absorption line of the sample. The sideband intensities depend on the vibration amplitude and its distribution along the sample. We developed a model of this distribution, which adequately describes the spectra of powder and stainless steel (SS) absorbers. We propose to filter $\gamma$-radiation through a small hole in the mask, placed before the absorber. In this case only a small spot of the vibrated absorber is observed. We found for SS foil that nuclei, exposed to $\gamma$-radiation in this small spot, vibrate with almost the same amplitudes whose difference does not exceed a few picometers.

Methyl tunnelling sidebands in the low-field NMR spectrum of 3-pentanone: Driving A–E transitions using rf irradiation

Using magnetic field-cycling at cryogenic temperatures, low-field dipole–dipole driven NMR spectra have been recorded on 3-pentanone (CH3CH2C(O)CH2CH3). The spectra are characterised by tunnelling sidebands arising from the quantum dynamics of the methyl (CH3) rotors. From the sideband frequencies, the CH3 tunnelling frequency is determined to be νt=3.05±0.01MHz. The tunnelling sidebands are characterised by A–E transitions in nuclear spin-symmetry, involving simultaneous changes in tunnelling and nuclear spin states. To gain further insight, a theoretical analysis of the spin Hamiltonian matrix has been used to calculate the sideband transition probabilities. These are subsequently used in a thermodynamic model to simulate the low-field NMR spectrum which is compared with experiment. The level-crossings encountered as part of the magnetic field-cycling NMR sequence are found to play an essential role in determining the tunnelling sideband intensities.

Adsorption of Trimethylphosphine Oxide on Silicalite Studied by Solid-State NMR

Abstract The adsorption state of trimethylphosphine oxide (TMPO) on siliceous MFI-type zeolite, silicalite, has been studied by solid-state NMR. TMPO was loaded by vapor as well as the solvent methods, and 31P and 1H magic-angle-spinning (MAS) NMR spectra were measured. Most of the 31P signals are located at lower frequency than that of crystalline TMPO, among which the 30-ppm signal is the largest. This is the first case of which the signal at about 30 ppm is dominant. The observation of the 30-ppm signal is independent of the TMPO introduction method, vapor or solvent. The dominant signal at about 30 ppm in the sample prepared by vapor shifts to about 37 ppm for ten months, being accompanied by increase in the spinning sideband intensities. This fact indicates that TMPO molecules move to a more stable site with a smaller space, resulting in suppression of the molecular motion. The temperature increase leads to increase in the fraction of mobile TMPO molecules giving a 31P signal at 33.0 ppm. Comparison with the results of silica nanoparticle and mesoporous silica leads to the conclusion that the signals in the frequency range lower than crystalline TMPO are attributed to TMPO molecules confined in the micropores of the MFI-type framework and not interacting with Brønsted acid sites.

ChemInform Abstract: Tensors and Rotations in NMR

AbstractReview: 26 refs.

Temperature-Dependent Phase Behavior of the Synaptosomal Membranes from Mammalian and Marine Invertebrate Synaptosomes

Given reports of raft domains in rodent brain synaptosomes, we probed for their conservation in a poikilotherm, the Woods Hole squid Loligo. Because rafts are described as liquid-ordered phase-separated domains, we expected phase transition temperatures above body temperature if raft function is important to neuronal activity. We tested this hypothesis by comparing synaptosomes, intact nerve endings, from animals that live at two very different temperatures: mouse (body temperature-37°C) and squid (body temperature-20°C). We measured the temperature-dependence of the lipid phase of intact synaptosomes in the absence of exogenous probes by using line-width and spinning sideband intensities of lipid hydrocarbon chain resonances, using proton magic angle spinning NMR spectra as a function of temperature between 0 and 40°C. We also determined the phase behavior of total synaptosomal lipids by repeating the NMR protocol on extracted lipids. To our surprise, there was no detectable signal for liquid-ordered lipid phases at the body temperature of either species. However, there was a difference in the temperature of the onset of order as synaptosomes were cooled below body temperature: the phase state of mouse synaptosomal membranes changes drastically below 24°C, whereas this change occurs below 8°C for the squid synaptosomal membranes. We then measured the composition of synaptosomes in terms of total lipid heads and tails, and the main difference arises from high concentrations of omega-3 poly-unsaturated fatty acids and cholesterol in the squid. Fluorescence microscopy images of squid synaptosomes stained with lipid dyes confirmed the formation of domains below, but not above the phase transition temperatures obtained from NMR measurements. Thus although the membranes of synaptosomes contain lipids that can phase-separate, these lipids remain in the liquid-disordered state at the usual physiological temperatures for squid and mouse.

Interplay between intrachain and interchain interactions in semiconducting polymer assemblies: The HJ-aggregate model

A new model for analyzing the photophysics of polymer aggregates is introduced taking into account exciton motion along a polymer chain and across polymer chains. Excitonic coupling and vibronic coupling are treated on equal footing using a Holstein-based Hamiltonian represented in a multi-particle basis set. In the HJ-aggregate model the competition between intrachain (through-bond) coupling leading to Wannier-Mott excitons, and interchain (through-space) coupling leading to Frenkel excitons, is studied in detail for two model dimers: one composed of red-phase polydiacetylene (PDA) chains and the other composed of regioregular P3HT chains. The resulting photophysical properties are shown to depend critically on the relative magnitudes of the intrachain and interchain exciton bandwidths. Dominant intraband (interband) coupling favors a photophysical response resembling J-aggregates (H-aggregates). In PDA dimers, where intrachain coupling prevails, the absorption spectrum is dominated by the 0-0 peak, as is characteristic of J-aggregates. The photoluminescence (PL) spectrum displays hybrid character: the ratio of the main (0-0) band to the first vibronic sideband intensities is initially zero at T = 0 K due to the forbidden nature of the 0-0 transition, but then increases with temperature in a manner characteristic of H-aggregates, peaking when kT ≈ ΔE, where ΔE is the interchain splitting. Further increases in temperature result in a decline of the PL ratio, as in a J-aggregate. This remarkable H to J transition is also predicted for the temperature dependence of the radiative decay rate, k(rad). The maximum (peak) rate scales as, k(rad) (max)∼(W(intra)/W(inter))(1/2), where W(intra) (W(inter)) is the intrachain (interchain) exciton bandwidth. Hence, when W(intra) is sufficiently larger than W(inter) the dimer displays thermally activated superradiance. In P3HT the intrachain coupling is far weaker than in PDA making the intrachain and interchain couplings comparable in the crystalline phase. Although the absorption spectral line shape is still well-accounted for by the conventional H-aggregate model, the photoluminescence is more sensitive, with H or J behavior tunable by changes in morphology. Long range intrachain order which coincides with weaker interchain interactions induces J-aggregate behavior, while short range intrachain order and the resulting stronger interchain coupling induces H-aggregate behavior. Our predictions neatly account for the H-like dominance exhibited by the PL from spin-cast films and the J-like dominance exhibited by the PL from highly ordered P3HT nanofibers self-assembled in toluene.

Tensors and rotations in NMR

AbstractThe transformation of second‐rank Cartesian tensors under rotation plays a fundamental role in the theoretical description of nuclear magnetic resonance experiments, providing the framework for describing anisotropic phenomena such as single crystal rotation patterns, tensor powder patterns, sideband intensities under magic‐angle sample spinning, and as input for relaxation theory. Here, two equivalent procedures for effecting this transformation—direct rotation in Cartesian space and the decomposition of the Cartesian tensor into irreducible spherical tensors that rotate in subgroups of rank 0, 1, and 2—are reviewed. In a departure from the standard formulation, the explicit use of the spherical tensor basis for the decomposition of a spatial Cartesian tensor is introduced, helping to delineate the rotational properties of the basis states from those of the matrix elements. The result is a uniform approach to the rotation of a physical system and the corresponding transformation of the spatial components of the NMR Hamiltonian, expressed as either Cartesian or spherical tensors. This clears up an apparent inconsistency in the NMR literature, where the rotation of a spatial tensor in spherical tensor form has typically been partnered with the inverse rotation in Cartesian form to produce equivalent transformations. © 2011 Wiley Periodicals, Inc. Concepts Magn Reson Part A 38: 221–235, 2011.

GaPO4–EuPO4 System in NanoSize Dimensions: An Investigation Based on Luminescence and 31P Magic Angle Spinning Nuclear Magnetic Resonance Techniques

GaPO4 nanoparticles having hexagonal structure with different amounts of Eu3+ ions were prepared at 130°C based on precipitation method in glycerol medium. The interaction between GaPO4 nanoparticles and Eu3+ ions has been investigated using Eu3+ luminescence and 31P magic angle spinning nuclear magnetic resonance (MAS NMR) techniques. Based on these studies, it is established that Eu3+ ions up to 2.5 at.% replace the protons of the hydroxyl groups attached on Ga3+ ions present on the surface of the nanoparticles and above 2.5 at.%, a separate EuPO4 phase is formed. The anisotropy parameters derived from the side band intensities of the 31P MAS NMR patterns from these samples confirmed the surface ion exchange at low Eu3+ concentration (2.5 at.%) and EuPO4 phase formation at high Eu3+ concentration (5 at.% and more). The increase in anisotropy at high Eu3+ contents has been attributed to the presence of paramagnetic EuPO4 phase.

Resolution of Sample Heterogeneity in Solid-State NMR Dipolar Recoupling and Magic Angle Spinning Sideband Analyses

We have engineered algorithms to characterize heterogeneous distributions of chemical shift tensor parameters from magic angle spinning sideband intensities, as well as distances from rotational-echo double-resonance (REDOR) data. In the case of REDOR data, the method can reveal multiple distances with relatively few data points, which is of particular benefit in application to biological systems. This reverses the common practice of comparing REDOR data to dephasing curves simulated for several preconceived structural models, by providing the information necessary to construct models based on unbiased data analysis. In the case of chemical shift tensor analysis, it allows arbitrarily complex phospholipid mixtures to be analyzed for subtle perturbations, for example by association with antimicrobial peptides.The method uses an adaptation of Boltzmann statistics maximum entropy, and provides for a model-free approach to data analysis, as one need not assume the presence of any specific number of different chemical shift tensors or distances that contribute to observed signal. The strategy differs from the more common practice of including a single weighted term in a fitting procedure, as each datum constitutes additional “information” and independently adds to or subtracts from the entropy of the distribution. A constrained optimisation problem with 100s of unknowns (the number of points used to approximate a continuous probability distribution of the desired parameter(s)) is thereby turned into an unconstrained optimisation problem with one coefficient for each data point.The Boltzmann Statistics method also offers intriguing philosophical implications -- it gives the broadest, and perhaps most “honest” probability distribution consistent with the data, but also helps to determine which data points hold the greatest information content, such that experimental time can be focussed on gaining the best signal-to-noise where it is likely to benefit most.

Effect of SiO2 on the dynamics of proton conducting [Nafion/(SiO2)X] composite membranes: a solid-state 19F NMR study

Composite membranes, consisting of Nafion and inorganic oxide additives, are frequently discussed alternative materials to overcome the known low conductivity of pure Nafion at temperatures above 100 °C and at low relative humidity. It has been reported that under dry conditions, these membranes show enhanced water uptake and diffusion as compared to filler-free Nafion. This work focuses on the polymer mobility in Nafion/SiO(2) composites and on the impact of the silica particles on the polymer dynamics. [Nafion/(SiO(2))(X)] composite membranes (with X ranging from 0 to 15 wt%) in the dry and wet states were investigated by variable temperature solid-state (19)F NMR spectroscopy. (19)F T(1) and T(1ρ) relaxation times, and NMR lineshapes (linewidths and spinning sideband intensities) were analyzed to get information about the polymer mobility. It is found that Nafion composite membranes, in general, possess a higher mobility as compared to recast Nafion which is in agreement with previous results from conductivity studies. These findings are attributed to the ability of the SiO(2) particles to keep more water inside the composite membranes which also leads to a higher mobility of the polymer component. The results are further supported by the experimental (19)F{(1)H} CP/MAS NMR spectra. It is also shown that the structure of the composite membranes is more stable after dehydration, and possible condensation reactions are diminished in these membranes. In addition, the decrease in ionic exchange capacity after dehydration is less pronounced for the composite membranes as compared to filler-free Nafion.

Effects of varying water adsorption on a Cu3(BTC)2 metal–organic framework (MOF) as studied by 1H and 13C solid-state NMR spectroscopy

The process of water adsorption on a dehydrated Cu(3)(BTC)(2) (copper (II) benzene 1,3,5-tricarboxylate) metal-organic framework (MOF) was studied with (1)H and (13)C solid-state NMR. Different relative amounts of water (0.5, 0.75, 1, 1.5, 2, and 5 mole equivalents with respect to copper) were adsorbed via the gas phase. (1)H and (13)C MAS NMR spectra of dehydrated and water-loaded Cu(3)(BTC)(2) samples gave evidence on the structural changes due to water adsorption within the MOF material as well as information on water dynamics. The analysis of (1)H spinning sideband intensities reveals differences in the (1)H-(63/65)Cu hyperfine coupling between dehydrated and water-loaded samples. The investigation was continued for 60 days to follow the stability of the Cu(3)(BTC)(2) network under humid conditions. NMR data reveal that Cu(3)(BTC)(2) decomposes quite fast with the decomposition being different for different water contents.

Thin-film solid-state proton NMR measurements using a synthetic mica substrate: Polymer blends

Solid-state proton nuclear magnetic resonance (NMR) measurements are performed successfully on polymer blend thin films through the use of synthetic mica as a substrate. When used as a substrate, synthetic fluorophlogopite mica with its proton-free, diamagnetic character, allows for adequate measurement sensitivity while minimally perturbing the proton thin-film spectra, especially relative to more commonly available natural micas. Specifically, we use multiple-pulse techniques in the presence of magic-angle spinning to measure the degree of mixing in two different polymer blend thin films, polystyrene/poly(xylylene ether) and poly(1-methyladamantyl methacrylate) (PMAdMA)/triphenylsulfonium perfluorobutanesulfonate (TPS-PFBS), spin-coated onto mica substrates. Our earlier studies had focused on bulk systems where NMR signals are stronger, but may not be representative of thin films of the same systems that are relevant to many applications such as photoresist formulations in the electronics industry. The superiority of synthetic over natural paramagnetic mica is demonstrated by the maintenance of resolution and spinning sideband intensities (relative to bulk samples) for the synthetic mica samples. In contrast, degraded resolution and large spinning sidebands are shown to typify spectra of the natural mica samples. This approach can be applied to many other proton measurements of solid thin films, thereby greatly extending the types of systems to be investigated. Magnetic susceptibility measurements are also reported for all micas used.

Improved quantification of alite and belite in anhydrous Portland cements by 29Si MAS NMR: Effects of paramagnetic ions

The applicability, reliability, and repeatability of 29Si MAS NMR for determination of the quantities of alite (Ca 3SiO 5) and belite (Ca 2SiO 4) in anhydrous Portland cement was investigated in detail for 11 commercial Portland cements and the results compared with phase quantifications based on powder X-ray diffraction combined with Rietveld analysis and with Taylor–Bogue calculations. The effects from paramagnetic ions (Fe 3+) on the spinning sideband intensities, originating from dipolar couplings between 29Si and the spins of the paramagnetic electrons, were considered and analyzed in spectra recorded at four magnetic fields (4.7–14.1 T) and this has led to an improved quantification of alite and belite from 29Si MAS NMR spectra recorded at “high” spinning speeds of ν R=12.0–13.0 kHz using 4 or 5 mm rotors. Furthermore, the impact of Fe 3+ ions on the spin-lattice relaxation was studied by inversion-recovery experiments and it was found that the relaxation is overwhelmingly dominated by the Fe 3+ ions incorporated as guest-ions in alite and belite rather than the Fe 3+ sites present in the intimately mixed ferrite phase (Ca 2Al x Fe 2− x O 5).

Fast acquisition of multi-dimensional spectra in solid-state NMR enabled by ultra-fast MAS

The advantages offered by ultra-fast (>60 kHz) magic angle spinning (MAS) rotation for the study of biological samples, notably containing paramagnetic centers are explored. It is shown that optimal conditions for performing solid-state 13C NMR under 60 kHz MAS are obtained with low-power CW 1H decoupling, as well as after a low-power 1H, 13C cross-polarization step at a double-quantum matching condition. Acquisition with low-power decoupling highlights the existence of rotational decoupling sidebands. The sideband intensities and the existence of first and second rotary conditions are explained in the framework of the Floquet–van Vleck theory. As a result, optimal 13C spectra of the oxidized, paramagnetic form of human copper zinc superoxide dismutase (SOD) can be obtained employing rf-fields which do not exceed 40 kHz during the whole experiment. This enables the removal of unwanted heating which can lead to deterioration of the sample. Furthermore, combined with the short 1H T 1s, this allows the repetition rate of the experiments to be shortened from 3 s to 500 ms, thus compensating for the sensitivity loss due to the smaller sample volume in a 1.3 mm rotor. The result is that 2D 13C– 13C correlation could be acquired in about 24 h on less than 1 mg of SOD sample.

Calcium orthophosphates: crystallization and dissolution.

Calcium orthophosphates: crystallization and dissolution.

119Sn NMR chemical shift tensors in anhydrous and hydrated Si8O20(SnMe3)8 crystals

(119)Sn chemical shift tensors of crystalline trialkyltin functionalized octameric spherosilicates, Si(8)O(20)(SnMe(3))(8), have been determined by fitting sideband intensities in solid-state magic angle spinning (MAS) NMR spectra. Tin chemical shift parameters are exquisitely sensitive to the presence of water of crystallization. Both hydrogen bonding and incipient oxygen-tin bonding from molecular water impact the local tin environment. Tin chemical shift tensors in the crystalline derivatives reflect the changes in geometry and coordination number at the tin centers. Chemical shift correlations on the crystalline derivatives, with known x-ray structures, are used to infer the tin coordination environment in an amorphous sample.

Progressive ordering with decreasing temperature of the phospholipids of influenza virus

Using linewidth and spinning sideband intensities of lipid hydrocarbon chain resonances in proton magic angle spinning NMR spectra, we detected the temperature-dependent phase state of naturally occurring lipids of intact influenza virus without exogenous probes. Increasingly, below 41 degrees C ordered and disordered lipid domains coexisted for the viral envelope and extracts thereof. At 22 degrees C much lipid was in a gel phase, the fraction of which reversibly increased with cholesterol depletion. Diffusion measurements and fluorescence microscopy independently confirmed the existence of gel-phase domains. Thus the existence of ordered regions of lipids in biological membranes is now demonstrated. Above the physiological temperatures of influenza infection, the physical properties of viral envelope lipids, regardless of protein content, were indistinguishable from those of the disordered fraction. Viral fusion appears to be uncorrelated to ordered lipid content. Lipid ordering may contribute to viral stability at lower temperatures, which has recently been found to be critical for airborne transmission.