Fourier-transform NMR Research Articles

Partition Equilibria for Alcohols in Reverse Micellar AOT-Oil-Water Systems Studied by PGSE-FT NMR. A Comparison Between AOT-containing and the Corresponding AOT-free Systems

Microemulsions of the reverse micellar type were investigated by determining the self-diffusion coefficients of the components using the Pulsed Field Gradient Spin Echo – Fourier Transform NMR method (PGSE-FT NMR). The microemulsions were composed of the surfactant AOT, water and an oil (either benzene or cyclohexane), forming a water core in an oil continuum. The primary alcohols ranging from methanol to 1-decanol were added to the microemulsions as a fourth component. The degree of binding, p, of the alcohol to the micelles was determined from the measured self-diffusion coefficients for this component. Partition equilibrium constants were calculated from the values of p. Thermodynamic partition equilibrium constants, Kc, calculated from the partition coefficients are presented and compared with values based on literature data for AOT-free systems. Similarities and differences between these cases are revealed and interpreted.

Poly(ε-caprolactone)-Functionalized Carbon Nanotubes and Their Biodegradation Properties

Biodegradable poly(ϵ-caprolactone) (PCL) has been covalently grafted onto the surfaces of multiwalled carbon nanotubes (MWNTs) by the “grafting from” approach based on in-situ ring-opening polymerization of ϵ-caprolactone. The grafted PCL content can be controlled easily by adjusting the feed ratio of monomer to MWNT-supported macroinitiators (MWNT-OH). The resulting products have been characterized with Fourier-transform IR (FTIR), NMR, and Raman spectroscopies, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). After PCL was coated onto MWNT surfaces, core/shell structures with nanotubes as the “hard” core and the hairy polymer layer as the “soft” shell are formed, especially for MWNTs coated with a high density of polymer chains. Such a polymer shell promises good solubility/dispersibility of the MWNT–PCL nanohybrids in low-boiling-point organic solvents such as chloroform and tetrahydrofuran. Biodegradation experiments have shown that the PCL grafted onto MWNTs can be completely enzymatically degraded within 4 days in a phosphate buffer solution in the presence of pseudomonas (PS) lipase, and the carbon nanotubes retain their tubelike morphologies, as observed by SEM and TEM. The results present possible applications for these biocompatible PCL-functionalized CNTs in bionanomaterials, biomedicine, and artificial bones.

(3,2)D GFT-NMR experiments for fast data collection from proteins.

High throughput structure determination of proteins will contribute to the success of proteomics investigations. The G-Matrix Fourier Transformation NMR (GFT-NMR) method significantly shortens experimental time by reducing the number of the dimensions of data acquisition for isotopically labeled proteins (Kim, S. and Szyperski, T. (2003) J. Am. Chem. Soc. 125, 1385). We demonstrate herein a suite of ten 3D-->2D or (3,2)D GFT-NMR experiments using (13)C/(15)N-labeled ubiquitin. These experiments were completed within 18 hours, representing a 4- to 18-fold reduction in data acquisition time compared to the corresponding conventional 3D experiments. A subset of the GFT-NMR experiments, (3,2)D HNCO, HNCACB, HN(CO)CACB, and 2D (1)H-(15)N HSQC, which are necessary for backbone assignments, were carried out within 6 hours. To facilitate the analysis of the GFT-NMR spectra, we developed automated procedures for viewing and analyzing the GFT-NMR spectra. Our overall strategy allows (3,2)D GFT-NMR experiments to be readily performed and analyzed. Nevertheless, the increase in spectral overlap and the reduction in signal sensitivity in these fast NMR experiments presently limit their application to relatively small proteins.

A generalized approach to automated NMR peak list editing: application to reduced dimensionality triple resonance spectra

We present an algorithm and program called Pattern Picker that performs editing of raw peak lists derived from multidimensional NMR experiments with characteristic peak patterns. Pattern Picker detects groups of correlated peaks within peak lists from reduced dimensionality triple resonance (RD-TR) NMR spectra, with high fidelity and high yield. With typical quality RD-TR NMR data sets, Pattern Picker performs almost as well as human analysis, and is very robust in discriminating real peak sets from noise and other artifacts in unedited peak lists. The program uses a depth-first search algorithm with short-circuiting to efficiently explore a search tree representing every possible combination of peaks forming a group. The Pattern Picker program is particularly valuable for creating an automated peak picking/editing process. The Pattern Picker algorithm can be applied to a broad range of experiments with distinct peak patterns including RD, G-matrix Fourier transformation (GFT) NMR spectra, and experiments to measure scalar and residual dipolar coupling, thus promoting the use of experiments that are typically harder for a human to analyze. Since the complexity of peak patterns becomes a benefit rather than a drawback, Pattern Picker opens new opportunities in NMR experiment design.

GFT NMR, a new approach to rapidly obtain precise high-dimensional NMR spectral information.

Widely used higher-dimensional Fourier transform (FT) NMR spectroscopy suffers from two major drawbacks: (i) The minimal measurement time of an N-dimensional FT NMR experiment, which is constrained by the need to sample N - 1 indirect dimensions, may exceed by far the measurement time required to achieve sufficient signal-to-noise ratios. (ii) The low resolution in the indirect dimensions severely limits the precision of the indirect chemical shift measurements. To relax on constraints arising from these drawbacks, we present here an acquisition scheme which is based on the phase-sensitive joint sampling of the indirect dimensions spanning a subspace of a conventional NMR experiment. This allows one to very rapidly obtain high-dimensional NMR spectral information. Because the phase-sensitive joint sampling yields subspectra containing "chemical shift multiplets", alternative data processing is required for editing the components of the multiplets. The subspectra are linearly combined using a so-called "G-matrix" and subsequently Fourier-transformed. The chemical shifts are multiply encoded in the resonance lines constituting the shift multiplets. This corresponds to performing statistically independent multiple measurements, and the chemical shifts can thus be obtained with high precision. To indicate that a combined G-matrix and FT is employed, we named the new approach "GFT NMR spectroscopy". GFT NMR opens new avenues to establish high-throughput protein structure determination, to investigate systems with a higher degree of chemical shift degeneracy, and to study dynamic phenomena such as slow folding of biological macromolecules in greater detail.

An Improved Synthesis of 5-(2,6-Dichlorophenyl)-2-(phenylthio)-6H-pyrimido[1,6-b]pyridazin-6-one (a VX-745 analog)

An improved procedure for the synthesis an analog of the p38 inhibitor compound VX- 745 is reported.

Synthesis and Characterization of Novel Melt-Processable Ionomers based on Radiation Induced Styrene Grafted Natural Rubber

Graft ionomers based on natural rubber were prepared by sulfonating radiation induced styrene grafted natural rubber (SGNR) with acetyl sulfate reagent, followed by the neutralization of the precursor acid using methanolic zinc acetate. The modified natural rubber was characterized using spectroscopic techniques such as X-ray fluorescence (XRFS), Fourier transform infrared (FTIR), Fourier transform NMR (FTNMR), thermo-gravimetric analysis (TGA) and also by the evaluation of mechanical properties. The IR studies of the ionomers reveal that the sulfonate groups are attached to the para-position of the benzene rings of the polystyrene blocks. NMR studies give credence to this observation. Thermal analyses show that incorporation of ionic groups makes profound improvement in the thermal stability of SGNR. The presence of ionic groups results in enhancement of mechanical properties as well as retention of properties even after three cycles of processing at 150°C.

Spectral estimation of NMR relaxation

In this paper, spectral estimation of NMR relaxation is constructed as an extension of Fourier Transform (FT) theory as it is practiced in NMR or MRI, where multidimensional FT theory is used. nD NMR strives to separate overlapping resonances, so the treatment given here deals primarily with monoexponential decay. In the domain of real error, it is shown how optimal estimation based on prior knowledge can be derived. Assuming small Gaussian error, the estimation variance and bias are derived. Minimum bias and minimum variance are shown to be contradictory experimental design objectives. The analytical continuation of spectral estimation is constructed in an optimal manner. An important property of spectral estimation is that it is phase invariant. Hence, hypercomplex data storage is unnecessary. It is shown that, under reasonable assumptions, spectral estimation is unbiased in the context of complex error and its variance is reduced because the modulus of the whole signal is used. Because of phase invariance, the labor of phasing and any error due to imperfect phase can be avoided. A comparison of spectral estimation with nonlinear least squares (NLS) estimation is made analytically and with numerical examples. Compared to conventional sampling for NLS estimation, spectral estimation would typically provide estimation values of comparable precision in one-quarter to one-tenth of the spectrometer time when S/N is high. When S/N is low, the time saved can be used for signal averaging at the sampled points to give better precision. NLS typically provides one estimate at a time, whereas spectral estimation is inherently parallel. The frequency dimensions of conventional nD FT NMR may be denoted D(1), D(2), etc. As an extension of nD FT NMR, one can view spectral estimation of NMR relaxation as an extension into the zeroth dimension. In nD NMR, the information content of a spectrum can be extracted as a set of n-tuples (omega(1), ellipsis omega(n)), corresponding to the peak maxima. Spectral estimation of NMR relaxation allows this information content to be extended to a set of (n + 1)-tuples (lambda, omega(1), ellipsis omega(n)), where lambda is the relaxation rate. Copyright 2000 Academic Press.

Pulsed Fourier-Transform Ultrasonic Spectroscopy for Ultralow Temperature Applications

Pulsed Fourier-Transform (FT) ultrasonic spectroscopy has been developed for the purpose of studying 3 He at ultralow temperatures. Our method is analogous to pulsed FT NMR and possesses several advantages over conventional time-of-flight acoustic techniques. For use at low temperatures, the most significant advantage is the ability to observe the frequency spectrum while the temperature, pressure, and magnetic field may be independently tuned. More specifically, using longitudinal LiNbO 3 transducers operating both on- and off-resonance, we are able to study several broadband windows of frequency, namely 16-25 MHz, 60-70 MHz, and 105-111 MHz, The determination of the energy gap of 3 He-B is presented as an effective application, and other novel uses are discussed.

Attractive potential effect on the self-diffusion coefficients of a solitary water molecule in organic solvents

H 1 -Fourier-transform pulsed field-gradient spin-echo NMR method is applied at 30 °C to measure the self-diffusion coefficients of water, acetonitrile, and benzene in dilute organic solutions of carbon tetrachloride, benzene, chloroform, dichloromethane, acetonitrile, acetone, and water. The dependence of the translational friction coefficients ζT of the apolar solute molecule, benzene, on solvent viscosity η is linear as predicted by the simple hydrodynamic theory. The η dependence of ζT of the polar solute molecule, acetonitrile, is linear, though the slope is different in apolar and polar solvents. The η dependence of ζT of the hydrogen-bonding solute molecule, water, is nonlinear and dependent on the strength of the solvent as a proton acceptor. The breakdown of the hydrodynamic theory is discussed in terms of the attractive part of the solute–solvent interaction. The role of the attractive interaction is illustrated through a linear relationship between the proton chemical shift of water and the residual friction coefficient, which is defined by removing the repulsive component from the overall translational friction coefficient.

The characterization of high-density polyethylenes functionalized with diethylmaleate: Correlation between FT-IR and 13C NMR data

High-density polyethylene with low levels of butyl branches has been functionalized with diethylmaleate in a solution process in order to obtain very clean products without branching, crosslinking and/or degradation. Analysis of the modificated polymers has been carried out by Fourier-transform IR and 13C NMR spectroscopy. Measurements of the relative areas and intensities of the carbonyl group at 1736 cm −1 have been performed in the 1780-1690 cm −1 region, taking as internal standards the peaks at 1463 and 720cm −1 of the polyethylene chain. The FT-IR method has been correlated with 13C NMR spectral data for a range of diethylmaleate levels between 0.5 and 1.6 mol %.

Solvent-induced allylic rearrangements in poly(trichlorobutadiene) chains

It was established by Fourier-transform IR and1H NMR spectroscopy that a portion of the units of poly(1,1,2- and 1,2,3-trichlorobuta-1,3-diene) chains rearrange with migration of the allylic chlorine (1–4%) and allylic hydrogen (3–10%) under the influence of chloroform. Rearrangement with the migration of hydrogen under the influence of CDCl3, CCl4, and THF was also observed.

Nuclear magnetic resonance: concepts and methods

Structure of Nuclear Magnetic Resonance Spectra. Basic Mathematics and Physics of NMR. Fourier Transform NMR and Data Processing. Dynamic Phenomena in NMR. Multipulse and Multidimensional NMR. Index.

A gravimetric and Spectroscopic Study on the Photoinduced Radical Co-polymerisation of Methyl and Allyl Methacrylates: Kinetic and Structural Properties.

The photoinduced radical co-polymerisation of methyl and allyl methacrylates has been monitored by gravimetric analysis, Fourier Transform infra-red (FTIR) and FT nmr spectroscopy using a range of different photofragmenting and hydrogen atom abstracting type initiators. Using both visible and UV light sources the rates of photo-co-polymerisation were found to follow similar trends in both bulk and solution phase. Furthermore, unlike thermal polymerisation wherecrosslinking can occur through the allyl group, only the acrylate double bonds undergo reaction to produce a copolymer. GPC analysis showed that the homopolymers produced had narrower polydispersities than those of the copolymers while the photofragmenting type photoinitiators produced polymers with lower number average molecular mass than those produced via a hydrogen atom abstracting type. The latter is associated with marked differences in the degree of self-termination by initiator fragments. Structural analysis of the homo and copolymers by 1H FT nmr showed that photoinduced polymerisation produce polymers with a greater degree of stereoregularity than those obtained by conventional thermal radical initiation. Thus, the initiating process appears to play a major role in controlling the orientation of propagating chains.

An improved synthesis of SF5(CN) and its cycloaddition reaction with SNSAsF6. Crystal structure of F5SCNSNSAsF6 and electron spin resonance spectrum of F5SCNSNS?

An improved synthesis of SF5(CN), by direct fluorination of SF3(CN), has been achieved. This product forms a stable adduct at low temperature with AsF5, and addition of MeCN to this adduct led to very pure SF5(CN). The SF5(CN)·AsF5 adduct has been characterized by vibrational and 19F Fourier-transform NMR spectroscopy and by its dissociation vapour-pressure curve. The salt SNSAsF6 and an excess of SF5(CN) reacted in sulfur dioxide solution to give the stable salt F5S[graphic omitted]AsF6 which has been characterized by vibrational, 19F NMR and mass spectroscopy and X-ray crystallography. The structure consists of discrete F5S[graphic omitted]+ cations and AsF6– anions. The mass spectrum of F5S[graphic omitted]AsF6 was consistent with loss of AsF5 and fluoride ion transfer to give F5S[graphic omitted] which dissociated to SF4 and F2[graphic omitted]. Reduction of a dilute solution of the salt in SO2 led to identification (ESR spectroscopy) of the radical F5S[graphic omitted]˙.

Interaction between Nonionic Micelles and a Nonionic Polymer Studied by Fourier Transform NMR Self-Diffusion

The interaction between octaethylene glycol mono-n-dodecyl ether (C 12 E 8 ) and ethylhydroxyethyl cellulose (EHEC) in aqueous solution has been studied by measuring the C 12 E 8 self-diffusion coefficient in the presence of EHEC at 25 o °C. Micelle diffusion is influenced by the polymer in two ways, i.e. obstruction due to the polymer network and association of micelles to the polymer chains. It is demonstrated that, from studies using polymers of different polarity, a separation between obstruction and association effects can be achieved. It is found that the interaction-between a relatively hydrophobic EHEC and the surfactant is dominated by a strong attraction leading to a formation of polymer-surfactant complexes. This observation is consistent with phase diagram findings

7Li and 31P NMR studies of monoclinic Li3In2(PO4)3.

Fourier-transform NMR spectra and spin-lattice relaxation rates were studied for $^{7}\mathrm{Li}$ and $^{31}\mathrm{P}$ in a monoclinic modification of the ${\mathrm{Li}}_{3}$${\mathrm{In}}_{2}$(${\mathrm{PO}}_{4}$${)}_{3}$ superionic conductor over a wide temperature range of 240--575 K. The static magnetic susceptibility of the lithium subsystem of the compound and the $^{31}\mathrm{P}$ NMR line shape exhibit anomalous changes with increasing temperature. Quadrupole structure of the $^{7}\mathrm{Li}$ NMR spectrum is observed under fast motion of the lithium ions in the superionic phase. In this phase the temperature behavior of the spin-lattice relaxation rates is different for $^{7}\mathrm{Li}$ and $^{31}\mathrm{P}$ nuclei. The results are discussed taking into account the preceding NMR data on monoclinic ${\mathrm{Li}}_{3}$${\mathrm{Sc}}_{2}$(${\mathrm{PO}}_{4}$${)}_{3}$ and rhombohedral ${\mathrm{Li}}_{3}$${\mathrm{In}}_{2}$(${\mathrm{PO}}_{4}$${)}_{3}$ compounds.

New possibilities of NMR in mechanistic studies of homogeneous and heterogeneous catalysis

Results are presented that demonstrate new possibilities provided by modern Fourier-transform NMR spectrometers in the mechanistic studies of both homogeneous and heterogeneous catalysis. As particular examples, are discussed: (1) in situ characterization of the intermediate alkylperoxo complexes of Mo(VI), V(V) and Co(III) in the course of homogeneous epoxidation of cyclohexene and oxidation of cyclohexane from simultaneously recorded 95Mo, 51V or 59Co NMR spectra and 1H, 17O NMR spectra. (2) in situ characterization of reaction intermediates from the rates of paramagnetic 1H and 13C nuclear relaxation in the course of homogeneous decomposition of cumyl hydroperoxide in the presence of μ 3-oxotricobalt (II,III,III) acetate and μ 3-oxotriruthenium (III) acetate and of propylene oxidation into propylene glycol by CuCl 2-I 2 catalytic system. (3) Characterization with 51V NMR of a family of V(V) sites in supported vanadium catalysts. (4) Elucidation from a combination of 13C CP/MAS NMR, 13C 2D/MAS NMR and 2H NMR of butyl silyl ether intermediates in the course of dehydration of butanols on H-ZSM-5 zeolite.

NOBEL CHEMISTRY PRIZE: Ernst honored for NMR achievements

Nuclear magnetic resonance spectroscopy has during the last 20 years developed into perhaps the most important instrumental measuring technique within chemistry, said the Royal Swedish Academy of Sciences last week in announcing its selection for the 1991 Nobel Prize in Chemistry. That honor goes to physical chemistry professor Richard R. Ernst of the Federal Technical Institute (ETH) in Zurich, Switzerland. The academy cited Ernst for important methodological developments in NMR spectroscopy. Ernst invented Fourier-transform NMR (FT-NMR), which multiplied sensitivity 10 to 100 times compared to dispersive instruments. And he devised two-dimensional NMR techniques, which increased resolution, enabled structure determinations of biologically important macromolecules, and aided studies of rates of chemical and conformational change. With the physics Nobel going to a French scientist, and the prize in physiology or medicine to two German scientists (C&EN, Oct. 14, page 4), U.S. scientists won no Nobel Priz...

Automatic phase correction of Fourier-transform NMR data and estimation of peak area by fitting to a Lorentzian shape

The proposed method for automatically phasing NMR spectra (zero-order and first-order corrections) involves two (possibly three) stages. The first stage deals with the relation between real and imaginary amplitudes of the peak maximum, whose location is deduced from the power spectrum. Because of digitization, it is generally necessary to refine the phase angle by making use of the data points above peak half-eight in the magnitude spectrum (second stage). A further refinement (third stage) is carried out by an iterative fitting procedure applicable only to Lorentzian lines