Fourier Transform NMR Spectroscopy Research Articles

Cooling overall spin temperature: Protein NMR experiments optimized for longitudinal relaxation effects

In experiments performed on protonated proteins at high fields, 80% of the NMR spectrometer time is spent waiting for the 1H atoms to recover their polarization after recording the free induction decay. Selective excitation of a fraction of the protons in a large molecule has previously been shown to lead to faster longitudinal relaxation for the selected protons [K. Pervushin, B. Vögeli, A. Eletsky, Longitudinal 1H relaxation optimization in TROSY NMR spectroscopy, J. Am. Chem. Soc. 124 (2002) 12898–12902; P. Schanda, B. Brutscher, Very fast two-dimensional NMR spectroscopy for real-time investigation of dynamic events in proteins on the time scale of seconds, J. Am. Chem. Soc. 127 (2005) 8014–8015; H.S. Attreya, T. Szyperski, G-matrix Fourier transform NMR spectroscopy for complete protein resonance assignment, Proc. Natl. Acad. Sci. USA 101 (2004) 9642–9647]. The pool of non-selected protons acts as a “thermal bath” and spin-diffusion processes (“flip-flop” transitions) channel the excess energy from the excited pool to the non-selected protons in regions of the molecule where other relaxation processes can dissipate the excess energy. We present here a sensitivity enhanced HSQC sequence (COST-HSQC), based on one selective E-BURP pulse, which can be used on protonated 15N enriched proteins (with or without 13C isotopic enrichment). This experiment is compared to a gradient sensitivity enhanced HSQC with a water flip-back pulse (the water flip-back pulse quenches the spin diffusion between 1H N and 1H α spins). This experiment is shown to have significant advantages in some circumstances. Some observed limitations, namely sample overheating with short recovery delays and complex longitudinal relaxation behaviour are discussed and analysed.

Observation of force-detected nuclear magnetic resonance in a homogeneous field.

We report the experimental realization of BOOMERANG (better observation of magnetization, enhanced resolution, and no gradient), a sensitive and general method of magnetic resonance. The prototype millimeter-scale NMR spectrometer shows signal and noise levels in agreement with the design principles. We present 1H and 19F NMR in both solid and liquid samples, including time-domain Fourier transform NMR spectroscopy, multiple-pulse echoes, and heteronuclear J spectroscopy. By measuring a 1H-19F J coupling, this last experiment accomplishes chemically specific spectroscopy with force-detected NMR. In BOOMERANG, an assembly of permanent magnets provides a homogeneous field throughout the sample, while a harmonically suspended part of the assembly, a detector, is mechanically driven by spin-dependent forces. By placing the sample in a homogeneous field, signal dephasing by diffusion in a field gradient is made negligible, enabling application to liquids, in contrast to other force-detection methods. The design appears readily scalable to microm-scale samples where it should have sensitivity advantages over inductive detection with microcoils and where it holds great promise for application of magnetic resonance in biology, chemistry, physics, and surface science. We briefly discuss extensions of the BOOMERANG method to the microm and nm scales.

G-matrix Fourier transform NMR spectroscopy for complete protein resonance assignment

A G-matrix Fourier transform (GFT) NMR spectroscopy-based strategy for resonance assignment of proteins is described. Each of the GFT NMR experiments presented here rapidly affords four-, five-, or six-dimensional spectral information in combination with precise measurements of chemical shifts. The resulting high information content enables one to obtain nearly complete assignments by using only four NMR experiments. For the backbone amide proton detected "out-and-back" experiments, data collection was further accelerated up to approximately 2.5-fold by use of longitudinal (1)H relaxation optimization. The GFT NMR experiments were acquired for three proteins with molecular masses ranging from 8.6 to 17 kDa, demonstrating that the proposed strategy is of key interest for automated resonance assignment in structural genomics.

Synthesis and Characterization of Poly(pyridinium salt)s with Organic Counterions Exhibiting Both Thermotropic Liquid-Crystalline and Light-Emitting Properties

Two poly(pyridinium salt)s with bulky organic counterions (tosylate and triflimide) were synthesized by either the ring-transmutation polymerization reaction of 4,4‘-(1,4-phenylene)bis(2,6-diphenylpyrylium tosylate) with 1,12-diaminododecane on heating in dimethyl sulfoxide (DMSO) at 145−150 °C for 24 h or the metathesis reaction of the corresponding tosylate polymer with lithium triflimide in a common organic solvent such as acetonitrile. Their polyelectrolyte behavior in DMSO was determined by solution viscosity measurements, and their chemical structures were determined by Fourier transform infrared and Fourier transform NMR spectroscopy. They were characterized for their thermotropic liquid-crystalline properties with a number of experimental techniques. Poly(pyridinium salt) with tosylate as a counterion had a crystal-to-smectic phase transition at 116 °C that persisted up to its decomposition temperature. The corresponding polymer with triflimide as a counterion had not only lower crystal-to-smectic phase transition at 80 °C but also a smectic-to-isotropic transition at about 180 °C. Both of these transitions were well below its decomposition temperature. It had better thermal stability than that of the corresponding tosylate polymer. Their fluorescence property in solutions of tetrahydrofuran and methanol as well as in the solid state was also included in this study.

29Si NMR Experiments in Solutions of Organosilicon Compounds

AbstractFor Abstract see ChemInform Abstract in Full Text.

Correlation of vapor pressure equation and film properties with trimethylindium purity for the MOVPE grown III–V compounds

The purity of trimethylindium (TMI) has improved significantly during the past few years, as a result of improvements in its synthesis and purification. However, consistent high purity and batch-to-batch variation remain as primary concerns. In the present study, the impurity concentrations in commercial TMI samples were analyzed at part per billion levels using Fourier transform-nuclear magnetic resonance spectroscopy, inductively coupled plasma-optical emission spectrometry, and inductively coupled plasma-mass spectrometry techniques. The impurity profiles of TMI were compared with the electrical characterization of grown InP layers, e.g. electron mobility, carrier concentration, and glow discharge mass spectrometry analyses of grown layers in order to establish a correlation. The vapor pressure equation for TMI was also re-evaluated using (a) dynamic concentration measurements by Epison™ monitor and (b) the direct measurement of vapor pressures at various temperatures using a solid-state Baratron™ capacitance manometer. The resultant equations are reported along with a novel delivery system (UNI-FLO™ cylinder) that provides consistent, reproducible delivery of TMI in the vapor phase. The influence of deleterious impurities on the optoelectronic properties is discussed along with the synthesis and purification strategies for the consistent manufacture of high-purity TMI.

Detection of motion through susceptibility fields in two-dimensional exchange diffusive–MASS experiments

We show that the off-diagonal coherence peaks in two-dimensional Fourier transform NMR spectroscopy of fluids contained in porous media undergoing magic angle sample spinning (MASS) arise from amplitude modulation of the fluid’s magnetization. The amplitude modulation originates from the combined effect of MASS and the molecular diffusion through the inhomogeneous magnetic fields created by the susceptibility contrasts in the porous medium. The magnitude of the off-diagonal peaks provides information on the porous medium’s structural length scales, which give rise to correlation length scales of the magnetic susceptibility.

Application of real time digital filters in NMR spectroscopy

AbstractSince the introduction of Fourier transform NMR spectroscopy, free induction decay (FID) has been available in a binary format, which is required to apply several mathematical treatments on the raw data. Those mathematical procedures are the application of window functions on the FID, baseline correction of the time domain data, and finally the Fourier transformation. Nevertheless, it took a long time until digital filtering was applied on NMR raw data. Digital filtering can be done as either a postprocessing procedure or on the fly. The on the fly concept is preferable, but it requires specialized and very fast processors. With the common availability of such processors, called digital signal processors (DSP), digital filtering on NMR raw data became a routine method. The application of digital filters allows us to overcome problems such as baseline distortion in the NMR spectrum due to nonperfect phase response of any common analog antialiasing filter, distortion of the signal amplitude due to a nonperfect amplitude response of any common analog antialiasing filter, a limited dynamic range due to aliased noise by nonoversampling techniques, reduced dynamic range due to quantization noise, and folded signals due to folded signals outside of the spectral window. The manner in which digital filters are used in a NMR spectrometer is the same as audio applications; it just requires stronger processors to apply high‐performance digital filters on the fly. This article is an introduction to the concept of digital filters. Therefore, the description is strongly simplified and the ideal case is assumed. © 2002 Wiley Periodicals, Inc. Concepts in Magnetic Resonance (Magn Reson Engineering) 15: 164–176, 2002

Main‐chain viologen polymers with organic counterions exhibiting thermotropic liquid‐crystalline and fluorescent properties*

AbstractA series of viologen polymers with bromide, tosylate, and triflimide as counterions were prepared by either the Menshutkin reaction or metathesis reaction in a common organic solvent. Their polyelectrolyte behavior in methanol was determined by solution viscosity measurements, and their chemical structures were determined by Fourier transform infrared and Fourier transform NMR spectroscopy. They were characterized for their thermotropic liquid‐crystalline properties with a number of experimental techniques. Each of the viologen polymers with organic counterions had a low melting transition or fusion temperature above which it formed either a high‐order smectic phase or a low‐order smectic phase. Each of them also exhibited a smectic‐to‐isotropic transition. The ranges of the liquid‐crystalline phase were 80–88 °C for viologen polymers with tosylate as a counterion and 120–146 °C for viologen polymers with triflimide as a counterion. They had excellent thermal stability. The ranges of thermal stability were 288–329 °C for viologen polymers with tosylate as a counterion and 343–350 °C for viologen polymers with triflimide as a counterion. The fluorescence property for all of the viologen polymers in either aqueous or methanol solution was also included in this study. For example, the viologen polymer containing the 4,4′‐bipyridinium and p‐xylyl units along the backbone of the polymer chain with triflimide as a counterion had an absorption spectrum (λmax = 265 nm), an excitation spectrum (λex values = 357, 443, and 454 with monitoring at 533 nm), and an emission spectrum (λem = 536 nm with excitation at 430 and 450 nm) in methanol. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 659–674, 2002; DOI 10.1002/pola.10134

New Ionic Polymer: Synthesis and Properties of “Zinc Sulfonated Natural Rubber”

Zinc sulfonated natural rubbers having different sulfonate contents were synthesized by the reaction of natural rubber with acetyl sulfate, followed by the neutralization of the resultant polymeric sulfonic acid with zinc acetate. The sample notation used for the ionomer is x y M-SNR, where x y is the degree of sulfonation expressed as meq/100 gm rubber, M is the neutralizing metal ion and SNR shows sulfonated natural rubber [Weiss, R.A., Fitzgerald, J.J. and Kim, D. (1991). Macromolecules, 1064: 24]. The modified samples of natural rubber were characterized using spectroscopic techniques such as X-ray Fluorescence Spectroscopy (XRFS), Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICPAES), Fourier Transform Infrared Spectroscopy (FTIR), Fourier Transform Nuclear Magnetic Resonance Spectroscopy (FTNMR), and by the evaluation of mechanical properties. The results show that the incorporation of sulfonate groups into NR improved its physical properties drastically. At a sulfonate level of 24.6 meq/100 g rubber, the tensile strength of the modified rubber incredibly increased to 13 MPa compared to the tensile strength of 0.36 MPa shown by unvulcanized base natural rubber. The Zn-SNR thus synthesized could be reprocessed at 150 C without sacrificing much of its tensile strength.

ChemInform Abstract: Evolution of Magnetic Resonance Spectroscopy

A review of magnetic resonance spectroscopy from its beginning to the current developments is presented. The phenomenological spin-Hamiltonian of nuclear magnetic resonance, the methods and constrains of high resolution NMR, evolution of Fourier transform NMR spectroscopy are presented. A brief introduction to 2D-FT NMR methods like COSY, NOESY and EXSY is given. Magnetic resonance imaging by 2D and 3D-FT NMR spectroscopy is described EPR spin-Hamiltonian the advantage of loop-gap resonators over the conventional cavity resonators are presented. The modern trends in EPR spectroscopy, its applications to biological systems, recent developments in EPR spectrocopy with the availability of fast computers and sophisticated EPR components including FT EPR spectrocopy, elelctron spin echoes, electron spin echo envelop modulation, and 2D-FT EPR spectrocopy are discussed. Electron-Zeeman resolved EPR spectrocopy, EPR imaging technique and in vivo EPR spectrocopy, electron-nuclear double resonance, Mossbauer and nuclear quadrupole resonance spectrocopies also find an expression in this report.

Measurement of Spin–Lattice Relaxation Times and Concentrations in Systems with Chemical Exchange Using the One-Pulse Sequence: Breakdown of the Ernst Model for Partial Saturation in Nuclear Magnetic Resonance Spectroscopy

A fundamental problem in Fourier transform NMR spectroscopy is the calculation of observed resonance amplitudes for a repetitively pulsed sample, as first analyzed by Ernst and Anderson in 1966. Applications include determination of spin–lattice relaxation times (T1's) by progressive saturation and correction for partial saturation in order to determine the concentrations of the chemical constituents of a spectrum. Accordingly, the Ernst and Anderson formalism has been used in innumerable studies of chemical and, more recently, physiological systems. However, that formalism implicitly assumes that no chemical exchange occurs. Here, we present an analysis of N sites in an arbitrary chemical exchange network, explicitly focusing on the intermediate exchange rate regime in which the spin–lattice relaxation rates and the chemical exchange rates are comparable in magnitude. As a special case of particular importance, detailed results are provided for a system with three sites undergoing mutual exchange. Specific properties of the N-site network are then detailed. We find that (i) the Ernst and Anderson analysis describing the response of a system to repetitive pulsing is inapplicable to systems with chemical exchange and can result in large errors in T1 and concentration measurements; (ii) T1's for systems with arbitrary exchange networks may still be correctly determined from a one-pulse experiment using the Ernst formula, provided that a short interpulse delay time and a large flip angle are used; (iii) chemical concentrations for exchanging systems may be correctly determined from a one-pulse experiment either by using a short interpulse delay time with a large flip angle, as for measuring T1's, and correcting for partial saturation by use of the Ernst formula, or directly by using a long interpulse delay time to avoid saturation; (iv) there is a significant signal-to-noise penalty for performing one-pulse experiments under conditions which permit accurate measurements of T1's and chemical concentrations. The present results are analogous to but are much more general than those that we have previously derived for systems with two exchanging sites. These considerations have implications for the design and interpretation of one-pulse experiments for all systems exhibiting chemical exchange in the intermediate exchange regime, including virtually all physiologic samples.

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.

Identification of Ambergris from the New Bedford Whaling Museum by Nuclear Magnetic Resonance Spectroscopy

Abstract A new method for the separation and identification of ambrein in ambergris using adsorption chromatography and 1H and 13C Fourier transform nuclear magnetic resonance spectroscopy (FT-NMR) is presented. We demonstrated the effectiveness of this method by analyzing an approximately 85-year-old sample of suspected ambergris from the New Bedford Whaling Museum (New Bedford, MA). Results prove that ambrein remains a major constituent of ambergris even after 85 years of storage under ordinary conditions.

Antifungal Activity against Food-Borne Fungi of Aspidistra elatior Blume

An antifungal compound was isolated from Aspidistra elatior Blume. The methanol extract showed antifungal activity against Saccharomyces cerevisiae, Hansenula anomala, Mucor mucedo, and Candida albicans. The powdered methanol extract was dissolved in water and partitioned with hexane, ethyl acetate, n-butanol, and then water. Only the n-butanol fraction exhibited antifungal activity. The antifungal compound in the n-butanol fraction was finally isolated by silica gel chromatography and HPLC. Analysis by fast-atom bombardment mass spectroscopy and Fourier-transform nuclear magnetic resonance spectroscopy revealed that the structure of the antifungal compound is aspidistrin (diosgenin 3-O-β-lycotetraoside). The minimum inhibitory concentration of aspidistrin was 2.5 μg/mL against S. cerevisiae, 10 μg/mL against H. anomala, 10 μg/mL against M. mucedo, and 50 μg/mL against C. albicans. This is the first report of antifungal activity against food-borne fungi of aspidistrin. Keywords: Aspidistra elatior Blume; aspidistrin; antifungal activity

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]˙.

Glycine crystallization during freezing: the effects of salt form, pH, and ionic strength.

The purpose of the study is to characterize glycine crystallization during freezing of aqueous solutions as a function of the glycine salt form (i.e., neutral glycine, glycine hydrochloride, and sodium glycinate), pH, and ionic strength. Crystallization was studied by thermal analysis, microscopy, x-ray diffraction, and pulsed Fourier transform nmr spectroscopy. A solution of neutral glycine with no additives undergoes rapid secondary crystallization during freezing, forming the beta polymorph, with a eutectic melting temperature of -3.4 degrees C. Glycine hydrochloride solutions undergo secondary crystallization relatively slowly, and the eutectic melting temperature is -28 degrees C. Sodium glycinate crystallizes from frozen solution at an intermediate rate, forming a eutectic mixture with a melting temperature of -17.8 degrees C. Where secondary crystallization does not occur rapidly, a complex glass transition is observed in the -70 degrees to -85 degrees C temperature range in the DSC thermograms of all systems studied. Rates of secondary crystallization and the type of crystal formed are influenced by solution pH relative the the pKs of glycine, and also by the change in ionic strength caused by adjustment of pH. Increased ionic strength significantly slows the crystallization of neutral glycine and promotes formation of the gamma polymorph. Thermal treatment or extended holding times during the freezing process may be necessary in order to promote secondary crystallization and prevent collapse during freeze drying. The results underscore the importance of recognizing that seemingly minor changes in formulation conditions can have profound effects on the physical chemistry of freezing and freeze drying.

Theoretical and Practical Aspects of NMR Studies of Cells

Various theoretical and practical aspects of biological nuclear magnetic resonance (NMR) spectroscopy that are relevant to the study of immune cells are discussed as a prelude to the following papers in this issue of ImmunoMethods. We explain some of the salient features of modern Fourier-transform NMR spectroscopy, including spectral acquisition, Fourier transformation, signal averaging, apodization, and relaxation phenomena. The major features of the one-dimensional NMR spectrum are summarized prior to a brief description of two-dimensional NMR spectroscopy. We consider various practical questions, such as which NMR-receptive nuclide might be most useful for discerning the metabolic information being sought; in particular, the relative advantages and disadvantages of 1H, 13C, 19F, and 31P NMR spectroscopy are discussed in the context of elucidating metabolic information. The relative merits and pitfalls of using cell extracts, cell suspensions, and perfused immobilized cells for studies of immune cell activation are also considered.