The application of the ERETIC method to 2D-NMR

As a means of obtaining precise quantitative data in 2D NMR spectroscopy, the use of an electronic reference signal (ERETIC) has been examined. The results presented demonstrate that the ERETIC method can be used in different situations encountered in 2D-NMR spectroscopy: homonuclear and heteronuclear spectra, phased or magnitude mode, symmetrization. The main restriction to introducing ERETIC in 2D spectra could be the need for several spectrometer channels. However, most modern NMR spectrometers are equipped with at least three channels, that allows the implementation of the ERETIC method as reference for 2D-NMR spectroscopy without needing any hardware modification.     

How to do the time sliced path integral of the H atom

In response to criticism concerning the formal nature of the Duru-Kleinert transformation of the path integral of the H atom, we perform this transformation explicitly in the time sliced form and arrive, of course, at the desired product of gaussian factors which yield the harmonic oscillator. We also point out where previous attempts to do the same thing went wrong.     

Refocussing of chemical and paramagnetic shift anisotropies in 2H NMR using the quadrupolar-echo experiment

A simple two-pulse spin-echo experiment is shown to refocus inhomogeneous broadening arising from both chemical and/or paramagnetic shift anisotropy and a first-order I=1 quadrupolar interaction. The method is shown to yield ²H NMR spectra of a paramagnetic solid (CuCl₂ · 2D₂O) and of a non-paramagnetic solid (D₂C₂O₄ · 2D₂O) that are significantly less distorted than those provided by the conventional quadrupolar-echo method. The technique will thus prove useful in studies of motion and dynamics where detailed analysis of the ²H lineshape is performed.     

3D H2BC: A novel experiment for small-molecule and biomolecular NMR at natural isotopic abundance

3D H2BC is introduced for heteronuclear assignment on natural abundance samples even for biomolecules up to at least 10 kDa in low millimolar concentrations as an overnight experiment using the latest generation of cryogenically cooled probes. The short pulse sequence duration of H2BC is maintained in the 3D version due to multiple use of the constant-time delay. Applications ranging from a small lipid to a non-recombinant protein demonstrate the merits of 3D H2BC and the ease of obtaining assignments in chains of protonated carbons.     

2H NMR in nearly stoichiometric yttrium dideuteride

²H NMR spectra and spin-lattice relaxation rates, R₁ are measured as functions of temperature (4.2-310 K) for YD_1.99 and YD_1.99+0.04. In YD_1.99 the measured temperature dependence of R₁ is explained by the interaction of deuteron spins with conduction electrons and the value s^-1 K^-1 is obtained for the inverse Korringa product . Most of the spectral features in the “rigid” lattice regime are described by the dipolar interaction. No evidence of the deuterium self-diffusion was observed in the measured temperature range. The low-temperature spectra in YD_1.99+0.04 consisted of two components: a central line and a doublet characteristic for the quadrupole interaction. The central line corresponds to zero electric field gradients (EFG) at the sites of the deuterons which have a surrounding with cubic symmetry like in YD_1.99. The doublet indicates a non-zero EFG which can be explained in terms of the presence of short-range ordered domains of the hypothetical YD_2.25 stoichiometry. Other possible interpretations of the spectra are also discussed. In the vicinity of 250 K both spectra and R₁ reflect the onset of the rapid motion of deuterium atoms. The linear dependence of R₁ at low temperatures yields s^-1 K^-1. Received 8 September 1998     

The carbon isotopic effect in photolysis of an aqueous solution of cyclopentanol measured by the NMR method

Using the¹³C NMR method, the manifestation of the carbon isotopic effect on the products of the photolysis of an aqueous solution of cyclopentanone is investigated. A relative enrichment by the isotope¹³C of the carbonyl (13%) and α-carbon (6%) atoms of initial cyclopentanone and of the carbonyl atom of pent-4-en-1-ale (11%), as well as the depletion of the carbonyl (15%) and methyl (7%) carbon atoms of valeric acid are revealed. The isotopic effect observed is shown to have a magnetic nature. Institute of Physical-Organic Chemistry, Academy of Sciences of Belarus, 13, Surganov St., Minsk, 220072, Belarus. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 2, pp. 260–262, March–April, 1997.     

Constant time steady gradient NMR diffusometry using the secondary stimulated echo

A pulse sequence producing a second stimulated echo is suggested for the compensation of relaxation and residual dipolar interaction effects in steady gradient spin echo diffusometry. Steady field gradients of considerable strength exist in the fringe field of NMR magnets, for instance. While the absolute echo time of the second stimulated echo is kept constant throughout the experiment, the interval between the first two radiofrequency pulses is augmented leading to a modulation of the amplitude of that second stimulated echo by self-diffusion only. The unique feature of this technique is that it is of a single-scan/single-echo-signal nature. That is, no reference signals neither of the same pulse sequence nor of separate experiments are needed. The new method was tested with poly(ethylene oxide) melts and proved to provide reliable data for (time dependent) self-diffusion coefficients down to the physical limit (D approximately 10(-15)m(2)/s) when flip-flop spin diffusion starts to become effective.     

Determining the parity of a permutation using an experimental NMR qutrit

We present the NMR implementation of a recently proposed quantum algorithm to find the parity of a permutation. In the usual qubit model of quantum computation, it is widely believed that computational speedup requires the presence of entanglement and thus cannot be achieved by a single qubit. On the other hand, a qutrit is qualitatively more quantum than a qubit because of the existence of quantum contextuality and a single qutrit can be used for computing. We use the deuterium nucleus oriented in a liquid crystal as the experimental qutrit. This is the first experimental exploitation of a single qutrit to carry out a computational task.     

Reduced data acquisition time in multi-dimensional NMR spectroscopy using multiple-coil probes

A new hardware-based approach is presented to reduce data acquisition times in multi-dimensional NMR spectroscopy using a multiple-coil probe. Using a four-coil setup, two-dimensional COSY and TOCSY spectra were acquired in one-quarter the time of conventional spectra by simultaneous acquisition of different effective t1 evolution times for each coil. Data processing consists of simple phase-shifting and intensity normalization of the individual data sets, and results in spectra almost identical to those acquired in a conventional manner. This method can potentially be integrated with other new data acquisition and processing schemes for further increases in data acquisition speed.     

How to introduce time operator

Time operator can be introduced by three different approaches: by pertaining it to dynamical variables; by quantizing the classical expression of time; and taken as the restriction of energy shift generator to the Hilbert space of a physical system.     

2H NMR and polyelectrolyte-induced domains in lipid bilayers

2H NMR studies of polyelectrolyte-induced domain formation in lipid bilayer membranes are reviewed. The 2H NMR spectrum of choline-deuterated phosphatidylcholine (PC) reports on any and all sources of lipid bilayer surface charge, since these produce a conformation change in the choline head group of PC, manifest as a change in the 2H NMR quadrupolar splitting. In addition, homogeneous and inhomogeneous surface charge distributions are differentiated. Adding polyelectrolytes to lipid bilayers consisting of mixtures of oppositely charged and zwitterionic lipids produces 2H NMR spectra which are superpositions of two Pake sub-spectra: one corresponding to a polyelectrolyte-bound lipid population and the other to a polyelectrolyte-free lipid population. Quantitative analysis of the quadrupolar splittings and spectral intensities of the two sub-spectra indicate that the polyelectrolyte-bound populations is enriched with oppositely charged lipid, while the polyelectrolyte-free lipid population is correspondingly depleted. The same domain-segregation effect is produced whether cationic polyelectrolytes are added to anionic lipid bilayers or anionic polyelectrolytes are added to cationic lipid bilayers. The 2H NMR spectra permit a complete characterization of domain composition and size. The anion:cation ratio within the domains is always stoichiometric, as expected for a process driven by Coulombic interactions. The zwitterionic lipid content of the domains is always statistical, reflecting the systems tendency to minimize the entropic cost of demixing charged lipids into domains. Domain formation is observed even with rather short polyelectrolytes, suggesting that individual polyelectrolyte chains aggregate at the surface to form "superdomains". Overall, the polyelectrolyte bound at the lipid bilayer surface appears to lie flat along the surface and to be essentially immobilized through its multiple electrostatic contacts.     

How the money machine may help to reduce railway noise in Europe

The need to reduce railway noise, particularly from freight transport in international traffic, is recognized by all stakeholders in the field. Solutions are currently available to provide a significant reduction, and research is underway to investigate further options. Several recent studies clearly show that noise abatement at the source (i.e., vehicles and track) are to be preferred over solutions that affect noise propagation (e.g., barriers) or noise reception (façade insulation) when it comes to overall life cycle cost. In spite of these three important conclusions, the necessary noise reduction at source is not yet taking place, with some small-scale exceptions. The parties involved agree that financial and economical constraints prevent the process of noise reduction from starting. The present paper presents the results of the second consensus building workshop in the STAIRRS project. It explores the possible financial and economic instruments that may help to launch the necessary developments.     

Improving the 1H indirect dimension resolution of 2D CRAMPS NMR spectra: a simulation and experimental investigation

An experimental and simulation investigation regarding the effect of various CRAMPS parameters (delays interleaved with the decoupling shape, z-rotation symmetry and offset frequency) on the DUMBO decoupling performance is presented using two model compounds, glycine and tyrosine·HCl. Although the conclusions of this work may be extended to the other homonuclear-decoupling schemes, this work focuses essentially on the effect of adding interleaved delays to DUMBO decoupling during the indirect dimension using different 2D pulse-scheme architectures. While the simulations revealed an increasing loss of the spectral resolution with longer delays (from 0 to 6 μs), the experimental 2D (1)H DUMBO NMR correlation spectra revealed that the inclusion of delays, during the indirect dimension, improves the (1)H resolution whether the z-rotation symmetry was used or not. The best experimental spectra are obtained when z-rotation symmetry and windows are combined.     

Molecular dynamics of n-dodecylammonium chloride in aqueous solutions investigated by 2H NMR and 1H NMR relaxometry

Molecular dynamics in n-dodecylammonium chloride/water solutions for concentrations of 34 and 45 wt% was studied by 2H NMR and by 1H NMR dispersion of spin-lattice relaxation in the 2 kHz-90 MHz frequency range. The system exhibits a number of lyotropic liquid crystalline phases, which differ in symmetry and involve motions characterized by a wide frequency scale. The analysis of 2H NMR lineshapes of selectively deuterated DDACl molecules gave us an evidence for local trans-gauche conformational changes in the chains, whereas the dispersion of spin-lattice relaxation times T1 explored by fast field cycling method revealed fast local motions, translational diffusion and collective molecular dynamics of the chains. In particular, we have found that the order director fluctuation mechanism in smectic and nematic phases dominates spin-lattice relaxation below 1 MHz and that local motions and translational diffusion are responsible for the spin-lattice relaxation in the higher Larmor frequency range.     

Molecular dynamics of thermotropic liquid-crystalline polymer: Polydecamethyleneterephthaloyl-bis-4-oxybenzoate using2H NMR spectroscopy

²H NMR spectra of a selectively deuterated liquid crystalline, polydecamethylene-terephthaloyl-bis-4-oxybenzoate, have been investigated in the temperature range from 25 to 100°C. It was found that polymer regions exist with greatly differing molecular mobility. It was shown that the molecular mobility in the polymer depends on its thermal history. The molecular mobility in an aromatic fragment is caused by the vibrational motions of 1,4-phenylene rings with different amplitudes. The fractions of para-phenylene groups undergoing torsional vibrations with high amplitudes increase with temperature and flips of the central phenylene rings of mesogenic triads are observed. The mobility in aliphatic fragments is due to transgauche isomerization and translation motion with the participation of several bonds.