Cross correlations in the longitudinal relaxation of strongly coupled spins

A generalized set of magnetization modes for quantifying cross-correlation contributions to longitudinal relaxation in strongly coupled spin systems is described in this paper. Such a set of modes (called longitudinal multiple-quantum modes) is used to unravel cross-correlation information in strongly coupled systems, where the strength of the J coupling tends to obscure such effects. The applicability of such methods is demonstrated for a small molecule which exhibits some strong coupling effects even at high magnetic field strengths. The contribution of "remote" cross correlations to the longitudinal relaxation of strongly coupled spins is detailed. Copyright 2000 Academic Press.     

Quantum entanglement in the NMR implementation of the Deutsch-Jozsa algorithm

A scheme to execute an n-bit Deutsch-Jozsa (DJ) algorithm using n qubits has been implemented for up to three qubits on an NMR quantum computer. For the one- and the two-bit Deutsch problem, the qubits do not get entangled, and the NMR implementation is achieved without using spin-spin interactions. It is for the three-bit case, that the manipulation of entangled states becomes essential. The interactions through scalar J-couplings in NMR spin systems have been exploited to implement entangling transformations required for the three bit DJ algorithm.     

Resolving overlaps in diffusion encoded spectra using band-selective pulses in a 3D BEST-DOSY experiment

A novel diffusion-edited 3D NMR experiment that incorporates a BEST-HMQC pulse sequence in its implementation is presented. Heteronuclear 3D DOSY NMR experiments are useful in elucidating the diffusion coefficients of individual constituents of a mixture, especially in cases where the proton NMR 2D DOSY spectra show considerable overlap. The present 3D BEST-DOSY pulse sequence provides a more sensitive and less time-consuming alternative to standard 3D HMQC-DOSY experiments. Cleanly separated subspectra of individual mixture components are obtained, leading to the determination of diffusion coefficients with better accuracy. The feasibility of the technique is demonstrated on a mixture of amino acids, on a mixture of small molecules with similar diffusion coefficients, and on a complex mixture with large dynamic range (commercial gasoline). The implications of using adiabatic decoupling schemes and band-selective shaped pulses for selective BEST-DOSY experiments on proteins are also discussed.     

Using the 19F NMR chemical shift anisotropy tensor to differentiate between the zigzag and chiral forms of fluorinated single-walled carbon nanotubes

The structural characterization of different kinds of zigzag and chiral single-walled carbon nanotubes (SWNTs) has been investigated theoretically using (19)F NMR spectroscopy. The chemical shift anisotropy (CSA) tensor is computed at different levels of theory for the (19)F nuclei in different forms of functionalized fluorinated carbon nanotubes (CNT). A set of fluorine CSA parameters comprising the span, skew, and isotropic chemical shift is computed for each form of the fluoronanotubes and multidimensional CSA parameter correlation maps are constructed. We show that these correlations are able to clearly distinguish between the chiral and zigzag forms of fluorinated carbon nanotubes (F-SWNTs). Implications for solid-state and liquid-state NMR experiments are discussed.     

A Comparison of Corona-Treated and Flame-Treated Polypropylene Films

The comparison of corona-treated and flame-treated polypropylene (PP) films provides insight into the mechanism of these surface-oxidation processes. Atomic force microscopy (AFM), contact-angle measurements, and X-ray photoelectron spectroscopy (XPS or ESCA) were used to characterize surface-treated biaxially oriented PP. While both processes oxidize the PP surface, corona treatment leads to the formation of water-soluble low-molecular-weight oxidized materials (LMWOM), while flame treatment does not. Computational modeling of the gas-phase chemistry in an air corona was performed using a zero-dimensional plasma-chemistry model. The modeling results indicate that the ratio of O to OH is much higher in a corona discharge than in a flame. Chain scission and the formation of LMWOM are associated with reactions involving O atoms. The higher ratios of O to OH in a corona are more conducive to LMWOM production. Surface-oxidized PP exhibits considerable thermodynamic contact-angle hysteresis that is primarily caused by microscopic chemical heterogeneity.     

Synthesis and spectral studies on palladium and platinum complexes with mono- and bidentate N-donor organic ligands and their interaction with calf thymus DNA in solution

Palladium(II) and platinum(II) complexes of the types PdLX₂, PdL₂X₂, PtL₂X₂ and the Pt(IV) complexes PtLX₂Y₂, PtL₂X₂Y′₂ (where L = mono- or bidentate organic ligand containing nitrogen donor atoms; X = Cl or Br; Y = Br and Y′ = OH) have been synthesized and characterized by elemental analysis, IR and X-ray photoelectron spectral data. The Pd 3d_5/2 binding energies indicate that the 8-aminoquinoline ligand is a better electron donor to the metal than other ligands studied. The Cl 2p_3/2 binding energies in the square planar pd(II) complexes are observed in the range 198.0–199.56 eV. The ν(PdCl) vibrations (ca 340 and 320 cm^?1) corresponding to two cis-Cl ligands were observed in the IR spectra. Binding through probably N-7 of the guanine residue and the phosphate oxygen in a chelate form is implied from UV difference spectral data.     

Structural and dynamical aspects of PEG/LiClO4 in solvent mixtures via NMR spectroscopy

Motivated by the potential usefulness of polyethylene glycol (PEG)/Li⁺ salt mixtures in several industrial applications, we investigated the structure and dynamics of PEG/LiClO₄ mixtures in D₂O and its mixtures with CD₃CN and DMSO-d₆, in a series of PEG-based polymers with a wide variation in their molecular weights. ¹H NMR chemical shifts, T₁/T₂ relaxation rates, pulsed-field gradient NMR diffusion experiments, and 2D HOESY NMR studies have been performed to understand the structural and dynamical aspects of these mixtures. Increasing the temperature of the medium results in a significant perturbation in the H-bonded structure of PEG in its PEG/LiClO₄/D₂O mixtures as observed from the increase in chemical shifts. On the other hand, the addition of molecular cosolvents has a negligible effect. The hydrodynamic structure of PEG shows a pronounced variation at low temperature with increasing molecular weight, which, however, disappears at higher temperatures. Increasing the temperature leads to a decrease in the hydrodynamic structure of PEG, which can be explained on the basis of solvation–desolvation phenomena. The 2D HOESY NMR spectra reveal a new finding of Li⁺-water binding in the PEG/LiClO₄/D₂O mixtures with the addition of molecular solvents, suggesting that the Li⁺ cation diffuses freely in the D₂O mixtures of polymers as compared with the polymer mixtures with DMSO or CD₃CN.     

Experimental detection of qubit-ququart pseudo-bound entanglement using three nuclear spins

In this work, we experimentally created and characterized a class of qubit-ququart PPT (positive under partial transpose) entangled states using three nuclear spins on an nuclear magnetic resonance (NMR) quantum information processor. Entanglement detection and characterization for systems with a Hilbert space dimension $\ge 2?3$ is nontrivial since there are states in such systems which are both PPT as well as entangled. The experimental detection scheme that we devised for the detection of qubit-ququart PPT entanglement was based on the measurement of three Pauli operators with high precision, and is a key ingredient of the protocol in detecting entanglement. The family of PPT-entangled states considered in the current study are incoherent mixtures of five pure states. All the five states were prepared with high fidelities and the resulting PPT entangled states were prepared with mean fidelity ≥ 0.95. The entanglement thus detected was validated by carrying out full quantum state tomography (QST).     

Electrical properties of cerium fluoride thin films

Thin films of ionic conductors have low internal resistance. Hence, it could be used as an electrolyte material in sensors to operate at ambient temperatures. Cerium fluoride, a unipolar fluoride ion conductor, has got a different application in electrochemical sensor. In the present work, cerium fluoride thin films have been prepared by physical vapor deposition method and their electrical properties are studied. X-ray diffraction studies reveal the polycrystalline nature of the prepared thin films and the structure of the material. Scanning electron microscopy (SEM) images show grain-like structures. Conductivity analysis of the thin films has been studied by ac impedance analysis and the maximum conductivity value is found to be 1.04 × 10⁻⁶ S cm⁻¹. The impedance spectra emphasize intergranular conduction in the prepared thin films.     

Structural,electrical conductivity,and transport analysis of PAN–NH<Subscript>4</Subscript>Cl polymer electrolyte system

Poly (acrylonitrile) (PAN) and ammonium chloride (NH₄Cl)-based proton conducting polymer electrolytes with different compositions have been prepared by solution casting technique. The amorphous nature of the polymer electrolytes has been confirmed by XRD analysis. The FTIR analysis confirms the complex formation of the host polymer (PAN) with the salt (NH₄Cl). DSC measurements show a decrease in T_g with the increase in salt concentration. The conductivity analysis shows that the 25 mol% ammonium chloride doped polymer electrolyte has a maximum ionic conductivity, and it has been found to be 6.4 × 10^?3 Scm^?1, at room temperature. The temperature dependence of conductivity of the polymer electrolyte complexes appears to obey the Arrhenius nature. The activation energy (E_a = 0.23 eV) has been found to be low for 25 mol% salt doped polymer electrolyte. The dielectric behavior has been analyzed using dielectric permittivity (ε*), and the relaxation frequency (τ) has been calculated from the loss tangent spectra (tan δ). Using this maximum ionic conducting polymer electrolyte, the primary proton conducting battery with configuration Zn + ZnSO₄·7H₂O/75 PAN:25 NH₄Cl/PbO₂ + V₂O₅ has been fabricated and their discharge characteristics have been studied.