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This paper presents an NMR crystallography study of three polymorphs of furosemide. Experimental magic‐angle spinning (MAS) solid‐state NMR spectra are reported for form I of furosemide, and these are assigned using density‐functional theory (DFT)‐based gauge‐including projector augmented wave (GIPAW) calculations. Focusing on the three known polymorphs, we examine the changes to the NMR parameters due to crystal packing effects. We use a recently developed formalism to visualise which regions are responsible for the chemical shielding of particular sites and hence understand the variation in NMR parameters between the three polymorphs.

Single-walled carbon nanotubes (SWCNTs) have been the focus of intense research, and the body of literature continues to grow exponentially, despite more than two decades having passed since the first reports. As well as extensive studies of the fundamental properties, this has seen SWCNTs used in a plethora of applications as far ranging as microelectronics, energy storage, solar cells, and sensors, to cancer treatment, drug delivery, and neuronal interfaces. On the other hand, the properties and applications of double-walled carbon nanotubes (DWCNTs) have remained relatively under-explored. This is despite DWCNTs not only sharing many of the same unique characteristics of their single-walled counterparts, but also possessing an additional suite of potentially advantageous properties arising due to the presence of the second wall and the often complex inter-wall interactions that arise. For example, it is envisaged that the outer wall can be selectively functionalized whilst still leaving the inner wall in its pristine state and available for signal transduction. A similar situation arises in DWCNT field effect transistors (FETs), where the outer wall can provide a convenient degree of chemical shielding of the inner wall from the external environment, allowing the excellent transconductance properties of the pristine nanotubes to be more fully exploited. Additionally, DWCNTs should also offer unique opportunities to further the fundamental understanding of the inter-wall interactions within and between carbon nanotubes. However, the realization of these goals has so far been limited by the same challenge experienced by the SWCNT field until recent years, namely, the inherent heterogeneity of raw, as-produced DWCNT material. As such, there is now an emerging field of research regarding DWCNT processing that focuses on the preparation of material of defined length, diameter and electronic type, and which is rapidly building upon the experience gained by the broader SWCNT community. This review describes the background of the field, summarizing some relevant theory and the available synthesis and purification routes; then provides a thorough synopsis of the current state-of-the-art in DWCNT sorting methodologies, outlines contemporary challenges in the field, and discusses the outlook for various potential applications of the resulting material.

Three series of substituted 1,3,4-oxadiazoles were studied by 17O NMR spectroscopy. Chemical shifts values were correlated with empirical Hammett parameters as well as calculated bond lengths and chemical shielding values. Copyright © 2011 John Wiley & Sons, Ltd.

13C NMR chemical shifts have been calculated for structures of some substituted 3-anilino-2-nitrobenzo-[b]thiophenes (2o) and 2-anilino-3-nitrobenzo[b]thiophenes (3o) derivatives containing OH, NH2, OMe, Me, Et, H, F, Cl and Br. The molecular structures were fully optimized using B3LYP/6-31G(d,p). The calculation of the 13C shielding tensors employed the GAUSSIAN 03 implementation of the gauge-including atomic orbital (GIAO) and continuous set of gauge transformations (CSGT) by using 6-311++G(d,p) basis set at density functional levels of theories (DFT). The isotropic and the anisotropy parameters of chemical shielding for all compounds are calculated. The predicted 13C chemical shifts are derived from equation δ=δ0+δ where δ is the chemical shift, δ is the absolute shielding, and δ0 is the absolute shielding of the standard TMS. Excellent linear relationships have been observed between experimental and calculated 13C NMR chemical shifts for all derivatives

The direct implementation of GIAO and CSGT methods for calculation of 13 C isotropic shielding constants of fully protonated forms of six tripodal tetraamine ligands tren, pee, ppe, tpt, epb and ppb at the Hartree-Fock level of theory are presented. The shielding constants were determined using hybrid methods (including a mixture of Hartree-Fock exchange and DFT exchange-correlation) and are close to the experimental data. A splayed-like conformation was considered for fully protonated forms of all ligands, and it was confirmed that this is the most stable conformation for the latter form of such ligands. A good linear correlation between the calculated chemical shielding at gas-phase and experimental shift values in D 2 O solution was obtained.

Single-walled carbon nanotubes (SWCNTs) have been the focus of intense research, and the body of literature continues to grow exponentially, despite more than two decades having passed since the first reports. As well as extensive studies of the fundamental properties, this has seen SWCNTs used in a plethora of applications as far ranging as microelectronics, energy storage, solar cells, and sensors, to cancer treatment, drug delivery, and neuronal interfaces. On the other hand, the properties and applications of double-walled carbon nanotubes (DWCNTs) have remained relatively under-explored. This is despite DWCNTs not only sharing many of the same unique characteristics of their single-walled counterparts, but also possessing an additional suite of potentially advantageous properties arising due to the presence of the second wall and the often complex inter-wall interactions that arise. For example, it is envisaged that the outer wall can be selectively functionalized whilst still leaving the inner wall in its pristine state and available for signal transduction. A similar situation arises in DWCNT field effect transistors (FETs), where the outer wall can provide a convenient degree of chemical shielding of the inner wall from the external environment, allowing the excellent transconductance properties of the pristine nanotubes to be more fully exploited. Additionally, DWCNTs should also offer unique opportunities to further the fundamental understanding of the inter-wall interactions within and between carbon nanotubes. However, the realization of these goals has so far been limited by the same challenge experienced by the SWCNT field until recent years, namely, the inherent heterogeneity of raw, as-produced DWCNT material. As such, there is now an emerging field of research regarding DWCNT processing that focuses on the preparation of material of defined length, diameter and electronic type, and which is rapidly building upon the experience gained by the broader SWCNT community. This review describes the background of the field, summarizing some relevant theory and the available synthesis and purification routes; then provides a thorough synopsis of the current state-of-the-art in DWCNT sorting methodologies, outlines contemporary challenges in the field, and discusses the outlook for various potential applications of the resulting material.

NMR chemical shielding anisotropy tensors have been computed, employing several basis sets and the GIAO-RHF and GIAO-MP2 formalisms of electronic structure theory, for all the atoms of the five and nine typical backbone conformers of For-Gly-NH2 and For-L-Ala-NH2, respectively. Multidimensional chemical shift plots, as a function of the respective backbone fold, have been generated for both peptide models. On the 2D 1 H NH - 15 N NH and 15 N NH - 13 C plots the most notable feature is that at all levels of theory studied the backbone conformers cluster in different regions. Computed chemical shifts, as well as their averages, have been compared to relevant experimental values taken from the BioMagnetic Resonance Bank (BMRB). At the highest levels of theory, for all nuclei but the amide protons, deviations between statistically averaged theoretical and experimental shifts are as low as 1-3%. These results indicate that chemical shift information from selected multiple-pulse NMR experiments (e.g., 2D-HSQC and 3D-HNCA) could directly be employed to extract folding information for polypeptides and proteins. c 2000 John Wiley & Sons, Inc. J Comput Chem 21: 882-900, 2000

The effects of including correlation in the calculation of phosphorus nuclear magnetic resonance (NMR) chemical shielding has been investigated for a variety of molecules in the Hartree-Fock, second-order Moller-Plesset (MP2), and estimated infinite-order Moller-Plesset theory ab initio approaches in the gauge including atomic orbital (GIAO) scheme. The inclusion of correlation in the shielding calculations often leads to significant changes from the Hartree-Fock theory and provides results that are in improved agreement with experiment. © 1996 John Wiley & Sons, Inc.

Some examples demonstrating a correlation between the overall 13 C-chemical shielding (Σ 13 C) and the molecular mechanics steric energy observed for five-membered heterocycles are presented.

A direct method for the ab initio calculation of the magnetic susceptibility and chemical shielding tensors based on the individual gauge for localized molecular orbitals (IGLO) formalism is introduced. “Direct” in this context means we avoid storing the two-electron repulsion integrals in favor of recalculating them whenever necessary. In conjunction with the Direct-SCF package TURBOMOLE Direct IGLO (DIGLO) permits calculation of magnetic second-order properties for large molecules by minimizing peripheral disc storage requirements. The size of the molecules to be treated is limited only by the amount of CPU time available. The performance of DIGLO is demonstrated for some selected examples.

Nuclear magnetic resonance spectroscopy has evolved in complexity to the extent that it is often useful to carry out computer simulations of experiments as a way to refine experimental conditions, to maximize usable information, or to interpret results reliably. The starting point for such simulations is an appropriate quantum mechanical formulation. This article presents many of the physical ideas that are important in high-resolution NMR spectroscopy and then develops expressions for the contribution of each of these to the Hamiltonian for the system under consideration. The Hamiltonians for the Zeeman interaction, scalar coupling, and the chemical shielding effect are discussed with the aim of explaining the quantum mechanics of NMR in a manner understandable to a nontheoretician. Consequently, much of the discussion is explicit and includes points skimmed over in other presentations in the literature.

Phosphorus-31 Magic-Angle Spinning (MAS) NMR is shown to be an extremely useful and accurate method for the determination of the enantiomeric purity for chiral organophosphorus compounds. 31P and 13C chemical shielding tensors in racemic and enantiomeric crystals of organophosphorus compounds vary because of different crystal symmetries. This implies that solid-state 31P (13C) MAS spectra of an enantiomerically impure sample reveal separate signals from the racemic and enantiomer crystallites. Simple integration (or deconvolution) of the MAS NMR signals can thus be used to determine the enantiomeric purity of the sample. For organophosphorus compounds the application of this technique to 31P MAS NMR is of particular interest due to the high sensitivity and large shielding anisotropy of the 31P nucleus.

The original article to which this Addendum refers was published in Journal of Phisycal Organic Chemistry 2004; 17: 680–685.

A new method is presented to analyze the IGLO (individual gauge for localized orbitals) bond contributions in 13C chemical shielding. The IGLO bond contributions calculated in the molecular frame are rotated to a local bond frame, in which one component is selected along the bond. This procedure removes the explicit angular dependence of the IGLO bond contributions and allows a comparison of the bond contributions in different molecules. The results provide a new method to study the electronic basis of shielding interactions. The problems associated with the multiple gauge origins used in the IGLO method are discussed in their relationship to the bond contribution analysis.

Explicit expressions needed for the extraction of the chemical shielding tensor from the angle-dependent chemical shifts are derived for orthogonal and off-angle probe experiments. Assignment of symmetry-related chemical shielding tensors via 1) a semi-empirical method and 2) angle-dependent line-widths due to heteronuclear dipolar couplings are discussed.