Joan Mason

Bio: Joan Mason is an academic researcher from Open University. The author has contributed to research in topics: Nuclear magnetic resonance spectroscopy & Chemical shift. The author has an hindex of 12, co-authored 27 publications receiving 549 citations.

15N nuclear magnetic shielding scale from gas phase studies

Abstract: We have measured the 15N nuclear magnetic resonance frequencies in 15N‐labeled molecules (NNO, NNO, NH3, N2, and HCN) in gas phase samples and also in CH3NO2 as neat liquid. By using the previously determined temperature dependence of samples of the these gases at various densities, we are able to reduce the measured frequencies to the zero‐density limit at 300 K, and obtain shielding differences between rovibrationally averaged isolated molecules at this shielding measurements from molecular beam studies to provide an 15N absolute shielding scale based on 15NH3.

The Chemical Shift

Abstract: The chemical shift (as defined by IUPAC) in terms of measured frequencies $$ \delta = \left( { u - u _{{\text{ref}}} } \right){\text{/}} u _{{\text{ref}}} $$ (1) is related to a fundamental molecular property, the nuclear magnetic shielding, σ. For a molecule held in a fixed orientation in a uniform magnetic field B, the field at a selected point in the vicinity of the molecule is different from B because of the small field arising from the circulations of the electrons induced by the magnetic field*: $$ B_{{\text{local}}} {\text{ = }}\left( {1 - \sigma } \right)B $$ (2)

A comparison of models for calculating nuclear magnetic resonance shielding tensors

Abstract: The direct (recomputation of two‐electron integrals) implementation of the gauge‐including atomic orbital (GIAO) and the CSGT (continuous set of gauge transformations) methods for calculating nuclear magnetic shielding tensors at both the Hartree‐Fock and density functional levels of theory are presented. Isotropic 13C, 15N, and 17O magnetic shielding constants for several molecules, including taxol (C47H51NO14 using 1032 basis functions) are reported. Shielding tensor components determined using the GIAO and CSGT methods are found to converge to the same value at sufficiently large basis sets; however, GIAO shielding tensor components for atoms other than carbon are found to converge faster with respect to basis set size than those determined using the CSGT method for both Hartree‐Fock and DFT. For molecules where electron correlation effects are significant, shielding constants determined using (gradient‐corrected) pure DFT or hybrid methods (including a mixture of Hartree‐Fock exchange and DFT exchange...

Destruction and Detection of Chemical Warfare Agents

Abstract: 1. Scope of Article and Previous Related Reviews 5346 2. Introduction 5346 2.1. Destruction 5347 2.2. Sensing 5347 2.3. Historical Context 5348 2.3.1. Brief History and Molecular Structure 5348 2.4. Related Compounds and Nomenclature 5348 2.4.1. Phosphorus(V) Parent Compounds and Fundamental Chemistry 5348 2.4.2. Pesticides 5349 2.4.3. Simulants 5349 2.4.4. Decomposition Products 5350 2.5. Toxicology 5351 2.5.1. Acetylcholine Esterase (AChE) Inhibition 5351 2.5.2. Endocannabinoid System Activation 5352 2.6. Critical Needs To Decontaminate and Detect 5353 2.7. Treaties and Conventions 5354 3. Stockpile Destruction 5355 3.1. Agent Storage 5355 3.2. Protection Protocols and Logistics 5355 3.3. Background 5355 3.4. Methods Currently Employed 5355 3.4.1. Incineration 5355 3.4.2. Neutralization by Base Hydrolysis 5356 4. Decomposition Reactions 5357 4.1. Hydrolysis 5357 4.2. Autocatalytic Hydrolysis or Hydrolysis Byproducts 5358 4.3. Use of Peroxide 5359 4.4. Oxidation with Bleach and Related Reagents 5360 4.5. Alkoxide as Nucleophile 5360 4.5.1. Basic Media 5360 4.5.2. Metal-Catalyzed Reactions 5361 4.5.3. Metal-Assisted Reactions 5363 4.5.4. Biotechnological Degradation 5363 4.5.5. Cyclodextrin-Assisted Reactions 5370 4.6. Halogen as the Nucleophile 5370 4.6.1. Use of BrOx 5370 4.6.2. Use of Other Halogens 5371 4.6.3. Use of Group 13 Chelates 5371 4.7. Surface Chemistry 5371 4.7.1. Bare Metals and Solid Nanoparticles 5371 4.7.2. Metal Oxides 5371 4.7.3. Representative Elements 5372 4.7.4. d-Block (Groups 4 10) 5373 4.7.5. Solid Metal Oxides of Group 3 and the Lanthanides 5375 4.7.6. Porous Silicon and Related Systems 5375 4.7.7. Zeolites 5375 4.7.8. Comparative IR Data 5375 4.8. Other Types of Systems 5375 5. Decontamination 5376 5.1. Overview: Ability to React with All Types of Agents, Ease of Application, and Compatibility with Treated Objects 5376 6. Agent Fate and Disposal 5378 6.1. Indoor 5378 6.2. Concrete and Construction Surfaces 5378 6.3. Landfills 5379 7. Sensing and Detection 5379 7.1. Possible Metal Ion Binding Modes in Solution 5379 7.1.1. Early Reports of Phosph(on)ate [R3PdO 3 3 3M nþ] Interactions (R= Alkyl, Alkoxyl) 5380 7.1.2. Coordination Chemistry of Downstream Non-P-Containing Products of Decomposition 5380 7.2. Colorimetric Detection 5381 7.3. Chemiluminescence: Fluorescence and Phosphorescence 5382 7.3.1. Lanthanide-Based Catalysts 5382 7.3.2. Organometallic-Based Sensors 5382 7.3.3. Organic Design 5382 7.3.4. Biologically-Based Luminescence Detection 5382 7.3.5. Polymer and Bead Supports 5382 7.4. Porous Silicon 5383 7.5. Carbon Nanotubes 5383

Effects of electron correlation in the calculation of nuclear magnetic resonance chemical shifts

Abstract: Using second‐order many‐body perturbation theory [MBPT(2)] and the gauge‐including atomic orbital (GIAO) ansatz, electron correlation effects are investigated in the calculation of NMR chemical shieldings and shifts. A thorough discussion of the theory, aspects of the implementation as well as the computational requirements of the GIAO‐MBPT(2) method are presented. The performance of the GIAO‐MBPT(2) approach is tested in benchmark calculations of 13C, 15N, and 17O chemical shifts. Comparison with available experimental gas phase NMR data shows that GIAO‐MBPT(2) improves in all cases considered here over the GIAO results obtained at the Hartree–Fock self‐consistent‐field (HF‐SCF) level. Correlation effects turn out to be particularly important for molecules with multiple bonds, e.g., carbonyl or cyano compounds, and it seems that GIAO‐MBPT(2) slightly overestimates these effects for difficult cases having relatively large correlation contributions of 30 to 110 ppm. For CO, N2, N2O, additional calculations with large basis sets are presented to check the accuracy of the GIAO‐MBPT(2) method and the geometry dependence of the calculated chemical shieldings is analyzed.