Chemical Bonding and the Role of Node-Induced Electron Confinement.

The chemical bond is the cornerstone of chemistry, providing a conceptual framework to understand and predict the behavior of molecules in complex systems. However, the fundamental origin of chemical bonding remains controversial and has been responsible for fierce debate over the past century. Here, we present a unified theory of bonding, using a separation of electron delocalization effects from orbital relaxation to identify three mechanisms [node-induced confinement (typically associated with Pauli repulsion, though more general), orbital contraction, and polarization] that each modulate kinetic energy during bond formation. Through analysis of a series of archetypal bonds, we show that an exquisite balance of energy-lowering delocalizing and localizing effects are dictated simply by atomic electron configurations, nodal structure, and electronegativities. The utility of this unified bonding theory is demonstrated by its application to explain observed trends in bond strengths throughout the periodic table, including main group and transition metal elements.

From Intermolecular Interaction Energies and Observable Shifts to Component Contributions and Back Again: A Tale of Variational Energy Decomposition Analysis.

Quantum chemistry in the form of density functional theory (DFT) calculations is a powerful numerical experiment for predicting intermolecular interaction energies. However, no chemical insight is gained in this way beyond predictions of observables. Energy decomposition analysis (EDA) can quantitatively bridge this gap by providing values for the chemical drivers of the interactions, such as permanent electrostatics, Pauli repulsion, dispersion, and charge transfer. These energetic contributions are identified by performing DFT calculations with constraints that disable components of the interaction. This review describes the second-generation version of the absolutely localized molecular orbital EDA (ALMO-EDA-II). The effects of different physical contributions on changes in observables such as structure and vibrational frequencies upon complex formation are characterized via the adiabatic EDA. Example applications include red- versus blue-shifting hydrogen bonds; the bonding and frequency shifts of CO, N2, and BF bound to a [Ru(II)(NH3)5]2 + moiety; and the nature of the strongly bound complexes between pyridine and the benzene and naphthalene radical cations. Additionally, the use of ALMO-EDA-II to benchmark and guide the development of advanced force fields for molecular simulation is illustrated with the recent, very promising, MB-UCB potential.

Siloxyaluminate and Siloxygallate Complexes as Models for Framework and Partially Hydrolyzed Framework Sites in Zeolites and Zeotypes.

Anionic molecular models for nonhydrolyzed and partially hydrolyzed aluminum and gallium framework sites on silica, M[OSi(OtBu)3 ]4 - and HOM[OSi(OtBu)3 ]3 - (where M=Al or Ga), were synthesized from anionic chlorides Li{M[OSi(OtBu)3 ]3 Cl} in salt metathesis reactions. Sequestration of lithium cations with [12]crown-4 afforded charge-separated ion pairs composed of monomeric anions M[OSi(OtBu)3 ]4 - with outer-sphere [([12]crown-4)2 Li]+ cations, and hydroxides {HOM[OSi(OtBu)3 ]3 } with pendant [([12]crown-4)Li]+ cations. These molecular models were characterized by single-crystal X-ray diffraction, vibrational spectroscopy, mass spectrometry and NMR spectroscopy. Upon treatment of monomeric [([12]crown-4)Li]{HOM[OSi(OtBu)3 ]3 } complexes with benzyl alcohol, benzyloxide complexes were formed, modeling a possible pathway for the formation of active sites for Meerwin-Ponndorf-Verley (MPV) transfer hydrogenations with Al/Ga-doped silica catalysts.

Pattern-free generation and quantum mechanical scoring of ring-chain tautomers.

In contrast to the computational generation of conventional tautomers, the analogous operation that would produce ring-chain tautomers is rarely available in cheminformatics codes. This is partly due to the perceived unimportance of ring-chain tautomerism and partly because specialized algorithms are required to realize the non-local proton transfers that occur during ring-chain rearrangement. Nevertheless, for some types of organic compounds, including sugars, warfarin analogs, fluorescein dyes and some drug-like compounds, ring-chain tautomerism cannot be ignored. In this work, a novel ring-chain tautomer generation algorithm is presented. It differs from previously proposed solutions in that it does not rely on hard-coded patterns of proton migrations and bond rearrangements, and should therefore be more general and maintainable. We deploy this algorithm as part of a workflow which provides an automated solution for tautomer generation and scoring. The workflow identifies protonatable and deprotonatable sites in the molecule using a previously described approach based on rapid micro-pKa prediction. These data are used to distribute the active protons among the protonatable sites exhaustively, at which point alternate resonance structures are considered to obtain pairs of atoms with opposite formal charge. These pairs are connected with a single bond and a 3D undistorted geometry is generated. The scoring of the generated tautomers is performed with a subsequent density functional theory calculation employing an implicit solvent model. We demonstrate the performance of our workflow on several types of organic molecules known to exist in ring-chain tautomeric equilibria in solution. In particular, we show that some ring-chain tautomers not found using previously published algorithms are successfully located by ours.

Software for the frontiers of quantum chemistry: An overview of developments in the Q-Chem 5 package.

This article summarizes technical advances contained in the fifth major release of the Q-Chem quantum chemistry program package, covering developments since 2015. A comprehensive library of exchange-correlation functionals, along with a suite of correlated many-body methods, continues to be a hallmark of the Q-Chem software. The many-body methods include novel variants of both coupled-cluster and configuration-interaction approaches along with methods based on the algebraic diagrammatic construction and variational reduced density-matrix methods. Methods highlighted in Q-Chem 5 include a suite of tools for modeling core-level spectroscopy, methods for describing metastable resonances, methods for computing vibronic spectra, the nuclear-electronic orbital method, and several different energy decomposition analysis techniques. High-performance capabilities including multithreaded parallelism and support for calculations on graphics processing units are described. Q-Chem boasts a community of well over 100 active academic developers, and the continuing evolution of the software is supported by an "open teamware" model and an increasingly modular design.

The Dark Triad trait of psychopathy and message framing predict risky decision-making during the COVID-19 pandemic.

The effects of framing on risky decision-making have been studied extensively in research using Kahneman and Tversky's (1981) hypothetical scenario about a contagious Asian disease. The COVID-19 pandemic offers a unique opportunity to test how message framing affects risky decision-making when millions of real lives are at stake worldwide. In a sample of US adults (N = 294), we investigated the effects of message framing and personality (Dark Triad traits) in relation to risky decision-making during the COVID-19 crisis. We found that both gain- and loss-framing influenced risk choice in response to COVID-19. People were more risk-averse in the loss condition of the current study compared to the benchmark established by Tversky and Kahneman (1981). Among the Dark Triad traits, psychopathy emerged as the significant predictor of risk taking, suggesting that people who score high in psychopathy are more likely to gamble with other people's lives during the COVID-19 crisis. We suggest that both voters and pandemic-related public awareness campaigns should consider the possibility that decision-makers with psychopathic tendencies may take greater risks with other people's lives during a pandemic. In addition, the framing of public-health messages should be tailored to increase the chances of compliance with government restrictions.

Probing radical-molecule interactions with a second generation energy decomposition analysis of DFT calculations using absolutely localized molecular orbitals.

Intermolecular interactions between radicals and closed-shell molecules are ubiquitous in chemical processes, ranging from the benchtop to the atmosphere and extraterrestrial space. While energy decomposition analysis (EDA) schemes for closed-shell molecules can be generalized for studying radical-molecule interactions, they face challenges arising from the unique characteristics of the electronic structure of open-shell species. In this work, we introduce additional steps that are necessary for the proper treatment of radical-molecule interactions to our previously developed unrestricted Absolutely Localized Molecular Orbital (uALMO)-EDA based on density functional theory calculations. A "polarize-then-depolarize" (PtD) scheme is used to remove arbitrariness in the definition of the frozen wavefunction, rendering the ALMO-EDA results independent of the orientation of the unpaired electron obtained from isolated fragment calculations. The contribution of radical rehybridization to polarization energies is evaluated. It is also valuable to monitor the wavefunction stability of each intermediate state, as well as their associated spin density profiles, to ensure the EDA results correspond to a desired electronic state. These radical extensions are incorporated into the "vertical" and "adiabatic" variants of uALMO-EDA for studies of energy changes and property shifts upon complexation. The EDA is validated on two model complexes, H2O˙F and FH˙OH. It is then applied to several chemically interesting radical-molecule complexes, including the sandwiched and T-shaped benzene dimer radical cation, complexes of pyridine with benzene and naphthalene radical cations, binary and ternary complexes of the hydroxyl radical with water (˙OH(H2O) and ˙OH(H2O)2), and the pre-reactive complexes and transition states in the ˙OH + HCHO and ˙OH + CH3CHO reactions. These examples suggest that this second generation uALMO-EDA is a useful tool for furthering one's understanding of both energetic and property changes associated with radical-molecule interactions.

Energy decomposition analysis of single bonds within Kohn-Sham density functional theory.

An energy decomposition analysis (EDA) for single chemical bonds is presented within the framework of Kohn-Sham density functional theory based on spin projection equations that are exact within wave function theory. Chemical bond energies can then be understood in terms of stabilization caused by spin-coupling augmented by dispersion, polarization, and charge transfer in competition with destabilizing Pauli repulsions. The EDA reveals distinguishing features of chemical bonds ranging across nonpolar, polar, ionic, and charge-shift bonds. The effect of electron correlation is assessed by comparison with Hartree-Fock results. Substituent effects are illustrated by comparing the C-C bond in ethane against that in bis(diamantane), and dispersion stabilization in the latter is quantified. Finally, three metal-metal bonds in experimentally characterized compounds are examined: a [Formula: see text]-[Formula: see text] dimer, the [Formula: see text]-[Formula: see text] bond in dizincocene, and the Mn-Mn bond in dimanganese decacarbonyl.

Isomer-specific vibronic structure of the 9-, 1-, and 2-anthracenyl radicals via slow photoelectron velocity-map imaging.

Polycyclic aromatic hydrocarbons, in various charge and protonation states, are key compounds relevant to combustion chemistry and astrochemistry. Here, we probe the vibrational and electronic spectroscopy of gas-phase 9-, 1-, and 2-anthracenyl radicals (C14H9) by photodetachment of the corresponding cryogenically cooled anions via slow photoelectron velocity-map imaging (cryo-SEVI). The use of a newly designed velocity-map imaging lens in combination with ion cooling yields photoelectron spectra with <2 cm(-1) resolution. Isomer selection of the anions is achieved using gas-phase synthesis techniques, resulting in observation and interpretation of detailed vibronic structure of the ground and lowest excited states for the three anthracenyl radical isomers. The ground-state bands yield electron affinities and vibrational frequencies for several Franck-Condon active modes of the 9-, 1-, and 2-anthracenyl radicals; term energies of the first excited states of these species are also measured. Spectra are interpreted through comparison with ab initio quantum chemistry calculations, Franck-Condon simulations, and calculations of threshold photodetachment cross sections and anisotropies. Experimental measures of the subtle differences in energetics and relative stabilities of these radical isomers are of interest from the perspective of fundamental physical organic chemistry and aid in understanding their behavior and reactivity in interstellar and combustion environments. Additionally, spectroscopic characterization of these species in the laboratory is essential for their potential identification in astrochemical data.

Expanded Helicenes: A General Synthetic Strategy and Remarkable Supramolecular and Solid-State Behavior.

A divergent synthetic strategy allowed access to several members of a new class of helicenes, the "expanded helicenes", which are composed of alternating linearly and angularly fused rings. The strategy is based on a three-fold, partially intermolecular [2+2+n] (n = 1 or 2) cycloaddition with substrates containing three diyne units. Investigation of aggregation behavior, both in solution and in the solid state, revealed that one of these compounds forms an unusual homochiral, π-stacked dimer via an equilibrium that is slow on the NMR time scale. The versatility of the method was harnessed to access a selenophene-annulated expanded helicene that, in contrast to its benzannulated analogue, exhibits long-range π-stacking in the solid state. The new helicenes possess low racemization barriers, as demonstrated by dynamic 1H NMR spectroscopy.

Manganese-Cobalt Oxido Cubanes Relevant to Manganese-Doped Water Oxidation Catalysts.

Incorporation of Mn into an established water oxidation catalyst based on a Co(III)4O4 cubane was achieved by a simple and efficient assembly of permanganate, cobalt(II) acetate, and pyridine to form the cubane oxo cluster MnCo3O4(OAc)5py3 (OAc = acetate, py = pyridine) (1-OAc) in good yield. This allows characterization of electronic and chemical properties for a manganese center in a cobalt oxide environment, and provides a molecular model for Mn-doped cobalt oxides. The electronic properties of the cubane are readily tuned by exchange of the OAc- ligand for Cl- (1-Cl), NO3- (1-NO3), and pyridine ([1-py]+). EPR spectroscopy, SQUID magnetometry, and DFT calculations thoroughly characterized the valence assignment of the cubane as [MnIVCoIII3]. These cubanes are redox-active, and calculations reveal that the Co ions behave as the reservoir for electrons, but their redox potentials are tuned by the choice of ligand at Mn. This MnCo3O4 cubane system represents a new class of easily prepared, versatile, and redox-active oxido clusters that should contribute to an understanding of mixed-metal, Mn-containing oxides.

Preliminary experience on the use of PET/CT in the management of pediatric post-transplant lymphoproliferative disorder.

INTRODUCTION: Post-transplant lymphoproliferative disorder (PTLD) is a well-known complication following prolonged immunosuppression. Contrary to other lymphomas, there is no standardized imaging approach to assess PTLD either at staging or for response to therapy. Positron emission tomography/computed tomography (PET/CT) is an imaging modality that has proven to be useful in lymphoma. However, there is still limited data concerning its use in pediatric PTLD. Our study evaluates the use of PET/CT in pediatric PTLD at our institution. METHODS: To assess the role of PET/CT in pediatric PTLD, we reviewed the pediatric patients with PTLD who had undergone PET/CT at our institution between 2000 and 2016. RESULTS: Nine patients were identified. Six had PET/CT at diagnosis. All lesions seen on CT were identified with PET/CT. Fourteen PET/CTs were done during treatment. Eight PET/CTs were negative, including three where CT showed areas of uncertain significance. In these cases, PET/CT helped us to stop treatment and the patients remain in remission after a long follow-up (mean 74.3 months; range 12.4-180.9 months). PET/CT revealed additional disease in two cases, therefore treatment was intensified. Six biopsies and close follow-up was done to confirm PET/CT results. In one case, PET/CT did not identify central nervous system involvement demonstrated on magnetic resonance imaging. CONCLUSION: PET/CT may have an important role in the staging and follow-up of pediatric PTLD. In our cohort, PET/CT was helpful in staging and assessing treatment response and in clarifying equivocal findings on other imaging modalities.

Aryl Group Transfer from Tetraarylborato Anions to an Electrophilic Dicopper(I) Center and Mixed-Valence µ-Aryl Dicopper(I,II) Complexes.

The synthesis of discrete, cationic binuclear µ-aryl dicopper complexes [Cu2(µ-η(1):η(1)-Ar)DPFN]X (Ar = C6H5, 3,5-(CF3)2C6H3, and C6F5; DPFN = 2,7-bis(fluoro-di(2-pyridyl)methyl)-1,8-naphthyridine; X = BAr4(-) and NTf2(-); Tf = SO2CF3) was achieved by treatment of a dicopper complex [Cu2(µ-η(1):η(1)-NCCH3)DPFN]X2 (X = PF6(-) and NTf2(-)) with tetraarylborates. Structural characterization revealed symmetrically bridging aryl groups, and (1)H NMR spectroscopy evidenced the same structure in solution at 24 °C. Electrochemical investigation of the resulting arylcopper complexes uncovered reversible redox events that led to the synthesis and isolation of a rare mixed-valence organocopper complex [Cu2(µ-η(1):η(1)-Ph)DPFN](NTf2)2 in high yield. The solid-state structure of the mixed-valence µ-phenyl complex exhibits inequivalent copper centers, despite a short Cu···Cu distance. Electronic and variable-temperature electron paramagnetic resonance spectroscopy of the mixed-valence µ-phenyl complex suggest that the degree of spin localization is temperature-dependent, with a high degree of spin localization observed at lower temperatures. Electronic structure calculations agree with the experimental results and suggest that the spin is localized almost entirely on one metal center.

Vibrational and electronic structure of the α- and ß-naphthyl radicals via slow photoelectron velocity-map imaging.

Slow photoelectron velocity-map imaging (SEVI) spectroscopy has been used to study the vibronic structure of gas-phase α- and ß-naphthyl radicals (C(10)H(7)). SEVI of cryogenically cooled anions yields spectra with <4 cm(-1) resolution, allowing for the observation and interpretation of congested vibrational structure. Isomer-specific photoelectron spectra of detachment to the radical ground electronic states show detailed structure, allowing assignment of vibrational fundamental frequencies. Transitions to the first excited states of both radical isomers are also observed; vibronic coupling and photodetachment threshold effects are considered to explain the structure of the excited bands.

Incremental value and clinical impact of neck sonography for primary hyperparathyroidism: a risk-adjusted analysis.

BACKGROUND: Despite the different preoperative imaging modalities available for parathyroid adenoma localization, there is currently no uniform consensus on the most appropriate preoperative imaging algorithm that should be routinely followed prior to the surgical management of primary hyperparathyroidism (PHPT). We sought to determine the incremental value of adding neck ultrasonography to scintigraphy-based imaging tests. METHODS: In a single institution, surgically naive patients with PHPT underwent the following localization studies before parathyroidectomy: 1) Tc-99m sestamibi imaging with single photon emission computed tomography/computed tomography (SPECT/CT) or Tc-99m sestamibi imaging with SPECT alone, or 2) ultrasonography in addition to those tests. We retrospectively collected data and performed a multivariate analysis comparing group I (single study) to group II (addition of ultrasonography) and risk of bilateral (BNE) compared with unilateral (UNE) neck exploration. RESULTS: Our study included 208 patients. Group II had 0.45 times the odds of BNE versus UNE compared with group I (unadjusted odds ratio [OR] 0.45, 95% confidence interval [CI] 0.25-0.81, p = 0.008). When adjusting for patient age, sex, preoperative calcium level, use of intraoperative PTH monitoring, preoperative PTH level, adenoma size, and number of abnormal parathyroid glands, Group II had 0.48 times the odds of BNE versus UNE compared with group I (adjusted OR 0.48, 95% CI 0.23-1.03, p = 0.06). In a subgroup analysis, only the addition of ultrasonography to SPECT decreased the risk of undergoing BNE compared with SPECT alone (unadjusted OR 0.40, 95% CI 0.19-0.84, p = 0.015; adjusted OR 0.38, 95% CI 0.15-0.96, p = 0.043). CONCLUSION: The addition of ultrasonography to SPECT, but not to SPECT/CT, has incremental value in decreasing the extent of surgery during parathyroidectomy, even after adjusting for multiple confounding factors.

CONTEXTE: Malgré l'existence de diverses modalités d'imagerie préopératoire pour la localisation de l'adénome parathyroïdien, on déplore actuellement l'absence de consensus en ce qui concerne l'algorithme le plus approprié à suivre au chapitre de l'imagerie préalable à une prise en charge chirurgicale de l'hyperparathyroïdie primaire (HPTP). Nous avons voulu vérifier si l'ajout de l'échographie du cou aux tests d'imagerie scintigraphique offrait une valeur ajoutée. MÉTHODES: Dans un établissement, des patients atteints d'HPTP n'ayant jamais subi d'intervention chirurgicale ont été soumis à des examens de localisation préparathyroïdectomie : 1) imagerie au moyen du sestamibi marqué au Tc-99m avec tomographie par émission monophotonique/tomodensitométrie (SPECT/CT), ou imagerie au moyen du sestamibi marqué au Tc-99m avec SPECT seule, our 2) échographie en plus de ces tests. Nous avons recueilli les données rétrospectivement et effectué une analyse multivariée pour comparer le Groupe I (examen seul) au Groupe II (ajout de l'échographie) et la probabilité qu'ils subissent une exploration cervicale bilatérale (ECB) plutôt qu'unilatérale (ECU). RÉSULTANTS: Notre étude a recruté 208 patients. Le Groupe II s'est trouvé exposé à un risque 0,45 fois plus grand d'être soumis à une ECB plutôt qu'à une ECU, comparativement au Groupe I (rapport des cotes [RC] non ajusté 0,45, intervalle de confiance [IC] de 95 % 0,25­0,81, p = 0,008). Après ajustement pour tenir compte de l'âge et du sexe des patients, de leur taux préopératoire de calcium, de la surveillance peropératoire de l'HPT, du taux préopératoire de l'HPT, de la taille de l'adénome et du nombre de ganglions parathyroïdiens anormaux, le Groupe II s'est révélé exposé à un risque 0,48 fois plus grand à l'égard de l'ECB plutôt que de l'ECU comparativement au Groupe I (RC ajusté 0,48, IC de 95 % 0,23­1,03, p = 0,06). Selon une analyse de sous-groupe, seul l'ajout de l'échographie à la SPECT a réduit le risque de subir une ECB comparativement à la SPECT seule (RC non ajusté 0,40, IC de 95 % 0,19­0,84, p = 0,015; RC ajusté 0,38, IC de 95 % 0,15­0,96, p = 0,043). CONCLUSIONS: L'ajout de l'échographie à la SPECT, mais non à la SPECT/CT, a offert une valeur ajoutée pour ce qui est de réduire l'étendue de l'opération durant la parathyroïdectomie, même après ajustement pour tenir compte de plusieurs facteurs de confusion.

Large Computational Survey of Intrinsic Reactivity of Aromatic Carbon Atoms with Respect to a Model Aldehyde Oxidase.

Aldehyde oxidase (AOX) and other related molybdenum-containing enzymes are known to oxidize the C-H bonds of aromatic rings. This process contributes to the metabolism of pharmaceutical compounds and, therefore, is of vital importance to drug pharmacokinetics. The present work describes an automated computational workflow and its use for the prediction of intrinsic reactivity of small aromatic molecules toward a minimal model of the active site of AOX. The workflow is based on quantum chemical transition state searches for the underlying single-step oxidation reaction, where the automated protocol includes identification of unique aromatic C-H bonds, creation of three-dimensional reactant and product complex geometries via a templating approach, search for a transition state, and validation of reaction end points. Conformational search on the reactants, products, and the transition states is performed. The automated procedure has been validated on previously reported transition state barriers and was used to evaluate the intrinsic reactivity of nearly three hundred heterocycles commonly found in approved drug molecules. The intrinsic reactivity of more than 1000 individual aromatic carbon sites is reported. Stereochemical and conformational aspects of the oxidation reaction, which have not been discussed in previous studies, are shown to play important roles in accurate modeling of the oxidation reaction. Observations on structural trends that determine the reactivity are provided and rationalized.

Oligoprogression in Metastatic, Castrate-Resistant Prostate Cancer-Prevalence and Current Clinical Practice.

Aims: Oligoprogression is poorly defined in current literature. Little is known about the natural history and significance of oligoprogression in patients with hormone-resistant prostate cancer on abiraterone or enzalutamide treatment [termed androgen receptor-targeted therapy (ARTT)]. The aim of this study was to determine the prevalence of oligoprogression, describe the characteristics of oligoprogression in a cohort of patients from a single center, and identify the number of patients potentially treatable with stereotactic body radiotherapy (SBRT). Methods: Castration-resistant prostate cancer (CRPC) patients who radiologically progressed while on ARTT were included. Patients with oligoprogressive disease (OPD) (≤3 lesions) on any imaging were identified in a retrospective analysis of electronic patient records. Kaplan-Meier method and log-rank test were used to calculate progression-free and overall survival. Results: A total of 102 patients with metastatic CRPC on ARTT were included. Thirty (29%) patients presented with oligoprogression (46 lesions in total); 21 (21% of total) patients had lesions suitable for SBRT. The majority of lesions were in the bone (21, 46%) or lymph nodes (15, 33%). Patients with oligoprogression while on ARTT had a significantly better prostate-specific antigen (PSA) response on commencing ARTT as compared to patients who later developed polyprogression. However, PSA doubling time immediately prior to progression did not predict OPD. Median progression-free survival to oligoprogression versus polyprogression was 16.8 vs. 11.7 months. Time to further progression after oligoprogression was 13.6 months in those treated with radiotherapy (RT) for oligoprogression vs. 5.7 months in those treated with the continuation of ARTT alone. Conclusions: In this study, nearly a third of patients on ARTT for CRPC were found to have OPD. OPD patients had a better PSA response on ART and a longer duration on ARTT before developing OPD as compared to those developing polyprogressive disease (Poly-PD). The majority of patients (70%) with OPD had lesions suitable for SBRT treatment. Prospective randomized control trials are needed to establish if there is a survival benefit of SBRT in oligoprogressive prostate cancer and to determine predictive indicators.

Isolation of pure disubstituted E olefins through Mo-catalyzed Z-selective ethenolysis of stereoisomeric mixtures.

Monoaryloxide-pyrrolide (MAP) complexes of molybdenum were employed for the selective ethenolysis of 1,2-disubstituted Z olefins in the presence of the corresponding E olefins. Reactions were performed in the presence of 0.02-3.0 mol % catalyst at 22 °C under 20 atm ethylene. We have demonstrated that the Z isomer of an easily accessible E:Z mixture can be destroyed through ethenolysis and the E alkene thereby isolated readily in high yield and exceptional stereoisomeric purity.

Novel use of F-DOPA PET/CT imaging in a child with paraganglioma/pheochromocytoma syndrome.

We report the use of F-DOPA PET/CT imaging in the evaluation of a teenager with marked hypertension and right pararenal, left adrenal and left para-aortic mass lesions. The use of the modality for this clinical application has not been described previously within the pediatric imaging literature. The value of this technique relative to conventional imaging modalities is discussed and warrants consideration of its use, if available, for evaluating children with suspected paragangliomas/pheochromocytomas.

Clarifying the quantum mechanical origin of the covalent chemical bond.

Lowering of the electron kinetic energy (KE) upon initial encounter of radical fragments has long been cited as the primary origin of the covalent chemical bond based on Ruedenberg's pioneering analysis of H[Formula: see text] and H2 and presumed generalization to other bonds. This work reports KE changes during the initial encounter corresponding to bond formation for a range of different bonds; the results demand a re-evaluation of the role of the KE. Bonds between heavier elements, such as H3C-CH3, F-F, H3C-OH, H3C-SiH3, and F-SiF3 behave in the opposite way to H[Formula: see text] and H2, with KE often increasing on bringing radical fragments together (though the total energy change is substantially stabilizing). The origin of this difference is Pauli repulsion between the electrons forming the bond and core electrons. These results highlight the fundamental role of constructive quantum interference (or resonance) as the origin of chemical bonding. Differences between the interfering states distinguish one type of bond from another.