Formal Nickelate(−I) Complexes Supported by Group 13 Ions

Formal nickelate(?I) complexes bearing Group 13 metalloligands (M=Al and Ga) were isolated. These 17 e^? complexes were synthesized by one‐electron reduction of the corresponding Ni⁰→M^III precursors, and were investigated by single‐crystal X‐ray diffraction, EPR spectroscopy, and quantum chemical calculations. Collectively, the experimental and computational data support: 1) the strengthening of the Ni?M bond upon one‐electron reduction, and 2) the delocalization of the unpaired spin across the Ni and M atoms. An intriguing electronic configuration is revealed where three valence electrons occupy two σ‐type bonding interactions: Ni(3d )²→M and σ‐(Ni?M)¹. The latter is an unusual Ni?M σ‐bonding molecular orbital that comprises primarily the Ni 4p_z and M np_z/ns atomic orbitals.     

Improving on equilibrium isotropic nuclear shielding constants

Isotropic nuclear shielding constants at the equilibrium molecular structure σ_eq and zero‐point vibrational corrections (ZPVCs) to σ_eq are evaluated using the B3LYP/aug‐cc‐pVTZ level of theory, as well as the KT2/aug‐cc‐pVTZ level of theory. Various scaling factors and systematic corrections are obtained by linear regression to experimental shielding constants. Comparisons of the scaled and systematically corrected equilibrium and vibrationally averaged shielding constants reveal that, at the 99% confidence level, the ZPVCs via second‐order perturbation theory do not improve the agreement of B3LYP/aug‐cc‐pVTZ and KT2/aug‐cc‐pVTZ calculated shielding constants with experiment. This holds true when the same analysis is applied to CCSD(T)/aug‐cc‐pCV[TQ]Z calculated σ_eq of Teale et al. [Journal of Chemical Physics 2013, 138, 024111]. In addition, at the 99% confidence level, B3LYP/aug‐cc‐pVTZ and KT2/aug‐cc‐pVTZ scaled and systematically corrected shielding constants are found to be statistically no different from CCSD(T)/aug‐cc‐pCV[TQ]Z calculated σ_eq. The use of scaling factors and systematic corrections could thus provide a cheaper but yet reasonably accurate alternative for the study of nuclear shielding constants of larger systems.     

Synthesis and spectroscopic studies of highly fluorescent,solvatochromic diastereomers with differentially stacked bithiophene-substituted quinoxaline rings

Diastereomeric C-shaped molecules containing closely stacked bithiophene-substituted quinoxaline rings were synthesized and characterized by NMR, UV–vis absorption, and fluorescence spectroscopy. The unique geometry of each diastereomer resulted in different degrees of π-overlap between the bithiophene-substituted quinoxaline ring chromophores, modulating their spectroscopic properties. The donor-acceptor nature of this chromophore gave rise to its positive solvatochromism. ¹H NMR and UV–vis absorption spectroscopy confirmed the existence of π-π interactions in the ground state between the quinoxaline rings in both molecules but between the bithiophene rings only in the syn isomer. They exhibited significant emission maxima bathochromic shifts, a strong, positive solvatochromism, increased band broadening, and larger Stokes shifts when compared to a compound with an unstacked chromophore. Additionally, the syn isomer consistently showed λ_max,em value red-shifts and larger band broadening and Stokes shifts compared to the anti isomer due to the greater π-overlap in the syn isomer.     

Full-field measurements of flow through a scaled metal foam replica

Open-celled foam geometries show great promise in heat/mass transfer, chemical treatment, and enhanced mixing applications. Flow measurements on these geometries have consisted primarily of observations of the upstream and downstream effects the foam has on the velocity field. Unfortunately, these observations give little insight into the flow inside the foam. We have performed quantitative flow measurements inside a scaled replica of a metal foam, ϕ = 0.921, D _Cell = 2.5 mm, by Magnetic Resonance Velocimetry to better understand the fluid motion inside the foam and give an alternative method to determine the foam cell and pore sizes. Through these 3-D, spatially resolved measurements of the flow field for a cell Reynolds number of 840, we have shown that the transverse motion of the fluid has velocities 20–30% of the superficial velocity passing through the foam. This strong transverse motion creates and dissipates streamwise jets with peak velocities 2–3 times the superficial velocity and whose coherence length is strongly correlated to the cell size of the foam. This complex fluid motion is described as “mechanical mixing” and is attributed to the geometry of the foam. A mechanical dispersion coefficient, D _M, was formed which demonstrates the transverse dispersion of this geometry to be 14 times the kinematic viscosity and 10 times the thermal diffusivity of air at 20°C and 1 atm.     

Novel aerobic oxidation of primary sulfones to carboxylic acids

Primary alkyl aryl sulfones are converted to the corresponding carboxylic acids in fair to excellent yield through double deprotonation and exposure to atmospheric oxygen. The methodology allows for the convenient synthesis of (13)C labeled carboxylic acids.     

Virtual decoy sets for molecular docking benchmarks

Virtual docking algorithms are often evaluated on their ability to separate active ligands from decoy molecules. The current state-of-the-art benchmark, the Directory of Useful Decoys (DUD), minimizes bias by including decoys from a library of synthetically feasible molecules that are physically similar yet chemically dissimilar to the active ligands. We show that by ignoring synthetic feasibility, we can compile a benchmark that is comparable to the DUD and less biased with respect to physical similarity.     

Selective imaging and killing of cancer cells with protein-activated near-infrared fluorescing nanoparticles

We present a general approach for the selective imaging and killing of cancer cells using protein-activated near-infrared emitting and cytotoxic oxygen generating nanoparticles. Poly(propargyl acrylate) (PA) particles were surface modified through the copper-catalyzed azide/alkyne cycloaddition of azide-terminated indocyanine green (azICG), a near-infrared emitter, and poly(ethylene glycol) (azPEG) chains of various molecular weights. The placement of azICG onto the surface of the particles allowed for the chromophores to complex with bovine serum albumin when dispersed in PBS that resulted in an enhancement of the dye emission. In addition, the inclusion of azPEG with the chromophores onto the particle surface resulted in a synergistic ninefold enhancement of the fluorescence intensity, with azPEGs of increasing molecular weight amplifying the response. Human liver carcinoma cells (HepG2) overexpress albumin proteins and could be employed to activate the fluorescence of the nanoparticles. Preliminary PDT studies with HepG2 cells combined with the modified particles indicated that a minor exposure of 780 nm radiation resulted in a statistically significant reduction in cell growth.     

Comparison of AOAC 2005.06 LC official method with other methodologies for the quantitation of paralytic shellfish poisoning toxins in UK shellfish species

A refined version of the pre-column oxidation liquid chromatography with fluorescence detection (ox-LC-FLD) official method AOAC 2005.06 was developed in the UK and validated for the determination of paralytic shellfish poisoning toxins in UK shellfish. Analysis was undertaken here for the comparison of PSP toxicities determined using the LC method for a range of UK bivalve shellfish species against the official European reference method, the PSP mouse bioassay (MBA, AOAC 959.08). Comparative results indicated a good correlation in results for some species (mussels, cockles and clams) but a poor correlation for two species of oysters (Pacific oysters and native oysters), where the LC results in terms of total saxitoxin equivalents were found to be on average more than double the values determined by MBA. With the potential for either LC over-estimation or MBA under-estimation, additional oyster and mussel samples were analysed using MBA and ox-LC-FLD together with further analytical and functional methodologies: a post-column oxidation LC method (LC-ox-FLD), an electrophysiological assay and hydrophilic interaction liquid chromatography with tandem mass spectrometric detection. Results highlighted a good correlation among non-bioassay results, indicating a likely cause of difference was the under-estimation in the MBA, rather than an over-estimation in the LC results.     

Nevanlinna–Pick Interpolation and Factorization of Linear Functionals

If \mathfrakA{\mathfrak{A}} is a unital weak-* closed algebra of multiplication operators on a reproducing kernel Hilbert space which has the property \mathbbA₁(1){\mathbb{A}_1(1)}, then the cyclic invariant subspaces index a Nevanlinna–Pick family of kernels. This yields an NP interpolation theorem for a wide class of algebras. In particular, it applies to many function spaces over the unit disk including Bergman space. We also show that the multiplier algebra of a complete NP space has \mathbbA₁(1){\mathbb{A}_1(1)}, and thus this result applies to all of its subalgebras. A matrix version of this result is also established. It applies, in particular, to all unital weak-* closed subalgebras of H ^∞ acting on Hardy space or on Bergman space.