Evidence of enhanced conjugation in ortho-arylene ethynylenes with transition metal coordination

The effective conjugation of ortho and ortho-alt-para-arylene ethynylenes, with appropriately positioned pyridine and pyrazine heterocycles, increases upon binding to Ag(I) and Pd(II) cations. Significant bathochromic shifts in the electronic spectra, witnessed upon introduction of these metal bridges, are consistent with enhanced electron delocalization in the unsaturated backbone. Control studies suggest that this electronic behavior is attributable exclusively (in the case of Ag(I)) or partially (in the case of Pd(II)) to conformational restrictions of the conjugated backbones.     

Using Kinetic Modeling and Experimental Data to Evaluate Mechanisms in PET-RAFT

Reversible deactivation radical polymerization (RDRP) techniques have become important tools for polymer chemists because they control the structure and are tolerant to functionality. Photoinduced polymerizations have seen a growing interest due to their mild conditions, as well as spatial and temporal control over the polymerization. Among these techniques, photoinduced electron/energy transfer reversible addition–fragmentation chain transfer polymerization (PET-RAFT) is one of the most widely investigated. While PET-RAFT is seen as an increasingly useful tool, there is still much to understand about the mechanism of this process. In particular, there are ongoing questions regarding the kinetic contribution of electron versus energy transfer. In order to better understand the mechanism, this work aims to use kinetic modeling along with experimental data to help determine the likelihood of the proposed mechanisms for the PET-RAFT process using the trithiocarbonate-mediated polymerization of methyl acrylate with fac-tris[2-phenylpyridinato-C²,N]iridium(III) as a photocatalyst. Simulation data show that electron transfer without a corresponding reduction pathway cannot explain the experimental kinetics, while energy transfer offers a good fit to experimental data. © 2019 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 139–144     

Probing the anomeric effect. The diaminomethylene group: Calculations of N?C?N-containing molecular systems1

A study of systems containing the title moiety is described, with special reference to the anomeric effect. We have calculated ab initio, using Gaussian-80 with the 3-21G basis set, all basic conformations of methylene-diamine (H₂N? CH₂? NH₂) and its N-methyl derivative with full geometry optimization of energy minima and barriers. The structural data thus obtained, were then employed to parameterize Allinger's MM2-80 force field in a procedure similar to that described for oxygen derivatives, including hydrogen-bonding effects and C? N bond shortening in tertiary amines. This modification, termed MM2-AE was then used to calculate larger molecules, including N,N′-di- and N,N,N′,N′-tetramethyl-methylenediamine, various 1,3-diazane systems, and 1,4,5,8-tetraazadecalin derivatives of established (x-ray) structures. The results are discussed in light of their verificative and predictive power and appear to validate MM2-AE as a useful computational procedure.     

Ab initio calculations of intermolecular potentials. The ground state of the Ar?H2 van der Waals molecule

Hartree–Fock computations of the potential surface of Ar? H₂ have been carried out and supplemented with calculations of the dispersion energy, with use of the counterpoise method to remove the basis set superposition error. The collinear and perpendicular bisector geometries are considered. The resulting potentials agree quite well with the actual experimental data.     

Hydrogen Bonding of Carboxylic Acids in Aqueous Solutions—UV Spectroscopy, Viscosity, and Molecular Simulation of Acetic Acid

The UV spectra of aqueous acetic acid solutions up to 2M were investigated. At these wavelengths, the carboxylic acids exhibit an absorption peak, attributed to the C=O group, which shifts when hydrogen bonds are formed.. The measured spectra were best fitted to several bands, either of Gaussian or Lorentzian shape, which can be explained as several types of structural units formed by hydrogen bonds established between acetic acid and water molecules and between acetic acid molecules themselves. Molecular dynamics simulation of these mixtures was also performed, confirming the occurrence of several types of hydrogen bonds and showing the presence of dimers at higher concentrations. The viscosity and density of these solutions were also measured at different concentrations and temperatures. These results give a more complete picture of the hydrogen bond network of the system.     

Phenanthroline complexes bearing fused dipyrrolylquinoxaline anion recognition sites: efficient fluoride anion receptors

Novel anion recognition host molecules, tris-1,10-phenanthroline cobalt(III) and bis-2,2'-bipyridine mono-1,10-phenanthroline ruthenium(II) complexes bearing fused dipyrrolylquinoxaline moieties have been synthesized. As determined by UV-vis spectroscopic and electrochemical studies, these metal complexes bind fluoride with high affinity in polar media both in absolute terms and relative to the metal-free phenanthroline dipyrrolylquinozaline precursor from which they are derived (fluoride is bound to the tris-1,10-phenanthroline cobalt(III) dipyrrolylquinoxaline system with a 1:1 binding constant of 54 000 M-1 in DMSO). The large observed binding constants are ascribed to two factors, (i) the presence of a phenanthroline-coordinated cationic charge that decreases the electron density on the pyrrole NH protons and (ii) pure electrostatic effects.     

State-to-state scattering of D2 from Cu(100) and Pd(111)

Results from state resolved experiments are presented for the interaction of D2(v=1,J=2) with Cu(100) and Pd(111). The reflected molecules were probed using quantum state specific spectroscopy. For D2 scattered from Cu(100) the vibrational survival probability and some transition inelastic probabilities were measured for incident energies from 70-200 meV. The survival probability was found to be larger then that found previously for H2(v=1) scattered from the same surface; these differences are discussed in terms of the lower zero point energy and smaller vibrational energy spacings of D2. D2 translational energy exchange was studied for several different scattering channels and interpreted using simple classical calculations. The survival probability was also measured for D2(v=1) scattered from Pd(111) at one incident energy. Pd is reactive for D2 dissociation and this survival probability was measured to be small and also to be much smaller than that for H2(v=1) under similar conditions. Vibrational relaxation channels were studied for D2 scattering from both Cu(100) and Pd(111). The vibrational relaxation probability on both surfaces was also found to be smaller than that measured for comparable channels for H2. The smaller survival probability and vibrational relaxation probability for D2 on Pd(111) cannot be easily accounted for by the difference in zero point energy and vibrational energy spacings.     

Molecular Dynamics Simulation of Aqueous Solutions Using Interaction Energy Components: Application to the Solvation Gibbs Energy

Molecular dynamics simulations of aqueous solutions of the solutes acetamide (AcNH₂), acetic acid (AcOH), and acetaldehyde (AcH) were made using Lennard–Jones 12-6-1 potentials to describe the solute–solvent interactions. The Morokuma decomposition scheme and the ESIE solute atomic charges were used to reproduce the exchange, polarization, and electrostatic components of the solute–water interaction energy. A nonlinear perturbation was incorporated into the “slow-growth” technique in order to improve the results for the solvation Gibbs energy that were found to be in agreement with the available experimental and theoretical values.     

Construction of an inexpensive surface plasmon resonance instrument for use in teaching and research

The construction of an inexpensive SPR instrument that can be used for both teaching and research is described. Using a 2′ × 2′ optical table to construct this instrument allows both scientists and students full access to the operation of the spectrometer. Furthermore, the use of open platform instrumentation has the advantage of maintaining the focus on the relationship between emerging technology and analytical chemistry as well as allowing the user to modify the instrument to enhance the measurement process for a particular application. This is a change from the learning paradigm used in most research and teaching laboratories where commercial instrumentation is treated as a black box due to its complexity. Three studies, which were performed using this instrument, are presented to demonstrate the suitability of this instrument for both teaching and research. These studies include measuring the refractive index of alcohols, investigating the partitioning of ruthenium (II) trisbipyridine chloride into Nafion, and understanding the mechanism controlling metal ion adsorption by polyacrylamide hydrogels.     

α-Fluorination of β-keto sulfoxides

We have developed an efficient new procedure for α-fluorination of β-keto sulfoxide enolate anions which are generated $\text{in situ}$ via nucleophilic addition reactions to cyclopentenone sulfoxide 7. Perchloryl fluoride is used as the fluorinating agent. Characterization of the product α-fluoro β-keto sulfoxides includes ¹⁹F NMR spectroscopy.