Ortho effect in the Bergman cyclization: electronic and steric effects in hydrogen abstraction by 1-substituted naphthalene 5,8-diradicals

We present a detailed theoretical study of geometries, electronic structure, and energies of transition states and intermediates completing the full Bergman cycloaromatization pathway of ortho-substituted enediynes with a focus on polar and steric contributions to the kinetics and thermodynamics of hydrogen abstraction. This study provides a rare unambiguous example of remote substitution that affects reactivity of a neutral reactive intermediate through an sigma framework.     

B-H activation by frustrated Lewis pairs: borenium or boryl phosphonium cation?

Catechol borane reacts with the frustrated Lewis pairs tBu2RP (R = tBu, 2-C6H4(C6H5)) and B(C6F5)3 to give the species [(C6H4O2)BPtBu2R][HB(C6F5)3] that can formally be described as either borenium cation or boryl-phosphonium salts; the nature of these species was probed with DFT calculations.     

Biphenylamide ligand complexes of Li and Al: hemilabile arene donors?

Biphenylamide ligands were employed to prepare a series of Li and Al derivatives in which the ligand binds through N. Such species include: (2-C(6)H(4)Ph)Bu(t)NLi (), (2-C(6)H(4)Ph)Bu(t)NLi(THF)(2) (), (2-C(6)H(4)Ph)Bu(t)NLi.OEt(2) (), [(mu-(2-C(6)H(4)Ph)(2)N)Li](2) (), (2-C(6)H(4)Ph)(2)NLi(THF)(2) (), (2-C(6)H(4)Ph)(2)NLi.OEt(2) () amd (2-C(6)H(4)Ph)(2)NAlX(2) (X = Cl (), Me (), Et ()). Structural and spectroscopic data show that these species exhibit weak arene to metal donation. This donor is hemilabile being readily displaced by other stronger donors to give such species as (2-C(6)H(4)Ph)(2)NAlMe(2)(THF) () and (2-C(6)H(4)Ph)(2)NAlMe(2)(CH(2)PPh(3)) (). Reactions of with B(C(6)F(5))(3) results in methyl for C(6)F(5) exchange and isolation of (2-C(6)H(4)Ph)(2)NAl(C(6)F(5))(2) (). The presence the electron withdrawing groups in further strengthens the hemilabile interaction.     

Experimental and theoretical study of the OH vibrational spectra and overtone chemistry of gas-phase vinylacetic acid

In this study we present the gas-phase vibrational spectrum of vinylacetic acid with a focus on the nu = 1-5 vibrational states of the OH stretching transitions. Cross sections for nu = 1, 2, 4 and 5 of the OH stretching vibrational transitions are derived on the basis of the vapor pressure data obtained for vinylacetic acid. Ab initio calculations are used to assist in the band assignments of the experimental spectra, and to determine the threshold for the decarboxylation of vinylacetic acid. When compared to the theoretical energy barrier to decarboxylation, it is found that the nu OH = 4 transition with thermal excitation of low frequency modes or rotational motion and nu OH = 5 transitions have sufficient energy for the reaction to proceed following overtone excitation.     

The effect of pharmaceuticals on the nanoscale structure of PEO-PPO-PEO micelles

We present results on the effects of various hydrophobic drugs and additives on the micellar structure of Pluronic F127 solutions. Small-angle neutron scattering experiments on 5wt% F127 solutions were used to measure micelle core size (R(1)), micelle corona size (R(2)), intermicellar interaction distance (R(int)), polydispersity (sigma), and aggregation number (N(agg)); dynamic light scattering was used to measure critical micelle concentration (CMC); and ultraviolet spectroscopy was used to measure drug solubility and apparent micelle-water partition coefficient (K(mw)). The core and corona size were found to generally increase in the presence of the drugs, as did R(int). Both sigma and N(agg) were found to decrease in the presence of most of the drugs, and the CMC was found to vary considerably with no clear correlation. A design of experiments (DOE) approach was used to analyze the results and build empirical correlations. All of the parameters from the SANS experiments were found to depend strongly on drug solubility, with a weak dependence on K(mw) in most cases. The aggregation number, however, was found to depend strongly on both K(mw) and solubility. The correlations can be used to roughly predict the structural parameters of F127 micelles for other hydrophobic drugs.     

The pressure drop along rectangular microchannels containing bubbles

This paper derives the difference in pressure between the beginning and the end of a rectangular microchannel through which a flowing liquid (water, with or without surfactant, and mixtures of water and glycerol) carries bubbles that contact all four walls of the channel. It uses an indirect method to derive the pressure in the channel. The pressure drop depends predominantly on the number of bubbles in the channel at both low and high concentrations of surfactant. At intermediate concentrations of surfactant, if the channel contains bubbles (of the same or different lengths), the total, aggregated length of the bubbles in the channel is the dominant contributor to the pressure drop. The difference between these two cases stems from increased flow of liquid through the "gutters"-the regions of the system bounded by the curved body of the bubble and the corners of the channel-in the presence of intermediate concentrations of surfactant. This paper presents a systematic and quantitative investigation of the influence of surfactants on the flow of fluids in microchannels containing bubbles. It derives the contributions to the overall pressure drop from three regions of the channel: (i) the slugs of liquid between the bubbles (and separated from the bubbles), in which liquid flows as though no bubbles were present; (ii) the gutters along the corners of the microchannels; and (iii) the curved caps at the ends of the bubble.     

Ruthenium(II) trisbipyridine functionalized gold nanorods. Morphological changes and excited-state interactions

Gold nanorods synthesized using cetyltrimethylammonium bromide and tetraoctylammonium bromide as stabilizers are functionalized with a thiol derivative of ruthenium(II) trisbipyridyl complex [(Ru(bpy)3(2+)-C5-SH] in dodecanethiol using a place-exchange reaction. The changes in the plasmon absorption bands and transmission electron micrographs indicate significant changes in the gold rod morphology during the place-exchange reaction. The (Ru(bpy)(3)2+-C5-SH in its excited state undergoes quick deactivation when bound to gold nanorods. More than 60% of the emission was quenched when [(Ru(bpy)3(2+)-C5-SH] was bound to gold nanorods. Emission decay analysis indicates that the energy transfer rate constant is greater than 10(10) s(-1).     

Selective C?F Bond Activation of Tetrafluorobenzenes by Nickel(0) with a Nitrogen Donor Analogous to N‐Heterocyclic Carbenes

N, not NHC : A neutral, basic, strong σ‐donor nitrogen ancillary ligand with properties analogous to those of N‐heterocyclic carbenes (NHCs) was developed to aid in the oxidative additions of challenging substrates to late transition metals. Selective, room‐temperature C? F bond activation was observed with hexa‐, penta‐, and all three isomers of tetrafluorobenzene using a nickel(0) source in the presence of this donor.

     

A parameter-uniform Schwarz method for a coupled system of reaction–diffusion equations

We consider an arbitrarily sized coupled system of one-dimensional reaction–diffusion problems that are singularly perturbed in nature. We describe an algorithm that uses a discrete Schwarz method on three overlapping subdomains, extending the method in [H. MacMullen, J.J.H. Miller, E. O’Riordan, G.I. Shishkin, A second-order parameter-uniform overlapping Schwarz method for reaction-diffusion problems with boundary layers, J. Comput. Appl. Math. 130 (2001) 231–244] to a coupled system. On each subdomain we use a standard finite difference operator on a uniform mesh. We prove that when appropriate subdomains are used the method produces ε-uniform results. Furthermore we improve upon the analysis of the above-mentioned reference to show that, for small ε, just one iteration is required to achieve the expected accuracy.