Polar vs. bde effects on aldehydic hydrogen atom transfer reactions of benzaldehydes by t-butoxy radicals.

Aldehydic hydrogen atom abstractions from benzaldehydes by t-butoxy radicals from t-butylperoxide exhibit a Hammett rho of ?0.32, which is better correlated with σ⁺ than σ and rationalized in terms of the contribution of dipolar charge-separated transition state.     

Localized synthesis of polypyrrole in the nanopattern of monolayer films of diblock copolymer micelles

A single-layered array of polystyrene-block-poly(4-vinylpyridine), PS-PVP, micelles in hexagonal order, fabricated by spin coating, was employed as a nanostructured template for synthesis of polypyrrole, a conducting polymer, in nanometer-sized domains. Oxidative catalysts of FeCl3 for the polymerization were selectively loaded in spherical PVP nanodamains so that they were hexagonally arranged over the film but confined in the nanometer range. The vapor-phase polymerization of pyrrole was localized in the PVP nanodomains, leading to a morphological transition from spherical to wormlike domains. In addition, the nanodomains containing polypyrrole were converted to open cavities by ethanol, a PVP block-selective solvent.     

Characterization of supercooling suppression of microencapsulated phase change material by using DSC

Supercooling suppression of microencapsulated n-tetradecane was measured using differential scanning calorimetry. Results indicate that the degree of supercooling is positively affected by the amount and type of nucleating agent present in bulk and microencapsulated n-tetradecane which it is used as a phase change material (MPCM). Results also demonstrate that the melting point of the n-tetradecane is fairly independent of nucleating agent concentration (0 – 4%). Conversely, the latent heat of fusion of n-tetradecane decreases considerably with nucleating agent amount and the initiation of crystallization point is inversely proportional to cooling rate.     

Cross-linking of CD4 induces cytoskeletal association of CD4 and p56lck

A membrane glycoprotein CD4 functions as a co-receptor of a T lymphocyte. The co-receptor function has been attributed to a protein tyrosine kinase, p56lck, which is activated upon CD4 binding to MHC molecule. In this study, we present evidences that one of the pathways through which CD4 transmits its signal is cytoskeleton association of p56lck tyrosine kinase as well as CD4 itself. Cytoskeletal association of both proteins is inhibited by a tyrosine kinase inhibitor, genistein, indicating that tyrosine protein kinase activation is important for cytoskeletal association of CD4 and p56lck. Cytoskeletal association of these proteins by CD4 cross-linking is not affected by inhibitors of protein kinase C nor PI3-kinase. Taken together, these results suggest that CD4 cross-linking activates a tyrosine kinase which then induces the simultaneous association of CD4 and p56lck with cytoskeleton.     

DFT-PCM studies of solvent effects on the cross-interaction constants in benzhydryl cation and anion formation

The Hammett rho+ and rho- values have been determined by varying substituent Y' for a given Y in the benzhydryl cation and anion formation (YH4C6-CH-C6H4Y' where C is a cationic or an anionic center) at the RHF/3-21G, RHF/6-31G, RHF/6-31+G, and B3LYP/6-31+G levels. The failure of RHF theory in accounting for the stabilization by delocalization leads to the smaller magnitudes of rho+ and rho- with electron-donating and -withdrawing substituents, Y, respectively, than the corresponding DFT values. The effects of solvent (benzene, dichloroethane, and acetonitrile) on the rho values were calculated by applying the conductor polarizable continuum model method to the DFT results. Finally, the cross-interaction constants (rho(YY)') and their variation with solvent were determined. As the polarity (dielectric constant, epsilon) of the solvent is increased, the magnitude of rho+ and rho- decreased, whereas that of rho(YY)' increased. Satisfactory correlations were obtained between rho values (rho+, rho- and rho(YY)') and the Kirkwood function f(k) (= epsilon - 1/2epsilon + 1). The rho(YY)' values are negative with a magnitude greater for the anionic (rho(YY)'-) than the cationic (rho(YY)'+) system.     

Selective reductive cleavage of 2-(phenylthio)pyrimidines for efficient synthesis of 2-(H)pyrimidines

A reaction method is described for selective reductive cleavage of 2-(phenylthio)pyrimidines using Pd(OAc)₂ and Et₃SiH to produce 2-(H)pyrimidines. The reaction proceeds efficiently with a wide range of 2-(phenylthio)pyrimidines. Considering the ready availability of 2-(arylthio)pyrimidines derived from oxidative CS cross coupling of 3,4-dihydropyrimidin-1H-2-thiones (DHPMs), this method unambiguously provides a shortcut to the preparation of 2-(H)pyrimidines with unprecedented diversity.     

Electrically anisotropic thin films consisting of polymeric and metallic nanolayers from self-assembled lamellae of diblock copolymers

We demonstrated the fabrication of electrically anisotropic thin films of alternating polymeric layers and metallic layers in nanometer thickness by utilizing self-assembled nanodomains of symmetric diblock copolymers. Nanometer-thick metal layers macroscopically parallel to the film plane were synthesized by electroless Ag deposition on Au nanoparticles selectively in one of the blocks. Every Ag/Au layer was completely separated by nanometer-thick polymer layers in the direction perpendicular to the film plane. Therefore, the conductivity of the film was highly anisotropic, differing by at least 8 orders of magnitude in directions parallel and perpendicular to the film plane, even though the in-plane conductivity (2.8 x10(-6) S/cm) was in the range of semiconductors. If self-assembled nanodomains of diblock copolymers were not employed, a serial layer-by-layer process for each layer would be required to fabricate such an electrically anisotropic thin film.     

Characteristics of photoexcitations and interfacial energy levels of regioregular poly(3-hexythiophene-2,5-diyl) on gold.

We have studied characteristics of photoexcitations and interfacial electronic structures of regioregular poly(3-hexlythiophene-2,5-diyl) (P3HT) on gold using two-photon photoemission (2PPE) spectroscopy. The vacuum level threshold is decreased by 1.3 eV from that of bare gold, attributable to interface dipole effects. The 2PPE spectral width narrows as the film thickness increases. We tentatively understand that this is due to destabilization of long-lived localized polaron, attributed to strong interchain interactions. On the basis of the analysis of the 2PPE distribution as a function of photon energy and laser power, the polaron level is located at 3.1 eV below the vacuum level. Using this value and a polaron level of 1.75 eV above the HOMO, we indirectly estimate an ionization potential of 4.85 eV for P3HT. An increase in two-photon photoemission yield with increasing photon energy is attributed to an enhanced electron-hole pair dissociation yield at higher photo-excitation levels. The decrease in power law slope with increasing film thickness is understood by Langevin recombination kinetics and saturation of photoexcitations.     

The [Ru(CN)5(pyS)](4-) complex, an efficient self-assembled monolayer for the cytochrome c heterogeneous electron transfer studies

The organothiol 4-mercaptopyridine (pyS) has been used extensively as facilitator for the assessment of heterogeneous electron transfer reaction of cytochrome c (cyt c). Its efficiency, however, is strongly affected by the instability of the adlayer due to the C-S bond cleavage. The K(4)[Ru(CN)(5)(pyS)].3H(2)O complex was synthesized and characterized aiming its utilization as an inorganic self-assembled monolayer (SAM) that would enhance the gold adlayer stability. The SAM formed by this complex onto gold (RupySAu) was characterized by spectroscopic (FTIRRAS and SERS) and electrochemical (LSV) techniques. The ex situ vibrational SERS and FTIRRAS spectra data of this SAM formed onto gold suggest a sigma interaction between the gold and sulfur atoms of the complex, inducing a perpendicular arrangement in relation to the surface normal. Additionally, SERS and FTIRRAS spectra performed for freshly prepared RupySAu adlayer and for large immersion times in the precursor solution have not shown any significant change that would reflect the degradation of the adlayer. The LSV desorption curves of this SAM indicate an enhancement in the C-S bond strength of the pyS ligand when coordinated to the [Ru(CN)(5)](3-) moiety. Comparatively to the data obtained for the desorption process of the pyS monolayer, the reductive desorption potential, E(rd), of the RupySAu presents a shift of -17 mV. This bond strength intensification leads to an increase in the stability of the monolayer. The voltammetric curves of cyt c carried out with the RupySAu electrode showed electrochemical parameters consistent with those reported for the native protein, as well as the maintenance of the electrochemical kinetic data after repetitive cycles. The results all together suggest that the pi back-bonding effect from the [Ru(CN)(5)](3-) metal center plays an important role in the stability of the RupySAu adlayer, improving the assessment of the cyt c heterogeneous electron transfer reaction.