Effects of seeing the interlocutor on the production of prosodic contrasts (L)

This study investigated whether the production of prosodic focus and phrasing contrasts was modified when interlocutors could only hear each other [auditory only (AO)], compared to when they could hear and see each other [face to face (FTF)]. The prosodic characteristics of utterances produced by six talkers were examined using both acoustic and perceptual measures (ratings of the degree of focus or clarity of the statement-question contrast). The acoustic measures showed a range of differences between narrow focus and between phrasing contrasts and some of these differences were greater in the AO setting than the FTF one. The listener's ratings of focus and phrasing showed a clear difference between the AO and FTF conditions, with perceptual attributes of both narrow focus and echoic question phrasing being rated as clearer in the AO condition. To explain these results it is proposed that talkers compensate for the lack of visual prosodic cues in the AO condition by taking extra care (relative to FTF conditions) to ensure the effective transmission of prosodic cues.     

Adsorption of bromobenzene on periodically stepped and nonstepped NiO(100)

Periodically stepped NiO(100) surfaces were prepared and characterized with low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption (TPD). Two vicinal NiO(100) single-crystal samples were cut, oriented, and polished with regular, repeating monatomic steps in six-atom or seven-atom terrace widths. LEED diffraction patterns showed characteristic spot-splitting that corresponded to the appropriate terrace and step height. The nonstepped and stepped NiO(100) surfaces were exposed to bromobenzene at 130 K first to produce a molecularly adsorbed monolayer species and then, with increased exposure, a multilayer adsorbate. An additional adsorbate species, observed only on the stepped surfaces, was found to desorb at 145 K by two competing pathways. One pathway, which saturates at low coverages, leaves bromine behind on the substrate and results in dehalogenation. The other pathway yields molecular desorption at 145 K, but is only observed in detectable amounts after the dehalogenation pathway is saturated. On both stepped and nonstepped NiO(100) substrates, adsorbed bromine resulting from dehalogenation processes appears as nickel bromide, determined by the Br 3p XPS data.     

PNA/dsDNA complexes: site specific binding and dsDNA biosensor applications

The ability of peptide nucleic acids (PNA) to form specific higher-order (i.e., three- and four-stranded) complexes with DNA makes it an ideal structural probe for designing strand-specific dsDNA biosensors. Higher-order complexes are formed between a dye-labeled charge-neutral PNA probe and complementary dsDNA. Addition of a light-harvesting cationic conjugated polymer (CCP) yields supramolecular structures held together by electrostatic forces that incorporate the CCP and the dye-labeled PNA/DNA complexes. Optimization of optical properties allows for excitation of the CCP and subsequent fluorescence resonance energy transfer (FRET) to the PNA-bound dye. In the case of noncomplementary dsDNA, complexation between the probe and target does not occur, and dye emission is weak. The binding between PNA and noncomplementary and complementary dsDNA was examined by several methods. Gel electrophoresis confirms specificity of binding and the formation of higher-order complexes. Nano-electrospray mass spectrometry gives insight into the stoichiometric composition, including PNA/DNA, PNA(2)/DNA, PNA/DNA(2), and PNA(2)/DNA(2) complexes. Finally, structural characteristics and binding-site specificity were examined using ion mobility mass spectrometry in conjunction with molecular dynamics. These results give possible conformations for each of the higher-order complexes formed and show exclusive binding of PNA to the complementary stretch of DNA for all PNA/DNA complexes. Overall, the capability and specificity of binding indicates that the CCP/PNA assay is a feasible detection method for dsDNA and eliminates the need for thermal denaturing steps typically required for DNA hybridization probe assays.     

trans-Platinum planar amine compounds with [N2O2] ligand donor sets: effects of carboxylate leaving groups and steric hindrance on chemical and biological properties

Replacement of NH3 by a planar amine L to give trans-[PtCl2(L)(L')] (L = NH3, L'= pyridine or substituted pyridine, quinoline, isoquinoline, thiazole; L = L'= pyridine, thiazole), greatly enhances the cytotoxicity of the transplatinum geometry. The "parent" compound trans-[PtCl2(NH3)2] is therapeutically inactive. Modification of the ligands to an [N2O2] donor set, where O represents an acetate leaving group, enhances the aqueous solubility while retaining the cytotoxicity of the parent chloride compounds. The effect of two mutual trans leaving groups with weak trans influence is to impart remarkable chemical stability on the structure. This strategy is analogous to the use of the inert dicarboxylate leaving groups in the clinical compounds carboplatin and oxaliplatin. In this paper, systematic modification of the steric effects of carrier pyridine groups and, especially, carboxylate leaving groups in trans-[Pt(O2CR)2(NH3)(pyr)] is shown to modulate aqueous solubility and hydrolysis to the activated aqua species. The results presented here demonstrate the utility of the "carboxylate strategy" in "fine-tuning" the chemical and pharmacokinetic properties in the design of clinically relevant transplatinum complexes.     

The central role of metal coordination in selenium antioxidant activity

Oxidative DNA damage occurs in vivo by hydroxyl radical generated in metal-mediated Fenton-type reactions. Cell death and mutation caused by this DNA damage are implicated in neurodegenerative and cardiovascular diseases, cancer, and aging. Treating these conditions with antioxidants, including highly potent selenium antioxidants, is of growing interest. Gel electrophoresis was used to directly quantify DNA damage inhibition by selenium compounds with copper and H(2)O(2). Selenocystine inhibited all DNA damage at low micromolar concentrations, whereas selenomethionine showed similar inhibition at 40 times these concentrations, and 2-aminophenyl diselenide showed no effect. DNA damage inhibition by these selenium compounds does not correspond to their glutathione peroxidase activities, and UV-vis and gel electrophoresis results indicate that selenium-copper coordination is essential for DNA damage inhibition. Understanding this novel metal-coordination mechanism for selenium antioxidant activity will aid in the design of more potent antioxidants to treat and prevent diseases caused by oxidative stress.     

Palladium(0)-catalyzed synthesis of chiral ene-allenes using alkenyl trifluoroborates

Enantioenriched allenes serve as chiral transfer reagents, making them attractive synthetic targets. Herein, the synthesis of enantioenriched allenes utilizing a Pd(0)-catalyzed cross-coupling reaction of propargylic carbonates and phosphates with alkenyl trifluoroborates is reported. Di-, tri-, and tetrasubstituted allenes were synthesized in moderate to high optical yields. Several racemic allenes possessing various functional groups were also synthesized.     

Synthesis of homoallylic amines via the palladium-catalyzed decarboxylative coupling of amino acid derivatives

Protected homoallylic amines are synthesized by the decarboxylative coupling of alpha-amino acid derivatives. The catalytic C-C bond-forming reaction relies on the bioinspired decarboxylative metalation of alpha-amino acids to produce alpha-amino anion equivalents. The alpha-amino anion equivalents are intercepted by pi-allyl palladium electrophiles to produce substituted homoallylic amines.     

Electron donor-bridge-acceptor molecules with bridging nitronyl nitroxide radicals: influence of a third spin on charge- and spin-transfer dynamics

Appending a stable radical to the bridge molecule in a donor-bridge-acceptor system (D-B-A) is potentially an important way to control charge- and spin-transfer dynamics through D-B-A. We have attached a nitronyl nitroxide (NN*) stable radical to a D-B-A system having well-defined distances between the components: MeOAn-6ANI-Ph(NN*)-NI, where MeOAn = p-methoxyaniline, 6ANI = 4-(N-piperidinyl)naphthalene-1,8-dicarboximide, Ph = phenyl, and NI = naphthalene-1,8:4,5-bis(dicarboximide). MeOAn-6ANI, NN*, and NI are attached to the 1, 3, and 5 positions of the Ph bridge. Using both time-resolved optical and EPR spectroscopy, we show that NN* influences the spin dynamics of the photogenerated triradical states (2,4)(MeOAn(+)*-6ANI-Ph(NN*)-NI(-)*), resulting in slower charge recombination within the triradical compared to the corresponding biradical lacking NN*. The observed spin-spin exchange interaction between the photogenerated radicals MeOAn(+)(*) and NI(-)(*) is not altered by the presence of NN*, which only accelerates radical pair intersystem crossing. Charge recombination within the triradical results in the formation of (2,4)(MeOAn-6ANI-Ph(NN*)-(3)NI), in which NN* is strongly spin-polarized. Normally, the spin dynamics of correlated radical pairs do not produce a net spin polarization; however, net spin polarization appears on NN* with the same time constant as describes the photogenerated radical ion pair decay. This effect is attributed to antiferromagnetic coupling between NN* and the local triplet state (3)NI, which is populated following charge recombination. This requires an effective switch in the spin basis set between the triradical and the three-spin charge recombination product having both NN* and (3)NI present.     

Accurate potential energy curves for F(-)-Rg (Rg = He-Rn): spectroscopy and transport coefficients

High-quality ab initio potential energy curves are presented for the F(-)-Rg series (Rg = He-Rn). Calculations are performed at the CCSD(T) level of theory, employing d-aug-cc-pV5Z quality basis sets, with "small core" relativistic effective core potentials being used for Kr-Rn. The quality of the curves is judged by agreement with recent high-level calculations in the case of F(-)-He and F(-)-Ne and by excellent agreement with mobility data for the systems F(-)-Rg (Rg = He-Xe). Except for these recent high-level calculations on the two lightest systems, we are able to deduce that all other previous potentials for the whole set of these systems are inadequate. We also present spectroscopic information for the titular species, derived from our potential energy curves.     

Spin dynamics of photogenerated triradicals in fixed distance electron donor-chromophore-acceptor-TEMPO molecules

The stable free radical 2,2,6,6-tetramethylpiperidinoxyl (TEMPO, T*) was covalently attached to the electron acceptor in a donor-chromophore-acceptor (D-C-A) system, MeOAn-6ANI-Phn-A-T*, having well-defined distances between each component, where MeOAn = p-methoxyaniline, 6ANI = 4-(N-piperidinyl)naphthalene-l,8-dicarboximide, Ph = 2,5-dimethylphenyl (n = 0,1), and A = naphthalene-1,8:4,5-bis(dicarboximide) (NI) or pyromellitimide (PI). Using both time-resolved optical and EPR spectroscopy, we show that T* influences the spin dynamics of the photogenerated triradical states 2,4(MeOAn+*-6ANI-Phn-A-*-T*), resulting in modulation of the charge recombination rate within the triradical compared with the corresponding biradical lacking T*. The observed spin-spin exchange interaction between the photogenerated radicals MeOAn+* and A-* is not altered by the presence of T*, which interacts most strongly with A-* and accelerates radical pair intersystem crossing. Charge recombination within the triradicals results in the formation of 2,4(MeOAn-6ANI-Phn-3*NI-T*) or 2,4(MeOAn-3*6ANI-Phn-PI-T*) in which T* is strongly spin polarized in emission. Normally, the spin dynamics of correlated radical pairs do not produce a net spin polarization; however, the rate at which the net spin polarization appears on T* closely follows the photogenerated radical ion pair decay rate. This effect is attributed to antiferromagnetic coupling between T* and the local triplet state 3NI, which is populated following charge recombination. These results are explained using a switch in the spin basis set between the triradical and the three-spin charge recombination product having both T* and 3*NI or 3*6ANI present.