Strained graphene as a local probe for plasmon‐enhanced Raman scattering by gold nanostructures

We investigate with Raman spectroscopy how gold nanostructures of different shape, size and geometry locally modify a graphene cover layer through strain. The resulting phonon softening translates into frequency downshifts of up to 85 cm^–1 for the 2D‐mode of graphene. With spatially resolved and excitation dependent Raman measurements we demonstrate that the downshifted Raman peaks exclusively arise from strained graphene subject to plasmonic enhancement by the nanostructures. The signals arise from an area well below the size of the laser spot. They serve as a local probe for the interaction between graphene and intense light fields. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Assessing the attractive/repulsive force balance in axial cyclohexane C–Hax···Yax contacts: A combined computational analysis in monosubstituted cyclohexanes

The interactions of axial substituents in monosubstituted cyclohexane rings are studied in this work using an array of different computational techniques. Additionally, the anomalous axial preference for some bulky substituents is related to stabilizing dispersion interactions. We find that the C–H_ax···Y_ax contacts for various substituents with distances ranging from 2 to ～5 Å may include attractive dispersion forces that can affect the conformational equilibrium; these forces co‐exist with Pauli repulsive forces effected by Y_ax group due to van der Waals sphere penetration. At distances between 2 and 3 Å stabilizing electron transfer interactions were calculated and the combination of natural bond orbital and QTAIM analysis showed that, in certain cases, Y_ax = ^tBu, C_ax–O or C_ax = O or S_ax = O or C_ax = S this interaction can be characterized as an improper H‐bond. DFT‐D3 and non‐covalent interactions calculations (NCIs) in cyclohexane derivatives with Y_ax = SiOR₃ including H_Yax···H_cy surfaces at distances ranging between 4 and 6 Å suggest that dispersion has a clear effect on the experimentally observed stabilization of the axial conformer. NCIs computed from the reduced density gradient help to visually identify and analyze these interactions. © 2016 Wiley Periodicals, Inc.     

How wall properties control diffusion in grooved nanochannels: a molecular dynamics study

The effect of a geometrically-rough wall, amplified by its degree of wettability and stiffness on diffusion coefficient in cases of fluid flow in nanochannels is studied by non-equilibrium molecular dynamics. Diffusion coefficient values, either inside the grooves or as average channel values are affected by the rough wall characteristics. A significant anisotropy along the directions parallel and normal to the flow is observed inside the grooves, while a critical value of groove length below which this anisotropy is enhanced exists. Wall wettability is the property that affects diffusion the most and could be a means of controlling its behavior.     

Development of an impedimetric immunosensor based on electropolymerized polytyramine films for the direct detection of Salmonella typhimurium in pure cultures of type strains and inoculated real samples

The development of a faradic impedimetric immunosensor based on electropolymerized polytyramine (Ptyr) films for the detection of S. typhimurium in milk is described for the first time. Polyclonal anti-Salmonella was cross-linked, in the presence of glutaraldehyde vapors, on Ptyr-modified gold electrodes. The dielectric behaviour of Ptyr films was evaluated with capacitance measurements, while their stability in neutral aqueous solutions was examined with impedimetric measurements. The effect of the concentration of tyramine in the forming solution on both the sensitivity and the dynamic range of the resulted immunosensors was also investigated. The alteration of the interfacial features of the electrodes due to different modification or recognition steps, was measured by faradic electrochemical impedance spectroscopy in the presence of a hexacyanoferrate(II)/(III) redox couple. At samples containing a low initial concentration of 10 cfu mL⁻¹S. typhimurium, that actually defines the LOD of the immunosensors, signal changes of 33% and 88% were achieved after 3 and 10 h incubation, respectively. To achieve the working simplicity expected by a biosensor, immunoreaction was performed directly in cultures. This resulted in the elimination of various centrifugation and washing steps, which are used for the isolation of bacteria cells from the culture, thus making the proposed immunosensors promising candidates for on-site applications. Finally, the proposed immunosensors were successfully used for the detection of S. typhimurium in experimentally inoculated milk samples.     

Photoinduced Electron Transfer in Pentaammineruthenium(II) Complexes of 1-(4-Cyanophenyl)imidazole

A new bridging ligand, 1-(4-cyanophenyl)imidazole (CPI) has been prepared, as well as its N-methylated derivative 1-methyl-3-(4-cyanophenyl)imidazolium iodide (CPI-Me(+)I(-)). The mononuclear and binuclear complexes [(NH(3))(5)Ru-CPI-Me](3+) and [(NH(3))(5)Ru-CPI-Ru(NH(3))(5)](4+) have been obtained. Free CPI is planar, according to theoretical calculations (MMX and MNDO), and its luminescence properties suggest the occurence of a twisted internal charge transfer (TICT) state. The comparison of the two ruthenium complexes reveals the spectral and electrochemical features of coordination by the cyanophenyl or by the imidazole groups. Controlled oxidation of the binuclear complex [(NH(3))(5)Ru-CPI-Ru(NH(3))(5)](4+) yields the mixed valence species [(NH(3))(5)Ru-CPI-Ru(NH(3))(5)](5+) in which the ruthenium coordinated to the cyanophenyl group is ruthenium(II) while the ruthenium linked to imidazole is ruthenium(III). An intervalence band is observed at 640 nm (epsilon = 188), from which the effective metal-metal coupling through the bridging ligand is determined as 0.032 eV. This value is satisfactorily reproduced by a theoretical calculation using the effective Hamiltonian theory. Finally the binuclear complex exhibits a weak luminescence when excited either on the ligand band near 260 nm or on the metal-to-ligand charge transfer band near 410 nm. The CPI ligand is the first example of a TICT-forming species with appreciable coupling between metallic sites and can be considered as a first step toward a molecular switch.     

157-nm Laser ablation of polymeric layers for fabrication of biomolecule microarrays

A new methodology for protein microarray fabrication is proposed based on the ablation of polymer film using laser at 157 nm (F₂). The polymer has been selected among others with the criterion of negligible protein adsorption. Improved results have been obtained by pretreatment of the polymer surface with an inert protein. The use of 157-nm laser radiation allowed very good depth control during the polymeric layer ablation process. In addition the importance of laser ablation at 157 nm is based on the fact that irradiated surfaces indicate limited chemical change due to the fact that laser ablation at 157 nm is only photochemical, thus avoiding excessive surface heating and damage. Results of protein microarray fabrication are presented to illustrate the viability of the proposed method.     

New research findings in biotechnology for fuels and chemical production

Applied Biochemistry and Biotechnology -     

Deleting Outliers in Robust Regression with Mixed Integer Programming

In robust regression we often have to decide how many are the unusual observations, which should be removed from the sample in order to obtain better fitting for the rest of the observations. Generally, we use the basic principle of LTS, which is to fit the majority of the data, identifying as outliers those points that cause the biggest damage to the robust fit. However, in the LTS regression method the choice of default values for high break down-point affects seriously the efficiency of the estimator. In the proposed approach we introduce penalty cost for discarding an outlier, consequently, the best fit for the majority of the data is obtained by discarding only catastrophic observations. This penalty cost is based on robust design weights and high break down-point residual scale taken from the LTS estimator. The robust estimation is obtained by solving a convex quadratic mixed integer programming problem, where in the objective function the sum of the squared residuals and penalties for discarding observations is minimized. The proposed mathematical programming formula is suitable for small-sample data. Moreover, we conduct a simulation study to compare other robust estimators with our approach in terms of their efficiency and robustness.     

Sharp general local estimates for dyadic-like maximal operators and related Bellman functions

For each 1?q<p we precisely evaluate the main Bellman functions associated with the local Lp→Lq estimates of the dyadic maximal operator on Rn. Actually we do that in the more general setting of tree-like maximal operators and with respect to general convex and increasing growth functions. We prove that these Bellman functions equal to analogous extremal problems for the Hardy operator which can be viewed as a symmetrization principle for such operators. Under certain mild conditions on the growth functions we show that for the latter extremals exist (although for the original Bellman functions do not) and analyzing them we give a determination of the corresponding Bellman function.