Mikrobestimmung von Kupfer

Ohne Zusammenfassung     

Adsorption and decomposition of cyclohexanone (C6H10O) on Pt(111) and the (2 × 2) and (√3 × √3)r30°-Sn/Pt(111) surface alloys

Adsorption and decomposition of cyclohexanone (C(6)H(10)O) on Pt(111) and on two ordered Pt-Sn surface alloys, (2 × 2)-Sn/Pt(111) and (√3 × √3)R30°-Sn/Pt(111), formed by vapor deposition of Sn on the Pt(111) single crystal surface were studied with TPD, HREELS, AES, LEED, and DFT calculations with vibrational analyses. Saturation coverage of C(6)H(10)O was found to be 0.25 ML, independent of the Sn surface concentration. The Pt(111) surface was reactive toward cyclohexanone, with the adsorption in the monolayer being about 70% irreversible. C(6)H(10)O decomposed to yield CO, H(2)O, H(2), and CH(4). Some C-O bond breaking occurred, yielding H(2)O and leaving some carbon on the surface after TPD. HREELS data showed that cyclohexanone decomposition in the monolayer began by 200 K. Intermediates from cyclohexanone decomposition were also relatively unstable on Pt(111), since coadsorbed CO and H were formed below 250 K. Surface Sn allowed for some cyclohexanone to adsorb reversibly. C(6)H(10)O dissociated on the (2 × 2) surface to form CO and H(2)O at low coverages, and methane and H(2) in smaller amounts than on Pt(111). Adsorption of cyclohexanone on (√3 × √3)R30°-Sn/Pt(111) at 90 K was mostly reversible. DFT calculations suggest that C(6)H(10)O adsorbs on Pt(111) in two configurations: by bonding weakly through oxygen to an atop Pt site and more strongly through simultaneously oxygen and carbon of the carbonyl to a bridged Pt-Pt site. In contrast, on alloy surfaces, C(6)H(10)O bonds preferentially to Sn. The presence of Sn, furthermore, is predicted to make the formation of the strongly bound C(6)H(10)O species bonding through O and C, which is a likely decomposition precursor, thermodynamically unfavorable. Alloying with Sn, thus, is shown to moderate adsorptive and reactive activity of Pt(111).     

A trans-AB-bacteriochlorin building block

Synthetic bacteriochlorins are of interest for fundamental studies in photochemistry because of their strong absorption in the near-infrared spectral region and close similarity with natural bacteriochlorophylls. A de novo route to 5-methoxybacteriochlorins entails self-condensation of a dihydrodipyrrin-acetal, which in turn is prepared from a 2-(2-nitroethyl)pyrrole species and an α,β-unsaturated ketone-acetal (e.g., 1,1-dimethoxy-4-methylpent-3-en-2-one). Here, four new results are reported concerning the synthesis of substituted bacteriochlorins. First, a new, scalable route to 1,1-dimethoxy-4-methylpent-3-en-2-one removes a significant previous impediment to the overall route. Second, the new route was employed to gain access to new α,β-unsaturated ketones and corresponding dihydrodipyrrins bearing alternative substituents in place of the dimethoxy unit. Third, a dihydrodipyrrin bearing a 1,3-dioxolan-2-yl moiety afforded the bacteriochlorin (30% yield) containing a 2-hydroxyethoxy substituent at the 5-position. Fourth, subsequent bromination proceeded regioselectively at the 15-position to give a trans-(5,15)-AB-bacteriochlorin building block. The linear 5,15-substitution pattern is attractive for a number of molecular designs. The results taken together afford deeper understanding of the scope and limitations of the de novo route and also advance the capabilities for tailoring synthetic bacteriochlorins.     

Non-hemolytic α-AApeptides as antimicrobial peptidomimetics

We report a new class of peptide mimetics, α-AApeptides, that display broad-spectrum activity against both Gram-negative and Gram-positive bacteria and fungi. With non-hemolytic activity, resistance to protease hydrolysis, and easy sequence programmability, α-AApeptides may emerge as a novel class of antibiotics.     

A coordination polymer of (Ph3P)AuCl prepared by post-synthetic modification and its application in 1-hexene/n-hexane separation

PCM-10 is a porous phosphine coordination material based on Ca(II) and tris(p-carboxylated) triphenylphosphine. The material provides a unique 3-dimensional surface of P(III) Lewis base sites, which is ideal for post-synthetic functionalization. The addition of Au(I) yields an advanced material that can selectively adsorb 1-hexene over n-hexane at room temperature.     

Synthesis of terminally substituted stilbene-tolane liquid crystals

Methods for synthesizing substituted alkyl and fluoro stilbene-tolane (PTPDP) liquid crystal materials are presented. These compounds show a slightly higher birefringence than the analogous bistolanes, but higher melting points and heats of fusion. Potential applications of these compounds for optical communications and displays are discussed.     

PhotochemCAD‡: A Computer-Aided Design and Research Tool in Photochemistry

A database of absorption and fluorescence spectra, including molar absorption coefficients and fluorescence quantum yields, has been compiled for 125 photochemically relevant compounds. An accompanying program enables calculation of oscillator strengths, natural radiative lifetimes, transition dipole moments, Forster energy-transfer rates, multicomponent analysis, simulations of fluorescence spectra upon energy transfer among linear arrays of pigments, calculations of blackbody radiator curves at different temperatures and Lorentzian and Gaussian peak distributions. The program runs under Windows 95 and is equipped with extensive literature references and help features.     

Legierungen

Ohne Zusammenfassung