Functionalized single graphene sheets derived from splitting graphite oxide

A process is described to produce single sheets of functionalized graphene through thermal exfoliation of graphite oxide. The process yields a wrinkled sheet structure resulting from reaction sites involved in oxidation and reduction processes. The topological features of single sheets, as measured by atomic force microscopy, closely match predictions of first-principles atomistic modeling. Although graphite oxide is an insulator, functionalized graphene produced by this method is electrically conducting.     

Brightness-normalized Partial Least Squares Regression for hyperspectral data

Developed in the field of chemometrics, Partial Least Squares Regression (PLSR) has become an established technique in vegetation remote sensing. PLSR was primarily designed for laboratory analysis of prepared material samples. Under field conditions in vegetation remote sensing, the performance of the technique may be negatively affected by differences in brightness due to amount and orientation of plant tissues in canopies or the observing conditions. To minimize these effects, we introduced brightness normalization to the PLSR approach and tested whether this modification improves the performance under changing canopy and observing conditions. This test was carried out using high-fidelity spectral data (400–2510 nm) to model observed leaf chemistry. The spectral data was combined with a canopy radiative transfer model to simulate effects of varying canopy structure and viewing geometry. Brightness normalization enhanced the performance of PLSR by dampening the effects of canopy shade, thus providing a significant improvement in predictions of leaf chemistry (up to 3.6% additional explained variance in validation) compared to conventional PLSR. Little improvement was made on effects due to variable leaf area index, while minor improvement (mostly not significant) was observed for effects of variable viewing geometry. In general, brightness normalization increased the stability of model fits and regression coefficients for all canopy scenarios. Brightness-normalized PLSR is thus a promising approach for application on airborne and space-based imaging spectrometer data.     

Qualit?tskontrolle im klinisch-chemischen Routinelaboratorium

Zusammenfassung Die Anwendung des Kontrollkartenverfahrens zur Qualitätskontrolle im klinisch-chemischen Laboratorium wird besprochen und an Hand von praktischen Beispielen erläutert. Neben den sogenannten Standardkontrollkarten (Mittelwertkontrollkarte zur Kontrolle der Richtigkeit, R-Kontrollkarte zur Kontrolle der Präzision) wird Prinzip und Funktion der kumulativen Summenkarte eingehend dargestellt, da dieser Kontrollkartentyp verschiedene Vorteile gegenüber den bisher verwendeten zeigt. Weiterhin werden diskutiert die Herstellung und Zusammensetzung der für die Kontrolle benötigten Kontroll-Lösungen, die zweckmäßige Festlegung der Kontrollgrenzen sowie Organisation und Kosten eines Qualitätskontrollsystems.

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Summary The use of the control chart method for quality control in clinico-chemical laboratories is discussed and explained by giving practical examples. Besides the so-called standard control charts (average chart for the control of accuracy, R-chart for the control of precision) principle and function of the cumulative sum chart is represented in detail. This type of control chart is in advantage to the charts existing hitherto. Furthermore, production and composition of the solutions needed for control, the choice of the control limits, organization and costs of a quality control system are discussed.

     

Influence of backbone conformations of human carbonic anhydrase II on carbon dioxide hydration: hydration pathways and binding of bicarbonate

In this study, the hydration of carbon dioxide and the formation of bicarbonate in human carbonic anhydrase II have been examined. From semiempirical QM/MM molecular dynamics studies, dominant conformations of the protein backbone, possibly contributing to the catalytic activity, have been isolated and further examined by means of density functional QM/MM methods. In agreement with experimental observations, a binding site for cyanate, which acts as an inhibitor, has been located, whereas for carbon dioxide, depending on the conformation of the protein environment, either a different binding site or no binding site has been found. In the latter case, carbon dioxide diffuses barrierless to the zinc-bound oxygen, and then a weakly bound bicarbonate complex is formed. The formed complex is characterized by a long C-O bond to the zinc-bound hydroxide. The nature of the calculated stationary points was verified by determination of vibrational frequencies. Finally, the dissociation of the formed bicarbonate from zinc has been considered. Therefore, a water molecule was included in the QM zone of the QM/MM hybrid potential, and minimization yielded a pentacoordinated intermediate. From a potential energy scan, an activation energy of 6.2 kcal/mol for dissociation of bicarbonate from Zn has been found.     

Formation of phenylmagnesium halides in toluene

Formation reactions of phenylmagnesium chloride and bromide in toluene in the presence of one or two equivalents of diethyl ether or THF were investigated kinetically. Also, the reaction in diethyl ether and in chlorobenzene was addressed. Kinetic features of the reactions are similar to those found previously for the formation of alkylmagnesium halides in toluene and consist of rapid formation of a disolvated Grignard reagent followed by a slower formation of a monosolvated reagent. The latter is able of catalyzing the conversion of different halides into Grignard reagents. However, the contribution of Wurtz-type side reactions is considerable except when THF is used in toluene. Involving the kinetic data and the activation parameters some details of the reaction mechanism were discussed.     

Dye-sensitized solar cells based on Fe N-heterocyclic carbene photosensitizers with improved rod-like push-pull functionality

A new generation of octahedral iron(ii)–N-heterocyclic carbene (NHC) complexes, employing different tridentate C^N^C ligands, has been designed and synthesized as earth-abundant photosensitizers for dye sensitized solar cells (DSSCs) and related solar energy conversion applications. This work introduces a linearly aligned push–pull design principle that reaches from the ligand having nitrogen-based electron donors, over the Fe(ii) centre, to the ligand having an electron withdrawing carboxylic acid anchor group. A combination of spectroscopy, electrochemistry, and quantum chemical calculations demonstrate the improved molecular excited state properties in terms of a broader absorption spectrum compared to the reference complex, as well as directional charge-transfer displacement of the lowest excited state towards the semiconductor substrate in accordance with the push–pull design. Prototype DSSCs based on one of the new Fe NHC photosensitizers demonstrate a power conversion efficiency exceeding 1% already for a basic DSSC set-up using only the I⁻/I₃⁻ redox mediator and standard operating conditions, outcompeting the corresponding DSSC based on the homoleptic reference complex. Transient photovoltage measurements confirmed that adding the co-sensitizer chenodeoxycholic acid helped in improving the efficiency by increasing the electron lifetime in TiO₂. Time-resolved spectroscopy revealed spectral signatures for successful ultrafast (<100 fs) interfacial electron injection from the heteroleptic dyes to TiO₂. However, an ultrafast recombination process results in undesirable fast charge recombination from TiO₂ back to the oxidized dye, leaving only 5–10% of the initially excited dyes available to contribute to a current in the DSSC. On slower timescales, time-resolved spectroscopy also found that the recombination dynamics (longer than 40 μs) were significantly slower than the regeneration of the oxidized dye by the redox mediator (6–8 μs). Therefore it is the ultrafast recombination down to fs-timescales, between the oxidized dye and the injected electron, that remains as one of the main bottlenecks to be targeted for achieving further improved solar energy conversion efficiencies in future work.

Iron-based photosensitizers for dye-sensitized solar cells with a rod-like push–pull design. Solar cell performance was limited by ultrafast (sub-ps) recombination, but yielded better performance than the homoleptic parent photosensitizer.     

Synthese und Molekülstruktur von [{Cp′(μ‐η1 : η5‐C5H3Me)Mo(μ‐AlRH)}2] (Cp′ = C5H4Me,R = iBu,Et)

Synthesis and Molecular Structure of [{Cp′(μ‐η¹ : η⁵‐C₅H₃Me)Mo(μ‐AlRH)}₂] (Cp′ = C₅H₄Me, R = ⁱBu, Et) [Cp′₂MoH₂] reacts with HAlR₂ to give [{Cp′(μ‐η¹ : η⁵‐C₅H₃Me)Mo(μ‐AlRH)}₂] (Cp′ = C₅H₄Me, R = ⁱBu ( 1 ), Et ( 2 )). Crystal structure determinations were carried out on [Cp′₂MoH₂] and 1 . 1 exhibits a direct Mo–Al bond (2.636(2) Å).     

A remark about the justification of the nonlinear Schrödinger equation in quadratic spatially periodic media

We prove the validity of a technical assumption necessary in a proof of the validity of the nonlinear Schr?dinger equation as envelope equation in quadratic spatially periodic media.