Site selectivity in the protonation of a phosphinito bridged Pt(I)-Pt(I) complex: a combined NMR and density-functional theory mechanistic study

The protonation of the dinuclear phosphinito bridged complex [(PHCy2)Pt(mu-PCy2){kappa(2)P,O-mu-P(O)Cy2}Pt(PHCy2)] (Pt-Pt) (1) by Br?nsted acids affords hydrido bridged Pt-Pt species the structure of which depends on the nature and on the amount of the acid used. The addition of 1 equiv of HX (X = Cl, Br, I) gives products of formal protonation of the Pt-Pt bond of formula syn-[(PHCy2)(X)Pt(mu-PCy2)(mu-H)Pt(PHCy2){kappaP-P(O)Cy2}] (Pt-Pt) (5, X = Cl; 6, X = Br; 8, X = I), containing a Pt-X bond and a dangling kappa P-P(O)Cy2 ligand. Uptake of a second equivalent of HX results in the protonation of the P(O)Cy2 ligand with formation of the complexes [(PHCy2)(X)Pt(mu-PCy2)(mu-H)Pt(PHCy2){kappaP-P(OH)Cy2}]X (Pt-Pt) (3, X = Cl; 4, X = Br; 9, X = I). Each step of protonation is reversible, thus reactions of 3, 4, with NaOH give, first, the corresponding neutral complexes 5, 6, and then the parent compound 1. While the complexes 3 and 4 are indefinitely stable, the iodine analogue 9 transforms into anti-[(PHCy2)(I)Pt(mu-PCy2)(mu-H)Pt(PHCy2)(I)] (Pt-Pt) (7) deriving from substitution of an iodo group for the P(OH)Cy2 ligand. Complexes 3 and 4 are isomorphous crystallizing in the triclinic space group P1 and show an intramolecular hydrogen bond and an interaction between the halide counteranion and the POH hydrogen. The occurrence of such an interaction also in solution was ascertained for 3 by (35)Cl NMR. Multinuclear NMR spectroscopy (including (31)P-(1)H HOESY) and density-functional theory calculations indicate that the mechanism of the reaction starts with a prior protonation of the oxygen with formation of an intermediate (12) endowed with a six membered Pt(1)-X...H-O-P-Pt(2) ring that evolves into thermodynamically stable products featuring the hydride ligand bridging the Pt atoms. Energy profiles calculated for the various steps of the reaction between 1 and HCl showed very low barriers for the proton transfer and the subsequent rearrangement to 12, while a barrier of 29 kcal mol(-1) was found for the transformation of 12 into 5.     

A structure‐preserving doubling algorithm for Lur'e equations

We introduce a numerical method for the numerical solution of the Lur'e equations, a system of matrix equations that arises, for instance, in linear‐quadratic infinite time horizon optimal control. We focus on small‐scale, dense problems. Via a Cayley transformation, the problem is transformed to the discrete‐time case, and the structural infinite eigenvalues of the associated matrix pencil are deflated. The deflated problem is associated with a symplectic pencil with several Jordan blocks of eigenvalue 1 and even size, which arise from the nontrivial Kronecker chains at infinity of the original problem. For the solution of this modified problem, we use the structure‐preserving doubling algorithm. Implementation issues such as the choice of the parameter γ in the Cayley transform are discussed. The most interesting feature of this method, with respect to the competing approaches, is the absence of arbitrary rank decisions, which may be ill‐posed and numerically troublesome. The numerical examples presented confirm the effectiveness of this method. Copyright © 2015 John Wiley & Sons, Ltd.     

Inductive and Deductive Justification of Knowledge: Flexible Judgments Underneath Stable Beliefs in Teacher Education

Personal epistemological beliefs are considered to play an important role for processes of learning and teaching. However, research on personal epistemology is confronted with theoretical issues as there is conflicting evidence regarding the structure, stability, and context-dependence of epistemological beliefs. We give evidence how theoretical and methodological issues can partly be resolved by distinguishing between relatively stable “epistemological beliefs” and situation-specific “epistemological judgments.” A qualitative content analysis of a series of semistructured interviews (study 1) with pre-service teachers, teachers, and teacher educators as well as a statistical analysis of pre-service teachers’ extensive answers in questionnaires (study 2), both on the topic of “mathematical discovery,” reveal not only beliefs of the participants but also different qualities of judgments. Therefore, in further research both aspects of beliefs should be considered in a more differentiated manner when categorizing belief structures.     

An Experimental Study of the Kinetics of the Reactions of Isopropyl,sec‐Butyl,and tert‐Butyl Radicals with Molecular Chlorine at Low Pressures (0.5–7.0 Torr) in the Temperature Range 190–480 K

In this work, we have measured the rate coefficients of the reactions of isopropyl (propan‐2‐yl), sec‐butyl (butan‐2‐yl), and tert‐butyl (2‐methylpropan‐2‐yl) radicals with molecular chlorine as a function of temperature (190–480 K). The experiments were done in a tubular laminar flow reactor coupled to a photoionization quadrupole mass spectrometer employing a gas‐discharge lamp for ionization. The radicals were homogeneously produced in the reactor by photolyzing suitable precursor molecules with 193‐nm pulsed exciplex laser radiation. The bimolecular rate coefficients were obtained by monitoring the radical decay signals in real time under pseudo–first‐order conditions. The rate coefficients of all three reactions showed negative temperature dependence. The bath gas used in the experiments was helium, and the rate coefficients appeared to be independent of the helium concentrations employed ([2.4–14] × 10¹⁶ cm^?3) for all three reactions. The rate coefficients of the reactions can be approximated in the studied temperature range by the following parameterizations: We estimate that the overall uncertainties of the measured rate coefficients are ±20%. We were able to observe 2‐chloropropane (i‐C₃H₇Cl) product for the i‐C₃H₇^● + Cl₂ reaction. No products were observed for the other two reactions, and the reasons for this are briefly discussed in the text.     

Photoswitching electron transport properties of an azobenzene containing thiol-SAM

The influence of conformational and electrical properties of azobenzene molecules on the electron transfer barrier properties of their SAMs was studied by SECM and ellipsometry.     

Europium(III)-chelates embedded in nanoparticles are protected from interfering compounds present in assay media

Lanthanide chelates are excellent labels in ligand binding assays due to their long lifetime fluorescence, which enables efficient background reduction using time-resolved measurement. In separation-free homogeneous assays, however, some compounds in the sample may cause quenching of the lanthanide fluorescence and extra steps are required before these samples can be measured. In this study we have evaluated whether europium chelates packed inside a polystyrene nanoparticle are better protected from the environment than individual Eu(III)-chelates, and do these particles have higher tolerance against known interfering compounds (bivalent metal ions and variation of pH). We also tested whether metal ions had any effect on a fluorescence resonance energy transfer (FRET) based detection of a bioaffinity binding reaction. The presence of metal ions or variation of pH did not affect the fluorescence of the Eu(III)-chelate dyed nanoparticles, while significant decrease of the fluorescence was detected with a 9-dentate Eu(III)-chelate. Metal ions also decreased the fluorescence lifetime of the 9-dentate Eu(III)-chelate from 0.960 to 0.050 ms. Coloured metal ions caused a minor decrease in sensitised emission generated by FRET when Eu(III)-chelate dyed nanoparticles were used as donor labels. The decreased signal was due to the absorption of the sensitised emission by the coloured metal ions, since the metal ions had no effect on the lifetime of the sensitised emission. Thus the Eu(III)-chelate dyed nanoparticles are preferred labels in homogeneous bioaffinity assays, when interfering compounds are known to be present.