Ferrocene compounds. XXV. Synthesis and characterization of ferrocene‐containing oligoamides,their precursors,and analogues

A general method for preparation of ferrocene‐containing monoamines (5–7) and diamines (10, 11) starting from the corresponding quaternary ammonium iodide 3 and ferrocene mono‐ (4) and dithiaaliphatic acids (8, 9) was developed. Amines obtained have been characterized as acet‐ and benzamides (12–15). The oligoamide precursors (16, 17, 22, 23) were synthesized by reactions of succinic or glutaric anhydride with amines (6, 7, 10, 11). Their conversion into oligoamide analogs (20, 21, 25) failed. The desired diamides (20, 21) were prepared by condensation of amines (6, 7) with alkanedioyl chlorides, (CH₂)_n(COCl)₂ (n = 0, 1, 2, 3). Reactions of diamine 10 with succinic or glutaric anhydride gave amino acids 28—formal monomers for the planned oligomerization. Oligomers 29 were synthesized by condensation of equimolar amounts of diamines 10 and the above mentioned alkanedioyl chlorides in dichloromethane at 0°C. The structure of oligomers 29 was indicated from their IR and ¹H‐NMR spectra in comparison with the model substances 12–28. The degree of polymerization of compounds 29 was determined by ¹H‐NMR end‐group analysis (DP_n = 4–6). © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 25–36, 1999     

On Stochastic Extremum Seeking via Adaptive Perturbation–Demodulation Loop

In this paper, we propose a stochastic approximation algorithm for optimization of functions based on an adaptive extremum seeking method. The essence of this method is to approximate the gradient direction by introduction of a probing sequence, that is added to approximations and subsequently demodulated using an adaptive gain. Assuming that the probing and the demodulation signals are martingale difference sequences with adaptive diminishing gains, it is proved that the approximations converge almost surely to the optimizing value, under mild constraints on the measurement disturbance, and without assuming a priori boundedness of the approximation sequence. The measurement disturbance can contain a stochastic component, as well as a mean-square bounded deterministic component. The stochastic component can be nonstationary colored noise or a state-dependent random sequence.     

Suppression of self-induced flavor conversion in the supernova accretion phase

Self-induced flavor conversions of supernova (SN) neutrinos can strongly modify the flavor-dependent fluxes. We perform a linearized flavor stability analysis with accretion-phase matter profiles of a 15M[symbol: see text] spherically symmetric model and corresponding neutrino fluxes. We use realistic energy and angle distributions, the latter deviating strongly from quasi-isotropic emission, thus accounting for both multiangle and multienergy effects. For our matter and neutrino density profile we always find stable conditions: flavor conversions are limited to the usual Mikheyev-Smirnov-Wolfenstein effect. In this case one may distinguish the neutrino mass hierarchy in a SN neutrino signal if the mixing angle θ13 is as large as suggested by recent experiments.     

Absence of Platinophilic Interactions in a Series of Tetracyanoplatinates Incorporating Cyclic Amines

Abstract  

Three novel compounds have been synthesized and structurally characterized: [1,10-Hphen]₂Pt(CN)₄·2H₂O (1a) space group P2₁/n, a = 8.73070(17) ?, b = 15.4609(2) ?, c = 9.82661(19) ?, β = 103.252(2)°; [2,2′-Hbipy]₂Pt(CN)₄·2H₂O (1b) space group P2₁/n, a = 7.0859(14) ?, b = 12.940(2) ?, c = 13.7486(19) ?, β = 100.708(16)°; K₂[Pt(CN)₄]·2phen (phen = 1,10-phenanthroline) (2) space group P2₁/c, a = 8.1393(4) ?, b = 20.4050(9) ?, c = 8.4085(4) ?, β = 105.284°. All three structures contain isolated [Pt(CN)₄]²⁻ ions and they all illustrate the absence of Pt⋯Pt interactions due to the presence of bulky cyclic amines or ammoniums. The structures of 1a and 1b contain large organic cations, 2,2′-bipyridinium and 1,10-phenanthrolinium, respectively while compound 2 contains neutral 1,10-phenanthroline molecules co-crystallized between the potassium tetracyanoplatinate framework.     

Characterization of a two-color pump-probe setup at FLASH using a velocity map imaging spectrometer

We report on the implementation of a high-count-rate charged particle imaging detector for two-color pump-probe experiments at the free electron laser in Hamburg (FLASH). In doing so, we have developed a procedure for finding the spatial and temporal overlap between the extreme UV free electron laser (FEL) pulses and the IR pulses, which allows for complete alignment of the setup in situations where the region of overlap between the FEL and the IR is not easily accessible by means of imaging optics.     

Model systems with extreme aspect ratio, tunable geometry, and surface functionality for a quantitative investigation of the Lotus effect

Superhydrophobicity and superhydrophilicity of surfaces are key properties for fabrication of self-cleaning surfaces (Lotus effect). It is well known that the mechanism behind this is based on the surface roughness and surface functionalization. To obtain an understanding of the details of the underlying mechanism, a metal system based on a eutectic is suggested. In this study, a wide range tunability of its needlelike narrow size distributed nanostructure is demonstrated. The length of the needles as well as their density can be varied independently. In addition, an important parameter for the wettability, the roughness, is related directly to the growth parameters, which lead to excellent controllable and reproducible eutectic structures. Simply by varying etching time very high aspect ratios can be achieved, allowing studying the interaction of the very long needles with liquids. Moreover, the surface functionality can be tuned by RF-magnetron sputtering of PTFE onto the metal needles. As those layers can be very thin, our system allows, in principle, studying the transition from a metal to a polymer surface using submonolayers. Furthermore, the first contact angle measurements on the nanostructured and functionalized eutectic structures are presented and discussed.     

Spectroscopic and potentiometric studies on derivatized natural humic acid.

Isolated soil humic acid (HA) and commercial Aldrich HA were derivatized by esterification with methanol-thionyl and acetylation with acetic anhidride, in order to obtain derivatives with selectively blocked carboxyl and phenol groups, respectively. Results obtained by FT-IR spectroscopy and potentiometry show that the methanol-thionyl procedure is a selective, specific and efficient route for blocking carboxyl groups. The good correlation between results obtained by direct potentiometry after HA esterification and by classical calcium-acetate and baryta exchange methods suggests that esterification followed by direct acid-base potentiometric titration can be used as a method for the estimation of carboxyl and phenol group contents. Phenol groups can not be specifically identified by the acetylation method, due to the low selectivity of the acetylation method. The average values of apparent and intrinsic pK of underivatized and derivatized HAs confirm decrease in ionizable groups content due to derivatization and their values are related to the different chemical structures of the acids.     

Positron transport in CF4 and N2/CF4 mixtures

Investigations on freestanding binary and ternary clusters of Fe _x Co _y Ir _z (x + y + z = 5, 6) are carried out using ab initio density functional theory techniques. The geometry, chemical order, binding energy, magnetic moment and electronic structure of the clusters are analyzed for the entire range of composition. Composition dependent structural transition is observed in the five atom clusters, while octahedral geometry prevailed in clusters with six atoms. Both the clusters show increment in binding energy with the increase in number of heterogeneous bonds. Analysis based on the chemical order parameter indicates that clusters favor mixing rather than segregation. The clusters exhibit ferromagnetic ordering and the inter-dependence of optimal cluster geometry to the magnetic moments and electronic structure is observed.