Performance of (consensus) kNN QSAR for predicting estrogenic activity in a large diverse set of organic compounds

A novel method (in the context of quantitative structure-activity relationship (QSAR)) based on the k nearest neighbour (kNN) principle, has recently been introduced for the derivation of predictive structure-activity relationships. Its performance has been tested for estimating the estrogen binding affinity of a diverse set of 142 organic molecules. Highly predictive models have been obtained. Moreover, it has been demonstrated that consensus-type kNN QSAR models, derived from the arithmetic mean of individual QSAR models were statistically robust and provided more accurate predictions than the great majority of the individual QSAR models. Finally, the consensus QSAR method was tested with 3D QSAR and log P data from a widely used steroid benchmark data set.     

Island growth in submonolayer deposition with aggregation and fragmentation

Island growth is studied in the case of island aggregation and break-up during submonolayer deposition. It is demonstrated that the island size distributions are of the scaling form and the mean island size has a power-law behaviour corresponding to hyperthermal deposition conditions. The corresponding scaling exponents are analytically derived and compared with the simulations by the revised particle coalescence method developed here. The scaling exponents are found to depend only on the homogeneity exponents of aggregation and fragmentation kernels.Received: 4 September 2003, Published online: 30 January 2004PACS: 68.55.-a Thin film structure and morphology - 68.35.Fx Diffusion; interface formation - 36.40.Sx Diffusion and dynamics of clustersPresent addressM. Rusanen: Institut Français du Pétrole, Groupe de Modélisation Moléculaire, BP 311, 92852 Rueil-Malmaison, France;Present address J. Asikainen: HRS F27, ETH Zentrum, 8092 Zürich, Switzerland     

Evaluation of surface composition of surface active water-alcohol type mixtures: a comparison of semiempirical models

We study adsorption at planar liquid-vapor interface of surface active binary mixtures and test three well-known models for the composition of surface phase. The models were originally presented by Guggenheim. These are compared to results for model fluids from density functional theory (DFT). The model of Laaksonen and Kulmala is in best agreement with DFT calculations. Surface mole fraction of the solute component from the Guggenheim model exceeds one for a mixture with high surface activity. The failure of the Guggenheim model is also evident in our calculations for water-methanol, water-ethanol, and water-n-propanol mixtures.     

Allenyl ester precursors for 1H-inden-1-ol carboxylates: comparisons with their propargylic equivalents having terminal alkyne functions

The reactivity of allenyl carboxylates, Ar(R¹)CCCH(O₂CR²) and their isomeric equivalents the terminal propargylic carboxylates, ArC(R¹)(O₂CR²)CCH, in gold-catalyzed carbocyclization to indenes provides information on 1,3 and 1,2-carboxylate shifts associated with their interconversion. Allenyl carboxylates transform specifically to 1H-inden-1-yl carboxylates in high yields, under Au^I-catalysis. Their equivalent propargylic carboxylates give complex mixtures of indene isomers and elimination products. Mechanistic tests indicate that interconversion of the terminal propargylic carbonate to its allene is at best slow in this case.     

Dynamical scaling and kinetic roughening of single valued fronts propagating in fractal media

We consider the dynamical scaling and kinetic roughening of single-valued interfaces propagating in 2D fractal media. Assuming that the nearest-neighbor height difference distribution function of the fronts obeys Lévy statistics with a well-defined algebraic decay exponent, we consider the generalized scaling forms and derive analytic expressions for the local scaling exponents. We show that the kinetic roughening of the interfaces displays intrinsic anomalous scaling and multiscaling in the relevant correlation functions. We test the predictions of the scaling theory with a variety of well-known models which produce fractal growth structures. Results are in excellent agreement with theory. For some models, we find interesting crossover behavior related to large-scale structural instabilities of the growing aggregates. Received 22 May 2002 Published online 19 November 2002     

An SN2′ displacement approach to allenyl acetates

Reaction of cuprates derived from R³MgBr/CuI/LiBr (R³ = n-alkyl) with R¹CCCH(O₂CR²)₂ (R¹ = sp² hybridised substituent, R² = mainly Me, alkyl, Ph) provides access to allenyl esters R¹R³CCCH(O₂CR²) (51-88%). Such species are not accessible via rearrangement of precursor propargylic R¹R³C(O₂CR²)CCH.     

Performance of (consensus) kNN QSAR for predicting estrogenic activity in a large diverse set of organic compounds

A novel method (in the context of quantitative structure–activity relationship (QSAR)) based on the k nearest neighbour (kNN) principle, has recently been introduced for the derivation of predictive structure–activity relationships. Its performance has been tested for estimating the estrogen binding affinity of a diverse set of 142 organic molecules. Highly predictive models have been obtained. Moreover, it has been demonstrated that consensus-type kNN QSAR models, derived from the arithmetic mean of individual QSAR models were statistically robust and provided more accurate predictions than the great majority of the individual QSAR models. Finally, the consensus QSAR method was tested with 3D QSAR and log?P data from a widely used steroid benchmark data set.     

Effects of intermediate zinc pulses on properties of TiN and NbN films deposited by atomic layer epitaxy

The reasons for the improvements gained by using intermediate zinc pulses in atomic layer epitaxy growth of TiN and NbN films were examined by a comprehensive characterization and comparison of films prepared from TiCl₄ or NbCl₅ and NH₃ with and without zinc. The characterization techniques used comprise time-of-flight elastic recoil detection analysis, secondary ion mass spectrometry, Rutherford backscattering spectrometry, nuclear resonance broadening, proton backscattering spectrometry, deuteron induced reactions, proton induced X-ray emission, atomic force microscopy, scanning electron microscopy, X-ray diffraction, and Hall effect and reflectance measurements. The effect of zinc was found to be manifold: both compositional and structural changes were observed. In the case of TiN the major improvement gained by using zinc was significantly decreased oxygen contamination whereas a marked increase of grain size was the dominant effect observed with NbN. A clear correlation between the compositional and structural changes and the improvements of the electrical properties was established.