The reaction of allene with β-diketonatoiridium(I) complexes: synthesis,properties and crystal structures of bis(η3-allyllic) complexes of iridium(III) and of iridocyclopentane derivatives

Allene reacts with compounds of the type (β-diketonato)Ir(η-C₈H₁₄)₂| (I) to give iridium(III) derivatives of formula (β-diketonato)IrC₁₂H₁₆ (II) in which an allene tetramer i.e. the 2,3,6,7-tetramethyleneoctane-1,8-diyl group, is bonded to the iridium atom by two η₃-allylic groups. The molecular structures of these complexes were deduced by ¹H NMR studies and by single-crystal X-ray analysis of (hfacac)IrC₁₂H₁₆ (IIb). The reactions of the complexes II with hydrogen and with CO are described.The reaction of (acac)Ir(η-C₈H₁₄)₂ with allene, at -78°C, gives a thermally unstable compound of probable stoichiometry (acac)Ir(C₃H₄)₄ (VI). Its low-temperature IR spectrum and its reaction with bromine indicate that VI contains two η²-bonded allene molecules and teh 3,4-dimethyleneiridocyclopentane moiety. VI reacts with pyridine with loss of an allene molecule to give an iridium(III) derivative of formula (acac)Ir(C₆H₈)(C₃H₄)py (IX). Complex IX was shown by single-crystal X-ray analysis to contain the 3,4-dimethyleneiridocyclopentane moiety and one η²-bonded allene molecule.The role of irido cycles as precursors of the bis(allylic) complexes II is discussed.     

Mining performance data through nonlinear PCA with optimal scaling

Performance data are usually collected in order to build well‐defined performance indicators. Since such data may conceal additional information, which can be revealed by secondary analysis, we believe that mining of performance data may be fruitful. We also note that performance databases usually contain both qualitative and quantitative variables for which it may be inappropriate to assume some specific (multivariate) underlying distribution. Thus, a suitable technique to deal with these issues should be adopted. In this work, we consider nonlinear principal component analysis (PCA) with optimal scaling, a method developed to incorporate all types of variables, and to discover and handle nonlinear relationships. The reader is offered a case study in which a student opinion database is mined. Though generally gathered to provide evidence of teaching ability, they are exploited here to provide a more general performance evaluation tool for those in charge of managing universities. We show how nonlinear PCA with optimal scaling applied to student opinion data enables users to point out some strengths and weaknesses of educational programs and services within a university. Copyright © 2009 John Wiley & Sons, Ltd.     

The structure of azomethine block copolymers from X-ray powder diffraction data

The crystal structure of a block copolymer, constituted by the periodic alternation of three thienyl- and two phenyl fragments separated by azomethine residues, has been determined and refined on powder X-ray diffraction data. Polymers of this kind are particularly interesting because of some evidences of electronic confinement, i. e. possible realization of multiple-quantum-dot sequences have been detected. Although the quality of the measured profile was poor, a molecular model is proposed giving a satisfactory agreement with the observed data.     

Assessing the influence of pH and cationic strength on i-motif DNA structure

The i-motif is a biologically relevant non-canonical DNA structure formed by cytosine-rich sequences. Despite the importance of the factors affecting the formation/stability of such a structure, like pH, cation type and concentration, no systematic study that simultaneously analysed their effect on the i-motif in vitro has been carried out so far. Therefore, here we report a systematic study that aims to evaluate the effect of these factors, and their possible interaction, on the formation of an i-motif structure. Our results confirm that pH plays the main role in i-motif formation. However, we demonstrate that the effect of the cation concentration on the i-motif is strictly dependent on the pH, while no significant differences are observed among the investigated cation types.

Graphical abstract

     

On decay estimates

We show here that decay estimates can be derived simply by integral inequalities. This result allows us to prove these kind of estimates, with an unified proof, for different nonlinear problems, thus obtaining both well known results (for example for the p-Laplacian equation and the porous medium equation) and new decay estimates.     

Resonances and spectral properties of detuned OPOs pumped by fluctuating sources

Twin-beam fluctuations are analyzed for detuned and mismatched OPO configurations. Resonances and frequency responses to the quantum noise sources (quantum and pump amplitude/phase fluctuations) are examined as functions of cavity decay rates, excitation parameters and detuning. The dependence of self- and mutual correlations of beam amplitudes and phases on detuning, mismatch and damping parameters is discussed. Received: 25 January 2002 / Revised version: 28 May 2002 / Published online: 15 November 2002 RID="*" ID="*"Corresponding author. Fax: +39-81/676-346, E-mail: alberto.porzio@na.infn.it     

The dimension spectrum of axiom a attractors

Some rigorous results on the dimension spectrum of expanding Markov maps of the interval are extended to Axiom AC ² diffeomorphisms of a compact two-dimensional manifold.