Synthesis and X-ray crystal structure of [2-(phosphinomethyl)ferrocenyl]diphenylphosphine

[2-(Phosphinomethyl)ferrocenyl]diphenylphosphine 2, is an air stable primary phosphine bearing a 1,2-disubstituted ferrocene framework, which has been prepared by reduction of the corresponding phosphonate. Confirmation of its structure has been obtained by X-ray single-crystals diffraction analysis. Despite its high stability toward oxidation, phosphine 2 still displays a normal coordinative behaviour toward [(p-cymene)RuCl₂]₂. The expected (p-cymene)RuCl₂(phosphine) complex is formed by coordination of the primary phosphine function, while the conceivably competitive complexation of the PPh₂ group was not observed.     

Uncertainty in aflatoxin B<Subscript>1</Subscript> analysis using information from proficiency tests

We describe how to calculate uncertainty in the determination of aflatoxin B₁ in nuts and maize using an HPLC method with prederivatisation with trifluoroacetic acid and fluorescence detection. The uncertainty is easily calculated using the information obtained from the participation in several proficiency tests. All the sources of uncertainty are grouped in two terms: (1) matrix variability, intermediate precision and sample heterogeneity, and (2) method concordance. This methodology has the advantage that no extra work needs to be done because all the information to calculate uncertainty comes from proficiency tests. The uncertainty values were calculated using samples whose concentration ranged between 2 and 20 g L^–1. The relative standard uncertainty computed for aflatoxin B₁ was 16.3%.     

Computational models of music perception and cognition I: The perceptual and cognitive processing chain

We present a review on perception and cognition models designed for or applicable to music. An emphasis is put on computational implementations. We include findings from different disciplines: neuroscience, psychology, cognitive science, artificial intelligence, and musicology. The article summarizes the methodology that these disciplines use to approach the phenomena of music understanding, the localization of musical processes in the brain, and the flow of cognitive operations involved in turning physical signals into musical symbols, going from the transducers to the memory systems of the brain. We discuss formal models developed to emulate, explain and predict phenomena involved in early auditory processing, pitch processing, grouping, source separation, and music structure computation. We cover generic computational architectures of attention, memory, and expectation that can be instantiated and tuned to deal with specific musical phenomena. Criteria for the evaluation of such models are presented and discussed. Thereby, we lay out the general framework that provides the basis for the discussion of domain-specific music models in Part II.     

Quantum confinement mediated enhancement of optical kerr effect in CdS x Se1−x semiconductor microcrystallites

We first discuss theoretically the enhancement of the optical nonlinearity due to quantum confinement in semiconductor-doped glasses. This quantum confinement mediated enhancement also pertains to the figure of merit x ⁽³⁾/, in which case it is due to a decrease in the spectral width rather than in an increase of the matrix elements. We then report on frequency and size-dependent measurements which confirm the theoretically expected enhancement due to quantum confinement.     

Application of unfold principal component analysis and parallel factor analysis to the exploratory analysis of olive oils by means of excitation-emission matrix fluorescence spectroscopy

Discrimination between virgin olive oils and pure olive oils is of primary importance for controlling adulterations. Here, we show the potential usefulness of two multiway methods, unfold principal component analysis (U-PCA) and parallel factor analysis (PARAFAC), for the exploratory analysis of the two types of oils. We applied both methods to the excitation-emission fluorescence matrices (EEM) of olive oils and then compared the results with the ones obtained by multivariate principal component analysis (PCA) based on a fluorescence spectrum recorded at only one excitation wavelength. For U-PCA and PARAFAC, the ranges studied were λ_ex=300-400 nm, λ_em=400-695 nm and λ_ex=300-400 nm, λ_em=400-600 nm. The first range contained chlorophylls, whose peak was much more intense than those of the rest of species. The second range did not contain the chlorophylls peak but only the fluorescence spectra of the remaining compounds (oxidation products and Vitamin E). The three-component PARAFAC model on the second range was found to be the most interpretable. With this model, we could distinguish well between the two groups of oils and we could find the underlying fluorescent spectra of three families of compounds.     

Synthesis of the complete carbocyclic skeleton of vinigrol

[reaction: see text] An efficient entry to the fully elaborated skeleton of vinigrol is described. The installation of the desired stereochemistry at C(12) and the construction of the eight-membered ring were achieved in one operation by a remarkably facile anionic oxy-Cope rearrangement of Z-isopropenyl isomer 24.     

Mechanism of the Stille reaction catalyzed by palladium ligated to arsine ligand: PhPdI(AsPh3)(DMF) is the species reacting with vinylstannane in DMF

The kinetics of the reaction of PhPdI(AsPh(3))(2) (formed via the fast oxidative addition of PhI with Pd(0)(AsPh(3))(2)) with a vinyl stannane CH(2)[double bond]CH[bond]Sn(n-Bu)(3) has been investigated in DMF. This reaction (usually called transmetalation step) is the prototype of the rate determining second step of the catalytic cycle of Stille reactions. It is established here that the transmetalation proceeds through PhPdI(AsPh(3))(DMF), generated by the dissociation of one ligand AsPh(3) from PhPdI(AsPh(3))(2). PhPdI(AsPh(3))(DMF) is the reactive species, which leads to styrene through its reaction with CH(2)[double bond]CH[bond]SnBu(3). Consequently, in DMF, the overall nucleophilic attack mainly proceeds via a mechanism involving PhPdI(AsPh(3))(DMF) as the central reactive complex and not PhPdI(AsPh(3))(2). The dimer [Ph(2)Pd(2)(mu(2)-I)(2)(AsPh(3))(2)] has been independently synthesized and characterized by its X-ray structure. In DMF, this dimer dissociates quantitatively into PhPdI(AsPh(3))(DMF), which reacts with CH(2)[double bond]CH[bond]SnBu(3). The rate constant for the reaction of PhPdI(AsPh(3))(DMF) with CH(2)[double bond]CH[bond]SnBu(3) has been determined in DMF for each situation and was found to be comparable.