Toward an objective measure for a "stream segregation" task

A procedure to estimate the relative contribution of "A" and "B" tones for a stream-segregation task is described. Listeners detected a delay in the penultimate A tone in an A-B-A-B sequence of tones. For small A-B frequency separations, for most listeners, classification models based on both the A and B tones were superior to models based on just the A tones. For large frequency separations, models based on just the A tones were superior, indicating the A and B tones were segregated. The results also revealed individual differences in the strategies adopted to complete the task.     

Introducing axial chirality into mesoionic 4,4'-bis(1,2,3-triazole) dicarbenes

Mesoionic 4,4'-bis(1,2,3-triazole-5,5'-diylidene) Rh(I) complexes having a C2 chiral 4,4'-axis were accessed from 3-alkyltriazolium salts in virtually complete de. Their structure and configurational integrity were assessed by NMR spectroscopy, X-ray crystallography, and chiral HPLC. Computational analysis of the MICs involved in the reaction suggested the formation of a highly stable and unprecedented cation-carbene intermediate species, which could be evidenced experimentally by cyclic voltammetry analysis.     

Dihydrogen generation from amine/boranes: synthesis, FT-ICR, and computational studies

A Fourier transform ion cyclotron resonance spectrometry (FT-ICR) study of the gas-phase protonation of ammonia-borane and sixteen amine/boranes R(1)R(2)R(3)N-BH(3) (including six compounds synthesized for the first time) has shown that, without exception, the protonation of amine/boranes leads to the formation of dihydrogen. The structural effects on the experimental energetic thresholds of this reaction were determined experimentally. The most likely intermediate and the observed final species (besides H(2)) are R(1)R(2)R(3)N-BH(4)(+) and R(1)R(2)R(3)N-BH(2)(+), respectively. Isotopic substitution allowed the reaction mechanism to be ascertained. Computational analyses ([MP2/6-311+G(d,p)] level) of the thermodynamic stabilities of the R(1)R(2)R(3)N-BH(3) adducts, the acidities of the proton sources required for dihydrogen formation, and the structural effects on these processes were performed. It was further found that the family of R(1)R(2)R(3)N-BH(4)(+) ions is characterized by a three-center, two-electron bond between B and a loosely bound H(2) molecule. Unexpected features of some R(1)R(2)R(3)N-BH(4)(+) ions were found. This information allowed the properties of amine/boranes most suitable for dihydrogen generation and storage to be determined.     

Synthesis of platinum(II) metallocycles using microwave-assisted heating

An efficient microwave-assisted self-assembly of dinuclear platinum metallocycles is reported. The reactions proceed to afford the products with high purity and yields within 3-4 h. We have used this methodology to synthesize a new 14.75 ? × 14.75 ? molecular square. The solid-state structure showed a perfect alignment of the squares along the c axis.     

Analytical and numerical methods for the stability analysis of linear fractional delay differential equations

In this paper, several analytical and numerical approaches are presented for the stability analysis of linear fractional-order delay differential equations. The main focus of interest is asymptotic stability, but bounded-input bounded-output (BIBO) stability is also discussed. The applicability of the Laplace transform method for stability analysis is first investigated, jointly with the corresponding characteristic equation, which is broadly used in BIBO stability analysis. Moreover, it is shown that a different characteristic equation, involving the one-parameter Mittag-Leffler function, may be obtained using the well-known method of steps, which provides a necessary condition for asymptotic stability. Stability criteria based on the Argument Principle are also obtained. The stability regions obtained using the two methods are evaluated numerically and comparison results are presented. Several key problems are highlighted.     

A first low‐resolution difference Fourier map of phosphorus in a membrane protein from near‐edge anomalous diffraction

Crystal diffraction of three membrane proteins (cytochrome bc₁ complex, sarcoplasmic reticulum Ca²⁺ ATPase, ADP‐ATP carrier) and of one nucleoprotein complex (leucyl tRNA synthetase bound to tRNAleu, leuRS:tRNAleu) was tested at wavelengths near the X‐ray K‐absorption edge of phosphorus using a new set‐up for soft X‐ray diffraction at the beamline ID01 of the ESRF. The best result was obtained from crystals of Ca²⁺ ATPase [adenosin‐5′‐(β,γ‐methylene) triphosphate complex] which diffracted out to 7 Å resolution. Data were recorded at a wavelength at which the real resonant scattering factor of phosphorus reaches the extreme value of ?20 electron units. The positions of the four triphosphates of the monoclinic unit cell of the ATPase have been obtained from a difference Fourier synthesis based on a limited set of anomalous diffraction data.     

Studies on the Stability of the Human Cone Visual Pigments†

The retina of vertebrates contains two kinds of photoreceptor cells, rods and cones, which contain their specific visual pigments that are responsible for scotopic and photopic vision, respectively. In cone photoreceptor cells, there are three types of color pigments: blue, green and red, each with a distinctive absorption maximum. The goal of this investigation was to identify optimal conditions under which these pigments could be obtained and isolated in a stable form, thereby facilitating structural studies using high‐resolution approaches. For this purpose, all three human cone opsins were initially expressed in mammalian cells, reconstituted with 11‐cis retinal, detergent solubilized, purified and their stability compared with rod rhodopsin. As all three pigments showed dramatically reduced stability relative to rhodopsin, site‐directed mutagenesis was used in an attempt to engineer stability into the green cone pigment. The mutations introduced some structural motifs and sites of posttranslational modification present in rhodopsin, as well as amino acid substitutions that have been found to stabilize the rod opsin apo‐protein. We also modified the hydrophobic environment of the green cone pigment by varying the detergent and detergent/lipid composition used during solubilization and purification, and compared them with the retinal reconstituted pigment in membranes. Our results show that these changes do not significantly improve the inherent instability of the human cone pigments, and in some cases, lead to a decrease in stability and protein aggregation. We conclude that further efforts are required to stabilize the human cone pigments in a form suitable for high‐resolution structural studies.     

Preparation of (1R,1′R)-1,1′-(anthracene-9,10-diyl)bis(2,2,2-trifluoroethanamine): a chiral diamine with low basicity

A new chiral diamine with low basicity was synthesized in enantiopure form. (1R,1′R)-1,1′-(Anthracene-9,10-diyl)bis(2,2,2-trifluoroethanamine) was obtained by means of several stereochemically controlled reactions. The structures of the title compound and several intermediates were studied.