Neighbouring Positions Research Articles

N^N^C-Cyclometalated rhodium(III) complexes with isomeric pyrimidine-based ligands: unveiling the impact of isomerism on structural motifs, luminescence and cytotoxicity.

The impact of isomerism of pyrimidine-based ligands and their rhodium(III) complexes with regard to their structures and properties was investigated. Two isomeric ligands, 4-(3,5-dimethyl-1H-pyrazol-1-yl)-2,5-diphenylpyrimidine (HL2,5) and 4-(3,5-dimethyl-1H-pyrazol-1-yl)-2,6-diphenylpyrimidine (HL2,6), were synthesized. The ligands differ by the degree of steric bulk: the molecular structure of HL2,5 is more distorted due to presence of pyrazolyl and phenyl groups in the neighbouring positions 4 and 5 of the pyrimidine ring. The complexation of HL2,5 and HL2,6 with RhCl3 leads to the sp2 C-H bond activation, resulting in the isolation of two complexes, [RhL2,5(Solv)Cl2]·nEtOH and [RhL2,6(Solv)Cl2]·nEtOH (Solv = H2O, EtOH), with the deprotonated forms of the pyrazolylpyrimidine molecules which coordinate the Rh3+ ion as N^N^C-tridentate ligands. According to DFT modelling, the mechanism of the deprotonation involves (i) the C-H bond breaking in the 2-phenyl group followed by the coordination of the C atom to the Rh atom, (ii) the protonation of coordinated chlorido ligand, (iii) the ejection of the HCl molecule and (iv) the coordination of the H2O molecule. The ligand isomerism has an impact on emission properties and cytotoxicity of the complexes. Although the excited states of the complexes effectively deactivate through S0/T1 and S0/S1 crossings associated with the cleavage of the weak H2O ligands upon excitation, the [RhL2,5(Solv)Cl2]·nEtOH complex appeared to be emissive in the solid state, while [RhL2,6(Solv)Cl2]·nEtOH is non-emissive at all. The complexes show significant cytotoxic activity against cancerous HepG2 and Hep2 cell lines, with the [RhL2,6(Solv)Cl2]·nEtOH complex being more active than its isomer [RhL2,5(Solv)Cl2]·nEtOH. On the other hand, noticeable cytotoxicity of the latter against HepG2 is supplemented by its non-toxicity against non-cancerous MRC-5 cells.

Internal calibration of Gaia BP/RP low-resolution spectra

Context. The full third Gaia data release will provide, for the first time, the calibrated spectra obtained with the blue and red Gaia slitless spectrophotometers (BP and RP, respectively). Gaia is a very complex mission and cannot be considered as a single instrument, but rather as many instruments. The two lines of sight with wide fields of view introduce strong variations of the observations across the large focal plane with more than one hundred different detectors. The main challenge when facing Gaia spectral calibration is that no lamp spectra or flat fields are available during the mission. Also, the significant size of the line spread function with respect to the dispersion of the prisms produces alien photons contaminating neighbouring positions of the spectra. This makes the calibration special and different from standard approaches. Aims. This work gives a detailed description of the internal calibration model for the spectrophotometric data used to obtain the content of the Gaia catalogue. The main purpose of the internal calibration is to bring all the epoch spectra onto a common flux and pixel (pseudo-wavelength) scale, taking into account variations over the focal plane and with time, producing a mean spectrum from all the observations of the same source. Methods. In order to describe all observations on a common mean flux and pseudo-wavelength scale, we constructed a suitable representation of the internally calibrated mean spectra via basis functions, and we described the transformation between non-calibrated epoch spectra and calibrated mean spectra via a discrete convolution, parametrising the convolution kernel to recover the relevant coefficients. Results. The model proposed here for the internal calibration of the Gaia spectrophotometric observations is able to combine all observations into a mean instrument to allow the comparison of different sources and observations obtained with different instrumental conditions along the mission and the generation of mean spectra from a number of observations of the same source. We derived a calibration model that can handle the self-calibrating nature of the problem. The output of this model provides the internal mean spectra, not as a sampled function (flux and wavelength), but as a linear combination of basis functions, although sampled spectra can easily be derived from them.

Quantum particle on dual root lattice in Weyl alcove

Classes of discrete quantum models that describe a free non-relativistic quantum particle propagating on rescaled and shifted dual root lattices inside closures of Weyl alcoves are constructed. Boundary conditions of the discrete quantum billiard systems on the borders of the Weyl alcoves are controlled by specific combinations of Dirichlet and Neumann walls that result from sign homomorphisms and admissible shifts inherent in generalized dual root lattice Fourier–Weyl transforms. The amplitudes of the particle’s jumps to neighbouring positions are controlled by a complex-valued dual root lattice hopping function with finite support. The solutions of the time-independent Schrödinger equation together with the eigenenergies of the quantum systems are explicitly determined. The matrix Hamiltonians and eigenenergies of the discrete models are exemplified for the rank two cases A 2 and C 2.

First-principles calculation of the effect of Mn element on the solid solubility of C in α-Fe

The mechanical and chemical properties of alloy materials strongly depend on their chemical composition. Among them, Mn is an essential alloying element. After adding Mn to the α-Fe matrix, Mn will substitute the position of Fe. In the Fe-C-Mn system, Mn atoms will interact with C atoms in their neighbouring positions, thereby affecting C atoms’ concentration distribution around them in equilibrium. Based on the first principles method, the interaction between the Mn and C atoms in α-Fe and its effect on C atoms’ solid solubility are calculated and analyzed. The results show an attractive force between the Mn atom and C atom at its nearest position. The interaction energy of the two gradually tends to 0 as the distance increases, especially when the distance exceeds 1.5×aα-Fe. The Mn element increases the solid solubility of the C element in the α-Fe matrix.

On regular reflection to Mach reflection transition in inviscid flow for shock reflection on a convex or straight wedge

The regular reflection to Mach reflection ( ) transition in inviscid perfect air for shock reflection over convex and straight wedges is investigated. Provided that the variation of shock intensity only has a second-order effect on the wave transition, the possible cases for the occurrence of the transition for curved shock reflection over a wedge are discussed. For a planar shock reflecting over a convex wedge, four different flow regions are classified and the mechanism of the disturbance propagation is interpreted. It is found that the flow-induced rarefaction waves exist between disturbances generated from neighbouring positions and isolate them. For a curved shock reflecting over a convex wedge, although the distributions of the flow regions are different from those in planar shock reflection, the analysis for the planar shock case can be extended to curved shock cases as long as the wedge is convex. When a diverging shock reflects off a straight wedge, the flow-induced rarefaction waves are absent. However, the disturbances generated earlier cannot overtake the reflection point before the pseudo-steady criterion is satisfied. In the cases considered, the flow in the vicinity of the reflection point will not be influenced by the unsteady flow caused by the shock intensity and the wedge angle variations. This is clearly a local property of the shock–wall interaction, no matter what the history of the shock trajectory is. For validation, extensive inviscid numerical simulations are performed, and the numerical results show the reliability of the pseudo-steady criterion for predicting the transition on a convex wedge.

Particle swarm optimisation with time varying cognitive avoidance component

Interactive cooperation of local best or global best solutions encourages particles to move towards them, hoping that better solution may present in the neighbouring positions around local best or global best. This encouragement does not guarantee that movements taken by the particles will always be suitable. Sometimes, it may mislead particles in the wrong direction towards the worst solution. Prior knowledge of worst solutions may predict such misguidance and avoid such moves. The worst solution cannot be known in prior and can be known only by experiencing it. This paper introduces a cognitive avoidance scheme to the particle swarm optimisation method. A very similar kind of mechanism is used to incorporate worst solutions into strategic movement of particles as utilised during incorporation of best solutions. Time varying approach is also extrapolated to the cognitive avoidance scheme to deal with negative effects. The proposed approach is tested with 25 benchmark functions of CEC 2005 special session on real parameter optimisation as well as with four other very popular benchmark functions.

A high temperature powder neutron diffraction structural study of the apatite-type oxide ion conductor, La 9.67Si 6O 26.5

High-resolution neutron powder diffraction studies of the oxide ion conductor La 9.67Si 6O 26.5 are reported for temperatures ranging between 25 and 900 °C. The best fit to the data was obtained for space group P6 3 and there was no evidence for any change in symmetry over the temperature range studied. Interstitial oxide ions are identified lying in sites similar to those predicted by previous computer modelling studies, and in agreement with structural studies on related materials. Furthermore, occupancy of these sites is enhanced by Frenkel-type disorder from neighbouring positions. The results thus add further weight to the interpretation that, in these apatite-type systems, the silicate substructure is important for the accommodation of interstitial oxide ions and their migration.

Retinotopic order in the absence of axon competition

The retinotectal projection has long been studied experimentally and theoretically, as a model for the formation of topographic brain maps. Neighbouring retinal ganglion cells (RGCs) project their axons to neighbouring positions in the optic tectum, thus re-establishing a continuous neural representation of visual space. Mapping along this axis requires chemorepellent signalling from tectal cells, expressing ephrin-A ligands, to retinal growth cones, expressing EphA receptors. High concentrations of ephrin A, increasing from anterior to posterior, prevent temporal axons from invading the posterior tectum. However, the force that drives nasal axons to extend past the anterior tectum and terminate in posterior regions remains to be identified. We tested whether axon-axon interactions, such as competition, are required for posterior tectum innervation. By transplanting blastomeres from a wild-type (WT) zebrafish into a lakritz (lak) mutant, which lacks all RGCs, we created chimaeras with eyes that contained single RGCs. These solitary RGCs often extended axons into the tectum, where they branched to form a terminal arbor. Here we show that the distal tips of these arbors were positioned at retinotopically appropriate positions, ruling out an essential role for competition in innervation of the ephrin-A-rich posterior tectum. However, solitary arbors were larger and more complex than under normal, crowded conditions, owing to a lack of pruning of proximal branches during refinement of the retinotectal projection. We conclude that dense innervation is not required for targeting of retinal axons within the zebrafish tectum but serves to restrict arbor size and shape.

Fluorenes as new molecular scaffolds for carbon–carbon σ-bond cleavage reaction: acylfluorenylation of arynes

Acyl and fluorenyl moieties are facilely installed into neighbouring positions of aromatic skeletons via C-C bond cleavage reaction using arynes.

Catalytic Cyclopropanation of Fluorine‐Containing Alkenes and Dienes with Diazomethane and Methyl Diazoacetate.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Catalytic Cyclopropanation of Fluorine‐Containing Alkenes and Dienes with Diazomethane and Methyl Diazoacetate

AbstractThe reactivities of various double bonds in fluorine‐containing unsaturated compounds toward cyclopropanation with diazomethane and methyl diazoacetate with catalysis by copper, rhodium and palladium compounds were studied. In general, the presence of fluorine atoms attached to the double bond or arranged at neighbouring positions exerted a suppressive effect on the cyclopropanation of this bond. As would be expected, diazomethane in the presence of palladium compounds primarily cyclopropanated less highly substituted double bonds. In the case of 2‐fluoro‐3‐methylbutadiene, the reaction took place at both of the double bonds. When methyl diazoacetate was used, [Rh2(OAc)4] was an efficient catalyst, yielding cyclopropanation products on monofluoro‐substituted double bonds in alkenes and cycloalkenes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

IUE and H I observations of gas components towards HD 174632*

IUE spectra of gas components towards the nearby star HD 174632 are reported, together with λ21-cm H I emission profiles obtained in the direction of the star and at several neighbouring positions some 1° from the star. These new observations reveal a far more complex velocity structure of the interstellar gas than that reported through optical spectroscopy by Crawford, with components at the approximate LSR velocities −68, −18, −7.7, +5,5 and +15,5 km s −1 . From the optical, UV and radio data, we show that the star is embedded in diffuse gas (+ 5,5 km s −1 component) of large anngular extent, which has a similar velocity to those of the Riegel & Crutcher cold cloud and the R CrA dark cloud

Site-directed cross-linking of mRNA analogues to 16S ribosomal RNA; a complete scan of cross-links from all positions between '+1' and '+16' on the mRNA, downstream from the decoding site.

mRNA analogues containing 4-thiouridine residues at selected sites were used to extend our analysis of photo-induced cross-links between mRNA and 16S RNA to cover the entire downstream range between positions +1 and +16 on the mRNA (position +1 is the 5'-base of the P-site codon). No tRNA-dependent cross-links were observed from positions +1, +2, +3 or +5. Position +4 on the mRNA was cross-linked in a tRNA-dependent manner to 16S RNA at a site between nucleotides ca 1402-1415 (most probably to the modified residue 1402), and this was absolutely specific for the +4 position. Similarly, the previously observed cross-link to nucleotide 1052 was absolutely specific for the +6 position. The previously observed cross-links from +7 to nucleotide 1395 and from +11 to 532 were however seen to a lesser extent with certain types of mRNA sequence from neighbouring positions (+6 to +10, and +10 to +13, respectively); no tRNA-dependent cross-links to other sites on 16S RNA were found from these positions, and no cross-linking was seen from positions +14 to +16. In each case the effect of a second cognate tRNA (at the ribosomal A-site) on the level of cross-linking was studied, and the specificity of each cross-link was confirmed by translocation experiments with elongation factor G, using appropriate mRNA analogues.

Details of the fine structure of nigeran revealed by the kinetics of its oxidation by periodate

A theoretical analysis of the kinetics of periodate oxidation of nigeran from Aspergillus niger revealed that, whereas 78% of the 4-linked d-glucopyranosyl residues were present as isolated singlets (with 3-linked residues in both neighbouring positions), the remaining 22% were present as isolated doublets. Sequences of more than two contiguous 4-linked residues were not detected.

Electronic rearrangement in the dilute vanadium and niobium hydrides

The electronic (or chemical) binding energy between one hydrogen atom and another hydrogen atom or a substitutional impurity in vanadium and niobium is estimated in a tight-binding formalism. The hydrogen-hydrogen binding energy is found to be considerably repulsive for nearest and next-nearest neighbouring positions. In the case of vanadium-based alloys we have estimated the binding energy between hydrogen and substitutional scandium, titanium, chromium and manganese. For niobium-based alloys we have estimated the binding energy between hydrogen and substitutional yttrium, zirconium and molybdenum. In both vanadium and niobium the binding energy between hydrogen and substitutional impurities located at nearest neighbouring positions is found to be attractive for impurities located to the left of the host metal in the periodic table and changes sign when the impurities are located to the right.

Histidine sensitive strain of the blue-green alga Nostoc muscorum: possible nif-his interactions

A variant strain of the nitrogen-fixing bluegreen alga Nostoc muscorum, displaying impairment in its elemental nitrogen dependent growth and complete inhibition of growth by L-histidine in otherwise nitrogen-free medium, has been isolated and characterized for its response to L-glutamic acid and L-glutamine in presence of other inorganic nitrogen sources. A model based on the possibility of nif-his interaction has been proposed to account for the observed behaviour of the strain. It is inferred that the two sets of genes may occupy neighbouring positions on the blue-green algal genome.

The unique green phenomenon and colour vision.

The mode of inheritance of the Unique Green phenomenon is investigated by a new technique. This involves a spectrometer which generates the stimulus in such a manner that the exact position that is neither blue-green nor yellow-green can be compared with neighbouring positions in the spectrum. This technique is used in conjunction with the single field techniques of Waaler to confrim the mode in inheritance he has suggested: that it is an effect carried on the X chromosome. The placing of the Unique Green point in the spectrum is shown to correlate with the mid-matching point in the blue-yellow axis on the Pickford Nicolson Anomaloscope. It is concluded that there may be a highly photolabile visual pigment present, which absorbs maximally at about the yellow region of the spectrum,

視知覚にわける散乱光効果について

The fact that the visual threshold of one stimulus figure is influenced by another one presented in spatio-temporal proximity to it has usually been regarded as products of some psychophysiological interaction or “induction”. The strength of the induction, or of the “field” influenced by one figure at a certain point around it, is usually determined in terms of the change, in general heightening, of the threshold of a small test spot (TS) presented there.For instance, Yokose, following Kohler's isomorphism, has studied this effect systematically, and has proved that the properties of psychophysiological “potential field” could exactly be predicted in terms of the formula derived from these of electromagnetic field. On the other hand, some have insisted that this effect is to be attributed to the stray light in the eye, and have called it the “glare effect”.In the present experiment, it was attempted to decide which of the two theories was correct. Four experiments were performed.(1) The threshold of TS was measured under two conditions: First, TS was exposed at the center of a dimmly illuminated disc, and second, at the center of the enclosed dark area by a bright ring. (In the former, the stimulus situation was that of direct adaptation, and in the latter, of indirect adaptation.) A value of the illuminance of the disc and of the ring respectively was determined experimentally so that the thresholds of TS was the same under both conditions. The ratio of illuminance of the disc to the ring thus obtained being kept constant, five levels of illuminance of these two figures were set in equal logarithmic interval. Thresholds of TS were measured at each of the five levels of illuminance for two figures. If the glare effect theory was correct, the threshold of TS at each of the five levels should be identical under both conditions. Our results confirmed the prediction.(2) Area-intensity interchangeability of glare effect was examined. As stimuli, contour figures of a ring and a square, or segmental parts of each were used. Illuminance of the stimuli was determined such as to increase in proportion to the decrease of the area. The test spot was always exposed at the center of the ring or square, or at the corresponding position for segment figures. No remarkable differences were found among these conditions.(3) Boynton has recently studied the nature of stray light in an excised eye, and obtained a regular functional relationship between the strength of stray light and distance. We have tried to compare following two conditions. One was to vary the distance of the disc figure from the centrally fixated TS at the fovea (glare stimulation). The other was to vary the illuminance of the disc, presented always at the central retina (figure-ground relationship). Illuminance conditions in our experiment were determined by calculation from Boynton's result, in order to show the strength of stray light at each distance. If Boynton's result was right, it would be expected that in the two conditions the adaptative liluminance at the position of TS should be equal. Results showed that this expectation was correct and the threshold of TS was quite the same under two conditions.(4) Optic disc is receptor-free. Even if light is casted there, no physiological changes occur. In this experiment, a light stimulus was casted to optic disc and to the neighbouring positions, while the thresholds of TS were measured always at the fovea. Results showed that the threshold of TS in this case was not lower than when a light stimulus was casted to any other positions. The threshold was merely a function of the distance from the light stimulus to TS.It was concluded that these findings could. be explained more plainly in terms of stray light rather than of physiological induction.