Synthesis, crystal structures, and nonlinear optical (NLO) properties of new Schiff-base nickel(II) complexes. Toward a new type of molecular switch?

An H2L Schiff-base ligand that was obtained from the monocondensation of diaminomaleonitrile and 4-(diethylamino)salicylaldehyde is reported together with four related nickel(II) complexes formulated as [Ni(L)(L')] (L' = MePhCHNH2, iPrNH2, Py, and PPh3). Crystal structures have been solved for H2L, [Ni(L)(MePhCHNH2)], and [Ni(L)(iPrNH2)]. Surprisingly, the complexation process leads to the formation of a rather unusual nickel amido (-NH-Ni(II)) bond by deprotonation of the primary amine of H2L. A reduction of the quadratic hyperpolarizability (beta) from 38 x 10(-30) to 17.5 x 10(-30) cm5 esu(-1) is evidenced on H2L upon metal complexation by the electric-field-induced second-harmonic (EFISH) technique. Qualitative ZINDO/SCI quantum chemical calculations indicate that, in [Ni(L)(MePhCHNH2)], the beta orientation strongly depends on the laser wavelength. In particular, a beta rotation strictly equal to 90 degrees could be obtained with 1.022 microm incident light on passing from [Ni(L)(MePhCHNH2] to a hypothetical [Ni(HL)(MePhCHNH2]+ protonated complex, thus raising the possibility for a new type of molecular switch.     

Electroosmotic flow analysis of a branched U-turn nanofluidic device

In this paper, we present the analysis of electroosmotic flow in a branched -turn nanofluidic device, which we developed for detection and sorting of single molecules. The device, where the channel depth is only 150 nm, is designed to optically detect fluorescence from a volume as small as 270 attolitres (al) with a common wide-field fluorescent setup. We use distilled water as the liquid, in which we dilute 110 nm fluorescent beads employed as tracer-particles. Quantitative imaging is used to characterize the pathlines and velocity distribution of the electroosmotic flow in the device. Due to the device's complex geometry, the electroosmotic flow cannot be solved analytically. Therefore we use numerical flow simulation to model our device. Our results show that the deviation between measured and simulated data can be explained by the measured Brownian motion of the tracer-particles, which was not incorporated in the simulation.     

Relaying asymmetry of transient atropisomers of o-iodoanilides by radical cyclizations

Atropisomers of N-2 degrees -alkyl-N-acryloyl-2-iodoanlides have been resolved by chromatography and crystallization-induced asymmetric transformation. These molecules have atropisomerization barriers of 23-24 kcal/mol and return to equilibrium ratios over several hours at ambient temperature in solution. The transient chirality can be locked in by radical cyclizations, which provide N-2 degrees -alkyl-3-methyl-1,3-dihydroindol-2-ones with high levels of chirality transfer. The mechanistic model features a stereoselective aryl radical cyclization that is more rapid than the rotation of the N-aryl bond of the anilide.     

Regularity of the density of states in the Anderson model on a strip for potentials with singular continuous distributions

We derive regularity properties for the density of states in the Anderson model on a one-dimensional strip for potentials with singular continuous distributions. For example, if the characteristic function is infinitely differentiable with bounded derivatives and together with all its derivatives goes to zero at infinity, we show that the density of states is infinitely differentiable.     

Sur les ensembles linéairement connexes

Résumé Sur la droite projective, la notion de connexité est intuitive. Dans un espace projectif E_n, un ensemble est dit:linéairement connexe, si toutes ses traces sur les droites de E_n sont connexes. Deux ensembles complémentaires sont simultanément linéairement connexes ou non. On définit l'index (d'expansion linéaire intérieure) d'un ensemble linéairement connexe, possèdant des points intérieurs, comme le nombre maximum de dimensions des multiplicités linéaires qu'on peut mener à l'intérieur de l'ensemble. C'est uń nombre positif ou nul. Soient dans E_n deux ensembles complémentaires linéairement connexes possèdant chacun des points intérieurs: A_n et B_n. Leurs index respectifs α_n et β_n, satisfont à la relation: α_n + β_n +1 ≤ n. L'essentiel des résultats du Mémoire est le suivant: Si α_n et β_n sont tout deux nuls ou positifs, la frontière commune F_n, à A_n et B_n, estalgébrique et du secoud degré; si un seul est nul, F_n estconvexe, dégénérée ou non, mais pas nécessairement algébrique. Dans tous les cas la connaissance de α_n et β_n permet de préciser la nature de F_n. En particulier, si α_n + β_n +1 = n, F_n est sans singularité, et réciproquement.     

Some electronic properties of TMPD,CA and TCNQ molecules and their mono- and diions

Semiempirical RHF and UHF PPP calculations have been performed on three molecules involved in charge transfer systems. The same set of parameters has been used for the three ionic states of each molecule. Particular attention has been given to the choice of both number and type of configurations taken into account in the Cl treatment following the RHF SCF calculation; it is shown that they have a great influence on the results. Calculations carried out for several experimental molecular geometries showed that their influence is not always negligible. Experimental data have been collected in a critical way. The unique set of parameters gives satisfactory results for the optical spectra of the neutral molecules and monoions but gives a poor agreement for diions. Spin densities appeared to be very sensitive to both the methods of calculations and the variation of parameters.     

On Strong Uniform Distribution,III

We construct infinite dimensional chains that are ¹ good for almost sure convergence, which settles a question raised in this journal [7] and earlier in [6] by R. Nair. In [7] it was stated that the construction proposed in [4] was invalid. We complete the construction proposed in [4], where it is true that a piece of proof was forgotten. The technic remains the same and the completion of the proof rather natural.     

Imaging iron stores in the brain using magnetic resonance imaging

For the last century, there has been great physiological interest in brain iron and its role in brain function and disease. It is well known that iron accumulates in the brain for people with Huntington's disease, Parkinson's disease, Alzheimer's disease, multiple sclerosis, chronic hemorrhage, cerebral infarction, anemia, thalassemia, hemochromatosis, Hallervorden-Spatz, Down syndrome, AIDS and in the eye for people with macular degeneration. Measuring the amount of nonheme iron in the body may well lead to not only a better understanding of the disease progression but an ability to predict outcome. As there are many forms of iron in the brain, separating them and quantifying each type have been a major challenge. In this review, we present our understanding of attempts to measure brain iron and the potential of doing so with magnetic resonance imaging. Specifically, we examine the response of the magnetic resonance visible iron in tissue that produces signal changes in both magnitude and phase images. These images seem to correlate with brain iron content, perhaps ferritin specifically, but still have not been successfully exploited to accurately and precisely quantify brain iron. For future quantitative studies of iron content we propose four methods: correlating R2' and phase to iron content; applying a special filter to the phase to obtain a susceptibility map; using complex analysis to extract the product of susceptibility and volume content of the susceptibility source; and using early and late echo information to separately predict susceptibility and volume content.