Geometric and electronic structure of lanthanide orthophosphate nanoparticles determined with X-rays

The evolution of the geometric and electronic structures within the entire series of lanthanide orthophosphate nanoparticles ( approximately 2- approximately 5 nm) has been determined experimentally with X-ray diffraction and near edge X-ray absorption fine structure spectroscopy. In particular, the interplay between electronic structure, crystal morphology, and crystal phase has been systematically studied. A missing local order in the crystal structure accompanied by multiple ion sites in the nanoparticles was revealed to be due to the small crystal size and large surface contribution. All lanthanide ions were found to be in "3+" configuration and accommodated in three different crystallization states: the larger lanthanide ions (La, Ce, Pr, Nd, Sm) in the monoclinic phase, the smaller ones (Er, Tm, Yb, Lu) in the tetragonal phase, and the intermediate lanthanide ions (Eu, Gd, Tb, Dy, Ho) in a "mixed phase" between monoclinic and tetragonal phases.     

Fast light, slow light, and phase singularities: a connection to generalized weak values

We demonstrate that Aharonov-Albert-Vaidman weak values have a direct relationship with the response function of a system, and have a much wider range of applicability in both the classical and quantum domains than previously thought. Using this idea, we have built an optical system, based on a birefringent photonic crystal, with an infinite number of weak values. In this system, the propagation speed of a polarized light pulse displays both superluminal and slow light behavior with a sharp transition between the two regimes. We show that this system's response possesses two-dimensional, vortex-antivortex phase singularities. Important consequences for optical signal processing are discussed.     

Catalysis-based and protecting-group-free total syntheses of the marine oxylipins hybridalactone and the ecklonialactones A, B, and C

Concise and protecting-group-free total syntheses of the marine oxylipins hybridalactone (1) and three members of the ecklonialactone family (2-4) were developed. They deliver these targets in optically pure form in 14 or 13 steps, respectively, in the longest linear sequence; five of these steps are metal-catalyzed and four others are metal-mediated. The route to either 1 or 2-4 diverges from the common building block 22, which is accessible in 7 steps from 2[5H]furanone by recourse to a rhodium-catalyzed asymmetric 1,4-addition reaction controlled by the carvone-derived diene ligand 35 and a ring-closing alkene metathesis (RCM) catalyzed by the ruthenium indenylidene complex 17 as the key operations. Alternatively, 22 can be made in 10 steps from furfural via a diastereoselective three-component coupling process. The further elaboration of 22 into hybridalactone as the structurally most complex target with seven contiguous chiral centers was based upon a sequence of cyclopropanation followed by a vanadium-catalyzed epoxidation, both of which were directed by the same free hydroxy group at C15. The macrocyclic scaffold was annulated to the headgroup by means of a ring-closing alkyne metathesis reaction (RCAM). In response to the unusually high propensity of the oxirane of the targeted oxylipins for ring opening, this transformation had to be performed with complexes of the type [(Ar(3)SiO)(4)Mo≡CPh][K·OEt(2)] (43), which represent a new generation of exceedingly tolerant yet remarkably efficient catalysts. Their ancillary triarylsilanolate ligands temper the Lewis acidity of the molybdenum center but are not sufficiently nucleophilic to engage in the opening of the fragile epoxide ring. A final semireduction of the cycloalkyne formed in the RCAM step to the required (Z)-alkene completed the total synthesis of (-)-1. The fact that the route from the common fragment 22 to the ecklonialactones could follow a similar logic showcased the flexibility inherent to the chosen approach.     

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“Isonitramines”: Nitrosohydroxylamines or hydroxydiazenium oxides?

In the crystalline state and in solution isonitramines are hydroxydiazenium oxides.     

Interference of traveling nondiffracting beams

We study numerically the interference resulting from the superposition of two Bessel beams propagating in free space. We discuss how to obtain such beams and show the existence of the self-imaging effect during propagation. The evolution of the superimposed Bessel beams is analyzed on the basis of the evolution of the individual beams. Our exact numerical predictions contradict previous approximated analytical treatments, showing that they can lead to quantitatively wrong results and misleading conclusions.