Palladium-catalysed α-allylation of chiral sulfinimines derived from symmetric cyclic ketones

A diastereoselective mono-allylation reaction at the α-position of symmetric cyclic ketones by using tert-butanesulfinamide as a chiral auxiliary is explored. Excellent yields and high diastereomeric ratios were achieved under palladium(0) catalysis in the presence of a readily available achiral phosphine ligand.     

Unilateral NMR applied to the conservation of works of art

In conventional NMR, samples from works of art in sizes above those considered acceptable in the field of art conservation would have to be removed to place them into the bore of large superconducting magnets. The portable permanent-magnet-based systems, by contrast, can be used in situ to study works of art, in a noninvasive manner. One of these portable NMR systems, NMR-MOUSE®, measures the information contained in one pixel in an NMR image from a region of about 1 cm², which can be as thin as 2–3 µm. With such a high depth resolution, profiles through the structures of art objects can be measured to characterize the materials, the artists’ techniques, and the deterioration processes. A novel application of the technique to study a deterioration process and to follow up a conservation treatment is presented in which micrometer-thick oil stains on paper are differentiated and characterized. In this example, the spin–spin relaxation T ₂ of the stain is correlated to the iodine number and to the degree of cross-linking of the oil, parameters that are crucial in choosing an appropriate conservation treatment to remove them. It is also shown that the variation of T ₂ over the course of treatments with organic solvents can be used to monitor the progress of the conservation interventions. It is expected that unilateral NMR in combination with multivariate data analysis will fill a gap within the set of high-spatial-resolution techniques currently available for the noninvasive analysis of materials in works of art, where procedures to study the inorganic components are currently far more developed than those suitable for the study of the organic components.     

Enhanced second-harmonic generation by metal surfaces with nanoscale roughness: nanoscale dephasing, depolarization, and correlations

On the basis of spectral-expansion Green's function theory, we theoretically describe the topography, polarization, and spatial-coherence properties of the second-harmonic (SH) local fields at rough metal surfaces. The spatial distributions of the fundamental frequency and SH local fields are very different, with highly enhanced hot spots of the SH. The spatial correlation functions of the amplitude, phase, and direction of the SH polarization all show spatial decay on the nanoscale in the wide range of the metal fill factors. This implies that SH radiation collected from even nanometer-scale areas is strongly depolarized and dephased, i.e., has the nature of hyper-Rayleigh scattering, in agreement with recent experiments. The present theory is applicable to nanometer-scale nonlinear-optical illumination, probing, and modification.     

Absolute phase effect in ultrafast optical responses of metal nanostructures

We predict that nonlinear ultrafast electron photoemission by strong optical fields and, potentially, other nonlinear optical responses of metal nanostructures significantly depend on the absolute (carrier–envelope) phase of excitation pulses. Strong enhancement of the local optical fields produces these responses at excitation intensities lower by order(s) of magnitude than for known systems. Prospective applications include control of ultrafast electron emission and electron injection into nanosystems. A wider class of prospective applications is the determination of the absolute phase of pulses emitted by lasers and atoms, molecules, and condensed matter at relatively low intensities. PACS  78.67.-n; 78.47.+p; 79.60.Jv; 73.20.Mf     

Combining two-directional synthesis and tandem reactions: desymmetrisation by intramolecular cycloaddition/triazoline fragmentation

A tandem azide formation/intramolecular cycloaddition/triazoline fragmentation/Michael addition, which results in a non-symmetrical quinolizidine from an acyclic symmetrical precursor, is presented.     

Fractals: giant impurity nonlinearities in optics of fractal clusters

A theory of nonlinear optical properties of fractals is developed. Giant enhancement of optical susceptibilities is predicted for impurities bound to a fractal. This enhancement occurs if the exciting radiation frequency lies within the absorption band of the fractal. The giant optical nonlinearities are due to existence of high local electric fields in the sites of impurity locations. Such fields are due to the inhomogeneously broadened character of a fractal spectrum, i.e. partial conservation of individuality of fractal-forming particles (monomers). The field enhancement is proportional to theQ-factor of the resonance of a monomer. The effects of coherent anti-Stokes Raman scattering (CARS) and phase conjugation (PC) of light waves are enhanced to a much greater degree than generation of higher harmonics. In a general case the susceptibility of a higher-order is enhanced in the maximum way if the process includes “substraction” of photons (at least one of the strong field frequencies enters the susceptibility with the minus sign). Alternatively, enhancement for the highest-order harmonic generation (when all the photons are “accumulated”) is minimal. The predicted phenomena bear information on spectral properties of both impurity molecules and a fractal. In particular, in the CARS spectra a narrow (with the natural width) resonant structure, which is proper to an isolated monomer of a fractal, is predicted to be observed.