Intense femtosecond extreme ultraviolet pulses by using a time-delay-compensated monochromator

Extreme-ultraviolet pulses, produced by high-order harmonic generation, have been spectrally selected by a time-delay-compensated grating monochromator. Temporal characterization of the harmonic pulses has been obtained using cross-correlation method: pulses as short as 8 fs, with high photon flux, have been measured at the output of the monochromator.     

Theoretical study of the reaction mechanisms involved in the thermal intramolecular reactions of 1,6-fullerenynes

Substitution of a H atom by an alkyl group on the terminal carbon of the alkyne moiety of 1,6-fullerenynes has a strong impact on the products of the reaction undergone by this species after thermal treatment. While the reaction of 1,6-fullerenynes bearing an unsubstituted alkyne moiety results in the cycloaddition of the alkyne group to the fullerene double bond leading to cyclobutene-fused derivatives, the presence of an alkyl substituent leads to the formation of allenes. In the present work, we have performed an exhaustive theoretical analysis of all possible reaction mechanisms leading to cyclobutene-fused derivatives and allenes to offer an explanation of the reactivity differences observed. The results obtained show that formation of cyclobutene-fused derivatives occurs through a stepwise diradical reaction mechanism, while allene formation proceeds through a concerted way involving an uncommon intramolecular ene process. For the 1,6-fullerenynes bearing a substituted alkyne, the ene reaction path leading to allenes has an energy barrier somewhat lower than the stepwise diradical mechanism for the cyclobutene-fused derivative formation, thus explaining the outcome of the reaction.     

A CNDO/2 STUDY OF ROTATIONAL BARRIERS IN THIOAMIDOPYRIDINES

Abstract

Barriers to rotation about C[sbnd]C and C[sbnd]N bonds in 2-, 3- and 4-thioamidopyridine have been calculated by the CNDO/2 method. Comparisons between computed and experimental data are used to assess reliability of the calculations.     

Structural evidence of differential forms of nanosponges of beta-cyclodextrin and its effect on solubilization of a model drug

Nanosponges (NS) are a recently developed class of hyper-branched polymers, nano-structured to form three dimensional meshwork; obtained by reacting cyclodextrins with a cross linker like diphenyl carbonate. Herein, we report an anomalous behavior of NS with regards to physical and morphological characteristics and drug encapsulation behavior by minor synthetic modification. Two distinct forms viz. crystalline and para-crystalline of NS were identified and extensively characterized by use of high resolution transmission electron microscopy (HR-TEM), X-ray powder diffraction (XRPD), scanning electron microscope, atomic force microscope, optical microscope and Fourier transform infra-red attenuated total reflectance spectroscopy (FTIR-ATR). Dimension of the crystal lattice was found to be equal to 0.61 nm. Higher magnifications clearly showed a zone axis with a hexagonal symmetry as that of beta-cyclodextrin. XRPD patterns were in concurrence with the HR-TEM results. Solubility studies with a model drug dexamethasone (DEX) showed more than three folds increase in the solubility of the drug in the crystalline NS as compared to the para-crystalline ones. Percent drug association and drug loading for DEX was found to be higher in the crystalline type of NS. An In vitro drug kinetic study evidenced a faster release of DEX from the crystalline type NS. The particle sizes of the formulations were as follows: crystalline NS: 688.6 ± 38.0 nm, para-crystalline NS: 702.2 ± 21.2 nm with polydispersity indices of 0.155 and 0.132; zeta-potential of ?26.55 ± 1.7 and ?23.42 ± 2.1 respectively. Differential scanning calorimetry and thermogravimetric analysis revealed that both forms encapsulated the drug satisfactorily. FTIR-ATR and Raman spectroscopy showed weak interactions. Crystallinity of NS was thus found to be an important factor in solubilization, in vitro kinetics and encapsulation behavior and can be tuned to give a tailored drug release profile or formulation characteristics.     

Orthogonal geometry of wave interaction in a photorefractive crystal for linear phase demodulation

We present a novel configuration of an interferometer which is implemented by using vectorial wave mixing in the orthogonal geometry of wave interaction in a cubic photorefractive crystal, for the detection of small phase transients. The orthogonal geometry of wave interaction allows the linear regime of the phase-to-intensity transformation even when phase transients are encrypted in a depolarized wave without using any polarizing element. The use of a depolarized beam without a polarizing element strongly diminishes the noise level, thus increasing the sensitivity to phase transients.     

Was Poisson's spot an intentional discovery?

This short historical note deals with the phenomenological aspect of diffraction patterns in obstacles having central or axial symmetry. In the special case of the circular symmetry the light spot at the centre of the shadow is called “Poisson's spot” and it is often quoted as a crucial moment in the development of the theories about light. In this paper the phenomenon is seen only as a typical case of poor knowledge of the scientific Literature and of an unattentive observation of the men involved.