Geometry and Conformation of Thietanium Ions from Diffraction Data and Ab Initio Calculations

Four‐membered ring thiosulfonium ions may be obtained quantitatively and under mild conditions by anionotropic rearrangement of C‐(tert‐butyl)‐substituted thiiranium ion precursors. Thus, t‐4‐(tert‐butyl)‐r‐1,2,2,c‐3‐tetramethylthietanium tetrafluoroborate or hexachloroantimonate ( 2a or 2b , resp.) were formed from thiiranium ion 1 . The thietanium salts 2a and 2b were characterized by X‐ray crystal‐structure analysis. Their cation geometry was also optimized by ab initio calculations at the RHF/6‐31G*//RHF/6‐31G* level, as were those of its stereoisomer 3 and of the unsubstituted S‐methylthietanium ion 5 . Comparison of 2 , 3 , and 5 with 4 – the only other thietanium ion studied by XRD, where the C‐atoms of the thioniacyclobutane ring are part of a trinorbornane skeleton – indicates that, in these systems, relief from substituent overcrowding is easily achieved by a folding of the four‐membered ring along the line connecting the two opposite C‐atoms. The corresponding ring‐deformation normal mode has a calculated frequency as low as 109 cm⁻¹ in ion 5 , to be compared with a frequency of 138 cm⁻¹ in methylcyclobutane. For thietanium ion 2 , the frequencies of the two normal modes involving such ring deformation have calculated values of 61 and 85 cm⁻¹.     

Small-angle neutron-scattering study of concentrated nonionic-amphiphile solutions

The structure of aqueous solutions of two polyoxyethylene non-ionic amphiphiles, C₁₀E₅ and C₈E₄, is studied by small-angle neutron-scattering along isothermal paths crossing the isotropic single-phase region from 0% to 100% amphiphile volume fractions. The scattered intensityI(k) shows a peak at a valuek _m , which grows monotonically as the amphiphile volume fraction increases. The interpretation of the scattering data lead to the following conclusion: as increases the micellar structure becomes less and less sharp, but some orientational correlations between neighboring amphiphile molecules are preserved even in the pure amphiphile phase.     

The extracellular matrix of the human aortic wall: ultrastructural observations by FEG-SEM and by tapping-mode AFM

Fragments of human ascending aorta harvested during heart surgery were cryofractured and observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Elastic fibers appear as irregular, undulated laminae of variable size and shape. Their surface shows an evident fibrous texture suggestive of a criss-crossed, delicate filamentous scaffold and is marked by a number of features such as ridges, holes and protruding ribs. At higher magnification, both SEM and AFM show the surface composed of a finely granular material, with a bead size of approximately 20 nm. However, the thickness of the metal coating in one case, and the tip convolution effect on the other, may equally result in an artifactual enlargement of the structures, so that the beads may be significantly smaller. The surfaces created by the fracture always appear smooth and compact and with this technique do not reveal significant detail. The collagen component is mostly represented by small, uniform fibrils gathered in flexuous bundles and following a wavy course not unlike that of the elastic laminae. An orthogonal lattice of small proteoglycans is readily evident even without a specific treatment. Occasionally, the fibrils appear encrusted or engulfed in a grainy matrix reminiscent of the elastic fiber surface. Fluid Tapping-Mode Atomic Force Microscopy simultaneously reveals the surface-bound proteoglycans and the inner architecture of the fibrils, composed of smaller subunits following a spiral course with a winding angle of approximately 17 degrees.     

The female gonad of the epizoic platyhelminth Troglocaridicola sp. (Rhabdocoela, Temnocephalida, Scutariellidae): ultrastructural and cytochemical investigations

The cytoarchitecture of the female gonad of the scutariellid Troglocaridicola sp. has been investigated by means of electron microscopy and cytochemical techniques. It consists of a single germarium and two rows of vitelline follicles, both enveloped by an outer extracellular lamina (EL) and an inner cellular tunica constituted by accessory cells. Some ultrastructural features which differ from the basic pattern of all the other Rhabdocoela studied so far have been found. In the germarium the following are observed: (a) The presence in the oocytes of peripheral translucent vesicles containing glycoproteins, which differ in diameter and substructure from the peripheral egg granules observed in all the other neoophoran Platyhelminthes. These vesicles can be considered an autapomorphic feature of the taxon Troglocaridicola; (b) The presence of proteinaceous acorn-shaped granules which remain scattered in the ooplasm throughout oogenesis and can be interpreted as residual yolk. This situation is shared with some Proseriata and Tricladida; (c) The precence of accessory cell processes between growing and mature oocytes, as is typical of some Proseriata and Tricladida. In the vitellarium, the presence of polyphenolic shell globules whose substructure does not correspond either to the multigranular pattern prevailing in representatives of Eulecithophora (Prolecithophora+Rhabdocoela) or to the homogeneous pattern found in Lecithoepitheliata. They have a meandering/concentric pattern of the content similar to that described in some Proseriata and Tricladida. On the basis of the ultrastructural characteristics of the female gonad described above, the position of Troglocaridicola in the taxon Rhabdocoela is discussed.     

Existence and concentration of positive solutions for a super-critical fourth order equation

In this paper we investigate the problem of existence of solutions for a super-critical fourth order Yamabe type equation and we exhibit a family of solutions concentrating at two points, provided the domain contains one hole and we give a multiplicity result if we are given multiple holes.     

Silicon nitride PhC nanocavities as versatile platform for visible spectral range devices

We propose silicon nitride two-dimensional photonic crystal resonators as flexible platform to realize photonic devices based on spontaneous emission engineering of nanoemitters in the visible spectral range. The versatility of our approach is demonstrated by coupling the two dipole-like modes of a closed band gap H1 nanocavity with: (i) DNA strands marked with Cyanine 3 organic dyes, (ii) antibodies bounded to fluorescent proteins and (iii) colloidal semiconductor nanocrystals localized in the maximum of the resonant electric field. The experimental results are in good agreement with the numerical simulations, highlighting the good coupling of the nanocavities with both organic and inorganic light emitters.     

Time Gauge Fixing and Hilbert Space in Quantum String Cosmology

Recently the low-energy effective string theory has been used by Gasperini and Veneziano to elaborate a very interesting scenario for the early history of the universe (birth of the universe as quantum scattering). Here we investigate the gauge fixing and the problem of the definition of a global time parameter for the quantum form of the model, and obtain the positive norm Hilbert space of states.     

Cycloaddition reactions of ketoimines. Part II. Synthesis of substituted phenanthridines and cyclopenta[c]quinolines

Substituted 4-benzoyl-3a,4,5,9b-tetrahydro-3H-cyclopenta[c]quinolines 3 and 6-benzoyl-5,6,6a,7,8,10a-hexahydrophenanthridines 10 are obtained through Lewis acid catalyzed addition of 1-phenyl-2-arylamino-2-methoxyethanones 2 to cyclopentadienes and 1,3-cyclohexadiene respectively. Compounds 3 can be converted to the aromatized analogues by reaction with 2,3-dichloro-5,6-dicyanobenzoquinone in refluxing benzene. Compounds 10 are oxidized by sulfur either in decalin or in quinoline to substituted 6-benzoylphenanthridines.