Diterpenes from Xylopia langsdorffiana

The phytochemical investigation of Xylopia langsdorffiana A.St.‐Hil. & Tul . led to the isolation of eight diterpenes, i.e., of the four new compounds (5β,7β,8α,9β,10α,12α)‐atisane‐7,16‐diol 7‐acetate ( 1 ), named xylodiol 7‐acetate, (5β,8α,9β,10α,12α)‐16‐hydroxyatisan‐7‐one ( 2 ), named xylopinone, (3α,12Z)‐3‐hydroxy‐ent‐labda‐8(20),12,14‐trien‐18‐oic acid ( 3 ), named labdorffianic acid A, and 8,20‐epoxy‐13‐hydroxy‐ent‐labd‐14‐en‐18‐oic acid ( 4 ), named labdorffianic acid B, and of the four known compounds 5 – 8 , i.e., ent‐kauran‐16‐ol, ent‐kaur‐16‐en‐19‐oic acid, ent‐kaur‐16‐en‐19‐ol, and ent‐trachyloban‐18‐oic acid. The structures were established by IR, HR‐ESI‐MS, and NMR data analysis with the aid of 2D techniques.     

Sulfuric Acid Adsorbed on Silica Gel. A Multipurpose Acid Catalyst

A series of acid catalyzed reactions like the dehydration of alcohols, conversion of ketones to 1,3-dioxolanes and their hydrolysis, α,β-unsaturated ketones to enol ethers, and alcohols to methyl-methoxyethyl ethers are performed efficiently in high yield with sulfuric acid adsorbed on silica gel as catalyst.     

Eigenvector sensitivity under general and structured perturbations of tridiagonal Toeplitz‐type matrices

The sensitivity of eigenvalues of structured matrices under general or structured perturbations of the matrix entries has been thoroughly studied in the literature. Error bounds are available, and the pseudospectrum can be computed to gain insight. Few investigations have focused on analyzing the sensitivity of eigenvectors under general or structured perturbations. This paper discusses this sensitivity for tridiagonal Toeplitz and Toeplitz‐type matrices.     

Synthesis of derivatives of pyrazolo[1,5-a]pyrrolo[1,2-c][1,3,6]-benzotriazocine,a new class of compounds with potential CNS activity

The synthesis of derivatives of pyrazolo[1,5-a]pyrrolo[1,2-c][1,3,6]benzotriazocine was obtained by the reaction of arylaldehydes with some 1-(2-aminophenyl)-5-(pyrrol-1-yl)pyrazoles, as hydrochlorides. Characterization of this new class of compounds was effected with ir, pmr and ¹³C nmr spectral data.     

Ising model with isotropic competing interactions in the presence of a field

Summary We consider a spin system with competing interactions isotropic with respect to the axes of a cubic lattice in the presence of an external field. We show that for small values of the external fieldH, the paramagnetic to modulated phase transition is fluctuation-induced first order, while for larger fields, such transition changes to continuous at a tricritical point. Applications for fluids systems are proposed. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

The complex of pant decompositions of a surface

We exhibit a set of edges (moves) and 2-cells (relations) making the complex of pant decompositions on a surface a simply connected complex. Our construction, unlike the previous ones, keeps the arguments concerning the structural transformations independent from those deriving from the action of the mapping class group. The moves and the relations turn out to be supported in subsurfaces with 3g−3+n=1,2 (where g is the genus and n is the number of boundary components), illustrating in this way the so-called Grothendieck principle.     

Gender differences in hemispheric asymmetry for face processing

Background  

Current cognitive neuroscience models predict a right-hemispheric dominance for face processing in humans. However, neuroimaging and electromagnetic data in the literature provide conflicting evidence of a right-sided brain asymmetry for decoding the structural properties of faces. The purpose of this study was to investigate whether this inconsistency might be due to gender differences in hemispheric asymmetry.     

An aminoisoflavone — salicyloylindole ring transformation

A series of 2′‐nitroisoflavones 8–10, 15, 22, 27 and 28 was prepared via the (2‐nitro‐phenyl)‐acetic acids 1, 13, 19 and 25. In order to obtain the corresponding 2′‐aminoisoflavones the reduction of 8–10, 15, 22, 27 and 28 was undertaken. Surprisingly, new 3‐salicyloylindoles instead of the expected 2′‐aminoisoflavones were the main reduction products. In the following paper the preparation of the 2′‐nitroisoflavones 8–10, 15, 22, 27 and 28 as well as the reduction experiments obtaining the 2′‐aminoisoflavones 33 and 35 and the 3‐salicyloylindoles 29–32, 34 and 36 will be described. Furthermore, a possible mechanism responsible for the formation of the 3‐salicyloylindoles from 2′‐nitroisoflavones under reductive conditions will be discussed.     

STUDIES ON PHYTOCHROME PHOTOCONVERSIONS IN VITRO WITH LASER-INDUCED OPTOACOUSTIC SPECTROSCOPY*

After excitation at room temperature with a 15 ns dye laser pulse, phytochrome (60 kDalton) from etiolated oat seedlings was studied by optoacoustic spectroscopy, which records the heat emission caused by non-radiative deactivation processes of the photoexcited molecule. The action spectrum for the heat emitted by P_r deviates from the absorption spectrum around 610 and 695 nm, indicating the build-up of photoproduct(s) within 15 ns after excitation. It is proposed that the 695 nm product is identical with I₇₀₀ and lumi-R known to be the first intermediate on the P_r× P_fr pathway, and that the photochemical back reaction of I₇₀₀ to P_r occurs on the same time scale. About 90% of the absorbed light energy was lost by radiationless deactivation. Values for the rate constants of excited state deactivation of P_r and for the internal energy content difference of the primary photoproducts are calculated.     

On the derivations of semigroup rings

In questo lavoro studiamo i generatori del modulo delle derivazioni di anelli di semigruppoR=k[S], dandone una caratterizzazione sotto opportune ipotesi suS.