Photoinduced addition of phthalimide to unactivated alkynes

Photoexcited phthalimide in equilibrium with its conjugated base produces the regioselective hydrophthalimidation of conjugated alkynes. The vinylphthalimide thus obtained is hydrolyzed to the corresponding carbonyl compound. With unconjugated alkynes, the outcome is a double addition of phthalimide to the triple bond. The reaction is assumed to take place via single electron transfer from either the alkyne or the phthalimide anion to the excited phthalimide as the primary photoprocess.     

Formation and reactivity of novel pyranosidic nicholas oxocarbenium ions: access to C-ketosides and branched-chain C-ketosides

[Structure: see text] Dicobalt hexacarbonyl propargyl complexes, prepared from alkynyl ketoses, display an unexpected reactivity when treated with Lewis acids in the presence of nucleophiles and furnish C-ketosides, branched-chain C-ketosides, or branched-chain C-glycals depending on the nucleophile and the carbohydrate starting material.     

Improving the knowledge on Piper betle: Targeted metabolite analysis and effect on acetylcholinesterase

Piper betle is a species growing in South East Asia, where its leaves are economically and medicinally important. To screen the highest possible number of volatile and semivolatile components, the leaves were subjected to headspace solid‐phase microextraction, hydrodistillation and Soxhlet extraction, prior to analysis by GC/MS. Fifty compounds (identified by comparison with standard compounds or tentatively by National Institute of Standards and Technology database) were determined, 23 being described for the first time in this matrix. An aqueous extract was also analysed, in which only seven compounds were characterized. The organic acids' composition of this extract was determined by HPLC/UV and eight compounds are reported for the first time in P. betle. This extract also displayed acetylcholinesterase inhibitory capacity.     

<Emphasis Type="Italic">Euphorbia antisyphilitica</Emphasis> residues as a new source of ellagic acid

In this study, a new source of ellagic acid (EA) is reported. Euphorbia antisyphilitica or “candelilla” was used to extract phenolic dilactone. Cereous layers and fibrous tissue were analyzed. A completely randomized experimental design with a treatment factorial arrangement was employed. The factors considered were: plant/extracting agent ratio, extraction temperature and time. Candelilla wax does not contain EA. Temperature and the ratio plant/extracting agent were determinant during the EA extraction process. Around 20 mg of free EA per gram of fibrous tissue were found. Residues of candelilla are a good source of EA.     

Substituent,solvent and steric effects on the electrochemical reduction of aziridinium salts

The polarographic behavior of a series of N,N-dimethyl-2-arylaziridinium fluorosulfonates was investigated as another example of ring-opening reactions of this important class of compounds. Half-wave potentials showed that in water reduction was facilitated by electron-donating groups. This unusual result was explained in terms of electron transfer to an aminocarbonium ion-like species. In methylene chloride, however, two one-electron waves were observed, with the first showing a normal substituent effect (? = 0.17 ± 0.03 V). This result indicated direct electron transfer to the aziridinium ion itself to form a radical species which was detected by cyclic voltammetry. Reasons for the change in mechanism are presented, and E_1/2 values for selected aziridinium salts illustrate the importance of steric effects on the reduction process.     

Liquid–liquid phase separation in linear low-density polyethylene

The issue of multiple equilibrium phases in compositionally heterogeneous random copolymers is studied with an ethylene-butene copolymer representative of many linear low-density polyethylenes (LLDPE). This material has a dispersed minority phase (volume fraction ?^β ≈ 0.02) of highly branched, amorphous chains. A thermodynamic calculation of the equilibrium liquid state is done using the distribution of chain branching from temperature rising elution fractionation and the Flory-Huggins interaction parameter χ_AB for linear and ethyl branched C₄H₈ repeat units. The calculation indicates that this copolymer is metastable, between the binodal and spinodal at a melt temperature of 150°C. The predicted volume fraction of the second phase, ?^β = 0.016, is in good agreement with experiment. This work is the first to compare directly the observed and calculated two-phase behaviors in a random copolymer. © 1994 John Wiley & Sons, Inc.     

Polymer fracture—A simple model for chain scission

A simple model for calculating the fracture process for a single extended-chain molecule such as polyethylene is considered. The model consists of a chain of N coupled Morse oscillators. There exists a critical overall extension ΔL_c below which the fracture is energetically unfavorable but above which fracture is favored both energetically and kinetically. This elongation ΔL_c scales as N^1/2. For the critically stretched chain, the activation energy for rupture increases with N. Long chains must be stretched beyond this critical value to fail within experimentally meaningful times. Chains of all lengths subjected to the same force will fail with the same activation energy, provided this force is large enough to stretch each chain to ΔL > ΔL_c. Observed activation energies are less than 1/3D_e, where D_e is the bond energy.     

Motion estimation of magnetic resonance cardiac images using the Wigner-Ville and hough transforms

Myocardial motion analysis and quantification is of utmost importance for analyzing contractile heart abnormalities and it can be a symptom of a coronary artery disease. A fundamental problem in processing sequences of images is the computation of the optical flow, which is an approximation of the real image motion. This paper presents a new algorithm for optical flow estimation based on a spatiotemporal-frequency (STF) approach. More specifically it relies on the computation of the Wigner-Ville distribution (WVD) and the Hough Transform (HT) of the motion sequences. The latter is a well-known line and shape detection method that is highly robust against incomplete data and noise. The rationale of using the HT in this context is that it provides a value of the displacement field from the STF representation. In addition, a probabilistic approach based on Gaussian mixtures has been implemented in order to improve the accuracy of the motion detection. Experimental results in the case of synthetic sequences are compared with an implementation of the variational technique for local and global motion estimation, where it is shown that the results are accurate and robust to noise degradations. Results obtained with real cardiac magnetic resonance images are presented. The text was submitted by the authors in English.