Particle multiplicities in the fission-like reactions of 340 MeV Si on Th

Pre-scission and post-scission multiplicities of neutrons and alpha particles have been simultaneously measured for the fission-like reactions of 340 MeV ²⁸Si on ²³²Th. Dynamical model calculations using HICOL code predict that about 90% of the observed events are of quasi-fission type while the remaining 10% are from compound nucleus fission decay. Moving source fits were carried out to the observed neutron and alpha particle spectra, measured at different angles with respect to the fragment directions. The pre-scission and post-scission neutron multiplicities are deduced to be 8.7±2.0 and 9.4±2.0, respectively. The corresponding multiplicity values for alpha particles are found to be 0.22±0.08 and 0.1±0.03. From the measured post-scission neutron multiplicity, it is inferred that about 65±20 MeV of the initial excitation energy remains at scission. This may be compared to the value of 85±30 MeV estimated from PACE2 statistical model calculations, adjusted to reproduce the measured pre-scission neutron multiplicity. From a comparison of the Statistical Model predictions with the measured pre-scission neutron multiplicity, the fission delay is estimated to be of 5⁺⁷₋₃×10⁻²⁰ s which overlaps with the average duration of fission-like process from the contact to the scission point (2×10⁻²⁰ s) as determined from HICOL-based dynamical calculations. For the delay time deduced as above, the pre-scission alpha particle multiplicity calculated by the PACE2 code is about a factor two larger than the experimental one, demonstrating the difficulties in modelling the alpha particle emission from highly elongated shapes that characterize the fissioning system from the contact point to scission.     

Synthesis of protected norcysteines for SPPS compatible with Fmoc strategy

We report the synthesis of racemic Alloc-Ncy(Tmob)-OH, the resolution of its methyl ester and demonstrate its application to form a norcystine bridge in octreotide-amide using the Fmoc strategy on solid phase. N-Alloc and S-Tmob protections of norcysteine (Ncy) were found to be a preferred choice for Fmoc strategy over three other protected norcysteines synthesized, that is, Fmoc-Ncy(tBu)-OH, Alloc-Ncy(tBu)-OH, and Alloc-Ncy(Trt)-OH.     

Volumetric studies and thermodynamics of viscous flow of hydroxamic acids in acetone + water solvent at temperatures 303.15 and 313.15 K

Densities ρ and viscosities η of two hydroxamic acids, N-phenyl-2-chlorobenzo- and N-o-tolyl-4-chlorobenzo-, have been determined as a function of their concentration in aqueous acetone solution at temperatures 303.15 and 313.15 K. Apparent molar volumes, standard-state partial molar volumes and relative viscosities have been calculated. The viscosity data have been analyzed using Jones-Dole equation. The activation thermodynamic parameters of viscous flow have been evaluated using Feakins equation. These were obtained to throw light on the mechanism of viscous flow. Thermodynamic interactions in solutions have been studied in terms of a number of excess functions calculated from the experimental data. The effect of hydroxamic acid concentration and temperature on these parameters has been discussed. The results were interpreted in the light of solute-solvent interactions in aquo-organic media.     

Investigation of Diels–Alder Reaction of 7‐Substituted 4‐Styrylcoumarins with Symmetrical Dienophiles Leading to 3,4‐Annulated Coumarins

The thermal [4 + 2] cycloaddition reaction of 7‐substituted 4‐styrylcoumarins with N‐phenylmaleimide and tetracyanoethylene in nitrobenzene under reflux conditions rapidly gives 3,4‐annulated coumarins as the Diels–Alder adducts. The position of the surviving double bond was determined on the basis of NMR and supported by energies of the possible structures. The effects of the 7‐substituent and the solvent on the reaction were studied.     

Facile intramolecular Diels–Alder reaction of 4-(o-propargyloxy)styrylcoumarins leading to highly fluorescent coumarin-containing polycyclic compounds

The 4-(o-propargyloxy)styrylcoumarins are prepared by the condensation of O-propargylated salicylaldehyde with substituted coumarin-4-acetic acids. The intramolecular Diels–Alder reaction of 4-(o-propargyloxy)styrylcoumarins, without any catalyst gives fused-ring coumarins. The reaction in boiling nitrobenzene leads to aromatization of the initial Diels–Alder adduct and these aromatized products are highly fluorescent.     

A Facile Method for Detection and Speciation of Inorganic Selenium with Ion Chromatography

Chromatographia - In this work, we present a new method for the determination and speciation of selenium in water with ion chromatography (IC) using a conductometric detector. Chromatographic...     

Metal-free oxidative aromatization of 2-aryloxycyclohex-2-en-1-ones to 2-aryloxyphenols using DDQ/Amberlyst-15

Efficient metal-free oxidative aromatization of 2-aryloxycyclohex-2-en-1-ones was achieved by a combination of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and Amberlyst-15. The conditions for oxidative aromatization are mild and applicable for a variety of substrates, and Amberlyst-15 can be successfully recovered and recycled.