Diels-Alder reactions of bis(spirodienone) derivatives of calix[4]arene with acetylenes: highly regio- and stereoselective synthesis of bisbicyclo[2.2.2]octenone derivatives

Highly regio- and stereoselective Diels-Alder reactions of bis(spirodienone) derivatives of calix[4]arene with acetylenes that provide easy access to bisbicyclo[2.2.2]octenones are described.     

Hydrolysis of Cyclic Ureas under Microwave Irradiation: Synthesis and Characterization of 7,8‐Diaminopelargonic Acid

A simple and efficient method for the synthesis of 7,8‐diaminopelargonic acid, a key intermediate in the biotin biosynthesis pathway, is reported. The d‐desthiobiotin powder was dissolved in concentrated hydrochloric acid, and the solution was exposed to microwave radiation of 2.45 GHz for varying lengths of time ranging from 60 s to 2 min. The product thus obtained was characterized by spectroscopic techniques and confirmed through bioassay. Further, the protocol was extended to the synthesis of several diamines from their corresponding cyclic ureas. The results show that the method is generally applicable and not only accelerates the hydrolysis reaction but also offers excellent yields.     

Giant dipole resonance and shape transitions in warm and rapidly rotating nuclei

We discuss the shape transitions in few medium heavy-mass nuclei with emphasis on low-temperature behaviour of the giant dipole resonance (GDR) observables. We employ a macroscopic approach towards GDR in which the GDR observables are related to the nuclear shapes. Shape calculations were done using the cranked Nilsson-Strutinsky method (CNSM) extended to finite temperature. Thermal shape fluctuations are computed with free energies calculated employing Landau parameterization as well as those calculated exactly (without using parameterizations) at given spin and temperature. The results obtained are confronted with the experimental data wherever available. Our study reveals that if the fluctuations are treated properly, then, in spite of thermal fluctuations, GDR observables could very well reflect the shape transitions at low temperature.     

Preferred conformations of enol ethers in solution: Detection of an equilibrium by kinetic nuclear overhauser effects

n.O.e. difference spectra reveal that the preferred solution conformation of methyl enol ethers has the methyl group $\text{syn}$-periplanar to the double bond; n.O.e kinetics in a methoxy—heptatriene demonstrate the presence of both possible periplanar conformations, the energy difference being $\text{ca}$ 1 kcal/mole.     

Photocatalytic water oxidation: tuning light-induced electron transfer by molecular Co4O4 cores

Isostructural cubane-shaped catalysts [Co(III)(4)(μ-O)(4)(μ-CH(3)COO)(4)(p-NC(5)H(4)X)(4)], 1-X (X = H, Me, t-Bu, OMe, Br, COOMe, CN), enable water oxidation under dark and illuminated conditions, where the primary step of photoinduced electron transfer obeys to Hammett linear free energy relationship behavior. Ligand design and catalyst optimization are instrumental for sustained O(2) productivity with quantum efficiency up to 80% at λ > 400 nm, thus opening a new perspective for in vitro molecular photosynthesis.     

Thermodynamic, transport, and spectroscopic studies for mixtures of isomeric butanediol and N-methyl-2-pyrrolidinone

The thermodynamic parameters viz. excess molar volume V^E and speed of sound u, transport parameter viscosity η, and spectroscopic parameters viz. IR, ¹H, ¹³C NMR have been measured for the mixtures of isomeric butanediol (1,2-, 1,3-, 1,4-, and 2,3-butanediol) and N-methyl-2-pyrrolidinone over the whole composition range at 308.15 K. The partial molar quantities , isentropic compressibility , viscosity deviation Δη, deviation in Gibbs free energies of activation for viscous flow g(x), and excess NMR chemical shift δ^E have been estimated and analyzed. Results show that the interaction between unlike molecules takes place through hydroxyl groups of isomeric butanediol and CO group of N-methyl-2-pyrrolidinone. Excellent agreement between thermodynamic and spectroscopic measurements is observed.     

Graft copolymerization of ethyl acrylate onto gelatin using hydrogen peroxide and ascorbic acid in aqueous medium

Gelatin a derived protein from collagen can be modified at 60°C by allowing it to react with ethyl acrylate by use of a novel initiator technique. The polymeric ethyl acrylate side chain is chemically bonded to gelatin. The effects of synthetic variable in the graft copolymerization reactions have been discussed in the light of percent grafting, grafting efficiency, and the rate of polymerization.     

Investigations on monotropic liquid crystalline polyurethanes based on biphenylol

2,2′-Azobis-[2-cyano-(4-ethylphenol)] (ABCP) was prepared from parahydroxyacetophenone, using hydrazine sulfate and sodium cyanide. Biphenylol ester of ABCP, 2,2′-azobis-[2-p-biphenyloxy-(4-ethylphenol)] (BECP) was synthesized via the acid route. Combined liquid crystalline polyurethanes (CLCPUs) were synthesized from 1,6-diisocyanatohexane (HDI) and BECP in dimethylformamide (DMF) at 110°C under nitrogen atmosphere. The effect of partial replacement of BECP by 4,4′-dihydroxy biphenyl (DHBP) on liquid crystalline (LC) properties was studied. The polymers were characterized by proton and ¹³C NMR, FTIR, and UV spectroscopy. Elemental analysis were done for determining the percentage content of C, H, and N and the molecular weights of the polymers were determined by gel permeation chromatography (GPC). Thermogravimetric investigations (TGA) of the polyurethanes (PUs) were performed to study the decomposition. The LC nature of the PUs was confirmed by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Cross-polarized optical microscopy studies demonstrated the existence of two distinct crystalline morphologies, a spherulitic morphology with high mole ratio of DHBP and a thread-like crystalline morphology with that of BECP. All the PUs synthesized showed a LC nature with a wide temperature range. Partial replacement of BECP by DHBP changed the mesomorphic nature, transition temperature, and temperature range of the mesophase. © 1995 John Wiley & Sons, Inc.