Mn site substitution of La0.67Ca0.33MnO3 with closed shell ions: Effect on magnetic transition temperature

Mn site is substituted with closed shell ions (Al, Ga, Ti, Zr and a certain combination of Zr and Al) and also with Fe and Ru ions carrying the magnetic moment (S=5/2 and 2 respectively) at a fixed concentration of 5 at %. Substitution did not change either the crystal symmetry or the oxygen stoichiometry. All substituents were found to suppress both the metal-insulator and ferromagnetic transition temperatures (T _p(ρ) and T _C, respectively) to varied extents. Two main contributions identified for the suppression are the lattice disorder arising due to difference in the ionic radii between the substituent (r _M) and the Mn³⁺ ion (r _Mn ³⁺) and in the case of the substituents carrying a magnetic moment, the type of magnetic coupling between the substituent and that of the neighboring Mn ion.     

Palladium-catalyzed carbonylative annulation of terminal alkynes: synthesis of coumarins and 2-quinolones

o-Iodophenols and o-iodoaniline derivatives react with terminal alkynes under 1 atm of CO in the presence of pyridine and catalytic amounts of Pd(OAc)₂ to generate coumarins and 2-quinolones, respectively, as the only products. Terminal alkynes bearing alkyl, aryl, silyl, hydroxyl, ester and cyano substituents are effective in these processes affording the desired products in moderate yields. The formation of coumarins and 2-quinolones in this process is in stark contrast with all previously described palladium-catalyzed reactions of o-iodophenols or o-iodoanilines with terminal alkynes and CO, which have afforded chromones and 4-quinolones. Moreover, under our reaction conditions terminal alkynes insert into the carbonpalladium bond instead of undergoing a Sonogashira-type coupling as confirmed by an isotope labeling experiment.     

Palladium-catalyzed carbonylative annulation of internal alkynes: synthesis of 3,4-disubstituted coumarins

The palladium-catalyzed annulation of internal alkynes by o-iodophenols in the presence of CO results in exclusive formation of coumarins. No isomeric chromones have been observed. The best reaction conditions utilize the 2-iodophenol, 5 equiv of alkyne, 1 atm of CO, 5 mol % Pd(OAc)2, 2 equiv of pyridine, and 1 equiv of n-Bu4NCl in DMF at 120 degrees C. The use of a sterically unhindered pyridine base is essential to achieve high yields. A wide variety of 3,4-disubstituted coumarins containing alkyl, aryl, silyl, alkoxy, acyl, and ester groups have been prepared in moderate to good yields. Mixtures of regioisomers have been obtained when unsymmetrical alkynes are employed. 2-iodophenols with electron-withdrawing and electron-donating substituents and 3-iodo-2-pyridone are effective in this annulation process. The reaction is believed to proceed via (1) oxidative addition of the 2-iodophenol to Pd(0), (2) insertion of the alkyne triple bond into the aryl-palladium bond, (3) CO insertion into the resulting vinylic carbon-palladium bond, and (4) nucleophilic attack of the phenolic oxygen on the carbonyl carbon of the acylpalladium complex with simultaneous regeneration of the Pd(0) catalyst. This annulation process is the first example of intermolecular insertion of an alkyne occurring in preference to CO insertion.     

DSC analysis of Cu–Zn–Sn shape memory alloy fabricated via electrodeposition route

Cu–Zn–Sn shape memory alloy strips with composition range of 13.70–46.30 mass% Sn were fabricated by electrodepositing Sn on a shim brass surface and then subsequently annealed at a constant temperature of 400 °C for 120 min under flowing nitrogen. Subjecting the Sn-plated strips to differential scanning calorimetry (DSC) analysis revealed that the austenitic start (A _s) temperature was essentially constant at 225 °C while the martensite start (M _s) temperature was consistently within the 221.5–222 °C interval. Austenite to martensite phase transformation showed two distinct peaks on the DSC thermogram which can be attributed to the non-homogeneity of the bulk Cu–Zn–Sn ternary alloy. The latent heats of cooling and heating were found to increase with the mass% Sn plated on the shim brass. Effect of annealing temperature was also investigated wherein strips with an essentially constant composition of 26 mass% Sn were annealed at a temperature range of 350–420 °C for 120 min under flowing nitrogen. Varying the annealing temperature has no significant effect on the transformation temperatures of the ternary alloy.     

Experimental evidence of time-delay-induced death in coupled limit-cycle oscillators

Experimental observations of time-delay-induced amplitude death in two coupled nonlinear electronic circuits that are individually capable of exhibiting limit-cycle oscillations are described. The existence of multiply connected death islands in the parameter space of coupling strength and time delay for coupled identical oscillators is established. The existence of such regions was predicted earlier on theoretical grounds [Phys. Rev. Lett. 80, 5109 (1998); Physica (Amsterdam) 129D, 15 (1999)]. The experiments also reveal the occurrence of multiple frequency states, frequency suppression of oscillations with increased time delay, and the onset of both in-phase and antiphase collective oscillations.     

Synthesis of 2-quinolones via palladium-catalyzed carbonylative annulation of internal alkynes by N-substituted o-iodoanilines

The palladium-catalyzed annulation of internal alkynes by N-substituted o-iodoanilines under 1 atm of carbon monoxide results in the formation of 3,4-disubstituted 2-quinolones. The nature of the substituent on the nitrogen is crucial to obtaining high yields of 2-quinolones. The best results are obtained using alkoxycarbonyl, p-tolylsulfonyl, and trifluoroacetyl substituents. The nitrogen substituent is lost during the course of the reaction resulting in the formation of N-unsubstituted 2-quinolones. A variety of internal alkynes, bearing alkyl, aryl, heteroaryl, hydroxyl, and alkoxyl substituents, are effective in this process. Electron-rich and electron-poor N-substituted o-iodoanilines, as well as heterocyclic analogues, can be employed as annulating agents.     

Autosoliton model of the spinning fronts of reaction

Experiments with reaction fronts (detonation waves and solidflames) reveal that, near the combustion limit, the fronts movein a spinning regime when localized zones of intensive reactiontravel along spiral trajectories. In the paper, the spinningwave is interpreted as an autosoliton and described phenomenologicallyby a nonlinear partial differential equation. The equation isstudied numerically, and the presence of the stable spinningand autosoliton solutions is shown.     

Synthesis of coumarins via palladium-catalyzed carbonylative annulation of internal alkynes by o-iodophenols

A variety of substituted coumarins have been prepared in good yields by the palladium-catalyzed coupling of o-iodophenols with internal alkynes and 1 atm of carbon monoxide. Unlike most of the previous work on the palladium-catalyzed carbonylation of alkynes, the insertion of the internal alkyne occurs in preference to the insertion of CO.