An expedient synthesis of ferrocene grafted spirooxindolopyrrolizidines via [3+2]-cycloaddition of azomethine ylides

A facile and rapid one-pot synthesis of ferrocene bearing novel spiropyrrolizidines has been accomplished by [3+2]-cycloaddition reaction of various azomethine ylides derived from isatin/5,7-dibromoisatin and l-proline with various ferrocene derivatives as dipolarophile in good yield. The protocol is general and applicable to a wide variety of ferrocenyl derived dipolarophiles. Effect of various solvents on [3+2]-dipolar cycloaddition reaction is also studied.     

An alternative approach to selective sea water oxidation for hydrogen production

Sea water electrolysis is one of the promising ways to produce hydrogen since it is available in plentiful supply on the earth. However, in sea water electrolysis toxic chlorine evolution is the preferred reaction over oxygen evolution at the anode. In this work, research has been focused on the development of electrode materials with a high selectivity for oxygen evolution over chlorine evolution. Selective oxidation in sea water electrolysis has been demonstrated by using a cation-selective polymer. We have used a perm-selective membrane (Nafion^®), which electrostatically repels chloride ions (Cl⁻) to the electrode surface and thereby enhances oxygen evolution at the anode. The efficiency and behaviour of the electrode have been characterized by means of anode current efficiency and polarization studies. The surface morphology of the electrode has been characterized by using a scanning electron microscope (SEM). The results suggest that nearly 100% oxygen evolution efficiency could be achieved when using an IrO₂/Ti electrode surface-modified by a perm-selective polymer.     

Temporal envelope compensation for robust phoneme recognition using modulation spectrum

A robust feature extraction technique for phoneme recognition is proposed which is based on deriving modulation frequency components from the speech signal. The modulation frequency components are computed from syllable-length segments of sub-band temporal envelopes estimated using frequency domain linear prediction. Although the baseline features provide good performance in clean conditions, the performance degrades significantly in noisy conditions. In this paper, a technique for noise compensation is proposed where an estimate of the noise envelope is subtracted from the noisy speech envelope. The noise compensation technique suppresses the effect of additive noise in speech. The robustness of the proposed features is further enhanced by the gain normalization technique. The normalized temporal envelopes are compressed with static (logarithmic) and dynamic (adaptive loops) compression and are converted into modulation frequency features. These features are used in an automatic phoneme recognition task. Experiments are performed in mismatched train/test conditions where the test data are corrupted with various environmental distortions like telephone channel noise, additive noise, and room reverberation. Experiments are also performed on large amounts of real conversational telephone speech. In these experiments, the proposed features show substantial improvements in phoneme recognition rates compared to other speech analysis techniques. Furthermore, the contribution of various processing stages for robust speech signal representation is analyzed.     

Intermittency route to rheochaos in wormlike micelles with flow-concentration coupling

We show experimentally that the route to chaos is via intermittency in a shear-thinning wormlike micellar system of cetyltrimethylammonium tosylate, where the strength of flow-concentration coupling is tuned by the addition of salt sodium chloride. A Poincaré first return map of the time series and the probability distribution of laminar lengths between burst events shows that our data is consistent with type-II intermittency. The coupling of flow to concentration fluctuations is evidenced by the "butterfly" intensity pattern in small angle light scattering (SALS) measurements performed simultaneously with the rheological measurements. The scattered depolarized intensity in SALS, sensitive to orientational order fluctuations, shows the same time dependence (like intermittency) as that of shear stress.     

Increasing the sensitivity of 2D high-resolution NMR methods applied to quadrupolar nuclei

Gan and Kwak recently proposed a soft-pulse added mixing (SPAM) idea in the classical two-pulse multiple-quantum magic-angle spinning scheme. In the SPAM method, a soft pi/2 pulse is added after the second hard-pulse (conversion pulse) and all coherence orders in between them are constructively used to obtain the signal. We, here, further extend this idea to distributed samples where the signal mainly results from echo pathways and that from anti-echo pathways dies out after a few t1 increments. We show that, with a combination of SPAM and collection of fewer anti-echoes, an enhancement of the signal to noise ratio by a factor of ca. 3 may be obtained over the z-filtered version. This may prove to be useful even for samples with long T2' relaxation times.     

Solid state NMR of a molecular self-assembly: multinuclear approach to the cyanuric acid-melamine system

[see structure]. Trinuclear MAS NMR, involving naturally abundant (13C, 15N) and easily deuterated (2H) nuclei, is shown to offer newer opportunities to study molecular self-assembly in noncrystalline supramolecular systems.     

Spatiotemporal dynamics of shear induced bands en route to rheochaos

We show experimentally that the route to rheochaos in shear rate relaxation measurements is via Type-III intermittency and mixed mode oscillations in the shear-thinning wormlike micellar system of cetyltrimethylammonium tosylate in the presence of salt sodium chloride. Depolarised small angle light scattering measurements performed during flow show that scattered intensity temporally follows the shear rate/stress dynamics and portrays the crucial role played by nematic ordering. Direct visualization of the gap of the Couette cell, illuminated by an unpolarised laser sheet, in the (vorticity, velocity gradient) plane shows that the spatiotemporal dynamics of the shear induced structures is closely related to the temporal behaviour of shear rate/stress fluctuations.     

PHOTOISOMERIZATION OF SIXTEEN ISOMERS OF RETINAL. INITIAL PRODUCT DISTRIBUTION IN DIRECT AND SENSITIZED IRRADIATION. PHOTOCHEMISTRY OF POLYENES 31*

Abstract— Initial product distributions of all 16 geometric isomers of retinal in hexane solutions have been determined. With direct irradiation, the product ratios are characterized by a preference for isomerization at the 13,14-bond. In particular, all isomers containing the 13-cis geometry give the corresponding 13-trans isomer as the major product. Preference for one-photon-one-bond isomerization was also noted, although a substantial amount of the all-trans isomer was detected for all poly-cis, 13-trans isomers. In sensitized irradiation, the initial mixture shows extensive one-photon-two(or multiple)-bond isomerization to the corresponding unhindered isomers. In cases of hindered isomers, multiple-bond isomerized products are dominant. The different results are accountable by the different shapes of the excited state potential curves for singlet and triplet states.     

Diels-alder reactivity of vinylsulfoxyallenes

Vinylsulfoxyallenes 3a-c are prepared from propargylic alcohols in 47-65% yield. Vinylsulfoxyallenes undergo facile [4 + 2] cycloadditions with methyl triazolidenedione (MTAD) and singlet oxygen to afford phenylsulfinylpyridazines and spirocyclic phenylsulfinyl-2H-pyran-3(6H)-ones in excellent yields (60-90%). Spirocyclic phenylsulfinyl-2H-pyran-3(6H)-ones are oxidized to the corresponding phenylsulfones with peracid or can be epoxidized with basic hydrogen peroxide. Spirocyclic pyranone formation is thought to proceed via the rearrangement of a labile cyclic peroxide intermediate 14.     

The evaluation and characterization of voigt lineshape

Methods used to evaluate and characterize the resonance lineshapes observed in magnetic resonance experiments are presented, with particular reference to the treatment of Voigt lineshape which results from the convolution of Gaussian and Lorentzian broadening functions. Since the Voigt integral lacks an analytical solution, a simple numerical procedure is suggested to compute the Voigt function for any value of r, the ratio of the Lorentzian linewidth (σ_L) to the Gaussian linewidth (σ_G). The method is used to characterize the profiles by their incomplete moments. Using least-squares procedure , the Voigt profiles are fitted to a polynomial of sixth degree. The methods discussed here are quite general, and can be applied to the analysis of lineshapes in other branches of spectroscopy.