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91.
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93.
Kurt Hostettmann Andr Jacot-Guillarmod Vedantha M. Chari 《Helvetica chimica acta》1976,59(7):2592-2595
Phytochemistry of genus Gentiana, XVIII: Structure of gentiabavarutinoside, a new acylated xanthone glycoside from Gentiana bavarica L. In a previous work [1], we isolated from Gentiana bavarica L . an acylated xanthone glycoside (1,8-dihydroxy-3-methoxy-xanthone-7-O-acetylrutinoside 1 or gentiabavarutinoside) without locating the acetyl group. By 13C-NMR. spectroscopy, the attach position of the acetyl is now shown to be at 4 of the rhamnose moiety. In addition, a new compound ( 2 ), the desacetyl derivative of 1 , has also been isolated and identified. 相似文献
94.
M. Sarangapani D. Sridhar M. Arjun M. Adharvana Chari 《Journal of heterocyclic chemistry》2008,45(4):1187-1190
An efficient synthesis of some novel 2‐substituted‐N‐aryl‐benzoxazole‐5‐carboxamides from 2‐substituted — 5‐carbomethoxy benzoxazole on treatment with different substituted anilines promoted by cobalt dipyridine dichloride as a catalyst is described. This new approach has the advantage of excellent yields (90%) and short reaction times 1‐2 h. 相似文献
95.
D. Shobha M. Adharvana Chari P. Sadanandam K. Mukkanti 《Journal of heterocyclic chemistry》2008,45(4):1225-1227
DDQ catalyzes efficiently the three‐component condensation reaction of aldehyde, β‐ketoester and urea in refluxing acetonitrile to afford the corresponding dihydropyrimidinones. Compared to the classical Biginelli reaction conditions, this new approach consistently has the advantage of excellent yields (80‐92%) and short reaction times 1.5‐2.5 h. 相似文献
96.
Kobzar K Luy B Khaneja N Glaser SJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2005,173(2):229-235
A novel class of pulses is presented which can be regarded as a generalization of both frequency-selective pulses and B1-selective pulses. The excitation profile of these pulses forms a pre-defined pattern in two dimensions, which are spanned by pulse offset and radio-frequency (RF) amplitude. The presented pulses were designed numerically based on principles of optimal control theory. For simple test patterns, we demonstrate the flexibility of this approach by simulations and experiments. This previously unknown flexibility may trigger novel applications in NMR spectroscopy and imaging. As a first practical application, we demonstrate a direct approach for calibrating RF pulses. 相似文献
97.
98.
R. A. Ganeev H. Singhal P. A. Naik J. A. Chakera M. Tayyab A. K. Srivastava T. S. Dhami M. P. Joshi A. Singh R. Chari S. R. Kumbhare R. P. Kushwaha R. A. Khan R. K. Bhat P. D. Gupta 《Optics and Spectroscopy》2010,108(5):787-803
The wavelength conversion of femtosecond laser pulses in laser plasmas containing clusters of different nature and dimension (fullerenes, metal nanoparticles) is studied. Pulses of a titanium-sapphire laser are used in combination with orthogonally polarized second-harmonic pulses as radiation to be converted. Variations in the generation efficiency of higher harmonics are analyzed under conditions of phase-modulated pulses. It is shown that the optimization of components of a nonlinear optical plasma medium, of plasma excitation conditions by single- and two-color pumps, and of phase and spectral parameters of radiation to be converted leads to a considerable increase in the generation efficiency of higher harmonics. 相似文献
99.
The efficiency of dipole-dipole coupling driven coherence transfer experiments in solid-state nuclear magnetic resonance (NMR) spectroscopy of powder samples is limited by dispersion of the orientation of the internuclear vectors relative to the external magnetic field. Here we introduce general design principles and resulting pulse sequences that approach full polarization transfer efficiency for all crystallite orientations in a powder in magic-angle-spinning experiments. The methods compensate for the defocusing of coherence due to orientation dependent dipolar coupling interactions and inhomogeneous radio-frequency fields. The compensation scheme is very simple to implement as a scaffold (comb) of compensating pulses in which the pulse sequence to be improved may be inserted. The degree of compensation can be adjusted and should be balanced as a compromise between efficiency and length of the overall pulse sequence. We show by numerical and experimental data that the presented compensation protocol significantly improves the efficiency of known dipolar recoupling solid-state NMR experiments. 相似文献
100.
Reiss TO Khaneja N Glaser SJ 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2003,165(1):95-101
Broadband implementations of time-optimal geodesic pulse elements are introduced for the efficient creation of effective trilinear coupling terms for spin systems consisting of three weakly coupled spins 1/2. Based on these pulse elements, the time-optimal implementation of indirect SWAP operations is demonstrated experimentally. The duration of indirect SWAP gates based on broadband geodesic sequence is reduced by 42.3% compared to conventional approaches. 相似文献