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Jonali Goswami Rajiv L. Bezbaruah Amrit Goswami Naleen Borthakur 《Tetrahedron: Asymmetry》2002,12(24):3343-3348
β-Adrenoreceptor agonists (R)-(−)-denopamine (R)-1 and (R)-(−)-salmeterol (R)-2 have been prepared in good overall yield and high enantioselectivity through a biotransformative pathway. 相似文献
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Charagundla SR Borthakur A Leigh JS Reddy R 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2003,162(1):113-121
Significant artifacts arise in T(1rho)-weighted imaging when nutation angles suffer small deviations from their expected values. These artifacts vary with spin-locking time and amplitude, severely limiting attempts to perform quantitative imaging or measurement of T(1rho) relaxation times. A theoretical model explaining the origin of these artifacts is presented in the context of a T(1rho)-prepared fast spin-echo imaging sequence. Experimentally obtained artifacts are compared to those predicted by theory and related to B(1) inhomogeneity. Finally, a "self-compensating" spin-locking preparatory pulse cluster is presented, in which the second half of the spin-locking pulse is phase-shifted by 180 degrees. Use of this pulse sequence maintains relatively uniform signal intensity despite large variations in flip angle, greatly reducing artifacts in T(1rho)-weighted imaging. 相似文献
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Shapiro EM Borthakur A Bansal N Leigh JS Reddy R 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2000,143(1):213-216
We describe the characterization of a (23)Na temperature-dependent chemical shift and relaxation rates in the complex, Na(4)HTm[DOTP]. This is the first characterization of a (23)Na temperature-dependent chemical shift in a nonmetallic sample. The (23)Na temperature-dependent chemical shift coefficient is approximately -0. 5 PPM/ degrees C for both an aqueous solution and a 6% agarose gel of this compound. This is 50 times the magnitude of the temperature-dependent chemical shift coefficient of water protons. The relaxation times, T(1), T(2f), and T(2s) increased by 0.1, 0.01, and 0.05 ms/ degrees C, respectively. Applications of these unique properties for designing an MRI technique for monitoring heat deposition in tissue and tissue phantoms are discussed. 相似文献
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Tin oxide (SnO2) thin films have been grown on glass substrates using atmospheric pressure chemical vapour deposition (APCVD) method. During
the deposition, the substrate temperature was kept at 400°C–500°C. The structural properties, surface morphology and chemical
composition of the deposited film were studied by X-ray diffraction (XRD), scanning electron microscope (SEM) and Rutherford
back scattering (RBS) spectrum. XRD pattern showed that the preferred orientation was (110) having tetragonal structure. The
optical properties of the films were studied by measuring the transmittance, absorbance and reflectance spectra between λ = 254 nm to 1400 nm and the optical constants were calculated. Typical SnO2 film transmits ∼ 94% of visible light. The electrical properties of the films were studied using four-probe method and Hall-voltage
measurement experiment. The films showed room temperature conductivity in the range 1.08 × 102 to 1.69 × 102 Ω−1cm−1. 相似文献
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Moyurima Borthakur 《Tetrahedron letters》2010,51(39):5160-8806
A fast solvent-less synthesis of 5-hydroxy-benzo[g]indole scaffolds is accomplished from Lewis acid-catalyzed one-pot reaction of naphthoquinone, ω-morpholinoacetophenone, and urea under microwave irradiation. The key step in the synthesis is the Michael addition followed by in situ aza cyclization reaction using urea as an environmentally benign source of ammonia. 相似文献
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Bitupon Borthakur Prof. Ashwini K. Phukan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(32):11603-11609
The effect of ylide substitution at the α position to the carbene carbon (Cc) atom on the stability and σ‐donating ability of a number of cyclic carbenes has been studied theoretically. The stabilities of all of the carbenes were investigated from an evaluation of their singlet–triplet energy gaps and stabilization energies. All carbenes were found to have a stable singlet state. The energy of the σ‐symmetric lone‐pair orbital at the Cc atom increases as a result of the introduction of ylide centers near to the Cc atom. This indicates an enhanced σ‐donating ability of the ylide‐containing carbenes. The calculated carbonyl‐stretching frequencies of the corresponding rhodium complexes, proton affinities, and nucleophilicity index values correlate well with the σ basicity of the carbenes. 相似文献
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A generalized expression is used on the basis of relaxation time approximation to facilitate calculation of lattice thermal
conductivity of dielectric materials as well as skutterudite family consists of compounds of the form AB3. It is assumed that phonon scattering processes are independent and is represented by frequency dependent relaxation times.
The contributions of normal three phonon scattering processes are included explicitly as redistribution of phonon momentum
between two oscillation branches is considered. Magnitudes of relaxation times are estimated from the experimental data. The
result for CoSb3 is in reasonably good agreement with the experimental result in the temperature range 1–1000°K. It is observed that redistribution
of phonon momentum between two oscillation branches leads to a significant suppression of thermal conductivity maximum and
it is observed that for unfilled skutterudite the main dominant mechanism at the thermal conductivity maximum is three phonon
normal scattering process. 相似文献
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Jannai T. Yafuso Vishal Singh Negi Jon-Paul Bingham Dulal Borthakur 《Applied biochemistry and biotechnology》2014,173(5):1157-1168
In plants, the final step of cysteine formation is catalyzed by O-acetylserine (thiol) lyase (OAS-TL). The purpose of this study was to isolate and characterize an OAS-TL from the tree legume Leucaena leucocephala (leucaena). Leucaena contains a toxic, nonprotein amino acid, mimosine, which is also formed by an OAS-TL, and characterization of this enzyme is essential for developing a mimosine-free leucaena for its use as a protein-rich fodder. The cDNA for a cytosolic leucaena OAS-TL isoform was obtained through interspecies suppression subtractive hybridization. A 40-kDa recombinant protein was purified from Escherichia coli and used in enzyme activity assays where it was found to synthesize only cysteine. The enzyme followed Michaelis-Menten kinetics, and the K m was calculated to be 1,850?±?414 μM sulfide and the V max was 200.6?±?19.92 μM cysteine min?1. The N-terminal affinity His-tag was cleaved from the recombinant OAS-TL to eliminate its possible interference in binding with the substrate, 3-hydroxy-4-pyridone, for mimosine formation. The His-tag-cleaved OAS-TL was again observed to catalyze the formation of cysteine but not mimosine. Thus, the cytosolic OAS-TL from leucaena used in this study is specific for only cysteine synthesis and is different from previously reported OAS-TLs that also function as β-substituted alanine synthases. 相似文献
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Hacene Serrai Arijitt Borthakur Lotfi Senhadji Ravinder Reddy Navin Bansal 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2000,142(2):341
The application of continuous wavelet transform (CWT) analysis technique is presented to analyze multiple-quantum-filtered (MQF) 23Na magnetic resonance spectroscopy (MRS) data. CWT acts on the free-induction-decay (FID) signal as a time-frequency variable filter. The signal-to-noise ratio (SNR) and frequency resolution of the output filter are locally increased. As a result, MQF equilibrium longitudinal magnetization and the apparent fast and slow transverse relaxation times are accurately estimated. A developed iterative algorithm based on frequency signal detection and components extraction, already proposed, was used to estimate the values of the signal parameters by analyzing simulated time-domain MQF signals and data from an agarose gel. The results obtained were compared to those obtained by measurement of signal height in frequency domain as a function of MQF preparation time and those obtained by a simple time-domain curve fitting. The comparison indicates that the CWT approach provides better results than the other tested methods that are generally used for MQF 23Na MRS data analysis, especially when the SNR is low. The mean error on the estimated values of the amplitude signal and the apparent fast and slow transverse relaxation times for the simulated data were 2.19, 6.63, and 16.17% for CWT, signal height in frequency domain, and time-domain curve fitting methods, respectively. Another major advantage of the proposed technique is that it allows quantification of MQF 23Na signal from a single FID and, thus, reduces the experiment time dramatically. 相似文献