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611.
d-Homotryptophan and its sulfur analogue have been synthesized by Sonogashira coupling between 3-iodoheteroarenes and ethynyloxazolidine followed by reduction of triple bond and oxidation of alcohol to acid. l-Homotryptophan and its oxygen analogue have been synthesized from silylated internal alkyne using Larock’s heteroannulation as the key reaction. The alkynyloxazolidines were synthesized from l-serine and l-glutamic acid, respectively. 相似文献
612.
Exploration of environmental dynamics using intrinsic biological probe tryptophan is very important; however, it suffers from various difficulties. An alternative probe, kynurenine (KN), has been found to be an efficient probe for the ultrafast dynamics in the biological environment ( 1 ] J. Phys. Chem. B., 114, 15236–15243). In the present study, we have investigated the efficacy of KN for the exploration of relatively slower dynamics of biologically relevant environments. A detailed investigation involving UV–Vis, steady‐state/time‐resolved fluorescence spectroscopy and Förster resonance energy transfer (FRET) studies on KN compared to a well‐known solvation probe, H33258, a DNA‐minor groove binder in a model nonionic reverse micelle reveals that ultrafast internal conversion associated with the hydrogen‐bonding dynamics masks KN to become a dynamical reporter of the immediate environments of the probe. 相似文献
613.
Shyamaprosad Goswami Avijit Kumar DasDebabrata Sen Krishnendu AichHoong-Kun Fun Ching Kheng Quah 《Tetrahedron letters》2012,53(36):4819-4823
A new naphthalene based receptor (L) has been designed and synthesized which shows a remarkable color change from colorless to pink on selective binding with acetate. The anion recognition property of the receptor via hydrogen bonding interactions is monitored by UV-vis, fluorescence, and 1H NMR titrations. It is observed that in each case, the receptor shows a specific selectivity toward the acetate ion over other interfering anions. Thus, a significant bathochromic shift in UV-vis spectrum with a sharp pink color in ‘naked-eye’ makes the receptor suitable for the detection of the acetate ion. 相似文献
614.
The 1-octanol-water partition coefficient log K(ow) of a solute is a key parameter used in the prediction of a wide variety of complex phenomena such as drug availability and bioaccumulation potential of trace contaminants. In this work, adaptive biasing force molecular dynamics simulations are used to determine absolute free energies of hydration, solvation, and 1-octanol-water partition coefficients for n-alkanes from methane to octane. Two approaches are evaluated; the direct transfer of the solute from 1-octanol to water phase, and separate transfers of the solute from the water or 1-octanol phase to vacuum, with both methods yielding statistically indistinguishable results. Calculations performed with the TIP4P and SPC∕E water models and the TraPPE united-atom force field for n-alkanes show that the choice of water model has a negligible effect on predicted free energies of transfer and partition coefficients for n-alkanes. A comparison of calculations using wet and dry octanol phases shows that the predictions for log K(ow) using wet octanol are 0.2-0.4 log units lower than for dry octanol, although this is within the statistical uncertainty of the calculation. 相似文献
615.
Ultrafast nonlinear optical response of carbon nanotubes functionalized with water soluble porphyrin
Jyotsana Gupta C. Vijayan Sandeep Kumar Maurya D. Goswami 《Optics Communications》2012,285(7):1920-1924
A new nanocomposite is obtained by functionalizing carbon nanotubes (CNTs) with a water soluble metalloprophyrin using a simple chemical technique and characterized by optical absorption, IR, and Raman spectroscopy. Results from spectroscopic studies indicate the noncovalent nature of interaction between CNTs and porphyrin. The ultrafast nonlinear response is characterized by measuring the nonlinear absorption coefficient and refractive index by z-scan technique in the femtosecond pulse regime. The nanocomposite is found to exhibit two-photon absorption (TPA) with a reasonably large nonlinear optical coefficient, whereas pure CNTs is known to exhibit saturable absorption. Design of such water soluble nanocomposites offers scope for obtaining materials with enhanced ultrafast optical nonlinearity. 相似文献
616.
T. Ghosh S. Bandopadhyay K. K. Roy A. K. Maiti K. Goswami 《Crystal Research and Technology》2009,44(8):879-882
A standard sol‐gel method was used to deposit ZnO thin films of suitable thickness on glass substrate.The optical characteristics of the visible to infrared range on thermal stress were critically observed. Morphological signature of the films was detected by X‐ray diffraction (XRD) and the crystallite size determined by Scherrer method from XRD data were consistent with grain size estimated from spectroscopic data through Meulenkamp equation. The optical band gap value from the transmission spectrum was found to corroborate with the existing works. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
617.
The problem of estimating the mode of a discrete distribution is considered. New characterizations of discrete unimodal and
multi-modal distributions are obtained. The proposed mode estimator is essentially the sample mode, modulo appropriate modifications
when the sample mode is not well defined. In the case of i.i.d. observations coming from a unimodal discrete distribution,
our proposed mode estimator is shown to possess a number of strong asymptotic properties. Many of these results extend to
the case of multi-modal discrete distributions as well. Our method also applies — and we have similar asymptotic results —
to the problem of mode estimation based on finitely many observations on a Markov chain whose equilibrium distribution is
the underlying unimodal distribution. For unimodal discrete distributions, we also propose a consistent large sample test
of mode based on the proposed statistic. Applications of mode estimation problem in Monte-Carlo optimization problem using
the Hastings Metropolis chain and in prediction problem using binary response variable, specially in the context of dose-response
experiments, are also illustrated. 相似文献
618.
Some clarifications about a model for the internal structure of black holes developed in an earlier paper are presented to
remove confusion in the interpretation of certain results. 相似文献
619.
Due to the presence of a relatively cold electron component in a plasma, the ion acoustic solitary wave of a given width has a larger amplitude. When the temperature difference between the two electron components is sufficiently large, the strength of dispersion is reduced to an extent that a solitary solution is no longer possible. 相似文献
620.
A. G. C. Nair N. Chakravarty A. Goswami B. K. Srivastava Satya Prakash 《Journal of Radioanalytical and Nuclear Chemistry》1987,109(1):37-43
Using radiochemical and gamma spectrometric technique the branching fractions in the beta decay of117Cd isomers and the internal transition branching of117mIn have been established. The beta branching fraction of117gCd117gIn was obtained as 0.86±0.06 and the value of117mCd117gIn was found to be less than 1%. The internal transitin branching and the isomer cross-section ratio were obtained as 0.31±0.02 and 0.197±0.002, respectively. From the measured isomer cross-section ratio the spin cut-off parameter was evaluated, which agreed with the value reported in the literature. 相似文献