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101.
Yelamaggad CV Shanker G Ramana Rao RV Shankar Rao DS Prasad SK Babu VV 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(33):10462-10471
Herein, we demonstrate that with the widespread theme of residue patterning and stereochemical restraints of self-complimenting proteinogenic amino acids, a new and rich class of homomeric dipeptides exhibiting two-dimensional fluid aggregates with hierarchical ordering can be obtained. In particular, a simple way of achieving a class of functional dipeptides, wherein the first and the second residues chosen are L-/D-alanines and L-/D-leucines, has been accomplished. The supramolecules synthesized can be regarded as intermediates between polycatenars and taper-shaped amphiphiles because they possess two lipophilic segments interlinked by a peptide unit (spacer). Two pairs of enantiomers and their respective diastereomers derived from these amino acids are evidenced to self-organize into a helical columnar phase through hydrogen bonding by means of FTIR, UV/Vis, and chiroptical circular dichroism (CD) spectral analyses as well as by optical, calorimetric, electrical switching, and X-ray studies. The CD and X-ray studies have revealed that the form chirality (handedness) and the magnitude of out-of-plane fluctuations of the lattice planes of the fluid supramolecular columnar structures are solely directed by the stereochemistry encoded in the spacer. Of special significance, the less frequently found oblique helical columnar phase formed by a pair of enantiomers derived from L-/D-alanines, unlike those derived from other amino acids, exhibit ferroelectric behavior; the measured spontaneous polarization is as high as 440 nC cm(-2). Besides, all these supramolecules form stable organogels in ethanol and the CD and SEM studies on a representative gel suggest the presence of helical structures. 相似文献
102.
Shuguang Wang Wentong Lu Oleg Tovmachenko Uma Shanker Rai Hongtao Yu Paresh Chandra Ray 《Chemical physics letters》2008,463(1-3):145-149
As the nanotechnology field continues to develop, assessing nanoparticle toxicity is very important for advancing nanoparticles for biomedical application. Here we report cytotoxicity of gold nanomaterial of different size and shape using MTT test, absorption spectroscopy and TEM. Spherical gold nanoparticles of different sizes are not inherently toxic to human skin cells, but gold nanorods are highly toxic due to the presence of CTAB as coating material. Due to toxicity of CTAB, and aggregation of gold nanomaterials in the presence of cell media, we have demonstrated that it is difficult to understand the cytotoxicity of gold nanomaterials individually. 相似文献
103.
Pulaganti Vijaya Prasad Medi Shanker Avudoddi Venkanna Marapala Kumara Swamy K. Gopichand 《合成通讯》2018,48(9):1040-1044
A facile and efficient synthesis of pyrrole and pyrrole-fused heterocyclic compounds has been demonstrated. The current protocol involves the in situ generation of azomethine ylides which undergoes intermolecular cycloaddition reaction and subsequent treatment with DDQ provides the pyrrole and fused heterocyclic compounds in good yields. 相似文献
104.
Uma Shanker Vidhisha Jassal Manviri Rani Balbir Singh Kaith 《International journal of environmental analytical chemistry》2016,96(9):801-835
Current advancements in green synthesis of materials especially nanoparticles have led to conservation of natural and non-renewable resources along with reduction in environmental pollution. Development of cost-effective, simple and eco-friendly routes for the synthesis of nanoparticles is very important. All over the world, a wide variety of biogenic sources have been put to trial as a source of green agents to facilitate synthesis process. In addition to this, environmentally benign solvents are also being used these days in order to promote green synthesis. In this review, an attempt has been made to familiarise the readers with the different green routes for the synthesis of nanoparticles. 相似文献
105.
This work addresses a way to combine isotherm determination and nonlinear calibration. In this method, like the classical inverse method, experimental elution profiles are compared with the results of a detailed model that accounts for nonlinearity in equilibrium, axial dispersion, and mass transfer kinetics. However, unlike the classical inverse method, the calibration of detector is carried out simultaneously with isotherm determination thereby reducing cost and saving time. In this study no limitation is imposed on the linearity of the detector signal or on the overlapping of elution profiles for the separation of enantiomers. The method has been experimentally validated for the separation of a mixture of guaifenesin enantiomers over a wide range of concentration. 相似文献
106.
Vadde Ravinder Sigala Ashok M. Satish Varma C. V. Raghunath Babu Kanne Shanker Gubba Balaswamy 《Chromatographia》2009,70(1-2):229-232
A rapid isocratic chiral LC method has been developed for the separation of (S)-cinacalcet from (R)-cinacalcet. Good resolution with R S > 3 was obtained using a Chiralpak-IA column (250 × 4.6 mm, particle size 5 μm) and n-hexane, ethanol and trifluoroacetic acid as the mobile phase (95:5:0.1, v/v) at ambient temperature. Flow rate was kept at 1.0 mL min–1 and elution was monitored by UV detection at 223 nm. This method was further used to determine the presence of (S)-cinacalcet in enantiopure pharmaceutical formulations containing (R)-cinacalcet. This method allowed for the detection and quantitation of (S)-cinacalcet of levels at 0.04 and 0.16 μg mL–1, respectively. The method was validated following ICH guidelines. 相似文献
107.
Bhupendra Singh Rathore Mulayam Singh Gaur Kripa Shanker Singh 《Journal of Thermal Analysis and Calorimetry》2012,107(2):675-680
The thermally stimulated charge relaxation properties of polycarbonate (PC) filled with SiO2 nanofiller were studied by means of thermally stimulated discharge current (TSDC). The nanocomposite samples were further
characterized by UV–vis spectroscopy, scanning electron microscopy, energy dispersive X-ray spectra, and differential scanning
calorimetry (DSC) techniques to investigate the dispersion of nanofillers in polymer matrix and glass transition temperature.
All pristine and nanocomposites samples of thickness about 25 μm were prepared using solution mixing method. The suitable
weight percentage of SiO2 nanofillers has been chosen to prevent the nonuniform dispersion. TSDC measurement of PC (Pristine) and PC+ (7% SiO2) shows the single peak, while TSDC characteristic of other nanocomposites are showing two peaks. The higher temperature TSDC
peak of pristine and nanocomposites samples is originated due to the charge relaxation from shallower and deeper trapping
sites, however, low temperature peak is caused by dipolar relaxation of charge carriers. Since the position of higher temperature
TSDC peak is generally an analysis of glass transition temperature of polymer/polymer nanocomposites. The authors have observed
that the temperature of this peak is almost same as the T
g measured by DSC with 0 to ±5% variation. This article presents the deeper understanding of charge relaxation mechanism caused
by SiO2 nanofillers in polycarbonate. 相似文献
108.
We present new experimental data on thick target bremsstrahlung spectra generated from the interaction of energetic electrons
with bulk matter. The ‘photon yields’ in terms of double differential cross-sections (DDCS) are measured for pure elements
of thick targets: Ti (Z = 22), Ag (Z = 47), W (Z = 74) and Pt (Z = 78) under the impact of 10 keV electrons. Comparison of DDCS obtained from the experimental data is made with those predicted
by Monte-Carlo (MC) calculations using PENELOPE code. A close agreement between the experimental data and the MC calculations
is found for all the four targets within the experimental error of 16%. Furthermore, the ratios of DDCS of bremsstrahlung
photons emitted from Ag, W and Pt with those from Ti as a function of photon energy are examined with a relatively lower uncertainty
of about 10% and they are compared with MC calculations. A satisfactory agreement is found between the experiment and the
calculations within some normalizing factors. The variations of DDCS as a function of Z and of photon energy are also studied which show that the DDCS vary closely with Z; however, some deviations are observed for ‘tip’ photons emitted from high Z targets. 相似文献
109.
110.
Chitosan acetate-ammonium nitrate (NH4NO3) films have been prepared by the solution-cast technique. Fourier transform infrared spectroscopy (FTIR) showed that complexation has occurred. FTIR exhibited shifts in amine and carbonyl bands from 1553 to 1520 cm−1 and 1636 to 1617 cm−1. A new peak was also observed at 1746 cm−1. XRD shows that all complexes are amorphous. The highest conductivity at room temperature is 2.53×10−5 S cm−1 for the film containing 45 wt% NH4NO3. The conductivity of the samples is dependent on the number of mobile ions and mobility. 相似文献