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71.
Danoff EJ Wang X Tung SH Sinkov NA Kemme AM Raghavan SR English DS 《Langmuir : the ACS journal of surfaces and colloids》2007,23(17):8965-8971
We demonstrate the unique ability of catanionic vesicles, formed by mixing single-tailed cationic and anionic surfactants, to capture ionic solutes with remarkable efficiency. In an initial study (Wang, X.; Danoff, E. J.; Sinkov, N. A.; Lee, J.-H.; Raghavan, S. R.; English, D. S. Langmuir 2006, 22, 6461) with vesicles formed from cetyl trimethylammonium tosylate (CTAT) and sodium dodecylbenzenesulfonate (SDBS), we showed that CTAT-rich (cationic) vesicles could capture the anionic solute carboxyfluorescein with high efficiency (22%) and that the solute was retained by the vesicles for very long times (t1/2 = 84 days). Here we expand on these findings by investigating the interactions of both anionic and cationic solutes, including the chemotherapeutic agent doxorubicin, with both CTAT-rich and SDBS-rich vesicles. The ability of these vesicles to capture and hold dyes is extremely efficient (>20%) when the excess charge of the vesicle bilayer is opposite that of the solute (i.e., for anionic solutes in CTAT-rich vesicles and for cationic solutes in SDBS-rich vesicles). This charge-dependent effect is strong enough to enable the use of vesicles to selectively capture and separate an oppositely charged solute from a mixture of solutes. Our results suggest that catanionic surfactant vesicles could be useful for a variety of separation and drug delivery applications because of their unique properties and long-term stability. 相似文献
72.
Raghavan Rangarajan 《Pramana》1999,53(6):1061-1067
We review various attempts to create the observed baryon asymmetry of the Universe. In particular, we consider models of GUT
baryogenesis, baryogenesis via leptogenesis, the Affleck-Dine mechanism, electroweak baryogenesis and baryogenesis via topological
defects and primordial black holes. 相似文献
73.
Spatiotemporal nonlocal diffusion in a bounded system is addressed by considering fractional diffusion in a linear, composite system. By considering limiting conditions, solutions for combinations of Neumann and Dirichlet boundary conditions (either zero or nonzero) at the ends of a finite system are derived in terms of Mittag–Leffler functions by the Laplace transformation. Computational viability is demonstrated by inverting the solutions numerically and comparing resulting calculations with asymptotic solutions. Time and space fractional derivatives, defined by variables \(\alpha \) and \(\beta \), respectively, are employed in the Caputo sense; a single-sided, asymmetric space derivative is used. Inspection of the asymptotic solutions leads to insights on the structure of the solutions that may not be available otherwise; the resulting deductions are verified through the numerical inversions. For pure superdiffusion, characteristics of some of the solutions presented here are very similar to those of classical diffusion but combined effects for the corresponding situation result in power-law behaviors. Incidentally, to our knowledge, the pressure distribution for space fractional diffusion at long enough times in a finite system is derived based on first principles for the first time. 相似文献
74.
Zn1 − xFexS (x=0.0, 0.1, 0.2, 0.4 and 0.6) nanocrystals have been obtained by chemical co-precipitation from homogeneous solutions of zinc and iron salt compounds, with S2− as precipitating anion formed by decomposition of thiophenol. The TEM micrographs show a spherical shape for ZnS nanocrystals and their average size is around 7 nm. The optical absorption spectra indicate a blue shift of the absorption edge with increasing Fe-content. The luminescence of nanoparticles excite at about 370 nm with an emission peak at around 490 nm. At room temperature, ESR signal characteristic of Fe3+ was observed in samples of all concentrations. 相似文献
75.
Doping induced magnetism in Co-ZnS nanoparticles 总被引:1,自引:0,他引:1
Zn1−xCoxS nanoparticles with x=0, 0.1, 0.2, and 0.3 were synthesized by the co-precipitation method using thiophenol as capping agent. The effect of Co doping on the structural, optical and magnetic properties are investigated. The X-ray diffraction patterns show single phase with cubic structure and the images of Transmission Electron Microscopy indicate an average particle size of 39 nm. Significant blue shift in the optical absorbing band edge was observed with increasing Co doping. In the Co doped samples, room-temperature (RT) magnetic hysteresis is observed and the magnetization reduces with increasing Co content. However, these samples show paramagnetic resonance instead of ferromagnetic resonance at both 300 and 80 K, suggesting that the origin of RT magnetization in these Zn1−xCoxS nanoparticles involves with the frustration of antiferromagnetic interactions. 相似文献
76.
Venkatramani Lakshmibai Komaranapuram N. Raghavan Parameswaran Sankaran 《Central European Journal of Mathematics》2009,7(2):214-223
It is shown that the proof by Mehta and Parameswaran of Wahl’s conjecture for Grassmannians in positive odd characteristics
also works for symplectic and orthogonal Grassmannians.
相似文献
77.
78.
Sahoo P Sankolli R Lee HY Raghavan SR Dastidar P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(26):8057-8063
An easy access to a library of simple organic salts derived from tert-butoxycarbonyl (Boc)-protected L-amino acids and two secondary amines (dicyclohexyl- and dibenzyl amine) are synthesized following a supramolecular synthon rationale to generate a new series of low molecular weight gelators (LMWGs). Out of the 12 salts that we prepared, the nitrobenzene gel of dicyclohexylammonium Boc-glycinate (GLY.1) displayed remarkable load-bearing, moldable and self-healing properties. These remarkable properties displayed by GLY.1 and the inability to display such properties by its dibenzylammonium counterpart (GLY.2) were explained using microscopic and rheological data. Single crystal structures of eight salts displayed the presence of a 1D hydrogen-bonded network (HBN) that is believed to be important in gelation. Powder X-ray diffraction in combination with the single crystal X-ray structure of GLY.1 clearly established the presence of a 1D hydrogen-bonded network in the xerogel of the nitrobenzene gel of GLY.1. The fact that such remarkable properties arising from an easily accessible (salt formation) small molecule are due to supramolecular (non-covalent) interactions is quite intriguing and such easily synthesizable materials may be useful in stress-bearing and other applications. 相似文献
79.
Helical tubules are a fascinating and an intriguing class of self-assemblies. They occur frequently in biology and are believed to be intermediates in formation of gallstones. The pathway by which amphiphiles transform from an initial state of vesicles or micelles into such tubules has puzzled soft matter physicists, and it has raised important questions about the interplay between molecular chirality and self-assembly. Here, for the first time, we demonstrate direct, real-time observations by light microscopy of the pathway to helical microtubules from an initial solution of nanoscale vesicles. The tubules are formed in aqueous mixtures of the single-tailed diacetylenic surfactant, 10,12-pentacosadiynoic acid (PCDA), and a short-chain alcohol. The stepwise process involves nucleation of thin helical microribbons from the vesicle solution. These ribbons then thicken, rearrange, and fold into closed tubules. Subsequently, most tubules further rearrange into plate-like structures, and once again, we are able to visualize this process in real time. A notable aspect of the above system is that the precursors are achiral; yet, the tubules are formed from helical ribbons. Our study provides new insights into tubule formation that will be valuable in clarifying and refining theoretical models for these fascinating structures. 相似文献
80.
The vapor phase pyridine synthesis from acetaldehyde, formaldehyde and ammonia over HZSM-5 catalyst was studied. The process
parameters like temperature, aldehyde ratio, and Si/Al ratio in HZSM-5 was investigated and the process conditions were optimized
using surface response methodology (RSM) based on Box-Behnken design. The influence of process parameters investigated using analysis of variance (ANOVA), to identify
the significant parameters. The optimum conditions for high yield of pyridine were identified to be a reaction temperature
400°C, aldehyde ratio 1: 1 and Si/Al ratio 106.7. A maximum of 55% yield of pyridine formed under the optimum experimental
conditions. The proposed model equation using RSM has shown good agreement with the experimental data, with a correlation
coefficient R
2 = 0.99. 相似文献