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991.
992.
Yucelen GI Choudhury RP Vyalikh A Scheler U Beckham HW Nair S 《Journal of the American Chemical Society》2011,133(14):5397-5412
We report the identification and elucidation of the mechanistic role of molecular precursors and nanoscale (1-3 nm) intermediates with intrinsic curvature in the formation of single-walled aluminosilicate nanotubes. We characterize the structural and compositional evolution of molecular and nanoscale species over a length scale of 0.1-100 nm by electrospray ionization mass spectrometry, nuclear magnetic resonance spectroscopy ((27)Al liquid-state, (27)Al and (29)Si solid-state MAS), and dynamic light scattering. Together with structural optimization of key experimentally identified species by solvated density functional theory calculations, this study reveals the existence of intermediates with bonding environments, as well as intrinsic curvature, similar to the structure of the final nanotube product. We show that "proto-nanotube-like" intermediates with inherent curvature form in aqueous synthesis solutions immediately after initial hydrolysis of reactants, disappear from the solution upon heating to 95 °C due to condensation accompanied by an abrupt pH decrease, and finally form ordered single-walled aluminosilicate nanotubes. Detailed quantitative analysis of NMR and ESI-MS spectra from the relevant aluminosilicate, aluminate, and silicate solutions reveals the presence of a variety of monomeric and polymeric aluminate and aluminosilicate species (Al(1)Si(x)-Al(13)Si(x)), such as Keggin ions [AlO(4)Al(12)(OH)(24)(H(2)O)(12)](7+) and polynuclear species with a six-membered Al oxide ring unit. Our study also directly reveals the complexation of aluminate and aluminosilicate species with perchlorate species that most likely inhibit the formation of larger condensates or nontubular structures. Integration of all of our results leads to the construction of the first molecular-level mechanism of single-walled metal oxide nanotube formation, incorporating the role of monomeric and polymeric aluminosilicate species as well as larger nanoparticles. 相似文献
993.
R.P. Drake F.W. Doss R.G. McClarren M.L. Adams N. Amato D. Bingham C.C. Chou C. DiStefano K. Fidkowski B. Fryxell T.I. Gombosi M.J. Grosskopf J.P. Holloway B. van der Holst C.M. Huntington S. Karni C.M. Krauland C.C. Kuranz E. Larsen B. van Leer B. Mallick D. Marion W. Martin J.E. Morel E.S. Myra V. Nair K.G. Powell L. Rauchwerger P. Roe E. Rutter I.V. Sokolov Q. Stout B.R. Torralva G. Toth K. Thornton A.J. Visco 《High Energy Density Physics》2011,7(3):130-140
994.
Nair V Sinu CR Rejithamol R Seetha Lakshmi KC Suresh E 《Organic & biomolecular chemistry》2011,9(15):5511-5514
An unexpected transformation of 2H-chromene-3-carboxaldehydes to coumarin derivatives, mediated by NHC, is reported. 相似文献
995.
Nair Abreu Domingos M. Cardoso Ivan Gutman Enide A. Martins Mar?´a Robbiano 《Linear algebra and its applications》2011,435(10):2365-2374
The energy of a graph G is the sum of the absolute values of the eigenvalues of the adjacency matrix of G. The Laplacian (respectively, the signless Laplacian) energy of G is the sum of the absolute values of the differences between the eigenvalues of the Laplacian (respectively, signless Laplacian) matrix and the arithmetic mean of the vertex degrees of the graph. In this paper, among some results which relate these energies, we point out some bounds to them using the energy of the line graph of G. Most of these bounds are valid for both energies, Laplacian and signless Laplacian. However, we present two new upper bounds on the signless Laplacian which are not upper bounds for the Laplacian energy. 相似文献
996.
The water-exchange reaction in two diastereoisomers of the clinical magnetic resonance imaging contrast agent [Gd(HP-DO3A)(H(2)O)] (also known as ProHance) has been studied using ab initio simulations. On the basis of the molecular-level details of the mechanism derived from these simulations in aqueous solution, we unravel the underlying difference in the free energies and mechanisms of water exchange in the two diastereoisomers. These findings reveal the crucial role played by hydrogen-bonding dynamics and thus suggest their appropriate control in tailoring improved gadolinium-based constrast agents. 相似文献
997.
Fathima NN Rao JR Nair BU 《Journal of photochemistry and photobiology. B, Biology》2011,105(3):203-206
Collagen is the main component of connective tissue and finds immense applications as a biomaterial. In this study, effect of UV irradiation on collagen crosslinked with iron has been carried out. The physical and optical properties of crosslinked collagen affected by UV irradiation were analyzed using electrospectral and fluorescence studies. The electronic spectral studies showed that the photoproducts formed on UV radiation decrease in the presence of iron. Circular dichroic studies revealed that the conformational changes brought about in the protein due to UV irradiation have been reduced owing to the crosslinking with iron. However, prolonged irradiation does bring about conformational changes to the protein. 相似文献
998.
Silver sensitized titanium vanadium mixed Ag/TiV oxide photocatalyst was synthesized using sol-gel technique. The catalyst was characterized using XRD, SEM, EDAX, HRTEM, UV-DRS, XPS, and PL analysis which reveal the formation of a predominantly rutile mixed phase nanoparticles of 25-30 nm crystallite size. The catalyst showed a marked red-shift in the absorption spectrum compared to Degussa P25. It exhibited a remarkable enhancement in the visible light photocatalytic activity in inactivating Escherichia coli, a gram-negative pathogenic bacterium, too. The conclusions are supported by a comparison with an identically synthesized TiV oxide sample. A microbicidal photonic efficiency (MPE) has been defined and a method for its determination has been proposed to facilitate quantification of the performance of the photocatalyst and the disinfection system taking into account the response of the catalyst to the radiation intensity. 相似文献
999.
Rejinold NS Muthunarayanan M Divyarani VV Sreerekha PR Chennazhi KP Nair SV Tamura H Jayakumar R 《Journal of colloid and interface science》2011,360(1):39-51
This study aims at the formulation of curcumin with biodegradable thermoresponsive chitosan-g-poly (N-vinylcaprolactam) nanoparticles (TRC-NPs) for cancer drug delivery. The spherical curcumin-loaded nanoparticles of size 220 nm were characterized, and the biological properties were studied using flow cytometry and cytotoxicity by MTT assay. The in vitro drug release was higher at above LCST compared to that at below LCST. TRC-NPs in the concentration range of 100-1000 μg/mL were non-toxic to an array of cell lines. The cellular localization of the curcumin-loaded TRC-NPs was confirmed from green fluorescence inside the cells. The time-dependent curcumin uptake by the cells was quantified by UV spectrophotometer. Curcumin-loaded TRC-NPs showed specific toxicity to cancer cells at above their LCST. Flow cytometric analysis showed increased apoptosis on PC3 compared to L929 by curcumin-loaded TRC-NPs. These results indicate that novel curcumin-loaded TRC-NPs could be a promising candidate for cancer drug delivery. 相似文献
1000.
Mini PA Balakrishnan A Nair SV Subramanian KR 《Chemical communications (Cambridge, England)》2011,47(20):5753-5755
We report on the development and characterization of high performance supercapacitor electrodes synthesized using electrophoretic deposition of graphene, upon which the poly(pyrrole)-layer was electropolymerised. The highly capacitive electrode had a specific capacitance of 1510 F g(-1), area capacitance of 151 mF cm(-2) and volume capacitance of 151 F cm(-3) at 10 mV s(-1). 相似文献