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61.
Investigating structural aspects to understand the putative/claimed non‐toxicity of the Hg‐based Ayurvedic drug Rasasindura using XAFS 下载免费PDF全文
Nitya Ramanan Debdutta Lahiri Parasmani Rajput Ramesh Chandra Varma A. Arun T. S. Muraleedharan K. K. Pandey Nandita Maiti S. N. Jha Surinder M. Sharma 《Journal of synchrotron radiation》2015,22(5):1233-1241
XANES‐ and EXAFS‐based analysis of the Ayurvedic Hg‐based nano‐drug Rasasindura has been performed to seek evidence of its non‐toxicity. Rasasindura is determined to be composed of single‐phase α‐HgS nanoparticles (size ~24 nm), free of Hg0 or organic molecules; its structure is determined to be robust (<3% defects). The non‐existence of Hg0 implies the absence of Hg‐based toxicity and establishes that chemical form, rather than content of heavy metals, is the correct parameter for evaluating the toxicity in these drugs. The stable α‐HgS form (strong Hg—S covalent bond and robust particle character) ensures the integrity of the drug during delivery and prevention of its reduction to Hg0 within the human body. Further, these comparative studies establish that structural parameters (size dispersion, coordination configuration) are better controlled in Rasasindura. This places the Ayurvedic synthesis method on par with contemporary techniques of nanoparticle synthesis. 相似文献
62.
Thijs Stuyver Rajeev Ramanan Dibyendu Mallick Sason Shaik 《Angewandte Chemie (International ed. in English)》2020,59(20):7915-7920
This contribution follows the recent remarkable catalysis observed by Groves et al. in hydrogen‐abstraction reactions by a) an oxoferryl porphyrin radical‐cation complex [Por?+FeIV(O)Lax] and b) a hydroxoiron porphyrazine ferric complex [PyPzFeIII(OH)Lax], both of which involve positively charged substituents on the outer circumference of the respective macrocyclic ligands. These charge‐coronated complexes are analogues of the biologically important Compound I (Cpd I) and synthetic hydroxoferric species, respectively. We demonstrate that the observed enhancement of the H‐abstraction catalysis for these systems is a purely electrostatic effect, elicited by the local charges embedded on the peripheries of the respective macrocyclic ligands. Our findings provide new insights into how electrostatics can be employed to tune the catalytic activity of metalloenzymes and can thus contribute to the future design of new and highly efficient hydrogen‐abstraction catalysts. 相似文献
63.
Ramanan Krishnamoorti Richard A. Vaia 《Journal of polymer science. Part A, Polymer chemistry》2007,45(24):3252-3256
Polymer nanocomposites are distinguished by the convergence of length scales corresponding to the radius of gyration of the polymer chains, a dimension of the nanoparticle and the mean distance between the nanoparticles. The consequences of this convergence on the physics of the polymer chains are considered, and some of the outstanding issues and their potential consequences on structure—property relations for polymer nanocomposites are highlighted. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3252–3256, 2007 相似文献
64.
Formation of high nuclearity mixed-valent polyoxovanadates in the presence of copper amine complexes
Jency Thomas Sanjeev Sharma S. E. Lofland K. V. Ramanujachary A. Ramanan 《Journal of Chemical Sciences》2006,118(1):79-86
Two new Müller-type clusters, a one-dimensional solid [Cu(en)]2
4[Cl ⊂V15O36]−12H2O1, and a three-dimensional solid [Cu(pn)]2
4[Cl ⊂V18O42]·12H2O2, have been synthesised by employing identical hydrothermal conditions except varying the nature of organic diamine.1 crystallised in a chiral space groupP212121 witha = 12.757(1),b = 18.927(2) andc = 28.590(3) ?, andZ =4.2 crystallised in a tetragonal system with space groupP4/nnc,a = 15.113(1) andc = 18.542(3) ?, andZ = 2. Mixed-valent vanadium ions in structures1 and2 have been established both by magnetisation and bond-length bond-valence measurements. Chemistry of formation of high nuclearity
polyoxovanadate clusters is discussed.
Dedicated to Prof J Gopalakrishnan on his 62nd birthday. 相似文献
65.
Karl W. Putz Cynthia A. Mitchell Ramanan Krishnamoorti Peter F. Green 《Journal of Polymer Science.Polymer Physics》2004,42(12):2286-2293
Dynamic mechanical analysis, nuclear magnetic resonance, and thermogravimetric analysis experiments were performed on pure poly(methyl methacrylate) and on in situ polymerized single-walled carbon nanotube (SWNT)/PMMA nanocomposites. The addition of less than 0.1 wt % SWNT to PMMA led to an increase in the low-temperature elastic modulus of approximately 10% beyond that of pure PMMA. The glass-transition temperature and the elastic modulus at higher temperatures of the nanocomposites remained unchanged from those of pure PMMA. These changes were associated with excessive cohesive interactions between the large-surface area nanotubes and PMMA and were not due to changes in the microstructural features of the polymer during synthesis. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2286–2293, 2004 相似文献
66.
Cynthia A. Mitchell Ramanan Krishnamoorti 《Journal of Polymer Science.Polymer Physics》2002,40(14):1434-1443
The melt‐state viscoelastic properties of nanocomposites prepared with a symmetrical polystyrene–polyisoprene block copolymer and organically modified layered silicates are examined. Nanocomposites based on three thermodynamically equivalent organically modified layered silicates, primarily differing in lateral disk diameter (d), are studied with small‐amplitude oscillatory shear. The effects of the domain structure of the ordered block copolymer and the mesoscale dispersion of the layered silicates on the rheological properties are examined via a comparison of data for the nanocomposites in the ordered and disordered states of the block copolymer. Hybrids prepared with 5 wt % organically modified fluorohectorite (d ~ 10 μm) and montmorillonite (d ~ 1 μm) demonstrate a notable decrease in the frequency dependence of the moduli at low frequencies and a significant enhancement in the complex viscosity at low frequencies in the disordered state. This behavior is understood in terms of the development of a percolated layered‐silicate network structure. However, the viscoelastic properties in the disordered state with 5 wt % organically modified laponite (d ~ 30 nm) and in the ordered state of the block copolymer for all layered silicates demonstrate only minor changes from those observed for the unfilled polymer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1434–1443, 2002 相似文献
67.
Packard CE Aidala KE Ramanan S Bulović V 《Langmuir : the ACS journal of surfaces and colloids》2011,27(15):9073-9076
We demonstrate that "contact patterning" subtractively patterns a wide range of molecular organic films of nanoscale thickness with nanometer-scale accuracy. In "contact patterning", an elastomeric stamp with raised features is brought into contact with the organic film and subsequently removed, generating patterns by the diffusion of the film molecules into the stamp. The mechanism of material removal via diffusion is documented over spans of minutes, hours, and days and is shown to be consistently repeatable. Contact patterning provides a photolithography-free, potentially scalable approach to subtractive patterning of a wide range of molecular organic films. 相似文献
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Dr. Johannes Moll Dr. Robert Naumann Lukas Sorge Dr. Christoph Förster Niklas Gessner Lukas Burkhardt Naz Ugur Prof. Dr. Patrick Nuernberger Prof. Dr. Wolfram Seidel Dr. Charusheela Ramanan Prof. Dr. Matthias Bauer Prof. Dr. Katja Heinze 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(57):e202201858
Increasing the metal-to-ligand charge transfer (MLCT) excited state lifetime of polypyridine iron(II) complexes can be achieved by lowering the ligand's π* orbital energy and by increasing the ligand field splitting. In the homo- and heteroleptic complexes [Fe(cpmp)2]2+ ( 12+ ) and [Fe(cpmp)(ddpd)]2+ ( 22+ ) with the tridentate ligands 6,2’’-carboxypyridyl-2,2’-methylamine-pyridyl-pyridine (cpmp) and N,N’-dimethyl-N,N’-di-pyridin-2-ylpyridine-2,6-diamine (ddpd) two or one dipyridyl ketone moieties provide low energy π* acceptor orbitals. A good metal-ligand orbital overlap to increase the ligand field splitting is achieved by optimizing the octahedricity through CO and NMe units between the coordinating pyridines which enable the formation of six-membered chelate rings. The push-pull ligand cpmp provides intra-ligand and ligand-to-ligand charge transfer (ILCT, LL'CT) excited states in addition to MLCT excited states. Ground and excited state properties of 12+ and 22+ were accessed by X-ray diffraction analyses, resonance Raman spectroscopy, (spectro)electrochemistry, EPR spectroscopy, X-ray emission spectroscopy, static and time-resolved IR and UV/Vis/NIR absorption spectroscopy as well as quantum chemical calculations. 相似文献