@article { ISI:000226473300004, title = {DNA and PNA as templates for building nanoassemblies via electrostatic complexation with gold nanoparticles}, journal = {Current Applied Physics}, volume = {5}, number = {2}, year = {2005}, note = {Indo-Japan Workshop on Advanced Molecular Electronics and Bionics, Kyushu Inst Technol, Grad Sch Life Sci \& Syst Engn, Kitakyushu, JAPAN, DEC 11-13, 2003}, month = {FEB}, pages = {102-107}, publisher = {ELSEVIER SCIENCE BV}, address = {PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS}, abstract = {

Organisation of nanoparticles on structurally well-defined templates is a first step towards creating nanomachines. In this respect, nucleic acids are ideal structural templates and a variety of secondary structures realizable from DNA/RNA - e.g., duplexes, hairpins, triplexes, cruciforms, tetraplexes can be exploited to engineer nanoparticle organization at will. We have used oligonucleotides and their analogues such as phosphorothioates and peptide nucleic acids to electrostatically encapsulate cationic-capped gold nanoparticles. This article describes synthesis and characterization of DNA/PNA-gold nanoparticle composites using TEM and UV-T-m techniques. These types of assemblies may have potential for creating nanowires and lithographic circuits. (C) 2004 Elsevier B.V. All rights reserved.

}, keywords = {DNA, DNA-gold nanoparticle interactions, nanoassemblies, PNA}, issn = {1567-1739}, doi = {10.1016/j.cap.2004.06.020}, author = {Gourishankar, A and Shukla, S and Pasricha, R and Sastry, M and Ganesh, Krishna N.} } @article { ISI:000233789900025, title = {Free-standing nanogold membranes as supports for the growth of calcium phosphate crystals}, journal = {Biotechnology Progress}, volume = {21}, number = {6}, year = {2005}, month = {NOV}, pages = {1759-1767}, publisher = {WILEY-BLACKWELL}, type = {Article}, address = {111 RIVER ST, HOBOKEN 07030-5774, NJ USA}, abstract = {

Current strategies for bone tissue regeneration focus on the development of implantable matrices that mimic biological tissues. Inorganic composites are of special interest for bone substitute applications. It is necessary to create an artificial three-dimensional scaffold-like porous material with certain geometrical structure to induce bone growth. We report here the growth of calcium phosphate crystals on free-standing carboxylic acid functionalized gold nanoparticle membranes. The gold nanoparticle membrane is synthesized by the spontaneous reduction of aqueous chloroaurate ions by a diamine molecule at a liquid-liquid interface. This membrane is robust and malleable, and most importantly, the gold nanoparticles in the membrane may be functionalized with suitable ligands. In this study, the amino acids aspartic acid and cysteine together with an aromatic bifunctional molecule, anthranilic acid, were used to modify the surface of the gold nanoparticles in the membrane. The free carboxylic acid groups on the gold nanoparticles further to functionalization with these molecules were then used to bind Ca2+ ions and reacted with phosphate ions to yield calcium phosphate. The nature of the nanogold surface modifier directed the formation of either crystalline hydroxyapatite or amorphous calcium phosphate. The nanogold membrane thus suggests potential biomedical application as biocompatible implants and grafts.

}, issn = {8756-7938}, doi = {10.1021/bp050144n}, author = {Rautaray, D and Sastry, M} } @article { ISI:000228531500004, title = {Gold nanotriangles biologically synthesized using tamarind leaf extract and potential application in vapor sensing}, journal = {Synthesis and Reactivity in Inorganic Metal-Organic and Nano-Metal Chemistry}, volume = {35}, number = {1}, year = {2005}, month = {FEB}, pages = {19-26}, publisher = {TAYLOR \& FRANCIS INC}, type = {Article}, address = {325 CHESTNUT ST, SUITE 800, PHILADELPHIA, PA 19106 USA}, abstract = {

The size and shape dependent electronic and chemical properties of metal nanoparticles has drawn the attention of chemists, physicists, biologists, and engineers who wish to use them for the development of new generation nanodevices. In this article, we report the synthesis of gold nanotriangles using tamarind leaf extract as the reducing agent. On treating aqueous chloroauric acid solution with tamarind leaf extract, rapid reduction of the chloroaurate ions is observed leading to the formation of flat and thin single crystalline gold nanotriangles. Atomic force microscopy analysis of the gold nanotriangles indicated that they ranged in thickness from 20 to 40 nm. These gold nanotriangles with unique and highly anisotropic planer shapes might find application in photonics, optoelectronics, and optical sensing. We investigated the effect of different organic solvent vapors like methanol, benzene and acetone on the conductivity of tamarind leaf extract reduced gold nanotriangles. I-V characteristics measurement of these nanotriangles was done in presence of these organic solvent vapors. The observed characteristics suggest the application of gold nanotriangles to future chemical sensors.

}, keywords = {Biosynthesis, gold nanotriangles, tamarind leaf, vapor sensing}, issn = {1553-3174}, doi = {10.1081/SIM-200047527}, author = {Ankamwar, Balaprasad and Chaudhary, M and Sastry, M} } @article { ISI:000227893300004, title = {Hollow gold and platinum nanoparticles by a transmetallation reaction in an organic solution}, journal = {Chemical Communications}, number = {13}, year = {2005}, month = {FEB}, pages = {1684-1686}, publisher = {ROYAL SOC CHEMISTRY}, type = {Article}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {Transmetallation reaction between hydrophobized silver nanoparticles with hydrophobized chloroaurate and chloroplatinate ions in chloroform results in the formation of hollow gold and platinum shell nanoparticles respectively.}, issn = {1359-7345}, doi = {10.1039/b418566h}, author = {Selvakannan, PR and Sastry, M} } @article { ISI:000227629300008, title = {Illustration of HIV-1 protease folding through a molten-globule-like intermediate using an experimental model that implicates alpha-crystallin and calcium ions}, journal = {Biochemistry}, volume = {44}, number = {10}, year = {2005}, month = {MAR}, pages = {3725-3734}, publisher = {AMER CHEMICAL SOC}, type = {Article}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

The folding of HIV-1 protease to its active form involves the coordination of structure formation and dimerization, which follows a hierarchy consisting of folding nuclei spanning from the active site, hinge region, and dimerization domain. However, the biochemical characteristics of the folding intermediates of this protein remain to be elucidated. In an experimental model, the denaturation of the tethered dimer of HIV-1 protease by guanidine hydrochloride revealed an alternative conformation resembling the molten globule state. The molten-globule state binds to the molecular chaperone alpha-crystallin and prevents its aggregation; however, the chaperone alone failed to reconstitute HIV-1 protease into its active form. Calcium ion assisted in the release of active enzyme from the chaperone complex. alpha-crystallin, a member of the small heat-shock protein, assists proteins to fold correctly; however, the underlying principle of signals responsible for chaperone-mediated protein folding remains enigmatic. X-ray photoelectron spectroscopy has been employed to provide the evidence of calcium binding to alpha-crystallin and to decipher the effect of calcium binding on the chaperone-mediated refolding of HIV-1 protease. On the basis of our spectroscopic data, we propose that calcium ions interact with the carboxyl groups of the surface-exposed acidic amino acids of alpha-crystallin bringing electrostatic interference, which plays a pivotal role in inducing conformational changes in the chaperone responsible for the release of the active enzyme.

}, issn = {0006-2960}, doi = {10.1021/bi048378n}, author = {Dash, C and Sastry, M and Rao, M} } @article { ISI:000233914500027, title = {Synthesis of CdS and alloyed CdMnS nanocrystals using aqueous foams}, journal = {Journal of Nanoscience and Nanotechnology}, volume = {5}, number = {12}, year = {2005}, month = {DEC}, pages = {2144-2154}, publisher = {AMER SCIENTIFIC PUBLISHERS}, type = {Article}, address = {25650 NORTH LEWIS WAY, STEVENSON RANCH, CA 91381-1439 USA}, abstract = {

Certain surfactant-stabilized aqueous foams provide a potentially efficient and simple chemical route for the synthesis of various nanomaterials with controllable structure, size, and shape. In the present work, a one-step process for the synthesis of CdS and Cdl(1-x)Mn(x)S (0 \< x \< 10) nanocrystals has been described. Aqueous CdCl2 and the aerosol-OT solutions are homogeneously mixed together and thereafter, nitrogen is bubbled through this solution to produce stable aqueous foam. After drainage of the foam, the freestanding dry foam consisting of cadmium cations electrostatically complexed with the anionic aerosol-OT molecules at the liquid-gas interface is treated with H2S vapor. The foam turns yellowish-orange and collapses, in the process yielding CdS nanoclusters of variable morphology. This morphology variation is appropriately attributed to growth of the CdS as well as alloyed Cd1-xMnxS nanoparticles in different regions of the foam contributing to the varying topological structure. Optical absorption spectra of both CdS and Cd1-xMnxS nanoparticles clearly show a well-defined exciton absorption feature around 450 nm due to quantum confinement effects. The interesting band edge emission characteristics of these AOT-capped CdS and Cd1-xMnxS nanoparticles produced in the foam are discussed with respect to their size and shape. Particular interest in the present novel aqueous foam approach arises due to the fact that the cubic zincblende CdS and alloyed Cd1-xMnxS nanocrystals could easily be obtained even under ambient experimental conditions itself.

}, keywords = {absorption and fluorescence, aerosol-OT, alloyed CdMnS nanocrystals, aqueous foams, CdS nanoclusters, quantum confinement, zincblende}, issn = {1533-4880}, doi = {10.1166/jnn.2005.401}, author = {Kumar, P. Senthil and Kasture, Manasi and Raghavan, U and Pasricha, R and Sastry, M} } @article { ISI:000232857900012, title = {Transmetalation reaction between hydrophobic silver nanoparticles and aqueous chloroaurate ions at the air - Water interface}, journal = {Journal of Physical Chemistry B}, volume = {109}, number = {42}, year = {2005}, month = {OCT}, pages = {19620-19626}, publisher = {AMER CHEMICAL SOC}, type = {Article}, address = {1155 16TH ST, NW, WASHINGTON, DC 20036 USA}, abstract = {

The transmetalation reaction between a sacrificial nanoparticle and more noble metal ions in solution has emerged as a novel method for creating unique hollow and bimetallic nanostructures. In this report, we investigate the possibility of carrying out the transmetalation reaction between hydrophobic silver nanoparticles assembled and constrained at the air-water interface and subphase gold ions. We observe that facile reduction of the subphase gold ions by the sacrificial silver nanoparticles occurs resulting in the formation of elongated gold nanostructures that appear to cross-link the sacrificial silver particles. This transmetalation reaction may be modulated by the insertion of an electrostatic barrier in the form of an ionizable lipid monolayer between the silver nanoparticles and the aqueous gold ions that impacts the gold nanoparticle assembly. Transmetalation reactions between nanoparticles constrained into a close-packed structure and appropriate metal ions could lead to a new strategy for metallic cross-linking of nanoparticles and generation of coatings with promising optoelectonic behavior.

}, issn = {1520-6106}, doi = {10.1021/jp0530552}, author = {Pasricha, R and Swami, A and Sastry, M} } @article { ISI:000225786100016, title = {Using the dynamic, expanding liquid-liquid interface in a Hele-Shaw cell in crystal growth and nanoparticle assembly}, journal = {Faraday Discussions}, volume = {129}, year = {2005}, month = {JAN}, pages = {205-217}, publisher = {ROYAL SOC CHEMISTRY}, address = {THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND}, abstract = {

The liquid-liquid interface has been used with considerable success in the synthesis of advanced materials ranging from (bio)minerals to inorganic membranes to nanoparticles. In almost all such cases, the interface is static. The Hele-Shaw cell in which a viscous fluid is displaced by a less viscous one in a constrained manner has been invaluable in the study of dynamic instabilities at interfaces and in the study of viscous fingering pattern formation. However, the potential of the Hele-Shaw cell in carrying out reactions at the interface between the two fluids leading to the formation of inorganic materials has been largely unrecognized and underexploited. Realizing that the dynamic liquid-liquid interface in a Hele-Shaw cell would provide opportunities to control a variety of time-scales associated with material formation, we have started a program on the use of the Hele-Shaw cell in materials synthesis. In this discussion paper, we present some of our recent results on the growth of calcium carbonate crystals in the Hele-Shaw cell by the reaction of Ca2+ ions electrostatically complexed with carboxylate ions pinned to the interface with carbonate ions present in the aqueous part of the biphasic reaction medium. We show that both polymorph selectivity and the morphology of the crystals may be modulated by varying the experimental conditions in the cell. We also discuss the possibility of using the dynamic interface in the Hele-Shaw cell to cross-link gold nanoparticles in water through bifunctional linkers present in the oil phase and investigate the nature of the structures formed.

}, issn = {1364-5498}, doi = {10.1039/b405599n}, author = {Rautaray, D and Kavathekar, R and Sastry, M} }