Showing papers by "National Chemical Laboratory published in 2004"

Biological synthesis of triangular gold nanoprisms

Abstract: The optoelectronic and physicochemical properties of nanoscale matter are a strong function of particle size. Nanoparticle shape also contributes significantly to modulating their electronic properties. Several shapes ranging from rods to wires to plates to teardrop structures may be obtained by chemical methods; triangular nanoparticles have been synthesized by using a seeded growth process. Here, we report the discovery that the extract from the lemongrass plant, when reacted with aqueous chloroaurate ions, yields a high percentage of thin, flat, single-crystalline gold nanotriangles. The nanotriangles seem to grow by a process involving rapid reduction, assembly and room-temperature sintering of 'liquid-like' spherical gold nanoparticles. The anisotropy in nanoparticle shape results in large near-infrared absorption by the particles, and highly anisotropic electron transport in films of the nanotriangles.

Gain and Loss of Fruit Flavor Compounds Produced by Wild and Cultivated Strawberry Species

Abstract: The blends of flavor compounds produced by fruits serve as biological perfumes used to attract living creatures, including humans. They include hundreds of metabolites and vary in their characteristic fruit flavor composition. The molecular mechanisms by which fruit flavor and aroma compounds are gained and lost during evolution and domestication are largely unknown. Here, we report on processes that may have been responsible for the evolution of diversity in strawberry (Fragaria spp) fruit flavor components. Whereas the terpenoid profile of cultivated strawberry species is dominated by the monoterpene linalool and the sesquiterpene nerolidol, fruit of wild strawberry species emit mainly olefinic monoterpenes and myrtenyl acetate, which are not found in the cultivated species. We used cDNA microarray analysis to identify the F. ananassa Nerolidol Synthase1 (FaNES1) gene in cultivated strawberry and showed that the recombinant FaNES1 enzyme produced in Escherichia coli cells is capable of generating both linalool and nerolidol when supplied with geranyl diphosphate (GPP) or farnesyl diphosphate (FPP), respectively. Characterization of additional genes that are very similar to FaNES1 from both the wild and cultivated strawberry species (FaNES2 and F. vesca NES1) showed that only FaNES1 is exclusively present and highly expressed in the fruit of cultivated (octaploid) varieties. It encodes a protein truncated at its N terminus. Green fluorescent protein localization experiments suggest that a change in subcellular localization led to the FaNES1 enzyme encountering both GPP and FPP, allowing it to produce linalool and nerolidol. Conversely, an insertional mutation affected the expression of a terpene synthase gene that differs from that in the cultivated species (termed F. ananassa Pinene Synthase). It encodes an enzyme capable of catalyzing the biosynthesis of the typical wild species monoterpenes, such as α-pinene and β-myrcene, and caused the loss of these compounds in the cultivated strawberries. The loss of α-pinene also further influenced the fruit flavor profile because it was no longer available as a substrate for the production of the downstream compounds myrtenol and myrtenyl acetate. This phenomenon was demonstrated by cloning and characterizing a cytochrome P450 gene (Pinene Hydroxylase) that encodes the enzyme catalyzing the C10 hydroxylation of α-pinene to myrtenol. The findings shed light on the molecular evolutionary mechanisms resulting in different flavor profiles that are eventually selected for in domesticated species.

Biosynthesis of zirconia nanoparticles using the fungus Fusarium oxysporum

Abstract: Zirconia nanoparticles may be produced by challenging the fungus Fusarium oxysporum with aqueous ZrF62− anions; extra-cellular protein-mediated hydrolysis of the anionic complexes results in the facile room temperature synthesis of nanocrystalline zirconia. Extracellular hydrolysis of the metal anions by cationic proteins of molecular weight around 24 to 28 kDa, which are rather similar in nature to silicatein, is shown to be responsible for the synthesis of zirconia nanoparticles, opening up the exciting possibility of large-scale biological synthesis of technologically important oxide materials.

Pt and Pd Nanoparticles Immobilized on Amine-Functionalized Zeolite: Excellent Catalysts for Hydrogenation and Heck Reactions

Abstract: Development of simple and reliable protocols for the immobilization of catalytically active metal nanoparticles is an important aspect of the nanomaterials field. Amine groups bind very strongly to platinum and palladium nanoparticles; therefore, we have attempted to entrap aqueous platinum and palladium nanoparticles on the surface of micron-sized zeolite particles functionalized with amine groups. In this paper, we demonstrate that platinum and palladium nanoparticles bound at high surface coverage on 3-aminopropyltrimethoxysilane (APTS)-functionalized Na−Y zeolites are excellent heterogeneous catalysts for hydrogenation and Heck reactions. The assembly of platinum or palladium nanoparticles on the zeolite surface occurs via an interaction with the amine groups present in APTS leading to a new class of catalyst. The synthesized catalysts were well-characterized by UV−vis, FTIR, TGA, XRD, XPS, and TEM. TEM images of the fresh and used catalysts indeed show that the platinum and palladium nanoparticles su...

Synthesis of aqueous Au core-Ag shell nanoparticles using tyrosine as a pH-dependent reducing agent and assembling phase-transferred silver nanoparticles at the air-water interface.

Abstract: We demonstrate that the amino acid tyrosine is an excellent reducing agent under alkaline conditions and may be used to reduce Ag+ ions to synthesize stable silver nanoparticles in water. The tyrosine-reduced silver nanoparticles may be separated out as a powder that is readily redispersible in water. The silver ion reduction at high pH occurs due to ionization of the phenolic group in tyrosine that is then capable of reducing Ag+ ions and is in turn converted to a semi-quinone structure. These silver nanoparticles can easily be transferred to chloroform containing the cationic surfactant octadecylamine by an electrostatic complexation process. The now hydrophobic silver nanoparticles may be spread on the surface of water and assembled into highly ordered, linear superstructures that could be transferred as multilayers onto suitable supports by the versatile Langmuir-Blodgett technique. Further, tyrosine molecules bound to the surface of Au nanoparticles through amine groups in the amino acid may be used to selectively reduce silver ions at high pH on the surface of the Au nanoparticles, thus leading to a simple strategy for realizing phase-pure Au core-Ag shell nanostructures.

Novel one-step synthesis of amine-stabilized aqueous colloidal gold nanoparticles

Abstract: We demonstrate a simple one-step process for the synthesis of water-dispersed spherical gold nanoparticles using the multifunctional molecule oleyl amine (OLA) that electrostatically complexes with aqueous chloroaurate ions, reduces them, and subsequently caps the nanoparticles thus formed. The gold particles thus formed were of the fcc phase and were fairly monodisperse with particular concentrations of capping molecules.

Active Sites and Reactive Intermediates in Titanium Silicate Molecular Sieves

Abstract: This review is a summary and critical analysis of recent advances in the understanding of (a) the nature and coordination state of Ti ions and other functional groups (such as OH) on dehydrated titanium silicate molecular sieves, (b) the type and structure of the oxo intermediates generated by the interaction of these active sites with oxidant/reactant molecules during catalytic reactions, and (c) the factors that influence the reactivity and selectivity of these active sites and reaction intermediates. In the dehydrated state, most of the Ti 4+ ions have the tetrapodal (Ti(OSi) 4 ) or the tripodal (Ti(OSi) 3 OH) structure. On contact with H 2 O 2 , titanium oxo species, Ti(O 2 H) and Ti(O 2 − ), respectively, are formed. On reaction with organic reactants, O–O bond cleavage in these titanium oxo species occurs in a hetero- or homolytic manner. Product selectivity is determined by the relative importance of these two modes of O–O cleavage. Factors such as the coordinative environment of titanium, substituents on the O–O bond (H or alkyl), temperature, solvent, nature of the organic reactant, etc. influence the mode of O–O cleavage. Correlations between the structure and catalytic activity of titanium sites and oxo-titanium intermediates are also described.

Identification of Surface Species on Titania-Supported Manganese, Chromium, and Copper Oxide Low-Temperature SCR Catalysts

Abstract: TiO2-supported transition metal oxides (Mn, Cr, and Cu) for the SCR of NO with NH3 have been synthesized by wet impregnation. The adsorption and coadsorption of NH3, NO, and O2, in conjunction with in situ FT-IR spectroscopy, was used to elucidate the reaction mechanism as the samples were heated from 323 to 673 K. While Cr was the only transition metal that generated significant amounts of Bronsted acidity, strong Lewis acid sites were present over all of the materials. The peak strength corresponding to the δs(NH3) coordinated to Lewis acid sites decreased in the following order: Ti > Mn > Cr ∼ Cu. Similarly, the peak strength corresponding to the δas(NH3) coordinated to Lewis acid sites decreased as follows: Mn > Cr ∼ Cu. Exposing the catalysts to oxygen before the introduction of NO did not impact the adsorption of NO as nitrates on the catalysts, suggesting that labile lattice oxygen plays an important role in the formation of nitrates. Three types of nitrates were observed after the adsorption of ...

Azetidin-2-ones, synthon for biologically important compounds.

Abstract: Azetidin-2-one, a four-membered cyclic lactam (β-lactam) skeleton has been recognised as a useful building block for the synthesis of a large number of organic molecules by exploiting the strain energy associated with it, in addition to its use in the synthesis of a variety of β-lactam antibiotics. Efforts have been made in exploring such new aspects of β-lactam chemistry using enantiomerically pure β-lactams as versatile intermediates for the synthesis of aromatic β-amino acids and their derivatives, peptides, polyamines, polyamino alcohols, amino sugars and polyamino ethers. The development of methodologies based on β- lactam nucleus is now referred as the β-lactam synthon methods. The selective bond cleavage of the strained ring coupled with further interesting transformation render this fascinating molecule as a powerful building block. This provides an access to diverse structural type of synthetic target molecules lacking β-lactam ring structure. This review provides an account of synthesis of organic compounds having biological significance at the same time lacking β-lactam ring, by using β-lactam as synthon.

Isothermal Titration Calorimetry Studies on the Binding of Amino Acids to Gold Nanoparticles

Abstract: Isothermal titration calorimetry (ITC) is a powerful and highly sensitive technique commonly used to study interactions between biomolecules in dilute aqueous solutions, both from thermodynamic and kinetics points of view. In this report, we show that ITC may be used to follow the binding of ligands such as amino acids to the surface of inorganic materials such as gold nanoparticles. More specifically, we have studied the binding of one basic amino acid, lysine, and an acidic amino acid, aspartic acid, with aqueous gold nanoparticles at physiological pH. Strong binding of aspartic acid with the gold nanoparticles under these conditions is indicated by ITC, while weak binding was observed in the case of lysine. The differences in binding are attributed to protonation of amine groups in lysine at physiological pH (pI 9.4) while they are not protonated for aspartic acid (pI 2.77). That this is the likely mechanism is indicated by the ITC measurement of binding of lysine with nanogold at pH 11 (when the amine groups are not protonated). The binding of the amino acids with gold nanoparticles has been validated with other techniques such as gel electrophoresis and X-ray photoemission spectroscopy.

Room temperature ionic liquid promoted regioselective synthesis of 2-aryl benzimidazoles, benzoxazoles and benzthiazoles under ambient conditions

Abstract: A regioselective one-pot synthesis of 2-aryl benzimidazoles, benzoxazoles and benzthiazoles has been achieved in excellent isolated yields under ambient conditions using the ionic liquids, 1-butylimidazolium tetraflouroborate ([Hbim]BF4) and 1,3-di-n-butylimidazolium tetrafluoroborate ([bbim]BF4) as reaction media and promoters. There was no need for the use of an additional catalyst normally employed in the methodologies reported so far.

A 3-month, randomized, placebo-controlled, neuroleptic discontinuation study in 100 people with dementia: the neuropsychiatric inventory median cutoff is a predictor of clinical outcome.

Abstract: BACKGROUND: Although few placebo-controlled neuroleptic discontinuation studies have been conducted in people with dementia, such studies are essential to inform key clinical decisions. METHOD: A 3-month, double-blind, placebo-controlled, neuroleptic discontinuation study (June 2000 to June 2002) was completed in 100 care-facility residents with probable or possible Alzheimer's disease (according to National Institute of Neurological and Communicative Diseases and Stroke/Alzheimer's Disease and Related Disorders Association criteria) who had no severe behavioral disturbances and had been taking neuroleptics for longer than 3 months. The Neuropsychiatric Inventory (NPI) was used to measure changes in behavioral and psychiatric symptoms. Quality of life was evaluated using Dementia Care Mapping. RESULTS: Eighty-two patients completed the 1-month assessment (36 placebo, 46 active). The number of participants withdrawing overall (N = 14 [30%] placebo, N = 14 [26%] active treatment) and because of exacerbation of behavioral symptoms (N = 6 [13%] placebo, N = 5 [9%] active treatment) was similar in the neuroleptic- and placebo-treated patients. As hypothesized, patients with baseline NPI scores at or below the median (< or = 14) had a particularly good outcome, with a significantly greater reduction of agitation in the patients receiving placebo (Mann-Whitney U test, z = 2.4, p =.018), while patients with higher baseline NPI scores were significantly more likely to develop marked behavioral problems if discontinued from neuroleptics (chi(2) = 6.8, p =.009). There was no overall difference in the change of quality of life parameters between groups. DISCUSSION: A standardized evaluation with an instrument such as the NPI may be a clinical indicator of which people with dementia are likely to benefit from discontinuation of neuroleptic treatment.

Silica functionalised sulphonic acid groups: synthesis, characterization and catalytic activity in acetalization and acetylation reactions

Abstract: A simple synthesis procedure for the immobilization of propyl thiol groups on silica is investigated using various concentrations of 3-mercapto propyl trimethoxy silane (3-MPTS) in the range of 5–40%. The thiol group functionalised silicas (SiO2–SH) were then oxidized to Bronsted sulphonic acid silica materials (SiO2–SO3H) using aqueous H2O2 as oxidizing agent. The surface structures of the functionalized catalysts were analyzed by a series of characterization techniques like elemental analysis, FTIR, TG-DTA, Surface area measurements, XPS, 13 C CP MAS NMR and 29 Si MAS NMR. The 13 C CP MAS NMR analyses confirm that disulphide species are not formed under the present preparation condition of catalysts. The acidity of the synthesized catalysts were further confirmed by the temperature programmed desorption of ammonia. The catalytic activity of the sulphonic acid functionalized silicas was evaluated in the liquid phase acetalization of ethyl acetoacetate with ethylene glycol and in the acetylation of anisole with acetic anhydride. The catalysts were found to be active in the acetalization reaction, which needs mild acidic sites, while the acetylation reactions gave lower activity, probably it needs stronger acid sites. A 30 wt.% SO3H loaded silica (SiO2–SO3H30) was recycled two times in the acetalization of ethyl acetoacetate and no major change in the conversion of EAA and selectivity to fructone is seen, which further argue against the possibility of leaching of the anchored sulphur containing species during reactions.

Assessment of genetic diversity in Trigonella foenum-graecum and Trigonella caerulea using ISSR and RAPD markers

Abstract: Background Various species of genus Trigonella are important from medical and culinary aspect. Among these, Trigonella foenum-graecum is commonly grown as a vegetable. This anti-diabetic herb can lower blood glucose and cholesterol levels. Another species, Trigonella caerulea is used as food in the form of young seedlings. This herb is also used in cheese making. However, little is known about the genetic variation present in these species. In this report we describe the use of ISSR and RAPD markers to study genetic diversity in both, Trigonella foenum-graecum and Trigonella caerulea.

Neuropathological Substrates of Psychiatric Symptoms in Prospectively Studied Patients With Autopsy-Confirmed Dementia With Lewy Bodies

Abstract: OBJECTIVE: This investigation was undertaken to clarify the neuropathological substrates of key psychiatric symptoms in dementia with Lewy bodies. METHOD: The authors studied 112 autopsy-confirmed cases of dementia with Lewy bodies in patients who had had annual standardized clinical evaluations until their death. The relationships of persistent psychiatric symptoms (visual hallucinations, delusions, depression) to plaques (Consortium to Establish a Registry for Alzheimer’s Disease protocol), tangles (Braak staging), and Lewy bodies (consensus Lewy body staging) were evaluated. In addition, symptom frequency and persistent symptoms were compared in the patients with Lewy body dementia and 90 patients with autopsy-confirmed Alzheimer’s disease studied prospectively during life. RESULTS: The main neuropathological correlate of persistent visual hallucinations was the presence of less severe tangle pathology, but there was no significant association between tangle pathology and persistent delusions. Lewy bod...

Isothermal Titration Calorimetry Studies on the Binding of DNA Bases and PNA Base Monomers to Gold Nanoparticles

Abstract: An isothermal titration calorimetric (ITC) investigation of the interaction of DNA bases and PNA base monomers with gold nanoparticles is described revealing a binding sequence in the order C > G > A > T. Direct measurement of the strength of interaction of ligands with nanogold by ITC has important implications in surface modification strategies for biomedical, catalysis, and nanoarchitecture applications.

Creating Spaces of Resistance: Development NGOs and their Clients in Ghana, India and Mexico

Abstract: Development NGOs have been accused by some of being new instruments of control, domesticated by the neoliberal project. For others, they elaborate and pursue alternative dreams. In this paper, we argue that, although the majority of NGOs have been co-opted to serve hegemonic development agendas, they nevertheless present a fluid, contradictory web of relations, within which a significant minority seeks to make spaces of resistance, and where even the most neoliberal NGOs are used by some clients to create new associational spaces. Drawing on work with NGOs in Ghana, India, Mexico and Europe, we explore various strategies deployed by this minority of “independent thinking NGOs”. We argue that there is an important production of Melucci's submerged networks or latent social movements, however limited their political impact to date.