Showing papers by "National Chemical Laboratory published in 1997"

Low-Temperature Nonoxidative Activation of Methane over H-Galloaluminosilicate (MFI) Zeolite

Abstract: Conversion of methane to higher hydrocarbons by its low-temperature activation without forming undesirable carbon oxides is of great scientific and practical importance Methane can be highly activated, yielding high rates of conversion to higher hydrocarbons and aromatics (10 to 45 percent) at low temperatures (400° to 600°C), by its reaction over H-galloaluminosilicate ZSM-5 type (MFI) zeolite in the presence of alkenes or higher alkanes The methane activation results from its hydrogen-transfer reaction with alkenes

On the stability of carboxylic acid derivatized gold colloidal particles: the role of colloidal solution pH studied by optical absorption spectroscopy

Abstract: Results of an investigation into the influence of hydrosol pH on the optical properties of gold colloidal particles capped with a novel aromatic bifunctional molecule, 4-carboxythiophenol (4-CTP), are presented. Changes in the optical properties of the carboxylic acid derivatized clusters have been interpreted as arising due to flocculation of the clusters and quantified using a “flocculation parameter” (Weisbecker, C. S.; Merritt, M. V.; Whitesides, G. M. Langmuir 1996, 12, 3763). It is observed that there is a large fall in the flocculation parameter above hydrosol pH = 4 which then is constant above pH = 7. This indicates that the cluster distribution is very stable at high pH due to complete charging of the clusters and maximization of the repulsive electrostatic interaction. Contact angle titration measurements on a self-assembled monolayer of 4-CTP on gold revealed an analogous trend with the contact angle falling above pH = 6 and then remaining constant above pH = 8. This indicates that monolayer f...

Microbial Extracellular Glycolipid Induction of Differentiation and Inhibition of the Protein Kinase C Activity of Human Promyelocytic Leukemia Cell Line HL60

Abstract: The biological activities of 7 microbial extracellular glycolipids including mannosylerythritol lipid (MEL)-A, MEL-B, polyol lipid (PL), rhamnolipid (RL), sophorose lipid (SL), succinoyl trehalose lipid (STL)-1, and STL-3 were investigated. All glycolipids except for RL were found to induce cell differentiation instead of cell proliferation in the human promyelocytic leukemia cell line HL60. To identify the differentiation direction of the induced cells, the leukocyte esterase activities were cytologically investigated, and the results showed that MEL-A, MEL-B, and PL induced HL60 to differentiate into granulocytes, while SL, STL-1, and STL-3 induced differentiation into monocytes. The 6 effective glycolipids also increased nitroblue tetrazolium (NBT) reducing ability, which is a common differentiation-associated characteristic in monocytes and granulocytes. Furthermore, it was also observed that these 6 glycolipids inhibited the activity of phospholipid- and Ca(2+)-dependent protein kinase. Additionally, the 6 effective glycolipids also induced the human myelogenous leukemia cell line K562 and the human basophilic leukemia cell line KU812 to differentiate into monocytes, granulocytes, and megakaryocytes.

Langmuir−Blodgett Films of Carboxylic Acid Derivatized Silver Colloidal Particles: Role of Subphase pH on Degree of Cluster Incorporation

Abstract: In this paper, we demonstrate that reasonably ordered multilayer films of silver clusters can be deposited by the Langmuir−Blodgett (LB) technique. The approach consists of electrostatically immobilizing negatively charged carboxylic acid derivatized silver colloidal particles at the air−water interface using positively charged fatty amine Langmuir monolayers. The degree of cluster incorporation into the Langmuir monolayer has been controlled by varying the charge on the amine molecules through the colloidal subphase pH. Pressure−area isotherms were used to follow adsorption of the silver colloidal particles at the amine surface, while quartz crystal microgravimetry (QCM), optical absorption spectroscopy, infrared spectroscopy, contact angle measurements, and optical interferometry were used to characterize the multilayer LB films. The films were found to grow in the classical Y-type mode. Optical interferometry indicated a bilayer thickness of 106 A, which yields a cluster size of ∼55 A, in reasonable ag...

Direct conversion of methane to methanol

Abstract: Methane has been converted to a mixture of methanol and formaldehyde at ambient conditions with high activity (TON above 100) and selectivity (CO 2 less than 5%) using phthalocyanine complexes of Fe and Cu encapsulated in zeolites as catalysts and O 2 / tert -butyl hydroperoxide as oxidants.

Differentiation of human promyelocytic leukemia cell line HL60 by microbial extracellular glycolipids

Abstract: Microbial extracellular glycolipids, succinoyl trehalose lipid (STL), and mannosylerythritol lipid (MEL) inhibited the growth of a human promyelocytic leukemia cell line, HL60, and induced their morphological changes. The results of specific and nonspecific leukocyte esterase activities showed that STL induced monocytotic differentiation while MEL induced granulocytic differentiation. STL and MEL markedly increased common differentiation-associated characteristics in monocytes and granulocytes, such as nitroblue tetrazolium (NBT) reducing ability, expression of Fc receptors, and phagocytic activities in HL60 cells, respectively. Neither sugar moieties nor fatty acids in the free form, the individual components of STL and MEL, were effective at inducing the differentiation of HL60 cells. The induction of differentiation was not due to surface activities of STL and MEL on the basis of the complete ineffectiveness of the analogues tested. The composition of cell surface glycosphingolipids (GSL) changed such that the GM3/LacCer ratio increased in STL-treated cells, whereas it decreased in MEL-treated cells. HL60 cells treated with STL and MEL exhibited a significant decrease in the activity of the intracellular phospholipid- and Ca2+-dependent protein kinase (protein kinase C). Furthermore, the serine/threonine phosphorylations in intact HL60 cells were clearly inhibited by the presence of GM3 and MEL, but not by LacCer and STL. These results suggest that the differentiation-inducing activity of STL and MEL is not due to a simple detergent-like effect but due to a specific action on the plasma membrane. The inhibitory effect of STL on protein kinase activity was through increasing GM3, but MEL had a direct inhibitory effect.

Adsorption of Silver Colloidal Particles through Covalent Linkage to Self-Assembled Monolayers

Abstract: Self-assembled monolayers of a small bifunctional molecule (4-carboxythiophenol) have been formed on Al and Au surfaces. The nature of coordination of the molecules to the two metal surfaces is different, leading to different terminal functionality of the monolayer surface. This aspect has been favorably exploited to self-assemble Ag particles from a colloidal solution on the monolayer-covered Al surface which is thiol rich. The self-assembly of the Ag particles does not take place on the monolayer-covered Au surface with carboxylic acid surface functionality. The adsorption of the monolayer on Al and Au surfaces and Ag colloidal particles on the self-assembled monolayer has been followed using electron microscopy, quartz crystal microbalance, and X-ray photoemission measurements. The two-dimensional array of strongly bonded metal nanoparticles shows potential for application as metal-supported catalysts and sensors, generation of submicrometer electronic devices, high density data storage, etc.

Kinetics of hydroformylation of l-dodecene using homogeneous HRh(CO) (PPh3)3 catalyst

Abstract: The kinetics of the HRh(CO(PPh 3 ) 3 catalyzed hydroformylation of l-dodecene has been investigated in a temperature range of 323–343, K. The effect of l-dodecene and catalyst concentration, P H and P CO , on the rate of reaction has been studied. The rate was found to be first order with respect to catalyst concentration and partial pressure of hydrogen. The rate vs. P CO shows a typical case of substrate inhibited kinetics. The rate was found to be first order with respect to l-dodecene in the lower concentration range while at higher concentrations a zero order dependence was observed. A rate equation has been proposed and kinetic parameters evaluated. The activation energy was found to be 57.12 kJ/mol. A batch reactor model has been a used to predict the concentration-time profiles which were found to agree well with the experimental data at different temperatures. This indicates the applicability of the rate model over a wide range of conditions.

Synthesis and study of organically capped ultra small clusters of cadmium sulphide

Abstract: Ultra small clusters of cadmium sulphide are synthesized using non-aqueous and aqueous chemical methods. Thiophenol has been used as a capping agent for non-aqueous synthesis whereas various reagents such as mercaptoethanol, hexametaphosphate, ethylene glycol and ethanol have been used as additives for an aqueous method of synthesis. Properties of the clusters synthesized are discussed based on optical absorption, X-ray diffraction, transmission electron diffraction and photoelectron spectroscopy. Particles as small as ∼0.7 nm diameter could be synthesized with thiophenol and mercaptoethanol as additives. The effect of varying the molarities of the different additives on the properties of the CdS nanoclusters synthesized are discussed. Systematic ageing studies of the nanoclusters showed that larger particles age faster than the smaller clusters. Ageing also leads to better crystallization of the particles. It has been observed that the smallest particles (∼0.7 nm diameter) possess tetrahedrally bonded fragments of CdS and intercluster structural long range order does not exist. However, bigger particles (∼2.0 nm diameter) show bulk cubic structure. X-ray photoelectron spectroscopy studies have been done to study the purity and stoichiometry of the clusters synthesized and strongly support the existing proposal of the formation and stability of CdS nanoclusters.

Hydrogenation of diene elastomers, their properties and applications : A critical review

Abstract: This chemistry and technology of hydrogenation of diene elastomers have substantially grown during the past decade. New applications of hydrogenated elastomers have emerged. Homogeneous hydrogenation has several advantages over heterogeneous hydrogenation because of its higher selectivity, faster rate and cleaner end products. However, separation of catalysts and recycle/reuse of expensive metals still poses problems. The preferred alternative for the hydrogenation of elastomers in solution is the use of Zeigler type catalyst which are less expensive than the noble metal catalysts like Rh, Pd etc. However, such catalysts are not effective when strongly coordinating groups are present in the elastomer. One approach would be to use transition metals, which have less tendency to coordinate with polar monomers in the elastomer. Research is also warranted in the use of less expensive metals for elastomer hydrogenation (Ni, Co, Ru). Use of large quantities of solvent (to keep the solution viscosity low) is another significant cost center in elastomer hydrogenation. Novel agitator systems/reactor configuration to handle higher concentration of rubber in solution, yet provide adequate heat and mass transfer in gas-liquid hydrogenation reaction, needs to be explored. Hydrogenation of diene elastomers in the latex form using water soluble catalyst appear to be hold great promise at the present time since many diene elastomers (like SBR, CR and NBR etc.) are commercially produced directly in the form of latex. Creative exploitation of biphasic catalysts for hydrogenation is expected to gain momentum since early results look promising. This would require greater fundamental understanding of the aqueous-organic interphase in a latex process and the mechanism of transport of catalytic reagent across this interphase. More studies are needed to achieve homogeneous chemical reaction inside of each individual latex particles.

Prediction of all India summer monsoon rainfall using error-back-propagation neural networks

Abstract: In this paper, multilayered feedforward neural networks trained with the error-back-propagation (EBP) algorithm have been employed for predicting the seasonal monsoon rainfall over India. Three network models that use, respectively, 2, 3 and 10 input parameters which are known to significantly influence the Indian summer monsoon rainfall (ISMR) have been constructed and optimized. The results obtained thereby are rigorously compared with those from the statistical models. The predictions of network models indicate that they can serve as a potent tool for ISMR prediction.

In vitro induction of multiple shoots and plant regeneration in cotton (Gossypium hirsutum L.)

Abstract: Induction of multiple shoots in cotton (Gossypium hirsutum L. cv. Anjali-LRK 516) has been achieved with cotyledonary nodes devoid of cotyledons and apical meristems. Explants from 35-day-old seedlings yielded the maximum number of shoots (4.7 shoots/explant) using Murashige and Skoog (MS) basal medium supplemented with 6-benzylaminopurine and kinetin (2.5 mg/1 each). Explants from 35-day-old seedlings raised in glass bottles produced a higher number of multiple shoots (8.3 shoots/explant) than those grown in glass tubes and cultured on the same shoot induction medium. Elongation of multiple shoots was obtained on liquid or agar MS basal medium without phytohormones. In vitro shoots were rooted on half-strength agar-solidified MS basal medium or with 0.05 or 0.1 mg/1 naphthaleneacetic acid. Hardening and survival of tissue culture plantlets was 95% under greenhouse conditions.

Single-Component Sorption/Diffusion of Cyclic Compounds from Their Bulk Liquid Phase in H-ZSM-5 Zeolite

Abstract: Single-component sorption/diffusion of cyclohexane, pyridine, benzene, toluene, aniline, ethylbenzene, xylene isomers, n-propyl- and isopropylbenzenes, and mesitylene in H-ZSM-5 (Si/Al = 39.7) zeol...

Beneficial effects of cobalt addition to Ni-catalysts for oxidative conversion of methane to syngas

Abstract: Addition of cobalt to NiO Yb 2 O 3 , NiO ZrO 2 and NiO ThO 2 catalysts causes a drastic reduction in the rate of carbon formation and also results in a large decrease in the reaction start (or the catalyst activation) temperature in the oxidative conversion of methane to syngas

Influence of binder on the acidity and performance of H-Gallosilicate (MFI) zeolite in propane aromatization

Abstract: Influence of the addition of alumina or kaolin, as a binder at a concentration of 10 or 50 wt% to H-Gallosilicate (MFI) zeolite on its inter- and intracrystalline acidity, initial activity, product selectivity and distribution of aromatics formed in the propane aromatization (at 550°C) and also on its deactivation due to coking in the aromatization process has been thoroughly investigated. Kaolin binder caused an appreciable decrease in the acidity (both inter- and intracrystalline) and propane aromatization activity of the zeolite. Whereas, alumina binder has no significant effect on the intracrystalline acidity and propane aromatization activity but caused a significant increase in the intercrystalline acidity. The catalyst deactivation and coke deposition on the zeolite are increased due to the alumina binder. But when kaolin binder is used, the coke deposition is not changed significantly. However, the deactivation rate constant for the initial fast deactivation is decreased but for the later slow deactivation is increased by kaolin binder. The selectivity for aromatics and para selectivity of the zeolite are increased by both the binders. The product selectivity, dehydrogenation/cracking and aromatization/cracking activity ratios and para selectivity, particularly for the zeolite with alumina (50 wt%) binder, are strongly influenced by the catalyst deactivation. However, the influence of binder and/or catalyst deactivation on the distribution of aromatics is very small.

HZSM-5 catalysed conversion of aqueous ethanol to hydrocarbons

Abstract: The conversion of aqueous ethanol to hydrocarbons, over HZSM-5 of silica-alumina ratio 206 and 40, is described. The effect of temperature (673–773 K) on product distribution reveals definite trends. The yield and distribution of the products were influenced by catalyst-binder (alumina) composition, dilution of feed and the silica-alumina ratio of the catalyst. It is seen that light olefins can be obtained in good yield at high temperature, in absence of a binder, with dilution of the feed and with higher silica-alumina ratio.

Activity of homogeneous transition metal catalysts for oxidative carbonylation of aniline to N,N′diphenyl urea

Abstract: Oxidative carbonylation of aniline to N,N′diphenyl urea was achieved at 100°C and atmospheric pressure conditions. The screening of several homogeneous transition metal complexes was carried out. The best catalytic activity was shown by [Ru(CO)3I3]NBu4 catalyst. The effect of solvents, temperature, aniline and promoter concentration etc. on the activity and selectivity of this catalyst was studied. The activation energy of the reaction is evaluated as 26.6 kcal/mol. A plausible mechanistic pathway for oxidative carbonylation of aniline to diphenyl urea has also been proposed.