NOPR Collection:

Measuring the similarity of spectra of molecular graphs

Sun, 01 Jan 1995 00:00:00 GMT

Title: Measuring the similarity of spectra of molecular graphs Authors: Gutman, Ivan; Turker, Lemi; Balint, Imre Abstract: Three measures of the similarity of the spectra of molecular graphs are considered. Two of them are previously known: the "almost-isospectrality measure", aim, and the "angle of isomerization", ais. We now introduce a third such quantity-the "vectorial isospectrality measure", vim. The previous definitions of aim and ais are modified so as to make them applicable to arbitrary pairs of molecular graphs with equal number of vertices. We establish relations between aim, ais & vim, and point out some of their other properties. Page(s): 1-4

Photocatalytic activity of metallised titania systems

Sun, 01 Jan 1995 00:00:00 GMT

Title: Photocatalytic activity of metallised titania systems Authors: Viswanathan, B; Viswanath, R P; Mary, U D Abstract: Noble metals (Pt, Pd, Rh and Ru) loaded titania systems are active for the photocatalytic dehydrogenation of methanol. The activities of these systems have been found to be dependent on the nature and extent of metal loaded and the pretreatments given to the catalyst system. Spectroscopic and microscopic examinations show that the activity of these systems can be associated with the size and nature of metal clusters formed on these systems. Page(s): 5-10

Evidence of compartmentalization of naphthols in microemulsions from fluorescence quenching study

Sun, 01 Jan 1995 00:00:00 GMT

Title: Evidence of compartmentalization of naphthols in microemulsions from fluorescence quenching study Authors: Panda, M; Behera, P K; Mishra, B K; Behera, G B Abstract: The fluorescence characteristics of 1- and 2-naphthols (1-ROH and 2-ROH) and their corresponding naphtholates (l-RO ^- and 2-RO^-) have been studied in NaLS-isobutanol-hexane-water microemulsions. On excitation, l-ROH dissociates completely and 2-ROH partially in water. In microemulsion system, however, on excitation 2-ROH does not undergo any dissociation whereas 1-ROH dissociates partially. The extent of dissociation of 1-ROH varies with changing microemulsion formulation. This phenomenon and the fluorescence quenching characteristics of naphthols and the corresponding naphtholates with carbon tetrachloride have been explained as due to compartmentalization of fluorophores and quencher in microemulsion media. Page(s): 11-14

Effect of presorbed water and temperature on adsorption of nitrogen and oxygen in NaCaA and NaMgA zeolites

Sun, 01 Jan 1995 00:00:00 GMT

Title: Effect of presorbed water and temperature on adsorption of nitrogen and oxygen in NaCaA and NaMgA zeolites Authors: Jasra, R V; Choudary, N V; Bhat, S G T Abstract: Adsorption of N₂ and O₂has been studied on Ca²⁺ exchanged NaA zeolites (NaCaA) and on a NaMgA zeolite using elution gas chromatography. N₂specific retention volume and adsorption selectivity increase with increase in calcium content (0 to 97% exchange) of the zeolite. However, the increase in much higher at above 90% calcium exchange. Specific retention volumes and adsorption selectivity decrease with increase in temperature for both the adsorbates. N₂ specific retention volume decreases with presorbed water in the zeolite. For zeolite samples NaA and NaCaA having > 90% calcium exchange even 0.9 mmol/g of presorbed water suppressed the N₂ selectivity substantially. Zeolite NaMgA shows higher heats of adsorption and lower specific retention volume and selectivity compared to NaCaA with similar ion exchange for nitrogen. Pronounced decrease in N₂ specific retention volume, selectivity and heat of adsorption is observed for NaMgA even with 0.9 mmol/g of presorbed water. These results have been explained in terms of interaction of adsorbate molecules with extra-framework cations and their distribution in zeolite A. Page(s): 15-21