A secondary ion mass spectrometric study of thallium oxide thin films grown via metal organic chemical vapour deposition

Within a comprehensive programme including synthesis via metal organic chemical vapour deposition (MOCVD) and characterization of inorganic compounds and materials of possible interest in technologies based on thin films, results concerning the deposition of metal oxides by means of volatile organometal precursors are reported. In particular, thallium oxide films obtained by the MOCVD technique and commercial powders of Tl₂O₃ and Tl₂O adsorbed on several metal substrates (stainless steel, Si, Cu, Mo, Pt) were studied by secondary ion mass Spectrometry (SIMS) under ion beam bombardment at different ion energies. The positive- and negative-ion mass spectra exhibit typical isotopic patterns of several ionic species produced by interesting interfacial reactions, and the analysis of their relative abundances provides a measure of oxide reactivity towards different substrates. SIMS measurements of metal substrates were also performed. The ability and limits of SIMS in the reactivity study of thallium oxide powders and films and, in addition, in the identification of reaction products evidencing impurity species that, in turn, can be ascribed to the substrates or to the precursors used for the oxide synthesis is pointed out.     

Acid catalyzed rearrangements in the arylimino indoline series. Part IV . Reactions of 1,2-dihydro-2-phenyl-2-(indol-3-yl-derivatives)-3-phenylimino-3H-indole with trichloroacetic and hydrochloric acids. Crystal structure of 1,2-dihydro-2-phenyl-2-(indol-3-yl)-3-phenylimino-3H-indole

2-Phenyl-3-phenylimino-3H-indole reacts with indole, 2-methylindole and 1,2-dimethylindole in the presence of stoichiometric trichloroacetic acid to form 1,2-dihydro-2-phenyl-2-(indol-3-yl-derivatives)-3-phenylimino-3H-indole, which during a longer period of time (16 hours) undergoes indolyl transposition to carbon-3 and elimination of aniline affording the 3,3′-bis-indolyls. In the case of 1,2-dimethylindole the intermediate coming from the indolyl migration may undergo a nucleophilic addition to carbon-2 of another molecule of indole; the new intermediate leads to the formation of 2-phenyl-3,3′-di-(1,2-dimethylindol-3-yl)-3H-indole by elimination of aniline and migration to carbon-3 of the second molecule of indole. By treatment with hydrochloric acid in refluxing ethanol, 1,2-dihydro-2-phenyl-2-(indol-3-yl-derivatives)-3-phenylimino-3H-indole afford to 3,3′-bis-indolyls and 1,2-dihydro-2-phenyl-2-(indol-3-yl-derivatives)-3H-indol-3-one (indoxyls). The crystal structure of 1,2-dihydro-2-phenyl-2-(indol-3-yl)-3-phenylimino-3H-indole is also reported. The latter compound does not give rearrangement products by acid treatment, only untreatable tarry material.     

Characterization of the ionization and spectral properties of mercapto-carboxylic acids Correlation with substituents and structural features

The ionization constants in aqueous solutions of meso- and dl-dimercaptosuccinic acid and of monomethyl and dimethyl meso-succinates were carefully determined by potentiometric and spectrophotometric methods as a result of the increasing interest in these molecules as heavy metal chelators. In order to explain the influence of various substituents on ionization and (13)C NMR properties, the study was extended to the related oxygen derivatives of succinic acid and to simpler ethanoic derivatives. With the Swain-Lupton dual substituent treatment it was possible to clarify the influence of substituents on both spectral and equilibrium parameters. The differences in pK due to conformation are also discussed.     

Bounded solutions for 119-01119-01119-01-problem in pseudo-Siegel domains

Summary We study the problem of the existence of bounded solutions for the equation on pseudo-Siegel domains when the data satisfies the condition .

---

Sunto Si studia il problema dell'esistenza di soluzioni limitate per l'equazione sui domini pseudo-Siegel quando il dato soddisfa alla condizione .

---

---

Work done within the Project 40% M.U.R.S.T. «Geometria Reale e Complessa».     

Analysis of native carotenoid composition in orange juice using C30 columns in tandem

In the present contribution, a novel analytical approach based on using serial coupled conventional LC columns is proposed to the study of the native carotenoid composition of orange juice. The great difficulties that are found when analyzing complex carotenoid samples, due to the high natural variability of these compounds as well as to the presence of carotenoid esters are well documented. To overcome some of these limitations, we have developed a methodology including the study of both the saponified and the intact sample by means of two different LC-DAD/APCI-MS methods. The increase in the resolution and separation power obtained when using two serial coupled C(30) columns is demonstrated, and significant increases in peak capacity have been achieved. By using this new methodology, 44 different carotenoids have been tentatively identified. Among them, several violaxanthin diesters have been directly identified in orange juice for the first time. The main carotenoids in orange juice were violaxanthin, lutein, luteoxanthin, 9-cis-antheraxanthin, and beta-cryptoxanthin. Some of them were found in both their free and esterified forms. To the best of our knowledge, this is the first application of serial couplings of C(30) columns for the identification of the native carotenoid composition of natural matrices.     

Bioconjugation of alkaline phosphatase to mechanically processed, aqueous suspendible electrospun polymer nanofibers for use in chemiluminescent detection assays

Aqueous suspendible polymer nanostructures were prepared by simple microtome processing of electrospun nylon 6 nanofibers and were used to immobilize calf intestinal alkaline phosphatase (ALP) by either covalent or noncovalent bioconjugation chemistries. It was found that noncovalent immobilization of ALP to the mechanically cut nanofibers (mean length approximately 4 microm; mean diameter approximately 80 nm) using a multi-stacked, layer-by-layer (LBL) approach with the cationic polymer Sapphire II resulted in the highest enzyme loading (48.1 +/- 0.4 microg . mg(-1) nanofiber) when compared to other covalent immobilization methods based on glutaraldehyde crosslinking. The biofunctionalized nanofibers were also characterized for their chemiluminescent activity with the dioxetane substrate, CSPD. The results indicate that the kinetic parameters, K(m) and V(max), for the catalytic activity of the nanostructure-bound ALP enzyme were influenced by the particular types of immobilization methods employed. In terms of the overall catalytic performance of the various immobilized ALP systems, a single-stacked LBL assembly approach resulted in the highest level of enzymatic activity per unit mass of nanofiber support. To the best of our knowledge, this study represents the first report examining the preparation of mechanically shortened, aqueous dispersed electrospun polymer nanofibers for potential application as enzyme scaffolds in chemiluminescent-based assay systems.     

Infinite Classes of Dihedral Snarks

Flower snarks and Goldberg snarks are two infinite families of cyclically 5–edge–connected cubic graphs with girth at least five and chromatic index four. For any odd integer k, k > 3, there is a Flower snark, say J _k , of order 4k and a Goldberg snark, say B _k , of order 8k. We determine the automorphism groups of J _k and B _k for every k and prove that they are isomorphic to the dihedral group D _4k of order 4k. Research performed within the activity of INdAM–GNSAGA with the financial support of the Italian Ministry MIUR, project “Strutture Geometriche, Combinatoria e loro Applicazioni”.     

An Unsual Cys-Glu-Lys Catalytic Triad is Responsible for the Catalytic Mechanism of the Nitrilase Superfamily: A QM/MM Study on Nit2

Nitrilase 2 (Nit2) is a representative member of the nitrilase superfamily that catalyzes the hydrolysis of α-ketosuccinamate into oxaloacetate. It has been associated with the metabolism of rapidly dividing cells like cancer cells. The catalytic mechanism of Nit2 employs a catalytic triad formed by Cys191, Glu81 and Lys150. The Cys191 and Glu81 play an active role during the catalytic process while the Lys150 is shown to play only a secondary role. The results demonstrate that the catalytic mechanism of Nit2 involves four steps. The nucleophilic attack of Cys191 to the α-ketosuccinamate, the formation of two tetrahedral enzyme adducts and the hydrolysis of a thioacyl-enzyme intermediate, from which results the formation of oxaloacetate and enzymatic turnover. The rate limiting step of the catalytic process is the formation of the first tetrahedral intermediate with a calculated activation free energy of 18.4 kcal/mol, which agrees very well with the experimental k_cat (17.67 kcal/mol).     

Shock waves in virus fitness evolution

We consider a nonlinear partial differential equation of conservation type to describe the dynamics of transmission with sampling of viral populations observed in aliquots of fixed particle number taken from an evolving clone at periodic intervals of time [I.S. Novella, E.A. Duarte, S.F. Elena, A. Moya, E. Domingo, Exponential increases of RNA virus fitness during large population transmissions, Proc. Natl. Acad. Sci. USA 92 (1995) 5841–5844]. The fast processes of mutation and natural selection that occur within each transmission are incorporated into the conservation equation as parameters. With this, the changes in time behavior of fitness function noticed in experimental data are related to a crossover exhibited by the solutions to this equation in the transient regime for pulse-like initial conditions. As a consequence, the average replication rate of the population is predicted to reach a plateau as a power t^-1/2$t^{-1/2}$.     

Gloriosaols A and B, two novel phenolics from Yucca gloriosa: structural characterization and configurational assignment by a combined NMR-quantum mechanical strategy

Gloriosaols A (1) and B (2), two novel phenolic derivatives characterized by unusual spirostructures made up of two C₁₅ units linked via a γ-lactone to a central stilbenic portion were isolated from the roots of Yucca gloriosa. On the basis of an extensive NMR analysis, the same basic structure was established for the two compounds but no further information about their structural difference could be deduced. Thus two hypotheses were formulated: (1) gloriosaols A and B could be atropisomers caused by a restriction of the free rotation around the double bond due to a steric congestion of the bulky phenolic portions; (2) gloriosaols A and B could be two configurational isomers, indicating, in this case, a nonstereoselective biogenetic formation of the stereogenic center C-2. Semi-empirical calculations of the potential energy surfaces on gloriosaols A and B, together with the ¹H NMR spectra recorded at various temperatures, allowed us to unambiguously exclude the hypothesis of two restricted rotational conformers of a single configurational isomer. Finally, quantum mechanical calculations of the geometries and of the ¹H chemical shifts on the gloriasols A and B in combination with the analysis of the ROE data allowed us to deduce a diastereomeric relation between the two compounds and to assess the relative configuration of the two diastereomers.