Hydrogenation of naphthalene on noble-metal-containing mesoporous MCM-41 aluminosilicates

Aromatic saturation of oil fractions is a key process in the refining industry due to increasing demand for cleanest distillates with superior performances. In this study, the behavior of different catalysts containing 1 wt.% of noble-metal inside a mesoporous MCM-41 (Si:Al=20) framework was investigated in the hydrogenation of naphthalene, as preliminary step to investigate bimetallic catalysts. While at atmospheric pressure only Rh and Pd showed a low hydrogenation activity, in the tests performed at 6.0 MPa the catalytic activity grew, exhibiting the following order: Pt>RhPd>>>Ru≈Ir. However, all the catalysts required a large H₂ excess, to avoid a decrease in hydrogenation and ring-opening activity, and gave rise to the best performance for a contact time of 6.8 s, favouring at lower values the partial hydrogenation to tetralin and at higher values cracking reactions. Finally, all the catalysts showed low thio-tolerance, with significant deactivation already feeding 100 ppm wt. of dibenzothiophene (DBT), with a partial reversibility only for the Pt-containing catalyst (CAT 3).     

First-principles simulations of boron diffusion in graphite

Boron strongly modifies electronic and diffusion properties of graphite. We report the first ab initio study of boron interaction with the point defects in graphite, which includes structures, thermodynamics, and diffusion. A number of possible diffusion mechanisms of boron in graphite are suggested. We conclude that boron diffuses in graphite by a kick-out mechanism. This mechanism explains the common activation energy, but large magnitude difference, for the rate of boron diffusion parallel and perpendicular to the basal plane.     

Base‐Free Iron Catalyzed Transfer Hydrogenation of Esters Using EtOH as Hydrogen Source

Herein, we report on the use of the iron pincer complex Iron‐MACHO‐BH, in the base‐free transfer hydrogenation of esters with EtOH as a hydrogen source. More than 20 substrates including aromatic and aliphatic esters and lactones were reduced affording the desired primary alcohols and diols with moderate to excellent isolated yields. It is also possible to reduce polyesters to the diols with this method, enabling a novel way of plastic recycling. Reduction of the renewable substrate methyl levulinate proceeds to form 1,4‐pentanediol directly. The yields are largely governed by the equilibrium between the alcohol and the ethyl ester.     

Microwave-assisted synthesis of 4-quinolylhydrazines followed by nickel boride reduction: a convenient approach to 4-aminoquinolines and derivatives

Nickel(II) chloride/sodium borohydride combination was employed for the reduction of 4-hydrazinoquinoline derivatives to the corresponding anilines. This reductive protocol was efficiently applied for the reductive cleavage of monosubstituted hydrazines. We described herein the microwave-assisted synthesis of 4-hydrazinoquinolines, which furnished a high yielding and rapid two-step procedure for the synthesis, under mild conditions, of 4-aminoquinolines as antimalarial precursors.     

Free monadic Tarski algebras

The free monadic Tarski algebra FMT(n) with a finite set G of n free generators, was determined by A. Figallo in [7]. In this paper we indicate a formula, as a function of n, which is an easier way of calculating the number of elements of FMT(n). Received November 3, 1995; accepted in final form August 26, 1996.     

Fluorescence lifetime distribution of folded and unfolded proteins

Time-resolved fluorescence of single tryptophan proteins have demonstrated the complexity of protein dynamic and protein structure. In particular, for some single tryptophan proteins, their fluorescence decay is best described by a distribution of fluorescence lifetimes rather than one or two lifetimes. Such results have provided further confirmation that the protein system is one which fluctuates between a hierarchy of many conformational substates. With this scenario as a theoretical framework, the correlations between protein dynamic and structure are investigated by studying the time-resolved fluorescence and anisotropy decay of holo and apo human superoxide dismutase (HSOD) at different denaturant concentrations. As a function of guanidine hydrochloride (GdHCl), the width of the fluorescence lifetime distribution of HSOD displays a maximum which is not coincident with the fully denatured form of HSOD at 6.5M GdHCl. Furthermore, the width of the fluorescence lifetime distribution for the fully denatured forms of holo and apo HSOD is greater than that of the native forms.     

Algebraic hull of maximal measurable cocycles of surface groups into Hermitian Lie groups

Geometriae Dedicata - Following the work of Burger, Iozzi and Wienhard for representations, in this paper we introduce the notion of maximal measurable cocycles of a surface group. More precisely,...     

I n -symmetrical Heyting algebras

In [11, p. 210] A. Monteiro suggested the possibility of generalizing the results of L. Iturrioz [4] to theI _n -symmetrical Heyting algebras which he namedI _n -algebras. We prove that these algebras are semi-simple. We characterize simple algebras and their subalgebras. Finally, we determine the structure of theI _n -algebra with a finite set of free generators and we give an answer to one of the problems posed by A. Monteiro.Presented by W. Taylor.Some of the results of this paper were presented at the Annual Meeting of the Union Matemática Argentina (September, 1987) ([14]).     

Forensic Biochemical Markers to Evaluate the Agonal Period: A Literature Review

Currently, forensic research is multidisciplinary with new methods and parameters useful to define the cause and time of death as well as survival/agony times. The identification of biochemical markers able to estimate agonal period has been studied by many forensic researchers. It is known that the estimation of agonal time in different types of death is not always easy, hence our interest in literature’s data. The studies analyzed in this review confirm the important role of thanatobiochemistry for the estimation of survival times. Regardless of the death cause, the survival/agony time between the primary event and death influences markers concentrations in biological samples (e.g., blood, urine, cerebrospinal fluid). Different biomarkers can be used for qualitative evaluations in deaths with short and long agony (e.g., C-reactive protein, ferritin, GFAP, etc.). Instead, the quantitative interpretation showed limits due to the lack of reference cut-offs. Thanatobiochemistry is a useful tool to confirm what emerged from autopsies findings (macroscopic and histological analysis), but further studies are desirable to confirm the evidence emerging from our review of the literature.     

Catalytic and spectroscopic properties of cytochrome-c, horseradish peroxidase, and ascorbate oxidase embedded in a sol-gel silica matrix as a function of gelation time

In this study, we investigated the optical features of the redox metal-dependent proteins cytochrome-c, horseradish peroxidase (HRP), and ascorbate oxidase embedded in a sol-gel-processed silica matrix as a function of gelation time. Circular dichroism, absorbance, and fluorescence spectroscopies revealed that the sol-gel process affects the complex structure of the dimeric ascorbate oxidase (although the prosthetic coppers still remain bound to the enzyme) but not that of monomeric cytochrome-c and HRP. Any modifications in ascorbate oxidase occurred in the initial gelation phase; the drying process induced no further alterations and the enzyme remained stable for months. Unfolding-refolding experiments on cytochrome-c revealed severely restricted motility in the protein moiety in the xerogel, the concentrated matrix that forms after drying. The diffusion time of the solvent within the matrix, which regulated the enzyme-substrate reaction rate, depended on the thickness of the monolith, not on the dryness of the specimen.