Search results for " base"

Conversion of levulinic acid to γ-valerolactone over Zr-containing metal-organic frameworks: Evidencing the role of Lewis and Brønsted acid sites

2021

Zr-containing UiO-66 and MOF-808 are evaluated for converting levulinic acid (LA) into γ-valerolactone (GVL) through various routes: (i) Step-wise esterification of LA to n-butyl levulinate (nBuL) and Meerwein-Ponndorf-Verley (MPV) reduction to GVL; (ii) One-pot two-steps esterification with n-butanol followed by MPV reduction with sec-butanol; and (iii) direct conversion of LA into GVL through a tandem reaction. Selection of this multistep complex reaction evidences the participation of the different acid sites (Lewis or Brønsted) of the material in each individual step: Brønsted-induced acid sites catalyze esterification reaction efficiently, while Lewis acid sites are the preferred sites…

Magnetic Properties of End-to-End Azide-Bridged Tetranuclear Mixed-Valence Cobalt(III)/Cobalt(II) Complexes with Reduced Schiff Base Blocking Ligands…

2019

Two tetranuclear mixed-valence cobalt(III/II) complexes having the general formula [(μ1,3-N3){CoII(Ln)(μ-O2CC6H4NO2)CoIII(N3)}2]PF6 (where H2L1 and H2L2 are two reduced Schiff base ligands) have been synthesized and characterized. The structures of both complexes show cobalt(II) and cobalt(III) centers with a distorted octahedral geometry with cobalt(III) and cobalt(II) centers located at the inner N2O2 and outer O4 cavities of the reduced Schiff base ligands, respectively. The oxidation states of both cobalt centers have been confirmed by bond valence sum (BVS) calculations. The magnetic properties show that both compounds behave as cobalt(II) dimers connected through an end-to-end azido b…

o-Ethoxybenzamid-Mannichbasen als potentielle Prodrugs. o-Ethoxybenzamide Mannich Bases as Potential Prodrugs

1986

Cationic mono- and bi-nuclear iron complexes as Lewis acid catalysts in Mukaiyama reactions

1992

Organometallic Lewis acids derived from photolysis of mono- and bi-nuclear cationic iron carbonyl complexes function as excellent catalysts for the Mukaiyama aldol reaction.

Synthesis of a New Fluorinated Oxazolidinone and Its Reactivity as a Chiral Auxiliary in Aldol Reactions.

2007

A new enantiomerically pure fluorinated oxazolidinone has been prepared from a fluorinated imidoyl chloride and an optically pure sulfoxide. The diastereoselective reduction of the β-iminosulfoxide thus formed followed by elimination of the sulfoxide and cyclization of the created aminoalcohol furnishes the desired product. The fluorinated oxazolidinone was subsequently used as a chiral auxiliary in Aldol reactions. We also found that the selective formation of the syn-Evans and syn-non-Evans diastereoisomer can be controlled by adjusting the Lewis acid/base ratio.

Liquid chromatography–mass spectrometry as a tool for wastewater-based epidemiology: Assessing new psychoactive substances and other human biomarkers

2017

Wastewater-based epidemiology (WBE) started to develop significantly in the last 8 years due, in part, to the advance of liquid chromatography–mass spectrometry (LC–MS). Its initial objective ― to estimate the consumption of illicit drugs ― has been expanded to new psychoactive substances (NPS) and other human biomarkers of health, lifestyle and disease. The purpose of this review is to introduce recent methods and outstanding challenges in the application of LC–MS to these new targets, including target, suspect and non-target screening and, outline the workflows developed for discovering metabolites of NPS and biomarkers. Further, we discuss a number of specific methodological challenges t…

“Team Based Learning” in Political Science studies

2019

En los estudios de Ciencia Política ha predominado tradicionalmente la metodología basada en la clase magistral y el trabajo individual. Sin embargo, la implantación del sistema de Bolonia implica un trabajo más autónomo de los estudiantes y el desarrollo de nuevas habilidades como el trabajo en grupo. Desde esta perspectiva, se ha aplicado una nueva metodología denominada Aprendizaje Basado en Grupos (TBL de sus siglas en inglés) a un grupo de 100 alumnos de Ciencia Política y se la ha comparado con otros tres métodos también utilizados por los mismos estudiantes en otras asignaturas del grado (práctica semanal, trabajo semestral y Aprendizaje Basado en Problemas). El objetivo del trabajo …

Spectroscopic study of the interaction of Ni(II)-5-triethyl ammonium methyl salicylidene ortho-phenylendiiminate with native DNA.

2009

The interaction of native calf thymus DNA with the cationic Ni(II) complex of 5-triethyl ammonium methyl salicylidene ortho-phenylendiimine (NiL(2+)), in 1mM Tris-HCl aqueous solutions at neutral pH, has been monitored as a function of the metal complex-DNA molar ratio by UV absorption spectrophotometry, circular dichroism (CD) and fluorescence spectroscopy. The dramatic modification of the DNA CD spectrum, the appearance of a broad induced CD band in the range 350-400nm, the strong increase of the DNA melting temperature (T(m)) and the fluorescence quenching of ethidium bromide-DNA solutions, in the presence of increasing amounts of the NiL(2+) metal complex, support the existence of a tig…

The interaction of Schiff Base complexes of nickel(II) and zinc(II) with duplex and G-quadruplex DNA

2017

The duplex and G-quadruplex DNA-binding of six nickel(II) and zinc(II) complexes of three salphen-like ligands (salphen = N,N?-bis-salicylidene-1,2-phenylenediaminato) was investigated by UV-visible absorption and circular dichroism spectroscopy. The results obtained, in particular the values of the DNA-binding constants, Kb, point out that the nickel(II) complexes show a higher affinity toward both duplex and G-quadruplex DNA, compared to the analogous zinc(II) complexes. Interestingly, the zinc(II) complexes possess high selectivity toward G-quadruplex DNA, being negligible their binding with duplex DNA. Molecular dynamics (MD) simulations provided atomistic models for the interpretation …

Synthesis and Structural Stability of α-Helical Gold(I)-Metallopeptidesy

2020

AbstractThe synthesis of hexa- and dodecapeptides functionalized with two Au(I)–phosphine complexes is reported. The high stability of the Au(I)–phosphine bond allowed orthogonal peptide-protecting-group chemistry, even when using hard Lewis acids like boron tribromide. This enabled the preparation of an Fmoc-protected lysine derivative carrying the Au(I) complex in a side chain, which was used in standard Fmoc-based solid-phase peptide synthesis protocols. Alanine and leucine repeats in the metallododecapeptide formed α-helical secondary structures in 2,2,2-trifluoroethanol–H2O and 1,1,1,3,3,3-hexafluoroisopropanol–H2O mixtures with high thermal stability, as shown by temperature-dependent…