1,721,221 research outputs found
Summer school “Marinella Ferrari”
No full textQuesto laboratorio di approfondimento per la chimica ha lo scopo di mostrare come il pervenire ad un prodotto richieda la convergenza di diverse competenze e conoscenze. Nel Laboratorio si propone un progetto di ricerca integrato, lungo un percorso precostituito, che permetta allo studente di affrontare direttamente i diversi aspetti della ricerca/sperimentazione nei vari settori della chimica, permettendo di mettere in luce la necessità di coordinamento delle diverse competenze. Preliminare alla frequenza del laboratorio è una procedura di autovalutazione effettuata attraverso la partecipazione al Laboratorio di autovalutazione per studenti, nel quale si vuole ricalcare il livello del modulo di chimica che viene somministrato per l'iscrizione ai corsi di Laurea Scientifici, ma dando rilievo alle capacità intuitive.
L’attività proposta prevede la preparazione di una cella fotoelettrochimica (cella di Graetzel); annunciate per la prima volta nel 1991, queste celle furono inizialmente concepite per mimare il processo di fotosintesi perchè convertono la radiazione solare in energia elettrica
Conformational Analysis of GM1 Oligosaccharide in Water Solution with a New Set of Parameters for the Neu5Ac Moiet
No full textAn unconstrained Monte Carlo/energy minimization (MC/EM) conformational search was performed on ganglioside GM1 oligosaccharide, and the results were compared to the known solution conformation of this molecule. The search was performed using the continuum dielectric water solvation model as implemented in MacroModel/Batchmin and the force field AMBER*. The latter was modified to include new parameters for the Neu5Ac residue contained in GM1. The parameters were developed based on molecular orbital calculations on simple model systems and therefore should have general validity for molecular mechanics calculations on sialyl oligosaccharides. A nice agreement was reached between the computed GM1 structure and the available NMR data
Stereoselection in reactions of chiral allyl ethers: The case of 1,3-dipolar cycloaddition
No full textThe stereochemical outcome of 1,3-dipolar cycloaddition reactions to chiral allyl ethers is described, and a proposed interpretation is discussed
Conformational Analysis of GM1 Oligosaccharide in Water Solution
No full textAn unconstrained Monte Carlo/energy minimization (MC/EM) conformational search was performed on ganglioside GM1 oligosaccharide, and the results were compared to the known solution conformation of this molecule. The search was performed using the continuum dielectric water solvation model as implemented in MacroModel/Batchmin and the force field AMBER. The latter was modified to include new parameters for the Neu5Ac residue contained in GM1. The parameters were developed based on molecular orbital calculations on simple model systems and therefore should have general validity for molecular mechanics calculations on sialyl oligosaccharides. A nice agreement was reached between the computed GM1 structure and the available NMR data
Configurational and conformational analysis of silyl ketene thioacetals by NMR spectroscopy and computational studies
No full textThe configuration and conformation of silyl ketene thioacetals derived from 2-pyridyl thioesters were studied by combined NMR and computational analysis. The results revealed that the (E)-silyl ketene thioacetal is always the thermodynamically favoured diastereoisomer; the equilibrium ratio is reversed /E/Z>2:98/ for steric reasons when two O-silyl substituents are present on the C=C double bond, The preferred conformational minima for the E and Z isomers are proposed on the basis of Monte Carlo conformational searches performed on selected model compounds; the computational results are in excellent agreement with the NMR data
THEORETICAL SECONDARY KINETIC ISOTOPE EFFECTS AND THE INTERPRETATION OF TRANSITION-STATE GEOMETRIES .2. THE DIELS-ALDER REACTION TRANSITION-STATE GEOMETRY
No full textTheoretical secondary deuterium and primary C-14 kinetic isotope effects have been calculated for concerted and stepwise Diels-Alder reactions of butadiene with ethylene and acrolein. Comparisons between theory and experiment on substituted cases give definitive evidence for the mechanism and transition state geometries of the Diels-Alder reactions. Five levels of ab initio theory up to MCSCF/6-31G* are used for isotope effect calculations. The isotope effects for the retro-Diels-Alder reaction of ethanoanthracene are calculated and compared directly to experiment
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