ABSTRACT
Triggered by an increasing consensus on the importance of science education for the economy and society as a whole, in recent years, a growing number of educational programs, initiatives and projects have been launched by various players (from educational policy makers over teacher education institutions to industry). Many of these initiatives have a direct or indirect link to molecular sciences. In this article, we develop a two-dimensional framework which can be used as a guideline in the classification and discussion of existing projects as well as in the planning and design of future initiatives. The framework incorporates three organizational levels or groups of persons and the two very central fields of objectives 'knowledge and skills' and 'motivation and interest'. On the basis of this framework, we discuss four projects in which our science and technology education center has been involved, with respect to their influence on the knowledge, skills and interest of pupils, teachers and school administration representatives in science.
Subject(s)
Science/educationABSTRACT
The adsorption of cinchonidine (CD) and cinchonine (CN) on Pt(111) and Pd(111) single crystals has been investigated by means of scanning tunneling microscopy (STM) in an ultrahigh vacuum system. In time-lapse series the mobilities of different adsorption species have been determined on a single molecule basis and with varying hydrogen background pressures in the system. The diastereomeric cinchona alkaloids, CD and CN, which are widely used as chiral modifiers of platinum group metals in catalytic enantioselective hydrogenation, showed similar adsorption modes and diffusion behavior on Pt(111), except that the flatly adsorbed CN molecules which were free (not in a dimer/cluster) were significantly more mobile than their CD analogues. CD adsorbed on Pd(111) showed similar adsorption modes as observed on Pt(111) but at considerably higher mobility of the flatly absorbed species already in the low-pressure region. The observed adsorption behaviors are discussed in the context of independent ATR-IR measurements and theoretical calculations. Special emphasis is put on the nonlinear effect observed in hydrogenation reactions with CD/CN mixtures. Our observations corroborate that this effect is mainly a consequence of the different adsorption strengths of CD and CN on Pt.
ABSTRACT
Pt supported on alpha-Al2O3, gamma-Al2O3 and SiO2 pre-modified with cinchonidine gives over 50% ee in the hydrogenation of methyl pyruvate to methyl lactate using gas phase reactants at 40 degrees C giving the first clear observation of high enantioselection at the gas/solid interface.
ABSTRACT
The influence of acetic acid (AcOH) and trifluoroacetic acid (TFA) on the hydrogenation of ethyl-4,4,4-trifluoroacetoacetate has been investigated by using Pt/Al(2)O(3) modified by cinchonidine and O-methylcinchonidine. We have shown that the sometimes dramatic changes in enantioselectivity and rate cannot simply be interpreted by protonation of the alkaloid modifier. We propose a new three-step reaction pathway, involving interaction of the carboxylic acid with the reactant and the chiral modifier. The mechanism is supported by IR spectroscopic identification of cyclic TFA-modifier ion pairs. This new approach can rationalise the poorly understood role of acids in the enantioselective hydrogenation of activated ketones over cinchona-modified platinum metals.
ABSTRACT
Two competing reaction pathways, which lead to opposite enantiomers, occur in the hydrogenation of 1 over chirally modified platinum, as revealed by catalytic and NMR spectroscopic experiments: the fast reduction of the ketoform 1 a (minor species) and the slow hydrogenolysis of the hydrate 3 (major species).
