Solvent effects on stereoselectivity: more than just an environment

Solvent‐Dependent Self‐Assembly Behaviour and Speciation Control of Pd6L8 Metallo‐supramolecular Cages

“…Solvent-effects have been reported for equilibria between diastereomers of the atrane structure of a hemicryptophaneoxidovanadium complex, [20] and solvent may affect stereoselectivity in organic synthesis. [21] A platinum(II) congener, [Pt 6 (L1) 8 ]·12ClO 4 , is formed but not in quantitative yields. The 1 H NMR spectrum in [D 6 ]DMSO was symmetrical and displayed the characteristic downfield shifts of the pyridyl resonances, similar to the palladium (II) analogue described above; yet, due to the decreased lability of the metal centre, conversion to the cage was measured to be only 75%, despite heating to 70°C overnight, then standing for a week (see Figure S15).…”

Polarimetry as a Tool for the Study of Solutions of Chiral Solutes

“…If we focus our interest on the changes in SR due to concentration, we find in the literature that they are usually attributed to two different causes: they may be the result of the changes of population values of various conformers of the solute molecules (which have different individual SR values) [2] or of solute aggregation (e.g. For instance, Cainelli and co-workers [11] analyzed temperature dependences (Eyring plots) of enantiomeric (or diastereomeric) ratios, which are equal to the ratios of kinetic constants along two distinct reaction pathways, in a variety of stereoselective reactions. in solution.…”

“…dimerization etc.) [11] In their hypothesis, "T inv represents the interconversion temperature between two supramolecules, and does not imply any change in the rate-determining step or in the reaction mechanism". [3][4][5] A third possibility, by far less considered in the literature, [6][7][8][9][10] is related to the solvent distribution around the solute molecules, which is also dependent on concentration.…”

“…in solution. [11] The interconversion of solvation clusters at T inv could involve an internal rearrangement of the solvation cluster and/ or solvent shell reorganization with transfer of solvent mole-Optical rotation of aqueous solutions of d-levoglucosan was studied experimentally in the 0.03-4.0 mol L À1 concentration range and a nonlinear concentration dependence of specific optical rotation (SR) was revealed. Perhaps by a heritage of the models developed for ideal solutions, such distribution is assumed almost always to be homogeneous.…”

Inverting the Regioselectivity of the Berberine Bridge Enzyme by Employing Customized Fluorine‐Containing Substrates

“…Nevertheless, their excellent selective nature is sometimes considered as a limitation to their substrate and reaction spectrum. Consequently, several strategies were developed to widen their catalytic spectrum, preferentially by protein engineering,3 but also by medium engineering 4. The berberine bridge enzyme (BBE),5 a flavoenzyme naturally occurring, for example, in Eschscholzia californica (California poppy),6 catalyzes the regioselective oxidative C–C bond formation transforming the 1,2,3,4-tetrahydrobenzylisoquinoline ( S )-reticuline 1 a to ( S )-scoulerine 2 a , a 9-hydroxy functionalized tetrahydroprotoberberine derivative (Scheme 1).…”