202798-01-4Relevant articles and documents
Chemical Potential of the Solvent: A Crucial Player for Rationalizing Host–Guest Affinities
Baudet, Karine,Guerra, Sebastiano,Piguet, Claude
, p. 16787 - 16798 (2017/10/07)
Access to reliable values of the thermodynamic constants βH,G1,1, which control simple host–guest ([HG]) association, is crucial in medicine, biology, pharmacy, and chemistry, since the optimum concentration of an effector (i.e., a drug) acting on a receptor is set to 1/βH,G1,1. Intermolecular association between charged species in polar solvents, for which water is the archetype, largely obeys this principle. Any deviation from ideality, which alters the speciation in solution, is mastered by the Debye–Hückel theory of ionic atmosphere. Much less is known for related association reactions involving neutral species in non-polar (lipophilic) media such as membranes, bilayers, or organic polymers. Taking the intermolecular association between [La(hfa)3dig] guest (hfa=hexafluoroacetylacetonate, dig=2-{2-methoxyethoxy}ethane) and tridentate polyaromatic host receptors L1–L3 in dichloromethane as a proof-of-concept, we show that the progress of the association reactions, as measured by the increase in the mole fraction of occupied sites of the receptors, disrupt the chemical potential of the solvent to such an extent that βH,G1,1 may seemingly be shifted by two orders of magnitude, thus leading to erroneous dose-response prescriptions. A simple chemical model, which considers a subset of solvent molecules in surface contact with the partners of the association reaction, restores reliable access to true and interpretable thermodynamic constants. The concomitant emergence of a concentration-dependent corrective parameter reestablishes satisfying dose-dependent response under real conditions. This “complement” to the law of mass action offers a simple method for safely taking care of the non-predictable variations of the activity coefficients of the various partners when host–guest reactions are conducted in non-polar media.
From Highly Enantioselective Monomeric Catalysts to Highly Enantioselective Polymeric Catalysts: Application of Rigid and Sterically Regular Chiral Binaphthyl Polymers to the Asymmetric Synthesis of Chiral Secondary Alcohols
Huang, Wei-Sheng,Hu, Qiao-Sheng,Pu, Lin
, p. 7940 - 7956 (2007/10/03)
A 1,1′-binaphthyl-based polymeric chiral catalyst with the most general enantioselectivity for the alkylzinc addition to a broad range of aldehydes has been obtained. This polymer can be easily recovered, and the recycled polymer shows the same catalytic properties as the original polymer. A highly enantioselective catalytic diphenylzinc addition to aldehydes has also been achieved by using the chiral binaphthyl monomer and polymer catalysts. Particularly, the excellent enantioselectivity observed for the addition of diphenylzinc to aromatic aldehydes allows the preparation of optically active diaryl carbinols that are synthetically useful but difficult to access by asymmetric catalysis. A novel asymmetric reduction of ketones catalyzed by the mono- and polybinaphthyl zinc complexes has been discovered. Our work on the asymmetric organozinc addition to aldehydes and the asymmetric reduction of ketones catalyzed by the zinc complexes of chiral binaphthyl monomer (R)-12 and polybinaphthyl (R)-43 has not only provided new methods to prepare optically active secondary alcohols but also demonstrated that incorporation of an enantioselective monomeric catalyst into a rigid and sterically regular polymer structure could almost completely preserve the catalytic properties of the monomeric catalyst. This strategy may find general application in converting existing highly enantioselective monomer catalysts into polymer catalysts of similar enantioselectivity provided that the catalytically active species of the monomer catalysts contain only the monomeric units rather than the aggregates of the monomers. By using this strategy, it is possible to overcome the drawbacks associated with the traditional approach to preparing polymeric chiral catalysts where the microenvironments of the catalytic sites in the polymers are often significantly altered from those in the monomeric catalysts due to the flexible and sterically irregular polymer chains.
