- Dissection of complex molecular recognition interfaces
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The synthesis of a family of zinc porphyrins and pyridine ligands equipped with peripheral H-bonding functionality has provided access to a wide range of closely related supramolecular complexes featuring between zero and four intramolecular H-bonds. An automated UV/vis titration system was used to characterize 120 different complexes, and these data were used to construct a large of number of different chemical double mutant cycles to quantify the intramolecular H-bonding interactions. The results probe the quantitative structure-activity relationship that governs cooperativity in the assembly of complex molecular recognition interfaces. Specifically, variations in the chemical structures of the complexes have allowed us to change the supramolecular architecture, conformational flexibility, geometric complementarity, the number and nature of the H-bond interactions, and the overall stability of the complex. The free energy contributions from individual H-bonds are additive, and there is remarkably little variation with architecture in the effective molarity for the formation of intramolecular interactions. Intramolecular H-bonds are not observed in complexes where they are geometrically impossible, but there are no cases where excellent geometric complementarity leads to very high affinities. Similarly, changes in conformational flexibility seem to have limited impact on the values of effective molarity (EM). The major variation that was found for all of the 48 intramolecular interactions that were examined using double mutant cycles is that the values of EM for intramolecular carboxylate ester-phenol H-bonds (200 mM) are an order of magnitude larger than those found for phosphonate diester-phenol H-bonds (30 mM). The corresponding intermolecular phosphonate diester-phenol H-bonds are 2 orders of magnitude more stable than carboxylate ester-phenol H-bonds, and the large differences in EM may be due to some kind of compensation effect, where the stronger H-bond is harder to make, because it imposes tighter constraints on the geometry of the complex.
- Hunter, Christopher A.,Misuraca, Maria Cristina,Turega, Simon M.
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supporting information; experimental part
p. 582 - 594
(2011/04/16)
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- Acrolein diethyl acetal: A three-carbon homologating reagent for the synthesis of β-arylpropanoates and cinnamaldehydes by heck reaction catalyzed by a Kaiser oxime resin derived palladacycle
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A polymer palladacycle derived from Kaiser oxime resin was used as a source of palladium(0) in the chemoselective Heck reaction of acrolein diethyl acetal with aryl halides under ligand-free conditions. The use of typical Heck conditions afforded 3-arylpropionic esters, and the process can be directed to the synthesis of cinnamaldehydes under Cacchi conditions. These processes take place with rather low loading of the catalyst, which can be recovered by simple filtration and reused for at least five runs without competitive dehalogenation. This is the first time that a supported palladium complex has been reused under Cacchi conditions. ICP-OES analyses of the Pd content of the crude products in both transformations indicated lower leaching for the esters than for the aldehydes in the range up to 0.08 ppm for the esters and 0.8 ppm for the aldehydes. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Alacid, Emilio,Najera, Carmen
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experimental part
p. 3102 - 3106
(2009/04/11)
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