- PH Influenced molecular switching with micelle bound cavitands
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A series of resorcinarene host-amphiphilic guest complexes have been developed where guest orientation in the host is drastically influenced by pH. Guests appended with a trimethylammonium and a tert-butyl group switch orientation by 180° in response to a
- Kim, Yeon Joo,Lek, Mark T.,Schramm, Michael P.
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- A priori phase prediction of zeolites: Case study of the structure-directing effects in the synthesis of MTT-type zeolites
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This study first uses molecular modeling to examine the structure-directing effects of small amines that are selective for the crystallization of MTT-type zeolite phases. The optimized van der Waals interactions of these small amines are compared within the one-dimensional pore zeolites with the MTT, TON, and MTW frameworks. From these results and our previous molecular modeling studies of structure-directing agents (SDA) for MTT-type zeolites, a large number of amines or quaternary ammonium molecules are successfully predicted to be selective for MTT phases. These molecules were chosen by matching the crystallographic periodicity of the pore structure with the distances between the centers of branched groups in these molecules. These molecules vary in length and in the number of branched moieties, and a few of these molecules are polymeric or oligomeric. In test cases where the distances between the branched groups are not multiples of the pore periodicity, with few exceptions these molecules usually do not produce MTT phases. Finally, we discuss the inorganic conditions necessary for crystallization of MTT phases in borosilicate preparations with some of the diamines in this investigation.
- Burton, Allen W.
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- The Relevance of Size Matching in Self-assembly: Impact on Regio- and Chemoselective Cocrystallizations
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Decamethonium diiodide is reported to perform the chemo- and regioselective encapsulation of para-dihalobenzenes through the competitive formation of halogen-bonded cocrystals starting from solutions that also contain ortho and meta isomers. Selective caging in the solid occurs even when an excess ortho or meta isomers, or even a mixture of them, is present in the solution. A prime matching between the size and shape of the dication and the formed dianions plays a key role in enabling the selective self-assembly, as proven by successful encapsulation of halogen-bond donors as weak as 1,4-dichlorobenzene and by the results of cocrystallization trials involving mismatching tectons. Encapsulated para-dihalobenzenes guest molecules can be removed quantitatively by heating the cocrystals under reduced pressure and be recovered as pure materials. The residual decamethonium diiodide can be recycled with no reduction in selectivity.
- Cao, Rong,Daolio, Andrea,Li, Hongfan,Lin, Jing-Xiang,Resnati, Giuseppe,Scilabra, Patrick,Terraneo, Giancarlo
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supporting information
p. 11701 - 11704
(2020/08/14)
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- A Microscopic Hydrophobicity Parameter
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p-Nitrophenyl laurate at 1x1E-5 M in water forms aggregates within which the ester groups hydrolyze slowly (about 1E3 less than a short-chain monomer).Salts of the general structure RNMe3+X- disrupt or destroy the aggregates; the ester groups are thereby "deshielded", and the observed hydrolysis rate increases.The magnitude of the rate increase at a given salt concentration depends on R: the more hydrophobic the R group, the greater the rate enhancement.This observation provided the basis of a "microscopic" hydrophobicity parameter MH which was evaluated for 25 different Rs (e.g., MH=0.73, 0.97, and 1.33 for R=ethyl, n-butyl, and n-hexyl).MH values were used to assess the role of branching, unsaturation, cyclization, aromaticity, halogenation, etc., in hydrophobic association.The parameters correlate well with Hansch ? values for aliphatic substituents but not for aromatic groups.Since the MH scale is based on the specific binding of one molecule to another, it may be well suited for modeling association among bioactive species.
- Menger, F. M.,Venkataram, U. V.
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p. 2980 - 2984
(2007/10/02)
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