Paired carceroisomers.
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Biomedical subjects
Kyungsoo Paek
Publications and source records attributed to Kyungsoo Paek.
Structural properties of benzimidazole cavitand and its selective recognition toward 4-methylbenzamide over 4-methylanilide.
The conformations and properties of cavitand 5 with four benzimidazole flaps are studied by (1)H NMR. The benzimidazole cavitand 5 can form very stable vase structures with an enforced concave cavity by intermolecular hydrogen bonding with four hydroxyl-containing molecules, X-OH, such as methanol (X = Me), acetic acid (X = CH(3)CO), and trifluoroacetic acid (X = CF(3)CO). The stronger hydrogen bond donor strengths of X-OH are, the stronger hydrogen bonds are formed between the NH and N atoms of the neighboring benzimidazole fragments and the more vase structures of 5.4HOX are stable. The annular tautomerism of 5 in CDCl(3)/CD(3)OD (9:1, v/v) due to the proton exchange between NH and N atoms of the neighboring benzimidazole fragments is observed by 400 MHz (1)H NMR, and the free energy of activation is measured as DeltaG++(210) = 10.2 kcal/mol at a coalescence temperature of 210 K. Cavitand 5 forms inclusion complexes with 4-methylbezamide guests such as 4-methyl-N-p-tolylbenzamide 6 and N,4-dimethylbenzamide 7 in water-saturated CDCl(3). However, an isomorphic 4-methylanilide guest such as N-4-tolylacetamide 8 cannot be recognized in the concave cavity of 5. This high selectivity toward 4-methylbenzamide over 4-methylanilide seems attributable to the hydrogen-binding interaction between the NH proton of 4-methylbezamide guest 7 and the oxygen atom of the closest water molecule.
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Unusually stable molecular capsule formation of a tetraphenyleneurea cavitand.
An unusually stable molecular capsule was formed by heating phenyleneurea-spanned resorcinarene cavitand with 4-methyl-N-p-tolylbenzamide. The molecular capsule behaved as a discrete molecular entity showing a cylindrical D(4d) structure and showed no guest exchange in toluene-d(8) even at 100 degrees C. [structure: see text]
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Oligobisvelcraplex: self-assembled linear oligomer by solvophobic pi-pistacking interaction of bisvelcrands based on resorcin[4]arene.
[reaction: see text] Bisvelcrand 3 based on resorcin[4]arene was obtained by a stepwise route, and the formation of oligobisvelcraplex 3(n) by solvophobic pi-pistacking interaction was observed. (1)H NMR spectroscopic studies revealed that DeltaG(++)(pseudorotation) of oligobisvelcraplex 3(n) is 16.7 kcal mol(-1) in C(6)D(5)NO(2) solution. The pulsed field gradient spin-echo (PGSE) NMR experiment and VPO experiment showed that the number of aggregation (n) ranges from 7 to 10 in CHCl(3) solution at 298 K. In high concentration, bisvelcrand 3 tends to form gels or fiber.
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Small cavitands specifically binding a water molecule.
[structure: see text] Three new C(2v) cavitands based on resorcin[4]arene bind water specifically at low temperature in CD(2)Cl(2) or CDCl(3) due to their complementarity to water as well as the solvophobic interaction. The averaged DeltaH(o) and DeltaS(o) values are -2.3 kcal mol(-1) and -128 cal mol(-1) K(-1), which gave the averaged -DeltaG(o) of 1.9 kcal mol(-1) at -50 degrees C in water saturated CD(2)Cl(2).
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