Kyungsoo Paek

Hydrazide as a New Hydrogen-Bonding Motif for Resorcin[4]arene-Based Molecular Capsules

The resorcin[4]arene-based benzoylhydrazide cavitands formed stable molecular capsules in nonpolar solvents by the eight intermolecular N-H...O=C hydrogen bondings, two from each four paired hydrazides, and the four intramolecular O-H2C-O...H-N hydrogen bondings on each cavitand. The stability of these molecular capsules depends on the encapsulated guest in the following order: CH3SO3(-) > CH3CO2(-) > CH3CH2NH2 x HCl approximately = CH3NH2 x HCl > (CH3)4N(+) > toluene > C2D2Cl4.

Encapsulation of Anionic guests in a New Hydantoinylamido Molecular Capsule

Resorcin[4]arene-based tetrakis(N-hydantoinylamido)cavitand 1 forms a stable molecular capsule in the presence of suitable anionic guests such as CH(3)OSO(3)(-) or BF(4)(-) in C(2)D(2)Cl(4). Molecular capsule G(2)@1(2) is stabilized by the eight intermolecular imide N-H···O═C hydrogen bondings, two from each four paired hydantoinyl units, and the eight intramolecular amide N-H···O-CH(2)-O hydrogen bondings, four on each two cavitands. The formations of molecular capsules were confirmed by (1)H, 2D NOESY, and 2D-DOSY NMR.

New deep cavitand with imidazoquinoxaline flaps: formation of static helical alkane inclusion complexes by enhanced CH/π interactions

A new deep imidazoquinoxaline cavitand formed static helical alkane inclusion complexes by CH/pi stabilization of alkanes with the enlarged aromatic pi surfaces of the cavity inside.

Carceroisomerism and twistomerism in C4c tetraoxatetrathiahemicarceplexes

Four new C4v tetraoxatetrathiahemicarceplexes were synthesized and characterized. Their carceroisomers and half-twistomers were simultaneously observed by 1H NMR spectra at low temperature. The largest isomerization energy barrier of carceroisomers was 15.5 kcal mol−1 and the isomerization energy barriers of twistomers are significantly larger than those of carceroisomers.

NEW SALT BINDERS WHOSE LIGANDS WERE COMPOSED OF FOUR AROMATIC SP2 NITROGENS AND PURELY BASED ON A CAVITAND

Abstract New salt binders whose ligands were composed of four aromatic sp 2 nitrogens and purely based on a cavitand were efficiently synthesized and characterized. Imidazolylcavitand 3 showed high affinity for picrate salts (− Δ G 0 =7.0 ∼ 11.0 kcal mol −1 ) and pyrazolylcavitand 4 showed unusual high selectivity for silver picrate.

Versatile cavitands for small molecules: the entropically driven ethanol selectivity

Abstract Two new C 2 v cavitands based on resorcin[4]arene were synthesized and their binding properties for nine small molecules were studied. The alcohol selectivity was in the order of CH 3 OH∼CH 3 CHOHCH 3 3 CH 2 CH 2 OH≪CH 3 CH 2 OH with the highest K a =260 M −1 at 23°C in CDCl 3 . Their carceroisomerism was observed by 1 H NMR spectra and the quinone-capped cavitands complexation of ethanol was driven entropically.

Facile synthesis and binding properties of C2ν container hosts based on resorcin[4]arene

Two new C2ν container hosts were synthesized by the capping of catechol- or resorcinol-fenced resorcin[4]arene with 1,2,4,5-tetrakis(bromomethyl)benzene and their Ka values were calculated directly from 1H NMR spectra. These hosts showed the binding properties for alkyl alcohols, methylene chloride, and teterahydrofuran in CDCl3 or (CDCl2)2 at −40 °C.

Investigation of some amino acids conformations at the interface of binary mixture using the solvation free energy density model

Abstract The behavior of terminally blocked amino acids, N -acetyl alanine amide (NAA), N -acetyl leucine amide (NAL), and N -acetyl glutatmine amide (NAQ) at the 1-octanol/water continuum interface was investigated by Monte Carlo simulation with the solvation free energy density (SFED) calculation method. All the model amino acids have free energy minimum near the interface. These amino acids can have various conformations such as α-helix, β-sheet, and C 7−eq , however the minimum energy conformations are obtained as α-helix for all the model amino acids at the interface region.

CONFORMATIONAL STUDY OF A RIGID-STRUCTURED OCTATHIABISCAVITAND FROM 2 + 2 COUPLING OF CAPS AND BRIDGING UNITS

Abstract An octathiacavitand was stereoselectively obtained in good yield by [2 + 2] coupling reaction between a tetrakis(thiomethyl)cavitand and 1,2,4,5-tetrakis(bromomethyl)benzene. Its NOESY spectrum showed that its cavity was divided into two small ones by π -π stacking of two bridging benzene units.

Molecular engineering. Part 2.1 Influence of side-chainsubstituents in lariat-type upper-rim calix[4]crowns on their bindingproperties and the reversal of these

Cone-structured upper-rim 1,3-calix[4]crowns have been synthesized from the distal dibromo diol 6 which is itself regioselectively synthesized from p-bromocalix[4]arene hexyl ether by transmetallation, quenching with B(OMe)3 and oxidation. The dibromo substituents in these calix[4]crowns have been transformed into hydrophobic or hydrophilic groups to give lariat-type hosts. Picrate extraction experiments show that alkylammonium ions bind more strongly than alkali-metal cations to hosts having hydrophobic side-arms such as bromo or p-methoxyphenyl, which means that the hydrophobic binding of the calix[4]arene unit and the hydrophilic binding of the crown unit synergistically increase the affinity of the calix[4]crowns for alkylammonium ions. 1H NMR spectra also support the conformational change of the calix[4]crowns from pinched-cone to cone upon complexation. With amide or ester side-arms the affinity tendency is reversed. It is presumed that the hydrophilic side-arms have a high affinity for the charged part of the guest, which leads to a collapse of the hydrophobic cavity.