Hyejae Ihm

An Electrochemically Controllable Nanomechanical Molecular System Utilizing Edge-to-Face and Face-to-Face Aromatic Interactions

[formula: see text] A new molecular system, 2,11-dithio[4,4]metametaquinocyclophane containing a quinone moiety, was designed and synthesized. As the quinone moiety can readily be converted into an aromatic pi-system (hydroquinone) upon reduction, the nanomechanical molecular cyclophane system exhibits a large flapping motion like a molecular flipper from the electrochemical redox process. The conformational changes upon reduction and oxidation are caused by changes of nonbonding interaction forces (devoid of bond formation/breaking) from the edge-to-face to face-to-face aromatic interactions and vice versa, respectively.

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.

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.

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.