Sang-Ok Lee

Controlling the crystal morphology of one-dimensional tunnel structures: induced crystallization of alkane/urea inclusion compounds as hexagonal flat plates

Abstract We propose a general strategy for controlling the crystal morphology of tunnel inclusion compounds in order to induce crystal growth as flat plates rather than long needles. The strategy employs additive molecules designed to selectively inhibit crystal growth along the tunnel direction. The successful application of this strategy is illustrated by the induced crystallization of alkane/urea inclusion compounds as hexagonal flat-plate crystals using 5-octadecyloxyisophthalic acid as the selective crystal growth inhibitor (in the absence of inhibitor, alkane/urea crystals grow spontaneously as long hexagonal needles).

Hydrogen-bonded chains of α,ω-diaminoalkane and α,ω-dihydroxyalkane guest molecules lead to disrupted tunnel structures in urea inclusion compounds

Structural features of the urea inclusion compounds containing 1 ∶ 1 mixtures of α,ω-diaminoalkane and α,ω-dihydroxyalkane guest molecules, reported in this paper, provide interesting contrasts to those of conventional urea inclusion compounds. All the α,ω-diaminoalkane/α,ω-dihydroxyalkane/urea inclusion compounds reported have a hydrogen-bonded chain of alternating α,ω-diaminoalkane and α,ω-dihydroxyalkane guest molecules, which is surrounded by urea molecules in a manner that bears some resemblance to the conventional urea tunnel structure, but with the urea–urea hydrogen bonding scheme disrupted by the formation of N–H⋯O hydrogen bonds between NH2 groups of the urea molecules and OH groups of the α,ω-dihydroxyalkane molecules. As a consequence, the guest and host components have the same periodicity, and these inclusion compounds are commensurate, in contrast to conventional urea inclusion compounds. So far, attempts to prepare α,ω-diaminoalkane/α,ω-dihydroxyalkane/urea inclusion compounds for α,ω-dihydroxyalkanes longer than 1,3-dihydroxypropane have been unsuccessful, suggesting that there may be an upper limit to the length of the α,ω-dihydroxyalkane component in this family of structures.

Towards molecular sieve inorganic catalysts that are akin to enzymes: studies of a selective cyclo-dimerization over ferrierite at ambient temperature

The solid-acid (Brønsted)-catalyzed cyclo-dimerization of 3-hydroxy-3-methylbutan-2-one (HMB) over a synthetic ferrierite molecular sieve is reported. HMB is a stable liquid at ambient temperatures but in acidic solutions it readily undergoes reaction to generate a variety of products. However, in the acidic molecular sieve catalyst studied here, only one product – the cyclic dimer (proven by in situ solid state 13C NMR and other evidence) – is observed, together with some unreacted HMB. A plausible, proton-catalyzed mechanism is proposed, and prompts comparison between the cyclo-dimerization of HMB within ferrierite and the mode of action of certain enzymes.

A theoretical framework for the experimental determination of host–guest interaction energies in solid inclusion compounds

A mathematical model is developed to provide the framework of an experimental approach for determining host–guest interaction energies in solid inclusion compounds with one-dimensional tunnel host structures. The approach considers the competitive inclusion of two different types of potential guest molecules X(S)qX and X(S)rX (q≠r) within the tunnel host structure, where X represents a given type of end group (e.g., CH3, halogen, etc.) and S represents an appropriate spacer unit (e.g., CH2, CH, etc.). Sequential and simultaneous models for the growth of the guest substructure within the host tunnel are considered. The relative proportions (m and 1−m) of the two types of guest molecule included within the host tunnel depend on the relative proportions (γ and 1−γ) of the two types of guest molecule in the external “pool” of potential guest molecules and the relative “affinities” (χ and 1/χ) of the host tunnel structure for including the two different types of guest molecule. Expressions linking χ, m, and γ ...

Probing host-guest interaction energies in solid inclusion compounds from experimental studies of competitive inclusion

Abstract An approach to assess host-guest interaction energies in solid inclusion compounds with tunnel host structures is described, based on experimental studies of competitive inclusion of two different types of potential guest molecules X(S) q X and X(S) r X (q ≠ r) within the host tunnel. The proportions (m and 1-m) of the two types of guest molecule included within the host tunnel depend on the proportions (γ and 1-γ) of the two types of guest in the external “pool” of potential guest molecules and the relative “affinities” (χ and 1/χ) of the host tunnel for including the two types of guest. Expressions linking χ, m and γ can be applied to determine χ directly from experimental measurements of m for inclusion compounds prepared with different values of γ. The value of χ depends on the intermolecular interaction energies per unit length of tunnel for the two types of guest molecule, and χ may be expressed in terms of the host-guest interaction energies for the spacer units S and the end-groups X, and the guest-guest (X…X) interaction energy. Preliminary experimental results for urea inclusion compounds containing binary mixtures of α,Ω-dibromoalkane guest molecules are presented.