Nungruethai Yoswathananont

Dependence of selective enclathration on types of cholic acid crystals

Competitive recrystallizations of cholic acid (CA) from 1:1 binary mixtures of seven mono-substituted benzenes are demonstrated. The order of preference for guests to be incorporated into the cholic acid crystals are as follows: benzene, toluene > n-amylbenzene, n-hexylbenzene > ethylbenzene, n-propylbenzene, n-butylbenzene. These seven compounds afford bilayer type inclusion crystals that are classified into four types based on the host frameworks and host-guest stoichiometries. The order of selective enclathration corresponds to the four types as follows: 1:1 alpha G > 2:1 alpha G > 1:1 beta T or 2:1 alpha T. The preference for the alpha G type was also confirmed by investigating the host frameworks of the crystals obtained from binary mixtures. The dependence of the selectivity on the different types of CA crystals can be understood in terms of the fit of the guest molecule in the host cavity.

Guest-induced inversion of an asymmetric host layer in inclusion crystals of cholic acid

Cholic acid, a typical asymmetric host, forms inclusion crystals with six 1,2,3-trisubstituted benzenes and five 1,2,4-trisubstituted benzenes as guests. All the eleven crystals have a bilayer structure composed of hydrophilic and lipophilic layers. The guest molecules are included in one-dimensional (1-D) cavities within the lipophilic layers, where the host molecules array in an antiparallel mode. On the other hand, in the absence of host–guest hydrogen bonds, the host arrangements in the hydrophilic layers change depending on the guest shape; 1,2,3- and 1,2,4-trisubstituted benzenes give the parallel and antiparallel arrangements that are categorized into shv and shv# patterns, respectively. The former crystals have a size-fit relationship between the guest molecule and the host cavity lesser than usual inclusion crystals involving the latter crystals. Therefore, the shape-fit relationship plays an important role in the formation of the host arrangements with the shv pattern. Moreover, the crystal structures of cholic acid with 1,2,3-trisubstituted benzenes are similar to those of deoxycholic acid with the identical guests. This is a rare example that hosts with a different number of hydroxyl groups in their molecular structure form an isomorphous crystal structure.

A novel host framework of cholic acid inclusion crystals by slide and flip of the layers

A novel host framework of cholic acid (CA) has been observed in the crystal structure of m-chloroaniline clathrate. Crystallographic study reveals that CA forms a bilayer-type structure; however, slide and flip of the lipophilic layers give a different host framework to those of over 100 inclusion crystals previously reported. Structural comparison between the clathrates of aniline and m-chloroaniline indicates that the addition of a chlorine atom leads to isomerization of the open host framework due to a steric effect between adjacent guests within the host cavities.

Inclusion Compounds of Cholic Acid with Large Aliphatic Alcohols

Inclusion compounds and crystal structures of cholic acid ( CA ) with 1-pentanol and 1-hexanol have been reported. They form bilayer type structures, which are different from the crossing type structure of other small aliphatic alcohols. Addition of the less common aromatic compounds as poor solvents enables CA to form clathrates with larger aliphatic alcohols.

Silica surface modified with benzoxazine-functional silane

Silica surface modified with silylbenzoxazine monomers having different bulky groups at ortho and para positions on the oxazine ring, i.e. 3-triethoxysilyl-n-propyl-3,4-dihydro-2H1,3-benzoxazine coupled with silica (4), 3-triethoxysilyl-n-propyl-3,4-dihydro-6-methyl-2H-1,3-benzoxazine coupled with silica (5), and 3-triethoxysilyl-n-propyl-3,4-dihydro-6,8-dimethyl-2H-1,3- benzoxazine coupled with silica (6) are synthesized to obtain a series of ion extraction resins. Fourier transform infrared spectroscopy (FT-IR) and elemental analysis support the successful coupling of benzoxazine-functional silane onto silica surface. The ion extraction studies of various alkali and alkaline earth metal ions from aqueous phase via the surface treated silica column chromatography shows the significant ion extraction ability of (6) compared to those of (4) and (5).