Jongmin Kang

Immobilized β-cyclodextrin as a simple and recyclable method for cholesterol removal in milk

This study was designed to determine the optimum conditions of three different factors (mixing time, mixing temperature, and tube size) in reduction of cholesterol in milk using immobilized β-CD beads. Immobilized β-CD glass beads were prepared at different conditions of silanization and β-CD immobilization reactions. In result, the glass beads (diameter 1 mm) at 20 mM 3-isocyanatopropyltriethoxysilane and 30 mM β-CD without base showed the highest cholesterol removal rate as 41%. Using above immobilized β-CD glass beads, the cholesterol removal rate was 40.2% with 6 h of mixing time in 7 mm diameter tube at 10°C. After cholesterol removal from milk, the glass beads were washed for cholesterol dissociation and reused. In recycling study, the cholesterol removal rate was 41%, which was mostly same as that using new glass beads. These results indicated that cholesterol removal rate was about 40% with β-CD immobilized glass beads, however, the recycling efficiency was almost 100%.

A naked-eye detection of fluoride with urea/thiourea receptors which have both a benzophenone group and a nitrophenyl group as a signalling group

Two new colorimetric anion sensors have been synthesised where both a benzophenone group and a nitrophenyl group were used as signalling units and urea/thiourea moieties as binding sites. The receptors, effectively and selectively, recognised fluoride and carboxylate anions from other anions such as chloride, bromide, iodide, perchlorate, hydrogen sulphate and nitrate in DMSO.

Novel Ionophores with 2n-Crown-n Topology: Anion Sensing via Pure Aliphatic C–H···Anion Hydrogen Bonding

A series of novel coronands having a 2n-crown-n topology based on trioxane (6-crown-3) derivatives are designed and characterized. These neutral hosts can sense anions through pure aliphatic C-H hydrogen bonding (HB) in condensed phases due to the unusual topology of 2n-crown-n. C-H bonds are strongly polarized by two adjacent oxygen atoms in this scaffold. These hosts provide a rare opportunity to modulate anion binding strength by changing the electronic nature of aliphatic C-H bonds and offer ease of synthesis.

A New Anion Receptor with a Glycoluril Molecular Scaffold

The rational design and synthesis of a new anion receptor containing a glycoluril molecular scaffold are reported. This new receptor utilizes four amide hydrogen bonds arranged at the corner of the glycoluril unit. This new anion receptor binds spherically shaped halide ions in a 1:1 stoichiometry and has a high affinity for fluoride.

Dihydrogen phosphate as a hydrogen-bonding donor element: anion receptors based on acylhydrazone.

Chromogenic anion receptors based on acylhydrazone are designed and synthesized. UV-vis and (1)H NMR titration showed that receptors 1 and 2 are selective receptors for dihydrogen phosphate (H2PO4(-)). Both showed strong association constants with H2PO4(-) even in polar solvents. Receptor 1 was found to recognize H2PO4(-) through three types of hydrogen-bonding (H-bonding) donors: indole N-H, amide N-H, and imine C-H hydrogens. However, receptor 2 seemed to sense H2PO4(-) through two types of H-bonding donors. Despite this seemingly different number of H-bonding elements, the binding constants of receptors 1 and 2 with H2PO4(-) were almost equal. To understand this puzzling result, we investigated the binding poses of complexes using density functional theory. The proposed 2·H2PO4(-) complex structure revealed another possible H-bonding element involving an aromatic nitrogen acting as a H-bonding acceptor. To confirm this, we synthesized receptor 3, which is devoid of this nitrogen. The binding constant of receptor 3 for H2PO4(-) was 2 orders of magnitude lower than those of receptors 1 and 2. This decreased binding affinity strongly supports the existence of a N(aromatic)···H-O(phosphate) interaction. These results provide a rare opportunity to identify H2PO4(-) acting as a H-bonding donor during an anion-recognition event.

Chromogenic anion receptors based on 4-nitrophenylhydrazone and phenylhydrazone

Chromogenic anion receptors based on 4-nitrophenylhydrazone and phenylhydrazone have been designed and synthesized. UV–Vis and 1H NMR titration showed that receptor 1 responded to anions according to their basicity. Although the nature of hydrogen bonds in hydrazone N–H and vinylic C–H is weak, receptor 1 bound weakly basic anions such as chloride, bromide, iodide and hydrogen sulfate utilizing only hydrogen bond in CH3CN. No color change was observed with these anions. However, for more basic anions such as acetate dihydrogen phosphate and fluoride, color change due to deprotonation observed. Furthermore, the solution color of 1 changed to deep blue with fluoride. Fluoride could be distinguished from acetate and dihydrogen phosphate with naked eye. However, phenylhydrazone based receptor 2 showed only hydrogen bonding association with all anions investigated except fluoride. Due to low deprotonation tendency and its structure, color change of solution 2 was not observed.Graphical Abstract

An anion sensing photonic gel by hydrogen bonding of anions to the N-allyl-N′-ethyl urea receptor

In this paper, a new concept for an anion sensor is demonstrated. We synthesized anion-responsive N-allyl-N′-ethylurea (AEU) that can form hydrogen-bonded complexes with various anions. An allyl functional group enables AEU to participate in copolymerization with hydroxyethyl methacrylate (HEMA) and a crosslinker to form a crosslinked gel. Photopolymerization of the mixed monomer was conducted in the presence of a polymeric opal template, and the subsequent removal of the template resulted in a blue-colored photonic gel in organic solvents owing to light reflection by an inverse opal (IO) structure. After immersing the photonic gel into an acetonitrile (MeCN) solution containing an anion sample with tetrabutylammonium counterion, the reflective color of the gel red-shifted from swelling. For anions such as acetate and dihydrogen phosphate, the photonic gel exhibited color changes within the entire visible spectrum for anion concentration ranges of 10−5 to 10−2 M. Assuming that the charge increase by anion binding is mainly responsible for the longitudinal swelling of a photonic gel sensor, we proposed a mathematical relationship between the swelling factor α and the equilibrium constant K for hydrogen bonding (H-bonding) of an anion with AEU. For five different anion samples, variations in the normalized reflectance peak were plotted as a function of anion concentration, and the equilibrium constant K was calculated by fitting the experimental data to a mathematical function. The sequence of anion sensitivity for five samples was found to be in good accordance with previous investigations on urea–anion complexation, while the lower K values obtained in our system were presumably from the weak electron donating substituent in AEU and the hindered diffusion of the analyte within the gel. However, a photonic gel anion sensor has advantages from the standpoint of simplicity. For instance, a detection apparatus is not required, and the sensor can be used multiple times. With further modification of the urea receptor, the photonic gel will find useful applicability, such as in reusable probe sensors and for the in situ monitoring of ionic species in a continuous process.

Anion Receptor with Two Imidazolium Rings on the Glycoluril

We have synthesized an anion receptor with two imidazolium groups on the glycoluril. This receptor showed high affinity for Y-shaped anions such as acetate and benzoate. Although the association constants of these anions for the receptor 4 are too large to be estimated from 1H NMR titration, the receptor 4 has at least 560-fold selectivity for acetate or benzoate over iodide and 360-fold selectivity over nitrate.

Anion Receptors with Glycoluril Molecular Scaffold

For a synthetic receptor with an amide group, the amide groups are arranged through a space in a rigid and convergent manner. This has been achieved by incorporating amide groups into various molecular scaffolds. The geometry of diphenylglycoluril allows the synthesis of concave molecular structures. In addition, the rigidity of the molecule provides a solid molecular scaffold to arrange suitable binding moieties such as hydrogen bonds. We have developed various anion receptors based on diphenylglycoluril. The association of these receptors with various anions reflects the shape, size and basicity of the anions.

The contribution of polar C–H hydrogen bonds to anion binding

The contribution of C–H hydrogen bonds is one of the key factors to consider in anion binding receptor design. To investigate the participation of C–H hydrogen bonds through C–H polarization in an anion binding event, we have designed and synthesized three new anion receptors (receptors 1, 2 and 3). Essentially, the only difference between these receptors is the relative magnitude of the C–H(Ha) polarization. These receptors utilize two amide N–H, two aromatic C–H(Ha), anthracene 9-C–H and possibly two methyl groups as hydrogen bonding moieties. From the titrations and DFT calculations, we found that the anion binding abilities of these receptors mainly depend on the magnitude of the polarization of C–H(Ha) and receptors 1 and 2 are selective for H2PO4−.