Kwan Mook Kim

Ratiometric Fluorescent Chemosensor for Silver Ion at Physiological pH

Bis-pyrene derivative 1, bearing two pyrene and pyridine groups, was synthesized as a ratiometric fluorescent chemosensor for Ag(+) in aqueous solution. Fluorescent chemosensor 1 displayed a selective ratiometric change with Ag(+), which was attributed to the excimer-monomer emissions of pyrenes. A mechanism for the binding mode was proposed based on fluorescence changes, NMR experiments, and theoretical calculations.

Tight binding and fluorescent sensing of oxalate in water.

A dinuclear copper complex that binds tightly and selectively to oxalate over other dicarboxylates like malonate, succinate, and glutarate has been developed. This receptor can be used for fluorescent detection of oxalate in water at physicological pH by chemosensing ensemble approach. Crystal structure of oxalate bound to the receptor together with molecular mechanics and DFT computations provide insights into the tight and selective binding of the anion by the receptor.

BINOl-Based Chiral Receptors as Fluorescent and Colorimetric Chemosensors for Amino Acids

Three representative BINOL derivatives were examined for their chiral recognitions with D- and L-t-Boc-amino acid anions: an open system 1, which bears two urea groups and two pyrene groups; a closed ring system 2, which bears two urea groups with a closed ring system; and a dimeric system 3, which bears two benzylic amine groups and two pyrene groups. Dimeric system 3 displayed a ΔI(D)/ΔI(L) of 12.95 for t-Boc-alanine.

Enantioselective Liquid–Liquid Extractions of Underivatized General Amino Acids with a Chiral Ketone Extractant

The chiral ketone (S)-3 shows high kinetic enantioselectivities toward the L form for general underivatized amino acids with hydrophobic side chains and a high thermodynamic enantioselectivity toward the D form for cysteine with its -SH polar side chain when used as an extractant in enantioselective liquid-liquid extractions in the presence of Aliquat 336. Consecutive extractions by imine formation and hydrolysis increase the enantiopurity of the amino acid, as both of these reactions are L-form-selective.

Reactive extraction of enantiomers of 1,2-amino alcohols via stereoselective thermodynamic and kinetic processes.

(R)-amino alcohol with an enantiomeric excess of >95% was resolved by reactive extraction processes from 2 equiv of racemic alcohol using a chiral receptor 2 as an enantioselective extractant. One resolution cycle is composed of three extractions: a stereoselective reversible imine formation, a stereoselective irreversible imine hydrolysis, and the recovery of 2 and enantiomeric amino alcohols.

Formation, stability, and reactivity of a mononuclear nonheme oxoiron(IV) complex in aqueous solution

A mononuclear nonheme oxoiron(IV) complex bearing a pentadentate N5 ligand was prepared in aqueous solution; the pH dependence of its stability and reactivities was reported along with the mechanistic details of sulfide oxidation by the oxoiron(IV) species.

Highly Enantioselective Extraction of Underivatized Amino Acids by the Uryl-Pendant Hydroxyphenyl-Binol Ketone

The hydroxyphenyl chiral ketone, (S)-3, reacts with D-amino acids bearing hydrophobic side chains exclusively over the L-amino acids in a two-phase liquid-liquid extraction, and thus acts as a highly stereoselective extractant. Calculations for the energy-minimized structures for the imine diastereomers and the comparison of the selectivities with other phenyl ketones, (S)-4 and (S)-5, demonstrate that the hydrogen bond between the carboxylate group and the phenolic hydroxyl group contributes to the remarkable enantioselectivities. The multiple hydrogen bonds present in the imine of (S)-3 reinforce the rigidity, and results in the difference between the stabilities of the imine diastereomers. The imine could be hydrolyzed in methanolic HCl solution, and the extraction of the evaporated residues revived the organic layer of (S)-3, which could enter into a new extractive cycle and leaves the D-amino acid with enantiomeric excess (ee) values of over 97 % in the aqueous layer.

Tuning the intermolecular dative interactions by altering the ligand planarity and counter cations in vanadyl(IV) complexes

A vanadyl(iv) complex, K2V(O)(dtoym)2, forms polymeric interactions via intermolecular dative bonds; the intermolecular dative interaction is tuned by changes of the ligand planarity and counter cations of the vanadyl complex.

Cocrystallization of two conformers of (2S, 3S, 9S, 10S)-2,3,9,10-tetraphenyl-1,4,8,11-tetraoxacyclotetradecane-6,13-dione

The title compound, C 34 H 32 O 6 , was synthesized from the ozonolysis of (2S,3S,9S,10S)-6,13-dimethylene-2,3,9,10-tetraphenyl-1,4,8,11-tetraoxacyclotetradecane. Two different conformers of the title compound cocrystallized in a tetragonal unit cell and were structurally analyzed by X-ray crystallography.