Kyu Seong Choi

Donor-set-induced coordination sphere and oxidation-state switching in the copper complexes of O2S2X (X = S, O and NH) macrocycles.

Reaction of the O(2)S(2)X-macrocycles (L(1), X = S; L(2), X = NH; and L(3), X = O) with Cu(ClO(4))(2) x 6 H(2)O affords 1:1 (M/L) square-pyramidal Cu(II) complexes when X = S and NH but yields a rare 1:2 sandwich-type tetrahedral Cu(I) complex when X = O; the X-ray structures of all three complexes are reported. Substitution of O for S or NH in the ligand structure thus results in a donor-set-induced II/I oxidation state change of the copper, and this is accompanied by a square-pyramidal to tetrahedral topological change in the solid state. Spectrophotometric titration data (including Job plots) indicate that similar behavior occurs in acetonitrile. In further experiments aimed at investigating the generality of the above redox behavior, it was shown that the 16- and 18-membered analogs of the 17-membered L(3) also induce a similar II/I redox change in acetonitrile. It was demonstrated for L(3) that the above-induced Cu(II/I) change is also maintained when the reaction solvent is changed from acetonitrile to methanol or ethanol.

Exo-coordinated discrete and continuous supramolecular silver(I) complexes with thiaoxa-macrocycles

Two thiaoxa-macrocycles (L1: S3O2 and L2: S2O3) with a dibenzo-subunit were synthesised and structurally characterised by X-ray analysis. Reactions of L1 and L2 with silver(I) salts (NO3− and PF6−) afforded the respective ligand- and/or anion-directed complexes 1–3 with different topologies; tetranuclear sandwich [Ag4(L1)2(NO3)4] (1), cyclic tetramer [Ag4(L1)4](PF6)4 (2) and poly(bicyclic dimer) [Ag(L2)NO3]n (3). The formation of such supramolecular complexes is discussed in terms of donor or anion effect.

Donor effect on supramolecular structures of silver(I) perchlorate complexes of macrocycles with O2S2X (XS, O and NH) donor sets

By virtue of simple one donor variations of O(2)S(2)X-donor macrocycles (L(1): X=S, L(2): X=O and L(3): X=NH) towards silver(I) perchlorates, four supramolecular complexes (1-3) with different topologies have been isolated; L(1) afforded solvent- and anion-free sandwich complex (1), otherwise L(2) and L(3) gave the dimeric (2a), 1-D polymeric (2b), and tetrameric bowl-type (3) complexes with solvent or anion coordination.

Characterization of single-stranded DNA separation by capillary gel electrophoresis

We have investigated the effect of polymer gel reconditioning, the shape of the capillary, the applied electric field, and the capillary length for single-stranded DNA. The polyethylene oxide gel had deformed under the high electric field causing the degradation of the separation power. By the reintroduction of the fresh polyethylene oxide gel for the next run, one-base resolution was recovered. It turned out that the tip of the capillary at the injection side needed to be clean and symmetric for much improved resolution. Changing DNA motion by the pulsed electric field resulted in the separation of DNA far more than 500 bases.

Development of soft plasma ionization (SPI) source for analysis of organic compounds.

We present a newly designed soft plasma ionization (SPI) source developed for mass spectrometric study of organic compounds in this study. The SPI cell having a relatively small size consists of a hollow anode and a hollow mesh cathode. The voltage-current characteristic depending on the pressure was investigated, indicating that it has similar characteristics to conventional hollow cathode glow discharges. To investigate the emission characteristics of the SPI source, some molecular band emission spectra (N(2), N(2)(+) and OH(+)) were measured by using argon and helium discharge gases. The SPI source was installed to a commercially used quadrupole mass analyzer for analyzing organic compounds. To demonstrate the SPI source, the mass spectra of some organic compounds (methylene chloride, toluene, benzene, cyclohexane and chloroform) were measured. The organic compounds were ionized with good stability in the plasma, and the fragmentation depended on the applied current. When helium and argon gases were used as the discharge gas, the helium plasma was more suitable for SPI-MS rather than argon because the argon plasma not only suffers from spectral interference but also has lower sensitivity.