Joung-Min Kim

Facile synthesis of anthracene-appended amino acids as highly selective and sensitive fluorescent Fe3+ ion sensors

We designed new fluorescent chemical sensors for Fe3+ ion detection, by conjugating amino acids as receptors into an anthracene fluorophore. The conjugates were synthesized in solid phase by Fmoc-chemistry. Fluorescence sensors containing Asp (1) and Glu (2) both had exclusive selectivity for Fe3+ in 100% aqueous solution and in a mixed organic-aqueous solvent system. Other metal ions did not interfere with the detection ability of the sensors for Fe3+. The sensors detect Fe3+ ions via a chelation-enhanced fluorescent quenching effect. The binding affinity, reversible monitoring, and pH sensitivity of the sensors were investigated. In addition, detection of fluoride ion among halide ions was done by a chemosensing ensemble method with 1-Fe3+ and 2-Fe3+ complexes.

Design and synthesis of cyclic disulfide-bonded antibacterial peptides on the basis of the α helical domain of Tenecin 1, an insect defensin

We synthesized cyclic disulfide-bonded (i, i+4) peptides with various net positive charges (+2-+5) from linear peptides derived from the alpha helical domain of Tenecin 1, an insect defensin, and investigated the effect of the intradisulfide bridge (i, i+4) on hydrophobicity, secondary structure, leakage activity and binding activity for large unilamellar vesicles, antimicrobial activity, and hemolytic activity. Intradisulfide bridge formation of the peptides resulted in the increase of amphiphilicity and hydrophobicity. Cyclic forms of the peptides did not deeply penetrate into PG/PC (1:1, mole ratio) large unilamellar vesicles and had a decreased lipid membrane perturbation activity for PG/PC LUVs. When the peptides interacted with PG/CL (2:1, mole ratio) LUVs, cyclic peptides with a high net positive charge (+4-+5) showed similar binding affinities and leakage activities for vesicles to those of linear forms, whereas cyclic peptides with a low net positive charge (+2-+3) exhibited lower leakage activity than their linear forms. CD spectra indicate that the intradisulfide bridge (i, i+4) provided little conformational constraint to linear peptides in buffer solution but resulted in the decrease of alpha helicity of the peptides in lipid membrane mimic conditions. The cyclic peptide with the highest net positive charge had a similar antibacterial activity to that of the linear peptide, whereas the cyclic peptides with a low net positive charge (+3-+4) exhibited lower antibacterial activity than their linear forms. The cyclic peptides of an appropriate net charge showed more potent activities against some bacteria than those of linear forms under high salt conditions.

Synthesis of antibacterial pseudopeptides with less hemolytic activity from a cytotoxic peptide and their pH-dependent activity

We synthesized antibacterial pseudopeptides with less hemolytic activity by incorporation of reduced amide bond psi[CH2NH] into alpha helical antibacterial peptide with hemolytic activity. As the pKa value of reduced amide bond is 7-8, it is protonated depending on the pH. We investigated the secondary structure, the binding affinity and the leakage activity for the vesicles, and the antibacterial activity of the peptide and its pseudopeptides at neutral and basic pH. Unlike the peptide, the pseudopeptides showed a more potent leakage activity when pH increased. The peptide exhibited a lower antibacterial activity at basic pH than at neutral pH, whereas the pseudopeptide showed the same antibacterial activity at basic and neutral pH. Overall results indicated that hydrophobicity of backbone of the pseudopeptide plays an important role in the increase of leakage activity and retention of antibacterial activity at basic pH.

Dual-functionalized mesoporous TiO(2) hollow nanospheres for improved CO(2) separation membranes.

Simultaneous improvement in CO2 permeability and CO2/N2 selectivity was obtained from mixed matrix membranes (MMMs) containing dual-functionalized mesoporous TiO2 hollow nanospheres (f-MTHS). Dual functionality resulted in the increased CO2 affinity and improved interfacial properties between inorganic nanofillers and the polymer matrix.