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Biomedical subjects

Kimoon Kim

Publications and source records attributed to Kimoon Kim.

At least 19 recordsLinked to original sources
PubMed2006

Chiral recognition in cucurbituril cavities.

For the first time, achiral cucurbiturils (CBs) were endowed with significant enantiomeric and distereomeric discrimination by incorporating a strong chiral binder. Calorimetric, nuclear magnetic, light-scattering, and mass spectral studies revealed that (S)-2-methylbutylamine (as a strong binder) can be discriminated by two enantiomeric supramolecular hosts, composed of CB[6] and (R)- or (S)-2-methylpiperazine, with an unprecedented 95% enantioselectivity in aqueous NaCl solution. This is the highest enantioselectivity ever reported for a supramolecular system derived from an achiral host. Similarly, CB[7], with a larger cavity, exhibited diastereoselectivities up to 8 times higher for diastereomeric dipeptides, as demonstrated for L-Phe-L-Leu-NH3+ versus L-Phe-D-Leu-NH3+.

Journal Article↗
PubMed2006

pH-responsive movement of cucurbit[7]uril in a diblock polypseudorotaxane containing dimethyl beta-cyclodextrin and cucurbit[7]uril.

[Structure: see text] A polypseudorotaxane consisting of cucurbit[7]uril (CB[7])/N,N'-(3-phenylenebis(methylene)dipropargylamine (PMPA), [2]pseudorotaxane, and 2,6-O-dimethyl beta-cyclodextrin (DM-beta-CD)/alpha,omega-bisazidopropylene glycol 400 [2]pseudorotaxane was synthesized using the "click" reaction. The polypseudorotaxane structure was maintained in aqueous solution over a wide range of pH values with the DM-beta-CD units contributing to increased solubilization of the polypseudorotaxane without dethreading. The pH-responsive movement of the CB[7] units in the polypseudorotaxane was also observed.

Bridged-Ring Compounds↗
PubMed2006

Circular dichroism of intra- and intermolecular charge-transfer complexes. Enhancement of anisotropy factors by dimer formation and by confinement.

The dynamic behavior of new CT-dyads (CT = charge transfer) has been studied by means of UV-vis, fluorescence, and NMR spectroscopies under a variety of conditions. It was found that the CT-dyads exhibit conformational variations, such as extended and folded monomers and an antiparallel dimer complex, depending on the conditions. The CT interaction was found in the folded conformation at ambient temperature, while the contribution of the dimeric species became evident at lower temperatures. Most interestingly, close examinations of the circular dichroism spectra of these CT-dyads reveal that the anisotropy (g) factors of the dimers are significantly enhanced by a factor of approximately 30 in the CT transition region. Such enhancement is rationalized in terms of the stronger CT interactions in the dimer through the double electronic coupling element, which imposes stronger restrictions on the rotation of alkyl group(s). Confinement of the CT-dyads in cyclodextrin (CD) and cucurbituril cavities afforded further insights into the chiroptical properties of the CT-dyad. The effects of confinement are clearly size-dependent, exhibiting a substantial enhancement of the g factors by a factor of 5-10 upon inclusion by beta-CD and also by cucurbit[8]uril, but with no appreciable changes upon complexation with the other CDs. These results indicate that the conformational fixation of CT-dyads, for example by dimer formation or by confinement in size/shape-matched cavities, is a conventional, yet powerful, tool for manipulating (mostly enhancing) the chiroptical properties of the CT transition, which should be applicable in general to a variety of molecular and supramolecular CT systems.

Journal Article↗
PubMed2006

Sequential formation of a ternary complex among dihexylammonium, cucurbit[6]uril, and cyclodextrin with positive cooperativity.

A unique ternary 1:1:1 cucurbit[6]uril (CB[6])-cyclodextrin (CD)-dihexylammonium (DHA) complex was designed and noncovalently synthesized in stepwise fashion: first, CB[6] interacts strongly with DHA to form a 1:1 complex; second, addition of CD into the solution of the 1:1 complex leads to the exclusive formation of the 1:1:1 ternary complex. The ternary complex was characterized by various experimental techniques including ITC, NMR, and ESI-MS.

Bridged-Ring Compounds↗
PubMed2006

Characterization of host-guest complexes of cucurbit[n]uril (n = 6, 7) by electrospray ionization mass spectrometry.

When an intramolecular cavity exists in a molecule, it can trap another chemical species to form a host-guest complex. We examine the formation of such an inclusion complex with cucurbit[n]uril (CBn, n = 6, 7) as the host to trap alkali metal or ammonium ions as the guest, by electrospray ionization mass spectrometry (ESI-MS). The results show that the inclusion complexes are formed between the three-dimensional cylinder of CBn hosts and the guest cations. Selectivity of the complex formation is dependent both on (1) ion-dipole interactions between the cylindrical portal of the CBn hosts and the guest cations and (2) the hydrophobic interactions at the inner cavity of CBn.

Journal Article↗
PubMed2005

The inverted cucurbit[n]uril family.

We report the isolation, characterization, and recognition behavior of iCB[6] and iCB[7], which are diastereomers of CB[6] and CB[7], respectively, containing a single inverted glycoluril unit. Product resubmission experiments establish that these inverted CB[n] are intermediates in the mechanism of CB[n] formation. As a consequence of the inverted glycoluril ring, these inverted cucurbiturils possess a permanent dipole moment, are slightly smaller than their diastereomers, show distinctive selectivity in their recognition behavior, and report directly on the contents of their hydrophobic cavity.

Bridged-Ring Compounds↗
PubMed2005

Complexation of ferrocene derivatives by the cucurbit[7]uril host: a comparative study of the cucurbituril and cyclodextrin host families.

The formation of inclusion complexes between cucurbit[7]uril (CB[7]) and ferrocene and its derivatives has been investigated. The X-ray crystal structure of the 1:1 inclusion complex between ferrocene and CB[7] revealed that the guest molecule resides in the host cavity with two different orientations. Inclusion of a set of five water-soluble ferrocene derivatives in CB[7] was investigated by 1H NMR spectroscopy and calorimetric and voltammetric techniques. Our data indicate that all neutral and cationic guests form highly stable inclusion complexes with CB[7], with binding constants in the 10(9)-10(10) M(-)(1) and 10(12)-10(13) M(-1) ranges, respectively. However, the anionic ferrocenecarboxylate, the only negatively charged guest among those surveyed, was not bound by CB[7] at all. These results are in sharp contrast to the known binding behavior of the same guests to beta-cyclodextrin (beta-CD), since all the guests form stable inclusion complexes with beta-CD, with binding constants in the range 10(3)-10(4) M(-1). The electrostatic surface potentials of CB[6], CB[7], and CB[8] and their size-equivalent CDs were calculated and compared. The CD portals and cavities exhibit low surface potential values, whereas the regions around the carbonyl oxygens in CBs are significantly negative, which explains the strong affinity of CBs for positively charged guests and also provides a rationalization for the rejection of anionic guests. Taken together, our data suggest that cucurbiturils may form very stable complexes. However, the host-guest interactions are very sensitive to some structural features, such as a negatively charged carboxylate group attached to the ferrocene residue, which may completely disrupt the stability of the complexes.

Bridged-Ring Compounds↗
PubMed2005

Synthesis, X-ray crystal structures, and gas sorption properties of pillared square grid nets based on paddle-wheel motifs: implications for hydrogen storage in porous materials.

A systematic modulation of organic ligands connecting dinuclear paddle-wheel motifs leads to a series of isomorphous metal-organic porous materials that have a three-dimensional connectivity and interconnected pores. Aromatic dicarboxylates such as 1,4-benzenedicarboxylate (1,4-bdc), tetramethylterephthalate (tmbdc), 1,4-naphthalenedicarboxylate (1,4-ndc), tetrafluoroterephthalate (tfbdc), or 2,6-naphthalenedicarboxylate (2,6-ndc) are linear linkers that form two-dimensional layers, and diamine ligands, 4-diazabicyclo[2.2.2]octane (dabco) or 4,4'-dipyridyl (bpy), coordinate at both sides of Zn(2) paddle-wheel units to bridge the layers vertically. The resulting open frameworks [Zn(2)(1,4-bdc)(2)(dabco)] (1), [Zn(2)(1,4-bdc)(tmbdc)(dabco)] (2), [Zn(2)(tmbdc)(2)(dabco)] (3), [Zn(2)(1,4-ndc)(2)(dabco)] (4), [Zn(2)(tfbdc)(2)(dabco)] (5), and [Zn(2)(tmbdc)(2)(bpy)] (8) possess varying size of pores and free apertures originating from the side groups of the 1,4-bdc derivatives. [Zn(2)(1,4-bdc)(2)(bpy)] (6) and [Zn(2)(2,6-ndc)(2)(bpy)] (7) have two- and threefold interpenetrating structures, respectively. The non-interpenetrating frameworks (1-5 and 8) possess surface areas in the range of 1450-2090 m(2)g(-1) and hydrogen sorption capacities of 1.7-2.1 wt % at 78 K and 1 atm. A detailed analysis of the sorption data in conjunction with structural similarities and differences concludes that porous materials with straight channels and large openings do not perform better than those with wavy channels and small openings in terms of hydrogen storage through physisorption.

Adsorption↗
PubMed2005

Novel molecular drug carrier: encapsulation of oxaliplatin in cucurbit[7]uril and its effects on stability and reactivity of the drug.

Oxaliplatin forms a stable 1:1 inclusion complex with cucurbit[7]uril as indicated by NMR, mass spectrometry, isothermal titration calorimetry and X-ray crystallography. The encapsulation of the drug results in a large enhancement in stability, a moderate decrease in reactivity toward guanosine but a much larger decrease in reactivity toward L-methionine, which suggests the encapsulation not only increases the stability of the drug but also may reduce unwanted side effects caused by protein binding of the platinum drug. A preliminary in vitro assay using various tumor cell lines reveals that the encapsulation results in a decrease in the antitumor activity of oxaliplatin.

Antineoplastic Agents↗
PubMed2005

Vesicle formed by amphiphilc cucurbit[6]uril: versatile, noncovalent modification of the vesicle surface, and multivalent binding of sugar-decorated vesicles to lectin.

We report a novel vesicle formed by an amphiphilic CB[6] derivative, the surface of which can be easily modified via host-guest interactions by taking advantage of molecular cavities, readily accessible at the vesicle surface, and their strong affinity toward polyamines. Amphiphilic CB[6] derivative 1 synthesized by reaction between (allyloxy)12CB[6] and 2-[2-(2-methoxyethoxy)ethoxy]ethanethiol affords a vesicle that has been characterized by TEM, light scattering, and fluorescent dye entrapment experiments. Treatment of vesicle 1 with FITC (fluorescein isothiocyanate)-spermine conjugate ligand 2, in which spermine serves as a binding motif to CB[6] and FITC as a fluorescent tag, produced a surface-modified vesicle, which can be easily visualized by a confocal microscope. This result provides us with a new noncovalent, modular approach to the modification of vesicle surfaces. By treating the vesicle derived from the amphiphilic CB[6] with a tag-attached polyamine, we can easily decorate the surface of the vesicle with the tag. Sugar-decorated vesicles were prepared by this noncovalent method, and their interactions with concanavalin A (ConA) were studied. The binding constant of the vesicle decorated with mannose-spermidine conjugate 3 to ConA was measured to be approximately 3 x 104 M-1, which is almost 3 orders of magnitude higher than that of free ligand 3 to ConA (K = approximately 50 M-1). On the other hand, the binding constant of the vesicle coated with galactose-spermidine conjugate 4 to ConA was too small to be measured. These results illustrate the specific and multivalent interactions between the mannose-decorated vesicle and ConA. The ability for facile surface modification suggests many practical applications, including its use in targeted drug delivery and immunization.

Bridged-Ring Compounds↗
PubMed2005

Supramolecular photochirogenesis in sensitizing chiral nanopore: enantiodifferentiating photoisomerization of (Z)-cyclooctene included and sensitized by POST-1.

By using homochiral mesoporous POST-1 (Scheme 1) as an inherently chiral sensitizing host, supramolecular enantiodifferentiating photoisomerizations of (Z)-cyclooctene (1Z) were performed for the first time to examine the sensitizing ability of the chiral nanopores, walls of which are decorated with pyridine chromophore. The homochiral nanopores of POST-1 crystals were demonstrated to function as an effective chiral-sensitizing cavity to give the optically active (E)-isomer 1E in up to 5% enantiomeric excess (ee), thus expanding the scope of porous material-mediated chirogenesis to both ground and excited electronic states.

Journal Article↗