• Bulletin of the Korean Chemical Society
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• 제32권9호
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• pp.3372-3376
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• 2011

We have studied the relative stability and atomic structures of five $C_{20}X_2$ regioisomers obtained as diadducts of a $C_{20}$ cage (X = H, F, Cl, Br, and OH). All the regioisomers are geometric isomers, i.e., they differ in their spatial arrangement. Full-geometry optimizations of the regioisomers have been performed using the hybrid density-functional (B3LYP/6-31G(d, p)) method. Our results suggest that the cis-1 regioisomer (the 1,2-diadduct) is the most stable and that the second most stable is the trans-2 (1,13-diadduct) regioisomer, implying that the long-range interaction between the two adducts and the resonance effect are more pronounced than the diadduct-induced strain in the $C_{20}$ cage. The HOMO and LUMO characteristics of each regioisomer with the same symmetry of structural regioisomers except $C_{20}(OH)_2$ are topologically same. This suggests that by using an entirely different set of characteristic chemical reactions for each regioisomer, we can distinguish between the five regioisomers for each $C_{20}$ diadduct derivative.

• Bulletin of the Korean Chemical Society
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• 제33권2호
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• pp.641-646
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• 2012

We used the hybrid density-functional (B3LYP/6-31G(d,p)) method to analyze the substitution patterns of $C_{20}H_{18}X_2$ derivatives (X = F, Cl, Br, or OH) obtained as disubstituted $C_{20}H_{20}$ cages. Our results suggest that the cis-1 regioisomers (1,2-dihalo derivatives) are less stable than the trans-1 regioisomers (1,20-dihalo derivatives), whereas in the case of the dihydroxy derivatives, the cis-1 regioisomer is more stable than the trans-1 regioisomer. This implies that in the dihalo-induced strain cages of $C_{20}H_{18}X_2$, the strain effect would affect the relative energies, while in the dihydroxide, the hydrogen bonds have a stronger effect on the relative energies in cis-1 regioisomer than the strain effect do. Thus this supports the experimental result in which the bisvicinal tetrol was of particular preparative-synthetic interest as a substitute for the lacking bisvicinal tetrabromide. Further, the topologies of the HOMO and LUMO characteristics of all $C_{20}H_{18}Cl_2$ and $C_{20}H_{18}Br_2$ regioisomers with the same symmetry are same, but they are different from those of $C_{20}H_{18}F_2$ and $C_{20}H_{18}(OH)_2$. This indicates that the five regioisomers of each $C_{20}H_{20}$ disubstituted derivative will have an entirely different set of characteristic chemical reactions.

• Bulletin of the Korean Chemical Society
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• 제35권3호
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• pp.899-904
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• 2014

The atomic structures and electronic properties of six classical and nonclassical $H_2O$@$C_{24}$ fullerene regioisomers are systematically studied using the hybrid density functional B3LYP method and M06-2X method with empirical dispersion in conjunction with the 6-31G(d,p) basis sets. The charge transfer, frontier orbitals, dipole moment, energy gap between the HOMO and LUMO, and volume change of the $C_{24}$ cage are analyzed upon encapsulation of a $H_2O$ molecule in each $C_{24}$ regioisomer. All encapsulation processes are endothermic and the relative stabilities of six $C_{24}$ fullerene regioisomers change upon encapsulation of $H_2O$.

• Bulletin of the Korean Chemical Society
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• 제34권8호
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• pp.2403-2407
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• 2013

The hybrid density-functional (B3LYP/6-31G(d,p)) method was used to analyze the substitution effect on the $C_{20}H_{20}$ cage based on calculation of the frontier orbitals of fifteen $C_{20}H_{17}(OH)_3$ derivatives. All substitution products were geometrically optimized without constraints and confirmed by frequency analysis. The results suggest that the cis-1 cis-1 cis-2 regioisomer is the most stable isomer, which implies that hydrogen bonding exerts a stronger effect on the relative energies of the trihydroxide than long-range interactions. Thus, this supports the experimental result in which the bisvicinal tetrol was of particular preparative-synthetic interest. While the LUMO of each of the $C_{20}H_{17}(OH)_3$ regioisomers was equivalently delocalized over the void within the cage, the HOMO was limitedly delocalized on substituents and carbons in close proximity to the substituents. The characteristics of the HOMO of each of the regioisomers vary based on the substitution sites. This indicates that the 15 regioisomers of each $C_{20}H_{20}$ trisubstituted derivative might undergo an entirely different set of characteristic chemical reactions with electrophilic reagents. The results further suggest that the penta-substituted OH groups on the surface of the fullerene cage are more likely to be localized on a pentagon than to be homogeneously delocalized.

• Bulletin of the Korean Chemical Society
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• 제33권9호
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• pp.2861-2866
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• 2012

Results of the comparisons of various density functional theory (DFT) methods with different basis sets for predicting the molecular geometry of TPOP24N-Oxide macrocycle, an oxoporphyrin N-oxide, are reported in this paper. DFT methods, including M06-2X, B3LYP, LSDA, B3PW91, PBEPBE, and BPV86, are examined. Different basis sets, such as 6-$31G^*$, 6-31+G (d, p), 6-311+G (d, p), and 6-311++G (d, p), are also considered. The M06-2X/6-$31G^*$ level is superior to all other density functional methods used in predicting the geometry of TPOP24N-Oxide. The geometries of regioisomeric chlorin N-oxide and oxoporphyrin N-oxide are reported using M06-2X/6-$31G^*$ method. The geometry effects of oxoporphyrin and chlorin N-oxide regioisomers are increased ${\beta}-{\beta}$ bond lengths by N-oxidation because the bond overlap index due to charge transfers is decreased. In N-oxidation ring (II, III), angles that include ${\beta}-{\beta}$ bond length increase as the bond overlap index of ${\beta}-{\beta}$ bond is decreased by N-oxidation. The potential energy surfaces of chlorin N-oxide and oxoporphyrin N-oxide are explored by M06-2X/6-$31G^*$, and single-point calculations are performed at levels up to M06-2X/6-311++G (d, p). Total and relative energies are then calculated. The results indicate that chlorin 24 N-oxides are more stable than chlorin 22 N-oxides in chlorin N-oxide regioisomers. Moreover, TPOP24N-Oxide is less stable than TPOP22N-Oxide.

• Bulletin of the Korean Chemical Society
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• 제25권12호
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• pp.1850-1854
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• 2004

Recently a fullerene isoxazoline was reported as an example for nanoscale connectors in molecular electronic devices. The construction of nanoscale devices is a potentially important area of technology. By using the semiempirical PM3 calculation, we optimized the structures for two fullerene isoxazoline derivatives and thirteen regioisomers of the second addition of a nitride oxide to a fullerene isoxazoline derivative. Our results suggest that fullerene isoxazoline derivatives could be used as nanoscale connectors with the possibility of attaching of spacer units in a specific angle arrangement.

• Bulletin of the Korean Chemical Society
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• 제30권4호
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• pp.917-923
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• 2009

The maize lipoxgyenase-1 is a non-traditional dual positional specific enzyme and the reaction proceeds via enzyme-initiated catalysis. Bioinformatic analysis indicated that the maize lipoxygenase-1 is structurally more similar to soybean LOX1 than pea LOXN2 in that it has an additional external loop (residues 318-351) in the carboxy-terminal catalytic domain. We analyzed the dependence of product distribution on concentration of linoleic acid and monitored the formation of hydroperoxyoctadecadienoic acid as a function of enzyme concentration. Product distribution was strongly influenced by substrate concentration, such that kinetically-controlled regioisomers were enriched and thermodynamically-controlled regioisomers were depleted at high substrate concentration. Kinetic studies indicated that the formation of hydroperoxyoctadecadienoic acid saturated rapidly in an enzyme concentration-dependent manner, which implied that reactivation by reoxidation of inactive Fe(II) failed to occur. Our results support the previously proposed enzyme-initiated catalytic mechanism of the maize lipoxgyenase-1 and reveals that a substrate molecule serves as a hydrogen atom donor in its enzyme-initiated catalysis.

• BMB Reports
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• 제42권7호
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• pp.401-410
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• 2009

We have developed a targeted lipidomics approach that makes it possible to directly analyze chiral eicosanoid lipids generated in cellular systems. The eicosanoids, including prostaglandins (PGs), thromboxanes (TXs), leukotrienes (LTs) and alcohols (HETEs), have been implicated as potent lipid mediators of various biological processes. Enzymatic formations of eicosanoids are regioselective and enantioselective, whereas reactive oxygen species (ROS)-mediated formation proceeds with no stereo-selectivity. To distinguish between enzymatic and non-enzymatic pathways of eicosanoid formation, it is necessary to resolve enantiomeric forms as well as regioisomers. High sensitivity is also required to analyze the eicosanoid lipids that are usually present as trace amounts (pM level) in biological fluids. A discovery of liquid chromatography-electron capture atmospheric pressure chemical ionization/mass spectrometry (LC-ECAPCI/MS) allows us to couple normal phase chiral chromatography without loss of sensitivity. Analytical specificity was obtained by the use of collision-induced dissociation (CID) and tandem MS (MS/MS). With combination of stable isotope dilution methodology, complex mixtures of regioisomeric and enantiomeric eicosanoids have been resolved and quantified in biological samples with high sensitivity and specificity. Targeted chiral lipidomics profiles of bioactive eicosanoid lipids obtained from various cell systems and their biological implications have been discussed.

• 대한화학회지
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• 제45권6호
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• pp.538-545
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• 2001

전자끌게 치환기를 함유하고 있는 몇 가지 대표적인 biphenyl 유도체의 니트로화 반응 생성물의 이성질체 비율을 조사하였다. 이성질체를 분리하여 각각의 $^1H$ NMR을 얻고 이를 근거로 반응 후 생성되는 혼합물의 $^1H$ NMR을 정량적으로 분석함으로서 이성질체의 생성비율을 결정하는 효율적인 방법을 확립하였다. 분리가 어려운 니트로 화합물의 경우 니트로를 아민으로 환원하고, 카르복실기는 에틸 에스테르로 전환하여 분리할 수 있었다. 이성질체의 생성비율을 향상시키기 위하여 몇 가지 대표적인 반응조건에서 니트로화 반응을 수행하였으며 확립된 방법을 이용하여 각 이성질체의 비율을 정확히 결정할 수 있었다. 반응 조건에 따라 또는 치환기의 위치 및 종류에 따라 위치 선택성이 상당히 다른 결과를 보였다.

• Archives of Pharmacal Research
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• 제26권1호
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• pp.9-14
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• 2003

For probing the importance of planarity of imidazolidinone motif of 4-phenyl-1-(benzenesulfonyl)imidazolidinones 1 for their cytotoxicity, 4-phenyl-2-(benzoyl)[1,2,5]thiadiazolidine-1,1-dioxide (2a), 4-phenyl-2-(p-toluoyl)[1,2,5]thiadiazolidine-1,1-dioxide (2b), 4-phenyl-2-(phenylcarbamoyl)[1,2,5]thiadiazolidine-1,1-dioxide (3a), and 4-phenyl-2-(p-tolylcarbamoyl)[1,2,5]thiadiazolidine-1,1-dioxide (3b) were prepared along with their regioisomers (5a, 5b, 9a, 9b) and their cytotoxicity were measured against human lung carcinoma (A549), human colon carcinoma (COLO205), human ovarian cancer (SK-OV-3), human leukemic cancer (K562), and murine colon adenocarcinoma (Colon26) cell lines in vitro. All compounds prepared do not show any activity against all five cancer cell lines unlike 1. Compounds 1 possess planarity of imidazolidinone, especially in sulfonylurea moiety ($-SO_2$NHCONH-). However compounds 2 and 3 have nonplanar 5-membered ring, [1,2,5]thiadiazolidine-1,1-dioxides. Such structural differentiation might result in the loss of activity. Therefore the inactivity of 2 and 3 could also be an indication for the necessity of planarity of imidazolidinone ring of 1 for their cytotoxic activity.