• Bulletin of the Korean Chemical Society
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• v.25 no.12
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• pp.1874-1876
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• 2004

Quantitative structure activity relationship has been probed for spirosuccinimide-fused tetrahydropyrrolo[1,2-a]pyrazine-1,3-dione derivatives acting as aldose reductase inhibitors. While the spirosuccinimide compounds contain a chiral center, the aldose reductase inhibition assay was performed with racemic mixtures in the published work. As the physicochemical descriptors of the QSAR analysis must be evaluated for a definite molecular structure, we devise a new 'racemic' descriptor as the arithmetic mean of the (R)-enantiomer descriptor and the (S)-enantiomer descriptor. The resultant QSAR model derived from the racemic descriptors outperforms the original QSAR models, closely reproducing the observed activity of optically pure enantiomers as well as racemic mixtures.

• Bulletin of the Korean Chemical Society
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• v.35 no.7
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• pp.2043-2048
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• 2014

Two isomers of a new tetraaza macrotricycle 2,2,4,9,9,11-hexaazamethyl-1,5,8,12-tetraazatricyclo[$10.2.2^{5.8}$]-octadecane ($L^2$) containing additional N-$CH_2CH_2$-N linkages, C-meso-$L^2$ and C-racemic-$L^2$, have been prepared by the reaction of 1-bromo-2-chloroethane with C-meso-$L^1$ or C-racemic-$L^1$ ($L^1$ = 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane). Both C-meso-$L^2$ and C-racemic-$L^2$ react with copper(II) ion to form $[Cu(C-meso-L^2)]^{2+}$ or $[Cu(C-racemic-L^2)]^{2+}$ in dehydrated ethanol, but do not with nickel(II) ion under similar conditions. Crystal structure of [Cu(C-racemic-$L^2$)($H_2O$)]$(ClO_4)_2$ shows that the complex has distorted square-pyramidal coordination geometry with an apically coordinated water molecule. Unexpectedly, the Cu-N distances [2.016(3)-2.030(3) ${\AA}$] of [Cu(C-racemic-$L^2$)($H_2O$)]$(ClO_4)_2$ are longer than those [1.992(3)-2.000(3) ${\AA}$] of [Cu(C-racemic-$L^1$)($H_2O$)]$(ClO_4)_2$. As a result, $[Cu(C-racemic-L^2)(H_2O)]^{2+}$ exhibits weaker ligand field strength than $[Cu(C-racemic-L^1)(H_2O)]^{2+}$. The copper(II) complexes readily react with CN- ion to yield the cyano-bridged dinuclear complex $[Cu_2(C-meso-L^2)_2CN]^{3+}$ or $[Cu_2(C-racemic-L^2)_2CN]^{3+}$. Spectra and chemical properties of $[Cu(C-meso-L^2)]^{2+}$ and $[Cu_2(C-meso-L^2)_2CN]^{3+}$ are not quite different from those of $[Cu(C-racemic-L^2)]^{2+}$ and $[Cu_2(C-racemic-L^2)_2CN]^{3+}$, respectively.

• Bulletin of the Korean Chemical Society
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• v.29 no.12
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• pp.2533-2536
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• 2008

• Bulletin of the Korean Chemical Society
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• v.35 no.8
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• pp.2299-2303
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• 2014

Two diastereoisomers of cyclo(Pro-Tyr) have been synthesized simultaneously. The crystal structures and conformations of both cyclo($\small{L}$-Pro-$\small{L}$-Tyr) and a racemic mixture of cyclo($\small{D}$-Pro-$\small{L}$-Tyr) and cyclo($\small{L}$-Pro-$\small{D}$-Tyr), abbreviated as rac-cyclo($\small{D}$-Pro-$\small{L}$-Tyr/$\small{L}$-Pro-$\small{D}$-Tyr), have been determined by a single-crystal X-ray diffraction study at low temperature. The crystals of rac-cyclo($\small{D}$-Pro-$\small{L}$-Tyr/$\small{L}$-Pro-$\small{D}$-Tyr) belong to orthorhombic space group $Pna2_1$ with a = 10.755 (1), b = 12.699 (1), c = 9.600 (1) ${\AA}$ and Z = 4. The tyrosine side chain is folded towards the diketopiperazine (DKP) ring. The DKP ring adopts a twist boat conformation with pseudo symmetry $C_{2v}$. The pyrrolidine ring has an envelope conformation with the N5, C4, C7 and C8 atoms in a plane. The crystal of rac-cyclo($\small{D}$-Pro-$\small{L}$-Tyr/$\small{L}$-Pro-$\small{D}$-Tyr) is stabilized by hydrogen bonds between amide N2-H2 and carbonyl oxygen O2 in the neighbor. The hydroxyl group of tyrosine residue is also hydrogen bonded to the oxygen of the carbonyl group of the DKP ring in the next molecule. The spectroscopic properties of both isomers are also described.

• Bulletin of the Korean Chemical Society
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• v.19 no.3
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• pp.340-344
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• 1998

A facile synthesis of 4,5-(1',2'-diphenylethylenedithio)-1,3-dithiole-2-thione (dPhEDT-DTT) is carried out via a Diels-Alder type [2+4] cycloaddition reaction of 1,3-dithiol-2,4,5-trithione oligomer and t-stilbene. Molecular structure of dPhEDT-DTT is determined by x-ray crystallography: space group P1, a=11.694(3) Å, b=12.117(3) Å, c=14.688(3) Å, α=113.12(2)°, β=102.23(2)°, γ=107.02(2)°, V= 1699.1(7) Å3, Z=2. It turns out that dPhEDT-DTT crystallizes as a racemic compound consisting of (R,R) and (S,S) enantiomers. Coupling reaction of dPhEDT-DTO undergone in neat P(OEt)3 yields TTF(SEt)4 instead of ET derivative. When PR3 (R=OEt, OPh, Ph) is used in benzene, toluene or xylene, however, dPhEDT-DTO is decomposed.

• Bulletin of the Korean Chemical Society
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• v.35 no.8
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• pp.2311-2316
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• 2014

Conformations and vibrational frequencies of the racemic (2RS,3RS)-5-amino-3-(4-phenylpiperazin-1-yl)-1,2,3,4-tetrahydronaphthalen-2-ol-(I) [(2RS,3RS)-(I)], a precursor of benzovesamicol analogues, have been carried out using various DFT methods (M06-2X, B3LYP, B3PW91, PBEPBE, LSDA, and B3P86) with basis sets of 6-31G(d), 6-31+G(d,p), 6-311+G(d,p), 6-311++G(d,p), cc-pVTZ, and TZVP. The LSDA/6-31G(d) level of theory shows the best performance in reproducing the X-ray powder structure. However, the PBEPBE/cc-pVTZ level of theory is the best method to predict the vibrational frequencies of (2RS,3RS)-(I). The potential energy surfaces of racemic pairs (2RS,3RS)-(I) and -(II) are obtained at the LSDA/6-31G(d) level of theory in the gas phase and in water. The results indicate that (2RS,3RS)-(I) are more stable by ~0.75 kcal/mol in energy than (2RS,3RS)-(II) in water, whereas conformer AIIg and BIIg are more stable by ~0.04 kcal/mol than AIg in gas phase. In particular, the hydrogen bond distances between the N of piperazine and the OH of tetrahydronaphthalen become longer in gas, compared with those in the water phase. Vibrational frequencies calculated at the PBEPBE/cc-pVTZ level of theory in the gas phase are larger than those in water, whereas their intensities in the gas phase are weaker than those in water.

• KSBB Journal
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• v.19 no.1
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• pp.42-49
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• 2004

A gene coding for epoxide hydrolase (EH) of Aspergillus niger LK, a fungus possessing the enantioselective hydrolysis activity for racemic epoxides, was characterized by phylogenetic analysis. The deduced protein of A. niger LK epoxide hydrolase shares significant sequence similarity with several bacterial EHs and mammalian microsomal EHs (mEH) and belongs to the a/${\beta}$ hydrolase fold family. EH from A. niger LK had 90.6% identity with 3D crystal structure of lqo7 in Protein Data Bank. Sequence comparison with other source EHs suggested that Asp$\^$l92/, Asp$\^$374/ and His$\^$374/ constituted the catalytic triad. Based on the multiple sequence comparison of the functional and structural domain sequence, the phylogenetic tree between relevant epoxide hydrolases from various species were reconstructed by using Neighbor-Joining method. Genetic distances were so far as 1.841-2.682 but characteristic oxyanion hole and catalytic triad were highly conserved, which means they have diverged from a common ancestor.

• Membrane and Water Treatment
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• v.7 no.3
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• pp.257-275
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• 2016

The enantiomeric and racemic effects of tartaric acid (TA) on the properties of polysulfone (PSn) ultrafiltration membranes were studied in terms of morphology and hydrophilicity (HPCT) of membrane. Asymmetric membranes were prepared by direct blending of polyvinyl pyrrolidone (PVP) with D-TA and DL-TA in membrane casting solution. FTIR analysis was done for the confirmation of the reaction of PVP and TA in blended membranes and plain PSn membranes. Scanning electron microscope (SEM), field emission scanning electron microscope (FESEM) and atomic force microscopy (AFM) were used for analyzing the morphology and structure of the resulting membranes. The membranes were characterized in terms of pure water flux (PWF), hydraulic permeability and HPCT. PWF increased from $52L/m^2h$ to $79.9L/m^2h$ for plain and D-TA containing PSn membrane, respectively. Water contact angle also found to be decreased from $68^{\circ}$ to $55^{\circ}$. In Additionally, permeation and rejection behavior of prepared membranes was studied by bovine serum albumin (BSA) solution. A considerable increase in BSA flux (from $19.1L/m^2h$ for plain membrane to $32.1L/m^2h$ for D-TA containing membrane) was observed. FESEM images affirm that the pore size of the membranes decreases and the membrane permeability increases from 0.16 to 0.32 by the addition of D-TA in the membrane. D-TA increases the HPCT whereas; DL-TA decreases the HPCT of PSn membrane. PVP (average molecular weight of 40000 Da) with D-TA (1 wt%) gave best performance among all the membranes for each parameter.

• Bulletin of the Korean Chemical Society
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• v.30 no.10
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• pp.2341-2344
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• 2009

Metallacyclodimers, [Ag(OTf)($L1)]_2$ and [Ag($L2)]_2(OTf)_2$ (L1 = 1,3-dibromo-2,2-bis[(isonicotinoyloxy)methyl] propane; L2 = 2,5-dimethyl-2,5-bis(isonicotinoyloxy)hexane) were constructed and characterized. The crystal structure of [Ag(OTf)($L1)]_2$ reveals a 32-membered cyclodimer, whereas that of [Ag($L2)]_2(OTf)_2$ shows a linked 34-membered cyclodimer chain via intercyclic argentophilic (Ag…Ag) interactions. [Ag(OTf)($(L1)]_2$ affords “intramolecular $\pi-\pi$ interaction cyclodimer” whereas [Ag($L2)]_2(OTf)_2$ produces a racemic mixture of “twisted cyclodimer”. Ring-conformation of the cyclodimers was affected via the competition of electrostatic interaction and argentophilic interaction.

• Bulletin of the Korean Chemical Society
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• v.28 no.4
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• pp.589-595
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• 2007

The conversion of both the racemic and resolved forms of the Co(III) complex of an hydroxymethyl-substituted tripodal hexamine to macrobicycles via reaction with formaldehyde and nitromethane (and subsequent reduction of the product) has been conducted. The prospect is that it will provide cage complexes in which the hydroxyl substituent is sufficiently remote from the metal ion centre for its nucelophilicity to be largely unaffected. X-ray structure determinations have been used to characterise these new cage species as well as some complexes of the precursor hexamine and its mono-aminal. The electrochemistry and optical activity of the complexes have also been studied in detail.