• Bulletin of the Korean Chemical Society
• /
• v.6 no.6
• /
• pp.362-366
• /
• 1985

The hydrogen atom transfer reaction between substituted methane, $CH_3X,$ and its radical, $CH_2X(X=H,F,CH_3,CN,OH\;and\;NH_2$ was studied by MINDO/3 method. The transition state(TS) structure and energy barriers were determined and variation of the transition state and of the reactivity due to the change of X were analyzed based on the potential energy surface characteristics. It was found that the greater the radical stabilization energy. the looser the TS becomes; the TS occurs at about 15% stretch of the C-H bond, which becomes longer as the radical stabilization energy of $CH_2X$ increasers. The intrinsic barrier, ${\Delta}E*_{x.x},$ of the reaction with X was found to increase in the order $H The degree of bond stretch of the C-H bond stretch of the C-H bond at the TS also had the same order indicating that the homolytic bond cleavage of the C-H bond is rate-determining. Orbital interactions at the TS between LUMO of the fragment $C{\ldots}H{\ldots}C$ and the symmetry adapted pair of nonbonding, $n{\pm}(=n_1{\pm}n_2),$ or pi orbitals of the two X atoms were shown to be the dominant contribution in determining tightness or looseness of the TS. The Marcus equation was shown to apply to the MINDO/3 barriers and energy changes of the reaction.

• Journal of Applied Biological Chemistry
• /
• v.54 no.2
• /
• pp.143-146
• /
• 2011

Novel pyrazoline (4) was synthesized from chalcone (3) which was prepared from 2'-hydroxy-l'acetonaphthone (1) and 4-methoxy benzaldehyde (2). Pyrazoline (4) forms resonance assisted hydrogen bond between naphthol hydroxyl group and imine nitrogen in a pyrazoline ring. Pyrazoline (4) shows Poly ADP-ribose Polymerase (PARP) cleavage ability as a proof of apoptosis in cancer cell, which reveals its anti-cancer property.

• YAKHAK HOEJI
• /
• v.26 no.3
• /
• pp.175-180
• /
• 1982

The intermediate of N'-nitrosonornicotine may bind to the guanine moiety of a G-C base pair. The hydrogen bond of the base pair may be broken and a new hydrogen bond can form between the intermediate and the guanine. It results in the "short" type of DNA repair.NA repair.

• YAKHAK HOEJI
• /
• v.18 no.3
• /
• pp.217-227
• /
• 1974

It was established that .alpha.-spinasterol (I) was isomerized by hydrogen chloride to a mixture of two isomers. These isomers were separated into each of components and identified as .DLETA.$^{8(14),22}$ -stigmastadienol (III) and ${\delta}$$^{14,22}$ -stigmastadienol (IV), respectively. The mass spectra of these compounds were found to be particularly suitable to idetify the position of nuclear double bond of sterols possessing 22 : 23 -double bond in side chain.

• Journal of the Korean Chemical Society
• /
• v.57 no.1
• /
• pp.99-103
• /
• 2013

The present communication deals with the Pharmacophore modeling, 3D QSAR and docking analysis on series of Pyrimidine derivatives as potential calcium channel blockers. The computational studies showed hydrogen bond donor, hydrogen bond acceptor, and hydrophobic group are important features for calcium channel blocking activity. These studies showed that Pyrimidine scaffold can be utilized for designing of novel calcium channels blockers for CVS disorders.

• Bulletin of the Korean Chemical Society
• /
• v.15 no.10
• /
• pp.868-873
• /
• 1994

We have re-examined the linear solvation energy relationships in reversed phase liquid chromatography by considering various solutes including quite a number of compounds of strong hydrogen bond capability. We observed that solutes of strong hydrogen bond ability should be excluded in order to obtain resonable correlations between In k' and solute polarity parameters and that inclusion of one or two such solutes causes severe distortions of correlation results. This anomaly may be due to existence of residual silanol groups in the stationary phase, that is, their specific interactions with solutes.

• Journal of the Korean Chemical Society
• /
• v.59 no.6
• /
• pp.541-544
• /
• 2015

• Proceedings of the Korean Vacuum Society Conference
• /
• 2000.02a
• /
• pp.25-25
• /
• 2000

In this talk we discuss the dynamics of hydrogen on the Si(100)-2xl surface. At room temperature the sticking coefficient for molecular hydrogen on this surface is less than 10sup-12. However, hydrogen molecules desorbing from the surface do not have an excess of energy, suggesting at best a small barrier on the exit channel. These observations have led to speculation about the validity of detailed balance in this system. Here we show that this discrepancy can be explained by considering both the surface-molecule co-ordinate and that associated with the Si-Si dimer bond tiltangle. By preparing the surface dimers with a specific tiltangle we demonstrate that the barrier to adsorption is a function of this angle and that the sticking coefficient dramatically increase for certain angles. The adsorption-desopption dynamics can then be described in terms of a common potential energy hypersurface involving both of these co-ordinates. The implications of these observations are also discussed. The dynamics of adsorbed hydrogen atoms on the Si(100) surface is also described. Paired dangling bonds produced following recombinative hydrogen desorption are mobile at elevated temperatures. Pairs of dangling bonds are observed to dissociate, diffuse, and ultimately recombine. At sufficiently elevated temperatures dangling bond exchange reactions are observed. These data are analyzed in terms of an attractive zone and an effective binding interaction between dangling bonds. Insights that this provides into the nature of surface defects and the localized chemistry that occurs on this surface, are also discussed.

• Bulletin of the Korean Chemical Society
• /
• v.20 no.9
• /
• pp.1067-1072
• /
• 1999

Structures of unprotonated [(NH3)n+(n = 1-6)] and protonated [NH4+(NH3)n-1(n = 1-6)] ammonia cluster cations have been optimized with ab initio Hartree-Fock (HF) and second-order MФller-Plesset (MP2)/6-31+G ** levels and the harmonic vibrational frequencies have also been evaluated. In unprotonated cluster cations, NH3+ forms as a central core of the first ammonia solvation shell. In protonated cluster cations, NH4+ forms as a central core. In unprotonated dimer and trimer cations, there are two types of isomers (hydrogen-bonded and head-to-head interactions). In both cluster cations, the hydrogen-bonded isomers are more stable. In the hydrogen-bonded dimer cation, the proton transfer reaction takes place from (NH3-HN+H2) to (NH4+-NH2). But in the other unprotonated cluster cations, the proton transfer does not take place. In unprotonated pentamer and hexamer, a NH3+ core has both interactions in a complex. On the other hand, in unprotonated tetramer a core has only the hydrogen-bonded type combined with neutral ammonia molecules. With increasing cluster cation size, the bond lengths [R(NN)] between two nitrogen atoms and the distances [R(N ...H)] of the hydrogen-bond increase reg-ularly. In the calculated infra-red absorption bands for ammonia cluster cations, the characteristic peaks of the bridged NH vibration of the hydrogen-bonded clusters appear near 2500 cm-1 . With increasing size, the peaks shift from 2306 cm-1 to 2780 cm-1 .

• Bulletin of the Korean Chemical Society
• /
• v.6 no.3
• /
• pp.162-164
• /
• 1985

Nucleophilic substitution reaction of dansyl chloride with anilines in various solvents have been investigated. The Bronsted ${\beta}$ and Hammett ${\rho}_N$ values indicated that the bond formation is advanced more than the bond breaking at the transition state. Solvatochromic correlations also predicted the importance of bond formation at the TS, showing a greater contribution of polarity (${\pi}^{\ast}$) compared to hydrogen bond donor acidity (${\alpha}$). The effect of solvent on rate was found to violate the reactivity-selectivity principle.