• Bulletin of the Korean Chemical Society
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• v.24 no.2
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• pp.197-204
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• 2003

The intracluster ion-molecule reactions of $Ti^+(H_2O)_n,\;Ti^+(CH_3OCH_3)_n,\;and\;Ti^+(CH_3OD)_n$ complexes produced by the mixing of the laser-vaporized plasma and the pulsed supersonic beam were studied using a reflectron time-of-flight mass spectrometer. The reactions of $Ti^+$ with water clusters were dominated by the dehydrogenation reaction, which produces $TiO^+(H_2O)_n$ clusters. The mass spectra resulting from the reactions of $Ti^+\;with\;CH_3OCH_3$ clusters exhibit a major sequence of $Ti^+(OCH_3)_m(CH_3OCH_3)_n$ cluster ions, which is attributed to the insertion of $Ti^+$ ion into C-O bond of $CH_3OCH_3$ followed by $CH_3$ elimination. The prevalence of $Ti^+(OCH_3)_m(CH_3OD)_n$ ions in the reaction of $Ti^+\;with\;CH_3OD$ clusters suggests that D elimination via O-D bond insertion is the preferred decomposition pathway. In addition, the results indicate that consecutive insertion reactions by the $Ti^+$ ion occur for up to three precursor molecules. Thus, examination of $Ti^+$ insertion into three different molecules establishes the reactivity order: O-H > C-O > C-H. The experiments additionally show that the chemical reactivity of heterocluster ions is greatly influenced by cluster size and argon stagnation pressure. The reaction energetics and formation mechanisms of the observed heterocluster ions are also discussed.

• Bulletin of the Korean Chemical Society
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• v.29 no.2
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• pp.319-322
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• 2008

The viability of acetylene addition in each step of aromatic formation initiated by vinyl radical and acetylene also with its competition with structure rearrangement is investigated by determining optimal geometries and barrier and reaction energies using quantum mechanical methods. In principle, the addition reaction has more difficult in term of free energy and enthalpy compared to geometry arrangement. Under combustion conditions, i.e. T = 1200 K, acetylene addition is unfavorable mechanism as the barrier energy values rise much higher than that of geometry arrangement. However, in longer chain hydrocarbon case, e.g. n-CxHx+1 where x ³ 8, C-C bond rotation is rather difficult and requires high energy to form a ring structure, elongation chain is preferable.

• Journal of Life Science
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• v.20 no.6
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• pp.853-860
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• 2010

The DevSR two-component system is a major regulatory system involved in redox sensing in Mycobacterium smegmatis. The DevSR system consists of the DevS histidine kinase and its cognate DevR response regulator. When exposed to hypoxic conditions, the DevS histidine kinase is activated to phosphorylate the DevR response regulator, leading to the transcriptional activation of the DevR regulation. The ligand-binding state of the heme embedded in the N-terminal GAF domain of DevS determines the kinase activity of DevS. In this study, we demonstrated that the redox-responsive cysteine (C547) in the C-terminal kinase domain is involved in the redox-dependent control of DevS kinase activity. The formation of an intersubunit disulfide bond between the C547 residues in the presence of $O_2$ led to inactivation of DevS kinase activity. The reduction of the oxidized DevS with reductants such as $\beta$-mercaptoethanol and dithiothreitol resulted in the restoration of DevS kinase activity. It was demonstrated in vivo by complementation test that the substitution of C547 to alanine partially impaired the sensory function of DevS in M. smegmatis.

• Bulletin of the Korean Chemical Society
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• v.29 no.6
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• pp.1195-1198
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• 2008

Kinetic studies of the additions of benzylamines to a noncyclic dicarbonyl group activated olefin, methyl $\alpha$-acetyl-$\beta$ -phenylacrylates (MAP), in acetonitrile at 30.0 ${^{\circ}C}$ are reported. The rates are lower than those for the cyclic dicarbonyl group activated olefins. The addition occurs in a single step with concurrent formation of the $C_\alpha$ -N and $C_\beta$ -H bonds through a four-center hydrogen bonded transition state. The kinetic isotope effects ($k_H/k_D$ > 1.0) measured with deuterated benzylamines ($XC_6H_4CH_2ND_2$) increase with a stronger electron acceptor substituent ($\delta\sigma$ X > 0) which is the same trend as those found for other dicarbonyl group activated series (1-4). The sign and magnitude of the cross-interaction constant, ρXY, is comparable to those for the normal bond formation processes in the $S_N2$ and addition reactions. The relatively low ${\Delta}H^\neq$ and large negative ${\Delta}S^\neq$ values are also consistent with the mechanism proposed.

• Bulletin of the Korean Chemical Society
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• v.35 no.5
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• pp.1479-1484
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• 2014

Based on the full optimized molecular geometric structures at B3LYP/cc-pvtz method, a new designed compound, 4,6,8-trinitro-4,5,7,8-tetrahydro-6H-furazano[3,4-f ]-1,3,5-triazepine was investigated in order to look for high energy density compounds (HEDCs). The analysis of the molecular structure indicates that the seven-membered ring adopts chair conformation and there exist intramolecular hydrogen bond interactions. IR spectrum and heat of formation (HOF) were predicted. The detonation velocity and pressure were evaluated by using Kamlet-Jacobs equations based on the theoretical density and condensed HOF. The bond dissociation energies and bond orders for the weakest bonds were analyzed to investigate the thermal stability of the title compound. The results show that $N_1-N_6$ bond is the trigger bond. The crystal structure obtained by molecular mechanics belongs to $Pna2_1$ space group, with lattice parameters Z = 4, a = 15.3023 ${\AA}$, b = 5.7882 ${\AA}$, c = 11.0471 ${\AA}$, ${\rho}=2.06gcm^{-3}$. In addition, the analysis of frontier molecular orbital shows the title compound has good stability and high chemical hardness.

• Bulletin of the Korean Chemical Society
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• v.26 no.12
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• pp.1946-1952
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• 2005

New group 15 organometallic compounds, M$(phenanthrenyl)_3$ (M = P (1), Sb (2), Bi (3)) have been prepared from the reactions of 9-phenanthrenyllithium with $MCl_3$. A reaction of 9-(diphenylphosphino)phenanthrene with 2,6-diisopropylphenyl azide led to the formation of (phenanthrenyl)${(Ph)}_2P$=N-(2,6-$^iPr_2C_6H_3$) (4). The crystal structures of 2 and 4 have been determined by single-crystal X-ray diffractions, both of which crystallize with two independent molecules in the asymmetric unit. Compound 2 shows a trigonal pyramidal geometry around the Sb atom with three phenanthrenyl groups being located in a screw-like fashion with an approximately $C_3$ symmetry. A significant amount of CH- -$\pi$ interaction exists between two independent molecules of 4. The phosphorus center possesses a distorted tetrahedral environment with P-N bond lengths of 1.557(3)$\AA$ (P(1) N) and 1.532(3)$\AA$ (P(2)-N), respectively, which are short enough to support a double bond character. One of the most intriguing structural features of 4 is an unusually diminished bond angle of C-N-P, attributable to the hydrogen bonding of N(1)-H(5A) [ca. 2.49$\AA$ between two adjacent molecules in crystal packing. The compounds 1-3 show purple emission both in solution and as films at room temperature with emission maxima ($\lambda_{max}$) at 349, 366, and 386 nm, respectively, attributable to the ligand centered $\pi$ $\rightarrow$ $\pi^\ast$ transition in phenanthrene contributed by the lone pair electrons of the Gp 15 elements. Yet the nature of luminescence observed with 4 differs in that it originates from $\pi$ (diisopropylbenzene)-$\pi^\ast$ (phenanthrene) transitions with the $\rho\pi$contribution from the nitrogen atom. The emission maximum of 4 is red-shifted ranging 350-450 nm due to the internal charge transfer from the phenanthrenyl ring to the N-arylamine group as deduced from the ab initio calculations.

• Bulletin of the Korean Chemical Society
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• v.18 no.9
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• pp.1010-1013
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• 1997

Nucleophilic substitution reactions of (Z)-phenylethyl (X)-benzenesulfonates with (Y)-pyridines were investigated in acetonitrile at 60 ℃ under respective pressures. The magnitudes of the Hammett reaction constants, ρX, ρY and ρZ indicate that a stronger nucleophile leads to a greater degree of bond formation of C-N and a better leaving group is accompanied by a less degree of bond breaking. The magnitude of correlation interaction term, ρij can be used to determine the structure of the transition state (TS) for the SN reaction. As the pressure is increased, the Hammett reaction constants, ρX and |ρY|, are decreased, but correlation interaction coefficient, ρXZ and |ρYZ|, are increased. The results indicate that the reaction of (Z)-phenylethyl (X)-benzenesulfonates with (Y)-pyridines probably moves from a dissociative SN2 to early-type concerted SN2 mechanism by increasing pressure. This result shows that the correlation interaction term ρij can be useful tool to determine the structure of TS, and also the sign of the product ρXZ·ρYZ can be predict the movement of the TS.

• Korean Journal of Materials Research
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• v.23 no.2
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• pp.104-111
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• 2013

In this study, GaN powders were synthesized from gallium oxide-hydroxide (GaOOH) through an ammonification process in an $NH_3$ flow with the variation of $B_2O_3$ additives within a temperature range of $300-1050^{\circ}C$. The additive effect of $B_2O_3$ on the hexagonal phase GaN powder synthesis route was examined by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transformation infrared transmission (FTIR) spectroscopy. With increasing the mol% of $B_2O_3$ additive in the GaOOH precursor powder, the transition temperature and the activation energy for GaN powder formation increased while the GaN synthesis limit-time ($t_c$) shortened. The XPS results showed that Boron compounds of $B_2O_3$ and BN coexisted in the synthesized GaN powders. From the FTIR spectra, we were able to confirm that the GaN powder consisted of an amorphous or cubic phase $B_2O_3$ due to bond formation between B and O and the amorphous phase BN due to B-N bonds. The GaN powder synthesized from GaOOH and $B_2O_3$ mixed powder by an ammonification route through ${\beta}-Ga_2O_3$ intermediate state. During the ammonification process, boron compounds of $B_2O_3$ and BN coated ${\beta}-Ga_2O_3$ and GaN particles limited further nitridation processes.

• Bulletin of the Korean Chemical Society
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• v.24 no.5
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• pp.583-592
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• 2003

The gas phase identity nucleophilic substitution reactions of halide anions (X = F, Cl, Br) with cyclopentadienyl halides (1) are investigated at the B3LYP/6-311+G**, MP2/6-311+G** and G2(+)MP2 levels involving five reaction pathways: σ-attack $S_N2$, β-$S_N$2'-syn, β-$S_N$2'-anti, γ-$S_N$2'-syn and γ-$S_N$2'-anti paths. In addition, the halide exchange reactions at the saturated analogue, cyclopentyl halides (2), and the monohapto circumambulatory halide rearrangements in 1 are also studied at the same three levels of theory. In the σ-attack $S_N2$ transition state for 1 weak positive charge develops in the ring with X = F while negative charge develops with X = Cl and Br leading to a higher energy barrier with X = F but to lower energy barriers with X = Cl and Br than for the corresponding reactions of 2. The π-attack β-$S_N$2' transition states are stabilized by the strong $n_C-{\pi}^{*}_{C=C}$ charge transfer interactions, whereas the π-attack γ-$S_N$2' transition states are stabilized by the strong $n_C-{\sigma}^{*}_{C-X}$ interactions. For all types of reaction paths, the energy barriers are lower with X = F than Cl and Br due to the greater bond energy gain in the partial C-X bond formation with X = F. The β-$S_N$2' paths are favored over the γ-$S_N$2' paths only with X = F and the reverse holds with X = Cl and Br. The σ-attack $S_N2$ reaction provides the lowest energy barrier with X = Cl and Br, but that with X = F is the highest energy barrier path. Activation energies for the circumambulatory rearrangement processes are much higher (by more than 18 kcal $mol^{-1}$) than those for the corresponding $S_N2$ reaction path. Overall the gas-phase halide exchanges are predicted to proceed by the σ-attack $S_N2$ path with X = Cl and Br but by the β-$S_N$2'-anti path with X = F. The barriers to the gas-phase halide exchanges increase in the order X = F < Br < Cl, which is the same as that found for the gas-phase identity methyl transfer reactions.

• Bulletin of the Korean Chemical Society
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• v.28 no.5
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• pp.751-757
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• 2007

To develop new COX-2 inhibitors, 1,5-diarylhydantoins and 1,5-diaryl-2-thiohydantoins were synthesized from phenylacetic acids by esterification, bromination, C-N bond formation and cyclization. Esters 1-3 were efficiently synthesized from the starting materials by reflux in absolute methanol for 3 h containing concentrated sulfuric acid as catalyst. Bromination was carried out with N-bromosuccinimide at rt in dichloromethane. Bromides 4-6 were reacted with aniline, p-anisidine, sulfanilamide in ethanol (or N,N-dimethylformamide) to provide the amines 7-15. Hydantoins and 2-thiohydantoins 16-46 were synthesized from amines 7-15 by treating them with potassium isocyanate (or potassium thiocyanate) and triethylamine. The synthetic process from alkyl α-anilinophenylacetate 7-15 to 3-alkylhydantoins was carried out in a one-pot reaction using alkyl isocyanate (alkyl isothiocyanate).