• Journal of the Korean Chemical Society
• /
• v.37 no.1
• /
• pp.105-111
• /
• 1993

The stability constants for lanthanides complexes with optically active L-proline (1 : 1) were determined in aqueous solution in the ionic medium of 0.1 M $NaClO_4$ at 25$^{\circ}C$ using a pH titration method. The results show called "gadolinium break" between lighter and heavier lanthanides. The linear relation between the stability constant (log$\beta$1) and the pKa values of ligands indicates that L-proline acts as a bidentate ligand in the complexation. The thermodynamic parameters (${\Delta}H$ and ${\Delta}S$) were also determined using an enthalpy titration method at the same condition. The positive endothermic enthalpy change and positive entropy change clearly indicate that the driving force for the complexation is an entropy effect. The comparison of the thermodynamic parameters of L-proline complexes with anthranilate complexes supports the conclusion that the heterocyclic nitrogen atom and carboxylate of L-proline are involved in the chleate formation. The enthalpy values for L-proline are more positive than the ones for anthranilate complex. The difference in enthalpy change for the complex formation between L-proline complex and anthranilate complex is explained in terms of the basicity of the nitrogen donor atom in the ligand. The relatively large entropy change may be described by the extra dehydration related to the rigidity of L-proline ring.

• Journal of the Korean Chemical Society
• /
• v.37 no.4
• /
• pp.442-447
• /
• 1993

The thermodynamic parameters (${\Delta}$G, ${\Delta}$H and ${\Delta}$S) of lanthanides(III)-benzoylformate complexes in aqueous solution have been determined in the ionic medium of 0.1M $NaClO_4$ at 25$^{\circ}C$, using pH and enthalpy titration method. The stability constants of the lanthanide(III)-benzoylformate complexes (1 : 1) agree well with the general relationships for the bidentate ligands (e.g., log${\beta}_1$ vs. p$K_a$). Thermodynamic evidences show that the oxygen atom in ketone group is coordinated along with the carboxylate group. It is ascribed to the increasing charge density on the oxygen atom in ketone group due to the conjugation effect in the benzoylformate ligand. Thermodynamic results also indicate that the complexes are stabilized by the enthalpy effect caused by the ionic interaction of metal-oxygen bond as well as the entropy effect.

• Polymer(Korea)
• /
• v.35 no.2
• /
• pp.183-188
• /
• 2011

Pentaerytritol triacrylate (PETA) was synthesized by a condensation reaction between pentaerytritol and acrylic acid. The highest yield of PETA was obtained when heptane was used as a solvent under the 1:4 mole ratio of pentaerytritol and acrylic acid. The 6-functional urethane acrylates(UA) were also synthesized by a condensation reaction between PETA and diisocyanate. Cured films were prepared from the mixtures of UA oligomer, reactive diluents and UV initiator to investigate their physical properties. The thermal stability of the aliphatic urethane acrylate was better than that of the aromatic urethane acrylate. The UA-2 showed good hardness and scratch resistance properties while the UA-l with a high degree of curing density exhibited a better chemical resistance. All the UA oligomers showed fairly good adhesion strengths but the other physical properties of UA-3 were poor due to its low curing density.

• Journal of the Korean Chemical Society
• /
• v.47 no.2
• /
• pp.104-108
• /
• 2003

The reaction of $[Cu(L)]Cl_2{\cdot}H_2O(L=3,14-dimethyl-2,6,13,17-tetraazatricyclo[14,4,0^{1.18},0^{7.12}]docosane)$ with 2,5-pyridinedicarboxylate(pdc) led to the formation of $[Cu(L)(H_2O)](pdc){\cdot}6H_2O(1)$. The structure was characterized by X-ray crystallography and spectroscopic method. The coordination geometry around the copper atom is a distorted square-pyramid with four secondary amines of the macrocycle occupying the basal sites and a water molecule at the axial position. Intermolecular hydrogen bonds in 1 form a three-dimensional molecular network.

• Journal of the Korean Chemical Society
• /
• v.29 no.6
• /
• pp.565-574
• /
• 1985

The rates of reaction between 4-substituted-2,6-dinitrochlorobenzenes with para-substituted anilines in methanol-acetonitrile mixtures were measured by conductometry. It was observed that the rate constant increases in the order of X = 4-$NO_2 {\gg}4-CN {\gg}4- CF_3$, where X is a substituent in the substrate. The rate constant also increases in the order of Y = p-O$CH_3{\gg}p- CH_3{\gg}H {\gg}p-Cl{\gg}m- NO_2$, where Y is a substituent in the aniline ring. Kinetic studies in the methanol-acetonitrile solvent system with various nucleophiles showed that the N-C bond forming step is making a great contribution to the overall second order rate constant. The electrophilic catalysis by methanol probably consists of the hydrogen bonding between alcoholic hydrogen and leaving chloride in the transition state. The nucleophilic catalysis by methanol may be ascribed to the formation of hydrogen bonds between alcoholic oxygen and hydrogens of amines in the transition state. All these experimental facts are supporting the operation of $S_N$Ar machanism with the second step being the rate determining. This mechanism can be successfully fitted to the PES model.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.11 no.2
• /
• pp.91-98
• /
• 1991

In this paper, the microscopic results of granular sludge from the two-phase UASB reactors are presented, particularly on the acidogenic phase where the distillery waste water is directly delivered. Distillery wastewater as a feed contained SS of 3.6~10.6 g/l and COD of 17.3~30.4 g/l. A 12.5 l and a 4.7 l UASB reactors were used for acidogenic and methanogenic phases, repectively. Morphological studies on the granular sludge consortia were made with both scanning and transmission electron microscopies. It was interesting enough to find the different colored and shaped granules at the acidogenic on the 90th day and at the methanogenic phase on the 120th day. The acidogenic granular sludge mainly consisted of acidogenic bacteria, such as long chains of large rods, short plump rods, and various size of cocci. Whereas the filamentous bacteria of Methanothrix spp. prevail in the methanogenic granule, with dirverse bacteria entrapped therein.

• Journal of the Korean Chemical Society
• /
• v.41 no.9
• /
• pp.460-464
• /
• 1997

(Allyloxy)methyl-Crown Ethers have been used as metal cation carriers in a bulk liquid membrane system. Competitive transports by the AMDT18C6 and the AM18C6 are selective for Pd(Ⅱ) ion and Pb(Ⅱ) ion over other transition metal cations respectively. Studies of complexations of (Allyloxy)methyl-Crown Ethers with metal cations have been carried out by titration calorimetry and potentiometry.

• Analytical Science and Technology
• /
• v.5 no.1
• /
• pp.33-39
• /
• 1992

THF-based crown-4 of 16-membered rings having tetrahydrofuran unit was synthesized by an acid-catalyzed condensation of furan and acetone followed by hydrogenation in an effort to obtain highly elective ionophores for lithium ions. The new ionophore was compared with previously reported ionophores under similar measurement conditions with the same plasticizer, tris(2-ethylhexyl) phosphate in poly(vinyl chloride)(PVC) membrane electrodes. Separate solution method was used to determine relative selectivity coefficients for the electrode. The selectivity coefficients($K_{LiM}^{POT}$) of lithium over ammonium, alkali and alkaline earth metal ions go from about $2.4{\times}10^{-1}$ to $2.3{\times}10^{-4}$ to working range and pH dependence have also been studied.

• Applied Chemistry for Engineering
• /
• v.30 no.2
• /
• pp.247-253
• /
• 2019

In this study, compounds with azo-mesogenic groups at 4-, 3,5-, or 3,4,5-positions of one phenyl ring were synthesized, and their liquid crystallinity and photochemistry were investigated. The compounds in the Azo1 and Azo2 series had linear and planar geometries, respectively, while those in the Azo3 series had relatively bulky structures. Compounds of BA-Azo2 and BA-Azo3 did not show any liquid crystallinity. Compounds of BE-Azo1 and BE-Azo2 exhibited a monotropic liquid crystallinity, while the other compounds showed an enantiotropic liquid crystallinity. The liquid crystalline behavior was imparted by the azo-mesogenic groups, and most of the liquid crystalline compounds formed a smectic phase. All the RM-AzoX compounds exhibited photoisomerism because of the presence of the azo groups in the molecule. The rate of photoisomerization followed the order of RM-Azo3 < RM-Azo1 < RM-Azo2 and was considered to depend on the steric hindrance around the azobenzene groups in the molecule. These results suggest that the liquid crystallinity and photochemical property of the compounds are affected by the position or the number of azo-mesogenic groups phenyl ring of the molecule.

• Polymer(Korea)
• /
• v.30 no.5
• /
• pp.373-379
• /
• 2006

Polymerizable discotic liquid crystals containing diacetylene and acryloyl groups were formed through hydrogen bonding between phloroglucinol core and polymerizable pyridine derivatives, and their photopolymerization behavior was investigated. The discotic complexes exhibited discotic columnar and rectangular columnar mesophases depending on the number of aromatic rings. Photopolymerization of the discotic complexes was carried out by UV irradiation in the liquid crystalline state. IR and UV-Vis spectroscopy affirmed that diacetylene and acryloyl groups were selectively Polymerized, and that crosslinked polymers containing short conjugated diacetylene oligomers were produced by 1,4-addition. X-ray diffraction experiment showed that the columnar order in the discotic complex containing phenyl-pyridine moiety was maintained after photopolymerization, and that the rectangular columnar order in he discotic Complex with biphenyl units was changed to the lamellar order.