• Bulletin of the Korean Chemical Society
• /
• v.32 no.2
• /
• pp.701-704
• /
• 2011

• Bulletin of the Korean Chemical Society
• /
• v.30 no.11
• /
• pp.2785-2788
• /
• 2009

• Advances in environmental research
• /
• v.7 no.2
• /
• pp.139-159
• /
• 2018

Green Leaf Volatiles (GLVs) is a class of biogenically emitted oxygenated hydrocarbons that have been identified as a potential source of Secondary Organic Aerosols (SOA) via aqueous oxidation. The physico-chemical properties of GLVs are vital to understanding their fate and transport in the atmosphere via fog processing, but few experimental data are available. We studied the aqueous solubility, 1-octanol/water partition coefficient, and Henry's law constant ($K_H$) of five GLVs at $25^{\circ}C$: methyl jasmonate, methyl salicylate, 2-methyl-3-buten-2-ol, cis-3-hexen-1-ol, and cis-3-hexenyl acetate. Henry's law constant was also measured at temperatures and ionic strengths typical of fog. Experimental values are compared to scarcely-available literature values, as well as estimations using group and bond contribution methods, property-specific correlations and molecular dynamics simulations. From these values, the partition coefficients to the air-water interface were also calculated. The large Henry's law constant of methyl jasmonate ($8091{\pm}1121M{\cdot}atm^{-1}$) made it the most significant GLV for aqueous phase photochemistry. The HENRYWIN program's bond contribution method from the Estimation Programs Interface Suite (EPI Suite) produced the best estimate of the Henry's constant for GLVs. Estimations of 1-octanol/water partition coefficient and solubility are best when correlating an experimental value of one to find the other. Finally, the scavenging efficiency was calculated for each GLV indicating aqueous phase processing will be most important for methyl jasmonate.

• Carbon letters
• /
• v.12 no.4
• /
• pp.229-235
• /
• 2011

Isotactic polyacrylonitrile (PAN) with triad isotacticity of 0.53, which was determined by $^{13}C$ NMR, using dialkylmagnesium as an initiator, was successfully synthesized. Isothermal treatment of iso-PAN was conducted in air at 200, 220, 250 and $280^{\circ}C$. Structural evolutions and chemical changes were studied with Fourier transformation infrared and wide-angle X-ray diffraction during stabilization. A new parameter $CNF={I_{2240cm}}^{-1}/ ({I_{1595cm}}^{-1}+f^*{I_{1595cm}}^{-1})$ was defined to evaluate residual nitrile groups. Crystallinity and crystal size were calculated with X-ray diffraction dates. The results indicated that the nitrile groups had partly converted into a ladder structure as stabilization proceeded. The rate of reaction increased with treatment temperature; crystallinity and crystal size decreased proportionally to pyrolysis temperature. The iso-conversional method coupled with the Kissinger and Flynn-Wall-Ozawa methods were used to determine kinetic parameters via differential scanning calorimetry analysis with different heating rates. The active energy of the reaction was 171.1 and 169.1 kJ/mol, calculated with the two methods respectively and implied the sensitivity of the reaction with temperature.

• Carbon letters
• /
• v.11 no.1
• /
• pp.22-27
• /
• 2010

The precipitation polymerization of acrylonitrile (AN) was carried out in a mixture solution of dimethyl sulfoxide (DMSO) and water at $50{\sim}65^{\circ}C$ using ${\alpha},{\alpha}'$-azobisisobutyronitrile (AIBN) as an initiator. The increased molecular weight polyacrylonitrile (PAN) was prepared with increasing the $H_2O$/DMSO ratio from 10/90 to 80/20. The viscosity average molecular weight of $H_2O$/DMSO solvent was 4.4 times larger than that of $H_2O$/DMF solvent, and precipitation polymerization was accelerlated due to the far decreased chain transfer effect of DMSO. Based on the experimental results, the increased PAN molecular weight was regarded as the summation of two mechanisms: i) particle-particle aggregation and ii) particle-radical attachment. The theoretical equation derived from the mechanisms was well coincided with the experimental results showing the linear relationship between the viscosity average molecular weight and the H2O/DMSO ratio.

• Proceedings of the Optical Society of Korea Conference
• /
• 2009.10a
• /
• pp.270-271
• /
• 2009

• Bulletin of the Korean Chemical Society
• /
• v.33 no.3
• /
• pp.925-928
• /
• 2012

The accurate expression for the steady-state velocity of an irreversible enzyme-catalyzed reaction obtained by Shin and co-workers (J. Chem. Phys. 2001, 115, 1455) is generalized to allow for the rebinding of the product. The amplitude of the power-law ($t^{-1/2}$) relaxation of the free- and bound-enzyme concentrations to steady-state values is expressed in terms of the steady-state velocity and the intrinsic (chemical) rate constants. This result is conjectured to be exact, even though our expression for the steady-state velocity in terms of microscopic parameters is only approximate.

• Bulletin of the Korean Chemical Society
• /
• v.23 no.12
• /
• pp.1729-1732
• /
• 2002

The LB71350,(3S, 4R)-Epoxy-(5S)-[[N-(1-methylethoxy)carbonyl]-3-(methylsulfonyl)-L-valinyl]amino]-N-[2-methyl-(1R)-[(phenyl)carbonylpropyl-6-phenylhexanamide, is a novel HIV protease inhibitor. Its equilibrium solubility at room temperature was less than $40{\mu}g/mL.$ It was speculated that the low aqueous solubility might be due to the high crystalline lattice energy resulting from intermolecular hydrogen bonds. The present study was carried out to learn the solid-state characteristics of LB71350 using analytical methods such as NMR, FT-IR and XRD. $^{13}C$ Solid-state NMR, solution NMR, and FT-IR spectra of the various solid forms of LB71350 were used to identify the conformation and structure of the solid forms. The chemical shifts of $^{13}C$ solid-state NMR spectra suggest that the crystalline form might have 3 intermolecular hydrogen bondings between monomers.

• Journal of Microbiology and Biotechnology
• /
• v.25 no.11
• /
• pp.1819-1826
• /
• 2015

Poly(ε-ʟ-lysine) (ε-PL) is a novel bioactive polymer secreted by filamentous bacteria. Owing to lack of a genetic system for most ε-PL-producing strains, very little research on enhancing ε-PL biosynthesis by genetic manipulation has been reported. In this study, an effective genetic system was established via intergeneric conjugal transfer for Streptomyces albulus PD-1, a famous ε-PL-producing strain. Using the established genetic system, the Vitreoscilla hemoglobin (VHb) gene was integrated into the chromosome of S. albulus PD-1 to alleviate oxygen limitation and to enhance the biosynthesis of ε-PL in submerged fermentation. Ultimately, the production of ε-PL increased from 22.7 g/l to 34.2 g/l after fed-batch culture in a 5 L bioreactor. Determination of the oxygen uptake rate, transcriptional level of ε-PL synthetase gene, and ATP level unveiled that the expression of VHb in S. albulus PD-1 enhanced ε-PL biosynthesis by improving respiration and ATP supply. To the best of our knowledge, this is the first report on enhancing ε-PL production by chromosomal integration of the VHb gene in an ε-PL-producing strain, and it will open a new avenue for ε-PL production.

• Carbon letters
• /
• v.11 no.3
• /
• pp.176-183
• /
• 2010

PAN precursor fibers were produced via wet-spinning process, and effects of polymerization and spinning processes, especially the stretching process, were investigated on mechanical properties and micro-morphologies of precursor fibers. An increase in molecular weight, dope solid and densification and a decrease in surface defects were possible by controlling polymerization temperature, the number of heating rollers for densification and the jet stretch ratio, which improved the mechanical properties of precursor fibers. The curves for strength, modulus, tensile power and diameter as a function of stretch ratio can be divided into three stages: steady change area, little change area and sudden change area. With the increase of stretch ratio, the fiber diameter became smaller, the degree of crystallization increased and the structure of precursor fibers became compact and homogeneous, which resulted in the increase of strength, modulus and tensile power of precursor fibers. Empirical relationship between fiber strength and stretch ratio was studied by using the sub-cluster statistical theory. It was successfully predicted when the strengths were 0.8 GPa and 1.0 GPa under a certain technical condition, the corresponding stretch ratio of the fiber were 11.16 and 12.83 respectively.