• Bulletin of the Korean Chemical Society
• /
• v.27 no.9
• /
• pp.1397-1400
• /
• 2006

A detailed spectroscopic study ($^1H$ NMR, COSY, ROESY) of complexation of venlafaxine hydrochloride (VEN) with $\beta$-cyclodextrin ($\beta$--CD) was carried out in solution. The stoichiometry of the complex was determined to be 1 : 1 and penetration of aromatic ring into $\beta$-Cyclodextrin cavity was confirmed from primary rim side, with the help of ROESY spectral data. The structure of the venlafaxine hydrochloride-$\beta$-CD complex has been proposed. The association constant was determined to be 234 $M^{-1}$.

• Bulletin of the Korean Chemical Society
• /
• v.27 no.9
• /
• pp.1445-1449
• /
• 2006

Molecular tweezers based on chenodeoxycholic acid bearing different lengths of arm were synthesized andtheir anion binding affinities were evaluated by $^1H$ NMR, isothermal calorimetric titration, and ESI mass spectrometry. Molecular tweezer 6 showed a high selectivity toward $H_2PO_4\;^-$ over $Cl^-,\;Br^-,\;I^-, $ and $CH_3CO_2\;^-$ by $^1H$ NMR titration, whereas the association constant for $F^-$ revealed the largest value as determined by ITC. The selectivity of 6 towards $F^-$ was about 103 times higher than that of $Cl^-,\;H_2PO_4\;^- $, and $CH_3CO_2\;^-$. ITCexperiment of 6 with $F^-$ in a DMSO showed two binding modes; two sequential association constants $K_1\;=\;2.77\;{\times}\;10^5\;M^{-1}$ and $K_2\;=\;8.68\;{\times}\;10^6\;M^{-1}$ were found. These sequential bindings were confirmed by ESI massspectrometry. 1 : 1 and 1 : 2 complexes of 6 and $F^-$ were found at m/z 868.08 and 884.04.

• Bulletin of the Korean Chemical Society
• /
• v.19 no.1
• /
• pp.68-74
• /
• 1998

The complexation of ethylammonium ion by alkyl p-tert-butylcalix[6]aryl ester derivatives was studied via measurements of proton and carbon spin-lattice relaxation times $(T_1)$ and chemical shift changes in solution state $(CDCl_3)$. The results indicate that the endo-type complexes are formed and that the overall tumbling rates of these complexes are more rapid than those of the corresponding free hosts. The association constants for these complexes in $THF-d_8$ were determined by $^1H$ NMR titration at several different temperatures to estimate the relevant thermodynamic parameters. The logK's for ethylammonium complexes of methyl, ethyl, and propyl esters at 313 K, for example, were found to be 1.56, 3.41, and 3.08, respectively. The complexes formed may be thought of as being kinetically stable in view of their $^1H$ NMR behavior in 2 : 1 host/guest solution.

• Bulletin of the Korean Chemical Society
• /
• v.16 no.4
• /
• pp.331-336
• /
• 1995

The macroscopic and microscopic redox potentials of tetrahemoprotein, cytochrome c3 from Desulfovibrio vulgaris(Hildenborough) (DvH) were estimated from 1H NMR and differential pulse polarography(DPP). Five sets of NMR resonances were confirmed by a redox titration. They represent cytochrome c3 molecules in five macroscopic redox states. The electron transfer in cytochrome c3 involves four consecutive one-electron steps. The saturation transfer method was used to determine the chemical shifts of eight heme methyl resonances in five different oxidation states. Thirty two microscopic redox potentials were estimated. The results showed the presence of a strong positive interaction between a pair of particular hemes. Comparing the results with those of Desulfovibrio vulgaris Miyazaki F (DvMF), it was observed that the two proteins resemble each other in overall redox pattern, but there is small difference in the relative redox potentials of four hemes.

• Macromolecular Research
• /
• v.13 no.6
• /
• pp.467-476
• /
• 2005

The main objective of this study was to develop and characterize pH-sensitive biodegradable polymeric materials. For pH-sensitivity, we employed three kinds of moieties: 2-amino-3-(lH-imidazol-4-yl)-propionic acid (H), N-[4-( 4,6-dimethyl-pyrimidin-2ylsulfamoyl)-phenyl]succinamic acid (SM), and 2- {3-[ 4-( 4,6-dimethyl-pyrim­idin- 2-ylsulfamoyl)-phenylcarbamoyl]-propionylamino} -3-(3 H - imidazol-4-yl)-propionic acid (SH). The pH -sensitive diblock copolymers were synthesized by ring opening polymerization and coupling reaction from poly(ethylene glycol) (MPEG), $\varepsilon$-caprolactone (CL), D,L-lactide (LA) and pH-sensitive moieties. The pH-sensitive SH molecule was synthesized in a two-step reaction. The first step involved the synthesis of SHM, a methyl ester derivative of SH, by coupling reaction of SM and L-histidine methyl ester dihydrochloride, whereas the second step involved the hydrolysis of the same. The synthesized SM, SHM and SH molecules were characterized by FTIR, $^{1}H$-NMR and $^{13}C$-NMR spectroscopy, whereas diblock copolymers and pH-sensitive diblock copolymer were characterized by $^{1}H$-NMR and GPC analysis. The critical micelle concentrations were determined at various pH conditions by fluorescence technique using pyrene as a probe. The micellization and demicellization studies of pH-sensitive diblock copolymers were also done at different pH conditions. The pH-sensitivity was further established by acid-based titration and DLS analysis.

• Macromolecular Research
• /
• v.13 no.5
• /
• pp.373-384
• /
• 2005

Novel pH-sensitive moieties containing an s-triazine ring were synthesized with sulfonamide and secondary amino groups. The synthesized pH-sensitive moieties were used for the synthesis of a pH-sensitive amphiphilic ABA triblock copolymer. The pH-sensitive triblock copolymer was composed of diblock copolymers, methoxy poly(ethylene glycol)-poly ($\varepsilon$-caprolactone-co-D,L-lactide) (MPEG-PCLA), and pH-sensitive moiety. These copolymers could be dissolved molecularly in both acidic and basic aqueous media at room temperature due to secondary amino and sulfonamide groups. The synthesized s-triazine rings containing pH-sensitive compounds were characterized by ${^1}H-NMR,\;{^13}C-NMR$, and LC/MSD spectral data. The synthesized diblock and triblock copolymers were also characterized by ${^1}H-NMR$ and GPC analyses. The critical micelle concentrations at various pH conditions were determined by fluorescence technique using pyrene as a probe. Furthermore, the micellization and demicellization study of the triblock copolymer was done with pH-sensitive groups. The sensitivity towards pH change was further established by acid-base titration.

• Bulletin of the Korean Chemical Society
• /
• v.17 no.9
• /
• pp.820-826
• /
• 1996

The p2H dependence of the NMR chemical shifts of the proton signals of heme methyl groups and ionizable groups in the vicinity of the heme were investigated. The p2H titration of heme methyl signals in four macroscopic oxidation states by saturation tranfer method was performed in the range between p2H 5.2 and 9.0. While the p2H dependence of the heme methyl resonance in fully oxidized state was small, most resonances in the intermediate oxidation states showed certain shifts. Particularly, methyl resonances of heme 1 (sequential heme numbering) exhibited sharp p2H dependence in acidic range. β-CH2 of the propionate of hemes 1 and 4 were titrated in the range of p2H 4.5-9.0. Only the 6-propionate group of heme 1 was protonated in this p2H range and its titration curve was similar to those of methyl resonances of heme 1 in intermediate oxidation states. Analysis of the microscopic redox potentials showed that they change depending on p2H. The ionizable groups responsible for the p2H dependence of these potentials are 6-propionate of heme 1 in acidic range and His 67 in basic range.

• Bulletin of the Korean Chemical Society
• /
• v.25 no.5
• /
• pp.609-616
• /
• 2004

Complexation of cesium ion by p-tert-butylcalix[6]arene ethyl ester was studied by NMR spectroscopy in nonpolar $CDCl_3$ and polar acetone-$d_6$ and the results were compared with each other. Analysis of temperature dependent $^1H$ spectra and titration curves reveals that both solvents result in a 1 : 1 cone-form complex with nonpolar $CDCl_3$yielding a more tightly bound one than acetone-$d_6$. Unexpectedly, at very low temperature, we have found that two phenyl ring proton peaks of equal intensity appear both in $CDCl_3$and in acetone-$d_6$ solution which gradually collapse and eventually coalesce into a single line as temperature is raised. This observation could be interpreted in terms of the chemical exchange through direct and/or indirect interconversion between two equivalent conformations possible the complex in both solvents over the temperature range observed. And broadening of $^{133}Cs$ (I = 7/2) nmr line with increasing temperature has also been observed, indicating the exchange of $^{133}Cs$ ion between the complex and the solvent. From numerical fitting of lineshape changes for one-dimensional $^1H$ and $^{133}Cs$ spectra, the exchange rate constants and other relevant parameters for this conformational interconversion and the complex-solvent exchange were deduced.

• Membrane Journal
• /
• v.9 no.3
• /
• pp.170-177
• /
• 1999

Asymmetric membranes for pervaporation were prepared with poly sulfone and sulfonated poly sulfone in order to separate water from 90% by weight butanol solution. Chlorosulfonic acid was reacted with trimethylchlorosilane for using as a sulfonating agent. The prepared polymers were characterized with FT-IR and $^1H$-NMR. The thermal properties of the polymers were examined with DSC and TGA. Back titration method was used for the evaluation of the degree of sulfonation or the ion ex¬change capacity. N-methyl-2-pyrrolidone (NMP) and diethyleneglycol dimethyl ether (DGDE) cosolvent were used for the preparation of asymmetric membranes. The cross section and skin layer of the mem¬branes were examined with scanning electron michroscopy to investigate membrane structure formed with cosolvent composition in the casting solution. In this article, the selectivity of the dense films were not different from each other so much. However, the permeation rates were significantly increased as much as 80 times compared to that of dense film.

• Bulletin of the Korean Chemical Society
• /
• v.33 no.7
• /
• pp.2145-2148
• /
• 2012

A new thiourea based receptor (1) was synthesized and applied to fluoride ion recognition in acetonitrile solution. Receptor 1 displayed dual changes in absorption and fluorescence emission intensities selectively for fluoride ions. The interaction of 1 with fluoride undergoes a deprotonation process that is confirmed by $^1H$ NMR titration.