• Natural Product Sciences
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• v.27 no.2
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• pp.122-127
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• 2021

A new steroidal saponin, (23S,24S)-spirosta-5,25(27)-diene-1𝛽,3𝛽,23,24-tetrol 1-O-((2,3-diacetyl-α-L-rhamnopyranosyl)-(1→2)-[𝛽-D-xylopyranosyl-(1→3)]-α-L-arabinopyranoside)-24-O-𝛽-D-glucopyranoside (humilisoside) together with the known 𝛽-sitosterol 3-O-glucopyranoside, adenosine, dioscin, and methylprotodioscin were isolated from the leaves of Dracaena humilis. Their structures were elucidated by spectral techniques including mass spectrometry (ESIMS, HRESIMS, tandem MS-MS), 1D NMR (¹H, ¹³C NMR), 2D NMR (HSQC, ¹H-¹H COSY, HMBC, NOESY), chemical method as well as by comparison with spectroscopic data reported in the literature. The chemotaxonomic significance of the isolation of these compounds is discussed. This is the first report on the phytochemical investigation of D. humilis.

• Bulletin of the Korean Chemical Society
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• v.30 no.12
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• pp.2895-2898
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• 2009

The complete structural characterization of dehydrodivanillin, an important natural product of interest to the food, cosmetics and aroma industries, has been carried out using multi-dimensional NMR spectroscopic techniques, and its previously $reported^{13}$C-NMR values have been reassigned. Dense and granular thin films of dehydrodivanillin have been grown by sublimation under high vacuum and studied using Scanning Electron Microscopy (SEM), electrical and optical techniques. The transmittance spectra of the films indicate a wide optical band gap of more than 3 eV. Typical J-V characteristics of Glass/ITO/dehydrodivanillin/Al structure exhibited moderate current densities ${\sim}10^{-4}\;A/cm^2$ at voltages > 25 V with an appreciable SCLC mobility of the order of $10^{-6}\;cm^2$/V-s.

• Macromolecular Research
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• v.15 no.7
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• pp.633-639
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• 2007

A variety of NMR techniques were applied to the micro-chemical structural characterization of polyanilines prepared via an efficient synthetic method in a self-stabilized dispersion medium in which the polymerization was conducted in a heterogeneous organic/aqueous biphasic system without any stabilizers. Here, the monomer and growing polymer chain were shown to function simultaneously as a stabilizer, imparting compatibility for the dispersion of the organic phase, and as a form of flexible template in an aqueous reaction medium. Polymerizations predicated on this concept generated polyanilines with a low defect content: solution state $^{13}C-NMR$ and solid $^{13}CDD/CP/MAS$ spectroscopy indicated that the synthesized HCPANi and its soluble derivative, HCPANi-t-BOC, evidenced distinctly different NMR spectra with fewer side peaks, as compared to conventionally prepared PANis, and the complete structural assignments of the observed NMR peaks could be determined via the combination of both 1D and 2D techniques. Ortho-linked defects in HCPANi were estimated to be as low as 7%, as shown by a comparison of the integration of the carbonyl carbon resonance peaks.

• Journal of the Korean Magnetic Resonance Society
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• v.10 no.1
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• pp.38-45
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• 2006

The NMR and MS techniques were applied to identification and quantitative analysis of oligomers in a commercialized poly (trimethylene terephthalate). Oligomers in a commercialized poly (trimethylene terephthalate) were extracted via a dissolving and reprecipitation method. Analysis of the components of the extract using NMR and MS revealed that it contained mainly cyclic oligomers with degrees of polymerization of 2, 4 and 5 (dimer, tetramer and pentamer). Trimer and cyclic oligomers with degrees of polymerization of more than 6 were not found in the extract in the present study. Quantitative analysis of dimer was performed by NMR spectroscopy.

• Journal of the Korean Magnetic Resonance Society
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• v.12 no.2
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• pp.81-88
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• 2008

Solid HETCOR (Hetero-Correlation) requires homo-dipolar decoupling between proton spins during the evolution and the mixing period in 2D-NMR. There are two different ways of achieving it with pulse sequences. One is based on the multiple pulse (MP) sequence where thousands of intense radio frequency (rf) pulses are used to remove the homo-dipolar interaction between protons. The other is utilizing the so-called Lee-Goldburg (LG) off-resonance scheme where a continuous rf-irradiation is used. In this report, the advantage of one technique to the other, is analyzed. LG version is evaluated better in S/N and easier in setup procedure with the same experimental time.

• YAKHAK HOEJI
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• v.40 no.3
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• pp.293-299
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• 1996

The $^1H$- and $^{13}C$-NMR signals of (20R)-panaxadiol and (20R)-panaxatriol were completely assigned by the extensive application of modern 2D-NMR techniques, $^1H-^1H$ COSY, HMQC and HMBC.

• Journal of the Korean Magnetic Resonance Society
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• v.14 no.1
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• pp.38-44
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• 2010

In liquids NMR, $^{1}H$ is the most widely observed nucleus, which is not the case in solids NMR. The reason is due to the strong homo-dipolar interactions between the hydrogen atoms which mask the useful chemical shift information. Therefore we must remove the strong homo-dipolar interactions in order to get structural information, which can be investigated by the isotropic chemical shift. There are two ways of obtaining it. One is the ultra-fast MAS of ca. 70 kHz spinning speed, which has become available only recently. The other way is devising a pulse sequence which can remove the strong homo-dipolar interaction. In the latter way, MAS with a moderate spinning rate of a few kHz, is enough to remove the chemical shift anisotropy. In this report, 1D-CRAMPS and 2D MASFSLG techniques are utilized and their results will be compared. This kind of highresolution $^{1}H$ NMR for solids, should become a valuable analytical tool in the understanding and the developing of a new class of hydrogen storage materials. Here ammonium borane $-NH_{3}BH_{3}$, whose hydrogen content is high, is used as a sample.

• Applied Biological Chemistry
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• v.47 no.2
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• pp.270-273
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• 2004

Two prenylated flavonoids were isolated from a chloroform extract of the root bark of Cudrania tricuspidata. Both compounds (1, 2) showed antibacterial activity against Gram positive bacteria, Staphylococcus aureus, Bacillus subtilis and Bacillus cereus. Their structures were determined as euchrestaflavanone B (1) and euchrestaflavanone C (2) on the basis of $^1H\;NMR,\;^{13}C\;NMR$ and long-range coupling NMR techniques.

• Journal of the Korean Magnetic Resonance Society
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• v.6 no.2
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• pp.142-154
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• 2002

One of the oldest, still unsolved, and often ignored problems in magnetic resonance remains the issue of how to observe undistorted, normal one-dimensional spectra where the frequencies and their relative intensities represent faithfully the distribution of spins and sites in the sample within the magnet. Often distortions in these parameters are accepted, as the price of sensitivity enhancement, or because it is unclear just how these distortions might be avoided. Surprisingly enough, the problem is exacerbated by the use of modern techniques of pulsed Fourier transform NMR. Noise spectroscopy is an approach to solving the problem of distorted NMR spectra, which is largely under appreciated; it promises virtually "unlimited" distortionless bandwidths without costly hardware investments. Nonetheless, its exploitation remains limited. We will discuss why noise spectroscopy belongs in the arsenal of tricks spectroscopists should be aware of, show examples where its use is essential if accurate, quantitative NMR is to be expected, and discuss some recent approaches which extend its applicability yet further, particularly in solid state NMR and in applications to quadrupolar nuclear spins.

• Bulletin of the Korean Chemical Society
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• v.32 no.9
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• pp.3425-3428
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• 2011

Apolipoprotein A-I (Apo A-I) is a major component for high density lipoproteins (HDL). A number of mimetic peptides of Apo A-I were screened from the phase-displayed random peptide library by utilizing monoclonal antibodies (A12). Mimetic peptide for A12 epitope against Apo A-I was selected as CPFARLPVEHHDVVGL (pA1). From the BLAST search, the mimetic peptide pA1 had 40% homology with Apo A-I. As a result of the structural determination of this mimotope using homo/hetero nuclear 2D-NMR techniques and NMR-based distance geometry (DG)/molecular dynamic (MD) computations, DG structure had low penalty value of 0.3-0.7 ${\AA}^2$ and the total RMSD was 0.6-1.6 ${\AA}$. The mimotope pA1 exhibited characteristic conformation including a ${\beta}$-turn from Pro[7] to His[11].