• Applied Chemistry for Engineering
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• v.10 no.1
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• pp.98-104
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• 1999

In this work, we investigated hydrogen content, bond structure, and electrical properties of a-Si:H films prepared by ECR plasma CVD as a function of pressure. In general, the photo sensitivity of a-Si:H films prepared by CVD method decreases as the deposition rate increases, but the photo sensitivity of a-Si:H films prepared by ECR plasma deposition method increases as the deposition rate increases. In the same condition of microwave power, the ratio of $SiH_4/H_2$, and pressure, though film thickness increases linearly with deposition time and hydrogen content in the film is constant, photo conductivity can be decreased because $SiH_2$ bond is made more than SiH bond in the short reaction time. According to increase pressure in the chamber, SiH bond in the film increase and optical energy gap decrease. So, photo conductivity can be increased. But photo sensitivity decreased as dark conductivity increase. It must be grown in the condition of low pressure and hydrogen gas for taking the a-Si:H film of high quality.

• Journal of the Korean Magnetic Resonance Society
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• v.11 no.2
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• pp.64-72
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• 2007

[ $^1H$ ] nuclear magnetic resonance (NMR) experiments have been performed at 30 - 300 K and 7 T to investigate dynamics of hydrogen bond network in the single crystal $(NH_4)_3H(SO_4)_2$. The two proton sites, ammonium proton and hydrogen-bond proton, are identified from the $^1H$ NMR MAS spectrum at 340 K. As temperature decreases, the $^1H$ NMR spectrum shifts to the higher frequency side with a larger linewidth. The spectrum at 65 K shows a distinctive change in line shape toward the ferroelectric transition at 63 K. The measured values of $T_1$ for ammonium and hydrogen-bond protons are similar in the whole range of temperature. $T_1$ of $^1H$ NMR shows a gradual decrease down to 120 K and starts to steeply increase below 100 K. Then $T_1$ shows abrupt decrease below 70 K with a sharp minimum at 63 K, where the ferroelectric transition occurs. This temperature dependence of spectrum and $T_1$ clearly prove that the large change in the dynamics of hydrogen bond network is associated with the ferroelectric phase transition at 63 K.

• Journal of the Korean Chemical Society
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• v.19 no.4
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• pp.233-239
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• 1975

The configuration of two oxime groups in cis-2-butenedialdioxime, unsymmetrical compound conjugated by three double bonds, is determined by a NMR study on the effects of the solvent, temperature and concentration; it is certain that, in solutions of usual conditions, the configuration exists as only "syn-syn". And the relative strengths of the hydrogen bond between these oxime groups and several solvents are compared and somc effects of the temperature and concentration are also considered. The several models of hydrogen bond between oxime and solvents are proposed; especially it is to be noted here that the hydrogen bond in pyridine solvent is not resulted from the interaction between a lone electron pair on nitrogen atom of pyridine and the hydroxyl proton of oxime, but the result of $\pi$-complex formed between the $\pi$-orbital of pyridine and the hydroxyl proton of the solute.

• Journal of the Korean Chemical Society
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• v.41 no.2
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• pp.63-68
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• 1997

Calorimetric measurements have been carried out for the binary mixture between protic, ROH (R=Me, Et) and dipolar aprotic solvents, MeCN,$Me_2CO,\;MeNO_2(or EtNO_2)$in order to investigate the molecular interaction and liquid structure of isodielectric solvents. From the measured partial molar enthalpies of the solutions, excess enthalpies for the mixing process were determined. The hydrogen bond strength between two components decreases in the order of$ROH-ROH>ROH-Me_2CO>ROH-MeCN>ROH-MeNO_2(or EtNO_2)$and the hydrogen bond donor acidity decreases in the order of MeOH>EtOH. From this result, we can conclude that the most important interaction for the formation of binary liquid mixture comes from the specific hydrogen bond.

• Analytical Science and Technology
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• v.36 no.3
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• pp.128-134
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• 2023

Centella asiatica (C. asiatica) extracts, including asiaticoside and madecassoside, are used in ointments to treat the wound and atopic dermatitis due to their antibacterial and skin-regenerating effects in Asia. Therefore, research on the cultivation and extraction efficiency of C. asiatica is being actively conducted to increase commercialization efficiency. In this study, various deep eutectic solvents (DESs) were prepared and used as the extraction solvents according to the mole ratio between the hydrogen bond acceptor (HBA) and hydrogen bond donor (HBD). And then, the extraction yields in distilled water (DW) and methanol (MeOH), commonly used extraction solvents for C. asiatica, were compared and analyzed by HPLC in the optimized operating condition. As a result, a mixture of DW and DES at a ratio of 3:7 showed about 1.4 times higher extraction efficiency than MeOH only. Conversely, the extraction efficiency in a mixture of MeOH and DES at a ratio of 3:7 was about 6 % lower than that in MeOH only.

• BMB Reports
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• v.31 no.6
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• pp.590-594
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• 1998

X-ray crystallographic studies of the deoxy form of human adult hemoglobin (Hb A) have shown that ${\beta}99Asp$ is hydrogen bonded to both ${\alpha}42Tyr$ and ${\alpha}97Asn$ in the ${\alpha}_1{\beta}_2$ subunit interface, suggesting that the essential role of ${\beta}99Asp$ is to stabilize the deoxy-Hb by creating the intersubunit hydrogen bond. In particular, for Hb Kempsey (${\beta}99Asp{\rightarrow}Asn$), molecular dynamics simulation indicated that a new hydrogen bond involving ${\beta}99Asn$ can be induced by replacing ${\alpha}42Tyr$ with a strong hydrogen-bond acceptor such as Asp. Designed mutant recombinant (r) Hb (${\beta}99Asp{\rightarrow}Asn$, ${\alpha}42Tyr{\rightarrow}Asp$) have been produced in the Escherichia coli expression system and have shown that functional defects of Hb Kempsey could be compensated by the ${\alpha}42Tyr{\rightarrow}Asp$ substitution. However, as the ${\alpha}42 Tyr{\rightarrow}Asp$ mutation has never been reported before, it is still possible that the functional properties of r Hb (${\beta}99Asp{\rightarrow}Asn$, ${\alpha}42Tyr{\rightarrow}Asp$) may be due to the mutation itself. Thus, it is required to produce r Hb (${\alpha}42Tyr{\rightarrow}Asp$) and r Hb Kempsey (${\beta}99Asp{\rightarrow}AsnX$( as controls, and to compare their properties with those of r Hb (${\beta}99Asp{\rightarrow}Asn$, ${\alpha}42Tyr{\rightarrow}Asp$). r Hb (${\alpha}42Tyr{\rightarrow}Asp$) could not be purified because it is an unstable hemoglobin which forms Heinz bodies. r Hb Kempsey (${\beta}99Asp{\rightarrow}Asn$) exhibits very high oxygen affinity and greatly reduced cooperativity. Thus, r Hb (${\beta}99Asp{\rightarrow}Asn$) and r Hb (${\alpha}42Tyr{\rightarrow}Asp)$ compensate each other.

• Molecules and Cells
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• v.38 no.5
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• pp.409-415
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• 2015

Low-barrier hydrogen bonds (LBHBs) have been proposed to have important influences on the enormous reaction rate increases achieved by many enzymes. ${\Delta}^5$-3-ketosteroi isomerase (KSI) catalyzes the allylic isomerization of ${\Delta}^5$-3-ketosteroid to its conjugated ${\Delta}^4$-isomers at a rate that approache the diffusion limit. Tyr14, a catalytic residue of KSI, has been hypothesized to form an LBHB with the oxyanion of a dienolate steroid intermediate generated during the catalysis. The unusual chemical shift of a proton at 16.8 ppm in the nuclear magnetic resonance spectrum has been attributed to an LBHB between Tyr14 $O{\eta}$ and C3-O of equilenin an intermediate analogue, in the active site of D38N KSI. This shift in the spectrum was not observed in Y30F/Y55F/D38N and Y30F/Y55F/Y115F/D38N mutant KSIs when each mutant was complexed with equilenin, suggesting that Tyr14 could not form LBHB with the intermediate analogue in these mutant KSIs. The crystal structure of Y30F/Y55F/Y115F/D38N-equilenin complex revealed that the distance between Tyr14 $O{\eta}$ and C3-O of the bound steroi was within a direct hydrogen bond. The conversion of LBHB to an ordinary hydrogen bond in the mutant KSI reduced the binding affinity for the steroid inhibitors by a factor of 8.1-11. In addition, the absence of LBHB reduced the catalytic activity by only a factor of 1.7-2. These results suggest that the amount of stabilization energy of the reaction intermediate provided by LBHB is small compared with that provided by an ordinary hydrogen bond in KSI.

• Journal of the Korean Chemical Society
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• v.14 no.2
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• pp.147-153
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• 1970

Band assignments in the infrared absorption spectra of the four substituted Urea compounds, Fenuron (3-phenyl-1,1-dimethyl urea), OMU (3-cyclooctyl-1,1-dimethyl urea), Herban (3-(hexahydro-4,7-methanoidan-5-yl)-l,1-dimethyl urea), and Monuron (3-(p-chlorophenyl)-1,1-dimethyl urea), are made by analyzing the spectra obtained with various solvents. The results suggest that Fenuron and Monuron, each of which contain an unsaturated benzene ring, have a strong tendency to bond through both the amino group and the carbonyl oxygen. Herban and OMU, however, exhibit a much greater change in strength of the carbonyl bond than of the amino bond. It means that a strong hydrogen bonding occurs only at the carbonyl oxygen in the compounds.

• Bulletin of the Korean Chemical Society
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• v.9 no.3
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• pp.126-129
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• 1988

Lithium bonded complexes with $H_2O$ molecule were investigated theoretically by varying the substituent of lithium compound as follows; LiH, LiLi, $LiCH_3,\;LiNH_2$, LiOH, LiF, and LiCl. Some hydrogen bonded complexes with $H_2O$ molecule were also investigated to be compared with lithium bonded analogues. Electron correlation effect on the structures and energies of lithium bond was also investigated through MP2 and MP4 corrections. Unlike hydrogen bond with $H_2O$ molecule, lithium bonded complexes with $H_2O$ molecule were found to be interacting linearly with $H_2O$ molecule. Electron correlation effect was very small for lithium bonded complexes. The lithium bond energies were found to be less affected by the choice of substituent of lithium compound.

• Applied Chemistry for Engineering
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• v.33 no.4
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• pp.425-430
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• 2022

L-alanine (LA, as an amino acid residue) pentamer model was used to investigate changes in the dihedral angle, intramolecular hydrogen bonding and formation energies during structural optimization. LA pentamers having four conformation types [𝛽: 𝜑/𝜓=t-/t+, 𝛼: 𝜑/𝜓=g-/g-, PP_II: 𝜑/𝜓=g-/t+ and P-like: 𝜑/𝜓= g-/g+] were carried out by quantum chemical calculations (QCC) [B3LYP/6-31G(d,p)]. In LA, 𝛽, 𝛼, and P-like types did not change by optimization, having an intra-molecular hydrogen bond: NH⋯OC (H-bond), and PP_II types in the absence of H-bond were transformed into P-like at the designated 𝜓 of 140°, and to 𝛽 at that of 160° or 175°. P-like and 𝛼 were about 0.5 kcal/mol/mu more stable than 𝛽. In order to understand the processes of the transformations, the changes of 𝜑/𝜓, distances of NH-OC (d_NH/CO) and formation energies (𝜟E, kcal/mol/mu) were examined.