• Bulletin of the Korean Chemical Society
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• 제19권8호
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• pp.847-851
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• 1998

13C, 15N, and 29Si NMR chemical shifts have been computed for selected X-substituted silatranes (X=Cl, F, H, CH3) using Gauge-Including Atomic Orbitals (GIAO) and Continuous Set of Gauge Transformations (CSGT) at the Hartree-Fock level of theory. The isotropic 13C chemical shifts are largely insensitive to substituent-induced structural changes. In this study, the isotropic 13C chemical shifts GIAO and CSGT calculations at the HF/6-31G and HF/6-31G* levels are sufficiently accurate to aid in experimental peak assignments. The isotropic 13C chemical shifts X-substituted silatranes at HF/6-31G* level are approximately 4 ppm different from the experimental values. In contrast, the isotropic 15N and 29Si chemical shifts and the chemical shielding tensors are quite sensitive to substituent-induced structural changes. These trends are consistent with those of the experiment. The 15N chemical shift parameters demonstrate a very clear correlation with Si-N distance, especially when we use the polarization function. Changes in anisotropy, 3a as well as in the 15N isotropic chemical shifts are due primarily to changes in the value of a.. But in case of "Si the correlations are not as clean as for the 15N chemical shift.

• 한국농공학회논문집
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• 제54권2호
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• pp.127-135
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• 2012

The processes of chemical and physical weathering occur simultaneously. The objective of this study was to estimate the degree weathered using fractal dimension through comparison with chemical characteristic of soil samples from Pohang (PH) and Kimpo (KP). Comparing chemical characteristics with fractal dimension, $SiO_2$, $Na_2O$, $K_2O$ content decreased and loss of ignition increased as fractal dimension increased. And fractal dimension showed high correlation with CWI while ATI, STI CIW, PI, CIA and RR demonstrated different degrees of correlation with fractal dimension. The tendency of the changes in oxide content and chemical weathering index with increasing fractal dimension appeared to be similar with the chemical changes due to weathering. Therefore, fractal dimension could be a good indicator representing the extent of weathering and chemical changes.

• Bulletin of the Korean Chemical Society
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• 제27권12호
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• pp.2067-2070
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• 2006

• Korea-Australia Rheology Journal
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• 제17권1호
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• pp.15-20
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• 2005

In this study, the relationship between morphology and viscosity of the main culture broth of Cephalosporium acremonium M25 was investigated in a 2.5 L bioreactor. The differentiation of C. acremonium M25 showed a complex pattern during the main culture. The morphological changes of C. acremonium M25 were related to the rheological properties of the culture broth and it was well agreed with the power law model. As a result of rheology study, it was found that rheological properties of the main culture broths of C. acremonium M25 in bioreactor were closely related to morphological changes. Also, fractal dimension fairly predicted morphological and rheological changes in the main culture broth.

• Bulletin of the Korean Chemical Society
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• 제18권9호
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• pp.981-985
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• 1997

13C, 15N, and 29Si NMR chemical shifts have been computed for selected X-substituted silatranes (X=Cl, F, H, CH3) using Gauge-Including Atomic Orbitals (GIAO) at the Hartree-Fock level of theory. The isotropic 13C chemical shifts are largely insensitive to substituent-induced structural changes. In this study, the isotropic 13C chemical shifts between 1-methyl- and 1-hydrogensilatranes by GIAO-SCF calculation at the HF/6-31G level are very similar. But the results of 1-chloro- and 1-fluorosilatranes are about 4 ppm different from the experimental values. In contrast, the isotropic 15N and 29Si chemical shifts and the chemical shielding tensors are quite sensitive to substituent-induced structural changes. These trends are consistent with those of the experiment. The isotropic 15N chemical shift demonstrates a very clear correlation with Si-N distance. But in case of 29Si the correlations are not as clean as for the 15N chemical shift; the calculated variation in the 29Si chemical shift is much larger.

• 대한화상학회지
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• 제23권1호
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• pp.7-12
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• 2020

Purpose: Due to rapid changes in the industrial structure in last decade, the wider various types of chemical agents were introduced. Burn surgeons should be well-informed with rapid changes of chemical burns. We present the recent incidence trends of causing agents of chemical burns. Methods: From 2010 to 2019, 92 chemical burn victims were included in this study. A retrospective study was made about the type, distribution and incidence of the causing agents of chemical burns. Initial treatments of most chemical burn wounds are copious saline irrigation by tap water, except hydrofluoric acid burn cases managed by 10% calcium gluconate injection. In alkali chemical burns on extremity, if thin eschars appear in postburn 2~3 days, acute early surgical escharectomy and split thickness skin graft were done. Results: More than 9 types of major chemicals causing chemical burns were surveyed, and the most common causing agent of chemical burns was Hydrofluoric acid (23.9%) followed by Acetic acid (19.6%) and Sodium hydroxide (8.7%). Conclusion: From 2010 to 2019, changes in the causing agent of chemical burns are that the types of major causing agents of chemical burns have increased and the distribution and incidence of causing agents have changed compared to previous reports. According to this study, more than 9 types of major chemicals causing chemical burns were surveyed, and the most common causing agent of chemical burns was Hydrofluoric acid (23.9%) followed by Acetic acid, Sodium hydroxide.

• BMB Reports
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• 제37권6호
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• pp.642-647
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• 2004

The lysine residues of Bacillus licheniformis $\alpha$-amylase (BLA) were chemically modified using citraconic anhydride or succinic anhydride. Modification caused fundamental changes in the enzymes specificity, as indicated by a dramatic increase in maltosidase and a reduction in amylase activity. These changes in substrate specificity were found to coincide with a change in the cleavage pattern of the substrates and with a conversion of the native endo- form of the enzyme to a modified exo- form. Progressive increases in the productions of $\rho$-nitrophenol or glucose, when para nitrophenyl-maltoheptaoside or soluble starch, respectively, was used as substrate, were observed upon modification. The described changes were affected by the size of incorporated modified reagent: citraconic anhydride was more effective than succinic anhydride. Reasons for the observed changes are discussed and reasons for the effectivenesses of chemical modifications for tailoring enzyme specificities are suggested.

• 한국재료학회지
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• 제24권12호
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• pp.682-688
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• 2014

Physical and chemical changes in a polished wafer and in $2.5{\mu}m$ & $4{\mu}m$ epitaxially grown Si layer wafers (Epilayer wafer) after surface treatment were investigated. We characterized the influence of surface treatment on wafer properties such as surface roughness and the chemical composition and bonds. After each surface treatment, the physical change of the wafer surface was evaluated by atomic force microscopy to confirm the surface morphology and roughness. In addition, chemical changes in the wafer surface were studied by X-ray photoemission spectroscopy measurement. Changes in the chemical composition were confirmed before and after the surface treatment. By combined analysis of the physical and chemical changes, we found that diluted hydrofluoric acid treatment is more effective than buffered oxide etching for $SiO_2$ removal in both polished and Epi-Layer wafers; however, the etch rate and the surface roughness in the given treatment are different among the polished $2.5{\mu}m$ and $4{\mu}m$ Epi-layer wafers in spite of the identical bulk structural properties of these wafers. This study therefore suggests that independent surface treatment optimization is required for each wafer type, $2.5{\mu}m$ and $4{\mu}m$, due to the meaningful differences in the initial surface chemical and physical properties.

• 한국막학회:학술대회논문집
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• 한국막학회 2004년도 추계 총회 및 학술발표회
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• pp.280-283
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• 2004

• 대한방사선기술학회지:방사선기술과학
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• 제43권4호
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• pp.273-280
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• 2020

In this study, the P contrast agent of Iopamidol, which is a nonionic iodide contrast agent most commonly used as a vascular contrast agent in medical institutions, and the O contrast agent of Ioversol, were studied. The physicochemical changes according to the temperature change were compared and analyzed using the Bruker Avance 500MHz Nuclear Magnetic Resonance Spectrometer owned by the Korea Basic Science Institute (KBSI). There was no physical or chemical change in the O contrast medium of Ioversol formulation in temperature change. However, in the P contrast agent of Iopamidol, a doublet peak began to appear in the 1.1 ppm region of the sample at 60℃, and the doublet peak was clearly observed in the sample at 80℃. As a result of this study, 1H-NMR analysis revealed that the P contrast agent of the Iopamidol formulation was dissociated from chemical bonds as it rose to a high temperature of 60℃ or higher, resulting in the formation of foreign substances. It was evaluated that the O contrast agent of Ioversol formulation had physico-chemical stability than the P contrast agent of Iopamidol formulation. As shown in this study, it is necessary to analyze the physical and chemical changes of contrast agents according to various environmental factors.