• Bulletin of the Korean Chemical Society
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• 제12권1호
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• pp.97-101
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• 1991

Gas-phase pyrolyses of carbonate esters, ${\alpha}$- and ${\beta}$-hydroxy esters and ${\beta}$-hydroxy ketones have been studied theoretically by the AM1 MO method. Carbonate esters were found to decompose by two types of processes; in the reaction pathway involving an intermediate, the decomposition of the intermediate was rate-limiting, but direct pyrolyses were also possible via a six-membered cyclic transition state in which the methoxy oxygen attacks a hydrogen atom on the ${\beta}$-carbon. The hydroxy esters and ketones were found to decompose in a concerted process involving a six-membered cyclic transition state. Successive methylation on the ${\alpha}$- and ${\gamma}$-carbon led to an increase in the reactivity in agreement with experiments.

• Journal of Ecology and Environment
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• 제45권3호
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• pp.143-151
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• 2021

Background: Plants are able to optimize defense responses induced by various herbivores, which have different feeding strategies. Local and systemic responses within a plant after herbivory are essential to modulate herbivore-specific plant responses. For instance, leaf-chewing herbivores elicit jasmonic acid signaling, which result in the inductions of toxic chemicals in the attacked leaf (tissue-specific responses) and also in the other unattacked parts of the plant (systemic responses). Root herbivory induces toxic metabolites in the attacked root and alters the levels of transcripts and metabolites in the unattacked shoot. However, we have little knowledge of the local and systemic responses against stem-boring herbivores. In this study, we examined the systemic changes in metabolites in the wild tobacco Nicotiana attenuata, when the stem-boring herbivore Trichobaris mucorea attacks. Results: To investigate the systemic responses of T. mucorea attacks, we measured the levels of jasmonic acid (JA), JA-dependent secondary metabolites, soluble sugars, and free amino acids in 7 distinct tissues of N. attenuata: leaf lamina with epidermis (LLE), leaf midrib (LM), stem epidermis (SE), stem pith (SP), stem vascular bundle (SV), root cortex with epidermis (RCE), and root vascular bundle (RV). The levels of JA were increased in all root tissues and in LM by T. mucorea attacks. The levels of chlorogenic acids (CGAs) and nicotine were increased in all stem tissues by T. mucorea. However, CGA was systematically induced in LM, and nicotine was systematically induced in LM and RCE. We further tested the resource allocation by measuring soluble sugars and free amino acids in plant tissues. T. mucorea attacks increased the level of free amino acids in all tissues except in LLE. The levels of soluble sugars were significantly decreased in SE and SP, but increased in RV. Conclusions: The results reveal that plants have local- and systemic-specific responses in response to attack from a stem-boring herbivore. Interestingly, the level of induced secondary metabolites was not consistent with the systemic inductions of JA. Spatiotemporal resolution of plant defense responses against stem herbivory will be required to understand how a plant copes with attack from herbivores from different feeding guilds.

• Advances in concrete construction
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• 제10권2호
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• pp.171-183
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• 2020

The main objective of this study is the assessment of the ability of limestone mortars to resist to different chemical attacks. The ability of polypropylene (PP) fibres waste used as reinforcement of these concrete materials to enhance their durability is also studied. Crushed sand 0/2 mm which is a fine limestone residue obtained by the crushing of natural rocks in aggregates industry is used for the fabrication of the mortar. The fibres used, which are obtained from the waste of domestic plastic sweeps' fabrication, have a length of 20 mm and a diameter ranging between 0.38 and 0.51 mm. Two weight fibres contents are used, 0.5 and 1%. The durability tests carried out in this investigation included the water absorption by capillarity, the mass variation, the flexural and the compressive strengths of the mortar specimens immersed for 366 days in 5% sodium chloride, 5% magnesium sulphate and 5% sulphuric acid solutions. A mineralogical analysis by X-ray diffraction (XRD) and a visual inspection are used for a better examination of the quality of tested mortars and for better interpretation of their behaviour in different solutions. The results indicate that the reinforcement of limestone mortar by PP fibres waste is an excellent solution to improve its chemical resistance and durability. Moreover, the presence of PP fibres waste does not affect significantly the water absorption by capillarity of mortar nether its mass variation, when exposed to chloride and sulphate solutions. While in sulphuric acid, the mass loss is higher with the presence of PP fibres waste, especially after an exposure of 180 days. The results reveal that these fibres have a considerable effect of the flexural and the compressive behaviour of mortar especially in acid solution, where a reduction of strength loss is observed. The mineralogical analysis confirms the good behaviour of mortar immersed in sulphate and chloride solutions; and shows that more gypsum is formed in mortar exposed to acid environment causing its rapid degradation. The visual observation reveals that only samples exposed to acid attack during 366 days have showed a surface damage extending over a depth of approximately 300 ㎛.

• Bulletin of the Korean Chemical Society
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• 제33권9호
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• pp.3048-3054
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• 2012

The use of aspirin is widely recommended for the prevention of heart attacks owing to its ability to inhibit platelet activation by irreversibly blocking cyclooxygenase 1. However, aspirin also affects the fibrinolytic and hemostatic pathways by mechanisms that are not well understood, causing severe hemorrhagic complications. Here, we investigated the ability of aspirin and aspirin metabolites to inhibit thrombin-activatable fibrinolysis inhibitor (TAFI), the major inhibitor of plasma fibrinolysis. TAFI is activated via proteolytic cleavage by the thrombin-thrombomodulin complex to TAFIa, a carboxypeptidase B-like enzyme. TAFIa modulates fibrinolysis by removing the C-terminal arginine and lysine residues from partially degraded fibrin, which in turn inhibits the binding of plasminogen to fibrin clots. Aspirin and its major metabolites, salicylic acid, gentisic acid, and salicyluric acid, inhibit TAFIa carboxypeptidase activity. Salicyluric acid effectively blocks activation of TAFI by thrombin-thrombomodulin; however, salicylates do not inhibit carboxypeptidase N or pancreatic carboxypeptidase B. Aspirin and other salicylates accelerated the dissolution of fibrin clots and reduced thrombus formation in an in vitro model of fibrinolysis. Inhibition of TAFI represents a novel hemostatic mechanism that contributes to aspirin's therapy-associated antithrombotic activity and hemorrhagic complications.

• Bulletin of the Korean Chemical Society
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• 제34권9호
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• pp.2635-2639
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• 2013

The rapid and accurate identification of biological agents is a critical step in the case of bio-terror and biological warfare attacks. Recently, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry has been widely used for the identification of microorganisms. In this study, we describe a method for the rapid and accurate discrimination of Bacillus anthracis spores using MALDI-TOF MS. Our direct in-situ analysis of MALDI-TOF MS does not involve subsequent high-resolution mass analyses and sample preparation steps. This method allowed the detection of species-specific biomarkers from each Bacillus spores. Especially, B. anthracis spores had specific biomarker peaks at 2503, 3089, 3376, 6684, 6698, 6753, and 6840 m/z. Cluster and PCA analyses of the mass spectra of Bacillus spores revealed distinctively separated clusters and within-groups similarity. Therefore, we believe that this method is effective in the real-time identification of biological warfare agents such as B. anthracis as well as other microorganisms in the field.

• Bulletin of the Korean Chemical Society
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• 제29권1호
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• pp.191-196
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• 2008

Kinetic studies of the reactions of a-bromoacetanilides [YC6H4NHC(=O)CH2Br] with substituted benzylamines (XC6H4CH2NH2) have been carried out in dimethyl sulfoxide at 35.0 oC. The Hammett plots for substituent (Y) variations in the substrate (log kN vs. sY) are biphasic concave upwards/downwards with breaks at Y = 4-Cl (sY = 0.23). The Hammett coefficients rY and the cross-interaction constant rXY (= +0.16) are positive for sY 0.23, while the rY values are positive/negative [rY > 0 for X = (4-MeO and 4-Me) and rY < 0 for X = (H, 4-Cl and 3-Cl)] and the rXY (= -1.51) value is negative for sY ³ 0.23. Based on these and other results, the benzylaminolyses of a-bromoacetanilides are proposed to proceed through rate-limiting expulsion of the bromide leaving group from a zwitterionic tetrahedral intermediate, T, with a bridged transition state for s Y 0.23, while the reaction proceeds through concerted mechanism with an enolate-like TS in which the nucleophile attacks the a-carbon for s Y ³ 0.23.

• Bulletin of the Korean Chemical Society
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• 제13권3호
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• pp.317-324
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• 1992

Structure and dynamics of $Na^+$ ions are investigated by molecular dynamics simulations of rigid dehydrated zeolite-A at several temperatures using a simple Lennard-Jones potential plus Coulomb potential. A best-fitted set of electrostatic charges is chosen from the results of simulation at 298.15 K and Ewald summation technique is used for the long-ranged character of Coulomb interaction. The calculated x, y, and z coordinates of $Na^+$ ions are in good agreement with the positions determined by X-ray crystallography within statistical errors, their random movings in different types of closed cages are well described by time-correlation functions, and $Na_Ⅰ$ type ions are found to be less diffusive than $Na_Ⅱ$ and $Na_{III}$. At 600.0 K, the unstable $Na_{III}$ type ion pushes down one of nearest $Na_{I}$ ions into the $\beta-cage$ and sits on the stable site Ⅰ, and the captured ion in the $\beta-cage$ wanders over and attacks one of 8 $Na_{I}$ type ions.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 봄 학술발표회논문집(II)
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• pp.637-640
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• 1998

Generally, the durability of the reinforced concrete structures reduce when they are constructed in marine environments. The Mg ions and sulfate ions in seawater cause chemical attacks in concrete and the cracks in concrete result from corrosion of steel due to chlorides. In this study, the mortar specimens made from 5 different types of cement were immersed in artificial seawater of 2 times concentration and then we measured the compressive strength, the length change and the weight change. As a result of this study, we found that the compressive strength ratio decreased in the immersed 56days. We also found the longer the immersed days were, the more the increase of weight ratio and the length change were.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.731-736
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• 2002

The degradation of reinforced concrete (RC) structures due to physical and chemical attacks has been a major issue in construction engineering. Deterioration of RC structures due to chloride attack followed by reinforcement corrosion is one of the serious problems. The objective of this study is to develop a form of mathematical model of chloride ingress into concrete. In order to overcome some limits of the previous approaches, a mathematical model of chloride ingress into concrete consisting of chloride solution intrusion through the capillary pore and chloride ion diffusion through the pore water was proposed. Moreover, the variability of diffusivity of chloride ion due to degree of hydration of concrete, relative humidity in pore, exposure condition, and variation of chloride binding was considered in the chloride ingress model.

• Journal of Microbiology and Biotechnology
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• 제21권2호
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• pp.183-186
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• 2011

Biochemical methods were selected to evaluate the role of exopolymeric substances in the stability of biofilms used in bioremediation processes. Biofilms of Thiomonas arsenivorans formed on pozzolana were thus treated with pronase (protein target), lectins (Con A or PNA), calcofluor or periodic acid (polysaccharides target), DNase (DNA target), and lipase (triglycerides target). Neither protease nor DNase treatments had any effect on bacterial adhesion. Lectins and calcofluor treatments mainly affected young biofilms. Lipase treatment had a noticeable effect on biofilm stability whatever the biofilm age. Results suggest that it would be an increased resistance of mature biofilms that protects them from external attacks.