Sangpill Hwang

Highly efficient production of monoglycerides by the continuous removal of fatty acids from lipase-catalyzed oil hydrolysis

Highly efficient production of monoglycerides was achieved from lipase-catalyzed oil hydrolysis by the continuous addition of CaCl2 to remove the fatty acids produced. A fusion protein produced by connecting a cellulose-binding domain of Trichoderma hazianum cellulase to Bacillus stearothermophilus L1 lipase was used as a model 1,3-regiospecific lipase. The reaction was performed at pH 10 and 50°C, and the relationship between continuous removal of fatty acids and the production of monoglyceride was investigated by microscopic and HPLC analysis of oil emulsions and the reaction products. Without the addition of Ca2 + the reaction was inhibited by fatty acids, with the decrease in reaction rate being proportional to the concentration of fatty acids. When CaCl2 was continuously added in a 1:2 molar ratio with the released fatty acids, the reaction progressed unimpeded due to the formation of Ca-soaps. Both the yield and the fraction of monoglyceride in the reaction product increased due to the continuous removal of fatty acids.

Oxidation of 17α-ethinylestradiol with Mn(III) and product identification

With increasing concern about the contamination of aquatic environments by estrogenic pollutants, removal of synthetic estrogens such as 17alpha-ethinylestradiol (EE2) has been widely studied, especially with respect to the treatment methods. However, the degradation products have rarely been identified. The purpose of this study was to identify structurally the oxidation products of EE2. Mn(III) was used as an oxidizing agent. To obtain sufficient oxidation products for HPLC, LC-MS and NMR spectroscopy, a highly concentrated solution of EE2 (1mM) was prepared in a mixture of water and a water-miscible organic solvent. From HPLC of the reaction products, a single compound (I) was found to be predominant. From LC-MS, its molecular mass was found to be 294, and two hydrogens were believed to have been removed from EE2 (M.W. 296) to form a C=C . The structure of compound I (position of the double bond) was determined using 1H NMR, 13C NMR, H-H COSY, HSQC and HMBC. As minor products, isomeric dimers (M.W. 590) of EE2, as well as the products (M.W. 588) in which EE2 was coupled to compound I were also formed during the Mn(III)-mediated oxidation of EE2.

Stability analysis ofBacillus stearothermopilus L1 lipase fused with a cellulose-binding domain

This study was designed to investigate the stability of a lipase fused with a cellulose-binding domain (CBD) to cellulase. The fusion protein was derived from a gene cluster of a CBD fragment of a cellulase gene inTrichoderma hazianum and a lipase gene inBacillus stearothermophilus L1. Due to the CBD, this lipase can be immobilized to a cellulose material. Factors affecting the lipase stability were divided into the reaction-independent factors (RIF), and the reaction-dependent factors (RDF). RIF includes the reaction conditions such as pH and temperature, whereas substrate limitation and product inhibition are examples of RDF. As pH 10 and 50°C were found to be optimum reaction conditions for oil hydrolysis by this lipase, the stability of the free and the immobilized lipase was studied under these conditions. Avicel (microcrystal-line cellulose) was used as a support for lipase immobilization. The effects of both RIF and RDF on the enzyme activity were less for the immobilized lipase than for the free lipase. Due to the irreversible binding of CBD to Avicel and the high stability of the immobilized lipase, the enzyme activity after five times of use was over 70% of the initial activity.

The effect of Cu contamination on device reliability in DRAM

Effects of copper (Cu) contamination on device reliability in DRAM have been investigated. With device size scaling, copper-related dielectric degradation becomes one of the most important concerns due to the scaled dielectric thicknesses. The Cu out-diffusion from the direct contact (DC) bottom to the adjacent gate was observed for the failed samples with high temperature storage (HTS) stressing. HTS tests were performed at various temperatures to extract the activation energy for HTS failure. The predicted lifetime for the samples with Cu contamination was found to be 12 years at normal operating condition without stressing bias. Even though the root cause of the Cu contamination was not clearly revealed, based on the diffusion distance of Cu in silicon (Si), we speculated that the Cu contamination can be caused by the Cu migration into Si from the backside of wafer when the contamination was involved with one of packaging processes.

DRAM standby current failure: the influence of hot carrier degradation on voltage level-up shifter circuit

In this report, the phenomenon of standby state current failure of dynamic random access memory (DRAM), which incorporates a low voltage to high voltage CMOS level-up shifter, was investigated. As a result, DRAM standby current failure due to on/off time delay of the level shifter circuit has been identified as being responsible for n-MOSFET ON-state current decrease by hot carrier injection (HCI).