Biomedical subjects

H M Nguyen

Publications and source records attributed to H M Nguyen.

5 recordsLinked to original sources

PubMed2001

Sulfide-mediated dehydrative glycosylation.

The development of a new method for glycosylation with 1-hydroxy glycosyl donors employing dialkyl sulfonium reagents is described. The process employs the reagent combination of a dialkyl sulfide and triflic anhydride to effect anomeric bond constructions. This controlled dehydrative coupling of various C(1)-hemiacetal glycosyl donors and nucleophilic acceptors proceeds by way of a sulfide-to-sulfoxide oxidation process in which triflic anhydride serves as the oxidant.

Glycoconjugates↗

PubMed1997

Age at first marriage in Viet Nam: patterns and determinants.

"Using data from the 1991 Viet Nam Life History Survey, this article examines the patterns and determinants of age at first marriage. It shows that socio-economic and political changes during the last few decades are associated with a shift to older ages of first marriage. It identifies regional variations and discusses the significant impact of warfare on the country's age patterns of marriage. It concludes by bringing out the implications of the study for policy purposes." The full text is of this article is available electronically through www.undp.org/popin.

Asia↗

PubMed1996

Design and application of a low-temperature Peltier-cooling microscope stage.

A light microscopy system has been designed for freezing and lyophilization studies of protein pharmaceuticals. The system consists of a cascade of four Peltier thermoelectric modules in the lyophilization cell to freeze samples to -60 degrees C, controllers to regulate temperature and pressure conditions, and a video camera to record the events under study. Specific demonstration of the system was conducted using recombinant CD4-IgG and human growth hormone (hGH) as model proteins. Observations of recrystallization during warming of frozen CD4-IgG solution and lyophilization of hGH solution are discussed. These examples demonstrate that the system is a useful tool for the fundamental understanding of freezing and lyophilization of protein pharmaceuticals.

CD4 Antigens↗

PubMed1995

Surface denaturation at solid-void interface--a possible pathway by which opalescent particulates form during the storage of lyophilized tissue-type plasminogen activator at high temperatures.

During protein lyophilization, it is common practice to complete the freezing step as fast as possible in order to avoid protein denaturation, as well as to obtain a final product of uniform quality. We report a contradictory observation made during lyophilization of recombinant tissue-type plasminogen activator (t-PA) formulated in arginine. Fast cooling during lyophilization resulted in a lyophilized product that yielded more opalescent particulates upon long term storage at 50 degrees C, under a 150 mTorr nitrogen seal gas environment. Fast cooling also resulted in a lyophilized cake with a large internal surface area. Studies on lyophilized products containing 1% (w/w) residual moisture and varying cake surface areas (0.22-1.78 m2/gm) revealed that all lyophilized cakes were in an amorphous state with similar glass transition temperatures (103-105 degrees C). However, during storage the rate of opalescent particulate formation in the lyophilized product (as determined by UV optical density measurement in the 360 to 340 nm range for the reconstituted solution) was proportional to the cake surface area. We suggest that this is a surface-related phenomenon in which the protein at the solid-void interface of the lyophilized cake denatures during storage at elevated temperatures. Irreversible denaturation at the ice-liquid interface during freezing in lyophilization is unlikely to occur, since repeated freezing/thawing did not show any adverse effect on the protein. Infrared spectroscopic analysis could not determine whether protein, upon lyophilization, at the solid-void interface would still be in a native form.

Calorimetry, Differential Scanning↗

PubMed1992

Determining the optimum residual moisture in lyophilized protein pharmaceuticals.

A general concern in the lyophilization of protein pharmaceuticals is how dry a product should be in order to maintain its stability during storage. This paper presents our exploratory studies on determining if there is an optimal residual moisture content for lyophilized recombinant protein products. The proteins used in this study were methionyl human growth hormone (met-hGH) and tissue type plasminogen activator (tPA). The amount of water adsorbed on each protein can be determined and approximated as a monolayer by the Brunauer-Emmett-Teller method. The result was in good agreement with the theoretical value calculated from the total number of strong polar groups in the molecule without regard to the conformation of the protein. This approach suggests that each protein may have a minimum moisture content that is necessary to shield the polar groups, and that over-drying will lead to exposure of these groups. The effect of residual moisture content on the stability of tPA in lyophilized excipient-free powder was studied. Samples that were dried to a water content below the calculated monolayer exhibited opalescence upon reconstitution, while those that were dried to either monolayer or multilayer water content tended to show a greater loss in biological stability upon storage under temperature stress conditions. The results of our studies reveal that the generally accepted concept "the drier the better" may not be appropriate for tPA. An optimum residual moisture content is required to balance the physical stability and the biological stability. These observations may apply to other protein products as well.

Amino Acid Sequence↗