Biomedical subjects

Zhimin Liu

Publications and source records attributed to Zhimin Liu.

63 records · Page 4Linked to original sources

PubMed2002

Chemical reaction in binary mixtures near the critical region: thermal decomposition of 2,2'-azobis(isobutyronitrile) in CO2/ethanol.

The effects of pressure and of the composition of the CO2/ethanol mixed solvent in the critical region on the kinetics of the decomposition of 2,2'-azobis(isobutyronitrile) (AIBN) were studied at 333.15 K. The rate constants (kd) in the mixed solvent far from the critical point and in liquid n-hexane and ethanol were also determined for comparison. It was found that kd is very sensitive to pressure in the mixed solvent near the critical point. However, in the mixed solvent outside the critical region kd is nearly independent of pressure. Interestingly, kd in the mixed solvent in the critical region can be higher than that in ethanol at the same temperature, suggesting that no significant enhancement in the reaction rate by a small pressure change in the critical region of the mixed solvent can be achieved by changing the composition of the liquid solvent in the traditional way. Transition-state theory can predict kd in the mixed solvent far from the critical point and in the liquid solvents well. However, it cannot predict kd in the mixed solvent in the critical region. The special intermolecular interaction between the solvent and the reaction species may contribute to this interesting phenomenon. This work also shows that if pure CO2 or ethanol are used as solvents, the reaction cannot be carried out in the critical region of the solvents at the desired temperature, while it can be conducted in the critical region of the mixed solvent of suitable composition, where the solvent is highly compressible.

Journal Article↗

PubMed2002

Why do co-solvents enhance the solubility of solutes in supercritical fluids? New evidence and opinion.

The effects of two polar co-solvents, chlorodifluoromethane and acetone, on the solubility and enthalpy of a solution of 1,4-naphthoquinone in supercritical (SC) CO2 were studied. We found that the dissolution process becomes less exothermic in the presence of the co-solvents relative to that in pure CO2, although the solubility is enhanced significantly by the co-solvents. This indicates that the increase in the solubility by adding co-solvents results from the increase of the entropy of solution. On the basis of the unexpected results we propose a new mechanism for the solubility enhancement of the solute by the co-solvents in supercritical fluids (SCF); this should be applicable to cases in which the local density of the SC solvent around the solute and the co-solvent is larger, and the co-solvent associates preferentially with the solute. The results are also very important for the understanding of other fundamental questions of SCF science, such as the effect of co-solvents on the thermodynamic and kinetic properties of the reactions in SCFs.

Journal Article↗

PubMed2002

Recovery of silver nanoparticles synthesized on AOT/C(12)E(4) mixed reverse micelles by antisolvent CO(2).

Silver nanoparticles were synthesized in sodium bis(2-ethylhexyl)sulfosuccinate (AOT) reverse micelles in isooctane with tetraethylene glycol dodecyl ether (C(12)E(4)) as a cosurfactant. Recovery of the Ag particles from the reverse micelles by dissolving antisolvent CO(2) in the micellar solution was investigated. All the Ag particles in the reverse micelles could be precipitated by compressed CO(2) at suitable pressures, while the surfactants remained in the isooctane continuous phase, and well-dispersed Ag nanoparticles were obtained. The effects of operating conditions on the size and size distribution of the Ag particles were investigated. The particle size decreased with decreasing molar ratio (w) of water to surfactant. A higher CO(2) pressure in the recovery process favored production of smaller particles. A decrease in the molar ratio of reductant KBH(4) to AgNO(3) resulted in larger Ag particles with higher polydispersity.

Journal Article↗

PubMed2002

Effect of phase behavior and pressure on the constant-volume heat capacity and intermolecular interaction of CO2-ethanol and CO2-n-pentane mixtures in the critical region.

Study on the properties of the fluids near the critical point of mixed systems is a key for the development of supercritical (SC) technology and for the further understanding of the features of supercritical fluids (SCFs). The constant-volume molar heat capacity (Cv) of a solution is directly related to the internal energy, intermolecular interaction, and the microstructure of the solution. In this work, the Cv of CO2-n-pentane and CO2-ethanol systems was determined at 308.15 K in different phase regions. This work focuses on how the properties of the mixtures change with pressure, composition, and the structure of the components near the critical point of the mixtures. It was found that at fixed composition, a maximum in Cv versus pressure curve exists (Cv(max)) that occurs at the pressure at which the isothermal compressibility (K(T)) is the largest. We deduced that breaking the "clusters" in the SC mixtures is an endothermic process. It is very interesting that Cv increases sharply as the pressure approaches the critical point (CP) or bubble point (BP), while Cv is nearly independent of pressure and composition at the pressures well above the CP or BP pressure, and that the Cv at CP or BP can be several times larger than that at the high pressures. It can be deduced that at fixed composition the degree of "clustering" changes significantly with pressure near the CP or BP, and is the largest at CP and BP.

Journal Article↗

PubMed2002

[Skewness and inequality of height distribution of young Pinus sylvestris var. mongolica stands introduced on sandy soil with lower limited precipitation for tree survival and normal growth].

Based on the investigation of a transect (20 m wide and 80 m long) along a gradient (bottom, middle, and top) of a dune, whose height was about 5-10 m, the population dynamics in young Pinus sylvestis var. mongolica stands was studied. The results showed that both skewness and height inequality declined before the self-thinning process occurred. Age, initial growth status, density of the population, and neighborhood competition were the main factors affected height inequality. The location at sand dune was also an important factor, and its effect was more obvious than that of density.

Chemical Precipitation↗

PubMed2002

[Expression of recombinant human serum albumin in genetically engineered Pichia pastoris in high-density fermentation].

The optimum culture conditions of genetically engineered Pichia pastoris in shake-flask cultivation and in fed-batch fermentation were investigated respectively in this paper. It showed that the cultural period induced with 5 g/L methanol is 96 h, optimum methanol concentration is 10 g/L, and pH range is 5.72-6.59 in shake-flask culture. Although the seed inoculum amount increased, the target protein productivity per cell optical density was decreased. Their relationship fit the equeation Y = 12.941x(-0.5059) (r = 0.9789, where x is inoculating OD600, Y is protein productivity per cell optical density), we postulated that the restricting factor may be dissolved oxygen (DO) at shake-flask culture. With the 10% inoculum and 20 OD600 of seed, the lag phase of cell growth is 2.11 h in batch cultivation, and the relationship between cell optical density (Y) and culture time (t) is Y = 0.7841e0.2319t (r = 0.9936); The cell dry weight of broth reached 115-160 g/L and the maximum rHSA concentration was 3.6 g/L at the 120th at the fed-batch fermentation phase.

Fermentation↗

PubMed2002

[Biology and pathobiology of death receptors in liver].

Death receptors induce apoptosis by intracellular signaling transmission and relate to body growth, development, disease and death. This paper reviews the structural character of death receptors, and the mechanisms by which apoptosis is induced. The biology and pathobiology of these death receptors in liver are discussed as well.

Apoptosis↗

PubMed2002

[Structure, function and regulation of MMPs].

The matrix metalloproteinases (MMPs) are a large family of proteolytic enzymes, which are involved in the degradation of many different components of the extracellular matrix. The MMPs have been classified into different groups including collagenases, gelatinases, stromelysins, membrane-type MMPs, etc. There is increasing evidence to indicate that MMPs play important roles in tumour invasion and metastasis. Moreover, MMPs not only play a direct role in tumour invasion by facilitating extracellular matrix degradation, but as a consequence they also have an important role in maintaining the tumour micro-environment and thus promoting tumour growth. In this paper, the structure, function and regulation of MMPs were reviewed.

Matrix Metalloproteinases↗

PubMed2002

[Prospect of the study on desertification and its restoration of Keerqin sandy land].

In this paper, the study on desertification and its restoration of the Keerqin sandy land was briefly reviewed. With reference to the trends in related scientific fields and pressing demand in restoring existing desertified lands, several key aspects, including vegetation processes, eco-hydrological processes, landscape processes, and assessment of regional environmental state, prediction of desertification trends and exploration of restoration measures for the whole Keerqin sandy land, aimed to discover mechanisms leading to desertification and to restore desertified lands, were raised.

Agriculture↗