Mechano-Chemical Coupling at Molecular Level: Forced Dissociation of Selectin/Ligand Binding

Mechano-chemical coupling is a common phenomenon that exists in various biological processes at different physiological levels. Bone tissue remodeling strongly depends on the local mechanical load. Leukocytes are sheared to form the transient aggregates with platelets or other leukocytes in the circulation. Flow pattern affects the signal transduction pathways in endothelial cells. Receptor/ligand interactions are important to cell adhesion since they supply the physical linkages...

Forced Dissociation of Selectin-ligand Complexes Using Steered Molecular Dynamics Simulation

Selectin-ligand interactions are crucial to such biological processes as inflammatory cascade or tumor metastasis. How transient formation and dissociation of selectin-ligand bonds in blood flow are coupled to molecular conformation at atomic level, however, has not been well understood. In this study, steered molecular dynamics (SMD) simulations were used to elucidate the intramolecular and intermolecular conformational evolutions involved in forced dissociation of three selectin-ligand systems: the construct consisting of P-selectin lectin (Lec) and epidermal growth factor (EGF)-like domains (P-LE) interacting with synthesized sulfoglycopeptide or SGP-3, P-LE with sialyl Lewis X (sLeX), and E-LE with sLeX. SMD simulations were based on newly built-up force field parameters including carbohydrate units and sulfated tyrosine(s) using an analogy approach. The simulations demonstrated that the complex dissociation was coupled to the molecular extension. While the intramolecular unraveling in P-LESGP-3 system mainly resulted from the destroy of the two anti-parallel sheets of EGF domain and the breakage of hydrogen-bond cluster at the Lec-EGF interface, the intermolecular dissociation was mainly determined by separation of fucose (FUC) from Ca2+ ion in all three systems. Conformational changes during forced dissociations depended on pulling velocities and forces, as well as on how the force was applied. This work provides an insight into better understanding of conformational changes and adhesive functionality of selectin-ligand interactions under external forces.

2D Kinetics and Forced Dissociation of Selectin-ligand Bindings

Cell adhesion is crucial to many pathophysiological processes, such as inflammatory reaction and tumor metastasis. It is mediated by specific interactions between receptors and ligands, and provides the physical linkages among cells. For example, interactions between selectins and glycoconjugate ligands mediate leukocyte initially tethering to and subsequently rolling on vascular surfaces in sites of inflammation or injury, which is determined by their fast kinetic rates. To mediate cell adhesion, the interacting receptors and ligands must anchor to apposing surfaces of two cells or a cell and the substratum, i.e. , the so-called two-dimensional (2D) binding, which differs from interactions in the fluid phase, i.e. , the three-dimensional (3D) binding. How structural variations and surface environments of interacting molecules affect their 2D kinetics, and how external forces manipulate their dissociation has little been known quantitatively, and nowadays attracts more and more attentions.

Calculations of bond dissociation energies and dipole moments in energetic materials using density-functional methods

We compare the effectiveness of six exchange/correlation functional combinations (Becke/Lee, Yang and Parr; Becke-3/Lee, Yang and Parr; Becke/Perdew-Wang 91; Becke-3/Perdew-Wang 91; Becke/Perdew 86; Becke-3/Perdew 86) for computing C-N, O-O and N-NO2 dissociation energies and dipole moments of five compounds. The studied compounds are hexabydro-1,3,5-trinitro-1,3,5-triazine (RDX), dimethylnitramine, cyanogen, nitromethane and ozone. The Becke-3/Perdew 86 in conjunction with 6-31G

Dissociation of egocentric and allocentric spatial processing in prefrontal cortex

Monkeys with lesions of areas 9 and 46 performed three variants of the spatial delayed response (SDR) task. There were no impairments in allocentric spatial memory in which geometrical relationships between environmental cues were used to identify spatial location; thus, memory of a 3D environmental map is intact. In contrast, there were severe impairments in egocentric spatial memory guided by visual or tactile cues that monkeys can relate to their viewing perspective during testing. These results strongly suggest that dorsolateral prefrontal cortex selectively mediates spatial memory tasks that are solved by referencing the location of targets to the body's orientation. (C) 2003 Lippincott Williams Wilkins.

Influence of 5A-Type Zeolite Powder on Tetrahydrofuran Hydrate Formation and Dissociation Process

Visual observations of tetrahydrofuran (THF) hydrate formation and dissociation processes with 5A-type zeolite powder were made at normal atmospheric conditions and below zero temperature by microscope. Results indicate that 5A-type zeolite powder can promote THF hydrate growth. At the same time, in the presence of 5A-type zeolite, agglomerated crystals and vein-like crystals of THF hydrate were also formed. SA-type zeolite powder increases the crystallization temperature and decreases the dissociation temperature. The particle size distribution of 5A-type zeolite powder influences THF hydrate formation and its dissociation characteristics significantly.

Study on the Dissociation Behavior of Gas Hydrate in Porous Sediment Based on Fractal Theory

The dissociation process of gas hydrate was regarded as a gas-solid reaction without solid production layer when the temperature was above the zero centigrade. Based on the shrinking core model and the fractal theory, a fractional dimension dynamical model for gas hydrate dissociation in porous sediment was established. The new approach of evaluating the fractal dimension of the porous media was also presented. The fractional dimension dynamical model for gas hydrate dissociation was examined with the previous experimental data of methane hydrate and carbon dioxide hydrate dissociations, respectively. The calculated results indicate that the fractal dimensions of porous media acquired with this method agree well with the previous study. With the absolute average deviation (AAD) below 10%, the present model provided satisfactory predictions for the dissociation process of methane hydrate and carbon dioxide hydrate.

Experimental Investigation on Propane Hydrate Dissociation by High Concentration Methanol and Ethylene Glycol Solution Injection

The dissociation behaviors of propane hydrate by high concentration alcohols inhibitors injection were investigated. Methanol (30.0, 60.1, 80.2, and 99.5 wt %) and ethylene glycol (30.0, 60.1, 69.8, 80.2, and 99.5 wt %) solution were injected, respectively, as alcohols inhibitors in 3.5 L transparent reactor. It is shown that the average dissociation rates of propane hydrate injecting methanol and ethylene glycol solution are 0.02059-0.04535 and 0.0302-0.0606 mol.min(-1).L-1, respectively. The average dissociation rates increase with the mass concentration increase of alcohols solution, and it is the biggest when 99.5 wt % ethylene glycol solution was injected. The presence of alcohols accelerates gas hydrate dissociation and reduces the total need of external energy to dissociate the hydrates. Density differences act as driving force, causing the acceleration effects of ethylene glycol on dissociation behaviors of propane hydrate are better than that of methanol with the same injecting flux and mass concentration.

Molecular Dynamics Simulation of Methane Hydrate Dissociation Process in the Presence of Thermodynamic Inhibitor

The dissociation of methane hydrate in the presence of ethylene glycol (11.45 mol.L-1) at 277.0 K was studied using canonical ensemble (NVT) molecular dynamics simulations. Results show that hydrate dissociation starts from the surface layer of the solid hydrate and then gradually expands to the internal layer. Thus, the solid structure gradually shrinks until it disappears. A distortion of the hydrate lattice structure occurs first and then the hydrate evolves from a fractured frame to a fractional fragment. Finally, water molecules in the hydrate construction exist in the liquid state. The inner dissociating layer is, additionally, coated by a liquid film formed from outer dissociated water molecules outside. This film inhibits the mass transfer performance of the inner molecules during the hydrate dissociation process.

In situ hydrate dissociation using microwave heating: Preliminary study

In this work, we investigate the dissociation behavior of natural gas hydrate in a closed system with microwave (MW) heating and hot water heating. The hydrate was formed at temperatures of 1-4 degrees C and pressures of 4.5-5.5 MPa. It was found that the gas hydrate dissociated more rapidly with microwave than with hot water heating. The rate of hydrate dissociation increased with increasing microwave power, and it was a function of microwave power. Furthermore, the temperature of the hydrate increased linearly with time during the microwave radiation.

Hydrate dissociation conditions for gas mixtures containing carbon dioxide, hydrogen, hydrogen sulfide, nitrogen, and hydrocarbons using SAFT

A new method, a molecular thermodynamic model based on statistical mechanics, is employed to predict the hydrate dissociation conditions for binary gas mixtures with carbon dioxide, hydrogen, hydrogen sulfide, nitrogen, and hydrocarbons in the presence of aqueous solutions. The statistical associating fluid theory (SAFT) equation of state is employed to characterize the vapor and liquid phases and the statistical model of van der Waals and Platteeuw for the hydrate phase. The predictions of the proposed model were found to be in satisfactory to excellent agreement with the experimental data.