Conformational equilibria 4 Transport properties

In the next section we describe the basic models that have been used in simulations so far and summarize the Monte Carlo and molecular dynamics techniques that are used. Some principal results from the scaling analysis of EP are given in Sec. 3, and in Sec. 4 we focus on simulational results concerning various aspects of static properties the MWD of EP, the conformational properties of the chain molecules, and their behavior in constrained geometries. The fifth section concentrates on the specific properties of relaxation towards equilibrium in GM and LP as well as on the first numerical simulations of transport properties in such systems. The final section then concludes with summary and outlook on open problems. 

These two methods are different and are usually employed to calculate different properties. Molecular dynamics has a time-dependent component, and is better at calculating transport properties, such as viscosity, heat conductivity, and difftisivity. Monte Carlo methods do not contain information on kinetic energy. It is used more in the lattice model of polymers, protein stmcture conformation, and in the Gibbs ensemble for phase equilibrium. 

Deviations from the aU-anti conformations occur even when only one C-X bond is present in a 1,2-disubstituted ethane moiety. For example, solutions of dopamine provide mixtures of trans and gauche conformers in the protonated forms whereas the isolated molecules prefer the gauche conformation. The conformational equilibrium in such species often depends on a number of factors but understanding their interplay is important because the shape of neurotransmitters influences their transport properties and plays a key role in the molecular recognition at the receptor site. 

The perplexing difficulties that arise in the crystallization of macromolecules, in comparison with conventional small molecules, stem from the greater complexity, lability, and dynamic properties of proteins and nucleic acids. The description offered above of labile and metastable regions of supersaturation are still applicable to macromolecules, but it must now be borne in mind that as conditions are adjusted to transport the solution away from equilibrium by alteration of its physical and chemical properties, the very nature of the solute molecules is changing as well. As temperature, pH, pressure, or solvation are changed, so may be the conformation, charge state, or size of the solute macromolecules. 

In these equations, Pj and P2 are the two conformational states of the transport protein, and equilibrium constants (K) and rate constants (k) in an electric field are shown to be these constants in zero field multiplied by a nonlinear term that is the product of A Me and the electric field across the membrane, Em. The r in these equations is the apportionation constant and has a value between 0 and 1 (14). This property of a membrane protein has been explored, and a model called electroconformational coupling has been proposed to interpret data on the electric activation of membrane enzymes (13-17). A four-state membrane-facilitated transport model has been analyzed and shown to absorb energy from oscillating electric fields to actively pump a substrate up its concentration gradient (see the section entitled Theory of Electroconformational Coupling). 

So far, we have treated the interfacial tension as an eqnilibriutn property that can be determined in a system that is relaxed dnring the time of the measurement. However, if the interface is off-eqnilibrinm, that is, dnring the relaxation process toward the equilibrium state, the interfacial tension is time dependent. Such a nonequilibrium, time-dependent interfacial tension is referred to as dynamic interfacial tension. Interpretation of dynamic interfacial tensions is nsnally in terms of surface rearrangements, transport of snrface-active componnds to or from the interface, conformational and orientational changes of adsorbed molecnles, and so on. 

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