Collision in solutions

Pick s laws describe the interactions or encounters between noninteracting particles experiencing random, Brownian motion. Collisions in solution are diffusion-controlled. As is discussed in most physical chemistry texts , by applying Pick s Pirst Law and the Einstein diffusion relation, the upper limit of the bimolecular rate constant k would be equal to... 

A reaction velocity equal to the rate of encounter of reacting molecular entities (also known as diffusion-con-trolled rate). For a bimolecular reaction in aqueous solutions at 25°C, the corresponding second-order rate constant for the encounter-controlled rate is typically about 10 ° M s See Diffusion Control for Bimolecular Collisions in Solution... 

Short-Lived Species in Fluid Solution. - In fluid solution, radical cations derived from saturated hydrocarbons are highly reactive oxidizing species and the rates of their bimolecular reactions are often determined by the frequency of diffusion collisions in solutions. It is known that the reactions of primary radical... 

Collisions in solution are diffusion-controlled and hence depend on the viscosity of the solvent. Due to Franck-Rabinowitch cage effect they occur in sets called encounters . 

Vogel, V.R. Rubtsova, E. T. Kotel nikov, A. I. Likhtenshtein, G. I. (1986) Study of protein collisions in solutions by triplet labels, Bioflzika 31, 152-154. 

The whole process of two species coming together and remaining together for a number of subsequent collisions in solution has been called an encounter . 

Crystallization is essentially a collision process Molecules collide to form a cluster called the nucleus, which then develops into a crystal with a characteristic internal structure and external shape. It therefore follows that factors such as stirring and degree of supersaturation, which influence the number of molecular collisions in solution, will affect the crystallization process. 

Stirring can enhance nucleation by promoting the frequency of collisions in solution, although excessive agitation can actually have the opposite effect (18). 

One approach concerns the chemistry of functional groups of the protein, such as imidazole. A second approach involves work on intramolecular reactions as a model for reactions within the enzyme substrate complex. One can look at an intramolecular model to determine rates and properties. Finally, the third area is catalysis and reactions in mixed complexes. This is the area under discussion chemistry in complexes, hopefully of well-defined geometry, rather than by random collision in solution. 

There is another aspect of collisions in liquid solution that is of particular interest with regard to chemical reactions. Collisions in solution are often repeated, so that multiple collisions of the same two molecules occur. Consider the molecules labeled A and B in Figure 7.1. Each molecule is surrounded by several neighboring molecules. In view of the short-range order typical of liquids, the neighboring molecules will all be located at... 

The density of molecules is substantially higher in liquids than in the gas phase. However, for reactions carried out in solution under relatively dilute conditions, the concentrations of reactants are not appreciably different from in tlie gas phase. Since reactant molecules A and B must undergo collision in solution in order to react, many of the same principles developed for gas-phase reactions also apply in solution. However, the presence of solvent molecules leads to important differences between reactions in solution and in the gas phase. In solution, the rate of diffusion often limits the rate of approach of molecule A to within a sufficient distance to B for reaction to occur. Once an encounter pair AB is formed, however, the solvent may act as a cage, effectively holding them in close proximity, thereby increasing the probability of reaction. 

In UV-VIS spectroscopy, the energy of an absorbed photon drives the molecule into an excited state via the promotion of an electron in accordance with the relationship M + hv----- M. The energy is dissipated via collisions in solution. In order for... 

The intensity of fluorescence can be decreased (quenched) by several processes, such as collisions (in solution), excimer or exdplex formation, and energy, electron or proton transfer [5]. In the context of polymer blends studies, the process of collisional fluorescence quenching, either static or dynamic (as described by the Stern-Volmer quenching), is not particularly relevant. 

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