Routes of simplifying the problem

The previous result is an important one. It indicates that there can be yet another fruitful route to describe lipid bilayers. The idea is to consider the conformational properties of a probe molecule, and then replace all the other molecules by an external potential field (see Figure 11). This external potential may be called the mean-field or self-consistent potential, as it represents the mean behaviour of all molecules self-consistently. There are mean-field theories in many branches of science, for example (quantum) physics, physical chemistry, etc. Very often mean-field theories simplify the system to such an extent that structural as well as thermodynamic properties can be found analytically. This means that there is no need to use a computer. However, the lipid membrane problem is so complicated that the help of the computer is still needed. The method has been refined over the years to a detailed and complex framework, whose results correspond closely with those of MD simulations. The computer time needed for these calculations is however an order of 105 times less (this estimate is certainly too small when SCF calculations are compared with massive MD simulations in which up to 1000 lipids are considered). Indeed, the calculations can be done on a desktop PC with typical... 

There are a number of problems associated with the use of peptides as drug molecules. Peptides are rapidly degraded by proteases and, therefore, their biological half lives are normally too short to be useful In a therapeutic sense. Most peptides exhibit more than one type of biological effect making lack of specificity a problem to be overcome. The size of even "small" peptides Is larger than most common drug molecules, and it is usually desirable, if for no other reason than ease of synthesis, to simplify the structures as much as possible. Finally, for the small number of peptides which have been studied by the oral route, poor bloavallablllty has been a problem. 

The problem now simplifies to one of preparing cyclopentanecarboxylic acid from cyclopentyl bromide. Two routes are possible ... 

It helps to understand the overall transformation before diving into the individual steps. We can get a good overview of the problem space by generalizing what has to happen First an addition has occurred to connect the two reactants, then probably some proton transfers to set up the next step, an elimination of water. This allows us to draw a simplified problem space to guide our route decisions (Fig. 10.3). 

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