Why is Cyclodextrin cavity hydrophobic? Actually this is going to be a list of interconnected questions. Please bear with me. 



Wikipedia article on cyclodextrin (CD) says that it is hydrophobic from inside. 

(1) How is it hydrophobic when there are so many hydroxyl groups on the interior surface ?

(2) This image
    labels the interir cavity as apolar rather than hydrophobic. I guess
    the apolarity is because of mutual cancellation of the dipole
    moments. 
Am I right on this?

In any case I don't understand how the cavity excludes water. 

There are reports on trapping organic substances such as naphthalene, toluene and crude oil in the CD cavity. Another report says that nitrosamime is trapped in CD by interacting with the hydroxyls. 

(3) How does this trapping exactly occur ? 

(4) Do the hydroxyls play a role in restricting the diffusion of the trapped organic molecules out of the cavity ? 

All of this, I started investigating because of a recent news about an alcoholic beverage in powder form- palcohol. Initially I didn't believe it but later I found that alcohol is absorbed in CD to make a dry powder. 

(5) What prevents alcohol from adsorbing on the exterior surface and not make the powder sticky ?

(6) Other studies say that there is a 1:1 ratio of trapping but palcohol claims that it is 58% alcohol by weight. Even this old patent says that CD absorbs a lot of alcohol. How does that happen ? In all it seems that CD behaves differently with different molecules.
Cyclodextrin hydroxyls are the external surface (hydrophilic and hydrogen-bonding).  They circle the larger open end.  The carbon and hindered ether skeleton is internal (hydrophobic).  A cyclodextrin looks like a bonded hollow detergent micelle in water.



Before you believe advertising hype, remember that underivatized cyclodextrins are nephrotoxic, crystallizing upon concentration, probably as the cholesterol endohedral complex.  Look it up. 

Ethanols insert their hydrocarbon tails into the center, then hydrogen bond their polar ends with each other and the rim.