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The unique molecular architecture of calixarenes makes them a suitable platform for constructing host molecules that can selectively bind a variety of guest substrates that range from cations and anions to fullerenes. Substrates can be bound within the hydrophobic bowl-cavity of the calixarenes through noncovalent interactions or outside the cavity by introducing suitable ligand systems on the upper or lower rim. Also, the self-assembly of some calixarene derivatives via non-covalent interactions leads to a new class of encapsulation agents, inclu-sion complexes, and molecular networks.The fascinating conformational and chemical reactivity of the calixarene systems has led to their use in a variety of applications that range from de-velopment of efficient separation systems, specific sensors, and molecular switches to a new generation of catalysts. The scientific interest in the applications of this class of molecules to solve separation problems is demonstrated by the number of recent publications as well as the award of numerous patents that utilizes the chemistry of calixarenes. These patents include the use of calixarenes as extraction agents for separations, such as recovering uranyl ion from sea water and removing cesium from nuclear wastes. Calixarenes are also being used as selective agents for metal ion transport through supported liquid membranes. It is important to point out that efficient chemical separations are now integral not only to manu-facturing processes, but also for compliance with subsequent industrial waste-discharge requirements.This book is the outcome of a recent symposium titled "Calixarene Molecules for Separations" that was held at the 217 th

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The preparation of partial esters of methylenebisphosphonic acids has been of recent interest due to their potential therapeutic applications. This paper describes a convenient method to prepare symmetrical methylenebis(alkyl hydrogen phosphonates) by the selective cleavage of the corresponding methylenebis(dialkyl phosphonate) with refluxing morpholine. The effects of structural variations on the amine as well as the substrate have been investigated to understand the scope and limitations of this reaction. A superior approach to hindered bisphosphonic acid esters involves the cleavage of their dimethyl esters, 4, using morpholine. This method is also useful to access a number of C-alkyl dialkyl methylenebisphosphonic acids such as 6. This study clearly shows that cleavage with morpholine is convenient, inexpensive, and allows for the preparation of a variety of P,P'-disubstituted partial esters in good yields and high purity.