**Part 1**

**The Importance of Stoichiometry in Host-Guest Chemistry** 

**1** 

*México* 

**Stoichiometric Ratio in Calixarene Complexes** 

Stoichiometry is a fundamental concept in chemistry that refers to the ratios of products and reactants in any chemical reaction. It is an important concept in both chemical reactions and biochemical processes. A stoichiometric ratio represents the relationship among the elements or molecules present in an equation. Using the correct stoichiometric amount of reactant will yield the maximum amount of product under the proper thermodynamic and

This chapter will be focused on the latest research, from our and other labs, on the determination of stoichiometric ratios for complexed species formed between substrates and calixarene receptors, the influence of size, conformation and functionalization site of calixarenes on the stoichiometry, as well as solvent effects and the stability of the complexes in the liquid and solid states. No formation (stability) constants will be discussed, although

Particular attention will be paid to the experimental methods used for stoichiometry determination. Furthermore, complexed calixarene molecules in 1:1, 1:2 and 2:1 (Substrate:Calixarene) stoichiometries calculated by Augmented MM3 and CONFLEX

The enormous number of sophisticated functionalized calixarenes published so far, forced us to be selective. Therefore, our attention will be devoted to the stoichiometry of complexes formed with parent calixarenes (Gutsche, 1989, 1998, Mandolini & Ungaro 2000) functionalized at the lower and upper rims, with linear arms, that were first reported

Calixarenes are an important group of macrocycles, considered the third best host (receptors) molecules after cyclodextrins and crown ethers (Shinkai, 1993). They are prepared by condensation reactions between para-substituted phenols and formaldehyde (Gutsche, 1989). Here, we focus on conventional *endo*-calixarenes, which have a lipophilic cavity and two rims: the polar lower rim and the apolar upper rim that provides an unusual flexibility to the calixarene that can be modulated by adjusting cavity size and the rim substituents size. Its basket-like structure, with a lipophilic cavity made up of aromatic

semiempirical procedures, and other computational calculations will be included.

**1. Introduction** 

kinetic conditions.

between 1999 and 2011.

in some cases these could be mentioned.

**2. A brief overview of calixarenes**

Flor de María Ramírez and Irma García-Sosa *Instituto Nacional de Investigaciones Nucleares* 
