Template general comments

In the present section we comment further on the chemical modifications of these materials when the R group is chosen for the preparation of micro-and mesoporous silicas. From a general point of view, the control of the porosity of silica via organic molecular templating is an attractive topic connected to molecular recognition, catalysis, chemical sensing and selective adsorption, etc. Many attempts have been made to control the pore size distribution in sol-gel derived silica30,196. 

Before considering template reactions involving isothiosemicarbazides, their structure and general properties deserve special comment. S-Alkylisothiosemi-carbazides, like other isochalcogensemicarbazides and amidrazones, are monoacid bases, which form salts with inorganic acids (Eq. 2.31). 

We would like to thank Dr. Thomas Lectka, Professor of Chemistry at Johns Hopkins University, who provided expert advice on a host of topics. His critical comments were invaluable. We would also like to thank Ms. Gillian McCallion, who laid out the basic design of this text. She also designed the cover and provided templates for many images within the text. There are many molecular models in this text. They were made in Spartan Student, and we would like to thank Sean Ohlinger— Vice President, General Manager, Wavefunction, Inc.—and his staff for their technical support. 

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