Texas Tech University
TTU HomeDepartment of Chemistry and Biochemistry Faculty Dr. Richard A. Bartsch

Dr. Richard A. Bartsch

 

Title:

Paul Whitfield Horn Professor, Emeritus

Education:

Ph.D., Brown University, 1967

Research Area:

Organic, Analytical, & Polymer Chemistry

Office:

Phone:

Fax:

Email:

Chemistry 226-A

806-834-6738

806-742-1289

Richard.Bartsch@ttu.edu

 

Research Group

Principal Research Interests

The central theme of Professor Bartsch’s research program is ionic and molecular recognition. Novel organic molecules for the complexation and separation of targeted ionic species (particularly metal ions) and molecules are designed and synthesized. Different types of metal ion complexants include acyclic (podand), cyclic (crown ether, calixarene), and bicyclic (calix-crown, cryptand) ligands. Using the concept of 'charge matching', a number of acidic functions equal to the charge of the metal ion is attached to the ligand. The presence of such ion-exchange sites markedly enhances the efficiency of metal ion complexation in separation systems and the ability to subsequently release the complexed metal ion from the ligand. In addition to customary proton-ionizable groups of carboxylic, phosphonic, and sulfonic acid functions, we use a new acidic group [-C(O)NHSO2X], in which the acidity can be 'tuned' by varying the electron-withdrawing ability of X.

Currently attention is focused upon the use of calix[4]arene as a scaffold for attachment of pendant acidic groups through the phenolic oxygens. For calix[4]arene, the limiting conformations of cone, partial cone, 1,3-alternate, and 1,2-alternate are shown below as structures (1-4), respectively.

With appropriate substitutions on the four phenolic oxygens, the conformation can be mobile or locked. For example, ligand (5) is conformationally mobile and ligand (6) in which the two methyl groups in (5) have been replaced in the butyl groups is locked in the cone conformation. Ligand (7) is conformationally locked in the 1,3-alternate conformation with the two acidic groups on the opposite side of calix[4]arene framework.

Evaluation of these ligands by solvent extraction of metal ions from aqueous solutions into chloroform reveals that the both the extraction efficiency and selectivity are influenced by the conformations of similarly substituted ligands.

Connection of two phenolic oxygens of the calix[4]arene scaffold with a polyether chain gives calixarene-crown ether ligands, also called calixcrowns. Attachment of two distal oxygens results in a calix[4]arene-1,3-crown ether ligand (8); whereas linking two proximal oxygens provides a calix[4]arene-1,2-crown ether analogue (9). (Both structures are shown with the calix[4]arene unit in the cone conformation.)

Attachment of two ionizable groups to the phenolic oxygens gives di-ionizable calix[4]arene-crown ethers in which the spatial relationship of the acidic side arms to the crown ether cavity is controlled by the conformation of the calix[4]arene unit. The influence of such systematic structural variations upon the metal ion complexing ability of the ligands is being probed by solvent extraction.

In a collaborative research effort with Professor Edward Quitevis of this department, fundamental features of ionic liquids are being examined. Ionic liquids are organic salts that are liquids at room temperature. These novel media are highly polar with unique solvating abilities that can be 'tuned' by structural variations within the cationic and/or anionic components. Ionic liquids such as those shown below are prepared by a Bartsch coworker for study by the Quitevis Research Group.

 

 

Representative Publications

(Publications 2000-Present)