P710: Solid-supported azo dye arrays in the development of a colorimetric anion-selective indicator
: Noel M. Paul, The Ohio State University, USA
Co-Author: Benjamin P. Mohr, J. Clay Harris and Chris S. Callam, The Ohio State University, USA
Time: 10:35 AM – 10:55 AM
Room: LMH 114
Related Symposium: S51
Sophomore organic chemistry students have collaborated in the search for an azo dye that elicits a unique ionochromic effect in the presence of specific anions. As a complement to existing methods, colorimetric anion-selective indictors hold promise as a method to quickly quantitate threshold levels of toxic anions in both remote and economically depressed regions where analytical instrumentation is out of reach. Although this effect was previously identified through a screen of commercially available dyes, synthetic challenges have impeded the investigation of a related series of dyes whose aim is to elaborate the mechanism of this selective color change effect. Students functionalized cellulose chromatography paper with the assistance of microwave radiation, then conducted unique azo-coupling reactions following a specific grid pattern to yield 42 unique arrays. Each dye array was separated into three identical test strips, and these strips were subsequently exposed to acid, nitrate, or bromide. Using diffuse reflectance UV-vis spectroscopy, 630 full spectra were collected and the resulting data was complied and returned to the students for analysis. These results have suggested new single-molecule targets for future investigation. Following the study, the massive data set was processed using principal component analysis to reveal correlations difficult to detect through graphical means. Through their participation in this project, students earned insight into the difficulties and rewards inherit in the development of new knowledge, and using their results, this solid phase approach has been confirmed as an effective method to screen a large number of candidates for the development of anion-selective indicators.
P665: Undergraduate student exploration of parameters affecting substitution, elimination, and solvolysis reactions
: Jonathan P. Ruffley, The Ohio State University, USA
Co-Author: Noel M. Paul, The Ohio State University, USA
Time: 5:15 PM – 6:30 PM
Related Symposium: S33
Substitution, elimination, and solvolysis reactions are fundamental processes in Organic Chemistry, and earning an understanding of their differences is a significant challenge for students in the first semester of the sophomore-level course. A matrix of reactions was developed to highlight the effects of temperature, nucleophilicity, basicity, solvent, and leaving group position on the favorability of each of these mechanism pathways. Implementing several reactions in each laboratory class, analyzing the reactions using TLC and GC/MS, and facilitating the collection of these results using a web-based form will give students access to a large, authentic data set. Through the comparison of product data, consistent and inconsistent data points can be identified, and conclusions regarding the importance of each parameter can be made. The class-wide investigation aims to demonstrate the principles of reactivity first-hand and foster a deeper understanding of these essential reaction types than can be accomplished through study on paper alone.
P628: Research experiences in the undergraduate organic laboratory: Synthesis and studies of quinone methide precursors as acetylcholinesterase reactivators
: Christopher S. Callam, The Ohio State University, USA
Co-Author: Brent E. Sauner and Noel M. Paul, The Ohio State University, USA; Ryan J. Yoder, The Ohio State University, Marion Campus, USA
Time: 3:40 PM – 4:00 PM
Room: LMH 114
Related Symposium: S51
Acetylcholinesterase (AChE) is an essential enzyme in the human body, which hydrolyzes acetylcholine into choline for essential biochemical processes. Organophosphorus (OP) nerve-agents such as Sarin, Soman and Tabun are covalent inhibitors of AChE. Following exposure to OPs, AChE in inhibited and undergoes a subsequent irreversible aging process in which the OP-AChE adduct is dealkylated, resulting in the accumulation of excess acetylcholine in the central nervous system. Current oxime-based pharmaceuticals can only be used to treat the inhibited AChE and are ineffective on the aged AChE. One of our research modules for the undergraduate organic laboratories has a focus on developing these molecules for the reactivation of the aged AChE. Previous studies have shown that high energy quinone methides (QM) could potentially reverse the damage done to the active site on aged AChE through a kinetically favored alkylation of a phosphor-diester. Guided by computational methods, over 100 students have synthesized different QM precursors and investigated their ability to alkylate a model enzyme as a screen of initial reactivity. Students GC-MS, 1H NMR, 13C NMR and HPLC-TOF for characterization of their new compounds and activity screening efforts. At the conclusion of the study, a number of students expressed a desire to continue the project as undergraduate researchers. These experiments complement the classic synthetic experiments that comprise a large portion of the organic chemical laboratory experience and at the same time serve to ignite the interest in research problems at the introductory and advanced level.