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Bis(Dimethylamino)Azobenzene-3,3'-Disulfonylchloride As a Cap for Beta-Cyclodextrin

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Bis(Dimethylamino)Azobenzene-3,3'-Disulfonylchloride As a Cap for Beta-Cyclodextrin W&M ScholarWorks Dissertations, Theses, and Masters Projects Theses, Dissertations, & Master Projects 2000 The Attempted Synthesis of 4,4'- Bis(dimethylamino)azobenzene-3,3'-disulfonylchloride as a Cap for beta-Cyclodextrin Katherine M. Ross College of William & Mary - Arts & Sciences Follow this and additional works at: https://scholarworks.wm.edu/etd Part of the Organic Chemistry Commons Recommended Citation Ross, Katherine M., "The Attempted Synthesis of 4,4'-Bis(dimethylamino)azobenzene-3,3'- disulfonylchloride as a Cap for beta-Cyclodextrin" (2000). Dissertations, Theses, and Masters Projects. Paper 1539626254. https://dx.doi.org/doi:10.21220/s2-nzy7-fn07 This Thesis is brought to you for free and open access by the Theses, Dissertations, & Master Projects at W&M ScholarWorks. It has been accepted for inclusion in Dissertations, Theses, and Masters Projects by an authorized administrator of W&M ScholarWorks. For more information, please contact [email protected]. THE ATTEMPTED SYNTHESIS OF 4,4’-BIS(DIMETHYLAMINO)AZOBENZENE- 3,3 ’-DISULFONYLCHLORIDE AS A CAP FOR P-CYCLODEXTRIN A Thesis Presented to The Faculty of the Department of Chemistry The College of William and Mary in Virginia In Partial Fulfillment Of the Requirements for the Degree of Master of Arts by Katherine M. Ross August 2000 APPROVAL SHEET This thesis is submitted in partial fulfillment of the requirements for the degree of Master of Arts Author Approved, August 2000 rs Dr. Christopher A pelt T Dr. Kathleen Morgan1* Dr. Robert Hinkle Table of Contents Acknowledgements List of Figures Abstract Introduction Background Cyclodextrins Capping of (3-Cyclodextrin Aromatic Azo Compounds Experimental 2-Acetamido-5-nitrobenzene sulfonic acid 2-Acetamido-5-aminobenzene sulfonic acid 3,3’-Diaminoazobenzene-4,4’-disulfonic acid Results Discussion Conclusion Appendix of Spectra References Acknowledgements The author would like to express her gratitude to Dr. Abelt for the opportunity to do graduate research under his tutelage. His endless patience and knowledge were deeply appreciated, as was his calm and collected way of looking at anything that happened in the lab. She would also like to thank Dr. Morgan and Dr. Hinkle for their critique of this manuscript and Dr. Starnes for her introduction to research as an undergraduate. Finally she would like her friends and colleagues in the Abelt lab, especially those from the Annex who know who they are. iv List of Figures Fu 1. General Features of fi-Cyclodextrin 3 2 . Symmetric Cap with Sulfonate Ester Linkages 5 3. An a-l,4-Glycosidic Linkage Between Two Glucopyranose Units 7 4. Three Most Widely Characterized Cyclodextrins 8 5. Hydrogen Bonding Between Adjacent Glucopyranose Units 10 6. Three Regioisomers of a Symmetrically Capped p-Cyclodextrin 12 7. Acid-Base Forms of an Azo Dye 16 8. Three Paths to 4,4’-bis(dimethylamino)azobenzene-3,3’-disulfonyl chloride 20 9. First Attempted Synthesis of 4,4,-bis(dimethylamino)azobenzene 21 10, Second Attempted Synthesis of 4,4’-bis(dimethylamino)azobenzene 22 11, Third Attempted Synthesis of 4,4’-bis(dimethylamino)azobenzene 23 12, Fourth Attempted Synthesis of 4,4’-bis(dimethylamino)azobenzene 24 13. Fifth Attempted Synthesis of 4,4’-bis(dimethylamino)azobenzene 25 14. Synthesis of 4,4’-diaminoazobenzene 26 15, First Methylation Attempt on 4,4’-diaminoazobenzene 27 16, Synthesis of 4,4’-bis(dimethylamino)azobenzene 27 17, Synthesis of 4,4’-bis(dimethylamino)azobenzene-3,3’-disulfonic acid 29 18, First Methylation Attempt on 4,4’-bis(diamino)azobenzene-3,3’- disulfonic acid 29 19 Second Methylation Attempt on 4,4,-bis(diamino)azobenzene-3,3’- 30 disulfonic acid 20 Mechanism for Acetylation of Amino Group 32 34 21 Mechanism for Azo Coupling 22 Hydrolysis of Acetyl Group back to an Amino Group 35 23 !H NMR of Recrystallized 2-Amino-5-nitrobenzene sulfonic acid 39 24 *H NMR of 2-Acetamido-5-nitrobenzene sulfonic acid 40 25 *H NMR of 2-Acetamido-5-aminobenzene sulfonic acid 41 *H NMR of 3,3’-bis(diamino)azobenzene-4,4’-disulfonic acid 42 lYL NMR of 4,4’-Diaminoazobenzene 43 44 *H NMR of 4,4’-Dimethylaminoazobenzene v Abstract The synthesis of an organic dye molecule, 4,4’-bis(dimethylamino)azobenzene- 3,3’-disulfonic acid, was attempted. This molecule was intended to be a pH sensitive cap for P-cyclodextrin. This cap would induce gross structural changes in the p-cyclodextrin with a change in pH, and thus affect its binding properties in host/guest chemistry. Numerous synthetic pathways were explored. Characterization of all products was by proton NMR spectroscopy. Complications caused by the electron withdrawing character of the sulfonate functionalities hindered development of the synthesis. vi THE ATTEMPTED SYNTHESIS OF 4,4’-BIS(DIMETHYLAMINO)-AZOBENZENE- 3,3 ’-DISULFONYLCHLORIDE AS A CAP FOR P-CYCLODEXTRIN Introduction Curiosity into the function of natural enzymes has long existed. Enzymes are proteins with catalytic activity that exhibit both high specificity and rate acceleration. Enzymes possess an active site, the part of the enzyme that binds to a specific substrate enabling the substrate to undergo a reaction at an increased rate. Developing an understanding of how enzymes function at this active site would be useful to those interested in synthetic techniques involving catalysis. Due to the vast number and size of biological enzymes it is necessary to study their function using model systems. An enzyme can be effectively modeled when the exact nature of the binding subsite has been synthetically mimicked in terms of shape, size and microscopic environment.1 For the model to completely succeed, numerous aspects of the active site must also be mimicked. These include the identity of functional groups, any stereochemistry involved and the mechanism behind how the enzyme functions. Although all of these criteria present a challenge, synthesizing these enzyme mimics is well documented in the literature.2,3,4 One example of a molecule that can function as an enzyme mimic is cyclodextrin. Cyclodextrins in general are cyclic oligomers of glucose that can form inclusion complexes with a substrate due to their shape. In particular, P-cyclodextrin has been used as a mimic for various specific enzymatic systems. Examples include model systems for ribonuclease5, carbonic anhydrase6, and chymotripsin.7 Formation of inclusion 2 complexes with various compounds is one of the most important characteristics of cyclodextrins.1 p-Cyclodextrin is able to catalyze reactions both covalently and non-co valently. The molecule’s structure provides functional groups for covalent catalysis and an interior cavity that is capable of binding in a non-covalent manner (Figure 1). ,OH Primary Face OH Secondary Face OH 70 nm Figure 1: General Features of p-CycIodextrin During covalent catalysis, the molecule’s numerous hydroxyl groups can act as nucleophiles or can be derivatized to other nucleophilic groups. During non-covalent catalysis, the molecule’s interior cavity acts as the active site and binds a substrate with the help of a hydrophobic interaction between the substrate and the aqueous medium. 3 The relationship between an enzyme and a substrate is a type of host/guest chemistry. In our model, the cyclodextrin plays the part of the host. However, our host lacks an important feature that naturally occurring enzymes possess, namely an ability to adjust based on environmental conditions. This is necessary in biological systems so that an organism can utilize different enzymes when it needs their help for whatever reaction is necessary to keep the system functioning at a specific moment in time. In the cyclodextrin mimic, the so-called “environmental switch” is absent; it can bind a variety of guests within a variety of environmental conditions. In order to devise an appropriate environmental switch for cyclodextrin, we had to consider the ease with which the environment could be altered. The goal was to allow some aspect of the environment to cue differences in how the host binds its guest. Perhaps one of the most easily controlled conditions in aqueous medium is hydrogen ion concentration. Therefore, the pH of the solution was chosen as the cue in our experiments. Once the cue was chosen, the question remained as to how to modify cyclodextrin to create a pH dependent host/guest relationship. The benefit of choosing organic indicator dyes as the environmental switches was two-fold. As the pH of the solution changes, the organic molecules can either protonate or deprotonate. This can change the hybridization and therefore the bond angles of the molecule altering its shape and dimensions. If the dye molecule is attached to cyclodextrin with two linkages, then this change in the molecule’s span could affect the host molecule’s ability to form inclusion complexes with guests. In order for the switch to be effective, the host/guest complex would exist at one pH and the guest would be completely excluded at another pH. 4 A second benefit to the use of the dye molecules is the ability to visually follow a reaction. When the structure of the organic dye is altered in some way it can be accompanied by a color change in the solution. Ideally, a color change in solution would signal that the organic dye molecule structure had changed in some way, thereby confirming or denying the presence of a guest in the host molecule. The pH indicator chosen for this study was a symmetric molecule consisting of two substituted aniline ring systems that are joined by a diazo linkage. This molecule would be attached to P-cyclodextrin by creating two sulfonate ester bonds at positions where the cyclodextrin contains hydroxyl functionalities (Figure 2). SO; Figure 2: Symmetric Cap with Sulfonate Ester Linkages 5 This newly altered cyclodextrin system derives its chromophoric behavior from the diazo linkage. As pH changes, protonation at one of the nitrogens of the diazo linkage leads to a difference in the electronics of the diazo bond.
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