Research
Relevant Disciplines
Physical Organic / Inorganic / Materials
Related Areas
Supramolecular Chemistry / Spectroscopy and Electrochemistry / Interfacial Science / Nanoscience
1. Anion Regulation
We have developed a novel shape-persistent macrocycle (see image below) that is easily constructed using click chemistry and displays a high affinity for anions. This is one of the first three examples of the weak CH•••anion hydrogen bond (the weakest among Nature's cohort) to be reported and therefore represents an iconoclastic breakthrough in the design of anion receptors. Consequently, the extreme modularity provided by the click chemistry as well as the high affinity (some approaching Ka values of 1,000,000 M–1) open up a new and uncharted realm of opportunities. One of our goals are to sequester toxic anions from aqueous environment, deliver them to safe locations and, by using our knowledge of molecular machines, to release them into captivity using a photo-driven light switch.
New goals include the chelation, sensing, regulation, and transport of chloride in biological mileu.
Funding:
NSF-CAREER Award (CHE-0844441)
DOE-BES
Indiana University (FRSP and Collaborative Research Award)
81 McDonald, K. P.; Hua, Y.; Lee, S.; Flood, A. H., Shape Persistence Delivers Lock-and-Key Chloride Binding in Triazolophanes, Chem. Commun. 2012, asap. DOI
80 Flood, A. H., Profile: Early Excellence in Physical Organic Chemistry J. Phys. Org. Chem. 2011 DOI
79 McDonald, K. P.; Ramabhadran, R. O.; Lee, S.; Raghavachari, K., Flood, A. H., Polarized Naphthalimide CH Donors Enhance Cl Binding Within an Aryl-Triazole Receptor, Org. Lett. 2011, ASAP. DOI
77 Ramabhadran, R. O.; Hua, Y.; Flood, A. H.; Raghavachari, K.*, From Atomic to Molecular Anions: A Neutral Receptor Captures Cyanide using Strong C–H Hydrogen Bonds, Chem. Eur. J. 2011, 17 accepted
74 Hua, Y.; Ramabhadran, R. O.; Karty, J. A.; Raghavachari, K.; Flood, A. H., Two levels of conformational pre-organization consolidate strong CH hydrogen bonds in chloride-triazolophane complexes, Chem. Commun. 2011, in press
73 Zahran, E. M.; Hua, Y.; Lee, S.; Flood, A. H.; Bachas, L. G., Ion-selective electrodes based on a pyridyl-containing triazolophane: Manipulating halide selectivity by mixing dipole-promoted cooperativity with hydrogen bonding, Anal. Chem. 2011, ASAP. DOI
72 Hua, Y.; Ramabhadran, R. O.; Uduehi, E. O.; Karty, J. A.; Raghavachari, K.; Flood, A. H., Aromatic and aliphatic CH hydrogen bonds fight for chloride while competing alongside ion pairing within triazolophanes, Chem. Eur. J. 2011, 17, 312-321. DOI.
71 Hua, Y.; Flood, A. H., Flipping the switch on chloride concentrations with a light-active foldamer, J. Am. Chem. Soc. 2010, 132, 12838-12840. DOI.
69 Lee, S.; Hua, Y. Park, H.; Flood, A. H., Intramolecular hydrogen bonds preorganize aryl-triazole receptor into a crescent for chloride binding, Org. Lett. 2010, 12, 2100-2101. DOI
65 Hua, Y.; Flood, A. H., Click chemistry generates priviliged CH hydrogen-bonding triazoles: the latest addition to anion supramolecular chemistry, Chem. Soc. Rev. 2010, 39, 1262-1271. DOI
63 Zahran, E.; Hua, Y.; Li, Y.; Flood, A. H.; Bachas , L. G., Triazolophanes: A new class of halide-selective ionophores for potentiometric sensors, Anal. Chem. 2010, 82, 368-375. DOI
60 Bandyopadhyay, I.; Raghavachari, K.; Flood, A. H., Strong CH•••halide hydrogen bonds from 1,2,3-triazoles quantified using pre-organized and shape-persistent triazolophanes, ChemPhysChem. 2009, 10, 2535-2540. DOI
59 Li, Y.; Vander Griend, D. A.; Flood, A. H., Modelling triazolophane-halide binding equilibria using Sivvu analysis of UV-vis titration data recorded under medium binding conditions, Supramolec. Chem. 2009, 21, 111-117. (Special Issue for the III International Symposium on Macrocyclic and Supramolecular Chemistry, Las Vegas 2008), DOI
55 Li, Y.; Pink, M.; Karty, J. A.; Flood, A. H., Dipole-Promoted and Size-Dependent Cooperativity between Pyridyl-Containing Triazolophanes and Halides Leads to Persistent Sandwich Complexes with Iodide, J. Am. Chem. Soc., 2008, 130, 17293-17295. DOI
53 Li, Y.; Flood, A. H., “Strong, size-selective, and electronically-tunable C–H•••halide binding with steric control over aggregation from synthetically modular, shape-persistent [34]triazolophanes, J. Am. Chem. Soc. 2008, 130, 12111-12122. DOI
52 Li, Y.; Flood, A. H., "Pure CH hydrogen bonding to chloride ions: A pre-organized and rigid macrocyclic receptor," Angew. Chem. Int. Ed. 2008, 47, 2649-2652. DOI
See also the news coverage by: Chem. & Eng. News, • Nature • Chemistry World
Book Chapter
* McDonald, K. P.; Hua, Y.; Flood, A. H., 1,2,3-Triazoles and the Expanding Utility of Charge Neutral CH•••Anion Interactions, Anion Receptors Special Issue in Topic in Heterocyclic Chemistry, Springer, 2010. DOI
2. Molecular Machines
Molecular robots are electromechanical machines that are integrated with feedback control systems to achieve autonomous operation at the nanoscale. This goal is increasingly becoming a reality. While many molecular actuators, in the form of molecular machines, are being realized, the true revolution in control will come once we begin to understand the mechanisms of motion. To this end, we are focused on quantifying the thermodynamics and kinetics of movement. We also contend that the integration with control systems will be facilitated with voltage-gated molecular systems. With that goal in mind, we have developed redox-active ligands that can serve as switches to the investigation of mechanical motion at the molecular level. Attention is focused on the Cu(I) as a labile transition metal coupled with non-innocent bridging ligands. . We intend to broaden the diversity of ligand-based switching to other metals and extend the complexity of what can be achieved using catenates and rotaxanes that can perform a range of functions -- such as molecular muscles. See also our work on light-driven foldamers for binding and releasing anions.
68 Parimal, K.; Witlicki, E. H.; Flood, A. H., Two different classes of architectures can be interconverted by reduction of a self-sorting mixture, Angew. Chem. Int. Ed. 2010, 49, 4628-4632. DOI
67 Share, A. I.; Flood, A. H., Thinking inside and outside the box (News and Views Article), Nature Chem. 2010, 2, 349-350. DOI
66 Share, A. I.; Parimal, K.; Flood, A. H., Bi-lability is defined when one electron is used to switch between concerted and step-wise pathways in Cu(I)-based bi-stable [2/3]pseudorotaxanes, J. Am. Chem. Soc. 2010, 132, 1665-1675. DOI
62 Li, G.; Parimal, K.; Vyas, S.; Hadad, C. M.; Flood, A. H.; Glusac, K. D., Pinpointing the extent of electronic delocalization in the Re(I)-to-tetrazine charge-separated excited state using time-resolved infrared spectroscopy, J. Am. Chem. Soc. 2009, 131, 11656-11657. DOI
57 McNitt, K. A.; Parimal, K.; Share, A. I.; Fahrenbach, A. C.; Witlicki, E. H.; Pink, M.; Bediako, D. K.; Plaisier, C. L.; Le, N.; Heeringa, L. P.; Vander Griend, D. A.; Flood, A. H., Reduction of a redox-active ligand drives switching in a Cu(I) pseudorotaxane by a bimolecular mechanism, J. Am. Chem. Soc. 2009, 131, 1305-1313. DOI
47 Li, Y.; Huffman, J. C.; Flood, A. H. “Can Terdentate 2,6-Bis(1,2,3-Triazol-4-yl)Pyridines form Stable Coordination Compounds?” Chem. Commun. 2007, 2692-2694. DOI
Book Chapter
* Flood, A. H.; Kaifer, A. E., Supramolecular Electrochemistry, for Supramolecular Chemistry: From Molecules to Nanomaterials, Eds. Steed, J. W.; Gale, P. A. John Wiley and Sons, in press
Collaborations on Molecular Switches
We are extending the capabilities learnt on Cu(I)-based supramolecular switches to redox-active systems of collaborators
Yi Liu
54 Koshkakaryan, G.; Parimal, K.; He, J.; Zhang, X.; Abliz, Z.; Flood, A. H.; Liu, Y., pi-Stacking enhanced dynamic and redox-switchable self-assembly of donor-acceptor metallo-[2]catenanes from diimide derivatives and crown ethers, Chem. Eur. J. 2008, 14, 10211-10218. DOI
Jan O Jeppesen
82 Hansen, S. W.; Stein, P. C.; Sorensen, A.; Share, A. I.; Witlicki, E. H.; Kongsted, J.; Flood, A. H.; Jeppesen, J. O., Quantification of the pi-pi Interactions that Govern Tertiary Structure in Donor-Acceptor [2]Pseudorotaxanes, J. Am. Chem. Soc. 2012, asap. DOI
49 Nygaard, S.; Laursen, B. W.; Hansen, T. S.; Bond, A. D.; Flood, A. H.; Jeppesen, J. O., “Preparation of cyclobis(paraquat-p-phenylene)-based [2]rotaxanes without flexible glycol chains”, Angew. Chem. Int. Ed. 2007, 46, 6093-6097. DOI
48 Nygaard, S.; Hansen, S. W.; Huffman, J. C.; Jensen, F.; Flood, A. H.; Jeppesen, J. O. “Two Classes of Alongside Charge-Transfer Interactions Defined in One [2]Catenane,” J. Am. Chem. Soc. 2007, 129, 7354-7363. DOI
46 Nygaard, S.; Liu, Y.; Stein, P. C.; Flood, A. H.; Jeppesen, J. O. “Using Molecular Force to Overcome Steric Barriers in a Spring-Like Molecular Ouroborous,” Adv. Funct. Mat. 2007, 17, 751-762.
42 Nygaard, S.; Flood, A. H.; Jeppesen, J. O.; Bond, A. D. “Cis- and Trans-Bis(2-cyanoethylsulfanyl)(decane-1,10-diyldithio)Tetrathiafulvalene,” Acta. Cryst. C 2006, 62, 677-680.
3. Active Plasmonics
Active molecular plasmonics involves the manipulation of light at the nanoscale using functional chromophores. Presently, large progress has been made in generating reproducible nanopatterns with tunable plasmons. The opportunity now emerges to interface functional molecules to these surfaces that have the potential information processing and sensing. However, fundamental questions remain such as how to tune molecular chromophores to couple the plasmons of patterned surfaces. This research program harnesses synthesis, spectroscopy and theory to address this question using colored host-guest complexes as the functional units. Here at IU, we make use of surface-enhanced resonance Raman scattering (SERRS) spectroscopy to quantify the coupling between plasmon and chromophore. Insight gained from these studies will also allow for quantitative studies of the numbers and identities of molecules on surfaces – laying the foundation for sensing.
75 Witlicki, E. H.; Johnsen, C.; Hansen, S. W.; Silverstein, D. W.; Bottomley, V. J.; Jeppesen, J. O.; Wong, E. W.; Jensen, L.; Flood, A. H.* Molecular Logic Gates Using Surface-Enhanced Raman-Scattered Light, J. Am. Chem. Soc.. 2011, 133, 7288–7291. DOI
70 Witlicki, E. H.; Andersen, S. S.; Hansen, S. W.; Jeppesen, J. O.; Wong, E. W.; Jensen, L. Flood, A. H., Turning on resonant SERRS using the chromophore-plasmon coupling created by host-guest complexation at a plasmonic nanoarray, J. Am. Chem. Soc. 2010, 132, 6099-6107. DOI
61 Witlicki, E. H.; Hansen, S.; Christensen, M.; Hansen, T.; Nygaard, S.; Jeppesen, J. O.; Wong, E. W.; Jensen, L.; Flood, A. H., Determination of binding strengths of a host-guest complex using resonance Raman scattering, J. Phys. Chem. A 2009, 113, 9450-9457. DOI
Past Projects