Surprising variations in the rate of ring opening for a series of rhodamine lactams with similar equilibrium endpoints

Michael J. Maher, Kevin Yehl, Farihah Haque, Amanda Faint, Ken D. Shimizu, Clifton J. Stephenson

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


Rhodamine amides are known to function as an important platform for molecular probe formation. The use of rhodamine-based probes has focused on the equilibrium between the off to on opening of the lactam form to the amide form. Herein, a series of four structurally similar rhodamine lactam derivatives is studied to show that the rate of conversion from the lactam form to the amide form can vary greatly (<1 s to >12 h) and that the rate trend is different from the trend for the absorbance measured at equilibrium. Slow or varying rates of ring opening for structurally similar rhodamine derivatives could produce inaccurate results. Rates were studied with both trifluoroacetic acid (TFA) and iron III. The rate of conversion changed depending on the structure of the substituent attached to the lactam nitrogen. Interestingly the rate of conversion varied even for compounds with similar absorbance at equilibrium. This work will help with the development of more effective rhodamine-based molecular probes.

Original languageEnglish (US)
Pages (from-to)1-8
Number of pages8
JournalSensors and Actuators, B: Chemical
StatePublished - Sep 2014

Bibliographical note

Funding Information:
Michael Maher earned his B.S. in chemistry in 2011 from Carthage College. He is currently a Ph.D. student in the lab of Dr. C. Grant Willson at the University of Texas at Austin. He is the recipient of both an IBM Ph.D. fellowship and a NSF graduate research fellowship.

Funding Information:
Kevin Yehl graduated from the University of South Carolina with a B.S. in Chemistry in 2008 and is now pursuing a Chemistry Ph.D. from Emory University in the lab of Dr. Khalid Salaita. Kevin's research interests are DNA technology, synthetic-biology, and nano-walkers. Kevin has received an NSF East Asia and Pacific Summer Institutes (EAPSI), honorable mention NSF Graduate Research, and a GAAN Fellowship and is an ACS-RISE and Magellan Scholar.

Funding Information:
We would also like to thank the following organizations for providing support; National Science Foundation ( NSF CHE1112431 and NSF CHE911616 ), Carthage College , and Loyola University New Orleans .

Copyright 2014 Elsevier B.V., All rights reserved.


  • Iron III
  • Rate study
  • Rhodamine-based sensor


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