title: Microwave synthesis of near infrared heptamethine cyanine dye.
abstract: Cyanine dyes are an interesting class of near infrared (NIR) dyes that have captured the interest of the scientific community. The NIR cyanine dye of interest, heptamethine cyanine dye NIR-1, exhibits characteristics that satisfy the qualifications as an acceptor in a Fluorescence Resonance Energy Transfer (FRET) biosensor [Wher, 1976]. Applications of FRET systems include structure determination and conformation of proteins [Hammer et al., 2002], receptor/ligand interactions [Hammer et al., 2002], and the cellular exposure to environmental toxins [Schwartz and Ulfelder, 1992]. This research stems from an interdepartmental collaboration to develop a NIR FRET biosensor, with significant advantages over the existing systems. A critical component of this endeavor is the development of an efficient environmentally conscious synthesis of novel NIR cyanine dyes utilizing microwave technology. Herein, we report the microwave synthesis of NIR-1. 2,3,3-Trimethyl-1-ethyl-3H-indolium iodide (I) synthesis is advantageous over the reported synthesis due to the significantly reduced reaction time of 450 s from 15 h and a decrease in the amount of iodoethane from 5 eq. to 3 eq. The condensation of heterocyclic salt I and bisaldehyde II has been accomplished in 220 s in 85% yield in the microwave oven; benzene has been eliminated from the condensation reaction procedure. Spectral characteristics of NIR-1 were determined and compared to commercially available NIR-1. A significant absence of asymmetry at the broad peak associated with the maximum absorbance wavelength, a slight increase in quantum yield (+ approximately .02) and the blue shift of the maximum absorbance wavelength (- approximately 5 nm) was observed.
authors.affiliation: Morgan State University, 1700 E. Cold Spring Lane, Baltimore, Maryland 21251, USA. angela.winstead@morgan.edu
authors.forename: Angela J
authors.initials: AJ
authors.lastname: Winstead
authors.forename: Richard
authors.initials: R
authors.lastname: Williams
authors.forename: Krystal
authors.initials: K
authors.lastname: Hart
authors.forename: Nicole
authors.initials: N
authors.lastname: Fleming
authors.forename: Ashley
authors.initials: A
authors.lastname: Kennedy