BODIPY-based azamacrocyclic ensemble for selective fluorescence detection and quantification of homocysteine in biological applications

Considering the significant role of plasma homocysteine in physiological processes, two ensembles (F-465-Cu2+ and F-508-Cu2+) were constructed based on a BODIPY (4,4-difluoro-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene) scaffold conjugated with an azamacrocyclic (1,4,7-triazacyclononane and 1,4,7,10-tetraazacyclododecane) Cu2+ complex. The results of this effort demonstrated that the F-465-Cu2+ ensemble could be employed to detect homocysteine in the presence of other biologically relevant species, including cysteine and glutathione, under physiological conditions with high selectivity and sensitivity in the turn-on fluorescence mode, while the F-508-Cu2+ ensemble showed no fluorescence responses toward biothiols. A possible mechanism for this homocysteine-specific specificity involving the formation of a homocysteine-induced six-membered ring sandwich structure was proposed and confirmed for the first time by time-dependent fluorescence spectra, ESI-MS and EPR. The detection limit of homocysteine in deproteinized human serum was calculated to be 241.4 nM with a linear range of 0-90.0 mu M and the detection limit of F-465 for Cu2+ is 74.7 nM with a linear range of 0-6.0 mu M (F-508, 80.2 nM, 0-7.0 mu M). We have demonstrated the application of the F-465-Cu2+ ensemble for detecting homocysteine in human serum and monitoring the activity of cystathionine beta-synthase in vitro. (C) 2015 Elsevier B.V. All rights reserved.