Modification and Optimization of the Bis-picolylamide-Based Relay Protection for Carboxylic Acids to be Cleaved by Unusual Complexation with Cu²⁺ Salts

A simple modification of our recently published protection scheme for carboxylic acids as amides resulted in a new protecting group with significantly improved properties. It requires shorter reaction times for deprotection and allows us to replace Cu­(OTf)₂ by CuCl₂, indicating at the same time the importance of the nature of the anion of the Cu²⁺ source. Since the new scheme fulfills all criteria required for an ideal protection group it should find widespread application in synthetic organic chemistry

Dye Dynamics in Three-Color FRET Samples

Time-resolved emission data (fluorescence decay and fluorescence depolarization) of two three-color Förster resonance energy transfer (tc-FRET) systems consisting of a carbostyril donor (D), a ruthenium complex (Ru) as relay dye, and a Cy5 derivative (Cy) or, optionally, an anthraquinone quencher (Q) were carefully analyzed using advanced distribution analysis models. Thereby, it is possible to get information on the flexibility and mobility of the chromophores which are bound to double stranded (ds) DNA. Especially the distance distribution based on the analysis of the fluorescence depolarization is an attractive approach to complement data of fluorescence decay time analysis. The distance distributions extracted from the experimental data were in excellent agreement with those determined from accessible volume (AV) simulations. Moreover, the study showed that for tc-FRET systems the combination of dyes emitting on different time scales (e.g., nanoseconds vs microseconds) is highly beneficial in the distribution analysis of time-resolved luminescence data in cases where macromolecules such as DNA are involved. Here, the short lifetimes can yield information on the rotation of the dye molecule itself and the long lifetime can give insight in the overall dynamics of the macromolecule