Picosecond activation of the DEACM photocage unravelled by VIS-pump-IR-probe spectroscopy

Abstract

The light-induced ultrafast uncaging process of the [7-(diethylamino)coumarin-4-yl]methyl (DEACM) cage is measured by time-resolved visible-pump-infrared-probe spectroscopy, and supported by steady-state absorption spectroscopy in the visible and infrared spectral regions. Understanding the uncaging process is important because its favorable properties make DEACM an interesting case for chemical and biological applications. It has a convenient absorption in the visible spectral range, and is relatively easily modified to carry leaving groups (LGs) such as nucleotides, substrates or inhibitors, which are inactive when bound and active when released. Previous work suggested a lower limit for the uncaging rate, which places it among the fastest available cages. Here, we determine the photodissociation directly to occur on the picosecond time scale by monitoring the appearance of the released LG in the infrared spectral region. In the present study, azide (N) is chosen as an LG to monitor photodissociation because its vibrational mode is spectrally isolated (hence easy to follow) and its absorption wavenumber is sensitive to local structural rearrangements. The uncaging process is recorded up to 3 nanoseconds and compared to the collected steady-state spectra. The free LG appears on a picosecond time scale, rendering this one of the fastest known cages. No evidence is found for a tight-ion pair (TIP) preceding the free LG. The uncaging mechanism is found to be slowed down upon the addition of water to acetonitrile.

Vibrationally resolved electronic spectra including vibrational pre-excitation: Theory and application to VIPER spectroscopy

“…DEACM-N 3 is also a coumarin derivative, with 102 vibrational modes. Photodissociation of the azide (N 3 ) leaving group ("uncaging") occurs on a picosecond time scale 6 . The S 0 -S 1 transition features a pronounced π-π *character and is localized to the coumarin moiety, very similar to Coumarin 6.…”

“…Notably, the laser dye Coumarin 6 is studied, which has served for demonstration of VIPER's capability to measure exchange beyond the vibrational T 1 lifetime 1 . Furthermore, [7-(diethylamino)coumarin-4-yl]methyl-azide (DEACM-N 3 ) and para-Hydroxyphenacyl thiocyanate (pHP-SCN) are investigated, which are model systems for photo-cleavable caging groups [4][5][6] , with the azide and thiocyanate groups representing the relevant leaving groups. We aim to establish a general understanding of which properties favor large spectral shifts that permit effective VIPER excitation.…”

Multivalent dextran hybrids for efficient cytosolic delivery of biomolecular cargoes

“…The bathochromic shift introduced by the electron‐donating groups at the C7 position results in an absorption maximum around 390 nm. In addition, the molecule displays a high quantum yield and an ultrafast release 50–53 …”

Investigation of Peptidic Templates for Bioorthogonal Ligations

“…Coumarin derived photocages have been extensively studied [147] and display high quantum yields and ultrafast release. [148][149][150][151] A 7-diethylamino-4methylcoumarin (DEACM) derivative, based on the work of Seyfried et al [152] , is therefore pursued as a viable alternative to the 4,5-dimethoxy-2-nitrobenzyl (DMNB) linker.…”

“…In addition, the molecule displays a high quantum yield (DEACM-puromycin, Φ = 0.47, 380 nm) and ultrafast release. [148][149][150][151] Once again, the uncaging mechanism offers insight about the advantages of this linker (see Figure 46). First, excitation of (coumarin-4-yl)methyl (CM)…”