# Pd(0)-Mediated Deallylation Chemistry: A Reassessment of Its Application in Sensing CO

## TL;DR

This study reevaluates how a CO-sensing probe works, finding that CO sources like CORM-2 and CORM-3 can interfere with results, and that CO's role may be more complex than previously thought.

## Contribution

The study reveals that CO detection using FL-CO-1 is affected by CO-independent factors and common biological compounds like vitamin C and cysteine.

## Key findings

- FL-CO-1 activation by CORM-2/-3 includes CO-independent components.
- Vitamin C and cysteine interfere with FL-CO-1 performance.
- Pd(0) alone causes only moderate fluorescence, but Pd(0) plus CO causes a strong response.

## Abstract

Pd­(0)-mediated deallylation has been employed for developing
fluorescent
probes for carbon monoxide (CO). The key idea relied on the ability
of CO to reduce Pd­(II) to Pd(0). However, most studies used Ru-based
CORM-2 and/or CORM-3 as CO sources, despite their known chemical reactivity
and idiosyncratic CO release. Herein, we conducted studies using one
of the most widely used probes (FL-CO-1), evaluating
its response to various CO sources and to Pd(0). We found that (1)
the activation of FL-CO-1 by CORM-2/-3 has CO-independent
component(s); (2) vitamin C and cysteine were found to interfere with
the probe’s performance; and (3) Pd(0) only led to moderate
fluorescence turn-on, while a combination of Pd(0) and CO resulted
in a pronounced fluorescence turn-on response. Such findings indicate
that the role(s) of CO goes beyond Pd­(II) reduction, and accurate in vivo detection of CO using this approach is unlikely
because of the presence of vitamin C and thiols in living systems.
These new insights suggest the need to reinterpret some results, particularly
when chemically reactive CORM-2 and CORM-3 were employed as CO surrogates.
We recommend that future studies avoid using reactive CORMs to ensure
experimental rigor.