We introduce a new class of semisynthetic fluorescent biosensors for the quantification of free nicotinamide adenine dinucleotide (NAD+) and ratios of reduced to oxidized nicotinamide adenine dinucleotide phosphate (NADPH/NADP+) in live cells. Sensing is based on controlling the spatial proximity of two synthetic fluorophores by binding of NAD(P) to the protein component of the sensor. The sensors possess a large dynamic range, can be excited at long wavelengths, are pH-insensitive, have tunable response range and can be localized in different organelles. Ratios of free NADPH/NADP+ are found to be higher in mitochondria compared to those found in the nucleus and the cytosol. By recording free NADPH/NADP+ ratios in response to changes in environmental conditions, we observe how cells can react to such changes by adapting metabolic fluxes. Finally, we demonstrate how a comparison of the effect of drugs on cellular NAD(P) levels can be used to probe mechanisms of action.

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A pair of structurally analogous macrocyclic iron(ii) complexes with a magnetic off-on relationship is reported that exhibit electroneutrality at neutral pH and high stability in physiological media. This has been achieved by external charge compensation using nicotinate pendent arms. No contact toxicity was observed for cells up to 4 mM for the low-spin and 2 mM for the high-spin complex. These results are a necessary precursor to the future design of turn-on probes with elevated biotolerance.

International audienceA new low-spin iron(II) triazacyclononane-based complex, selected from four different candidates, acts as a molecular probe that turns a diamagnetic aqueous sample into a paramagnetic one as a response to a chemical analyte. The four complexes are prepared by a highly convergent synthetic protocol and give precious insights into structure–activity relationship (SAR) tendencies

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