PROTON CAGED COMPOUNDS FOR INTRACELLULAR pH MONITORING

Intracellular pH plays a pivotal role in cellular processes and is highly regulated in every organelle. The structural stability and function of proteins are tightly associated with pH. Furthermore, cell cycle progression and programmed cell death have both been linked to changes in intracellular pH. Probing intracellular pH usually requires exogenous agents, such as fluorescent probes1 or Raman sensitive probes2. We have developed a new type of exogenous probe, based on Proton Caged Compounds (PCCs), which releases protons upon UV irradiation. In particular, we have purposely designed and synthesized a long alkyl-chained PCC, the 1-(2-nitrophenyl)- ethylhexadecyl sulfonate (HDNS), and probed it on 3T3-NIH cells, via infrared spectroscopy3. The light-induced pH variation may easily be monitored by infrared spectroscopy, since the release of protons acts on the equilibrium of the intracellular HCO3- . The generated H2CO3 decomposes yielding H2O and CO2, which has a characteristic signal in a clear region of the cellular infrared spectrum. Here, we report on a different mechanism of protonation for long-incubation of HDNS on 3T3-NIH cells as probe of the intracellular acidification. When the PCC is doses for more than 3 hours, the accumulation into the cells leads to a protonation of intracellular carboxylic groups upon irradiation, which is still a fingerprint of the acidification process and a probe of the intracellular pH.