Combination of experimental and theoretical methods were used to study NH-acidity and related spectral properties of tetrapyrazinoporphyrazines - octaazaanalogues of phtalocyanines. The theoretical values of deprotonation enthalpy (DPE) in gaseous phase indicate that substitution of benzene rings in phthalocyanine by pyrazine fragments strongly enhances the NH-acidity of the macrocycle which can be further tuned by introduction of substituents in pyrazine rings. Spectrophotometric titration study of octaethyl substituted tetrapyrazinoporphyrazine, [Et(8)TPyzPAH(2)], in organic solvents (CH2Cl2, THF and DMSO) has revealed that it is easily deprotonated hot only in the presence of strong bases such as tetrabutylammonium hydroxide, but also in such proton-acceptor solvent as DMSO. The thermodynamic acidity constants (pK(a1) = 7.77 and pK(a2) = 7.80) determined for [Et(8)TPyzPAH(2)] in DMSO solution using spectropotentiometric titration indicate that TPyzPA macrocycle has similar to 1000 times stronger NH-acidity than phthalocyanine. Deprotonation of [Et(8)TPyzPAH(2)] in pyridine solution is only possible in the presence of water playing a crucial role in formation of the dianion, which can be considered as a sensitive spectral sensor for water traces. Theoretical DFT B3LYB/631++G(p,d) study has confirmed that the dianion is only stabilized as bisaqua complex [TPyzPA(H2O)(2)](2-) with complementary H-bonds between water molecule and N-atoms of two opposite pyrrole rings (N center dot center dot center dot HOH center dot center dot center dot N).
