The stability constants, stoichiometry, and solution structures of copper(II) complexes of neuropeptide gamma (NPG) (D(1)-A-G-H(4)-G-Q-I-S-H(9)-K-R-H(12)-K-T-D-S-F-V-G-L-M(21)-NH(2)) and acethyl-neuropeptide gamma (Ac-D(1)-A-G-H(4)-G-Q-I-S-H(9)-K-R-H(12)-K-T-D-S-F-V-G-L-M(21)-NH(2)) were determined in aqueous solution. For both peptides the additional deprotonations were observed; therefore, the potentiometric data calculations for NPG were only made in 2.5-7.4 pH range. For Ac-NPG one additional deprotonation was observed, likely hydroxy group of Ser residue, and the potentiometric data calculations in the 2.5-10.5 pH range may be performed. The potentiometric and spectroscopic data (UV-vis, CD, EPR) for the neuropeptide gamma show that a D(1) residue stabilizes significantly the copper(II) complexes with 1N {NH(2),β-COO(-)}, 2N {NH(2),β-COO(-),N(Im)}, and 3N {NH(2),β-COO(-),2N(Im)} coordination modes as the result of coordination through the β-carboxylate group. The Ac-NPG forms with the copper(II) ions the 3N {3N(Im)} complex in a wide 4.5-7.5 pH range. At higher pH deprotonation and coordination of the sequential amide nitrogens occur. Metal-catalyzed oxidation of proteins is mainly a site-specific process in which amino acids at metal-binding sites to the protein are preferentially oxidized. To elucidate the products of the copper(II)-catalyzed oxidation of NPG and Ac-NPG the liquid chromatography-mass spectrometry method (LC-MS) and the Cu(II)/H(2)O(2) as a model oxidizing system were employed. For solutions containing a 1:4 peptide-hydrogen peroxide molar ratio oxidation of the methionine residue to methionine sulphone was observed. For the 1:1:4 Cu(II)-NPG-H(2)O(2) system oxidation of two His residues and cleavage of the G(3)-H(4) and R(11)-H(12) peptide bonds were detected, supporting involvement of His(4) and His(12) in binding of the copper(II) ions. Oxidations of three histidine residues to 2-oxohistidines and fragmentations of Ac-NPG near the His (H(4), H(9),H(12)) residues support participation of the histidyl-imidazole nitrogen atoms in coordination of the metal ions.

The acetone-sensitized photolysis of 5-bromo-2'-deoxyuridine (5-BrdU) in a water/isopropanol solution with 300 nm photons leads to the formation of 2'-deoxyuridine (dU) and a comparable amount of another photoproduct that has not been reported in the literature so far. The negative and positive mass spectra recorded for this species indicate that they originate from the molecular mass of 286 Da, which corresponds to an adduct of 2'-deoxyuridine and 2-propanol. Quantum chemical calculations carried out at the DFT and TDDFT levels reveal both the structure and the UV spectrum of that adduct. The latter computational characteristic matches well the experimental UV spectrum of the new photoproduct. Our findings indicate that the acetone-sensitized photolysis of 5-BrdU is more complicated than has hitherto been assumed. Nevertheless, since electron transfer is one of the pathways responsible for 5-BrdU decay, acetone-sensitized photolysis of the halogen derivatives of nucleobases could be a convenient tool for studying their radiosensitivity in aqueous solutions.

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