Weakly bound hydrogen and deuterium pairs in UV-photosensitized frozen aqueous solutions of KH2PO4 and KD2PO4

Abstract

Interesting chemical models, including several examples of ATP photosynthesis initiated by different kinds types of irradiation [1], were elaborated in study of mechanism of elementary chemical act of ATP synthesis. Paramagnetic compounds are generated under such conditions. To reveal the leading free radical intermediate of the reaction is essential for careful analysis of its EPR spectra by computer modeling.The lines of hydrogen atoms with a splitting of 508 G are revealed in EPR spectra at 77 K during UV irradiation of phosphate, a substrate of the reaction. These lines, and wasare also detected in the presence of the sensitizer adenine during irradiation by light with λ > 260 nm. In contrast to the signals of free-radical phosphates detected in EPR spectra at a sufficiently relatively high power of microwave irradiation ( P > 1.6 mW) and well detected at P > 20 mW, these signals became already saturated at P values as low as 0.1 mW. At very low power values of power ( P 0 .004 mW), when the signal of the phosphate radical is not detectable, EPR spectra along with hydrogen signal contain a doublet in the range g ~ 2.00. EPR spectra of hydrogen atoms are well known for different media; however, but the central signals that often are often present in irradiated systems are usually attributed to the radicals not bound with hydrogen [2][3][4].We hypothesized that the satellite central line (triplet EPR spectra) detected in EPR spectra is caused by isotropic exchange interaction between of hydrogen atoms in weakly bound hydrogen pairs. Earlier, Knight et al. ,[5] who studied by computer modeling the EPR spectra of hydrogen atoms in matrices of noble gases in the range of forbidden transition, discovered the existence of weakly bound hydrogen pairs [5]. The formation of hydrogen pairs, a the peculiar way to deposit atomic hydrogen, was also reported in other media. It is important that a in that way hydrogen atom thus stabilized, under proper conditions, may be released and implicated participate in chemical and cross-linking processes [6,7].Of special interest is the role of atomic hydrogen in the photochemical model of ATP synthesis, because as fixing hydrogen orthophosphate, which fixes hydrogen, is a substrate of this reaction. It is noteworthy that atomic hydrogen has a high stability, especially in phosphates, sometimes at temperatures up to room temperature [8]. The nature of this phenomenon is clarified by a detailed computer analysis of its EPR spectrum using an original four-spin program.The search for optimal values of parameters values for the description of experimental spectra was performed by variation of values of variable parameters in the model spectra. The mMinimum of the sum of squared deviations served as a criterion for concordance between the calculated theoretical and the experimental EPR spectra.For the isotropic spin Hamiltonian (for the sake of simplicity and counting rate increase, all anisotropic interactions in Hamiltonian were neglected in Hamiltonian) the system of equations disinte...