EPR, 1H and 2H NMR, and reactivity studies of the iron-oxygen intermediates in bioinspired catalyst systems

Complexes [(BPMEN)Fe(II)(CH(3)CN)(2)](ClO(4))(2) (1, BPMEN = N,N'-dimethyl-N,N'-bis(2-pyridylmethyl)-1,2-diaminoethane) and [(TPA)Fe(II)(CH(3)CN)(2)](ClO(4))(2) (2, TPA = tris(2-pyridylmethyl)amine) are among the best nonheme iron-based catalysts for bioinspired oxidation of hydrocarbons. Using EPR and (1)H and (2)H NMR spectroscopy, the iron-oxygen intermediates formed in the catalyst systems 1,2/H(2)O(2); 1,2/H(2)O(2)/CH(3)COOH; 1,2/CH(3)CO(3)H; 1,2/m-CPBA; 1,2/PhIO; 1,2/(t)BuOOH; and 1,2/(t)BuOOH/CH(3)COOH have been studied (m-CPBA is m-chloroperbenzoic acid). The following intermediates have been observed: [(L)Fe(III)(OOR)(S)](2+), [(L)Fe(IV)═O(S)](2+) (L = BPMEN or TPA, R = H or (t)Bu, S = CH(3)CN or H(2)O), and the iron-oxygen species 1c (L = BPMEN) and 2c (L = TPA). It has been shown that 1c and 2c directly react with cyclohexene to yield cyclohexene oxide, whereas [(L)Fe(IV)═O(S)](2+) react with cyclohexene to yield mainly products of allylic oxidation. [(L)Fe(III)(OOR)(S)](2+) are inert in this reaction. The analysis of EPR and reactivity data shows that only those catalyst systems which display EPR spectra of 1c and 2c are able to selectively epoxidize cyclohexene, thus bearing strong evidence in favor of the key role of 1c and 2c in selective epoxidation. 1c and 2c were tentatively assigned to the oxoiron(V) intermediates.     

Net Spaces and Boundedness of Integral Operators

In this paper we introduce new functional spaces which we call net spaces. Using their properties, necessary and sufficient conditions for the integral operators to be of strong or weak type are obtained. Estimates of the norm of the convolution operator in weighted Lebesgue spaces are presented.     

On the Equivalence of Some Conditions for Convex Functions

We study classes of convex functions on (1, ∞] that tend to zero at infinity. Relations between different elements of these classes are determined. __________ Translated from Ukrains'kyi Matematychnyi Zhurnal, Vol. 57, No. 3, pp. 427–431, March, 2005.     

Interaction of imidazoline- and imidazolidine-based nitroxides with chloroplasts

In this work, we investigated the interaction of a number of novel pH-sensitive spin probes (imidazoline- and imidazolidine-based nitroxides) with isolated chloroplasts. The light-induced changes in the electron paramagnetic resonance signals of these radicals are determined by several factors: ΔpH-driven accumulation of nitroxides inside the thylakoids, consumption (or evolution) of oxygen by chloroplasts, and irreversible loss of spin probe paramagnetism. A comparative study of these radicals characterized by different pK_a allowed us to conclude that these spin probes can be used as pH indicators for monitoring the intrathylakoid pH- and light-induced changes in oxygen concentration in chloroplast suspension.     

A mathematical model of electron and proton transport in oxygenic photosynthetic systems

Results of simulation of electron and proton transport in higher plant chloroplasts, taking into account the lateral heterogeneity of their lamellar system, were summarized. The existence of heterogeneous lateral profiles of pH inside thylakoids and in gaps between the thylakoids of grana was predicted. The basic kinetic relationships were simulated for photoinduced redox transformations of P₇₀₀, the primary electron donor for PS1. It was shown that, along with changes in pH inside thylakoids, an essential role in controlling the electron transport in chloroplasts can belong to alkalinization of the gap between thylakoids of grana, caused by deceleration of diffusion of hydrogen ions from the stroma to the PS2 complexes in thylakoids of grana.     

Modeling VHF emissivity of snow cover with account of its stratigraphy

In this paper, we discuss a model of emissivity of snow cover taking into account its structure. We assume that upward and downward radiation inside a snow layer are diffuse and apply the two-flux theory of Kubelka and Munk. Snow cover is modelled by a medium comprising discrete scatterers. In the case of dry snow, the scatterers are ice grains. Wet snow is modelled by a mixture of ice grains (with or without water envelopes) and water drops. We assume that the scatterers are spherical particles that have lognormal distribution over size. The brightness temperature of radio emission from snow cover on the soil is calculated using the data of glaciological measurements of physical parameters and microstructure of snow. Results of calculations are compared to measurements of the brightness temperature of radio emission from various types of snow covers. Space Research Institute of Russian Academy of Sciences, Moscow, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 9, pp. 845–857, August 1999.