GEOMETRY OF INTERCALATION OF PSORALENS IN DNA APPROACHED BY MOLECULAR MECHANICS*

The results of molecular mechanical calculations on intercalation complexes of 3-carbethoxypsoralen, 5-methoxypsoralen, 8-methoxypsoralen, 7-methylpyrido[3,4-c]psoralen (MepyPs) and 7-methylpyrido[4,3-c]psoralen (2N-MePyPs) with the double stranded duodecanucleotide d(CGCGATATCGCG)2 are presented. In the energy-minimized structures, the psoralens are intercalated with their plane orthogonal to the helix axis. Stacking interactions between the furan ring of the psoralen and the adjacent bases are maximized in most derivatives studied, whereas the effect of the various substituents of the psoralen ring is to specifically push part of the molecule towards either the minor or the major groove, preventing a symmetrical intercalation (with respect to the two strands of the DNA). The relative position of the psoralen ring and of the adjacent thymine foreshadows the formation of furan-side monoadducts in 3-CPs, MePyPs and 2N-MePyPs, whereas the formation of a pyrone-side monoadduct appears as geometrically more favourable in 5-MOP and both furan- and pyrone-side monoadducts can be geometrically envisaged in 8-MOP. A good correlation therefore exists between the more or less favourable equilibrium geometries and the experimentally observed photoreactions. The present study is the first attempt to characterize the geometrical parameters as part of a complex set of geometrical, dynamical and excited state parameters governing the overall DNA-psoralen photoreaction.     

Catalytic partial oxidation of hydrogen sulfide on chabazite tuff

The catalytic activity of a chabazite tuff in the partial oxidation of H₂S to sulfur has been determined. The effects of temperature, feed concentration and chemical composition of the tuff on H₂S conversion and selectivity to sulfur have been investigated. Encouraging results in view of a possible use in H₂S removal processes have been obtained.

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Experiences in the measurement of RBC-bound IgG as markers of cell age

An immunologically mediated pathway has been largely accepted to be one of the mechanisms involved in the clearance of senescent or prematurely damaged RBC. According to this pathway, RBC removal is mediated by binding of naturally occurring IgG to clustered integral membrane proteins, followed by complement deposition. The validation of an immunoenzymatic method for the detection of RBC-bound autologous IgG is presented. The use of RBC-bound IgG as an index related to red cell age was evaluated by measuring IgG binding in RBC treated with the clustering agent ZnCl2, in density fractionated RBC and in a selected group of patients expected to have an altered RBC life span. The immunoenzymatic method for IgG detection resulted to be reproducible (CV = 3.4%). IgG binding to in vitro clustered RBC was found to be enhanced to a very great extent, about 20 times higher with respect to untreated RBC. A slight but significant increase (about 1.8-fold) in membrane-bound IgG was observed in the highest density fraction of normal RBC, which constituted 1% of the total cells. A significantly greater number of RBC-bound IgG was measured in splenectomized beta-thalassemia intermedia patients and in subjects with secondary decreases in the C3 complement fraction concentration.