Atom-water molecule adducts

Photolysis of the matrix with 340-300nm light caused the metal atom-water molecule adduct to react to form the tin hydroxy-hydride molecule, HSnOH. Prolonged photolysis (ca. 60 minutes) of the HSnOH molecule, caused cleavage of the hydrogen bonds to form SnO, which has previously been assigned (11). The reaction product frequencies are listed In Table II. 

SI, Ge, Sn and Pb metal atoms initially reacted with water on cocondensation to form the metal atom-water molecule adduct as has been generally observed for metal atom-water reactions ( ). The shift in the water bending mode frequency on adduct formation decreases with increasing atomic number as illustrated in Table I. Using the results obtained from theoretical studies ( 3, 5), it is believed that the water bending mode shift might serve as a relative measure of the extent of interaction between the water molecule and the metal atom, for metals within a particular group. 

Tin. Tin metal atoms reacted with water molecules on cocondensation to form the metal atom and metal dimer-water molecule adducts. The adduct bands are shown in Figure 1, and the frequencies are listed in Table I. The metal dimer-water molecule adduct reacted on photolysis of the matrix with 400-340nm light. 

The product is exclusively carbon monoxide, and good turnover numbers are found in preparative-scale electrolysis. Analysis of the reaction orders in CO2 and AH suggests the mechanism depicted in Scheme 4.6. After generation of the iron(O) complex, the first step in the catalytic reaction is the formation of an adduct with one molecule of CO2. Only one form of the resulting complex is shown in the scheme. Other forms may result from the attack of CO2 on the porphyrin, since all the electronic density is not necessarily concentrated on the iron atom [an iron(I) anion radical and an iron(II) di-anion mesomeric forms may mix to some extent with the form shown in the scheme, in which all the electronic density is located on iron]. Addition of a weak Bronsted acid stabilizes the iron(II) carbene-like structure of the adduct, which then produces the carbon monoxide complex after elimination of a water molecule. The formation of carbon monoxide, which is the only electrolysis product, also appears in the cyclic voltammogram. The anodic peak 2a, corresponding to the reoxidation of iron(II) into iron(III) is indeed shifted toward a more negative value, 2a, as it is when CO is added to the solution. 

Another recent example of the question of the formation of intermediate metal-C02 complexes in these reactions was the theoretical study by Ohnishi et al. [84] of the hydrogenation of C02 to formic acid by Ru catalysts. In the presence of water, there was no direct metal coordination of C02, but formation of adducts in which the C and O atoms of C02 interacted with the H (hydride) ligand and the H atom of H20 rfs-Ru(H)2(PMe3)3(H20)(C02). In the absence of water molecules,... 

Interstrand cross-links are unstable in conditions close to physiological conditions [57]. The bonds between platinum and the N(7) of guanine residues are cleaved spontaneously, with essentially one cleavage reaction per cross-linked duplex in either of both DNA strands (tl/2 for the cleavage reaction is about 29 h). As shown in the reaction scheme (Fig. 2), the cleavage generates monofunctional adducts which can react further to yield interstrand and intrastrand cross-links. The distorted local conformation could allow the formation of adducts which are not usually formed in double-stranded DNA containing a monofunctional adduct. An attractive hypothesis to explain the instability of the interstrand cross-links is that one of the two water molecules, in apical position with respect to the square of the platinum atom, labilises the G-Pt bond in solvolysis reaction. When the local... 

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