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The bond dissociation energy for loss of C2H4 from Fe(CO)3(C2H4)2, produced by the reaction of C2H4 + Fe(CO)3(C2H4), has been determined as 21.3 ± 2.0 kcal/mol. An estimate is made for a lower limit for the bond dissociation energy of Fe(CO)4(C2H4), which can be formed by reaction of CO + Fe(CO)3(C2H4) or Fe(CO)4 + C2H4 with rate constants of (4.3 ± 0.8) × 10-12 and (1.7 ± 0.2) × 10-13 cm3/(molecule s) at 24 °C, respectively. The values for these bond dissociation energies are compared with those determined in prior studies of these systems. A new compound with infrared absorptions at 2147, 2091, and 2068 cm-1 is best assigned as Fe(CO)3(C2F4)2. A rate constant of (5.4 ± 1.7) × 10-12 cm3/(molecule s) at 24 °C is reported for the reaction of C2F4 with Fe(CO)3(C2F4) to form Fe(CO)3(C2F4)2. Fe(CO)4(C2F4) can be formed by reaction of C2F4 and Fe(CO)4, with a rate constant of (1.8 ± 0.4) × 10-14 cm3/(molecule s) at 24 °C. Infrared absorptions observed at 2135, 2074, and 2043 cm-1 are assigned to this species. ...

Time-resolved IR spectroscopy has been used to study the oxidative addition of H2 to Fe(CO)4 and its reverse reaction, the reductive elimination of H2 from Fe(CO)4H2, in the gas phase. The rate con...

The Escherichia coli adenine DNA glycosylase, MutY, plays an important role in the maintenance of genomic stability by catalyzing the removal of adenine opposite 8-oxo-7,8-dihydroguanine or guanine in duplex DNA. Although the x-ray crystal structure of the catalytic domain of MutY revealed a mechanism for catalysis of the glycosyl bond, it appeared that several opportunistically positioned lysine side chains could participate in a secondary beta-elimination reaction. In this investigation, it is established via site-directed mutagenesis and the determination of a 1.35-A structure of MutY in complex with adenine that the abasic site (apurinic/apyrimidinic) lyase activity is alternatively regulated by two lysines, Lys142 and Lys20. Analyses of the crystallographic structure also suggest a role for Glu161 in the apurinic/apyrimidinic lyase chemistry. The beta-elimination reaction is structurally and chemically uncoupled from the initial glycosyl bond scission, indicating that this reaction occurs as a consequence of active site plasticity and slow dissociation of the product complex. MutY with either the K142A or K20A mutation still catalyzes beta and beta-delta elimination reactions, and both mutants can be trapped as covalent enzyme-DNA intermediates by chemical reduction. The trapping was observed to occur both pre- and post-phosphodiester bond scission, establishing that both of these intermediates have significant half-lives. Thus, the final spectrum of DNA products generated reflects the outcome of a delicate balance of closely related equilibrium constants.