Transition-metal mediated heteroatom removal by reactions of FeL(+) [L=O, C 4H 6, c-C 5H 6, c-C 5H 5, C 6H 6, C 5H 4(=CH 2)] with furan, thiophene, and pyrrole in the gas phase.

Reactions of Fe(+) and FeL(+) [L=O, C4H6, c-C5H6, C5H5, C6H6, C5H4(=CH2)] with thiophene, furan, and pyrrole in the gas phase by using Fourier transform mass spectrometry are described. Fe(+), Fe(C5H5)(+), and FeC6H 6 (+) yield exclusive rapid adduct formation with thiophene, furan, and pyrrole. In addition, the iron-diene complexes [FeC4H 6 (+) and Fe(c-C5H6)(+)], as well as FeC5H4(=CH2)(+) and FeO(+), are quite reactive. The most intriguing reaction is the predominant direct extrusion of CO from furan by FeC4H6 (+), Fe(c-C5H6)(+), and FeC5H4(=CH2)(+). In addition, FeC4H 6 (+) and Fe(c-C5H6)(+) cause minor amounts of HCN extrusion from pyrrole. Mechanisms are presented for these CO and HCN extrusion reactions. The absence of CS elimination from thiophene may be due to the higher energy requirements than those for CO extrusion from furan or HCN extrusion from pyrrole. The dominant reaction channel for reaction of Fe(c-C5H6)(+) with pyrrole and thiophene is hydrogen-atom displacement, which implies D(O)(Fa(N5H5)(+)-C4H4X)>D(O)(Fe(C5H5)(+)-H)=46±5 kcal mol(-1). D(O)(Fe(+)-C4H4S) and D(O)(Fe(+)-C4H5N)=D(O)(Fe(+)-C4H6)=48±5 kcal mol(-1). Finally, 55±5 kcal mol(-1)=D(O)(Fe(+)-C6H6)>D(O)(Fe(+)-C4H4O)>D(O)(Fe(+)-C2H4)=39.9±1.4 kcal mol(-1). FeO(+) reacts rapidly with thiophene, furan, and pyrrole to yield initial loss of CO followed by additional neutral losses. D(O)(Fe(+)-CS)>D(O)(Fe(+)-C4H4S)≈48±5 kcal mol(-1) and D(O)(Fe(+)-C4H5N)≈48±5 kcal mol(-1)>D(O)(Fe(+)-HCN)>D(O)(Fe(+)-C2H4)=39.9±1.4 kcal mil(-1).

Elucidating the structures of isomeric silylenium ions (SiC3H 9 (+) , SiC 4H 11 (+) , SiC 5H 13 (+) ) by using specific ion/molecule reactions.

Specific ion/molecule reactions are demonstrated that distinguish the structures of the following isomeric organosilylenium ions: Si(CH3) 3 (+) and SiH(CH3)(C2H5)(+); Si(CH3)2(C2H5)(+) and SiH(C2H5) 2 (+) ; and Si(CH3)2(i-C3H7)(+), Si(CH3)2(n-C3H7)(+), Si(CH3)(C2H5) 2 (+) , and Si(CH3)3(π-C2H4)(+). Both methanol and isotopically labeled ethene yield structure-specific reactions with these ions. Methanol reacts with alkylsilylenium ions by competitive elimination of a corresponding alkane or dehydrogenation and yields a methoxysilylenium ion. Isotopically labeled ethene reacts specifically with alkylsilylenium ions containing a two-carbon or larger alkyl substituent by displacement of the corresponding olefin and yields an ethylsilylenium ion. Methanol reactions were found to be efficient for all systems, whereas isotopically labeled ethene reaction efficiencies were quite variable, with dialkylsilylenium ions reacting rapidly and trialkylsilylenium ions reacting much more slowly. Mechanisms for these reactions and differences in the kinetics are discussed.

Arginine synthesis and nitrogen excretion in the myxomycete Physarum polycephalum.

The nitrogen excretory metabolism of the myxomycete Physarum polycephalum was studied. When cultured in partially defined broth medium or on agar, the principal excretory product was ammonia nitrogen. A small, variable quantity of urea was excreted in liquid culture. No uric acid or other purines were detected in the cultures. When microplasmodia were incubated with sodium [14C]bicarbonate, radioisotope was incorporated into citrulline, arginine, and urea. Incubation with L-[carbamoyl-14C]citrulline yielded labelled arginine, urea, and CO2. Substantial urease activity was found in extracts of the microplasmodia. These results, in conjunction with the lack of an absolute nutritional requirement for arginine, provide evidence that Physarum has a functional arginine biosynthetic pathway, an arginase, and a urease.