Supramolecular cluster catalysis: facts and problems

By checking the chemistry underlying the concept of “supramolecular cluster catalysis” we identified two major errors in our publications related to this topic, which are essentially due to contamination problems. (1) The conversion of the “closed” cluster cation [H₃Ru₃(C₆H₆)(C₆Me₆)₂(O)]⁺ (1) into the “open” cluster cation [H₂Ru₃(C₆H₆)(C₆Me₆)₂(O)(OH)]⁺ (2), which we had ascribed to a reaction with water in the presence of ethylbenzene is simply an oxidation reaction which occurs in the presence of air. (2) The higher catalytic activity observed with ethylbenzene, which we had erroneously attributed to the “open” cluster cation [H₂Ru₃(C₆H₆)(C₆Me₆)₂(O)(OH)]⁺ (2), was due to the formation of RuO₂ · nH₂O, caused by a hydroperoxide contamination present in ethylbenzene.     

Tunneling and coupled motion in the Escherichia coli dihydrofolate reductase catalysis

H-transfer was studied in the complex kinetic cascade of dihydrofolate reductase. Intrinsic kinetic isotope effects, their temperature dependence, and other temperature-dependent parameters indicated H-tunneling, but no 1 degrees to 2 degrees coupled motion. The data also suggested environmentally coupled tunneling and commitment to catalysis on pre-steady-state isotope effects.     

Reductive dehydroxylation of allyl alcohols by IspH protein

The biosynthesis of natural products is a treasure trove of unusual reaction mechanisms. This Minireview summarizes recent work on the structure and mechanism of IspH protein, which catalyzes the reductive dehydroxylation of an allyl alcohol in a biosynthetic pathway leading to isoprenoid precursors.     

Spectroscopic studies of the corrinoid/iron-sulfur protein from Moorella thermoacetica

Methyl transfer reactions are important in a number of biochemical pathways. An important class of methyltransferases uses the cobalt cofactor cobalamin, which receives a methyl group from an appropriate methyl donor protein to form an intermediate organometallic methyl-Co bond that subsequently is cleaved by a methyl acceptor. Control of the axial ligation state of cobalamin influences both the mode (i.e., homolytic vs heterolytic) and the rate of Co-C bond cleavage. Here we have studied the axial ligation of a corrinoid iron-sulfur protein (CFeSP) that plays a key role in energy generation and cell carbon synthesis by anaerobic microbes, such as methanogenic archaea and acetogenic bacteria. This protein accepts a methyl group from methyltetrahydrofolate forming Me-Co(3+)CFeSP that then donates a methyl cation (Me) from Me-Co(3+)CFeSP to a nickel site on acetyl-CoA synthase. To unambiguously establish the binding scheme of the corrinoid cofactor in the CFeSP, we have combined resonance Raman, magnetic circular dichroism, and EPR spectroscopic methods with computational chemistry. Our results clearly demonstrate that the Me-Co3+ and Co2+ states of the CFeSP have an axial water ligand like the free MeCbi+ and Co(2+)Cbi+ cofactors; however, the Co-OH2 bond length is lengthened by about 0.2 angstroms for the protein-bound cofactor. Elongation of the Co-OH2 bond of the CFeSP-bound cofactor is proposed to make the cobalt center more "Co1+-like", a requirement to facilitate heterolytic Co-C bond cleavage.     

Synthesis and reactivity of a new octanuclear iron-sulfur nitrosyl cluster

The synthesis and spectroscopic properties of (PPN)2[Fe8S6(NO)8] as well as its reactivity toward sulfur are reported.     

Key players and their role during mitochondrial iron-sulfur cluster biosynthesis

Iron-sulfur clusters are multifaceted iron-containing cofactors coordinated and utilized by numerous proteins in nearly all biological systems. Fe-S-cluster-containing proteins help direct pathways essential for cell viability and participate in biological applications ranging from nucleotide biosynthesis and stability, protein translation, enzyme catalysis, and mitochondrial metabolism. Fe-S-containing proteins function by utilizing the unique electronic and chemical properties inherent in the Fe containing cofactor. Fe-S clusters are constructed of inorganic iron and sulfide arranged in a distinct caged structural makeup ranging from [Fe(2) -S(2) ], [Fe(3) -S(4) ], [Fe(4) -S(4) ], up to [Fe(8) -S(8) ] clusters. In eukaryotes, cluster activity is controlled in part at the assembly level and the major pathway for cluster production exists within the mitochondria. Recent insight into the pathway of mitochondrial cluster assembly has come from new in vivo and in vitro reports that provided direct insight into how all protein partners within the assembly pathway interact. However, we are only just beginning to understand the role of each protein within this complex pageant that is mitochondrial Fe-S cluster assembly. In this report we present results, using the yeast model for mitochondrial assembly, to describe the molecular details of how important proteins in the pathway coordinate for cluster assembly.     

大肠杆菌HB101感受态的热化学研究

利用LKB-2277生物活性检测系统,测定了在生理盐水中,采用氯化钙法建立大肠杆菌感受态过程中的代谢热输出。生理盐水中大肠杆菌及其感受态进行内源代谢的热化学方程满足:P=K~c+A,dc/dP~0=K'c^0,氯化钙处理后,K与P~0均增大,说明内源代谢活性增强,这与大肠杆菌感受态建立过程中一系列生理生化活性的调整是一致的,表明大肠杆菌感受态的建立很可能有其内在的调节机制,而不完全是人工诱导的。     

大肠杆菌中高丝氨酸琥珀酰基转移酶的同源模建与对接研究

利用同源模建和分子动力学模拟方法,模建了大肠杆菌中高丝氨酸琥珀酰基转移酶的三维结构.分析了活性位点的组成,从结构上佐证了Cys142而不是Lys47为亲核进攻的残基,并通过与其天然底物琥珀酰-辅酶A的对接研究,从理论上确认了对复合物形成起到重要作用的氨基酸残基.     

Bimetallic cluster complexes: synthesis, structures and applications to catalysis

A brief history of the seminal discoveries in the field of bimetallic cluster complexes with their structures is presented. A review of some recent studies of palladium and platinum-ruthenium cluster complexes is concluded with a discussion of applications of these complexes in the area of homogeneous hydrogenation catalysis of alkynes.     

Synthesis and catalysis of a silica-supported cobalt carbonyl cluster

The supported metal cluster, Co₄(CO)₈(μ₂-CO)₂(μ₄-PC₆H₄)/(SiO₂) (2), which decomposed at 290°C, was synthesized. The cobalt and phosphorus contents were 10.51 and 2.64%, respectively. The IR spectrum of 2 exhibits absorptions at 2010 and 1840 cm⁻¹ assigned to the terminal carbonyl and bridged carbonyl, respectively. The effects of the reaction conditions and the structure of olefins on the hydroformylation using 2 have been investigated. Nearly 100% conversion and selectivity could be reached by hydroformylation of 1-hexene under conditions of 130°C, 40 kg/cm², H₂/CO = 1, for 6 h. The rate order of hydroformylation of olefins was as follows: 1-hexene > cyclohexene > diisobutene > styrene. The catalytic activity was kept almost constant after ten-time repeated use (240 h).     

L-Arabinose transport and the L-arabinose binding protein of Escherichia coli.

The active accumulation of L-arabinose by arabinose induced cultures of Escherichia coli is mediated by 2 independent transport mechanisms. One, specified by the gene locus araE, is membrane bound and possesses a relatively "low affinity". The other, specified in part by the genetic locus araF, contains as a functional component the L-arabinose binding protein and functions with a "high affinity" for the substrate. The L-arabinose binding protein has been purified, partially characterized, crystallized, and sequenced.     

Artificial metalloenzymes for enantioselective catalysis: the phenomenon of protein accelerated catalysis

We report on the phenomenon of protein-accelerated catalysis in the field of artificial metalloenzymes based on the non-covalent incorporation of biotinylated rhodium-diphosphine complexes in (strept)avidin as host proteins. By incrementally varying the [Rh(COD)(Biot-1)]⁺ vs. (strept)avidin ratio, we show that the enantiomeric excess of the produced acetamidoalanine decreases slowly. This suggests that the catalyst inside (strept)avidin is more active than the catalyst outside the host protein. Both avidin and streptavidin display protein-accelerated catalysis as the protein embedded catalyst display 12.0- and 3.0-fold acceleration over the background reaction with a catalyst devoid of protein. Thus, these artificial metalloenzymes display an increase both in activity and in selectivity for the reduction of acetamidoacrylic acid.     

Some relationships between metal cluster chemistry and heterogeneous catalysis

Some analogies between organometallic chemistry and surface chemistry are developed. Comparison of Lewis acid promoted CO insertion and Zn²⁺ promotion of oxygenates in the hydroformylation of C₂H₄ over Rh, suggests that Zn²⁺ interaction with Rh-CO may promote migratory insertion which favors hydroformylation over hydrogenation of alkenes. CCO, which is observed in metal clusters should be a viable surface species. Finally, parallels can be found between the positioning of oxygen in clusters and on surfaces.     

Base-promoted ruthenium carbonyl cluster complexes: From fundamental reactions to catalysis

An attempt to establish a link between the rich chemistry of ruthenium carbonyl clusters doped by nucleophilic anions, and the known effect of promoters in some ruthenium-based catalytic processes.