Bioorganometallic chemistry: biocatalytic oxidation reactions with biomimetic NAD/NADH co-factors and [Cp*Rh(bpy)H] for selective organic synthesis

The biocatalytic, regioselective hydroxylation of 2-hydroxybiphenyl to the corresponding catechol was accomplished utilizing the monooxygenase 2-hydroxybiphenyl 3-monooxygenase (HbpA). The necessary natural 1,4-dihydronicotinamde adenine dinucleotide (NADH) co-factor for this biocatalytic process was replaced by a biomimetic co-factor, N-benzyl-1,4-dihydronicotinamide, 1b. The interaction between the flavin (FAD) containing HbpA enzyme and the corresponding biomimetic NADH compound, N-benzyl-1,4-dihdronicotinamide, 1b, for hydride transfer, was shown to readily occur. The in situ recycling of the reduced NADH biomimic 1b from 1a was accomplished with [Cp*Rh(bpy)H](Cl); however, productive coupling of this regeneration reaction to the enzymatic hydroxylation reaction was not totally successful, due to a deactivation process concerning the HbpA enzyme peripheral groups; i.e., -SH or -NH₂ possibly reacting with the precatalyst, [Cp*Rh(bpy)(H₂O)](Cl)₂, and thus inhibiting the co-factor regeneration process. The deactivation mechanism was studied, and a promising strategy of derivatizing these peripheral -SH or -NH₂ groups with a polymer containing epoxide was successful in circumventing the undesired interaction between HbpA and the precatalyst. This latter strategy allowed tandem co-factor regeneration using 1a or 2a, [Cp*Rh(bpy)(H₂O)](Cl)₂, and formate ion, in conjunction with the polymer bound, FAD containing HbpA enzyme to provide the catechol product.     

A new approach to helical primary structures of four-membered rings: (P)- and (M)-tetraspiro[3.0.0.0.3.2.2.2]hexadecane

A new approach to helical primary structures of four-membered rings uses a cycloaddition of a trimethylenketeniminium salt to suitable tailored methylenecyclobutanes to assemble the desired carbon framework. The results are short and effective syntheses of (M)-trispiro[3.0.0.3.2.2]tridecane [(M)-5], and (P)- and (M)-tetraspiro[3.0.0.0.3.2.2.2]hexadecane [(P)- and (M)-24]. Unlike helices of three-membered rings, the specific rotation decreases, as the length of the helix increases.     

Extendable Cycles in Multipartite Tournaments

An n-partite tournament is an orientation of a complete n-partite graph. If D is a strongly connected n-partite (n3) tournament, then we shall prove that every partite set of D has at least one vertex which lies on a cycle C_m of each length m for such that V(C₃)V(C₄)V(C_n), where V(C_m) is the vertex set of C_m for . This result extends those of Bondy [2], Guo and Volkmann [4], Gutin [6], Moon [8], and Yeo [12].Final version received: June 9, 2003     

Cumulants are universal homomorphisms into Hausdorff groups

This is a contribution to the theory of sums of independent random variables at an algebraico-analytical level: Let Prob denote the convolution semigroup of all probability measures on with all moments finite, topologized by polynomially weighted total variation. We prove that the cumulant sequence regarded as a function from Prob into the additive topological group ofall real sequences, is universal among continuous homomorphisms from Prob into Hausdorff topological groups, in the usual sense that every other such homomorphism factorizes uniquely through . An analogous result, referring to just the first cumulants,holds for the semigroup of all probability measures with existing rth moments. In particular, there is no nontrivial continuous homomorphism from the convolution semigroup of all probability measures, topologized by the total variation metric, into any Hausdorff topological group.Mathematics Subject Classification (2000): 60B15, 60E10, 60G50     

Power-law tail distributions and nonergodicity

We establish an explicit correspondence between ergodicity breaking in a system described by power-law tail distributions and the divergence of the moments of these distributions.     

Electron delocalization in cross-conjugated p-phenylenevinylidene oligomers

The synthesis, structure, and electronic properties of a series of cross-conjugated p-phenylenevinylidene oligomers with one to four double bonds are reported. The X-ray crystal structure of the compound with two double bonds reveals a nonplanar conformation with torsion angles about the C(phenylene)-C(vinylidene) and C(phenyl)-C(vinylidene) formal single bonds of 39.5(2) degrees and 30.5(2) degrees, respectively. Admixture of quinoid character in the ground state is observed. Infrared and Raman spectroscopy do not provide a clear picture of the degree of electron delocalization in the series, since the C=C stretching mode does not adequately reflect the C=C bond order and has a local nature. In contrast, electronic spectra and electrochemical data, as well as AM1 and PPP/SCF calculations, reveal that the cross-conjugated compounds basically behave as linearly pi-conjugated systems in the sense that molecular orbitals are delocalized over the entire structure and systematically change in energy. The electronic interaction between the repeating units is, however, not very strong, which has the consequence that spatial extension of the molecular orbitals does not lead to a red shift of the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) electronic transition. This is related to the feature that the modest narrowing of the HOMO-LUMO gap with the chain length is accompanied by a relatively large reduction of electron repulsion. This finding implies that care should be taken in the use of electronic spectra for the evaluation of conjugation phenomena.     

Synthesis of enantiopure B-nor-steroids by multiple Pd-catalyzed transformations

The synthesis of the novel enantiopure B-nor-steroid 9 is described employing a combination of a Suzuki- and a Heck-reaction. As substrates the 2-bromobenzylchloride (11) and the boronic ester 16 were used; the latter was prepared from the Hajos-Wiechert ketone derivative 17 in five steps. Noteworthy, the Heck-reaction was performed under microwave irradiation, which was much superior compared to the normal thermal reaction. The purpose of the described work is the design of novel estrogens, which bind to the β-unit of the maxi K⁺-channel located on the surface of the endothelium without showing the hormonal activity of estradiol 6.     

Studying the evaporation behavior of heavy metals by thermo-desorption spectrometry

"Thermal desorption experiments" were carried out during which heavy metal evaporation was studied by on-line monitoring. This could be achieved by the use of a tubular furnace connected to a heavy metal detector, i.e. an ICP-OES (inductively coupled plasma optical emission spectrometer), by a specially designed and patented interface. The spectrograms typically had a time resolution of four different elements per minute using a conventional (sequentially operating) ICP-OES. This study shows how thermo-desorption spectrometry (TDS) can be applied to study the evaporation of high boiling substances, such as heavy metal and alkali metal compounds. The future scope of the method is discussed.