Lead and thallium tetrakis(imidazolyl)borates: modifying structure by varying metal and anion

We are using the coordinating anions tetrakis(imidazolyl)borate and tetrakis(4-methylimidazolyl)borate to construct new metal-organic framework structures. In this report, we are exploring materials similar in composition to the previously reported layered network structure Pb[B(Im)(4)](NO(3))(nH(2)O). The metal in this compound can be replaced with isoelectronic Tl(I), affording Tl[B(Im)(4)], and the borate can be modified by using 4-methylimidazole, resulting in Pb[B(4-MeIm)(4)](NO(3)) and Tl[B(4-MeIm)(4)]. Like the parent Pb[B(Im)(4)](NO(3))(nH(2)O), Tl[B(Im)(4)] and Tl[B(4-MeIm)(4)] are layered network structures but both lack anions or solvent molecules in the interlayer spacing. The material Pb[B(4-MeIm)(4)](NO(3)), however, exhibits a 3D network structure that lacks an open topology, resulting from the increased stereochemical activity (greater steric bulk toward other ligands) of the 4-methylimidazole ring. Both of the Tl(I) solids display longer M-N bonds than observed in the analogous Pb(II) compounds; these lengths account for the decreased effect of the stereochemical activity of the 4-methylimidazole ring in Tl[B(4-MeIm)(4)].     

Enzymes in preparative mono- and oligo-saccharide synthesis

This review covers advances/developments in the use of enzymes in synthetic mono-/oligo-saccharide chemistry published in the literature between January 2001 and June 2003. Particular attention is paid to the use of aldolases, ketolases, glycosidases, glycosynthases, lipases, esterases and coupled multi-enzyme biotransformations and 132 references are cited.     

Fine structure in proton emission from 145Tm discovered with digital signal processing

Fine structure in proton emission from the 3.1(3) mus activity of 145Tm was discovered by using a novel technique of digital processing of overlapping recoil implantation and decay signals. Proton transitions to the ground state of 144Er and to its first excited 2(+) state at 0.33(1) MeV with a branching ratio I(p)(2(+))=9.6+/-1.5% were observed. The structure of the 145Tm wave function and the emission process were analyzed by using particle-core vibration coupling models.     

Directed denaturation: room temperature and stoichiometric unfolding of cytochrome C by a metalloporphyrin dimer

Using circular dichroism, UV-vis, and trypsin proteolysis, we have shown how a metalloporphyrin dimer induces the unfolding of a protein, cytochrome c, under physiologically relevant conditions and accelerates its rate of proteolytic degradation.     

Redox modulation of benzene triimides and diimides via noncovalent interactions

[reaction: see text] Mellitic triimides undergo three sequential one-electron reduction processes whose potentials are significantly lowered in the presence of alkyl thioureas. The two sequential reductions of benzene diimides are similarly stabilized. Calculation of the relative free energy change between the different electronic states of the imide acceptors and their corresponding alkyl thiourea complexes indicates dramatic increases in hydrogen bond strength with increasing acceptor charge density.     

Sets of Type (a, b) From Subgroups of ΓL(1, pR)

In this paper k-sets of type (a, b) with respect to hyperplanes are constructed in finite projective spaces using powers of Singer cycles. These are then used to construct further examples of sets of type (a, b) using various disjoint sets. The parameters of the associated strongly regular graphs are also calculated. The construction technique is then related to work of Foulser and Kallaher classifying rank three subgroups of AL(1, p ^R). It is shown that the sets of type (a, b) arising from the Foulser and Kallaher construction in the case of projective spaces are isomorphic to some of those constructed in the present paper.     

Abelian Subgroup Separability of Haken 3-Manifolds and Closed Hyperbolic n-Orbifolds

We prove that abelian subgroups of fundamental groups of Haken3-manifolds and closed hyperbolic n-orbifolds are separable.2000 Mathematical Subject Classification: 20E26, 51M10, 57M05.     

Shifted identical bands: A new phenomenon

The levels in ¹⁶²Gd were identified in spontaneous fission studies. Its transition energies are remarkably similar to those in ¹⁶⁰Gd. From that work, an analysis of yrast bands in even-even proton to neutron-rich Ba to Pb nuclei led to the discovery of a new phenomenon, shifted identical bands (SIB). SIBs are yrast bands in neighboring nuclei (a, b) with moments of inertia which are identical when shifted by a constant amount κ, so J _1a (1+κ)=J _1b , from 2⁺ to 8⁺ and higher to 16⁺. Out of over 700 comparisons, 55 SIBs were found from stable to the most neutron-rich Ce-W nuclei with $\left| {\bar k} \right|$ between 1.5% and 13%, where the spread in κ is less than ±1%, and only four identical bands ( $\bar k \cong 0$ ). As examples, we found for ¹⁵⁸Sm-¹⁶⁰Gd, $\bar k = \left( { - 3.2_{ - 0.2}^{ + 0.1} } \right)\%$ (where the ± is the total spread in κ from ?3.1 to ?3.4); ¹⁵⁶Nd-¹⁶⁰Gd, (?10.6 _?0.2 ^+0.4 )%; ¹⁵⁸Sm-¹⁶⁰Sm, (3.4 _?0.3 ^+0.5 )%. The J ₁ values were fitted to a variable moment of inertia model with parameters J ₀ and C whose values correlate with the SIB J ₁ values. The SIBs are not correlated either with deformation or with the N _p N _n product of the IBA model.     

Macrocyclization and molecular interlocking via Mitsunobu alkylation: highlighting the role of C-H...O interactions in templating

[reaction: see text] A series of diimide-based macrocycles have been prepared using Mitsunobu-mediated alkylation as the macrocyclization step. These macrocycles could not be incorporated into [2]catenanes using previously established building blocks and coupling methodology. However, when one of the macrocycle syntheses was conducted in the presence of a dinaphtho crown ether, catenane formation was achieved. This result is discussed in terms of the ability of the components to establish intermolecular C-H...O hydrogen-bonding contacts.