Oxoanionic or sulfur lone pair attack? The difference in reactivity of hydrogensulfite anion and neutral dimethylsulfite towards [Bu4N]2[MoO2(S2C2)CN)2)2] in the model reductive half reaction of sulfite oxidase

pH dependent reactivity differences of dimethylsulfite towards the title complex 1 demonstrate the crucial need of oxo-anionic coordination of sulfite to the molybdenum centre of 1 in the model reductive half reaction of sulfite oxidase.     

Archimedean Synthesis and Magic Numbers: "Sizing" Giant Molybdenum-Oxide-Based Molecular Spheres of the Keplerate Type

Pythagorean harmony can be found in the spherical polyoxometalate clusters described here (see illustration for an example of a structure), since there are interesting relationships between the so-called magic numbers (12, 32, 42, 72, 132) relevant for spherical viruses and the number of the building blocks in the cluster. The size of these Keplerate clusters can be tailored by varying the type of connections between the pentagons by means of different spacers.     

K X-ray emission spectra from ν-Al2O3

Summary η-Al₂O₃ sample was bombarded with 12.5 keV electron.K X-ray spectra of this sample were compared with those of pure Al and α-Al₂O₃.     

Isovalent and mixed-valent diruthenium complexes [(acac)2RuII (-bpytz)RuII(acac)2] and [(acac)2RuII(-bpytz)RuIII(acac)2](ClO4) (acac = acetylacetonate and bpytz = 3,6-bis(3,5-dimethylpyrazolyl)-1,2,4,5-tetrazine): synthesis, spectroelectrochemical, and epr investigation

The title compounds involving the structurally characterized bridging ligand bpytz were characterized, showing very strong electrochemical stabilization of the mixed-valent RuIIRuIII state (Kc = 10(13.9)) but no detectable (epsilon < 20 M(-1) cm(-1)) intervalence charge-transfer band in the infrared region. In situ reduction of the neutral precursor produces a diruthenium(II) complex of the bpytz radical anion according to EPR spectroscopy, whereas oxidation of the mixed-valent form leads to a diruthenium(III) species.     

A linear worst-case lower bound on the number of holes inside regions visible due to multiple diffuse reflections

It is known that the region V(s) of a simple polygon P, directly visible (illuminable) from an internal point s, is simply connected. Aronov et al. [2] established that the region V₁(s) of a simple polygon visible from an internal point s due to at most one diffuse reflection on the boundary of the polygon P, is also simply connected. In this paper we establish that the region V₂(s), visible from s due to at most two diffuse reflections may be multiply connected; we demonstrate the construction of an n-sided simple polygon with a point s inside it so that the region of P visible from s after at most two diffuse reflections is multiply connected. We also show that V₃(s), the region of P visible from s after at most three diffuse reflections, can have (n) holes.A part of this work was done when this author was visiting the University of Miami, Coral Gables, Florida, USA.     

On the nucleon self-energy in nuclear matter

We consider the nucleon self-energy in nuclear matter in the absence of Pauli blocking. It is evaluated using the partial-wave analysis of scattering data. Our results are compared with that of a realistic calculation to estimate the effect of this blocking. It is also possible to use our results as a check on the realistic calculations.PACS: 21.30.-x Nuclear forces - 21.65. + f Nuclear matter     

Force-extension behavior of folding polymers

The elastic response of flexible polymers made of elements which can be either folded or unfolded, having different lengths in these two states, is discussed. These situations are common for biopolymers as a result of folding interactions intrinsic to the monomers, or as a result of binding of other smaller molecules along the polymer length. Using simple flexible-chain models, we show that even when the energy ε associated with maintaining the folded state is comparable to k _B T, the elastic response of such a chain can mimic usual polymer linear elasticity, but with a force scale enhanced above that expected from the flexibility of the chain backbone. We discuss recent experiments on single-stranded DNA, chromatin fiber and double-stranded DNA with proteins weakly absorbed along its length which show this effect. Effects of polymer semiflexiblity and torsional stiffness relevant to experiments on proteins binding to dsDNA are analyzed. We finally discuss the competition between electrostatic self-repulsion and folding interactions responsible for the complex elastic response of single-stranded DNA. Received 7 August 2002 and Received in final form 7 March 2003 / Published online: 15 April 2003 RID="a" ID="a"e-mail: jmarko@uic.edu     

Chelation-control in nucleophilic addition to Cr(CO)3-complexed aryl aldehydes

One or more methoxy groups on the benzylic carbon at the ortho-position of tricarbonylchromium-complexed aryl aldehydes (2, 3 or 4) permit chelation-controlled addition of nucleophiles to the carbonyl function in the presence of Lewis acids. In the absence of a Lewis acid additive, a complementary set of diastereomeric products are obtained.     

Left-right model of Quark and Lepton masses without a scalar bidoublet

We propose a left-right model of quarks and leptons based on the gauge group SU(3)(C)xSU(2)(L)xSU(2)(R)xU(1)(B-L), where the scalar sector consists of only two doublets: (1,2,1,1) and (1,1,2,1). As a result, any fermion mass, whether it be Majorana or Dirac, must come from dimension-five operators. This allows us to have a common view of quark and lepton masses, including the smallness of Majorana neutrino masses as the consequence of a double seesaw mechanism.     

Electron beam irradiation induced changes in liquid-crystal compound 5CB

Electron beam irradiation studies on liquid crystal material 5CB have been carried out at a temperature where the compound exists in the isotropic liquid phase. In situ time-resolved spectroscopic characterization was carried out during the irradiation. Three different transients were observed during the 2-μs electron pulse. After about 50 μs, only one transient species was found to be present, which has an absorption peak at 360 nm. Radiolysed sample exhibits a broad absorption at ∼400 nm. The dielectric measurements show that even a low level of irradiation results in a dramatic increase in the component of dielectric permittivity normal to the long axes of the molecules ε_⊥^′, and a corresponding decrease in the dielectric anisotropy (Δε′=ε_∥^′−ε_⊥^′ ). These studies show that 5CB is prone to substantial radiation damage on exposure to the beam of high-energy electrons.