Incorporation of an Allene Unit into α‐Pinene via β‐Elimination

The two double‐bond isomers 3‐iodo‐2,6,6‐trimethylbicyclo[3.1.1]hept‐2‐ene ( 6b ) and 3‐iodo‐4,6,6‐trimethylbicyclo[3.1.1]hept‐2‐ene ( 11 ) were synthesized by reacting 2,6,6‐trimethylbicyclo[3.1.1]heptan‐3‐one ( 9 ) with hydrazine, followed by treatment with I₂ in the presence of Et₃N. Treatment of 11 with t‐BuOK as base in diglyme at 220° resulted in the formation of 9 and 6,6‐dimethyl‐4‐methylidenebicyclo[3.1.1]hept‐2‐ene ( 12 ). For the formation of 9 , the cyclic allene 7 is proposed as an intermediate. Treatment of the second isomer, 6b , with t‐BuOK at 170° gave rise to the diene 12 and the dimerization product 17 . The underlying mechanism of this transformation is discussed. On the basis of density‐functional‐theory (DFT) calculations on the allene 7 and the alkyne 15 , the formation of the latter as the intermediate was excluded.     

The elastic net algorithm and protein structure prediction

Predicting protein structures from their amino acid sequences is a problem of global optimization. Global optima (native structures) are often sought using stochastic sampling methods such as Monte Carlo or molecular dynamics, but these methods are slow. In contrast, there are fast deterministic methods that find near-optimal solutions of well-known global optimization problems such as the traveling salesman problem (TSP). But fast TSP strategies have yet to be applied to protein folding, because of fundamental differences in the two types of problems. Here, we show how protein folding can be framed in terms of the TSP, to which we apply a variation of the Durbin-Willshaw elastic net optimization strategy. We illustrate using a simple model of proteins with database-derived statistical potentials and predicted secondary structure restraints. This optimization strategy can be applied to many different models and potential functions, and can readily incorporate experimental restraint information. It is also fast; with the simple model used here, the method finds structures that are within 5-6 A all-Calpha-atom RMSD of the known native structures for 40-mers in about 8 s on a PC; 100-mers take about 20 s. The computer time tau scales as tau approximately n, where n is the number of amino acids. This method may prove to be useful for structure refinement and prediction.     

Synthesis,Structure and Chemistry of a Twisted Olefinic Bis-didentate Proligand: 5,5′-Bi-5H-cyclopenta[2,1-b : 3,4-b′]dipyridinylidene

The elusive chiral twisted alkene, 5,5′-bi-5H-cyclopenta[2,1-b : 3,4-b′]dipyridinylidene, known also as 9,9′-bi-4,5-diazafluorenylidene (BDAF), has been prepared in racemic form from 9-bromo-4,5-diazafluorene and from 9,9′-bi-4,5-diazafluorenyl and fully characterised. X-Ray measurements show that there is a twist of 37.8° about the double bond between the 4,5-diazafluorenylidene units. A 1 : 1 charge-transfer compound with 7,7,8,8-tetracyanoquinodimethane (TCNQ) contains an unusual packing arrangement which is centred around the formation of spiral stacks. Each BDAF molecule contributes one 4,5-diazofluorenylidene unit to the backbone of the stack, while the second half is involved in hydrogen-bonding interactions and additional stacking with TCNQ. Examples of complexes containing the axially symmetric tetradentate ligand binding to one and to two metal ions, [M(bdaf)Cl₂] and [(MCl₂)₂(bdaf)] (M=Co, Ni, Zn), are reported.     

Optical absorption of isotopically enriched Li2B4O7 single crystals irradiated by thermal neutrons

Induced absorption spectra in the range 200–900 nm at 77 and 290 K for Li₂B₄O₇ single crystals, isotopically Li and B enriched are presented after irradiation of these crystals by thermal neutrons with fluence 1.8×10¹⁶ cm⁻². The dependence of induced absorption spectra on the isotope composition was revealed: for ⁶Li₂¹⁰B₄O₇ and ⁷Li₂¹⁰B₄O₇ crystals intensive band in the region of 280–294 nm was observed. Under substitution of ⁷Li isotope by ⁶Li in the lithium tetraborate lattice no changes in the absorption spectra were observed. The nuclear reaction ¹⁰B(n,)⁷Li is proposed to be the main mechanism of formation of the radiation defects.     

Explicit horizontal open books on some Seifert fibered 3-manifolds

We describe explicit horizontal open books on some Seifert fibered 3-manifolds. We show that the contact structures compatible with these horizontal open books are Stein fillable and horizontal as well. Moreover we draw surgery diagrams for some of these contact structures.     

Generation of spatial solitons using non-linear guided modes

We investigate how two-dimensional spatial optical solitons can be generated in a non-linear Kerr medium using the non-linear guided modes of a weakly-guiding slab waveguide with a linear core and a non-linear cladding as the source of excitation. Symmetric, antisymmetric and asymmetric non-linear modes are considered, from which we determine the parameters of single solitons, oscillating two-soliton bound states, and two repelling solitons, respectively. Both the beam propagation method and inverse scattering transform are used.     

Mixed norm estimates for certain generalized Radon transforms

We obtain essentially optimal local mixed norm inequalities for certain generalized Radon transforms defined by integration over curves.

     

Novel antifoam for fermentation processes: fluorocarbon-hydrocarbon hybrid unsymmetrical bolaform surfactant

As foaming appears as a problem in chemical and fermentation processes that inhibits reactor performance, the eminence of a novel fluorocarbon-hydrocarbon unsymmetrical bolaform (FHUB: OH(CH2)11N+(C2H4)2(CH2)2(CF2)5CF3 I-) surfactant as an antifoaming agent as well as a foam-reducing agent was investigated and compared with other surfactants and a commercial antifoaming agent. The surface elasticity of FHUB was determined as 4 mN/m, indicating its high potential on thinning of the foam film. The interactions between FHUB and the microoganism were investigated in a model fermentation process related with an enzyme production by recombinant Escherichia coli, in V = 3.0 dm3 bioreactor systems with V(R) = 1.65 dm3 working volume at air inlet rate of Q(o)/V(R) = 0.5 dm3 dm(-3) min(-1) and agitation rate of N = 500 min(-1) oxygen transfer conditions, at T = 37 degrees C, pH(o) = 7.2, and C(FHUB) = 0 and 0.1 mM, in a glucose-based defined medium. As FHUB did not influence the metabolism, specific enzyme activity values obtained with and without FHUB were close to each other; however, because of the slight decrease in oxygen transfer coefficient, slightly lower volumetric enzyme activity and cell concentrations were obtained. However, when FHUB is compared with widely used silicon oil based Antifoam A, with the use of the FHUB, higher physical oxygen transfer coefficient (K(L)a) values are obtained. Moreover, as the amount required for the foam control is very low, minute changes in the working volume of the bioreactor were obtained indicating the high potential of the use of FHUB as an antifoaming agent as well as a foam-reducing agent.     

The Stability in Two Measures of Axially Compressed Elastic Cylinders

Two nonnegative integral functionals are taken as measures of deviation of the basic solution from a perturbed one. Sufficient conditions of stability in selected measures are obtained for the zero solution of the linearized equation of motion for isotropic elastic bodies acted upon by "dead" surface forces. The method of integral estimates is used to determine the critical values of the loading parameters. Such values are found for an axially compressed cylindrical body made of a standard material of the second order under various end conditions     

Effect of junction constraints on rubber elasticity in multiaxial states of stress

The strains obtained in an amorphous polymer network subject to multiaxial states of stress are calculated according to a recent molecular theory which takes account of constraints on junctions in real networks. Experimental measurements for biaxial states of stress, for pure shear superposed on tension, and for combined torsion and simple extension, are seen to compare favorably with the predictions of the theory.