Reaction of dimethoxycarbene-DMAD zwitterion with 1,2-diones and anhydrides: a novel synthesis of highly substituted dihydrofurans and spirodihydrofurans

The zwitterion formed by the reaction of dimethoxycarbene and DMAD adds efficiently to one of the carbonyl groups of 1,2-dicarbonyl compounds and anhydrides to generate dihydrofurans and spirodihydrofurans in good yields. In many cases, the carbene inserts into the C-C bond of the dione to yield masked vicinal tricarbonyl systems.     

Supramolecular Packing Drives Morphological Transitions of Charged Surfactant Micelles

The shape and size of self-assembled structures upon local organization of their molecular building blocks are hard to predict in the presence of long-range interactions. Combining small-angle X-ray/neutron scattering data, theoretical modelling, and computer simulations, sodium dodecyl sulfate (SDS), over a broad range of concentrations and ionic strengths, was investigated. Computer simulations indicate that micellar shape changes are associated with different binding of the counterions. By employing a toy model based on point charges on a surface, and comparing it to experiments and simulations, it is demonstrated that the observed morphological changes are caused by symmetry breaking of the irreducible building blocks, with the formation of transient surfactant dimers mediated by the counterions that promote the stabilization of cylindrical instead of spherical micelles. The present model is of general applicability and can be extended to all systems controlled by the presence of mobile charges.     

Classical gauge theories as dynamical systems—Regularity and chaos

In this review we present the salient features of dynamical chaos in classical gauge theories with spatially homogeneous fields. The chaotic behaviour displayed by both abelian and non-abelian gauge theories and the effect of the Higgs term in both cases are discussed. The role of the Chern-Simons term in these theories is examined in detail. Whereas, in the abelian case, the pure Chern-Simons-Higgs system is integrable, addition of the Maxwell term renders the system chaotic. In contrast, the non-abelian Chern-Simons-Higgs system is chaotic both in the presence and the absence of the Yang-Mills term. We support our conclusions with numerical studies on plots of phase trajectories and Lyapunov exponents. Analytical tests of integrability such as the Painlevé criterion are carried out for these theories. The role of the various terms in the Hamiltonians for the abelian Higgs, Yang-Mills-Higgs and Yang-Mills-Chern-Simons-Higgs systems with spatially homogeneous fields, in determining the nature of order-disorder transitions is highlighted, and the effects are shown to be counter-intuitive in the last-named system.     

Structural examination of ring-closing metathesis-derived 15-member macrocycles as Grb2 SH2 domain-binding tetrapeptide mimetics

Ring-closing metathesis (RCM) was employed to join carboxy-terminal alkenyl glycine side chains together with vinyl- and allyl-functionality appended to the beta-methylene of amino-terminal phosphotyrosyl (pTyr) mimetics. This required the synthesis of a variety of new pTyr mimetics, including a novel aza-containing analogue. Many of the resulting 15-member macrocyclic tetrapeptide mimetics exhibited low nanomolar Grb2 SH2 domain-binding affinities in spite of the fact that differing ring junction stereochemistries and geometries of the RCM-derived double bond were employed. The finding that significant latitude exists in the structural requirements for ring closure may facilitate the development of therapeutically relevant macrocyle-based Grb2 SH2 domain-binding antagonists. The synthetic approaches used in this study may also find application to peptide mimetics directed at other biological targets.     

Molecular interactions in β-alanine-water-methanol solutions at 308.15 K on volumetric, viscometeric, and acoustic data

The density, viscosity and ultrasonic velocity for β-alanine solutions in aqueous and aqueous methanol medium at different concentrations has been determined at 308.15 K. The experimentally obtained data were used to evaluate the apparent molal volume and apparent molal adiabatic compressibility. The related thermodynamic parameters like partial molal volume as well as partial molal adiabatic compressibility at infinite dilution along with their corresponding constants S _v and S _k , respectively, give an insight to the nature of molecular interactions. The viscosity coefficient has also been calculated using Jones-Dole equation.     

Doping and bond length contributions to Mn K-edge shift in La1 ? xSrxMnO3 (x=0?0.7) and their correlation with electrical transport properties

The room temperature experimental Mn K-edge X-ray absorption spectra of La_{1 − x} Sr _x MnO₃ (x = 0−0.7) are compared with the band structure calculations using spin polarized density functional theory. It is explicitly shown that the observed shift in the energy of Mn K-edge on substitution of divalent Sr on trivalent La sites corresponds to the shift in the center of gravity of the unoccupied Mn 4p-band contributing to the Mn K-absorption edge region. This correspondence is then used to separate the doping and size contributions to the edge shift due to variation in the number of electrons in valence band and Mn-O bond lengths, respectively, when Sr is doped into LaMnO₃. Such separation is helpful to find the localization behaviour of charge carriers and to understand the observed transport properties of these compounds.      

Synthesis and characterisation of immunogens for the production of antibodies against small hydrophobic molecules with biosignature properties

In the present study, five different classes of small hydrophobic molecular targets, atypical for antibody generation, were structurally modified in order to introduce suitable reactive functionalities and/or spacers which allow covalent coupling to a carrier protein resulting in a stable carrier-hapten complex. These targets were chosen to serve as markers of extant and/or extinct life in the context of the development of the Life Marker Chip (LMC), an antibody-based instrument, which is being developed by a UK-led international consortium for flight to Mars on board the joint ESA/NASA Mars exploration ExoMars mission. The hapten-protein conjugates were designed to be used as immunogens for antibody generation and immunoassay reagents in subsequent stages of the LMC development. The extent of protein modification due to covalent attachment of hapten was determined by two independent methods, i.e. trinitrobenzenesulfonic acid (TNBSA) titrations of remaining protein reactive groups and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) of the resultant hapten-protein conjugates. In a further quality validation step, the conjugates were presented to an animal's immune system and polyclonal antibody titres with moderate specificity were obtained. These results suggest that conjugates synthesized as described herein can successfully be used in the generation of antibodies targeting small hydrophobic molecules.     

Design of Serum Compatible Tetrary Complexes for Gene Delivery

A novel gene delivery system, called PoSC, consisting of PEI, PSP, and HA is described. In contrast to the DNA/PEI/HA ternary system whose transfection efficiency decreases significantly with increasing serum concentration, PoSC exhibits a high transfection efficiency of about 51 and 87% for NIH3T3 and HCT116 cells, respectively, at 50% serum concentration. Furthermore, PoSC shows no cytotoxic effect at its working concentration. The overall results suggest that HA adsorption on cationic complexes enhances the transfection efficiency, while PSP is essential for high transfection efficiency at higher serum concentration.